Systems and Methods for Enhancing Production of Viscous Hydrocarbons From a Subterranean Formation

Abstract

Systems and methods for enhancing production of viscous hydrocarbons from a subterranean formation. The methods may include heating a hydrocarbon solvent mixture to generate a vapor stream, injecting the vapor stream into the subterranean formation to generate reduced-viscosity hydrocarbons, and producing the reduced-viscosity hydrocarbons from the subterranean formation. The methods also may include selecting a composition of the hydrocarbon solvent mixture by determining a threshold maximum pressure of the subterranean formation, determining a stream temperature at which the vapor stream is to be injected into the subterranean formation, and selecting the composition of the hydrocarbon solvent mixture based upon the stream temperature and the threshold maximum pressure. The systems may include a hydrocarbon production system that may be configured to perform the methods and/or that may include an injection well, an injectant supply assembly, and a production well.

1 . A method of enhancing production of viscous hydrocarbons from a subterranean formation, the method comprising:
 heating a hydrocarbon solvent mixture to generate a vapor stream at a stream temperature, wherein:
 (i) the hydrocarbon solvent mixture includes a heavy hydrocarbon fraction that consists essentially of hydrocarbons with five or more carbon atoms and comprises greater than 30 mole percent of the hydrocarbon solvent mixture; and 
 (ii) the heavy hydrocarbon fraction includes a first compound, which has at least five carbon atoms and comprises at least 10 mole percent of the vapor stream, and a second compound, which has more carbon atoms than the first compound and comprises at least 10 mole percent of the vapor stream;
 injecting the vapor stream into the subterranean formation via an injection well that extends within the subterranean formation to decrease a viscosity of the viscous hydrocarbons within the subterranean formation and thereby generate reduced-viscosity hydrocarbons; and 
 producing the reduced-viscosity hydrocarbons from the subterranean formation via a production well that extends within the subterranean formation, wherein the production well is spaced apart from the injection well. 
 
   
     
     
         2 . The method of  claim 1 , wherein a composition of the hydrocarbon solvent mixture is selected such that a vapor pressure of the hydrocarbon solvent mixture at the stream temperature is less than a threshold maximum pressure of the subterranean formation. 
     
     
         3 . The method of  claim 1 , wherein the stream temperature is at least 30° C. and less than 250° C. 
     
     
         4 . The method of  claim 1 , wherein the injecting includes condensing at least 50% of the vapor stream within the subterranean formation to transfer a latent heat of the vapor stream to the viscous hydrocarbons and generate the reduced-viscosity hydrocarbons and to generate a condensate from the vapor stream. 
     
     
         5 . The method of  claim 4 , wherein the method further includes at least one of dissolving the condensate in the viscous hydrocarbons, dissolving the viscous hydrocarbons in the condensate, and diluting the viscous hydrocarbons with the condensate to generate the reduced-viscosity hydrocarbons. 
     
     
         6 . The method of  claim 4 , wherein the producing includes producing the condensate with the reduced-viscosity hydrocarbons, and further wherein the method includes separating a separated portion of the condensate from the reduced-viscosity hydrocarbons and utilizing a recycled portion of the condensate as the hydrocarbon solvent mixture. 
     
     
         7 . The method of  claim 6 , wherein the method further includes purifying the recycled portion of the condensate prior to the utilizing. 
     
     
         8 . The method of  claim 1 , wherein the injecting includes injecting into a stimulated region of the subterranean formation, wherein the stimulated region includes asphaltenes, and further wherein the producing includes producing at least 50 wt % of the asphaltenes that are present within the stimulated region prior to the injecting. 
     
     
         9 . The method of  claim 1 , wherein the method further includes preheating a portion of the subterranean formation that is proximal to the injection well prior to the injecting the vapor stream. 
     
     
         10 . The method of  claim 1 , wherein the method further includes regulating a composition of the hydrocarbon solvent mixture, wherein the regulating includes receiving a hydrocarbon feedstock and altering a composition of the hydrocarbon feedstock to generate the hydrocarbon solvent mixture, and further wherein the altering includes decreasing a proportion of the hydrocarbon feedstock that comprises hydrocarbons with fewer than five carbon atoms. 
     
     
         11 . The method of  claim 1 , wherein the threshold maximum pressure includes at least one of a fracture pressure for the subterranean formation, a hydrostatic pressure within the subterranean formation, a lithostatic pressure within the subterranean formation, a gas cap pressure for a gas cap within the subterranean formation, and an aquifer pressure for an aquifer that is at least one of above and under the subterranean formation. 
     
     
         12 . A method of selecting a composition of a hydrocarbon solvent mixture for injection into a subterranean formation to enhance production of viscous hydrocarbons therefrom, wherein the hydrocarbon solvent mixture is injected into the subterranean formation as a vapor stream at an injection pressure, the method comprising:
 determining a threshold maximum pressure of the subterranean formation;   determining a stream temperature at which the vapor stream is to be injected into the subterranean formation; and   selecting the composition of the hydrocarbon solvent mixture based, at least in part, on the stream temperature and the threshold maximum pressure, wherein the selecting includes:
 (i) selecting a first proportion of the hydrocarbon solvent mixture that comprises a first compound with at least five carbon atoms, wherein the first proportion comprises at least 10 mole percent of the hydrocarbon solvent mixture; and 
 (ii) selecting a second proportion of the hydrocarbon solvent mixture that comprises a second compound with more carbon atoms than the first compound, wherein the second proportion comprises at least 10 mole percent of the hydrocarbon solvent mixture. 
   
     
     
         13 . The method of  claim 12 , wherein the selecting includes selecting such that a vapor pressure of the hydrocarbon solvent mixture at the stream temperature is less than the threshold maximum pressure of the subterranean formation. 
     
     
         14 . The method of  claim 12 , wherein the selecting includes at least one of:
 (i) increasing the first proportion of the hydrocarbon solvent to increase a vapor pressure of the hydrocarbon solvent mixture;   (ii) the second proportion of the hydrocarbon solvent mixture to increase the vapor pressure of the hydrocarbon solvent mixture;   (iii) decreasing the first proportion of the hydrocarbon solvent mixture to decrease the vapor pressure of the hydrocarbon solvent mixture; and   (iv) increasing the second proportion of the hydrocarbon solvent mixture to decrease the vapor pressure of the hydrocarbon solvent mixture.   
     
     
         15 . The method of  claim 12 , wherein the stream temperature is at least 30° C. and less than 250° C. 
     
     
         16 . The method of  claim 12 , wherein the selecting includes selecting such that the first compound and the second compound together comprise at least 50 mole percent of the hydrocarbon solvent mixture. 
     
     
         17 . The method of  claim 12 , wherein the selecting includes selecting such that at least 50 weight % of asphaltenes that are present within the subterranean formation are soluble within the hydrocarbon solvent mixture at the injection pressure and the stream temperature. 
     
     
         18 . The method of  claim 12 , wherein the vapor stream is injected into the subterranean formation at an injection pressure, and further wherein the selecting includes selecting such that a difference between a dew point of the vapor stream and a bubble point of the hydrocarbon solvent mixture is at least 10° C. at the injection pressure. 
     
     
         19 . The method of  claim 12 , wherein the determining the threshold maximum pressure includes determining at least one of a fracture pressure for the subterranean formation, a hydrostatic pressure within the subterranean formation, a lithostatic pressure within the subterranean formation, a gas cap pressure for a gas cap within the subterranean formation, and an aquifer pressure for an aquifer that is at least one of above and under the subterranean formation. 
     
     
         20 . The method of  claim 12 , wherein the method further includes injecting the vapor stream into the subterranean formation to generate reduced viscosity hydrocarbons within the subterranean formation. 
     
     
         21 . The method of  claim 20 , wherein the method further includes producing the reduced viscosity hydrocarbons from the subterranean formation. 
     
     
         22 . A hydrocarbon production system, comprising:
 an injection well that extends within a subterranean formation;   an injectant supply assembly that is configured to provide a vapor stream to the injection well to generate reduced-viscosity hydrocarbons within the subterranean formation, the injectant supply assembly comprising:
 (i) a hydrocarbon solvent mixture, wherein the hydrocarbon solvent mixture includes a heavy hydrocarbon fraction that consists essentially of hydrocarbons with five or more carbon atoms and comprises greater than 30 mole percent of the hydrocarbon solvent mixture, and further wherein the heavy hydrocarbon fraction includes a first compound, which has at least five carbon atoms and comprises at least 10 mole percent of the hydrocarbon solvent mixture, and a second compound, which has more carbon atoms than the first compound and comprises at least 10 mole percent of the hydrocarbon solvent mixture; and 
 (ii) a vaporization assembly that is configured to receive and vaporize the hydrocarbon solvent mixture to generate the vapor stream; and 
   a production well that is spaced apart from the injection well and extends within the subterranean formation, wherein the production well is configured to receive the reduced-viscosity hydrocarbons and to convey the reduced-viscosity hydrocarbons from the subterranean formation.   
     
     
         23 . The system of  claim 22 , wherein, subsequent to being provided to the subterranean formation, the vapor stream condenses to a condensate stream, wherein the production well receives the condensate stream and conveys the condensate stream from the subterranean formation with the reduced-viscosity hydrocarbons, and further wherein the hydrocarbon production system further includes a condensate recovery system that is configured to separate at least a portion of the condensate stream from the reduced-viscosity hydrocarbons. 
     
     
         24 . The system of  claim 23 , wherein the hydrocarbon production system further includes a recycle conduit that is configured to convey the portion of the condensate stream to the vaporization assembly, wherein the vaporization assembly is configured to vaporize the portion of the condensate stream to generate the vapor stream. 
     
     
         25 . The system of  claim 23 , wherein the hydrocarbon production system further includes a purification system that is configured to receive a feed stream that includes at least one of a hydrocarbon feedstock stream and the condensate stream and to purify the feed stream to generate the hydrocarbon solvent mixture. 
     
     
         26 . The system of  claim 22 , wherein the hydrocarbon solvent mixture comprises at least one of a gas plant condensate and a crude oil refinery condensate. 
     
     
         27 . The system of  claim 22 , wherein at least 50 mole percent of the hydrocarbon solvent mixture comprises at least two of a compound with five carbon atoms, a compound with six carbon atoms, a compound with seven carbon atoms, and a compound with eight carbon atoms. 
     
     
         28 . The system of  claim 22 , wherein less than 30 mole percent of the hydrocarbon solvent mixture comprises a compound with one to three carbon atoms. 
     
     
         29 . The system of  claim 22 , wherein the production well extends at least partially below the injection well. 
     
     
         30 . The system of  claim 22 , wherein at least a portion of the production well is parallel to a corresponding portion of the injection well. 
     
     
         31 . The system of  claim 22 , wherein both of the injection well and the production well include a horizontal portion. 
     
     
         32 . The system of  claim 22 , wherein at least a portion of the production well is located vertically below a corresponding portion of the injection well. 
     
     
         33 . The system of  claim 22 , wherein the threshold maximum pressure is at least one of a fracture pressure for the subterranean formation, a hydrostatic pressure within the subterranean formation, a lithostatic pressure within the subterranean formation, a gas cap pressure for a gas cap within the subterranean formation, and an aquifer pressure for an aquifer that is above the subterranean formation.