Method for producing oil

Abstract

The present disclosure relates to enhanced oil recovery methods including the injection of solvent and polymer floods to increase hydrocarbon production from oil bearing underground rock formations. One method includes injecting a solvent slug into the underground formation for a first time period from a first well. The solvent slug solubilizes the oil and generates a mixture of mobilized oil and solvent. An aqueous polymer slug may then be injected into the underground formation for a second time from the first well. The polymer slug may have a viscosity greater than the solvent slug and thereby generates an interface between the solvent slug and the polymer slug. The solvent slug and the mobilized oil are then forced towards a second well using a buoyant hydrodynamic force generated by the aqueous polymer slug. Oil and/or gas may then be produced from the second well.

What is claimed is: 
     
         1 . A method for producing oil from an underground oil-bearing formation, comprising:
 placing a solvent slug into the underground oil-bearing formation for a first time period from a first well, the solvent slug being configured to solubilize the oil upon contacting the oil and generate a mixture of mobilized oil, wherein the solvent slug has a density that is less than 90% or at least 110% of a density of the oil;   placing an aqueous polymer slug into the underground formation for a second time period from the first well, the polymer slug having a viscosity greater than the mixture of mobilized oil and at least 5 centipoise;   displacing the mixture of mobilized oil and the solvent slug towards a second well with the aqueous polymer slug; and   producing oil and/or gas from the second well.   
     
     
         2 . The method of  claim 1  wherein an interface is generated between the polymer slug and the mixture of mobilized oil and solvent. 
     
     
         3 . The method of  claim 1  wherein the solvent slug comprises a carbon disulfide formulation. 
     
     
         4 . The method of  claim 1  further comprising placing a brine chase into the formation following the aqueous polymer slug. 
     
     
         5 . The method of  claim 1  further comprising repeating the placement of the solvent slug and the aqueous polymer slug in an alternating sequence. 
     
     
         6 . The method of  claim 1  wherein the polymer of the aqueous polymer slug is selected from the group of polymers consisting of polyacrylamides, partially hydrolyzed polyacrylamide, polyacrylates, ethylenic copolymers, biopolymers, carboxymethylcellulose, polyvinyl alcohol, polystyrene sulfonates, polyvinylpyrolidone, AMPS (2-acrylamide-2-methyl propane sulfonate), copolymers of acrylic acid and acrylamide, acrylic acid and lauryl acrylate, lauryl acrylate and acrylamide, xanthan gum, and guar gum. 
     
     
         7 . The method of  claim 1  wherein the aqueous polymer slug is placed in the formation in a pore volume that is at least 1.5 times more than a pore volume of the solvent slug placed in the formation immediately preceding placement of the aqueous polymer slug. 
     
     
         8 . The method of  claim 1  wherein the polymer slug has a viscosity greater than the solvent slug. 
     
     
         9 . A method for producing oil from an underground oil-bearing formation, comprising:
 placing a first carbon disulfide slug into the underground formation for a first time period from a first well;   contacting at least a portion of the oil with the first carbon disulfide slug, thereby generating a mixture of mobilized oil and carbon disulfide;   placing an aqueous polymer slug into the underground formation for a second time from the first well, wherein a quantity of the aqueous polymer slug is placed in the formation in a pore volume that is at least 1.5 times more than a pore volume of the first carbon disulfide slug placed into the formation, and the aqueous polymer slug has a viscosity ranging between 5 centipoise (MPa s) and 100 centipoise (MPa s);   creating a hydrodynamic force between the first carbon disulfide slug and the aqueous polymer slug;   impelling the first carbon disulfide slug and the mixture of mobilized oil and carbon disulfide across the formation using the hydrodynamic force; and   producing oil from a second well in fluid communication with the first well.   
     
     
         10 . The method of  claim 9  further comprising placing a second carbon disulfide slug into the underground formation for a third time period from the first well. 
     
     
         11 . The method of  claim 9  further comprising placing a brine chase into the formation following the aqueous polymer slug. 
     
     
         12 . The method of  claim 9  further comprising repeating the placement of the first carbon disulfide slug and the aqueous polymer slug in an alternating sequence. 
     
     
         13 . The method of  claim 9  wherein the underground formation interposes two adjacent underground formations which seal the underground formation on an upper edge and a lower edge. 
     
     
         14 . The method of  claim 9  wherein the first carbon disulfide slug has a density that is at least 110% of a density of the oil.