Methane enhanced liquid products recovery from wet natural gas

Abstract

A process is described for enhancing the yield of liquid products from natural gas from at least one extraction well. This process is achieved by injecting methane at a higher pressure than the rock pressure in at least one injection well site. The methane serves to maintain the pressure of gas in the formation, while also promoting the flow of liquid products away from the injection well and towards a collection well. The net effect is higher net yield of liquid products (referred to as “Y-Grade” liquids) from that well, with lower net yield of non-condensable methane. Because methane is naturally present in natural gas, the gas remaining underground is still a valuable product that can be trapped in the future. The use of the dry gas as the fracturing medium reduces or potentially eliminates the need to use water in fracturing process.

We claim: 
     
         1 . A method for increasing and maintaining the permeability of a fractured rock formation comprising:
 forming at least one injection well at least partially within a fractured rock formation;   injecting and flowing a high pressure gas into the at least one injection well over a predetermined time scale;   permeating the fractured rock formation with the injected high pressure gas flow as it flows underground to at least one extraction well; and   collecting the high pressure gas in the at least one extraction well, and then extracting additional liquid and gas products from the at least one extraction well.   
     
     
         2 . The method of  claim 1 , wherein fractures in the fractured rock formation are produced by hydraulic fracturing using a working fluid, followed by injecting the high pressure gas over a predetermined time scale of at least one week, to maintain the permeability created via the hydraulic fracturing process. 
     
     
         3 . The method of  claim 2 , wherein the working fluid comprises at least one of the following: non-aqueous liquid, water, brine, polymers, carbon dioxide, methane, or a combination thereof. 
     
     
         4 . The method of  claim 2 , wherein the working fluid includes 95% or more of the following: methane, ethane, or a combination thereof. 
     
     
         5 . The method of  claim 1 , wherein cracks and fissures in the fractured rock formation are created exclusively from a high pressure working fluid. 
     
     
         6 . The method of  claim 1 , wherein the collected high pressure gas is separated to remove methane from liquid fractions obtained from extracted natural gas. 
     
     
         7 . The method of  claim 6 , further comprising:
 compressing the methane to a higher pressure than the well bottom pressure of the at least one extraction well and then injecting or reinjecting the methane into a gas-bearing area of the fractured rock formation; and   blending the methane with natural gas stored inside a porous area of the fractured rock formation.   
     
     
         8 . The method of  claim 1 , wherein the pressure in the at least one extraction well is increased by injecting a non-condensable gas at a pressure higher than the pressure in the at least one extraction well, and creating an overburden pressure at the bottom of the at least one extraction well. 
     
     
         9 . A method for increasing permeability of a rock formation containing natural gas comprising:
 forming at least two boreholes in a rock formation, wherein a first borehole is externally pressurized with a working fluid to a level of at least 1,000 psi above the pressure of the rock formation and a second borehole is pressurized at a level below the pressure of the rock formation, such that the working fluid pressure differential is sufficient to cause fracturing in the rock formation between the first and second boreholes, and the working fluid to flow from one borehole to the other.   
     
     
         10 . The method of  claim 9 , wherein the external pressurization is decreased and residual natural gas is extracted from the first or second boreholes. 
     
     
         11 . The method in  claim 9 , further comprising:
 flowing a working fluid from the first borehole to the second borehole, thereby causing residual natural gas to flow into the second borehole; and   extracting liquid constituents of the natural gas from the second borehole.   
     
     
         12 . The method of  claim 9 , wherein the working fluid is composed of a substantially non-aqueous liquid. 
     
     
         13 . The method of  claim 9 , wherein the working fluid comprises a gas chosen from the group including methane, ethane, alkane gases, carbon dioxide, carbon monoxide, nitrogen, natural gas, other reducing gases, inert gases, non-oxidizing gases, or a combination thereof. 
     
     
         14 . The method of  claim 9 , wherein the external pressurization is applied intermittently to maintain permeability between the first borehole and the second borehole. 
     
     
         15 . The method of  claim 9 , further comprising utilizing particles from the working fluid to maintain permeability in the rock formation. 
     
     
         16 . A method for increasing the permeability of a rock formation containing natural gas comprising:
 forming at least two boreholes, wherein a first borehole is externally pressurized with a working fluid, and surrounding boreholes are pressurized; and   increasing the porosity in an outward direction of a rock formation between the first borehole and the surrounding boreholes, wherein the first borehole is externally pressurized with a working fluid to a level of at least 1,000 psi above the rock pressure and the surrounding boreholes are either maintained or below the over burden pressure, such that the working fluid pressure differential is sufficient to cause fracturing in the rock formation between the surrounding boreholes and the working fluid flows from one borehole to another.   
     
     
         17 . The method of  claim 16 , wherein the pressurization is applied intermittently between the first borehole and the second borehole. 
     
     
         18 . The method of  claim 16 , comprising carrying particles in the working fluid to partially fill cracks in the rock formation and maintain permeability in a preferred direction in the rock formation. 
     
     
         19 . The method of  claim 16 , wherein the working fluid comprises a gas, such as methane, ethane, carbon dioxide, nitrogen, a higher alkane compound, or a combination thereof. 
     
     
         20 . The process of  claim 16 , wherein the working fluid includes antimicrobial materials.