Microbial processes for increasing fluid mobility in a heavy oil reservoir

Abstract

Methods are provided for increasing overall fluid mobility in a near-wellbore region in an oil sands reservoir, for example in a reservoir having an inter-well region between a first well and a second well of a well pair in which at least a portion of the near-wellbore region is within the inter-well region. The methods may involve inoculating the near-wellbore region with a microorganism, wherein the near-wellbore region comprises a hydrocarbon phase and an aqueous phase, the viscosity of the hydrocarbon phase being greater than the viscosity of the aqueous phase. Conditions may be maintained in the near-wellbore region so that the microorganism metabolizes at least a portion of the hydrocarbon phase so that saturation of the near-wellbore region by the hydrocarbon phase decreases and saturation of the near-wellbore region by the aqueous phase increases.

1 . A method of increasing overall fluid mobility in a near-wellbore region in an oil sands reservoir, the method comprising:
 (a) inoculating the near-wellbore region with one or more microorganism, wherein the near-wellbore region comprises a hydrocarbon phase and an aqueous phase, the viscosity of the hydrocarbon phase being greater than the viscosity of the aqueous phase; and   (b) maintaining conditions in the near-wellbore region so that the one or more microorganism metabolizes at least a portion of the hydrocarbon phase so that saturation of the near-wellbore region by the hydrocarbon phase decreases and saturation of the near-wellbore region by the aqueous phase increases, increasing overall fluid mobility.   
     
     
         2 . The method of  claim 1 , wherein the method increases the overall fluid mobility in an inter-well region between a first well and a second well of a well pair in the oil sands reservoir,
 wherein the near-wellbore region is associated with at least one of the first and second well, and at least a portion of the near-wellbore region is within the inter-well region.   
     
     
         3 . The method of  claim 2 , wherein the first well is an injection well and the second well is a production well. 
     
     
         4 . The method of  claim 3 , wherein inoculating occurs prior to steam-assisted gravity drainage (SAGD) to pre-condition the oil sands reservoir for SAGD. 
     
     
         5 . The method of  claim 3 , wherein inoculating occurs after steam assisted gravity drainage (SAGD) is completed. 
     
     
         6 . The method of  claim 2 , wherein inoculating occurs instead of steam assisted gravity drainage (SAGD) in the oil sands reservoir, and wherein the method additionally includes the step of producing oil from the producing well. 
     
     
         7 . The method of  claim 2 , wherein (b) comprises maintaining propagating conditions in at least a portion of the inter-well region so that the one or more microorganism propagates within the inter-well region. 
     
     
         8 . The method of  claim 7 , wherein the propagating conditions comprise conditions in which the one or more microorganism metabolizes at least a portion of the hydrocarbon phase, decreasing saturation of the inter-well region by the hydrocarbon phase and increasing saturation of the inter-well region by the aqueous phase. 
     
     
         9 . The method of  claim 2 , further comprising a cycling process comprising:
 (c) injecting or circulating a heated cycling fluid within one or both of the first or second well in fluid communication with the near-wellbore region, to mobilize fluids within the near-wellbore region; and   (d) repeating steps (a) and (b) so that the one or more microorganism metabolizes a further portion of the hydrocarbon phase.   
     
     
         10 . The method of  claim 9 , wherein the cycling process steps (c) and (d) are repeated one or more times. 
     
     
         11 . The method of  claim 10 , wherein the cycling process steps are repeated for a period of about two weeks or greater. 
     
     
         12 . The method of  claim 1 , wherein the one or more microorganism is contained in an inoculant solution, and:
 following step (a) the inoculant solution is absorbed into the near-wellbore region over a soaking period, and after the soaking period additional inoculant solution is added into the near-wellbore region well to increase overall fluid mobility.   
     
     
         13 . The method of  claim 12  wherein unabsorbed inoculant solution is withdrawn from the near-wellbore region after the soaking period; and is combined with the additional inoculant solution for adding into the near-wellbore region, to re-circulate in the near-wellbore region. 
     
     
         14 . The method of  claim 13 , wherein the total volume of inoculant solution in step (a) plus the additional inoculant solution is from about 2× to about 3× the volume of the volume of inoculant solution used in step (a). 
     
     
         15 . The method of  claim 9 , wherein the heated cycling fluid comprises steam, water, a solvent, a surfactant, or a combination thereof. 
     
     
         16 . The method of  claim 1 , wherein:
 the saturation of the near-wellbore region by the aqueous phase increases by about 25% or greater; and/or   the saturation of the near-wellbore region by the hydrocarbon phase decreases by about 50% after about two weeks.   
     
     
         17 . The method of  claim 2 , wherein fluid communication is established between the first well and the second well following step (a) and (b). 
     
     
         18 . The method of  claim 17 , comprising injecting or circulating a fluid in: (i) the first well; (ii) the second well; or (iii) both the first well and the second well to establish the fluid communication between the first well and the second well. 
     
     
         19 . The method of  claim 1 , further comprising:
 determining a first saturation level of the aqueous phase in the near-wellbore region prior to inoculating, and determining a second saturation level of the aqueous phase in the near-wellbore region following inoculating, and optionally determining the increase in aqueous phase saturation; and/or   determining a first fluid mobility level of in the near-wellbore region prior to inoculating, and determining a second fluid mobility level in the near-wellbore region following inoculating, and optionally determining the increase in fluid mobility.   
     
     
         20 . The method of  claim 1 , wherein the one or more microorganism metabolizes hydrocarbons of C16 or greater. 
     
     
         21 . The method of  claim 1 , wherein the one or more microorganism preferentially metabolizes hydrocarbons of C20 or greater. 
     
     
         22 . The method of  claim 21 , wherein the one or more microorganism comprises bacteria that preferentially metabolizes heavy ends of the oil in the oil sands reservoir. 
     
     
         23 . The method of  claim 3 , further comprising a step of injecting a heated fluid into the injection well or circulating the heated fluid in the well pair prior to the step of inoculating. 
     
     
         24 . The method of  claim 2 , wherein the wells in the well pair each have a section that extends substantially in a horizontal direction, and wherein fluid communication is established between the substantially horizontal sections. 
     
     
         25 . The method of  claim 24 , wherein the substantially horizontal sections of the wells are substantially parallel, and vertically spaced apart. 
     
     
         26 . The method of  claim 1 , additionally comprising circulating or re-circulating the one or more microorganism within the near-wellbore region to increase exposure of the one or more microorganism to hydrocarbons of C20 or greater. 
     
     
         27 . A method of recovering hydrocarbon from in an inter-well region in an oil sands reservoir located between an injection well and a production well, the method comprising:
 (a) inoculating the inter-well region with a mixture of anaerobic and aerobic bacteria that metabolizes hydrocarbons of C16 or greater;   (b) maintaining viability of at least a portion of the mixture of bacteria in the inter-well region so that the mixture of bacteria metabolizes at least a portion of the hydrocarbon phase having C16 or greater, to produce a hydrocarbon phase of decreased viscosity; and   (c) recovering the hydrocarbon phase of decreased viscosity from the inter-well region.   
     
     
         28 . The method of  claim 27 , additionally comprising repeating steps (a) to (c). 
     
     
         29 . The method of  claim 27 , wherein inoculating the inter-well region comprises injecting the mixture of bacteria into the injection well together with a suitable carrier. 
     
     
         30 . A method of increasing overall fluid mobility of oil in a near-wellbore region in an oil sands reservoir, comprising:
 inoculating a well with an inoculant solution comprising one or more microorganism that metabolizes hydrocarbon of C16 or greater;   permitting the inoculant solution to become absorbed into the near-wellbore region over a soaking period; and   adding additional inoculant solution into the well to increase overall fluid mobility of oil.   
     
     
         31 . The method of  claim 30 , additionally comprising:
 withdrawing unabsorbed inoculant solution after the soaking period; and   combining the withdrawn solution with the additional inoculant solution added into the well to re-circulate in the well.   
     
     
         32 . The method of  claim 30 , wherein the total volume of inoculant solution used in the steps of inoculating and adding is at least about 3× the volume used in the step of inoculating. 
     
     
         33 . The method of  claim 30 , wherein the soaking period is from about 2 to about 3 weeks.