Improved Water-Soluble Polymers for Enhanced Recovery of Oil

Abstract

Abstract Two principal types of polymers have been used extensively for enhanced recovery of crude oil: partially hydrolyzed polyacrylamide (HPAM) and xanthan gum (XG). Because of its lower cost, HPAM is being used in a majority of the field projects when water-soluble polymers are applied. However, HPAM does lose viscosity in brine, particularly when divalent ions are present, and is susceptible to mechanical degradation under high shear conditions. Although many different polymer structures were evaluated in our laboratory tests, the main focus consisted of modifying the structure of HPAM and observing the effects on brine and shear stability. Testing of these analogs provided a systematic correlation of polymer structure with polymer performance so that improved compounds could be developed. Two modified acrylamide polymers were synthesized that show improved performance when compared to HPAM. The main improvement with these modified materials is the higher viscosities generated in salty waters. This paper presents highlights of the laboratory program and conclusions from the polymer synthesis work. Results obtained with the improved polymers are summarized and compared to commercially available products. Introduction In October 1978, we initiated a laboratory program to pursue the development of improved water-soluble polymers for enhanced oil recovery (EOR) applications. The three-year program, funded jointly by the U.S. Department of Energy (DOE) and the State of New Mexico, was concluded in December 1981. Since then, we have continued to follow up on some of the interesting leads that evolved from our work. Objectives of the program were to:Document the problems encountered with currently available polymers used in EOR processes.Design laboratory screening tests to evaluate polymers in these problem areas.Perform synthesis of new or modified polymers to establish relationships between polymer structure and performance.Develop improved water-soluble polymers using the structure-performance relationships. The initial phase of the project included a literature survey of surfactant/polymer flooding, a summary of the status of DOE-sponsored polymer and surfactant/polymer field projects, and a survey of oil industry personnel regarding difficulties encountered in the use of commercially available polymers. The major problems in the use of partially hydrolyzed polyacrylamides were identified as:mechanical degradation,viscosity loss in brines, andinteractions with divalent ions; whereas the most serious deficiencies with xanthan gum polymers were:high cost of the polymer,potential for plugging of injectio wells,microbial degradation of the polymer, andthe requirement for filtration of the polymer solution. Problems common to both polymer types include: lower injectivity, interactions with surfactants, long-term stability at elevated temperatures, and availability of bactericides that are compatible with the polymers. The laboratory tests in the second phase were designed with the most important problems in mind. The evaluation program with commercial polymers included:Viscosity and screen factor measurements in waters of varying salinityThermal stability experimentsMicrobial degradation studies