Polymers For Enhanced Oil Recovery In Reservoirs Of Extremely High Salinities And High Temperatures

Abstract

Abstract Polymers for low salinity reservoirs and lowviscosity crude oils are well known. For sandstone reservoirs with highly concentrated brines of low ph-values, reservoir temperatures up to 80 deg. C and crude oilviscosities of 20 to 200 mPa.s suitable polymers have hitherto not been available. Under consideration of these conditions rapid selection methods for polymers(biopolymers, HEC, PAA/HPAA etc.) were developed. By application of these novel test procedures to about 340 different products several promising polymers, aswell as general correlations could be ascertained. Test results concerning the shear stability, filtration, adsorption/retention and flow of polymer solutions in porous media allow reliable predictions about the efficiency of viscous flooding media. Moreover quality and application values of suitable polymers for enhanced oil recovery are critically compared. polymers for enhanced oil recovery are critically compared. Preselected polymers were tested in laboratory flooding Preselected polymers were tested in laboratory flooding experiments and have shown substantial increases in oil recovery of up to 24% OOIP. Introduction For less complicated reservoir conditions (low reservoir temperature, low salinity and low oil viscosity) numerous polymers for EOR processes are already known. The aim of these investigations is to find suitable viscous flooding media for application in reservoirs with–high oil viscosities (20 less than/equal to eta o lessthan/equal to 200 mPa.s)–high salinity of the reservoir brine (100 less than/equal to cs less than/equal to 250 g1-1 salt concentration)–elevated reservoir temperatures (45 less than/equal to less than/equal to 80 deg. C) (table 1). Moreover the flooding media should be economical to use and technically simple to handle. The working concept can be characterized by the following aspects:–Preservation of the reservoir properties: No permanent alterations of the permeability should result by application of polymers persistent pore plugging means damage to the reservoir rock. Additional oil recovery should come from reservoir zones already subjected to water flooding; it should not result from plugging effects, which divert the flow into reservoir zones previously untouched.–Development of appropriate rapid test methods: Because of the multitude of products being offered, rapid test programs must be developed, in order to permit the selection of suitable products in the shortest possible tine. The test procedures and programs must be designed to allow conclusions applicable to real systems.–Consideration of the boundary conditions for German oil reservoirs: The characteristic data pertaining to German oil reservoirs must be evaluated in order to provide a representative survey of the boundary conditions required for both the rapid test methods and the preliminary flooding experiments.–Testing of selected flooding media in the flooding tube: Polymer solutions, which have been classified as suitable by means of preliminary physico-chemical tests must subsequently be tested for their ability to mobilize residual oil in a flooding tube.–Conclusions with the most general applicability Since there is no restriction to any specific oil reservoir the results should be of the most general possible validity, and polymer solutions with a broad range of applications should be sought. Hence, maximal demands should be imposed on the viscous flooding media, in order to ensure test results, which are applicable to as many oil reservoirs as possible. P. 33