Note: Descriptions are shown in the official language in which they were submitted.
CA 02549782 2006-05-08
DESCRIPTION
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority from United States (US) utility patent
application
11 /279,305 filed 4/11 /2006 and provisional application 60/712,289 filed
8/30/2005 and United States Disclosure Document 521,535 by Dr. Henry
Crichlow.
INTRODUCTION
This invention relates generally to a new technology application and a new
type
of oil well for recovery of viscous hydrocarbons from subterranean oil bearing
formations. The technology involves the novel use and application of
equipment and techniques in which horizontal wells are drilled from the
surface
down to and across an oil bearing formation and back up to the surface, in a
manner similar to that of drilling under a river crossing when laying
pipelines
across country. This new type of horizontal well is called a UniwellT"'
because it
has two surface wellheads one at each end of the axis of the horizontal
system.
Either wellhead can be used for either injection or production as needed by
the
operator.
The technology is a new application using some elements of an existing
technology, which has hitherto been used in horizontal pipeline crossing
3
CA 02549782 2006-05-08
installations and some technology elements, which have been used in
conventional oil well drilling.
FIELD OF INVENTION:
THIS INVENTION is a unique new approach to drilling horizontal wells for oil
recovery. The invention is particularly suited to making heavy oil formations
and tar sands producible by a single wellbore drilled using a specialized form
of
horizontal directional drilling. The invention however is not limited to
recovery
of heavy oils only; it can be used for many oil recovery processes such as tar
sands and oil shale.
With this invention, the operator can drill a new type of well that has all
the
operational benefits of a horizontal well and in addition this drilling can be
implemented either by using modified equipment that is readily available in
allied industries such as pipeline laying or by modifying existing oil well
drilling
rigs. This novel drilling approach effectively lowers costs and increases
efficiencies because it can utilize available equipment to drill wells with
greater
productive capacity. This approach allows wells to be drilled over large
lateral
distances, up to as much as 5,000 feet in shallow depth oilfields. At greater
depths the lateral extension is limited by the rig capability and mechanical
limitations of torque and drag in the drilling process. With this innovation,
in
field practice, which involves in part, the injection and production from the
same well, albeit at different ends of the horizontal axis, increased levels
of oil
recovery are achievable. It is also possible to produce from the same wellhead
by using concentric tubular strings and allowing the produced fluid to be
4
CA 02549782 2006-05-08
removed from the same wellhead.
BACKGROUND OF THE INVENTION
Introduction:
Heavy hydrocarbons in the form of petroleum deposits are distributed
worldwide and the heavy oil reserves are measured in the hundreds of billions
of recoverable barrels. Because of the relatively high oil viscosity which can
exceed 106 cp, these crude deposits are essentially immobile and cannot be
easily recovered by conventional primary and secondary means. The only
economically viable means of oil recovery is by the addition of heat to the
oil
deposit, which significantly decreases the viscosity of the oil by several
orders
of magnitude and allows the oil to flow from the formation into the producing
wellbore. Today, the steam injection can be done in a continuous fashion or
intermittently as in the so-called "huff and puff' or cyclic steam process.
Oil
recovery by steam injection involves a combination of physical processes
including, gravity drainage, steam drive and steam drag to move the heated oil
from the oil zone into the producing wellbore.
The most significant oil recovery problem with heavy oil, tar sands and
similar
hydrocarbonaceous material is the extremely high viscosity of the native
hydrocarbons. The viscosity ranges from 10,000 cp at the low end of the range
to 5,000,000 cp at reservoir conditions. The viscosity of steam at injection
conditions is about 0.020 cp. Assuming similar rock permeability to both
CA 02549782 2006-05-08
phases steam and oil, then the viscosity ratio provides a good measure of the
flow transmissibility of the formation to each phase. Under the same pressure
gradient, gaseous steam can therefore flow from 500,000 to 250,000,000
times easier through the material than the oil at reservoir conditions.
Because
of this viscosity ratio, it is imperative and critical to any recovery
application
that the steam be confined or limited to an area of the reservoir by a seal.
This
seal can be physical, hydraulic or pneumatic and essentially must provide a
physical situation which guarantees no-flow of any fluid across an interface.
This can be implemented by several means. Without this "barrier" the steam
will bypass, overrun, circumvent, detour around the cold viscous formation and
move to the producer wellbore. This invention addresses and resolves this
major obstructive element in heavy oil recovery.
Horizontal wells have played a prominent part in recovery of oil. These wells
can be as much as 4 times as expensive as conventional vertical wells but the
increased expense is offset by the increased rates of oil production and
faster
economic returns. Several patents have described various approaches to using
horizontal wellbores. The need for horizontal wells requires a more efficient
economical and easily deployable system for developing and drilling these
horizontal wells. This novel utilization proposed herein addresses the needs
and teaches a method of horizontal well drilling and a production mechanism
that is more easily implemented, allows a larger portion of the reservoir to
be
exposed and allows more oil recovery to occur.
By implementing the new processes which are taught in this application by this
invention the oilfield operator can see improved performance, lower costs,
6
CA 02549782 2006-05-08
better oilfield management, and allow for efficient and orderly development of
petroleum resources.
Improvements have been made in enhancing the contact of the steam with the
native heavy oil by the introduction of horizontal well technology, which
allows
greater recovery than with the customary vertical wells. This current
invention
provides a further extension of the horizontal technology in which a novel
drilling methodology is applied to the drilling effort to allow wells of much
larger lateral extent, potentially larger diameters and thereby more efficient
recovery systems. This invention also describes the use of the single wellbore
as the injection and production system simultaneously without the need for
additional concentric or multiple complicated tubular systems in the well.
No fully operational cases of horizontal drilling with two weliheads have been
reported in the oil and gas drilling industry. To date, horizontal directional
drilling with two wellheads, i.e. with an entry and exit wellhead, has been a
technology limited almost exclusively to the pipeline construction industry in
which the engineers routinely use the horizontal directional drilling
techniques
to cross rivers by drilling a horizontal well from one side of the river bank,
several feet under the river bottom and across to the other bank. Refs.1 and
Ref. 2 are horizontal directional drilling publications, which show examples
where this technology has been successfully used in river crossings like the
Chinese Yangtze River where the crossing was 5,538 feet laterally and 170 feet
below the ground level. Some environmental uses have developed recently in
which horizontal wells are drilled under immovable structures like buildings
to
7
CA 02549782 2006-05-08
allow liquid contaminants to be siphoned off or produced from subsurface
layers.
Prior Art:
Various methods and processes have been disclosed for recovery of oil and gas
by using horizontal wells. There have been various approaches utilized with
vertical wellbores, to heat the reservoirs by injection of fluids and also to
create
a combustion front in the reservoir to displace the insitu oil from the
injection
wellbore to the production wellbore.
Wilson in US patent 5,165,491 provides a mechanism for putting more weight
on the drill bit by utilizing the weighted heavy drill collars in the general
vertical
portion of the well such that the maximum weight component is available on
the bit.
US Patent 5,467,834 provides the method and apparatus for drilling the curved
portion of a horizontal well by using a flexible composite drill pipe. US
Patent
6,202,761 further elaborates on the process of drilling the initial curved
portion
of the wellbore by placing a window turning shoe and drilling out a window
through the casing.
Keller in US Patent 5,803,666 indicates a process to allow a pilot hole to be
back-reamed in making a horizontal crossing with an inverted liner to support
the wall of the wellbore.
8
CA 02549782 2006-05-08
Landers in WO 99/66168 describes a drilling apparatus for horizontal wells
using a horizontal cutting jet blaster device under very high hydraulic
pressure.
US Patent 5,934,390 by Uthe discusses a similar jet drilling approach.
Rozendaal in US Patent application US2002/0066598 Al discloses a reaming
device which allows the pilot hole drilled by horizontal drilling machines
used in
underground utilities for gas, water, electric and phone lines to be reamed to
a larger diameter.
US Patent 6,357,537 illustrates the typical use of conventional horizontal
directional drilling equipment and the drilling process. This patent and
others
like it show the use of the drilling technology limited to shallow utility
type
crossings.
Rankin et al. in US Patent U52002/0096362 Al describe a back-reamer device
used to enlarge a pilot hole. This device is steer-able and allows the back-
reaming process to maintain correct alignment.
Balton in 5,402,851 teaches a method wherein multiple horizontal wells are
drilled to intersect or terminate in close proximity to the vertical well
bore. The
vertical weilbore is used to actually produce the reservoir fluids. The
horizontal
wellbore provides the conduits, which direct the fluids to the vertical
producing
wellbore.
Butler et al in 4,116,275 use a single horizontal wellbore with multiple
tubular
strings internal to the largest wellbore for steam recovery of oil. Steam was
9
CA 02549782 2006-05-08
injected via the annulus and after a soak period the oil is produced from the
inner tubing strings.
US Patent 5,626,193 by Nzekwu et al disclose a single horizontal well with
multiple tubing elements inside the major wellbore. This horizontal well is
used
to provide gravity drainage in a steam assisted heavy oil recovery process.
This
invention allows a central injector tube to inject steam and then the heated
produced fluids are produced backwards through the annular region of the
same welibore beginning at the farthest or distal end of the horizontal
wellbore.
The oil is then lifted by a pump. This invention shows a method where the
input
and output elements are the same single wellbore at the surface.
US Patent 5,215,149 Lu, uses a single wellbore with concentric injection and
production tubular strings in which the injection is performed through the
annulus and production occurs in the inner tubular string, which is separated
by a packer. This packer limits the movement of the injected fluids laterally
along the axis of the wellbores. In this invention the perforations are made
only
on the top portion of the annular region of the horizontal well. Similarly the
production zone beyond the packer is made on the upper surface only of the
annular region. These perforated zones are fixed at the time of well
completion
and remain the same throughout the life of the oil recovery process.
Huang in US Patent 4,700,779 describes a plurality of parallel horizontal
wells
used in steam recovery in which steam is injected into the odd numbered wells
and oil is produced in the even numbered wells. Fluid displacement in the
reservoir occurs in a planar fashion.
CA 02549782 2006-05-08
US Patents 6,951,247, 6,929,067, 6,923,257, 6,918,443, 6,932,155,
6,929,067, 6,902,004, 6,880,633, 20050051327, 2004021 1569 byvarious
inventors. and assigned to Shell Oil Company have provided a very exhaustive
analysis of the oil shale recovery process using a plurality of downhole
heaters
in various configurations. These patents utilize a massive heat source to
process and pyrolize the oil shale insitu and then to produce the oil shale
products by a myriad of wellbore configurations. These patents teach a variety
of combustors with different geometric shapes one of which is a horizontal
combustor system which has two entry points on the surface of the ground,
however the hydrocarbon production mechanism is considerably different from
those proposed herein by this subject invention.
Shell US Patent 6,953,087 shows that heating of the hydrocarbon formation
increases rock permeability and porosity. This heating also decreases water
saturation by vaporizing the interstitial water. The combination of these
changes increases the fluid transmissibility of the formation rock in the
heated
region.
US Patent 6,948,563 illustrates that increases in permeability may result from
a
reduction of mass of the heated portion due to vaporization of water, removal
of hydrocarbons, and/or creation of fractures. In this manner, fluids may more
easily flow through the heated portion.
US Patent 3,994,341 teaches a vertical closed loop system inside the wellbore
tubulars in which a vertical wellbore is used to generate a vertical
circulation of
11
CA 02549782 2006-05-08
hot fluids which heat the wellbore and nearby formation. Hot fluids and drive
fluids are injected into upper perforations which allow the driven oil to be
produced from the bottom of the formation after being driven towards the
bottom by the drive fluid.
US Patent 6,725,922 utilizes a plurality of horizontal wells to drain a
formation
in which a second set of horizontal wells are drilled from and connected to
the
first group of horizontal wells. These wells from a dendritic pattern
arrangement to drain the oil formation.
US Patent 6,729,394 proposes a method of producing from a subterranean
formation through a network of separate wellbores located within the formation
in which one or more of these wells is a horizontal wellbore, however not
intersecting the other well but in fluid contact through the reservoir
formation
with the other well or wells.
US Patent 6,708,764 provides a description of an undulating well bore. The
undulating well bore includes at least one inclining portion drilled through
the
subterranean zone at an inclination sloping toward an upper boundary of the
single layer of subterranean deposits and at least one declining portion
drilled
through the subterranean zone at a declination sloping toward a lower
boundary of the single layer of subterranean deposits. This embodiment looks
like a waveform situated in the rock formation.
US Patent 5,167,280 teaches single concentric horizontal wellbores in the
hydrocarbon formation into which a diffusible solvent is injected from the
distal
12
CA 02549782 2006-05-08
end to effect production of lowered viscosity oil backwards at the distal end
of
the concentric wellbore annulus.
US Patent 5,655,605 attempts to use two wellbores sequentially drilled from
the
surface some distance apart and then to have these wellbores intersect each
other to form a continuous wellbore with two surface wellheads. This
technology while theoretically possible is operationally difficult to hit such
a
small underground target, i.e the axial cross-section of a typical 8-inch
wellbore using a horizontal penetrating drill bit. It further teaches the use
of
the horizontal section of these intersecting wellbores to collect oil produced
from the formation through which the horizontal section penetrates. Oil
production from the native formation is driven by an induced pressure drop in
the collection zone by a set of valves or a pumping system which is designed
into the internal concentric tubing of this invention. The 5,655,605 patent
also
describes a heating mechanism to lower the viscosity of the produced oil
inside
the collection horizontal section by circulating steam or other fluid through
an
additional central tubing located inside the horizontal section. At no time
does
the steam or other hot fluid contact the oil formation where viscosity
lowering
by heat transfer is needed to allow oil production to occur.
US Patent 4,532,986 teaches an extremely complex dual well system including
a horizontal wellbore and a connecting vertical wellbore which is drilled to
intersect the horizontal well. The vertical well contains a massively complex
moveable diverter system with cables and pulleys attached to the two separate
wellheads to allow the injection of steam. This system is used to inject steam
from the vertical wellhead into the horizontal wellbore cyclically and
13
CA 02549782 2006-05-08
sequentially while the oil is produced from the wellhead at the surface end of
the horizontal well.
US Patent 4,037,658 teaches the use of two vertical shafts or wells connected
by a cased horizontal shaft or "hole" with a flange in the vertical well. This
type
of downhole flange connection is extremely difficult if not impossible to
implement in current oilfield practice. Two types of fluids are used in this
patent, one inside the horizontal shaft as a heater fluid and one in the
formation as a drive fluid. Both fluids are injected either intermittently of
simultaneously from the surface wellheads. The laboratory demonstration in
this patent shows that the annular steam zone is very conductive to oil
production and allows premature steam breakthrough. Based on this
demonstrated observation, it is difficult if not impossible, to conceive a
situation taught by this patent in which the injected steam as drive fluid
will not
preferentially flow under the hundreds of pounds injection pressure along the
heated annular zone and thus bypassing the cold viscous oil saturated
formation. It is noted that the cold viscous formation has an almost zero
mobility. This patent essentially teaches a system in which the injected steam
shall be cycled through the horizontal tube and the annular zone in the
formation under field conditions providing little if any sweep efficiency.
US Patent 3,986,557 claims a method using a horizontal well with two
wellheads that can inject steam into a tar sand formation mobilizing the tar
in
the sands. In this patent, during the injection of the steam it is hoped that
the
steam will enter the formation and not continue directly down the open
wellbore and back to the surface of the opposite wellhead. It is difficult to
visualize the steam entering a cold highly viscous formation while a highly
open
14
CA 02549782 2006-05-08
weilbore is available for fluid flow away from the formation. Furthermore,
3,986,557 teaches that the steam is simultaneously injected through
perforations into the cold bitumen formation while hot oil is flowing through
the same perforations, in the opposite direction through the rock pore
structure, against the invading high pressure steam. This situation is not
only
physically impossible but it thermodynamically impossible for the hot fluid to
flow "against the pressure gradient".
US Patent 4,445,574 teaches the drilling of a single well with two wellheads.
This well is perforated in the horizontal section and a working fluid is
injected
into the wellbore to produce a mixture of reservoir oil and injected working
fluid. Similar to the 3,986,557 patent it is difficult from a hydraulic point
of
view to visualize and contemplate the working fluid entering the formation
while an open wellbore is available for fluid flow horizontally and vertically
out
the distal end of this welibore.
US Patent application 20050045325 describes a recovery mechanism for heavy
oil hydrocarbons in which a pair of wells is used. A vertical injector well is
horizontally separated from a vertical production well. The hot fluid, steam
or
air is injected into the bottom portion of the injector and is expected to
displace the very viscous immobile oil from the cold reservoir and push this
hot
oil through the cold oil saturated formation eventually to the producer. The
invention expects oil flow to occur by drilling a web or radial channels from
the
injector to the producer. It is inconceivable that viscous cold oil, or even
lower
viscosity hot oil will preferably flow along these channels while extremely
low
viscosity high-pressure steam will flow through the cold formation. Flow in
porous media dictates that hot, saturated steam will completely bypass cold
CA 02549782 2006-05-08
viscous oil and the process will be a quick steam recycle process from
injector
to producer.
Ref. 4, the Society of Petroleum Engineers (SPE), 222 Palisades Creek Dr.,
Richardson, TX 75080, U.S.A, publishes several hundred papers on heavy oil
recovery.
SPE paper 37115 describes a single-well technology applied in the oil industry
which uses a dual stream well with tubing and annulus: steam is injected into
the tubing and fluid is produced from the annulus. The tubing is insulated to
reduce heat losses to the annulus. This technology tries to increase the
quality
of steam discharged to the annulus, while avoiding high temperatures and
liquid flashing at the heel of the wellbore.
SPE paper 78131 published an engineering analysis of thermal simulation of
welibore in oil fields in western Canada and California, U.S.A.
SPE paper 53687 shows the production results during the first year of a
thermal
stimulation using dual and parallel horizontal wells using the SAGD technology
in Venezuela.
SPE paper 50429 presents an experimental horizontal well where the horizontal
well technology was used to replace ten vertical injection wells with a single
horizontal well with limited entry. The limited-entry perforations enabled
steam
to be targeted at the cold regions of the reservoir.
16
CA 02549782 2006-05-08
SPE paper 75137 describes a THAI - 'Toe-to-Heel Air Injection' system
involving a short-distance displacement process, that tries to achieve high
recovery efficiency by virtue of its stable operation and ability to produce
mobilized oil directly into an active section of the horizontal producer well,
just
ahead of the combustion front. Air is injected via a separate vertical or a
separate horizontal wellbore into the formation at the toe end of different
horizontal producer well and the combustion front moves along the axis of the
producer well.
SPE paper 50941 presents the "Vapex" method which involves injection of
vaporized hydrocarbon solvents into heavy oil and bitumen reservoirs; the
solvent-diluted oil drains by gravity to a separate and different horizontal
production well or another vertical well.
SPE paper 20017 teaches a computer simulation of a displacement process
using a concentric wellbore system of three wellbore elements and complex
packers in which steam is injected in a vertical weilbore similar to that in
the
3994341 patent. Simulated steam injection occurs through one tubing string
and circulates in the wellbore from just above the bottom packer to the
injection perforations near the top of the tar sand. This perforations near
the
top of the tar sand. This circulating steam turns the wellbore into a hot pipe
which heats an annulus of tar sand and provides communication between the
steam injection perforations near the top of the tar sand and the fluid
production perforations near the bottom of the tar sand. This process requires
7 years to increase oil production from 20 BOPD to 70 BOPD.
17
CA 02549782 2006-05-08
SPE paper 92685 describes U-tube well technology in which two separate
wellbores are drilled and then connected to form a single wellbore. The U-tube
system was demonstrated as a means of circumventing hostile surface
conditions by drilling under these obstacles.
SPE 76727 describes that steam displacement in an underground hydrocarbon
reservoir occurs because of three components driving oil production. These are
gravity drainage, steam drag and steam drive. Gravity drainage is caused by
the
oil column height and the difference in density between the hot oil and the
steam vapor. Steam drag is caused by the relative motion between the steam
and oil and the steam dragging the oil along. Steam drive is the force created
by the steam pushing the oil ahead of the steam as it moves through the
reservoir.
Ref. 5 shows conclusively that the gravity drainage effect is the most
critical
factor in oil recovery in heavy oil systems undergoing displacement by steam.
Very few of these prior art systems have been used in the industry with any
success because of their technical complexity, operational difficulties, and
being physically impossible to implement or being extremely uneconomical
systems.
Shortcomings of prior art can be related a combination of effects. These
include;
the inability of the method to inject the hot fluid into a cold highly
viscous oil in the formation;
18
CA 02549782 2006-05-08
the inability to overcome the viscosity effect, wherein the viscosity of
steam is less than 0.020 cp under the reservoir conditions which makes the
flow of steam through porous media 5,000,000 times easier than cold high
viscosity oil of 100,000 cp. This flow ratio is based directly on the
viscosity
ratios of 100,000/.02;
the inability of the method or process to prevent bypass of injected fluid
directly from the injector source towards the producing sink;
the inability of the method or process to provide an effective seal to
prevent high pressure injected steam from bypassing cold viscous oil
impregnated formation and moving directly from the injector source towards
the producing sink;
the inability of the method or process to form a viable communication
zone from the steam zone or chamber to the producing sink while preventing
bypass and early breakthrough of steam;
the inability of the process to utilize the significant gravity drainage
effects created by the low density of the hot steam compared to condensed
water and hot oil;
the inability of the method to heat the formation effectively by physical
contact between the steam and the rock formation such that the latent heat,
which the major source of heat energy compared to the sensible heat, can be
transferred to the rock and hydrocarbons efficiently;
the requirement of long injection lead times of months to years of hot
fluid injection, before there is any production response of the displaced oil;
the use of overly complex equipment of questionable operational
effectiveness to implement the method in the field.
19
CA 02549782 2006-05-08
For example, in 3,994,341, this embodiment which although on the surface
resembles the invention herein differs significantly since the 3,994,341
patent
forms a vertical passage way only by circulating a hot fluid in the wellbore
tubulars to heat the nearby formation, the 3,994,341 patent claims the drive
fluid promotes the flow of the oil by vertical displacement downwards to the
producing perforations at the bottom, the 3,994,341 patent teaches that the
production perforations are set at the bottom of the vertical formation, a
distance which can be several hundred feet. In this 3,994,341 embodiment,
since no control mechanism like a back pressure system or pressure control
system is taught, it is obvious that the high pressure drive steam, usually at
several hundred pounds pressure, will preferentially flow down the vertical
passageway immediately on injection and bypass the cold formation with its
highly viscous crude and extremely low transmissibility. The same argument of
steam bypass applies to patent 4,037,658 which teaches a horizontal tube
arrangement instead.
Secondly, the large distance between the top of the formation and the bottom
of the formation will cause condensation of the drive steam allowing
essentially
hot water to be produced at the bottom with low quality steam, both fluids
being re-circulated back to the surface. In addition the mechanism to heat the
near wellbore can only be based on conductive heat transfer through the steel
casing. Since there is no formation rock contact with the steam fluid in which
latent heat transfer to formation fluids and rock is the major heat transport
system, the 3,994,341 method is incapable of delivering sufficient heat in a
reasonable time to heat the formation sufficiently lower the viscosity of the
oil,
CA 02549782 2006-05-08
raise the porosity and permeability of the formation as taught in the present
patent application.
To date, the majority of producing or injection horizontal well embodiments
shown in the petroleum industry have but a single wellhead and are all limited
by several physical and operational problems associated with the physical
nature of the embodiments. This new embodiment shown herein removes many
of the problems associated with the prior art.
In this new embodiment, using 3 drilling phases, a horizontal well is drilled
downward to the target formation and across the target producing formation at
the required depth and at a predetermined angle and then upward back to the
surface. Inside the formation the wellbore is drilled at a slant such that the
essential gravity flow component of the recovery process can be optimized. In
this phase of the drilling process, a typical drilling plan with a
conventional
drilling bottom hole assembly is used. At the end of the horizontal or lateral
portion, the start of the upward leg of the well is initiated. Since drilling
"uphill"
is operationally more difficult with heavy drill pipe and working against
gravity,
a novel solution is needed. This invention also teaches this novel solution.
In this upward portion a smaller bottom hole assembly with a smaller drill bit
used. A small pilot hole is drilled on the upward portion to allow for
operational
ease and to minimize any problems in the drilling process. This smaller hole
requires less drilling torque produces less drag and requires less weight on
the
bit. The portion is drilled in two phases. It also minimizes drilling fluid
loss
and any damage to the near surface water zones. This is one novel and
21
CA 02549782 2006-05-08
innovative part of this embodiment since the well involves drilling holes of
varying diameters drilled in two or more sequential sections in which the last
section is being drilled upwards to the surface of the ground. In one
embodiment when the pilot hole is completed, the upward section can be
enlarged by back reaming it to a larger size by using a reamer bit that is
pulled
from the exit side backward toward the horizontal leg of the well. This
approach is similar to that used in river crossings in the pipe laying
industry. In
another embodiment an option is to use a conventional rig and ream the hole in
the usual manner by drilling forward. This sequence of operations provides a
novel approach to building the upward section of the well bore. In both cases
the near surface groundwater must be protected by casing put in place or by
using low loss fluids during the drilling process.
All of the prior art relates to horizontal directional drilling used primarily
for
river crossings, highway crossings involved in pipeline laying, optical fiber
laying and environmental remediation. No effort to date has used this
technology effectively for oil recovery in a manner and form such as the
uniwellTM described herein.
It is seen that the above prior art techniques have several shortcomings and
disadvantages that can be avoided by the current invention while improving the
recovery process efficiency and lowering the costs.
There is a long felt need in the industry for a means of moving the heated low
viscosity crude oil that has been contacted by the steam in the steam zone to
a
place or location where it can be produced without having to move it through a
22
CA 02549782 2006-05-08
cold heavily viscous oil impregnated formation. This problem has continued to
baffle the contemporary and prior art with possibly the only exception being
the SAGD patent which uses two horizontal wells closely juxtaposed in a
vertical
plane. Even this SAGD approach has inherent difficulties in initiating the hot
oil
flow between the two wellbores. Trying to push the hot oil through a cold
formation is an intractable proposition. The subject invention offers a
solution
to this need and provides the mechanism by which the solution can be
implemented using conventional equipment and procedures.
THIS NEW INVENTION provides an improvement in the method whereby the
operator drills a specially designed horizontal well which is drilled from the
surface down to the producing formation and continues back up to the surface
as shown in the figures herein. This continuous wellbore behaves
simultaneously as both an injector and a producer. The techniques proposed
herein uses a combination of drilling activities that are known separately and
distinctly in the industry, but have not yet been utilized in this integrated
manner shown in this new invention.
THIS INVENTION allows the operator to rapidly drill a specialized horizontal
well
to the producing formation which allows efficient recovery of heavy oil from
the
subterranean formation. This new drilling technology can be applied to the
following systems; heavy oil deposits, tar sands and oil shale systems.
23
CA 02549782 2006-05-08
THIS INVENTION allows the orderly development of oil reserves, especially
heavy oil reserves by allowing the efficient and cost effective production of
these deposits.
SUMMARY OF THE INVENTION:
An object of this invention is to provide an improved method for recovery of
oils from subterranean formations by exploiting the advantages provided by
gravity drainage in the displacement process of heavy oils in porous
formations
using steam or combustion driven displacement processes. The use of a single
modified well bore, with a downward, lateral and upward section, the
uniwellTM,
has several engineering benefits including cost reduction, better fluid
displacement and more engineering control of the injection and oil recovery
process.
The invention presented herein utilizes two of the three components on steam
displacement discussed in the prior art. These are gravity drainage and steam
drive. There is very little relative motion between the steam and the oil so
there
is very little steam drag if any at all in this invention.
A more specific objective is to provide an improved means of drilling a
producing wellbore in subterranean formations by using a sequential drilling
method to build and drill the upward portion of the well after the lateral
portion
is drilled.
24
CA 02549782 2006-05-08
Another specific objective is to provide a means by which the operational
difficulties created by using heavy drill pipe and drilling "uphill" can be
overcome. The drilling of the upward portion of the wellbore is implemented by
using a pilot hole, a new oilfield concept, in which a small pilot hole is
drilled
upwards with a very small drilling assembly and bit and then the bore of this
section can be enlarged afterwards.
Another specific objective is to provide a means for enlarging the upward
section of the wellbore by using a back reaming process with a back reaming
bit from the exit end to the horizontal lateral.
Another specific objective is to provide a means for enlarging the upward
section of the wellbore by using a forward reaming process from the exit end
to
the horizontal lateral by using a typical conventional drilling rig with a
forward
drilling reaming bit.
Another specific objective is to provide for maximum gravity drainage during
oil production by drilling the lateral portion at an angle selected to
maximize oil
production while allowing maximum steam effect on the formation during
steam recovery processes.
Another specific objective is to provide a means whereby the lateral portion
of
the uniwellT"" can be extended below the target oil zone to allow maximum
contact and drainage within the oil zone of the injected steam and still
provide
the necessary gradient needed for gravity drainage of heated oil.
CA 02549782 2006-05-08
Another specific objective is to provide a means where the upward portion of
the uniwellTM can begin below the oil zone and be extended upwards to the
surface to accommodate the extended lateral wellbore as described above.
Another specific objective is to provide a means whereby the same wellbore
perforations along the horizontal section of the wellbore can be used
sequentially for either injection or production as required by the operator.
Another specific objective is to use the movable packer between the injection
and production perforations, which forces the steam to exit the wellbore and
enter the oil zone at a preset location upstream of the production
perforations.
Another specific objective is after the initial oil region is depleted, to
unseat
and move the movable packer between the injection and production
perforations a preset distance along the axis of the wellbore and reseat it to
allow the steam displacement process to continue throughout the reservoir in a
new undepleted oil zone.
Another specific objective is to provide a means to considerably reduce the
distance the heated oil has to move from the steam injection point to be
produced in the wellbore through the producing formations.
Another specific objective is to provide a concentric communication channel in
the formation, which allows the heated oil to move from the upper steam zone
to the perforations in the lower production zone.
26
CA 02549782 2006-05-08
Another specific objective is to provide a means whereby oil production begins
as early as possible during the injection process compared to existing
technologies like Steam Assisted Gravity Drainage (SAGD) and conventional
Thermal Enhanced Oil Recovery (TEOR).
Another specific objective is to minimize the need to preheat the producing
elements of the welibore and the near wellbore region for a long time to raise
the temperature and to lower oil viscosity in order to initiate oil production
into
the cold producer region.
Another specific objective is to maximize steam zone growth by keeping the
steam vertically isolated and higher within the oil formation thus allowing
greater steam growth and less potential for steam breakthrough.
Another specific objective is to allow the steam to replace oil and to
pressure
up the steam bank at the top, which helps to displace low viscosity, heated
oil
downwards along the interface of steam/cold reservoir oil to the producing
perforations where there exists a pressure sink because oil is being removed
during production.
Another specific objective is to minimize the effects of a bottom water drive
on
degrading the steam efficiency since the short distance between steam and oil
production perforations allows steam to maintain contact with new oil and not
be diffused into the bottom water and dissipate its heat content to the higher
heat capacity interstitial water.
27
CA 02549782 2006-05-08
Another specific objective is to allow the horizontal wellbore to be drilled
close
to the bottom of the formation where a water zone exists by making the
perforations on the upper side of the lateral wellbore using specialized
perforating techniques available in the industry. This allows the injected
steam
to enter the oil zone preferentially and to stay out of the bottom water zone,
while the hot produced oil can be produced from the perforations downstream
of the injector point.
Another specific objective is to preclude the need for two wellbores in the
same
vertical plane, to recover oil as shown in some conventional SAGD
technologies,
since in thin zones, it is impossible to successfully drill two workable oil
wells
within the same thin zone using existing drilling equipment.
Another specific objective is to overcome the need for two vertically
separated
wellbores within close tolerances as proposed in SAGD which is expensive and
depends on critical placement of two wells within a vertical axis of 2 meters
or
less to guarantee hot oil dripping from the top well will not bypass the
bottom
well.
Another specific objective is to allow the steam to be injected in a
horizontal or
planar manner into the reservoir. This planar flow from the horizontal axis of
the wellbore creates smaller pressure gradients as opposed to pure radial flow
in the customary steam injection process.
Another specific objective is to create smaller pressure gradients by the
inward
horizontal flow along a significant wellbore distance during the production
28
CA 02549782 2006-05-08
phase and therefore lower the possibility of coning of fluids, in this case
steam
and formation water. The coning of steam and/or water is an unwanted
condition in this type of recovery system since it wastes energy and produces
water that replaces oil.
Another specific objective is to drill the wellbore with different diameters
in
different sections particularly in the lateral portion and the upward leg to
minimize costs, increase production and control well bore location.
Another specific objective is to use the accumulated oil in the lateral and
upward portion of the wellbore to act as an U-tube device, which behaves
similarly to a P-trap in a household drain, allowing the steam to remain on
the
injector side of the wellbore and maximize growth of the steam zone in the
reservoir where it is more effective.
Another specific objective is to use the produced oil, which accumulates in
the
lateral and upward portion of the wellbore to act as a backpressure system
such
that the steam bank is prevented from break through by flowing down the
wellbore.
Another specific objective is to use the bottom hole pump and by controlling
surface production rates thereby allowing the reservoir pressure to be
maintained at a level such that no steam is produced because of the back
pressure in the production wellbore.
29
CA 02549782 2006-05-08
Another specific objective is to use the slim-hole drilling in the upward
portion
of the wellbore to minimize damage to near surface water zones on the
"punch-out" or exit side of the wellbore since drilling occurs through a small
rock volume limiting the potential for surface zone damages.
Another specific objective is to use the slim-hole drilling in the upward
portion
of the wellbore to minimize damage to near surface water zones since the
drilling time is very short and fluid loss during the short time is minimized.
Another specific objective is to use a plurality of parallel uniwellsTM
simultaneously over a large areal extent to maximize reservoir recovery by
minimizing the heat losses laterally from a single uniwellT"" and to provide a
steam drive process that increases production by literally having a steam
front
move through the reservoir as a vertical plane.
BRIEF DESCRIPTION OF THE DRAWINGS.
The present invention consists of the wellbore and associated components
shown in the figures below:
Fig.1 Shows an overview of the uniwellT"', with the downward, the
horizontal lateral and the upward sections of the wellbore.
Fig.2 Shows the completed downward and lateral portion of the
uniwellT"' with the initiation of the pilot hole using a smaller
bottom-hole drilling assembly.
CA 02549782 2006-05-08
Fig. 3 Shows the completion of the pilot hole.
Fig. 4 Shows and the initiation of the back reaming process
to enlarge the pilot hole.
Fig. 5 Shows and the initiation of the forward reaming
process to enlarge the pilot hole.
Fig. 6 Shows the extension of the lateral section of the
wellbore below the oil zone and into the under-burden to
allow maximum contact of steam in the oil zone. Also shown
is upward section.
Fig. 7 Shows a field use of the embodiment in steam recovery of
heavy oil.
Fig. 8 Shows a field use of the embodiment in an in-situ
combustion recovery of heavy oil or tar sands.
Fig. 9 Shows the flow lines in plan view of a single uniwellT"" during
a sequence of operational phases in which the movable
packer is unseated, moved and re-seated after local oil
depletion occurs.
31
CA 02549782 2006-05-08
Fig. 10 Shows a plurality of uniwellsTM located in parallel in a
reservoir system.
Fig. 1 1 Shows initial heating of the near wellbore zone to allow
communication pathway for heated oil. This is done by a
removable downhole heater or less effectively by circulating a
hot fluid like steam.
Fig. 12 Shows the reamed out open-hole zone which is concentric
to the wellbore and used for hot oil communication from the
injection zone steam bank to the production perforations.
Fig.13 Shows a block diagram of the operational aspects of
the invention.
Fig.14 Shows a block diagram continuing the operational
aspects of the invention.
Fig.15 Shows a block diagram continuing the operational
aspects of the invention.
Fig.16 Shows the graph of production during a typical operation
of the prior art in which a "huff and puff' steam field
operation is implemented.
Fig.17 Shows the graph of the almost continuous steam
32
CA 02549782 2006-05-08
injection operations implemented in this invention, with the
non-injection periods for wellbore annulus heating and
moving of retractable packers.
Fig.18 Shows the on-off oil production graph in a more
detailed version of a part of the production cycle early in the
life of the field operations.
Fig.19 Shows the graph of the growth trend in oil production
rates as the steam injection continues followed by the natural
decline accompanying oil reserves depletion.
Item No. Description of Elements
1 Uniwell Wellbore
2 Underburden Formations
3 Overburden Formations
4 Entry wellhead on input side.
Exit wellhead on punch-out side.
6 Downward section of horizontal well bore
7 Lateral or horizontal section of wellbore
8 Completed upward section of horizontal wellbore
9 Surface of ground
Kick off point for start of curved portion of wellbore
11 Drilling Assembly
12 Pilot Hole
33
CA 02549782 2006-05-08
13 Upward section of horizontal wellbore after pilot drilling
14 Back reamer Bit
15 Enlarged Wellbore of upward section
16 Drill Pipe
17 Pull back drill rig used in back reaming process
18 Drill rig used in forward reaming process
19 Drill Pipe used in forward reaming process
20 Forward Reaming Bit
21 Overshoot Extension of lateral into underburden
22 Direction of Bit Travel
23 Subterranean Oil Zone
24 Downhole Pump
25 Casing Tubular pipe
26 Liner tubular pipe
27a Perforations for injection
27b Perforations for production
28 Drilling Rig
29 Moveable Oilfield Packer
30 Injected Steam Zone or Steam Bank
31 Hot oil flow direction
32 Parallel welibores
33 Injected gases for combustion front
34 Burned zone behind combustion front
35 Combustion Front
36 Zone of vaporized oil
37 Light Hydrocarbon Zone
34
CA 02549782 2006-05-08
38 Hot Produced Oil
39 Downhole Heater
40 Power Cable to Heater
41 Annular steamed communications zone
42 Reamed out annular zone
43 Hydraulic P-Trap effect
44 Steam injection time.
45 Steam soak time
46 Oil production rate decline curve
47a Oil production cycle period.
47b Oil daily production rate
47c Well Shut-in period, zero production rate
48 Wellbore heating period.
49 Oil flow rate increase trend
50 Oil flow rate decreasing trend.
CA 02549782 2006-05-08
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:
Referring now to the drawings wherein like reference numerals designate
corresponding elements throughout all the figures and referring in particular
to
Fig. 1. an improved method for extracting hydrocarbons according to an
example embodiment of the invention includes a wellbore 1 consisting of three
primary sections. As shown in steps 100, 101, 102, in Fig. 13 and in Fig. 1, a
downward section 6, a lateral section 7 and an upward section 8 are drilled
with
conventional oilfield equipment. The downward section 6 has an entry
wellhead 4 and is more or less vertically drilled depending on the nature of
the
recovery operations. Within the scope of this description a horizontal well or
horizontal well section means a well or well section, which is substantially
at or
close to horizontal inclination. The horizontal or lateral section 7 is
drilled in
the producing oil formation 23, which is a porous medium containing oil, gas
and water in the pore spaces. The upward section 8 is a continuation of the
lateral section 7 upward along a predetermined curve to the surface 9. A steel
casing 25 or steel liner 26 depending on the type of well and the location
within
the formation can line the wellbore 1. In other embodiments an "open-hole"
completion can be used in which there is no steel casing. This can be done in
well consolidated rock formations. At the entry end of the well 1 there is an
entry wellhead 4 and an exit wellhead 5 is on the distal end.
Perforations 27b, 27a are made in the casing to allow oil to be produced or in
the case of injection operations to allow injected fluids to enter the oil
zone 23.
The oil zone 23 is overlain by an overburden 3 and under-burden zone 2.
36
CA 02549782 2006-05-08
These zones are impermeable and trap the hydrocarbons in the oil zone 23
and from which oil production is possible when the well 1 drilled into the oil
zone.
Referring to Fig. 2, a drilling assembly 11 is used to drill through the
formations. This assembly is connected to the drill rig 28 at the surface by a
drill pipe 16. In some cases the bottom hole assembly consists of a downhole
motor and a drill bit. In other cases coiled tubing can be used instead of
drill
pipe. All the drilling practices are well known in the industry and are not
part of
this invention. The point where the vertical hole section 6 changes to a
horizontal section 7 is called the kickoff point 10. Referring to Fig. 3, a
small
pilot hole 12 is that portion of wellbore 12, which extends from the lateral
section 7 to the surface 9 along a predetermined path 13.
Referring to Fig. 4, the back reaming process shown in step 101 is
implemented, using the back-reamer bit 14 which travels through the pilot hole
12. The bit 14 is pulled backwards by pull back drill rig 17 at surface 9
using
the drill pipe 16. The enlarged hole 15 develops behind the reamer bit 14.
Referring to Fig. 5, a forward reaming process is subsequently implemented by
using the forward reamer bit 20 is connected to the drill rig 18 at the exit
end 5
by drill pipe 19. The reamer bit 20 moves in a forward direction 22 as it
moves
down the pilot hole 12 while the rig 18 rotates the reamer bit 20. In Fig. 6,
the
lateral section 7 can be extended 21 below the oil zone 23 and into the under-
burden 2 in order to extend the range of the well and allow more gravity
effect
on production in the vertical direction. A downhole pump 24 is shown in this
37
CA 02549782 2006-05-08
embodiment. The pump is used to lift the produced fluids to the surface as
needed.
Fig. 7 shows an embodiment of the invention for steam recovery of heavy oil.
In
a conventional steam recovery process, steam usually generated on the surface
using combustion boilers or as a by product of a electric power cogeneration
operation, is injected into the injector wellbore to heat the heavy oil,
decrease
its viscosity and drive it towards a producer well some distance away from the
injector. Referring to Fig. 11, as indicated in steps 103 and 104b of Fig. 13
in
this embodiment, a downhole heater 39 is used to conductively preheat a near
wellbore annular region 41 to a relatively high temperature of several hundred
degrees Fahrenheit between 300 F and 700 F, in a short time. This temperature
is sufficient to increase the rock permeability, lower the in-situ hydrocarbon
viscosity significantly, raise the rock porosity and increase the oil
saturation in
the heated zone. After this preheat operation is implemented for a sufficient
period of time, the downhole heater is removed. Referring to Fig. 7, in this
embodiment, steam 30 is injected into the oil zone 23 through perforations
27a which are strategically placed in the well casing 25. As indicated in step
105 the steam is prevented from traveling down the wellbore by a movable
packer 29, which separates the steam injector section from the oil production
section. In an "open hole" completion, this packer 29 can be a retractable
inflatable packer in those situations where the well is completed without a
casing 25. This blocking packer is retracted and moved along the axis of the
lateral 1 as the steam zones are depleted and new oil production occurs as the
processes are repeated.
38
CA 02549782 2006-05-08
During the recovery process, the steam forms a zone or steam bank 30 in
which oil is heated creating a tremendous drop in viscosity allowing the oil
to
flow easier. A viscosity drop from 10,000 cp at reservoir conditions to 2 cp
at
steam conditions is possible. The annular region pre-heated in step 104b by
the downhole heater provides a high conductivity communication path 41 and
driven by gravity and other hydraulic forces, the hot low-viscosity oil 38
moves
to the lower downstream perforations 27b as shown in step 108 of Fig. 14. As
hot oil 38 accumulates in the lateral section 7 and fills the wellbore, it
provides
a hydraulic "P-trap" effect 43 shown in Fig. 6, which acts as a backpressure
valve preventing the bypass of steam from the upper perforations 27a to the
lower perforations 27b. In one embodiment, the wellbore segment liquid can be
pressured from the surface with natural gas or some inert gas to help
implement the "P-trap" effect pneumatically in addition to hydraulically. As
indicated in step 109 of Fig. 14, by modulating production rates a process
called "choking" in the industry, this backpressure can be used to minimize
and
prevent any steam bypass in step 110. Oil is produced with a pump 24 if the
pressure is insufficient to flow to the surface or it can flow to the surface
if the
driving pressure is sufficiently high. As can be seen from the physical
implementation of this new embodiment the heated oil 38 travels only a few
feet, a significantly shorter distance in the steam zone 31 to the producing
perforations 27b. This compares to the very large inter-well distances of
several hundred feet, through cold highly viscous oil zones with limited
transmissibility that the hot oil has to travel in conventional steam floods
as
shown in Ref. 3. The new embodiment shown herein allows oil recovery to
begin almost instantaneously via the highly communicative annular zone
developed by the preheat process described above. This is in stark comparison
39
CA 02549782 2006-05-08
to the long steam injection and steam soak times needed for the conventional
steam flood to displace oil to the producer well.
Referring to Fig. 8 which shows an embodiment of the invention in in-situ
combustion recovery of heavy oils or tar sands also called a fireflood. In
this
embodiment, a downhole heater 39 is used to conductively preheat a near
wellbore annular region 41. After this preheat the downhole heater is removed.
Air 33 is then injected down the downward section 6 of the uniwellT"" through
perforations 27a and into the oil zone 23. Following the operations of a
typical
fireflood a combustion front 35 is initiated in step 107a. This burning front
35
creates a zone of vapors 36 and a zone of light hydrocarbons 37 ahead of the
combustion front. In the conventional fireflood, the intent is to heat the oil
to
drop the viscosity and move the free flowing oil towards the producer wellbore
several hundred feet distance away. In this embodiment as the combustion
front moves forward through the reservoir, the heated oil 38 decreases in
viscosity and it flows downwards under gravity and other physical forces to
the
wellbore 1 and through the highly permeable annular communication zone 41
and enters through the perforations 27b. As can be seen from the physical
implementation of the embodiment the heated oil travels a significantly
shorter
distance from the combustion zone 35 to the producing perforations 27b and
not needing to flow through a cold formation. This compares to the very large
inter-well distances through cold highly viscous oil zones with limited
transmissibility, that the front has to travel in conventional combustion
floods
as shown in Ref. 3. The new embodiment shown herein allows oil recovery to
begin almost instantaneously compared to the long combustion times needed
for the conventional fireflood to displace oil to the producer well. Oil
recovery
CA 02549782 2006-05-08
begins in days via the highly communicative annular zone developed by the
early preheat process, rather than in months and years under conventional
combustion processes and this time shortened time factor increases the
economic viability and profitability of the overall process.
Referring to Fig. 9 a plan view of an embodiment is shown in which two cycles
of injection and production are superimposed. The first cycle show the stream
flow lines 30 from steam injected into the wellbore perforations 27a and the
oil
produced from the wellbore perforations 27b. After a prescribed time interval,
the downhole packer 29 is moved down from position 'a' to position 'b' in the
wellbore between the next set of injection and production perforations. A new
cycle of operations is initiated as shown in Fig. 15, steps 113, 114, 11 5a,
115b
and 116. The downhole heater 39 is re-installed and the new wellbore annular
zone is heated to provide a high conductivity zone for hot fluid movement.
Next the first production perforation is converted to steam injection and the
oil
is produced into the wellbore from the next perforation set along the axis of
the lateral wellbore. The stream flow lines 31 are shown in the figure.
Continued steam injection can still occur in the first set of steam
perforations
or they can be plugged off if needed to allow the steam front to advance more
rapidly.
Referring to Fig. 10 a plurality of parallel wellbores 32 used in an
embodiment
is shown. This parallel approach allows a planar displacement of oil by the
injected steam as injection continues into the reservoir.
41
CA 02549782 2006-05-08
Referring to Fig. 11 the initiation of a flow channel 41 is shown. It is made
by
initially heating the area around the lateral wellbore 7 by using a removable
downhole heater 39 which heats the rock to between 300 F and 700 F. This
heating lowers the oil viscosity, increases the rock porosity and permeability
and lowers the water saturation in the near wellbore region opposite the
downhole heater. !t is possible but not nearly as effective to form the
communication zone by injecting steam for a few days through the first sets of
injectors to allow the zone around the wellbore to be heated and to lower the
viscosity of oil in place in this near wellbore region.
Referring to Fig 12 which shows another embodiment of the invention in which
a section of the lateral wellbore 7 is reamed out in step 104a during the
drilling
process to make a large open-hole annular zone section 42. This annular
cylinder 42 around the wellbore forms the communication zone through which
the produced fluids 38 move from the steam zone 30 to the production zone.
The steam is injected down the wellbore 6, the wellbore packer 29 diverts the
steam into the cold formation 23 where a steam chamber 30 develops. The
formation oil is heated by the steam and flows down the sides and periphery
walls of the steam chamber under gravity towards the bottom of the steam
chamber. The produced oil and condensed steam flow down the reamed out
zone 42 towards the bottom of the wellbore. In this embodiment the produced
fluids accumulate in the lateral wellbore 7 and fill the production string.
A novel aspect of this invention is the use of the heated oil in the wellbore
sections to act as a hydraulic pressure control and a flow control device. By
modulating the production of the fluid produced the process creates a back
42
CA 02549782 2006-05-08
pressure and a fluid "P-trap" seal in the lateral section of the wellbore
which
prevents the injected steam from bypassing the cold formation and forcing the
steam to remain in the steam bank zone and then to grow vertically.
Operationally the drilling operation is summarized as follows; the downward
portion 6 is drilled in a conventional manner, at the kickoff point 10 the
lateral
portion 7 is drilled using the typical horizontal drilling operations found in
the
oilfield today. At the start of the upward portion 8, the drilling assembly is
changed to allow the process to continue less expensively with a slim hole
assembly 11, which employs a smaller bit to drill the pilot hole to the
surface
along a planned trajectory 12. On reaching the exit end on the surface the
pilot
hole 12 is reamed out to a larger size by either a back reamer 14 or by using
a
forward reamer bit 20. The extension 21 of the lateral below the oil zone 23
is
a simple modification of the basic drilling process. In a similar manner the
completion processes which include cementing of casings, perforating of
casings, or setting of liners in the wellbore, installing of pumps and valves
are
basic processes in the oil drilling industry and are well known to all versed
in
the art.
In engineering the steam injection operation, a computer or simulation
analysis
is routinely used in the industry to calculate the optimal required injection
time
of steam into the hydrocarbon bearing formation for optimal oil recovery. This
analysis incorporates steam flow rate, steam quality, steam pressure,
formation
rock properties, oil saturation and depth of formation from the surface.
43
CA 02549782 2006-05-08
In this invention, during the earliest steam injection time only, the
production
of hot oil is maintained at zero to allow the oil to accumulate in (a) the
bottom
of the steam bank, (b) in the vertical communication zone and (c) in the
wellbore segment. This accumulated hot oil behaves as a hydraulic seal
preventing steam from bypassing the formation and flowing into the wellbore.
In alternative embodiments, the backpressure system described herein prevents
the production of oil into the wellbore. These no-flow embodiments are
essential and by preventing oil flow, they allow a steam bank to grow since
the
injected steam is forced to enter the formation directly heating the rock and
in-
situ hydrocarbons.
After the requisite injection time, which is nominally a matter of days, the
production of hot oil and condensed water is initiated by permitting the
removal of hot fluids from the wellbore via the production system or by
lowering the backpressure on the fluid column in the wellbore. After the
production of accumulated hot oil is complete as evidenced by the incipient
flow of dry steam detectable at the surface, the fluid production is shut down
and the accumulation of hot oil and condensed water at the bottom of the
steam bank resumes. It should be noted that in this invention, except as noted
later, steam injection is a continuous operation and the oil production phase
is
started and stopped at specific operational conditions during this thermal
recovery process.
This invention differs significantly from the prior art in its implementation
in
the field. The ability of the well to be produced very soon after steam
injection
begins, allows oil revenue to begin almost immediately. Furthermore the
44
CA 02549782 2006-05-08
volumetric flow rate of oil remains relatively constant while the steam bank
is
growing and can even increase as cumulative steam injection occurs. This is
due to the larger volume of rock being contacted and heated thus lowering the
oil viscosity and also by increasing the vertical extent of the steam bank,
the
gravity effect on the oil flow column is increased, both results contribute to
increased oil flow rates.
A typical response of a steam heated heavy oil reservoir using the prior art
of
huff and puff operations is shown in Fig. 16. It should be noted that after
the
steam injection time 44, steam injection is curtailed and after the soak time
45,
the well is put on production as shown in curve element 46. There is an
initial
increase in oil production rate which immediately declines exponentially to
the
un-stimulated level after a number of days. This process is repeated several
times to fully develop the steam operations and deplete the oil reservoir.
On the other hand, the invention described herein, provides for a very
different
set of operations. Fig. 17 shows the steam injection period 44 followed by the
period 48 in one embodiment in which the wellbore heater 39 is installed in
the wellbore and is operated for a fixed time, and during which time the
packer
29 is also moved along the wellbore. Note that the steam injection rate is
essentially constant, however in practice it is usually necessary to increase
the
injection rate over time to offset the heat losses as the steam bank increases
in
size.
Fig. 18 shows a more detailed set of operational data where the well
production
is intermittent. This occurs early in the steam operations since the steam
zone
CA 02549782 2006-05-08
or steam bank 30 is still small and growing and the accumulated oil 38 is
insufficient to be produced continuously without compromising the hydraulic
seal 43 and allowing steam breakthrough in the communication zone 41 and
the wellbore 1. This figure shows the oil production rate 47b and the oil shut-
in period 47c.
As the steam bank 30 grows, there is more reservoir formation 23 volume
available for oil production and there is a concurrent increase in the oil
production rate as shown by the trend line 49 in Fig. 19. This trend continues
to a maximum point after which there is an inevitable decline due to heat
losses, oil depletion and other factors as shown by trend line 50.
Given the increased oil flow rates which begin soon after steam injection,
coupled with the growth of the steam bank by almost continuous steam
injection, as opposed to the intermittent injection of the prior art huff and
puff
method; and the concurrent oil production increase, this invention provides
for
an improvement in the technology and prior art in a manner which allows
significant rapid development of hydrocarbon reserves from heavy and viscous
oil from subterranean formations with existing equipment and field operations
applied in a manner that has been heretofore lacking.
Various modifications and alterations of this invention will become apparent
to
those skilled in the art without departing from the scope and spirit of this
invention and it should be understood that this invention in not unduly
limited
to that set forth herein for illustrative purposes.
46
CA 02549782 2006-05-08
In this patent certain U.S. patents, patent applications, and other materials
(e.g., articles) have been incorporated by reference. The text of such U.S.
patents, U.S. patent applications, and other materials is, however, only
incorporated by reference to the extent that no conflict exists between such
text and the other statements and drawings set forth herein. In the event of
such conflict, then any such conflicting text in such incorporated by
reference
U.S. patents, U.S. patent applications, and other materials is specifically
not
incorporated by reference in this patent
Further modifications and alternative embodiments of various aspects of the
invention may be apparent to those skilled in the art in view of this
description.
Accordingly, this description is to be construed as illustrative only and is
for the
purpose of teaching those skilled in the art the general manner of carrying
out
the invention. It is to be understood that the forms of the invention shown
and
described herein are to be taken as the presently preferred embodiments.
Elements and materials may be substituted for those illustrated and described
herein, parts and processes may be reversed, and certain features of the
invention may be utilized independently, all as would be apparent to one
skilled
in the art after having the benefit of this description of the invention.
Changes
may be made in the elements described herein without departing from the
spirit and scope of the invention as described in the claims.
47
CA 02549782 2006-05-08
References:
1 Robbins Horizontal Drilling, 29100 Hall St, Solon, OH. 44139.
www.robbinstbm.com
2. The Crossing Company Inc.,1807-8th Street, Nisku, Alberta, Canada T9E
7S8, www.thecrossingcompany.com
3 Improved Oil Recovery - Exxon Background Series (1982), NY. NY 10020.
4. The Society of Petroleum Engineers 222 Palisades Creek Dr., Richardson,
TX 75080, U.S.A. www.spe.org.
5. "A Comparison of Mass Rate and Steam Quality Reductions to Optimize
Steamflood Performance", Topical Report 108, Gregory L. Messner, July 1998,
Stanford University, Stanford, California
48
