Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR UNDERGROUND RECOVERY OF HYDROCARBONS
FIELD
The present invention relates generally to a lined shaft and tunnel-based
method and
system for installing, operating and servicing wells for recovery of
hydrocarbons, wherein the
underground space is always isolated from the formation.
BACKGROUND
Oil is a nonrenewable natural resource having great importance to the
industrialized
world. The increased demand for and decreasing supplies of conventional oil
has led to the
development of alternative sources of crude oil such as oil sands containing
bitumen or heavy
oil and to a search for new techniques for more complete recovery of oil
stranded in
conventional oil deposits.
The Athabasca oil sands are a prime example of a huge alternative source of
crude and
is currently thought to have proven reserves of over 200 billion barrels
recoverable by both
surface mining and in-situ thermal recovery methods. There are also equally
large untapped
reserves of stranded light and heavy oil deposits from known reservoirs
throughout North
America which cannot be recovered by traditional surface drilling methods.
These two sources
of oil, bitumen and stranded oil, are more than enough to eliminate dependence
on other
sources of oil and, in addition, require no substantial exploration.
Recovering Bitumen
The current principal method of bitumen recovery, for example, in the Alberta
oil sands
is by conventional surface mining of shallower deposits using large power
shovels and trucks to
excavate the oil sand which is then delivered to a primary bitumen extraction
facility.
Some of these bitumen deposits may be exploited by an appropriate underground
mining technology. Although intensely studied in the 1970s and early 1980s, no
economically
viable underground mining concept has ever been developed for the oil sands.
In 2001, an
underground mining method was proposed based on the use of large, soft-ground
tunneling
machines designed to backfill most of the tailings behind the advancing
machine. A
description of this concept is included in U.S. 6,554,368 " Method and System
for Mining
Hydrocarbon-Containing Materials".
When the oil sands deposits are too deep for economical surface mining, in-
situ
recovery methods are being used wherein the viscosity of the bitumen in the
oil sand must first
be reduced so that it can flow. These bitumen mobilization techniques include
steam injection,
solvent flooding, gas injection, and the like. The principal method currently
being implemented
on a large scale is Steam Assisted Gravity Drain ("SAGD"). Typically, SAGD
wells or well
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pairs are drilled from the earth's surface down to the bottom of the oil sand
deposit and then
horizontally along the bottom of the deposit and then used to inject steam and
collect mobilized
bitumen.
The SAGD process was first reduced to practice at the Underground Test
Facility
("UTF") in Alberta, Canada. This facility involved the construction of an
access shaft through
the overburden and oil sands into the underlying limestone. From this shaft,
self-supported
underground workings were developed in the underlying limestone from which
horizontal well
pairs were drilled up and then horizontally into the oil sands formation. The
UTF is an
example of "mining for access", a technique that is also described below for
recovery of
stranded oil. With the advent of horizontal drilling techniques, it became
possible to install
SAGD well pairs by drilling from the surface and this is now the commonly used
method of
implementing the SAGD process.
Mining for Oil
Until recently, oil economics have precluded efforts to recover what is known
as
stranded oil. Most heavy and light oil reserves are recovered by drilling
wells from the surface.
Typically, these operations recover 5% to 30% of the oil-in-place. Additional
oil (up to, in
some cases, 50% of the original oil in place) can be recovered from the
surface by secondary
and tertiary methods (also known as Enhanced Oil Recovery or FOR methods) such
as, for
example, water flooding, gas flooding and hydraulic fracturing. Nevertheless,
a substantial
fraction of the oil remains in the ground and is not recovered and is deemed
stranded. Much of
this stranded oil is mobile and can be recovered by a combination of mining
and/or drilling
methods with known reservoir engineering practice. It is estimated that
billions of barrels of
recoverable light and heavy oil remains in known deposits in the US and
Canada. Recovery
awaits the right combination of economics and technology.
The literature describes three basic oil mining approaches:
(1) Surface extractive mining. Surface extractive mining is currently being
implemented on a large scale in Alberta's Athabasca oil sands as discussed
above. This
method is generally applicable to oil deposits that are within a few tens of
meters of the surface.
(2) Underground extractive mining. Several methods of underground mining have
been
investigated especially in the past when oil prices have risen rapidly. For
example, a number of
studies were conducted in the 1980s for direct extraction of bitumen in oil
sands and for direct
mining of stranded light and heavy oil deposits in the US. These efforts were
discontinued
when oil prices subsequently fell. The economics of these methods were not
competitive with
conventional exploration and surface drilling at lower oil prices, and they
were thought to be
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potential difficulties with safety and environmental issues using the
underground technology
available at the time.
(3) Mining for access. The 1980s studies referred to above also described
methods of
"mining for access" to oil deposits. For example, a method was described
wherein shafts were
sunk and tunnels driven from the shafts to the rock beneath an oil deposit.
Rooms were then
excavated on either side of the tunnels in the rock underlying the reservoir.
These rooms were
used for drilling rigs that could drill up into the oil deposit. The wells
would collect oil driven
by a combination of gravity, gas or water drive. The mining for access
approach was
considered the most promising technique for economially recovering oil using
underground
mining methods.
The principal mining method of interest for stranded oil continues to be
mining for
access. Some studies indicate that up to 80 percent of the oil remaining after
primary and FOR
techniques may be recovered using mining for access methods on deposits that
are as deep as
1,500 meters. Mining for access can also be used to provide an underground
platform for
drilling rigs that can drill downward into a hydrocarbon formation below. Such
a method could
be applied, for example, to an offshore deposit. These mining methods, while
well-known and
feasible, do not adequately protect the underground workers from the gas, oil
and water hazards
associated with hydrocarbon reservoirs (both seepage of fluids and vapors as
well as substantial
inflows of water and gas, especially during installation of tunnels and
drifts). An exemplary
form of mining for access available during this time period is described in US
4,458,945
entitled "Oil Recovery Mining Method" and US 4,595,239 entitled "Oil Recovery
Mining
Apparatus" which describe how drainage wells may be drilled into the overlying
roof of a
tunnel cut into a competent rock zone below oil deposits containing
unrecovered or stranded
oil.
Heavy Civil Underground Technology
In recent years, there has been a substantial progress in heavy civil
underground
construction methods, especially in the area of soft-ground shaft sinking and
tunneling.
Soft-ground shafts are commonly concrete lined shafts and are sunk by a
variety of
methods often in the presence of pressurized aquifers. These methods include
drilling and
boring techniques sometimes where the shaft is filled with water or drilling
mud to counteract
local ground pressures. There are also shaft sinking techniques for sinking
shafts under water
using robotic construction equipment.
Soft-ground tunnels can be driven through water saturated sands and clays or
mixed
ground environments using large slurry, Earth Pressure Balance (" EPB") or
mixed shield
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systems. This new generation of soft-ground tunneling machines can now
overcome water-
saturated or gassy ground conditions and install tunnel liners to provide
ground support and
isolation from the ground formation for a variety of underground
transportation and
infrastructure applications
Developments in soft-ground tunneling led to the practice of micro-tunneling
which is a
process that uses a remotely controlled micro-tunnel boring machine combined
with a pipe-
jacking technique to install underground pipelines and small tunnels. Micro-
tunneling has been
used to install pipe from twelve inches to twelve feet in diameter and
therefore, the definition
for micro-tunneling does not necessarily include size. The definition has
evolved to describe a
tunneling process where the workforce does not routinely work in the tunnel.
Drilling technologies for soft and hard rock are also well known. Conventional
rotary
drilling and water jet drilling, for example, have been utilized in oil and
gas well drilling,
geothermal drilling, waste and groundwater control as well as for hard rock
drilling.
To date, underground access to hydrocarbon reservoirs has relied principally
on mining
methods that have not yet provided a fully safe working environment for
accessing and
producing oil and gas from underground.
There therefore remains a need for safe and economical process of installing a
network
of hydrocarbon recovery wells from an underground work space while maintaining
isolation
between the work space and the ground formation. Such an invention would have
the potential
to develop inaccessible deposits such as those under rivers, increase
hydrocarbon recovery
factors, lower costs, result in less surface disturbance while providing a
safe working
environment.
SUMMARY
These and other needs are addressed by the present invention which is directed
generally to removal of hydrocarbons, particularly flowable or fluid
hydrocarbons, from
hydrocarbon-containing formations using underground excavations.
In a first embodiment of the present invention, a method for extracting
hydrocarbons
from a hydrocarbon-containing deposit includes the steps of. (a) forming an
underground
excavation having a section extending through a hydrocarbon deposit; (b)
forming a
substantially fluid impermeable liner extending along the section of the
excavation; and (c)
from the section of the excavation, forming, through the liner, a plurality of
wells extending
into the hydrocarbon deposit, wherein the wells inject a fluid into the
hydrocarbon deposit
and/or extract a hydrocarbon from the deposit.
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In a second embodiment, a method for recovering hydrocarbons includes the
steps of:
(a) forming an excavation in a hydrocarbon-containing formation; and (b)
maintaining an
interior of the excavation behind an excavation device substantially sealed
from selected fluids
in the formation. Typically, the excavation device is a tunnel boring machine.
A number of different seals are preferably maintained. A first seal is
maintained
between an excavation face and an interior of an excavating machine by
modifying the
excavated material so as to maintain the excavated material at a pressure that
is approximately
the pressure of the formation. A second seal at the interface between the
tunnel boring machine
and the excavation is formed by a moveable shield that is part of the tunnel
boring machine. A
third seal is formed between a rear edge of the shield and a surface of the
liner using a brush
seal assembly. A fourth seal is formed in the excavation behind the tunnel
boring machine
using a liner. A fifth seal is formed at the mating surfaces of tunnel liner
segments and
sections.
The maintenance of a sealed work space can provide a safe working environment
for
accessing, mobilizing and producing hydrocarbons from underground. The seals
can prevent
unacceptably high amounts of unwanted and dangerous gases from collecting in
the excavation.
It can also allow the excavation to be located in hydrologically active
formations, such as
formations below a body of water or forming part of the water table.
Prior art underground mining-for-oil methods require a competent rock
formation underlying
the hydrocarbon deposit. Thus, the present invention can enable development of
hydrocarbon
deposits from an underground workspace, such as those deposits overlying soft
and/or fractured
ground while always providing a safe working environment. The underground
workspace of
the present invention can therefore be installed below, inside or above the
hydrocarbon
reservoir.
In yet another embodiment, a method for extracting a hydrocarbon is provided
that
includes the steps of (a) forming a liner in an underground excavation; and
(b) forming a
plurality of wells passing through the liner and into a hydrocarbon-containing
deposit. The
liner, when formed, comprises a tool to facilitate at least one of well
drilling, well completion,
and hydrocarbon production from a well. The tool, for example, can be an
anchor point for
engaging a wellhead control assembly used in the at least one of well
drilling, well completion,
and hydrocarbon extraction, a sensor for measuring and/or monitoring fluid
flow and/or
formation pressure.
In yet another embodiment, a method for recovering hydrocarbons includes the
steps of:
(a) in an underground excavation, providing a lined excavation, the lined
excavation extending
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through a hydrocarbon-containing formation, and a liner in the lined
excavation including a
plurality of fluid injection ports; (b) injecting a fluid, through the fluid
injection ports, into the
hydrocarbon-containing formation; and (c) collecting hydrocarbons mobilized by
the injected
fluid.
In one configuration, the lined tunnel has an impervious material positioned
between at
least first and second fluid permeable annular spaces positioned between the
liner and a surface
of the excavation, to inhibit the movement of the injected fluid from the
first annular space to
the second annular space. This configuration uses the liner as the fluid
injection and collection
mechanism in addition to or in lieu of wells drilled into the formation from
the excavation. It
therefore can provide substantial production increases relative to a tunnel
configuration used
only to install wells.
In another configuration, the fluid is steam or a diluent, and the method
further includes
the steps of transporting the fluid from the surface through the underground
excavation to a set
of injectors in communication with the injection ports and with the first and
second annular
spaces. If the fluid is steam, the temperature and/or pressure of the steam
may be returned to a
selected level during transportation.
The various embodiments can provide advantages relative to the prior art. For
example,
the use of underground excavations to recover hydrocarbons from many types of
hydrocarbon-
containing deposits, such as heavy oil and stranded oil deposits, can provide
higher recovery
rates and higher overall recovery factors at substantial cost savings relative
to conventional
surface-based techniques. Because hydrocarbon deposits and surrounding
formations are
typically soft and/or fractured rock, the invention can use tunnel boring
machines to form the
excavation. Tunnel boring machines are mature and highly robust continuous
excavation
technique. The location of the excavation in the hydrocarbon-containing
formation itself can
permit the liner to be used as the fluid injection and/or collection medium
without the need to
drill a large number of wells. Drilling a large number of wells from
underground can be cost
effective since each well does not have to traverse long distances of barren
overburden such as
is required by wells drilled from the surface. Finally, the use of liners can
inhibit long-term
surface subsidence above the excavation, thereby limiting the environmental
impact of
hydrocarbon recovery and enabling the recovery of hydrocarbons from deposits
under, for
example, developed farm lands, small towns, lakes, rivers and protected
wildlife habitats.
The following definitions are used herein:
A hydrocarbon is an organic compound that includes primarily, if not
exclusively, of
the elements hydrogen and carbon. Hydrocarbons generally fall into two
classes, namely
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aliphatic, or straight chain, hydrocarbons, cyclic, or closed ring,
hydrocarbons, and cyclic
terpenes. Examples of hydrocarbon-containing materials include any form of
natural gas, oil,
coal, and bitumen that can be used as a fuel or upgraded into a fuel.
Hydrocarbons are
principally derived from petroleum, coal, tar, and plant sources.
Hydrocarbon production or extraction refers to any activity associated with
extracting
hydrocarbons from a well or other opening. Hydrocarbon production normally
refers to any
activity conducted in or on the well after the well is completed. Accordingly,
hydrocarbon
production or extraction includes not only primary hydrocarbon extraction but
also secondary
and tertiary production techniques, such as injection of gas or liquid for
increasing drive
pressure, mobilizing the hydrocarbon or treating by, for example chemicals or
hydraulic
fracturing the well bore to promote increased flow, well servicing, well
logging, and other well
and wellbore treatments.
A liner as defined for the present invention is any artificial layer,
membrane, or other
type of structure installed inside or applied to the inside of an excavation
to provide at least one
of ground support, isolation from ground fluids (any liquid or gas in the
ground), and thermal
protection. As used in the present invention, a liner is typically installed
to line a shaft or a
tunnel, either having a circular or elliptical cross-section. Liners are
commonly formed by pre-
cast concrete segments and less commonly by pouring or extruding concrete into
a form in
which the concrete can solidify and attain the desired mechanical strength.
A liner tool is generally any feature in a tunnel or shaft liner that self-
performs or
facilitates the performance of work. Examples of such tools include access
ports, injection
ports, collection ports, attachment points (such as attachment flanges and
attachment rings), and
the like.
A mobilized hydrocarbon is a hydrocarbon that has been made flowable by some
means.
For example, some heavy oils and bitumen may be mobilized by heating them or
mixing them
with a diluent to reduce their viscosities and allow them to flow under the
prevailing drive
pressure. Most liquid hydrocarbons may be mobilized by increasing the drive
pressure on
them, for example by water or gas floods, so that they can overcome
interfacial and/or surface
tensions and begin to flow.
A seal is a device or substance used in a joint between two apparatuses where
the
device or substance makes the joint substantially impervious to or otherwise
substantially
inhibits, over a selected time period, the passage through the joint of a
target material, e.g., a
solid, liquid and/or gas. As used herein, a seal may reduce the in-flow of a
liquid or gas over a
selected period of time to an amount that can be readily controlled or is
otherwise deemed
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acceptable. For example, a seal between a TBM shield and a tunnel liner that
is being installed,
may be sealed by brushes that will not allow large water in-flows but may
allow water seepage
which can be controlled by pumps. As another example, a seal between sections
of a tunnel
may be sealed so as to (1) not allow large water in-flows but may allow water
seepage which
can-be controlled by pumps and (2) not allow large gas in-flows but may allow
small gas
leakages which can be controlled by a ventilation system.
A shaft is a long approximately vertical underground opening commonly having a
circular cross-section that is large enough for personnel and/or large
equipment. A shaft
typically connects one underground level with another underground level or the
ground surface.
A tunnel is a long approximately horizontal underground opening having a
circular,
elliptical or horseshoe-shaped cross-section that is large enough for
personnel and/or vehicles.
A tunnel typically connects one underground location with another.
An underground workspace as used in the present invention is any excavated
opening
that is effectively sealed from the formation pressure and/or fluids and has a
connection to at
least one entry point to the ground surface.
A well is a long underground opening commonly having a circular cross-section
that is
typically not large enough for personnel and/or vehicles and is commonly used
to collect and
transport liquids, gases or slurries from a ground formation to an accessible
location and to
inject liquids, gases or slurries into a ground formation from an accessible
location.
Well drilling is the activity of collaring and drilling a well to a desired
length or depth.
Well completion refers to any activity or operation that is used to place the
drilled well
in condition for production. Well completion, for example, includes the
activities of open-hole
well logging, casing, cementing the casing, cased hole logging, perforating
the casing,
measuring shut-in pressures and production rates, gas or hydraulic fracturing
and other well and
well bore treatments and any other commonly applied techniques to prepare a
well for
production.
Wellhead control assembly as used in the present invention joins the manned
sections of
the underground workspace with and isolates the manned sections of the
workspace from the
well installed in the formation. The wellhead control assembly can perform
functions
including: allowing well drilling, and well completion operations to be
carried out under
formation pressure; controlling the flow of fluids into or out of the well,
including shutting off
the flow; effecting a rapid shutdown of fluid flows commonly known as blow out
prevention;
and controlling hydrocarbon production operations.
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It is to be understood that a reference to oil herein is intended to include
low API
hydrocarbons such as bitumen (API less than -10 ) and heavy crude oils (API
from -10 to
-20 ) as well as higher API hydrocarbons such as medium crude oils (API from -
20 to -35 )
and light crude oils (API higher than -35 ) .
Primary production or recovery is the first stage of hydrocarbon production,
in which
natural reservoir energy, such as gasdrive, waterdrive or gravity drainage,
displaces
hydrocarbons from the reservoir, into the wellbore and up to surface.
Production using an
artificial lift system, such as a rod pump, an electrical submersible pump or
a gas-lift
installation is considered primary recovery. Secondary production or recovery
methods
frequently involve an artificial-lift system and/or reservoir injection for
pressure maintenance.
The purpose of secondary recovery is to maintain reservoir pressure and to
displace
hydrocarbons toward the wellbore. Tertiary production or recovery is the third
stage of
hydrocarbon production during which sophisticated techniques that alter the
original properties
of the oil are used. Enhanced oil recovery can begin after a secondary
recovery process or at
any time during the productive life of an oil reservoir. Its purpose is not
only to restore
formation pressure, but also to improve oil displacement or fluid flow in the
reservoir. The
three major types of enhanced oil recovery operations are chemical flooding,
miscible
displacement and thermal recovery.
As used herein, "at least one", "one or more", and "and/or" are open-ended
expressions
that are both conjunctive and disjunctive in operation. For example, each of
the expressions "at
least one of A, B and C", "at least one of A, B, or C", "one or more of A, B,
and C", "one or
more of A, B, or C" and "A, B, and/or C" means A alone, B alone, C alone, A
and B together,
A and C together, B and C together, or A, B and C together.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic side view of the excavating process for installing a
lined tunnel
in a hydrocarbon formation under pressure.
Figure 2 is a schematic end view of tunnel liner.
Figure 3 is an isometric view of a shaft, tunnel and well complex installed in
a
hydrocarbon formation.
Figure 4 is a plan view of a typical configuration of wells drilled from
tunnels in a
hydrocarbon formation.
Figure 5 is an end view of multiple tunnels and wells installed near the
bottom of a
hydrocarbon formation.
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Figure 6 is an end view of multiple tunnels and wells installed from below a
hydrocarbon formation.
Figure 7 is a sectioned side view through a tunnel liner segment illustrating
a ring
assembly embedded in a liner segment.
Figure 8 is an isometric view of a ring assembly such as shown in Figure 8.
Figure 9 shows an isometric view of a tunnel liner section with a type of
embedded
assembly in each liner segment.
Figure 10 shows an isometric view of a tunnel liner section with another type
of
embedded assembly in each segment.
Figure 11 shows a schematic side view of wellhead control equipment installed
in a
tunnel or shaft liner.
Figure 12 shows a schematic end view of drill rig in travel position mounted
on a tunnel
rail car.
Figure 13 shows a schematic plan view drill rig in drilling position to drill
a horizontal
well through the side of the tunnel liner.
Figure 14 shows a schematic end view of a method for recovery of hydrocarbons
from a
backfilled tunnel liner by SAGD.
Figure 15 is an isometric view of tunnel liner sections showing two types of
SAGD
injector and collector ports.
Figure 16 is an end view of a tunnel showing a SAGD steam chamber.
Figure 17 is a side view schematic of a soft-ground TBM showing its principal
sealing
points.
Figure 18 illustrates features of tunnel liner sealing.
DETAILED DESCRIPTION
As discussed in the BACKGROUND section, prior art "mining for access" methods
are
based on excavating tunnels, cross-connects and drilling caverns in competent
rock above or
below the target hydrocarbon formation. The competent rock provides ground
support for the
operation and, being relatively impermeable, to some extent protects the work
space from fluid
and gas seepages from the nearby hydrocarbon deposit. This approach cannot be
applied when
formation pressures are high; when the hydrocarbon reservoir is artificially
pressurized for
enhanced recovery operations ("EOR"); when the hydrocarbon formation is
heated, for
example, by injecting steam; or when the ground adjacent to the hydrocarbon
reservoir is
fractured, soft, unstable, gassy or saturated with ground fluids.
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The present invention discloses a method for installing, operating and
servicing wells in
a hydrocarbon deposit from a lined shaft and/or tunnel system that is
installed above, into or
under a hydrocarbon deposit. The entire process of installing the shafts and
tunnels as well as
drilling and operating the wells is carried out while maintaining isolation
between the work
space and the ground formation. In one aspect of the invention, well-head
devices may be
precast into the tunnel or shaft liners to facilitate well installation and
operation in the presence
of formation pressure and/or potential fluid in-flows. In another aspect of
the invention, the
tunnel itself can be used as a large diameter well for collecting hydrocarbons
and, if required,
for injecting steam or diluents into a formation to mobilize heavy
hydrocarbons such as heavy
crude and bitumen.
In certain embodiments, the present invention discloses a method for
installing an
underground workspace suitable for drilling wells into a hydrocarbon formation
wherein the
underground workspace is fully lined in order to provide ground support and
isolation from
formation pressures, excessive temperatures, fluids and gases. The lining also
provides anchor
points for various apparatuses or liner tools that allow drilling wells,
installing casing for
injection of fluids into the formation, measuring and monitoring the
formation, and collection
of fluids from the formation, all while maintaining a seal between the
interior working space
and the formation. The process of maintaining isolation of the underground
work space from
the formation includes the phases of (1) installation of underground workspace
and wells and
(2) all production and maintenance operations from the underground workspace.
The
underground work space is provided principally by lined shafts and lined
tunnels. The shafts
and tunnels themselves may also serve as large injection and collection
"wells" when they are
installed in the hydrocarbon formation. Because the underground workspace is
installed and
operated in full isolation from the formation pressures and fluids, the
workspace can be
installed above, inside or below the hydrocarbon formation in soft or mixed
ground.
In the descriptions below, it is understood that the functions described for
tunnel liners
also apply to shaft liners.
Development of Sealed Underground Workspace
Figure 1 is an idealized schematic side view of one aspect of the present
invention. A
hydrocarbon formation 102 is shown under an overlying layer of rock and earth
101 which has
a surface 103. The hydrocarbon deposit 102 lays on top of a basement rock 104.
A soft-ground
tunnel boring machine ("TBM") is shown near the bottom of the hydrocarbon
formation 102.
In the example of Figure 1, the TBM is moving from right to left. The TBM is
comprised of a
rotating cutter head 110 and a moveable shield 111. A tunnel liner 112 is
erected by sections
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105 inside the shield 111 as the TBM advances. The tunnel liner 112 may be
formed by
sections 105 which are joined together at joints 106 inside the shield 111
during the tunneling
process. The sections 105 are preferably precast concrete segments but may be
fabricated from
other structural materials such as, for example, structural steel or
composites of structural steel
and concrete. The sections are preferably formed from a high temperature
concrete mix and
well-cured before installation. The bottom of the finished tunnel is located
as shown by
separation 107 above the basement formation 104. When placed at the bottom of
the
hydrocarbon formation 102, the bottom of the tunnel liner 112 would typically
be located
within about 0 to 5 meters of the basement formation 104 depending on geologic
conditions
such as for example a zone of water or water saturated sand lying on the
basement formation
104. The liner 112 remains in place and provides ground support as the cutting
head 110 and
shield 111 are moved forward. Most soft-ground tunnel liners are installed by
slurry or earth-
pressure balance ("EPB") tunnel boring machines ("TBMs"). These machines make
it possible
to excavate and remove material ("muck") in isolation from the workers and
operators in the
TBM and tunnel as the tunnel is being installed. The material is excavated in
a forward
chamber of the TBM where it may be formed into a slurry or paste and removed
to the surface.
In this configuration, the excavating and muck removal processes are isolated
from the tunnel
interior and are often carried out at a different pressure (usually higher)
than that of the interior
of the tunnel. The pressure in the interior of the tunnel is often at or near
atmospheric pressure
as it is connected to surface ambient pressure by other tunnels, drifts and
shafts. Typically, a
soft-ground tunnel liner 112 is formed from 3 or 4 segments which are bolted
and gasketed
together to form a short cylindrical section 105 of tunnel liner. As the
tunnel is excavated,
short liner sections 105 are assembled and positioned within a shield that is
part of the
excavating machine, in such a way as to maintain a continuous seal between the
working area
2.5 and the formation being excavated. Installing the tunnel liner while
sealed against the
formation, controls the seepage of fluids and vapors from the hydrocarbon
deposit into the
tunnels and drifts of underground working space. The liner also allows the TBM
crew to
control more substantial water and/or gas inflows encountered during
excavation by well-
known methods such as water pumps and ventilation air flows. Thus the inside
of the tunnels
of the present invention are sealed and isolated from the formation at all
times during
installation of the tunnel network. This ability to seal the tunnel interior
from the formation
during installation makes it possible to install the tunnel network in the
hydrocarbon deposit
itself.
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The tunnel diameters envisioned by the present invention are in the range of
about 3
meters to about 12 meters. The tunnel liner thicknesses are typically in the
range of about 75
millimeters to about 600 millimeters. The liners may be formed from concrete
or other low-
cost structural materials and may contain layers of plastic or rubber
materials to provide
additional sealing. The liner may be formed by erecting segments or by
continuously extruding
concrete into a form.
The diameter of the cutter head 110 is typically slightly larger than the
diameter of the
shield. The TBM is used to install a fixed tunnel liner 112 which is shown as
having a slightly
smaller diameter than the TBM shield 111. As the TBM advances, it creates an
excavation
whose inside diameter is denoted by 109. A gap 113 is therefore formed between
the inner
diameter of the excavation 109 and the outer diameter of the tunnel liner 112.
The width of the
gap 113 may be controlled and backfilled with a suitable material to serve
several functions as
will be discussed later. The gapl 13 is typically in the range of 25
millimeters to about 300
millimeters and may be back-filled with an appropriate material such as grout,
gravel or not be
backfilled, depending on the application and ground situation. The tunnel
liner 112 is
preferably installed by using a slurry or Earth Pressure Balance ("EPB")
tunnel boring machine
("TBM") and conventional tunnel liner installation technology. This tunneling
method allows a
liner to be installed while following the desired trajectory through the
hydrocarbon deposit 102.
This trajectory may be designed to follow the deposit which may have been
formed by a river
or estuary for example. The length of the tunnel is dependent on the geology
of the
hydrocarbon deposit 102 and maybe in the approximate range of 500 meters to
10,000 meters
or longer if the deposit persists and/or if a number of deposits are separated
by short sections of
barren ground. The installation of the tunnel liner 112 may be initiated from
a portal developed
at the surface or by assembling the TBM and its equipment using an access
shaft excavated
from the surface 103 through the overburden 101 to the bottom of the
hydrocarbon deposit 102.
With currently available tunneling technology, a tunnel liner 112 can be
installed to within a
few millimeters of its desired design location. If the tunnel is used in a
thermal recovery
operation, this capability therefore places a desirable low limit on the
variance of placement of
injection and collection points that is considerably more precise than is
currently possible with
horizontal drilling methods operated from the ground surface 103. In current
practice, soft-
ground tunneling machines are limited to formation fluid pressures of about 10
to 12 bars. This
limitation is currently dictated by seal design for fluid seals between the
TBM shield 111 and
the section of tunnel liner 105 erected under the shield 111. This pressure
limitation can be
increased by improved seal design. For now, the present invention is limited
to hydrocarbon
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deposits where ambient formation fluid pressures do not exceed about 15 bars.
It is also
possible, using known tunneling techniques, to locally drain fluids
(dewatering and degassing).
If the formation is relatively impermeable, then this can reduce local
formation fluid pressures
and inflow rates to allow the tunneling machine to proceed without exceeding
the pressure
limits on its seals. Once the tunnel liner is installed, the pressure
limitation can be considerably
higher than 10 bars as the pressure limit is now dictated by the structural
integrity of the liner
and/or the sealing technology used to form gaskets between liner segments
(unless extruded
liner technology, which does not require gaskets, is used). The tunnel liner
serves a number of
purposes. These include isolating the interior of the tunnel from the
formation fluids and
vapors, protecting the formation from activities in the tunnel including
sparks and the like
which can cause ignition of hydrocarbon vapors and materials; serving as a
base for attaching
fluid cutting and control assemblies used for drilling, logging, operating and
servicing wells
drilled through the liner; insulating the interior of the tunnel from high
temperatures if steam
injection is used; and serving as a base for installing drains for collecting
oil around the tunnel
itself. The tunnel liner 112 can also be installed in the basement formation
104 if desired. If
the basement formation is soft or mixed ground, the tunnel would be formed
from liner sections
such as described above. If the basement formation is hard rock, the tunnel
can be excavated
by a hard rock TBM and the tunnel walls can be grouted or by other means to
provide a seal. If
necessary, the tunnel can be formed by using soft-ground techniques(including
installing a
liner) but with a hard rock TBM cutter head. This latter method may be
preferable, for
example, if there were substantial in-flows of water or gas anticipated, as
might be the case for
basement formations underlying many hydrocarbon deposits.
Figure 2 is a schematic end section view of a tunnel liner such as may be
installed over,
in or under a hydrocarbon reservoir. This view shows a tunnel liner 201
installed in a
hydrocarbon formation 202. The hydrocarbon formation 202 sits atop an
underlying basement
formation 203 and is overlain by a non-hydrocarbon bearing formation 204 which
reaches to
the surface 205. The tunnel liner 201 isolates the interior of the tunnel 206
from the
hydrocarbon deposit 202. The tunnel liner may have an optional backfill zone
207 around the
liner. The backfill zone is typically formed during the excavating process as
part of the
excavating and tunnel liner erection process. The backfill may include grout,
concrete, sand,
pebbles, small rock and the like and may provide additional sealing capability
or drainage
around the tunnel liner 201. The backfill zone 207 is not necessarily circular
in cross-section as
shown but maybe approximately elliptical in cross-section with much of the
backfill material
being above the spring-line 210 of the tunnel liner cross-section. It is also
possible in some
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hydrocarbon formations to not backfill the zone 207 but allow the ground to
expand and fill in
the zone 207. This may be desirable for some applications, for example, in
many oil sands
formations.
Figure 3 is an isometric view of a shaft, tunnel and well complex installed in
a
hydrocarbon formation. This figure shows a shaft 305 connecting the surface
301 with a
hydrocarbon formation 303. The hydrocarbon formation itself may be comprised
of one or
more zones of hydrocarbon, each separated by a thin permeable barrier. A shaft
305 penetrates
the formations 302 overlaying the hydrocarbon formation 303 and terminating in
a basement
formation 304. The shaft 305 may be sunk below the hydrocarbon formation 303
to
accommodate shaft elevator equipment or provide a sump volume for the oil
produced. In this
example, the shaft 305 connects the surface with two tunnels 306 and 307. The
upper tunnel
307 may be used for example to install producer or injection wells into the
top of the
hydrocarbon formation 303. The lower tunnel 306 maybe used for example to
install producer
or injection wells into the bottom of the hydrocarbon formation 303. In this
figure, blind wells
308 are shown drilled horizontally into the hydrocarbon formation. As can be
appreciated,
wells can be drilled at any angle into the formation as will be described in
subsequent figures.
A key feature of this installation are the junctions 309 between the shaft 305
and the tunnels
306 and 307. If these junctions are in a pressurized or gassy or fluid-
saturated portion of the
formation, they must be sealed junctions. The junctions are not necessarily
sealed during
installation as dewatering, degassing or other well known techniques can be
applied during
installation to cope with fluid or gas inflows. A method for maintaining a
seal at such junctions
309 during installation is described in Figure 18. As can be appreciated,
wells can be drilled
into the formation from the tunnels or shafts at any time after the tunnels
and shafts are
installed. Thus, it is straightforward to drill additional wells between
existing wells to in-fill
the well network, creating a dense network of wells in the formation. When
drilled from a
tunnel of the present invention located inside or adjacent to the hydrocarbon
formation, the well
lengths are almost entirely in the hydrocarbon formation and there is no cost
to drill through the
overburden as would be the case with wells drilled from the surface. This is a
substantial
advantage of the present invention.
Figure 4 is a schematic plan view of a typical configuration of wells drilled
from tunnels
in or adjacent to a hydrocarbon formation. The tunnels themselves may contain
provisions for
directly injecting steam and collecting fluids and therefore act as large
wells themselves. One
or more tunnels 401 are driven substantially horizontally into a hydrocarbon
formation,
approximately following the path of interest in the formation. In this
embodiment, a plurality
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of wells 402, 403, 404, 405 and 408 are drilled outwardly from each tunnel 401
into the
hydrocarbon formation. These wells are drilled from the tunnel and are
designed to remain
substantially within the hydrocarbon deposit. If more than one tunnel is
installed, then the
tunnels are spaced apart by a distance in the range of approximately 200 to
1,000 meters as
indicated by well 402 which connects two tunnels 401. As shown in Figure 4,
wells 403, 404,
405 and 408 are drilled from the tunnels 401 and terminate in the hydrocarbon
formation as
blind wells. The lengths of the wells 403, 404, 405 and 408 are approximately
half the distance
between adjacent tunnels. The lengths of wells are thus in the approximate
range of about 100
to about 400 meters. If all the wells are drilled as blind wells, the spacing
between tunnels may
be as much as about 2,000 meters and the blind wells may be up to about 1,000
meters in
length. Other wells 402 may be drilled from one tunnel to the other. Other
wells 405 may be
drilled into the hydrocarbon formation and then offshoot wells 406 can be
additionally drilled.
As can be appreciated any number of offshoot wells 406 can be drilled from the
initial well
405. The wells may be drilled from any location along the length of the
tunnels 401 but are
typically spaced in the range of approximately 25 to approximately 150 meters
apart. Wells
originating from adjacent tunnels may or may not overlap in lateral extent as
shown by
examples 408 (non-overlapping) and 404 (overlapping). As can be appreciated,
wells can be
drilled as pairs with one well above the other to form a well pair such as
used in SAGD
operations. The tunnels 401 which can be curved if necessary to follow the
meanderings of a
hydrocarbon formation. As can be appreciated, there can be one two or more
tunnels which
may or may not be connected with cross drifts or wells. In the present
invention, all the tunnels
and cross drifts are lined; all the wells are sealed where they penetrate the
tunnel liners; and
when in production, all the wells are connected to a closed piping system such
that the
produced oil is never exposed to the inside of the tunnel and shaft network.
Figure 5 is a schematic end section view of multiple tunnels and wells
installed near the
bottom of a hydrocarbon formation 501 showing a surface 504, an overburden 503
and an
underlying basement formation 502. It is understood that the hydrocarbon
formation 501 may
be comprised of multiple producing zones, each zone being separated by a thin
permeability
barrier. Each tunnel 505 provides an underground workspace for drilling and
operating wells in
the hydrocarbon formation 501. The tunnels 505 are driven roughly parallel to
each other with
a spacing 506. The spacing 506 between adjacent tunnels 505 is typically in
the range of about
100 to about 2,000 meters. The tunnel is formed by a structural liner (as
illustrated, for
example, in Figure 2) which is preferably constructed of approximately
cylindrical sections that
are gasketed and bolted together to form a workspace effectively sealed from
the surrounding
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formation. The diameter of the tunnels 505 is preferably in the range of about
3 meters to 12
meters. Several types of wells may be drilled to connect with the tunnels 505.
Well 511 is
drilled through the hydrocarbon formation 501 from tunnel to tunnel, the
tunnels 501 being
approximately in the range of about 200 meters to about 1,000 meters apart in
this case. Well
514 is drilled out into the hydrocarbon formation 501 and terminates as a
blind well in the
hydrocarbon formation 510. A blind well 514 is typically in the length range
of approximately
100 to 1,000 meters but may be longer as blind drilling techniques are
improved. Inclined well
515 is drilled to various desired locations in the hydrocarbon formation 510
and may be used,
for example, to inject fluids for enhanced oil recovery ("BOR"). Well 516 is
drilled down from
the surface to connect with a tunnel. Well 516 may have a horizontal section
513 in the
hydrocarbon formation 501 as shown. The horizontal section 513 of well 516 is
typically in
the length range of approximately 100 to 1,000 meters but may be longer as
surface drilling
techniques are improved. Well 517 is drilled vertically down and terminates as
blind well in
the basement formation 502. Well 517 may be used, for example to sequester
carbon dioxide
or other gases or fluids that may be sequestered in the underlying formation.
The diameters of
the wells, the lengths of the wells and the spacing of the wells around the
tunnels and along the
length of the tunnels are controlled by the instructions of the reservoir
engineer. The well
lengths are limited by the drilling technology employed but are at least in
the range of about
100 to 1,000 meters in length. The well diameters are in the range of about 50
mm to 1,000
millimeters, depending on the instructions of the reservoir engineer. The
wells may be drilled
as single wells, as well pairs such as commonly used in SAGD thermal recovery
operations or
as three well stacks such as used in some advanced SAGD thermal recovery
operations. The
methods of drilling from within the tunnels 505 may include, for example,
conventional soft
ground drilling methods using rotary or augur bits attached to lengths of
drill pipe which are
lengthened by adding additional drill pipe sections as drilling proceeds.
Drilling methods may
also include, for example, water jet drilling methods. Drilling methods may
also include, for
example, micro-tunneling techniques where a slurry excavation head is used and
is advanced
into the deposit by pipe jacking methods. Forms of directional drilling may be
used from
within a tunnel. More conventional directional drilling methods may be used
for wells or well
pairs drilled from the surface to intercept a tunnel such as described in
subsequent discussions.
Although not shown, wells may be drilled upwards at an inclination such as
well 515 and then
be directionally changed to be a horizontal well at a new elevation within the
formation.
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Figure 6 is and end view of multiple tunnels and wells installed, for example,
in a
basement formation 602 just below a hydrocarbon formation 601. This figure
also shows a
surface 604 and an overburden 603 formation 602. Figure 6 is similar to Figure
5 except the
tunnels 605 are driven into an underlying basement formation 602 and the wells
611, 612, 614
and 615 must be drilled upwards out of the basement formation 602 and then
horizontally at or
near the bottom of the hydrocarbon formation 601. The range of tunnel
diameters and spacings
and well pair diameters and spacings are the same as those described in Figure
5. In the case of
the blind well pairs 614, the techniques for drilling such well pairs from
basement formation
602 into the hydrocarbon formation 601 has been established previously during
the original
development of the SAGD method at the Underground Test Facility ("UTF") in
Alberta,
Canada. In this case, the drilling of well pairs was conducted from
underground workings
drilled & blasted into limestone underlying an oil sands deposit. If the wells
or well pairs are
drilled from tunnels installed into hard ground, then it is possible to drill
& blast small caverns
at each drilling location to provide additional working space for the well
drilling equipment.
Each tunnel 605 provides an underground workspace for drilling and operating
wells in the
hydrocarbon formation 601. Even if the basement formation is rock, the tunnel
may formed by
a structural liner (as illustrated in Figure 2) which is preferably
constructed of approximately
cylindrical sections that are gasketed and bolted together to form a workspace
effectively sealed
from the surrounding formation. Several types of wells may be drilled to
connect with the
tunnels 605. In the case of the well 611 drilled between adjacent tunnels 605,
the well can be
drilled from one tunnel and ultimately intercept the adjacent tunnel. This
will require an
innovation to presently available drilling technology. One way that this may
be accomplished,
for example, is to drill upwards from one tunnel out of the basement layer 602
and then
horizontally at or near the bottom of the hydrocarbon deposit 601 until the
horizontal well
passes over the adjacent tunnel. It then is possible to drill upwards from the
adjacent tunnel to
intercept the horizontal portion of the well 611 in the hydrocarbon deposit
601. Well pair 614
is drilled out into the hydrocarbon formation 601 and terminates as a blind
well pair in the
hydrocarbon formation 610. A blind well pair 614 is typically in the length
range of
approximately 100 to 1,000 meters but may be longer as blind drilling
techniques are improved.
Inclined well 615 is drilled to various desired locations in the hydrocarbon
formation 610 and
may be used, for example, to inject fluids for enhanced oil recovery ("EOR").
Well 616 is
drilled down from the surface to connect with a tunnel. Well 616 may have a
horizontal section
613 in the hydrocarbon formation 601 as shown. The horizontal section 613 of
well 616 is
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typically in the length range of approximately 100 to 1,000 meters but may be
longer as surface
drilling techniques are improved. Well 616 can be connected to tunnel 605 in
the same way
well 611 is connected. An example of this procedure was described previously.
Well 617 is
drilled vertically down and terminates as blind well in the basement formation
602. Well 617
may be used, for example to sequester gases or fluids. Although not shown,
wells may be
drilled upwards at an inclination such as well 615 and then be directionally
changed to be a
horizontal well at a new elevation within the formation. The diameters of the
wells, the lengths
of the wells and the spacing of the wells around the tunnels and along the
length of the tunnels
are controlled by the instructions of the reservoir engineer. The wells may be
drilled as single
wells, as well pairs such as commonly used in SAGD thermal recovery operations
or as three
well stacks such as used in some advanced SAGD thermal recovery operations. If
the basement
formation is soft or mixed ground the tunnel would be formed from liner
segments such as
described previously. If the basement formation is hard rock, the tunnel can
be excavated by a
hard rock TBM and the tunnel walls can be grouted or lined by other means to
provide a seal
unless the basement rock is impermeable. If necessary, the tunnel can be
formed by using soft-
ground techniques but with a hard rock TBM cutter head. This latter method may
be
preferable, for example, if there were substantial in-flows of water or gas
anticipated, as might
be the case for basement formations underlying many hydrocarbon deposits.
Access to the
basement formation is typically by vertical shafts sunk from the surface 604
through the
overburden layer 603 and hydrocarbon formation 601 and terminating in the
basement
formation 602. The shafts are of a sufficient diameter to accommodate
ventilation, access, and
the large components of the tunneling machines.
Utilizing Liners to Maintain Sealing While Drilling
Figure 7 is a side view through a liner segment illustrating a section through
a ring
assembly embedded in the liner segment. As will be shown subsequently, this
type of ring
assembly may serve as a mounting device for a fluid cutting and control
assembly including
blow-out preventers and allows drilling, logging, casing and servicing of
wells to be carried out
while the interior workspace is fully sealed from the formation. This ring
assembly also allows
drilling to be initiated from discrete orientations around the circumference
of the tunnel.
Threaded holes 705 are shown in each half 704 of the ring assembly. The holes
705 are on the
inside 701 of the liner segment. The liner segment is commonly made as a
precast concrete 703
component having an inside surface 701 and an outside surface 702. The ring
assembly is
preferably made from steel but may be fabricated using other structural
materials such as
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aluminum, high strength plastics or the like. A wellhead control assembly
(such as shown in
Figure 12) can then be mounted against the liner ring assembly with a gasket
(not shown)
forming a seal with surface 706. This example is meant to illustrate how well-
head equipment
can be mounted using mounting assemblies cast into the tunnel liner. As can be
appreciated,
other types of mounting hardware can be cast into the tunnel liner.
Figure 8 is an isometric view of the ring assembly shown in Figure 7. This
view shows
two ring halves 801 of the assembly. Threaded holes 805 are shown on the
inside (concave
surface) of the ring halves. Connectors 803 made for example from re-bar hold
the two ring
halves together. The connectors 803 and rods 804 also serve to maintain the
ring assembly in
position when the concrete segment is fabricated. The threaded holes 805 are
spaced at equal
angles around the ring halves and allow the wellhead control assembly to be
positioned at any
of a number of discrete angles around the finished tunnel liner. For example,
the wellhead
control assembly can be mounted at angular spacings of from about 5 to about
15 . This allows
wells to be drilled through the tunnel liner walls at any angle since a well's
final inclination
angle can be adjusted by directional drilling techniques with drilling angle
adjusted through
small angles as the well is being drilled. Once the wellhead control assembly
is positioned and
secured to the ring assembly, a drill can penetrate the liner wall by drilling
through the precast
concrete in between the connector bars 803 and, using well known techniques
can maintain a
seal between the formation and the interior work space.
Figure 9 shows an isometric view of three liner segments, each segment with a
ring
assembly 906 such as described in Figures 7 and 8 cast into the liner wall.
The liner segments
are bolted and gasketed together at overlapping joints 905 to form a short
cylindrical section
901 of tunnel liner. The liner section 901 has a diameter 902, a length 903
and a wall
thickness 904. The ring assemblies 906 are shown cast into the precast
concrete segments. The
ring assemblies are preferably located about halfway along the length of the
segments. As can
be appreciated, more than one ring assembly may be cast into the liner
segments and they may
be located anywhere along the length of the segments consistent with segment
structural
integrity.
Figure 10 shows a liner section 1001 with rows of drain ports 1004 and 1005
installed
in the tunnel liner. The tunnel liner 1001 is comprised of segments joined
lengthwise as
denoted by joint 1002. A bottom platform 1003 may be used to provide a flat
surface for laying
tracks or rails along the tunnel for transportation. In this example, drain
ports 1004 are shown
located along both sides of the tunnel liner 1001 under platform 1003. This is
a preferred
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location for drain ports since they can be plumbed into an oil/gas collection
piping system
installed inside the liner 1001 at the bottom for removing oil/gas that is
collected as it drains
around the outside of the tunnel liner 1001. Additional drain ports 1005 are
shown located
along both sides of the upper portion of the tunnel liner 1001. This is also a
good location for
drain ports is since they can be plumbed into an oil collection piping system
for removing oil
that is collected as it drains around the outside of the tunnel liner 1001 by
a piping system hung
inside the liner 1001 near the crown of the tunnel liner 1001 and therefore
above the traffic
lanes and drilling sites within the tunnel. These drain ports may be pre-cast
into the liner
during fabrication of liner segments or they may be installed in the liner
after the liner itself has
been installed in the ground. If pre-cast into the liner during fabrication of
liner segments, the
drain ports may be initially plugged by, for example, a threaded pipe plug
compatible with
connections to a piping system for oil/gas removal. If installed in the liner
after the liner itself
has been installed, the drain ports may be installed in a manner similar to
that used to install the
fluid cutting and control assemblies described in Figure 11.
Figure 11 is a close up cutaway side view of a tunnel liner wall 1107 with
well-head
equipment 1103 installed. The well-head equipment 1103 is attached and sealed
to the tunnel
liner 1107. Well-head equipment 1103 is secured, for example, to a flange 1104
pre-cast into
the tunnel liner wall 1107. A portion of the well-head equipment 1103 is set
into the formation
1105. As shown, that portion is typical of well-production operations and
collects
hydrocarbons and delivers them to a piping system 1106. The equipment shown is
a wellhead
control assembly which includes blow-out preventers. Equipment such as this
allows drilling,
logging, casing and servicing of wells to be carried out while the interior
workspace is fully
sealed from the formation.
Figure 12 shows a drill rig in travel position mounted on a tunnel rail car. A
platform
1202 is installed inside a tunnel liner 1201. Narrow gage rail tracks 1203 are
installed along
the platform 1202. These tracks are used for small tunnel locomotives and rail
cars used to
move men, materials, supplies and the like throughout the tunnel and, during
tunnel driving
operations, to supply, for example, backfilling material to the advancing face
and to remove
excavated material from the tunnel. A drill rig car 1204 with wheels 1205 is
shown in a
drilling position. Bearing pads 1206 are shown engaged with the liner walls by
hydraulic
cylinders 1207 and act to stabilize the drill rig during drilling, casing and
other operations. This
illustrates another advantage of a tunnel liner which is that it has a
predictably smooth bearing
surface on which the drill rig can stabilize itself and it can do so in almost
any angular
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orientation. The wheels 1205 can also be designed to grip the rails 1203 when
in drilling
position to further stabilize the drill rig during drilling and casing
operations. A drill with drill
motor 1209, drill rod 1208 and drill bit 1210 is shown mounted on a movable
mount. The drill
can be oriented as indicated by arrow 1212 to drill in any angular orientation
around the tunnel
liner. The drill can also be moved up or down as indicated by arrow 1211. As
can be
appreciated, the drill can be a mechanical drill such as a rotary or
percussive drill; or a water jet
drill; or a micro-tunnel machine; or a combination mechanical and water jet
drill. The drill rig
can be used with well-head equipment such as shown in Figure 11 to initiate
and complete a
well while maintaining a seal between the interior workspace and the
formation. The drill rigs
used in the present invention are designed to quickly add additional lengths
of drill rod either
by well-designed hand operations or by automatic addition of drill rod lengths
such as practiced
in petroleum drilling.
Figure 13 shows a plan view of a drill rig 1303 in drilling position to drill
a horizontal
well through the side of the tunnel liner 1301. Rail tracks 1302 are shown
along the platform
that forms the tunnel floor. Bearing pads are shown engaged with the liner
walls by hydraulic
cylinders 1304. A drill 1305 is shown in a number of positions viewed from
above with an
approximate range of drilling positions indicated by arrow 1306. The drill rig
shown in Figure
13 can be raised and lowered from the tunnel centerline through a distance of
approximately
about 1/4 of a tunnel diameter. The drill rig can also be rotated to allow
wells to be drilled at any
angular orientation (pitch angle). The drill rig can also be rotated laterally
to direct the drill line
at an angle with respect to normal to the tunnel liner wall (yaw angle).
Utilizing Tunnels for Thermal Recovery
Figure 14 shows an end view illustrating a method for using the tunnel liner
for thermal
recovery of heavy oil or bitumen. A backfilled tunnel liner 1404 illustrates a
means of isolating
steam from mobilized fluids. An end view of a tunnel is shown here embedded in
an oil sands
deposit 1401 just above the underlying basement rock 1402. A tunnel structural
liner 1404
provides ground support for an excavated bore 1403. As described previously in
Figure 2, the
liner 1404 is preferably fabricated using a high-strength, high-temperature
concrete to form
short liner segments that can be installed, gasketed and bolted together as
part of the tunneling
process. The excavated tunnel bore and tunnel liner installation are
preferably implemented
using a soft-ground tunnel boring machine and well-known liner segment
installation
techniques. The annular spaces 1405, 1411 and 1412 between the liner 1404 and
the inner
surface of the excavated bore 1403 are backfilled. In the bottom portion of
the annular space
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1405 backfill is provided by a low cost, readily available material such as,
for example, pea
gravel, coarse sand, small rocks and/or the like or combinations of these
materials. For a liner
diameter in the range of about 3 meters to about 12 meters, the annular gap
1405, 1411 and
1412 is preferably in the range of about 25 millimeters to about 300
millimeters wide. The
portion of the annular space 1411 above the previously mentioned annular space
1405 is
thereupon backfilled with a high-temperature grout shown as a solid grey
filler. The portion of
the annular space 1412 above the previously mentioned annular space 1411 is
then backfilled
with a low cost, readily available material such as used in annular space
1405. The grout in
annular space 1411 serves to form a seal between the filler material in
annular spaces 1405 and
1412. This feature can prevent injected steam from communicating or short-
circuiting from
injector ports 1407 to collector ports 1409. Steam may be injected through
both ports 1407 and
1409 so as to heat up the oil sand formation surrounding the tunnel. Steam is
not allowed past
the grout in annular space 1411 and cannot go around the grout because of the
un-mobilized
bitumen in the formation. The steam mobilizes the bitumen around the top and
bottom portions
of the tunnel. At some point, steam injection through ports 1409 is stopped
and the mobilized
bitumen is allowed to remain in place while steam continues to be injected
through injection
ports 1407. As bitumen is drained from around the tunnel through ports 1409,
volume is
created for steam to be further injected into the formation through ports
1407. In this figure,
steam is piped down the tunnel and a portion is injected at each injection
port 1407. The steam
pipes maybe wrapped with a common insulating material to minimize heat loss
before
injection into the formation. This is a significant advantage that the present
invention has over
SAGD using well pairs drilled from the surface. An injection port or ports
1407 are located
preferably in at least every tunnel liner segment as shown for example in
Figure 15. The steam
injection port 1407 can inject the steam at the outside surface of the liner
1404 or more
preferably just beyond the annular layer 1412 directly into the oil sand 1401
as shown in the
present figure. Since the steam, generated on the surface or in the tunnel
itself, is transported
from its point of origin down the inside of the tunnel liner 1404 by a piping
system 1406, its
pressure and temperature can be readily monitored. If the steam conditions
degrade with length
down the tunnel, they can be returned to their desired levels by heater and
compressor
apparatuses located at intervals along the tunnel. This later capability can
be an important
advantage over injector wells installed by directional drilling and allows the
tunnel-based steam
injection system to be as long as required by the oil sands deposit being
drained. The fluids are
collected through ports 1409 located near the bottom of the tunnel. In this
figure, two ports are
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shown at each cross-sectional location, although there may be any number of
ports from one to
many at each cross-sectional location. Along the length of the tunnel,
collection ports 1409
are located preferably in at least every tunnel liner segment as shown for
example in Figure 15.
The collection ports 1409 feed into a piping system 1408 which allows the
collected fluids to
be transported through the tunnel and eventually pumped to the surface for
further processing.
As can be appreciated the tunnel liner also serves to insulate the interior
workspace of the
tunnel from the steam-heated formation. It does so by limiting the rate of
heat flow through the
liner (which is commonly made of concrete which has a low thermal
conductivity) and by
allowing the tunnel ventilation system to rapidly remove heated air so
conducted into the
tunnel. The ability to over-cut a tunnel bore 1403, install an undersized
liner 1404 and fill the
resulting annular space with a number of different materials serving a number
of functions, is
an example of how modern tunneling technology can be used to enhance
implementation of a
SAGD process.
Figure 15 is an isometric view of a tunnel segment 1501 showing an example of
a
possible layout for slotted or circular injector and collector ports. This
illustrates how a tunnel
can be used, for example, as a large diameter SAGD well. In SAGD as currently
practiced, the
injector well is typically made from a steel tubing with long narrow slots
formed into the tubing
wall. The slots are approximately 150 millimeters long and 0.3 millimeters
wide. The narrow
width of these slots is dictated by the requirement to prevent sand from
entering into the slot
when steam is not being injected and hot fluids (principally mobilized bitumen
and condensed
steam) are collected. An injector port slot 1502 of the present invention is
shown on top of a
tunnel segment 1501. The injector port 1502 is a long slot through which steam
is injected into
the formation. The slot can be made during the fabrication of the tunnel liner
segment 1501. It
can be covered by a screen or screens that allow steam to be injected while
sand is prevented
from entering the slot when steam is not being injected. The screen mesh is of
a size that
allows as much or more injection area while having openings approximately in
the range of the
slot widths used in conventional SAGD well pipe. The collector port slots 1503
and 1504 can
be made in the same way as the injector port slot 1502. The injector port slot
1502 is typically
placed at or near the top of the segment 1501. One of more collector port
slots are typically
located in the bottom half of the segment 1501 as shown for example by the
location of slots
1503 and 1504. The circumferential strength of the liner segment 1501 can be
maintained for
example by embedding reinforcing bar in the concrete liners across the slots
in the
circumferential direction. The injection and collection port slots can be made
as long slots that
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can be almost as long as the tunnel liner segments but, if necessary,
substantially wider than the
slots used in conventional SAGD well tubing. Figure 15 also shows injector
ports 1505 and
collector ports 1506 and 1507. These ports are circular in section and it is
possible to locate
one to three circumferential rows of ports embedded in the liner 1501. These
ports can be in
the range of 100 mm to 400 mm in diameter. The length of the tunnel 1500 may
be in the
approximate range of 500 meters to 10,000 meters. The length 1511 of an
individual tunnel
liner segment 1501 is typically in the approximate range of 1 to 12 meters. If
each tunnel
segment 1501 has an injection port 1502 and collection ports 1504, the
injection of steam and
the collection of fluids, in effect, occurs along a line which corresponds to
the length of the
tunnel. Thus the tunnel, which need not be straight but can be sinuous as
shown in Figure 4,
acts as a single long horizontal well pair such as used in conventional SAGD.
Because the
tunnel can have a diameter in the range of about 3 meters to about 12 meters,
the collection area
is substantially greater than the collection area of a collector well
typically used in conventional
SAGD. Since the rate of fluid production is proportional to the pressure and
gravity gradients
and to the natural logarithm of the effective diameter of the collector, the
production rate per
unit length of the present invention should be higher by a factor of about 2
to 4 than the
production rate of a conventional SAGD collector well.
Figure 16 is an end view of a tunnel as represented by a tunnel liner 1609
showing a
SAGD steam chamber as represented by its outwardly moving condensation front
1605. Figure
16 also shows a ground surface 1602, an overburden layer 1603, an oil sand
deposit 1601 and
an underlying basement rock 1604. The steam chamber is formed by steam
injected 1608
through ports embedded in the tunnel liner 1609 and spaced along the length of
the tunnel liner.
The fluids which are comprised of mobilized bitumen and condensed steam, drain
1606 around
the condensation front 1605 of the steam chamber and are collected through the
collector ports
spaced along either or both sides of the bottom half of the tunnel liner 1609
as also described in
Figure 15. Since the characteristic size of a fully developed steam chamber is
on the order of
the thickness of the oil sand deposit 1601, the collector ports are
effectively along a line located
at precise vertical and horizontal distances from the line formed by the
injector ports. This
geometry is therefore, in effect, a steam injection well with a large
collector well spaced
appropriately beneath the injector well.
Sealing the Underground Workspace
The present invention is a method of recovering hydrocarbons by developing an
underground workspace that is isolated from the formation both during
installation and
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operations. This requires means of sealing the excavating machines, drilling
machines, and
working spaces at all times. The principal points of sealing are:
1. between the shaft walls and the formation
2. between the shaft walls and the tunneling machine
3. between the shaft walls and the tunnel liner
4. between the tunneling machine and the tunnel liner during installation
5. between the tunnel liner sections and segments during installation and
operation
6. between the tunnel liner and the wells drilled to or from the tunnel
1. Lined shafts can be sunk in soft ground in the presence of formation
pressure and fluids
by well-known methods. For example, drilling mud can be used in conjunction
with a large
diameter drill bit to excavate the shaft and thick concrete walls can be
installed before the mud
is pumped out. Often, the surrounding ground can be dewatered and degassed by
various well-
known means to reduce formation pressures and fluid in-flows sufficiently so
the shaft can be
installed in short sections by a sequence of alternately excavating and
pouring liner walls
without drilling muds.
2. Beginning a tunnel from a shaft is known practice. The shaft wall must be
thick enough
that the TBM can be sealed into place before it actually starts to bore. For
example, if the shaft
wall is, say 1.5 meters thick at the penetration point, the inside 1 meter may
be recessed into the
wall so the curvature of the shaft would be eliminated and the cutting face of
the boring
machine can bear squarely on a boring surface (fibre reinforced concrete for
example) over its
entire circumference. The outer shaft wall remaining would be thick enough to
maintain a rigid
seal under formation pressure but would be a boreable material such as for
example by a
fiber-reinforced concrete. Specially configured, very short tunnel liner
sections would be
bolted into the recess. Then the TBM machine can bore out of the wall and into
the formation
as sealed as it would be for each additional liner section.
3. As can be appreciated, the above tunnel started from inside a shaft results
in a tunnel
liner section being installed and grouted in the hole bored through the shaft
wall. As can be
appreciated, this joint can be further sealed by additional grouting the joint
and/or by
reinforcing it with a structural sealing ring system.
4. The seal between the tunnel boring machine and tunnel liner as it being
installed is
described in some detail below by Figure 17.
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5. The seals between the tunnel liner segments and liner sections are
described in some
detail below by Figure 18.
6. Once a lined shaft or lined tunnel is installed, wells can be drilled
through the shaft or
tunnel wall liners by first attaching a wellhead control assembly (used for
drilling, logging,
operating and servicing wells, for example, at the well-head of a surface-
drilled well) and then
using this assembly to drill through the liner wall while maintaining a seal
between the
formation from the inside of the shaft or tunnel liner as illustrated for
example in Figure 11.
This is also a well-known practice.
Figure 17 is a side view schematic of a soft-ground TBM showing its principal
sealing
points during excavation. This figure illustrates how an Earth Pressure
Balance ("EPB")
machine is sealed against formation pressures and fluids. It is understood
that the seals may not
be perfect seals but will substantially reduce the in-flow of, for example,
liquids to an amount
that can be readily controlled by pumps. Similarly, in the case of gases,
seals can substantially
reduce the in flow of gas to amounts that can be readily controlled by
ventilation systems.
Figure 17 shows a schematic of an EPB machine with a cutter head 1701 and muck
ingestion
ports 1702. The excavated material or muck is ingested into a chamber 1706
which is
maintained at about local formation pressure (hence the name earth pressure
balance). The
excavated material is mixed with a plasticizer that gives the muck cohesion. A
screw auger
1705, then transfers the plasticized muck to a conveyor system 1707. The muck
in the auger
forms an effective seal between the chamber 1706 and the conveyor 1707. The
conveyor
system 1707 may therefore be an open or closed system and may be operated at
the ambient
pressure in the manned working areas inside the TBM and tunnel. The cutter
head 1701 rotates
within a shield 1703 and is sealed by well-known mechanical rotating sealing
means. A tunnel
liner 1711 is assembled within the shield 1703. As the TBM moves
forward(towards the left in
Figure 17), the shield 1703 moves with it and exposes newly formed liner
sections 1712 to the
formation. A series of brush seals between the overlapping portion 1709 of the
shield 1703 and
liner sections 1712 form a substantial seal between the formation and the
interior of the TBM!
tunnel liner. In current practice, these brush seals are limited to formation
fluid pressures of
about 10 to 12 bars. The tunnel liner 1711 is formed by joining sections of
liner 1712 at joints
such 1713. These joints are sealed as described in the following figure. Once
the tunnel liner
is installed, the pressure limitation can be considerably higher than 10 bars
as the pressure limit
is now dictated by the structural integrity of the liner and/or the sealing
technology used to form
gaskets between liner sections and segments. A slurry TBM seals in a slightly
different way
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during excavation. The slurry TBM cutting head excavates by forming the ground
just ahead of
it into a dense slurry. The slurried muck is ingested into a pressurized
chamber and then
formed into a transportable slurry by adding additional water. The slurry may
be transported
out of the tunnel at approximately formation pressure in a closed slurry
system. Thus, like the
EPB TBM, the excavation and muck removal can be carried out at or near
formation pressure
while the working areas in the TBM and tunnel can remain at ambient pressure
and isolated
from the slurried muck.
Figure 18 illustrates features of tunnel liner sealing. A soft-ground tunnel
liner is
commonly comprised of short cylindrical liner sections. The sections are in
turn comprised of
segments. Alternately, a tunnel liner may be formed by continuously extruding
a concrete liner,
a newer method that does not require as much sealing as a liner assembled from
segments and
sections. An end view of a typical tunnel liner is shown in Fig. 18a showing
three segments
1801 joined together at joints 1802 which may include sealing gaskets (not
shown) and may be
bolted 1803. The segments are typically pre-cast and made from a high strength
material such
as for example concrete or fibre-reinforced concrete. An additional optional
sealing liner 1804
maybe installed to provide additional sealing. This sealing liner may be made
of rubber,
urethane or another tough sealing material. A side view of the tunnel liner is
shown in Fig. 18b
illustrating two sections 1810 of outer diameter 1813 joined together by a
joint 1811. A
longitudinal segment joint 1812 such as described in Fig. 18a is also shown.
Once each section
1810 is assembled inside the TBM shield (described previously in Figure 17),
it is compressed
against the previously installed section by the action of the TBM propelling
itself forward by its
hydraulic rams against the end of the tunnel liner. A seal is formed at
section joints 1811 by a
sealing gasket such as shown in Fig. 18c which illustrates a close-up section
view between two
liner sections 1820 and their joint surfaces. Typically a sealing gasket
mounting assembly 1821
2.5 is cast into the liner segments 1820. A compressible sealing material 1822
is installed in at
least one of the sealing gasket mounting assemblies 1821. When the liner
sections 1820 are
compressed by the propelling action of the TBM, the sealing material 1822 is
compressed
forming a seal between adjacent tunnel liner sections.
There are other advantages of the present invention not discussed in the above
figures.
For example, if there are problems during the operation of the system after
production
operations have begun, it is possible to perform servicing and repair. This
could include for
example repair of down hole pumps, valves and other production equipment. If
required,
additional wells can be drilled to offset declining production. Wells can
readily be cleaned and
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serviced in all weather conditions. Remotely operated robotic vehicles can be
operated inside
the tunnel and monitor or observe problem areas. This can be especially useful
when the tunnel
is for thermal production operations such as SAGD. Finally, much of the
installed equipment
(piping, pumps, sumps, diagnostics, heaters and the like) can be retrieved
from the tunnel for
use in other tunnel-based hydrocarbon recovery operations.
A number of variations and modifications of the invention can be used. As will
be
appreciated, it would be possible to provide for some features of the
invention without
providing others. The present invention, in various embodiments, includes
components,
methods, processes, systems and/or apparatus substantially as depicted and
described herein,
including various embodiments, sub-combinations, and subsets thereof. Those of
skill in the
art will understand how to make and use the present invention after
understanding the present
disclosure. The present invention, in various embodiments, includes providing
devices and
processes in the absence of items not depicted and/or described herein or in
various
embodiments hereof, including in the absence of such items as may have been
used in previous
devices or processes, for example for improving performance, achieving ease
and\or reducing
cost of implementation.
The foregoing discussion of the invention has been presented for purposes of
illustration
and description. The foregoing is not intended to limit the invention to the
form or forms
disclosed herein. In the foregoing Detailed Description for example, various
features of the
invention are grouped together in one or more embodiments for the purpose of
streamlining the
disclosure. This method of disclosure is not to be interpreted as reflecting
an intention that the
claimed invention requires more features than are expressly recited in each
claim. Rather, as
the following claims reflect, inventive aspects lie in less than all features
of a single foregoing
disclosed embodiment. Thus, the following claims are hereby incorporated into
this Detailed
Description, with each claim standing on its own as a separate preferred
embodiment of the
invention.
Moreover though the description of the invention has included description of
one or more
embodiments and certain variations and modifications, it is intended to obtain
rights which include
alternative embodiments to the extent permitted, including alternate,
interchangeable and/or
equivalent structures, functions, ranges or steps to those claimed, whether or
not such alternate,
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interchangeable. and/or equivalent structures, functions, ranges or steps are
disclosed herein,
and without intending to publicly dedicate any patentable subject matter.
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