Patent Publication Number: US-7909093-B2

Title: In situ combustion as adjacent formation heat source

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None 
     FIELD OF THE INVENTION 
     Embodiments of the invention relate to methods and systems for oil recovery with in situ combustion. 
     BACKGROUND OF THE INVENTION 
     In order to recover oils from certain geologic formations, injection of steam increases mobility of the oil within the formation via, for example, a process known as steam assisted gravity drainage (SAGD). Energy needed for steam generation represents a substantial cost for the SAGD. Ability to provide cost efficient recovery of the oils with the SAGD diminishes as zones for oil bearing formations decrease in thickness. 
     In situ combustion offers another approach for recovering the oil. With in situ combustion, an oxidant injected through an injection well into the formation reacts with some of the oil to propagate a combustion front through the formation. This process heats the oil ahead of the combustion front while the injection gas and combustion gas products drive the oil that is heated toward an adjacent production well. 
     Vertical stratification further presents problems with respect to recovery processes such as the SAGD and the in situ combustion since separate formations may be separated from one another by natural barriers. One or more of the separate formations may be too thin for economic recovery utilizing the SAGD. Further, the separate formations can present various control problems with the in situ combustion. For example, the injection and/or production wells utilized for the in situ combustion processes may lead to premature unregulated breakthrough across the separate formations, such as when producing, and may burn up prior to full recovery of the oil without proper control for each of the separate formations. 
     Therefore, a need exists for improved methods and systems for oil recovery with in situ combustion. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method provides recovering of oil with in situ combustion. The method includes injecting an oxidant through an injection well into a first reservoir to propagate combustion through the first reservoir. Further, the method includes recovering first hydrocarbons through a first production well in fluid communication with the injection well through the first reservoir and recovering second hydrocarbons through a second production well disposed in a second reservoir and spaced from the first production well. The first and second reservoirs are stratified with the first reservoir separated from the second reservoir by a stratum having lower permeability than the first and second reservoirs. In addition, the stratum isolates one of the first and second production wells from one of the first and second reservoirs. 
     According to one embodiment, a production system for recovering oil with in situ combustion includes an injection well coupled to an oxidant supply. The system further includes a first production well completion in fluid communication with the injection well through a first reservoir and a second production well completion in fluid communication with a second reservoir and spaced from the first production well completion. The first and second reservoirs are stratified with the first reservoir separated from the second reservoir by a stratum having lower permeability than the first and second reservoirs. Further, the stratum isolates one of the first and second production well completions from one of the first and second reservoirs. 
     For one embodiment, a method of recovering oil with in situ combustion includes injecting an oxidant into a first reservoir ignited to conduct the in situ combustion. A burn zone of the in situ combustion is defined by sweep of a combustion front from ignition until extinguished. The method also includes recovering through a first production well extending through the first reservoir first hydrocarbons heated by the in situ combustion and recovering second hydrocarbons through a second production well. The in situ combustion heats the second hydrocarbons within a second reservoir that is separated by a barrier from the first reservoir. The second production well extends from surface through the second reservoir and terminates without extending into the burn zone for the in situ combustion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a schematic sectional side view of an injection well and production wells that are disposed with an impermeable stratum between one another to contain in situ combustion within an oil bearing reservoir below the impermeable stratum, according to one embodiment of the invention. 
         FIG. 2  is a schematic top view of an injection well and production wells that are disposed with an impermeable stratum between one another to contain in situ combustion within an oil bearing reservoir above the impermeable stratum, according to one embodiment of the invention. 
         FIG. 3  is a schematic sectional side view of the injection well and production wells taken along line  3 - 3  of  FIG. 2 , according to one embodiment of the invention. 
         FIG. 4  is a schematic sectional side view of a formation having an impermeable stratum separating oil bearing reservoirs and showing an in situ combustion injection well, a fluid flooding injection well, and respective production wells disposed in the formation, according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention relate to in situ combustion. Configurations of injection and production wells facilitate the in situ combustion. A first production well disposed in a first oil bearing reservoir is spaced from a second production well disposed in a second oil bearing reservoir separated from the first oil bearing reservoir by a stratum having lower permeability than the first and second oil bearing reservoirs. The stratum isolates one of the first and second production wells from one of the first and second oil bearing reservoirs. In situ combustion through the first oil bearing reservoir generates heat that irradiates into the second oil bearing reservoir to enable producing hydrocarbon with the second production well. 
       FIG. 1  illustrates an injection well  100  disposed in a formation that includes an oil bearing first reservoir  102 , an oil bearing second reservoir  104  and a barrier stratum  106  stratified with the stratum  106  located between the first and second reservoirs  102 ,  104 . A first production well  108  extends through the first reservoir  102  located above the stratum  106  without intersecting the stratum  106 . A second production well  110  passes through the second reservoir  104  and is in fluid communication with the injection well  100  via the second reservoir  104 . The stratum  106  isolates the first production well  108  from the second reservoir  104  located below the stratum  106 . 
     The stratum  106  creates this isolation by being less permeable than the first and second reservoir  102 ,  104 . In some embodiments, the stratum  106  may block fluid communication between the first and second reservoir  102 ,  104  and is hence impermeable. A layer of shale provides an example of the stratum  106 . 
     For some embodiments, the production wells  108 ,  110  may each define horizontal portions that are parallel to one another. Further the horizontal portions of the production wells  108 ,  110  may align on top of one another. This correspondence in orientation and placement of the production wells  108 ,  110  locates the first production well  108  along regions heated by heat irradiated from in situ combustion that progresses as described herein along the horizontal portion of the second production well  110 . While a direct relationship between the first and second production wells  108 ,  110  is possible, the first production well  108  may intersect the first reservoir  102  anywhere the first reservoir  102  is in thermal proximity to areas of the second reservoir  104  burned during the in situ combustion. 
     In operation, an oxidant source  112  such as an air compressor introduces an oxidant  114  into the second reservoir  104 . Examples of the oxidant  106  include oxygen or oxygen-containing gas mixtures. The injection well  100  conveys the oxidant  114  to below the stratum  106  and may include casing or liners cemented in place. Open borehole, slotted liner, or perforated liner sections  116  within the injection well  100  limit locations for outflow of the oxidant  114  from an interior of the injection well  100 . Even if intersecting the first formation  102 , the injection well  100  may be sealed above the stratum  106  once cemented in place such that the oxidant  114  is prevented from entering the first reservoir  102 . 
     Initiation of the in situ combustion begins with ignition of the second reservoir  104 . Injection of the oxidant  114  propagates a combustion front  118  through the second reservoir  104  toward the second production well  110 . For some embodiments, the second production well  110  deviates from vertical toward the injection well  100  with a toe  120  at a distal terminus of the second production well  110  being closest to the injection well  100 . The combustion front  118  thus advances from the toe  120  to a heel  122  of the second production well  110  where the second production well  110  deviates from vertical. Second formation mobile oil  124  flows into the second production well  110  ahead of the combustion front  118 . 
     Temperatures at the combustion front  118  can reach in excess of 350° C. Since this heat irradiates to adjacent and surrounding regions, the in situ combustion through the second reservoir  104  heats the stratum  106  and then the first reservoir  102 . Heating of the first reservoir  102  reduces viscosity of hydrocarbons therein. With the viscosity reduction, first reservoir mobile oil  126  flows into the first production well  108 . 
     Production equipment  128  including hydrocarbon storage tanks receive the mobile oil  124 ,  126  produced from the production wells  108 ,  110 . Separate completions for the first and second production wells  108 ,  110  enable independent control of production through each of the first and second production wells  108 ,  110 . Customizing production procedures such as durations, flow rates, and secondary recovery approaches including fluid flooding enables depletion of the reservoirs  102 ,  104  according to criteria specific to each of the reservoirs  102 ,  104 . By contrast to an open production well in fluid communication with both the first and second reservoirs  102 ,  104 , the first production well  108  and the second production well  110  permit this customization. 
     Further, the first production well  108  lacks any portion where the in situ combustion occurs in the second reservoir  104 . The first production well  108  thereby remains protected from being burned by the in situ combustion. Since the first production well  108  is not damaged by the in situ combustion as is possible if the first production well  108  extends into where the in situ combustion occurs, production can continue through the first production well  108  even after completion of the in situ combustion in the second reservoir  104 . Continuing production through the first production well  108  after the in situ combustion through the second reservoir  104  provides time for the heat from the in situ combustion to dissipate through the first reservoir  102  and time for the first reservoir mobile oil  126  to migrate into the first production well  108 . 
     For some embodiments, the combustion front  118  passes through the second reservoir  104  without burning of the first reservoir  102  at any time between initiating the in situ combustion in the second reservoir  104  and when the combustion front  118  is extinguished. Even if the injection well  100  traverses part of the first reservoir  102 , any regions of the first formation  102  surrounding the injection well  100  remain unburned as the combustion front  118  contained within the second reservoir  104  progresses away from against the injection well  100  since the oxidant  116  is at least initially introduced into only the second reservoir  104 . Production of the first reservoir mobile oil  126  through the first production well  108  occurs concurrently while conducting the in situ combustion of the second reservoir  104  and without igniting the first reservoir  102 . 
       FIGS. 2 and 3  show schematic top and side views of an exemplary configuration for an injection well  200  and first and second production wells  208 ,  210 . Similar to  FIG. 1 , a formation through which the wells  200 ,  208 ,  210  are disposed includes an oil bearing first reservoir  302 . an oil bearing second reservoir  304  and a barrier stratum  306  stratified with the stratum  306  located with the first reservoir  302  above the stratum  306  and the second reservoir  304  below the stratum  306 . In contrast to the operation described with respect to  FIG. 1 , in situ combustion occurs, as depicted by a combustion front  218 , in the first reservoir  302  to heat the second reservoir  304 . The combustion front  218  advances from the injection well  200  toward or along the first production well  208 . An areal extent of combustion  219  extends through the first reservoir  208  out from the injection well  200  and encompasses the first production well  208 . 
     Neither the injection well  200  nor the first production well  208  intersect the stratum  306 . The stratum  306  isolates both the injection well  200  and the first production well  208  from the second reservoir  304 . The stratum  306  thus blocks oxidant  214  supplied through the injection well  200  from entering the second reservoir  304  and contains the in situ combustion to within the first reservoir  302 . 
     The first and second production wells  208 ,  210  provide benefits as discussed herein with respect to  FIG. 1 . First reservoir mobile oil  326  flows into the first production well  208  due to pressure gradients and heating created ahead of the combustion front  218 . The second reservoir  304  at areas in thermal proximity to the areal extent  219  of the first reservoir  302  burned during the in situ combustion becomes sufficiently heated to allow second reservoir mobile oil  324  to flow into the second production well  210 . Even without introducing heat other than that generated by the in situ combustion of the first reservoir  302 , the second reservoir mobile oil  324  may come from any part of the second reservoir  304  separated from the first reservoir in a vertical direction and corresponding to at least the areal extent  219  of the first reservoir  302  burned during the in situ combustion. 
     Conducting the in situ combustion in the first reservoir  302  that is located above the second reservoir  304  can influence placement of the second production well  210 . In particular, any place that the second production well  210  is drilled from surface to the second reservoir  304  inside of the areal extent  219  of the first reservoir  302  burned during the in situ combustion may experience thermal damage when the combustion front  218  passes unless drilled subsequent to passage of the combustion front  218 . Drilling through the first reservoir  302  where already burned provides access to the second reservoir  304  but requires drilling through zones with temperatures and pressures increased by the in situ combustion. As shown, location of a vertical section of the second production well  210  away from burn zones enables bypassing without intersecting the areal extent  219  of the first reservoir  302  burned during the in situ combustion since only a horizontal section of the second production well  210  extends under the areal extent  219  of the first reservoir  302  burned during the in situ combustion. While parallel relationships (see,  FIG. 1 ) or other angles are possible, the horizontal section of the second production well  210  exemplifies a perpendicular relationship relative to vertical deviation of the first production well  208 . Drilling the second production well  210  prior to the in situ combustion avoids potential safety issues associated with drilling while possible for the in situ combustion to burn out of control, even though the second production well  210  may be drilled before, during or after the in situ combustion in the first reservoir  302 . 
       FIG. 4  illustrates a formation that, like  FIG. 1 , includes a stratum  406  separating a first reservoir  402  above the stratum  406  from a second reservoir  404  below the stratum  406 . An in situ combustion injection well  400  provides a flow path isolated from the first reservoir  402  for conveying oxidant  414  from surface to the second reservoir  404 . A fluid flooding injection well  401  and a first production well  408  both extend through the first reservoir  402  located above the stratum  406  without intersecting the stratum  406 . A second production well  410  passes through the second reservoir  404  and is in fluid communication with the in situ combustion injection well  400  via the second reservoir  404 . The stratum  406  isolates the first production well  408  from the second reservoir  404  located below the stratum  406 . 
     During the in situ combustion, injection of the oxidant  414  propagates a combustion front  418  through the second reservoir  404  in a toe-to-heel direction with respect to the second production well  410 . As with the operation described with respect to  FIG. 1 , the in situ combustion remains contained within the second reservoir  404  without burning of the first reservoir  402 . Second formation mobile oil  424  flows into the second production well  410  ahead of the combustion front  418 . 
     Heat from the in situ combustion transfers across the stratum  406  and raises temperatures within the first reservoir  402 . A fluid  403  such as water and/or inert gas supplied through the fluid flooding injection well  401  facilitates in driving first reservoir mobile oil  426  into the first production well  408 . For some embodiments, hydrogen and/or catalysts for in situ hydro-cracking form the fluid  403 . Other than aforementioned heat transfer, such flooding procedures do not impact the in situ combustion, and vice-versa, since the fluid flooding injection well  401  and the first production well  408  lack fluid communications with the in situ injection well  400  and the second production well  410 . In some embodiments, the fluid flooding in the first reservoir  402  occurs simultaneous with the in situ combustion in the second reservoir  404 . 
     The preferred embodiment of the present invention has been disclosed and illustrated. However, the invention is intended to be as broad as defined in the claims below. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims below and the description, abstract and drawings are not to be used to limit the scope of the invention.