Evaluation of the Potential of High-Temperature, Low-Salinity Polymer Flood for the Gao-30 Reservoir in the Huabei Oilfield, China: Experimental and Reservoir Simulation Results

摘要

This paper summarizes the laboratory and simulation studies conducted to evaluate the potential ofrnlow-salinity polymer flood for the Gao-30 reservoir in Huabei Oilfield, China which has a high reservoirrntemperature of 113℃, moderate formation salinity of 9,000 ppm total dissolved solids and in-situ oilrnviscosity of 25 cP.rnOur studies have identified GL-100, a specially designed rigid structure modified polyacrylamide, asrna polymer candidate for the Gao-30 reservoir because it exhibits adequate thermal stability and acceptablerninjectivity. Laboratory results show that for GL-100, low-salinity brine has the dual benefits of improvedrnthermal stability and higher viscosity compared to formation brine. Spontaneous imbibition experimentsrnusing Gao-30 core plugs show that secondary mode imbibition by softened formation brine recovers morernoil than imbibition by formation brine. In addition, significant incremental oil recovery was observed withrninjection of low-salinity polymer into a heterogeneous Gao-30 core, compared with formation waterrnflooding.rnCorefloods in secondary mode were conducted with low-salinity and formation brines. Results werernhistory matched to obtain the relative permeability and capillary pressure curves. These results andrnlaboratory measured polymer rheology and adsorption were used as input into reservoir simulations tornforecast benefits of low-salinity polymer flood in two pilot locations chosen from full field historyrnmatching of 20 years of waterflood in the Gao-30 reservoir.rnReservoir simulations were run to compare the incremental oil recovery resulting from injection ofrnvarious slug sizes of formation-salinity polymer and low-salinity polymer. Our simulations only consideredrnthe increase in viscosity due to polymer and the improvement of thermal stability of polymer inrnlow-salinity brine. Low-salinity chemical effects through changes in the relative permeability curves werernnot included. Results show that injection of 0.3 PV formation-salinity polymer and low-salinity polymerrngives incremental oil recovery of 9% and 13%, respectively, compared to formation-salinity waterflood.rnPreliminary economic evaluations show that formation-salinity polymer flood based on 0.3 PV of 1800rnppm GL-100 to be economical in Gao-30 reservoir based on economics of on-going polymer projects inrnChina. The additional 4% incremental oil obtained by tuning the brine composition (the low-salinityrneffect) may be economical, especially if it is achieved through softened brine instead of low-salinity brine.