Evaluation and Economical Feasibility of Polymer-Assisted Surfactant Flooding for the Gullfaks Field, Norway

Abstract

Summary This paper presents parts of the work performed to develop and qualify a polymer-assisted surfactant flooding (PASF) system for economical use in the Gullfaks Field, Norway. The paper addresses experimental work done in the laboratory, numerical simulation of PASF, and the evaluation of the potential for PASF in full-field scale. The experimental part comprises core-flooding experiments at different temperatures, pressures, and gas/oil ratios (GOR) to optimize the PASF system for the Gullfaks Brent formation conditions. The surfactant in the PASF system is a branched sulphonate (5,000 ppm) and xanthan (500 ppm). The surfactant-polymer slug is followed by a slug of xanthan (500 ppm) for mobility control. No cosolvent is used. In coreflood experiments more than 70% of the waterflood residual oil was recovered. Using reservoir simulation, a suitable pilot area was found in the Brent reservoir. Additional results from simulations were the amount of chemicals, the time needed for the pilot test, and additional oil recovery. Much effort was put into estimating the full field PASF potential. First, the areas of the field where PASF possibly could be used were selected. Key factors were existing and planned well locations, production data, and long-term production forecasts. Then, the amount of chemicals needed and the expected technical efficiency for each area were calculated. To verify these calculations, an area of the field containing two possible injection wells and three producers was selected for a simulation study. This area was considered the most promising area for PASF. The main conclusion from this work is that, with the present crude-oil price and chemical costs, the PASF process is not economically attractive for use in the Gullfaks field, mainly because the residual oil was considerably lower than believed at project start.