Field Test of a Self-Conforming Oil Recovery Fluid
Authors: Farley R.W. , Ellebracht J.F. , Friedman R.H. 
Published: December 2007

Significant quantities of oil bypassed in previous waterflood operations were produced when a novel oil recovery, fluid was field tested in southeastern Illinois. Profile surveys show water injectivity substantial improvement in the distribution of injected water; and present water injectivity is markedly higher than before the fluid was injected.

Introduction
A Self-Conforming Fluid has been developed by Getty Oil Co. for additional oil recovery. The fluid is designed primarily to increase oil recovery by increasing the over-all conformance efficiency of the injected fluid. The fluid is based on the cross-linked polymer approach, with three main ingredients in addition to water: a cross-linkable polymer, carboxymethyl cellulose (CMC); a cross-linking agent, chrome alum; and a trigger, dicy-clohexylamine, to control cross-linking. In operation, the cross-linking agent links the polymer molecules to increase the viscosity; and under certain conditions, such as high oil saturation, the trigger agent is extracted, which reverses the cross-linking and restores the lower viscosity. The fluid will have a high viscosity in water zones and a low viscosity in oil zones, resulting in increased flow in the oil-bearing regions.
When mixed, the fluid used in this field test had a viscosity of about 3 cp, which would increase to about 20 cp in about 2 weeks. Viscosity would not increase in the presence of oil and would revert to the 3-cp level if presence of oil and would revert to the 3-cp level if contacted with oil. The cost of the fluid was about 30 cents per barrel of injected fluid for the test, and the present cost is estimated at about 50 cents per barrel of injected fluid. The limitations of this fluid are that it must be mixed in fresh water and is not stable at temperatures above 120 deg. F. Extensive displacement tests indicated that substantial amounts of oil were produced from laboratory models by improving the over-all sweep efficiency.

Site Evaluation
The laboratory research and development studies had progressed to the point where a field test was desirable. progressed to the point where a field test was desirable. The two major field-test objectives were to evaluate the oil recovery potential of the process, and to demonstrate the ability to mix and inject the fluid for an extended period of time with minimum manpower required. The period of time with minimum manpower required. The Barrick-Walters waterflood, located in Crawford County, Ill., was selected for conducting a field test. The Barrick-Walters flood area is situated on the northwest flank of an anticlinal structure in the northeast portion of the Main Consolidated field. The field, discovered in 1906. is on the southern extremity of the LaSalle anticline and on the eastern edge of the Illinois Basin. Oil and gas production is from 13 sands in the Pennsylvanian and production is from 13 sands in the Pennsylvanian and Mississippian system. The principal producer is the Robinson oil sand, a basal Pennsylvanian sand encompassing about 59,300 acres in Crawford and Lawrence Counties, Ill. The sands are erratic and rarely exhibit continuity for more than a few miles. Transition from sandstone to shale or an interbedded sand-shale is common within a space of 1 mile. This type of lithology indicates that deposition was in response to rapidly shifting loci of sedimentation. The Robinson Main sand in this area varies in thickness from 50 to 100 ft and is usually described as a medium- to fine-grained sand, white to grey, with shale lamination. The shale laminations are more numerous near the top and at the base of the sand. Although the lateral extent of these laminations is limited, the vertical permeability, if any, is probably much less than the horizontal permeability.
JPT
P. 1356