Process for enhancing oil recovery from an oil-bearing formation

Abstract

A process for recovering oil from an oil-bearing formation is provided. A first oil recovery fluid is introduced into a formation through a first well for a first time period and oil is produced from a second well. A second oil recovery fluid different from the first oil recovery fluid is introduced into the formation through the second well for a second time period after the first time period, and oil is produced from a third well, where the second well is located on a fluid flow path extending between the first and third wells.

What is claimed: 
     
         1 . A process for recovering oil from an oil-bearing formation, comprising:
 for a first time period, injecting a first oil recovery fluid into the oil-bearing formation through a first well extending into the formation and producing oil from the formation through a second well extending into the formation;   for a second time period, injecting a second oil recovery fluid into the formation through the second well, and producing oil from the formation through a third well extending into the formation, where the second well is located on a fluid flow path within the formation between the first well and the third well, where the first oil recovery fluid and the second oil recovery fluid have different compositions, and wherein the second time period is after the first time period, and the second time period commences, at the earliest, upon initial production of a mixture comprising oil and the first oil recovery fluid from the formation through the second well.   
     
     
         2 . The process of  claim 1 , further comprising, for a third time period injecting the first oil recovery fluid into the formation through the first well and producing oil from the formation through the third well, wherein the third time period commences upon cessation of injecting the second oil recovery fluid into the formation through the second well. 
     
     
         3 . The process of  claim 1 , further comprising the step of producing oil from the formation through the third well for at least a portion of the first time period. 
     
     
         4 . The process of  claim 1 , wherein the second time period commences, at the earliest, upon production of a mixture comprising oil, formation water, and the first oil recovery fluid having a weight ratio of the first oil recovery fluid plus formation water to oil of at least 1:1. 
     
     
         5 . The process of  claim 1  wherein the first oil recovery fluid is water or brine. 
     
     
         6 . The process of  claim 1 , wherein the second oil recovery fluid is selected from the group consisting of water having a total dissolved solids content of from 200 ppm to 10000 ppm and an ionic strength of at most 0.15M, brine, an aqueous solution of a surfactant or combination of surfactants, an alkaline-surfactant-polymer formulation, an aqueous solution of water soluble polymer, and an ether or an aqueous solution of an ether. 
     
     
         7 . The process of  claim 1 , wherein a slug of from 0.1 to 1 pore volumes, as measured between the second well and the third well, of the second oil recovery fluid is injected into the formation. 
     
     
         8 . The process of  claim 1  wherein the first well is part of an array of 2 to 500 first wells, the second well is part of an array of 2 to 100 second wells, and the third well is part of an array of 2 to 100 third wells, wherein each second well is located on a fluid flow path within the formation between a corresponding first well and a corresponding third well. 
     
     
         9 . The process of  claim 1  wherein the formation, the first well the second well, and the third well are located offshore. 
     
     
         10 . The process of  claim 1 , further comprising the step of injecting the first oil recovery fluid into the formation through the first well for at least a portion of the second time period. 
     
     
         11 . The process of  claim 1  wherein the injected first oil recovery fluid mobilizes oil for production from the formation upon injection into the formation and the injected second oil recovery fluid mobilizes residual oil for production from the formation upon injection into the formation, wherein the residual oil is oil that is not mobilized by the first oil recovery fluid. 
     
     
         12 . The process of  claim 1  further comprising producing oil from the formation for at least a portion of the second time period. 
     
     
         13 . The process of  claim 1  wherein the first well and the third well are at least 1 km apart.