Microbial enhanced treatment of carbonate reservoirs for in situ hydrocarbon recovery

Abstract

Techniques for hydrocarbon recovery from a carbonate reservoir include injecting a microbial stimulation fluid including H 2 which enters a region of the reservoir that includes CO 2 and a microbial culture which converts at least a portion of the H 2 and CO 2 into a byproduct to promote dissolution of carbonate compounds in the region of the reservoir, thereby increasing porosity of the region to promote hydrocarbon recovery.

1 . A process comprising:
 injecting a microbial stimulation fluid comprising H 2  into a carbonate reservoir so that at least a portion of the H 2  enters a region of the carbonate reservoir, wherein the region includes CO 2 , hydrocarbons and a microbial culture, such that the microbial culture converts at least part of the H 2  and the CO 2  into a byproduct to promote dissolution of carbonate compounds in the region, thereby increasing porosity of the region; and   recovering hydrocarbons from the region of increased porosity.   
     
     
         2 . The process of  claim 1 , further comprising:
 temperature treating the region to a reservoir temperature that promotes a microbial metabolic pathway of the microbial culture to convert the H 2  and CO 2  into the corresponding byproduct.   
     
     
         3 . The process of  claim 2 , wherein the temperature treating comprises:
 preheating the microbial stimulation fluid to a heated temperature, thereby producing a preheated microbial stimulation fluid, before injection; and   heating the region with heat conducted from the preheated microbial stimulation fluid.   
     
     
         4 . The process of  claim 3 , wherein the temperature of the preheated microbial stimulation fluid is between 15° C. and 80° C., or between 20° C. and 60° C. 
     
     
         5 . (canceled) 
     
     
         6 . The process of  claim 2 , wherein the temperature treating comprises heating the region of the carbonate reservoir by a separate heat source from the microbial stimulation fluid, and wherein the heating of the region by the separate heat source comprises operating a thermal in situ recovery operation adjacent to the region, before and/or during the injection of the microbial stimulation fluid, injecting a heating fluid into or adjacent to the region, and/or operating a heating device in or adjacent to the region. 
     
     
         7 - 9 . (canceled) 
     
     
         10 . The process of  claim 1 , further comprising, after the step of injecting the microbial stimulation fluid, the step of:
 soaking the region for a soak period during which the carbonate compounds dissolve and the porosity of the region is increased.   
     
     
         11 . (canceled) 
     
     
         12 . The process of  claim 1 , wherein the microbial stimulation fluid further comprises CO 2 . 
     
     
         13 . The process of  claim 1 , wherein the microbial stimulation fluid further comprises a carrier fluid. 
     
     
         14 . The process of  claim 13 , wherein the carrier fluid is a gaseous carrier fluid, or comprises water, a fracturing fluid or a drilling fluid. 
     
     
         15 - 18 . (canceled) 
     
     
         19 . The process of  claim 1 , wherein at least part of the CO 2  that is converted into the byproduct is natively present in the region of the carbonate reservoir. 
     
     
         20 - 21 . (canceled) 
     
     
         22 . The process of  claim 1 , wherein the hydrocarbons comprise heavy hydrocarbons, and the step of recovering the heavy hydrocarbons comprises:
 subjecting the region to a Steam-Assisted-Gravity-Drainage (SAGD) recovery operation; or   subjecting the region to a Cyclic-Steam-Stimulation (CSS) recovery operation.   
     
     
         23 . (canceled) 
     
     
         24 . The process of  claim 1 , further comprising:
 identifying the microbial culture indigenous to the region of the carbonate reservoir; and   providing the microbial stimulation fluid having a composition and temperature based on the identification and such that a microbial metabolic pathway of the identified microbial culture will convert the microbial stimulation fluid to generate the byproduct that promotes dissolution of carbonate compounds in the region.   
     
     
         25 . The process of  claim 24 , wherein the microbial stimulation fluid is provided so as to provide pre-determined molar proportions of H 2  and CO 2  available for the microbial culture in accordance with the byproduct to be produced. 
     
     
         26 . (canceled) 
     
     
         27 . The process of  claim 1 , wherein the region of the carbonate reservoir comprises a dense limestone matrix and at least a portion of the hydrocarbons are in the dense limestone matrix. 
     
     
         28 - 30 . (canceled) 
     
     
         31 . The process of  claim 1 , wherein the microbial culture converts the H 2  and the CO 2  into a bioacid as the byproduct, wherein the bioacid comprises formic acid, acetic acid, propanoic acid, butyric acid, or lactic acid, or a combination thereof. 
     
     
         32 - 33 . (canceled) 
     
     
         34 . The process of  claim 31 , wherein the microbial culture comprises an acetogen and the metabolic pathway comprises the Wood-Ljungdahl pathway, thereby producing the acetic acid as the byproduct. 
     
     
         35 . The process of  claim 34 , wherein the microbial stimulation fluid comprises the H 2  and the CO 2  in a molar proportion in accordance with the Wood-Ljungdahl pathway for production of the acetic acid. 
     
     
         36 - 41 . (canceled) 
     
     
         42 . The process of  claim 1 , wherein the microbial culture comprises an acetogen that is a  Clostridium , a Thermoanaerobacteriaceae or an  Acetobacterium.    
     
     
         43 . (canceled) 
     
     
         44 . The process of  claim 1 , wherein the injecting comprises injecting the microbial stimulation fluid into a remote zone that is spaced away from the region of the carbonate reservoir, such that the microbial stimulation fluid permeates from the remote zone into the region. 
     
     
         45 . The process of  claim 44 , further comprising:
 identifying the region of the carbonate reservoir;   identifying one or more of the remote zones located at distances from the region to allow permeation of the microbial stimulation fluid toward the target zones; and   injecting the microbial stimulation fluid into the remote zones.   
     
     
         46 . The process of  claim 45 , wherein the step of injecting the microbial stimulation fluid into the remote zones is performed at an injection pressure of at least 100 psi. 
     
     
         47 . The process of  claim 45 , wherein the region is identified based on having a permeability of at most 100 mD. 
     
     
         48 . The process of  claim 45 , wherein the region is identified based on comprising an oil-wet carbonate matrix. 
     
     
         49 - 50 . (canceled) 
     
     
         51 . The process of  claim 1 , further comprising:
 injecting the microbial stimulation fluid through a pre-treatment well;   terminating injection of the microbial stimulation fluid through the pre-treatment well; and   operating the pre-treatment well as part of the step of recovering hydrocarbons.   
     
     
         52 - 54 . (canceled) 
     
     
         55 . The process of  claim 51 , further comprising:
 providing the pre-treatment well as an infill well in a hydrocarbon bearing infill zone in between two steam chambers of previously operating thermal hydrocarbon recovery wells; and   operating the pre-treatment well to pre-treat the infill zone.   
     
     
         56 - 57 . (canceled) 
     
     
         58 . The process of  claim 1 , further comprising:
 injecting the microbial stimulation fluid through a first pre-treatment well and a second pre-treatment well that are in spaced-apart and generally parallel configuration and separated by an inter-well region, to form respective first and second pre-treated zones having increased porosity; and   providing sufficient flow of the microbial stimulation fluid and time to allow the first and second pre-treated zones to expand across the inter-well region and form a common pre-treatment zone having increased porosity.   
     
     
         59 - 73 . (canceled) 
     
     
         74 . A process for pre-treating a carbonate reservoir comprising hydrocarbons in preparation for hydrocarbon recovery, comprising:
 injecting a microbial stimulation fluid comprising H 2  into a carbonate reservoir so that at least a portion of the H 2  enters a region of the carbonate reservoir, wherein the region includes CO 2 , hydrocarbons and a microbial culture, such that the microbial culture converts at least part of the H 2  and the CO 2  into a byproduct to promote dissolution of carbonate compounds in the region; and   wherein the dissolution of the carbonate compounds increases porosity of the region.   
     
     
         75 - 90 . (canceled) 
     
     
         91 . A process comprising:
 injecting a gaseous microbial stimulation fluid comprising an electron donor component into a carbonate reservoir so that at least a portion of the electron donor component enters a region of the carbonate reservoir, wherein the region includes a carbon source, hydrocarbons and a microbial culture, such that the microbial culture utilizes the electron donor component as an energy source for conversion of the carbon source into a byproduct to promote dissolution of carbonate compounds in the region, thereby increasing porosity of the region; and   recovering hydrocarbons from the region of increased porosity.   
     
     
         92 . The process of  claim 91 , wherein the electron donor component comprises H 2 , the carbon source comprises CO 2  that is natively found in the region or injected with the H 2 , and the gaseous microbial stimulation fluid is injected into a remote zone located at a distance from the region such that the gaseous microbial stimulation fluid diffuses from the remote zone into the region. 
     
     
         93 - 100 . (canceled)