Method for using acid gas as lift-gas and to enhance oil recovery from a subsurface formation

Abstract

A method of enhancing crude oil recovery from a crude oil containing formation uses an integrated acid gas injection system, which injects a first fraction of an available volume of acid gas via an acid gas injection well into the formation and a second fraction of the available volume of acid gas as a lift gas into a crude oil production well traversing the formation at a selected distance from the acid gas injection well to inhibit early breakthrough of acid gas from the formation into the production well.

1 . A method of enhancing crude oil recovery from a crude oil containing formation using an integrated acid gas injection system which injects a first fraction of an available volume of acid gas into the formation and a second fraction of the available volume of acid gas as a lift gas into a crude oil production well traversing the formation;
 characterized in that the first fraction is injected into the formation via an acid gas injection well, which is located at a selected distance from the crude oil production well.   
     
     
         2 . The method of  claim 1 , wherein the acid gas comprises a mixture of produced gas and an acid gas from a natural or industrial source. 
     
     
         3 . The method of  claim 1 , wherein the first fraction is injected slug-wise into the formation, and injection of acid gas slugs is alternated by injection of water slugs into the formation. 
     
     
         4 . The method of  claim 1 , wherein the production well comprises a tapered production tubing. 
     
     
         5 . The method of  claim 1 , wherein the lift gas is injected solely using a lift gas injection conduit arranged within a production tubing in the production well. 
     
     
         6 . The method of  claim 5 , wherein use is made of a concentric completion comprising a main tubing in which an inner string is arranged and the lift gas is injected through the inner string and the mixture of produced fluids with the lift gas is produced through the annulus between the insert string and the main tubing. 
     
     
         7 . The method of  claim 1 , wherein a downhole safety valve is set below the bottom of the insert string of the concentric completion and above the production packer. 
     
     
         8 . The method of  claim 1 , wherein the available volume of acid gas comprises acid gas obtained from a natural or industrial acid gas source and the first fraction is injected into the formation through an acid gas injection well traversing the formation at a distance from the production well such that the first fraction mixes with and displaces crude oil within the pores of the formation and flows towards the production well. 
     
     
         9 . The method of  claim 4 , wherein at least some acid gas of the first fraction is produced through the production tubing and at least part of the first and/or second fraction is recycled into the available volume of acid gas. 
     
     
         10 . The method of  claim 1 , wherein the rate and/or pressure at which the second fraction is injected into the acid gas injection conduit is adjusted on the basis of one or more of the following parameters:
 target and/or fluctuation of crude oil production of the production well(s);   density and/or watercut of the well effluents in the production tubing of the production well(s);   available acid gas volume and/or acid gas compressor capacity:   bottom hole pressure in the production well.   
     
     
         11 . The method of  claim 10 , wherein the rate and/or pressure at which the second fraction is injected into the acid gas injection conduit is adjusted in relation to bottom hole pressure in the production well such that injection of the second fraction into the formation is inhibited. 
     
     
         12 . The method of  claim 1 , whereby the injected acid gas comprises significant mole fractions of H 2 S and CO 2 . 
     
     
         13 . The method of  claim 1 , wherein the selected distance is at least about 10 meters. 
     
     
         14 . The method of  claim 1 , wherein the selected distance is from about 15 meters to about 100 meters.