Note: Descriptions are shown in the official language in which they were submitted.
CA 02809204 2013-02-22
SYNCHRONIZED SYSTEM FOR THE PRODUCTION OF CRUDE OIL BY MEANS OF IN-
SITU COMBUSTION
The invention relates to a synchronized crude oil production system using in-
situ
combustion. The system measures, monitors and controls the operating
conditions
in real time and comprises at least one injection well, at least one
production well
and at least one inclined synchronization well. According to one aspect of the
invention, the end of at least one production well and the end of at least one
inclined synchronization well are oriented outward the injection well. In
addition, the
system comprises measurement, monitoring and control elements that transmit
signals and information detected thereby to one or more processing units
which,
together or independently, use an analytical model to assess the combustion
conditions and the advance of the combustion front and, depending on the
results,
synchronize the production operations, each well being operated and handled
remotely at the control valves thereof in order to influence the displacement
of the
combustion front.
BACKGROUND
Heavy crude oil or extra heavy crude oil is any type of high-density crude oil
which
does not flow easily. It is referred to as "heavy" because its density or API
gravity is
less than 21.9 API.
The largest reserves of heavy crude oil in the world are located north of the
Orinoco River in Venezuela, but 30 or more countries are known to have
reserves.
Canada has large heavy crude oil reserves, mainly in the provinces of Alberta
and
Saskatchewan. In this sense, in the last decades, specialized techniques have
been developed for the efficient and economical production of such deposits.
Production, of heavy and extra heavy crude oil present special challenges
compared to light crude oil due to their high viscosity, and consequently low
mobility and low API gravity.
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To overcome such challenges, several Thermal Recovery methods have been
developed. Among such methods, there are different types of steam injection
techniques such as Steam Assisted Gravity Drainage (SAGD). This technique
involves the use of two horizontal wells instead of vertical wells, wherein
the
operators inject high temperature steam into the upper wellbore, the steam
flows
through the well, heats the oil by heat transfer and reduces its viscosity,
causing
the heated oil to drain into the lower horizontal wellbore. According to
literature
available, SAGD has an estimated recovery rate of 20%-50% of in situ oil,
however, the implementation rate is limited to a type of oil reservoirs,
mostly those
not affected by strong aquifers and with an excellent vertical communication.
Another broadly used method, with a greater implementation range, is in situ
combustion. Such method involves heating and oxidizing a small amount of oil
existing within the reservoir in order to generate thermal energy. Such energy
allows displacement of a considerable oil bank from the injection wells to
production wells mostly due to the viscosity reduced, vaporization and carry
forward of the gases formed in the combustion process. Although this type of
process has existed for a long time, there have been technical-operating
difficulties
discouraging its application, such as the control and monitoring of the
combustion
front, which directly affects the volumetric sweep efficiency and, therefore,
the
recovery of the oil existing gin the reservoir. However, there have been
efforts to
overcome such difficulties which have reached reservoir recovery over 60%, as
reported in several bibliographic sources and pilot and commercial projects
carried
out around the world. Heavy crude oil reservoirs subjected to hydraulic
pressure
respond favorably to this type of method.
Generally, three chemical processes take place in an in situ combustion:
Oxidation:
The combustion zone acts like a piston displacing the fluids in the combustion
front
to the production wells. Coking: Oxygen combines with oil resulting in carbon
dioxide and heat. The combustion reaction is maintained by injecting air, and
the
CO2 released in the reservoir produces a decrease of the relative permeability
to
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water, which minimizes the water mobility respecting oil. Cracking: The
thermal
cracking creates a coke deposit in the fire front generating, in some cases,
an
improvement of the crude oil, combustion gases vaporize the water, improve the
displacement of fluids and increase the sweep efficiency of the process. In
summary, the in situ combustion process has a number of advantages, mainly in
reservoirs with high water saturation or direct influence of aquifers with
strong
hydraulic drive: improvement of the crude oil vs. water mobility ratio by
reducing
the relative permeability to water, positive influence on the gravitational
segregation by creating a secondary high pressure gas layer and reduction of
crude oil viscosity by heating and miscibility of CO2 produced. In addition,
the
saturation of residual oil is reduced and saturation of irreducible water
increases
due to the temperature increase as reported in the oil industry literature,
which
increases the oil flow and decreases the water flow.
Given the significant increase of heavy and extra-heavy crude oil reserves
worldwide, the search of technologies optimizing the above-mentioned
technologies has been a concern in the world oil industry. In particular,
there is a
need for a production method monitoring and controlling the specific
operations
existing in an in situ combustion, thereby increasing the hydrocarbon
production
and reserves, meaning the amount of oil recoverable from the reservoir in cost-
effective conditions.
Summary
The present invention may provide a synchronized crude oil production system
using in-situ combustion, comprising real time measurement, monitoring and
control elements for the combustion front and further comprising a geometry
and
type of well that make easier and more efficient the management of monitoring
and
control operations of such combustion front.
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The present invention also may provide a synchronized crude oil production
system using in-situ combustion comprising a type of well referred to as
inclined
"synchronization" well, also equipped with measurement and monitoring
elements,
that may fulfill different functions within the system making more efficient
the
control operations in the combustion front. The main purpose of the inclined
synchronization wells is not only to produce a higher volume of hydrocarbons,
but
to complement the measurement, monitoring and control of the combustion front
in
order to make the process for efficient and achieve a greater hydrocarbon
recovery. There is a significant economic justification regarding inclined
wells. An
inclined well is much more economical and easier to drill than a horizontal
well,
although it has its advantages due to its larger flow area. Its geometry or
architecture does not require the use of sophisticated drilling equipment like
horizontal wells, where it is necessary to "sail" through sometime very low-
density
sands that make difficult its trajectory. Such "Measurement While Drilling"
("MWD")
tools are very expensive and put up the cost of the well. In field with large
volumes
of reserves and where it is convenient to implement in situ combustion
processes
requiring to drill economical wells the cost of wells is extremely important,
representing over 60% of the overall cost of the investments in the project.
This is
why it is important to count on inclined, synchronized wells located at the
reservoir,
allowing to monitor and control the combustion front and to maintain and
improve
the volumetric sweep efficiency, maximizing the oil reserve recovery.
In accordance with one aspect of the invention, there is provided a
synchronized
crude oil production system using in-situ combustion that measures, monitors
and
controls the operating conditions in real time. Such system includes at least
one
injection well, at least one production well and at least one inclined
synchronization
well. The end of the production wells and the end of the inclined
synchronization
wells within the reservoir are oriented outward the injection well, wherein
such
wells include measurement, monitoring and control elements. Such measurement
and monitoring elements transmit the signals and data collected thereby to one
or
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more processing units which, together or independently, use an analytical
model to
assess the combustion conditions in the well-subsurface system and the forward
move of the combustion front and, depending on the results, synchronize the
production operations. Each well is operated and handled remotely at the
control
s valves thereof in order to influence the displacement direction of the
combustion
front.
The production wells may be inclined.
The production wells may be multilateral.
At least one injection well, at least one production well and at least one
inclined
synchronization well may be in a particular geometrical arrangement according
to
the requirements of the well-subsurface system to be produced.
The inclined synchronization wells may be in a relative position within the
arrangement relatively closer to the production well than to the injection
wells.
The inclined synchronization wells may be located within a zone (Z) between
the
production wells and the injection well.
The present invention provides a synchronized arrangement of wells in an oil
reservoir for measuring, monitoring and controlling in situ combustion front
parameters to achieve a more efficient hydrocarbon recovery from the well-
subsurface system. In order for the in situ combustion recovery process to be
efficient, mainly in reservoirs with high hydraulic pressure, it is necessary
to
improve the water/oil mobility ratio due to the decrease of the relative water
permeability respecting oil and due to the heat created in the reservoir,
taking
advantage of the positive effects of the miscibility of CO2 in crude oil. The
result is
an enhanced efficiency of displacement or volumetric sweep and, therefore, a
greater hydrocarbon reserves recovery.
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Thermal processes and kinetic reactions taking place in an in situ combustion
process are the typical ones. On the one hand, there will be a heat oil front
in the
combustion zone that will result in an oil viscosity decrease and, therefore,
will
increase mobility respecting water, making easier the entrance of oil into the
closest production well. Regarding the crude oil located in the non-combustion
zone or zone not affected directly by the combustion front, the heat
transferred will
also have a positive effect in reducing the crude oil viscosity, resulting in
an
improved oil mobility thus increasing the probability of more hydrocarbon
reserves
recovery.
Another beneficial aspect is the flowing of combustion byproduct gases to
higher
zones of the sand structure or the upper zone of the reservoir. The combined
effect
of the heat transfer, the oil viscosity reduction and gravitational
segregation
resulting from the formation of a secondary gas layer at a higher pressure
makes
the oil flow downwards thereby enhancing the sweep efficiency, increasing the
oil
displacement and thus increasing the hydrocarbon reserves recovery.
Brief Description of the Drawings
Figure 1 is a drawing of a prior art arrangement for crude oil recovery from a
reservoir by in situ combustion showing the two main zones of the well-
subsurface
system and the combustion front displacing from the injection well 1 to the
horizontal production well 2, combustion zone C and a zone adjacent to the
combustion front, the non-combustion zone D.
Figure 2 is an upper view of a prior art arrangement for crude oil recovery
showing
an ideal theoretical displacement of the combustion front of the well-
subsurface
system from an injection well 1 to vertical production wells 2. The arrows in
this
figure show the direction of the combustion front.
Figure 3 is an upper view of an arrangement for crude oil recovery from a
reservoir
showing one of many theoretical forms that a combustion front in the well-
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subsurface system might have due to the irregular displacement of the crude
oil.
This figure intends to show that in real life, the combustion front is not
homogeneous, which certainly affects the productivity of the process, the
volumetric sweep efficiency and accordingly the hydrocarbon reserve recovery.
In
this figure, the arrows show the direction of the combustion front.
Figure 4a is an upper view of an arrangement for crude oil recovery from a
well-
subsurface system according to a first embodiment of the invention with
inclined
production wells at instant t1 (referential), showing an irregular combustion
front
under undesired conditions without applying Synchronized Operations
Management "SOM" to monitor and control the combustion front and improve the
sweep or displacement efficiency and the hydrocarbon reserve recovery. In this
figure, the arrows show the direction of the combustion front.
Figure 4b is an upper view of an arrangement for crude oil recovery from a
well-
subsurface system according to the embodiment of Figure 4a at instant t2
(referential and subsequent to t1) showing a uniform, optimal combustion front
under desired operating conditions, after the synchronization operations by
monitoring and control of the invention. In this case, synchronized operations
management concepts have been applied for measuring, monitoring and
controlling the combustion front. In this figure, the arrows show the
direction of the
combustion front.
Figure 5 is an interior side view of zone X of Figure 4b, showing the relative
position among injection wells, inclined production wells and synchronization
wells,
highlighting a first embodiment of the invention with inclined synchronization
wells
and production wells.
Figure 6 is an upper view of an arrangement for crude oil recovery from a well-
subsurface system according to a second embodiment of the invention using
multilateral production wells and inclined synchronization wells strategically
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located. Such configuration of multilateral production wells and inclined
synchronization wells represents an optional embodiment of the invention. Note
that the direction of the multilateral section of production wells and
inclined
synchronization wells is outward. In this figure, the arrows show the
direction of the
combustion front.
Figure 7 is an interior side view of zone X of Figure 6 showing the relative
position
among the injection well, the multilateral wells and the inclined
synchronization
wells highlighting an optional embodiment of the invention.
Figure 8 is an upper view of an arrangement for crude oil recovery from a well-
subsurface system according to an optional embodiment of the invention showing
a uniform, optimal combustion front under desired operating conditions after
the
synchronization operations by monitoring and control of the invention. In this
figure,
the arrows show the direction of the combustion front.
Figure 9 is a map representing a referential reservoir used for a simulation
of an
arrangement according to Figure 6 of the invention showing several layers, oil
sands from which oil is recovered and the last layer represents an aquifer or
water
zone which is the main source of water.
Figure 10 is a chart representing the production data from synchronization
wells
(3a), (3b), (3c) and (3d) according to Figure 9 in barrels per day as a
function of
time obtained by simulation. Such wells are normally useful to support
production
wells in crude oil recovery.
Figure 11 is a chart representing the estimate production of barrels per day
as a
function of time for multilateral wells 2a, 2b, 2c and 3d resulting from a
referential
simulation.
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DETAILED DESCRIPTION
Figure 2 shows a prior art combustion crude oil recovery system showing an
arrangement of 5 inverted wells, which for referential purposes include a
vertical
injection well (1) and four vertical production wells (2). In this figure, the
injection
well (1) is located within the arrangement within the area defined by the
production
wells (2). The function of the injection well (1) is to provide air, oxygen or
a mixture
of oxidizing gases to displace the crude oil within its influence area and
maintain
the combustion reaction in the reservoir. Zone (A) represents the limits of
the
combustion front within the reservoir and the arrows thereon represent the
same
theoretical direction of the front as it goes forward to reach the production
wells (2)
and thus recover the oil from the reservoir. In real life, the combustion
front does
not travel homogeneously, and therefore, as time goes by, the form of zone A
departs from symmetry. Figure 3 shows a referential example of a combustion
crude oil recovery system wherein zone B represents a combustion zone near
reality, when no measures to control it are taken. As shown, the combustion
front is
amorphous and thus the oil in the vicinity of the production well (2c) cannot
be
recovered from the reservoir, affecting significantly the productivity of
production
wells, the volumetric sweep efficiency and the hydrocarbons reserves recovery.
This reality may be corrected by including a greater number of production
wells (2)
within the arrangement each including, in turn, monitoring and controlling
tools for
the combustion reactions and the forward move of the combustion front so as to
control the direction desired. However, such addition of production wells (2)
involves additional costs in well drilling and completion operations which are
useless once the combustion front (zone B) has passed through the area
underneath such wells.
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The synchronized crude oil production system using the in situ combustion
process
of the present invention provides: including measurement, monitoring and
control
elements in the vertical injection wells (1), production wells (2) present in
a well
arrangement, and further introducing a new type of well referred to as
inclined
"synchronization well" (3), including, in turn, measurement elements for
pressure
and temperature, among other variables, at different levels of the well, and
monitoring and control elements for the gases created from the combustion
front. A
system according to the invention comprises at least one injection well (1),
at least
one production well (2) and at least one synchronization well (3). Figures 4a
and
4b include for referential purposes at least four inclined synchronization
wells (3) in
an arrangement comprising one injection well (1) and four inclined production
wells
(2).
The term "inclined" used in reference to certain wells should be understood so
that
the inclination of the well may go from the surface to one end thereof or
comprise a
vertical section and an inclined section, where the inclined section is in
contrast
with a substantially horizontal or substantially vertical section. In this
sense, an
inclined production well (2) and an inclined synchronization well (3) of the
present
invention does not include a horizontal well configuration such as that of the
prior
art, which include a substantially vertical section and a substantially
horizontal
section attached thereto.
As mentioned above, each injection (1), productions (2) and synchronization
(3)
well has measurement, monitoring and control elements for the combustion front
(zone B), being such elements related to the functions of each well within the
arrangement. Generally air, oxidizing gas, a mixture of oxidizing gases and
other
fluids are injected through the injection well. (1) in order to displace the
crude oil
and maintain the combustion reaction to the production (2) and synchronization
(3)
wells more efficiently. Regarding new production wells that may exist in the
field
(2), they will fulfill a double function: first, such wells will serve to
produce the crude
oil displaced by the combustion front (combustion zone) and adjacent zones
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(zones influenced indirectly by heat transfer), including the crude oil
displaced by
gravitational segregation. Second, production wells (2) will serve as
monitoring
wells for the combustion conditions in the well-subsurface system. Inclined
synchronization wells (3), duly equipped with remote pressure and temperature
sensors, will have, among others, several functions. First, they serve as a
support
for production wells (2) for measuring, monitoring and controlling the
combustion
front by synchronized operations management; second, they will serve as
additional production wells, and third, they may serve as wells for the
release of
undesired gases from the well-subsurface system, when required. Finally, such
inclined synchronization wells (3) may be converted into oxidizing gas
injection
wells, if it is so required and permitted by the conditions of the process.
Their
construction is carried out so that such function is feasible technically (see
Figures
5 and 7).
Among the measurement and monitoring equipment to be installed there are
remote pressure and temperature sensors operating in real time, however, there
may be other combustion front control elements, such as 4D seismic data
recovery, flow logs and imaging equipment installed in some or all of the
wells.
Such measurement and monitoring elements send the signals and data collected
by them to a processing unit in charge of evaluating the combustion conditions
of
the well-subsurface system and the forward move of the combustion front. If
the
data collected in each type of well is within the desired operating
conditions, the
injection (1), production (2) and inclined synchronized (3) wells will
continue with
their basic functions within the arrangement. On the contrary, if the data
collected
show that a zone is being affected adversely or preferentially by the
combustion
process to an undesired direction, "Synchronized Operations Management",
"SOM", consisting in synchronizing the production operations so that each well
or
group of wells is handled remotely in its control valves to influence the
displacement direction of the combustion front and make it uniform. For
example, if
at certain moment the combustion front goes preferentially or prematurely
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CA 02809204 2013-02-22
certain direction, a temperature or pressure profile change will be detected
at any
inclined synchronization well (3) or production well (2), these changes being
immediately registered in the data processing unit, where the operators may
issue
instructions in real time to any or all inclined synchronization wells (3) or
production
wells (2). Such instructions consist in the synchronized and remote management
of
the production control valves of the wells, causing the modification of the
production pattern and accordingly the forward move of the combustion front,
redirecting it towards the direction desired. The operator may even send
instructions to the injection well in order to decrease, increase or regulate
the
amount of oxidizing gas being injected into the well-subsurface system.
Instruction may be also given for the complete shutdown of wells, including
the
activation of water injection systems to control any abnormal situation taking
place
in any well or the reservoir itself.
Another alternative is that inclined synchronization wells (3) may act as
release
wells or valves in case that gas concentration within the reservoir exceeds
permitted values; in such case, the control unit can send an instruction to
activate
the release or gas extraction function.
The number and geometry of the injection well (1), production well (2) and
inclined
synchronization well (3) in the arrangement of the system of the present
invention
will depend on the type of reservoir, the type of arrangement and the
exploitation
conditions of the reservoir. Injection (1), production (2) and inclined
synchronization
(3) wells are in a particular geometric arrangement according to the
requirements
of the well-subsurface system to be produced.
Each well of the arrangement of Figures 4a and 4b, whether injection wells
(1),
inclined production wells (2) or inclined synchronization wells (3), will be
connected
to one or several processing units jointly or independently. In any connection
configuration, the processing unit is capable of interpreting the measurements
from
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every well and sending the signals in order for the operator take the
necessary
correctives. Therefore, the invention provides an intelligent measurement,
monitoring and control system which steps comprise evaluating in real time and
constantly the conditions of in situ combustion reaction in the well-
subsurface
system (at different interest points duly identified), sending of signals to
the
processing unit, analyzing independent evaluations from each of the wells and,
based on the results, determining automatically by software or computing model
the correctives necessary to uniform the combustion front.
PREFERRED EMBODIMENTS OF THE INVENTION
1.0 In a first preferred embodiment of the invention, the injection wells
(1) are vertical,
the production wells (2) are inclined and synchronization wells (3) are
inclined as
shown in Figure 5. Such configuration allows a better coverage of the area of
the
well-subsurface system to be produced, making more efficient the monitoring
process and accordingly the production process. The use of vertical production
wells generally has the restriction that its function is limited to a single
point of the
well and/or subjacent area thereof. On the contrary, this preferred embodiment
of
the invention involves the use of vertical injection wells (1) and inclined
production
wells (2), so as to access to a specific region considered as relevant in the
well-
subsurface system. Regarding synchronization wells (3), strategically located
within the arrangement of the invention, their configuration is inclined,
permitting a
better position with a greater flow area and orientation towards the points
into the
well-subsurface system considered as relevant for monitoring purposes.
In a second preferred embodiment of the invention, injection wells (1) are
vertical,
production wells (2) are multilateral, and synchronization wells (3) are
inclined as
shown in Figures 6 and 7. This configuration allows a greater coverture of the
well-
subsurface area to be produced, making more efficient the monitoring process
and
accordingly, the production process. Such preferred embodiment involves the
use
of vertical injection wells (1) and multilateral production wells (2) so as to
cover a
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greater area of the well-subsurface system. Regarding the inclined
synchronization
wells (3), they are strategically located within the arrangement of the
invention,
their configuration is always inclined, which allows a better position with a
greater
flow area and orientation towards the points into the well-subsurface system
considered as relevant for monitoring purposes.
For the two preferred embodiments described above, the relative position of
the
inclined synchronization wells (3) in the arrangement is relatively close to
the
production well (2) and, if more than one production wells (2), preferably the
zone
adjacent to the two closest production wells (2). Preferably, however, the
synchronization wells (3) shall be close to an intermediate and strategic
position
from the geological point of view to the injection well and the production
wells (2),
and placed within the zone Z (shown in Figures 4a, 4b, 5, 6, 7 and 8).
Regarding the production wells (2) and inclined synchronization wells (3) they
are
oriented so that the end of the production wells (2) and the end of the
inclined
synchronization wells (3) within the reservoir is outward respecting the
injection
well (1). Generally, production wells (2) have a single inclined or
multilateral
portion. However, they may have a substantially vertical section and/or one or
more inclined sections, which make them multilateral. The number of production
wells (2) and inclined synchronization wells (3) may vary depending on the
features
of the reservoir and the location of existing wells in the field at the
beginning of the
in situ combustion process. Such preferred embodiments and relative
arrangements of the injection wells (1), production wells (2) and inclined
synchronization wells (3) to carry out the invention are shown in Figures 4a,
4b, 5,
6, 7, and 8.
EXAMPLE (NUMERICAL SIMULATION)
With the purpose of evidencing the advantages of the invention, a numerical
simulation was carried out by using the STARS numerical simulator by CMG in
one
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of the fields of Pacific Rubiales Energy. STARS include the multiphasic flow
of oil,
water and gas, the heat transfer, compositional changes and chemical, physical
and kinetic reactions taking place in the reservoir during in situ combustion.
In
order to evaluate the behavior of the reservoir subjected to in situ
combustion
using different well arrangements and in this case combination of injection
wells
(1), multilateral production wells (2) and inclined synchronization wells (3),
an
historical comparison of the production of production wells existing in the
field was
carried out and the typical kinetic reactions of the process were applied,
among
other reservoir and design variables, such as: Four inclined synchronization
wells
(3) four multilateral production wells (2), one vertical injection well (1)
injecting
constantly 2.5 million cubic feet of air per day during 5 years in an area of
25 acres
in a crude oil reservoir of more than 2,800 feet in depth.
The spacing and location of wells may be seen in Figure 9, showing an
schematic
view of the reservoir, where simulations where carried out in order to
determine the
behavior of the production for each of the wells involved and the hydrocarbon
reserves that may be recovered by using the process and well arrangement
described. Such spacing and location of the wells is related to the
arrangement
shown in Figure 6. The reservoir section selected in shown in Figure 9.
Results of Numerical Simulations
The results of numerical simulations are summarized as follows:
The estimated production of the inclined synchronization wells (3) used in the
simulation is shown in Figure 10. The production of vertical wells was higher
than
1,000 BPD at the beginning and it was maintained for a reasonable time period
as
a consequence of the in situ combustion process using the synchronization
technique explained in previous chapters.
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Likewise, Figure 11, shows the oil production of "outward" multilateral
production
wells 2a, 2b, 2c and 2d in the selected sector. Such wells began with
production
rates higher than 3,000 BPD and were maintained over 1,000 BPD.
The foregoing behavior and the one of synchronization wells allow concluding
that
the proposed well arrangement is successful in increasing the volumetric sweep
efficiency and accordingly the recovery of hydrocarbon reserves in over 40% of
the
oil originally on site.
The description of the present invention is referential, so it must be
understood
broadly. Also, figures and examples are for reference purposes to assist in
understanding the principles and contributions of the invention to the prior
art and
shall not be understood as exhaustive and/or exclusive.
