The Isenhour Unit — A Unique Polymer-Augmented Alkaline Flood

Abstract

Abstract The Almy sands in Sublette County, Wyoming have been subjected to various volumetric sweep improvement techniques since September, 1969. This paper describes the first field wide effort to reduce residual oil saturation in the swept area. Initially, a series of crude oil - alkaline agent screening tests were run to select, on the basis of interfacial tension reduction (IFT), the most cost effective alkaline agent. Follow up core tests showed that a combination of soda ash (Na2CO3) and anionic polymer would be effective in reducing oil saturations from 22 to 17 percent pore volume. The core tests also demonstrated that a properly prepared alkaline solution could be injected into the high clay content Almy. On the basis of these test results and ten years of experience injecting clay stabilizers, anionic polymers and wettability alteration products, the decision was made to go from the start with a total oil recovery program. The original plant design was modified to accommodate the requirements for adding one half million pounds of Na2CO3 in less than a year. This involved installing a second dry solids feed system, interchangeable with the regular polymer unit. Storage capacity at the plant site was increased to 50,000 pounds of dry product and on the Na2CO3 unit a second 100 gallon stainless steel solution tank was put in series with the regular mix tank. Operating people designed and built a rugged, inexpensive product handling system that allows the plant operator to service both feed units in less than one hour a day. Input side control tests include pH, O2, PO4, turbidity, screen factor and viscosity. Hall Plots are the primary monitor of injection well conditions with step rate tests and pressure fall-off measurements used as back up. Producing wells are tested once a month. Data is plotted on a time-rate basis as well as graphed in the form of water-oil ratio (WOR) vs. cumulative oil recovery. Produced water samples are checked for pH, chloride, tracers (thiocyanate and nitrate) and polymer breakthru. These results are also posted on the individual producing well graphs. Although only in its third year of operation, the project is far enough along to conclude the following: It is practical and profitable to employ, at the same time, techniques that will improve sweep and lower residual oil saturation. Selecting a "Total Oil Recovery" process and starting it early greatly simplifies plant design. EOR processes requiring fresh water should be started before breakthru to lower costs and lessen the problems related to lifting, treating and reuse or disposal of produced water.