A Successful Activator Flooding Pilot Test in Offshore Oilfield: A Comprehensive Evaluation and Interpretation

Abstract

Oil reserves with oil viscosity above 150 mPa·s account for a large proportion of the Bohai Oilfield. However, due to the low mobility of heavy oil, and low sweep efficiency of injected fluid, the recovery factor of heavy oil is always low. A new amphiphilic polymer (activator), which can effectively disassemble the accumulation of asphaltene molecular layer of heavy oil, thus reducing oil viscosity has been developed in the lab and applied for two injection wells in Bohai Oilfield for a pilot trial. In this paper, the pilot trial of heavy-oil activator flooding (HAF) is comprehensively evaluated in both injectivity, production, and interwell connectivity analyses. The apparent injectivity index, Hall plot analysis, injection profile measurement for different layers, and PI test methods are applied to study the seepage resistance build-up effect at injection wells. Waterflooding characteristic curve method is implemented for history matching and oil incremental analysis. The interwell connectivity between wells is characterized by the Capacitance Resistance model (CRM). The injection trials showed great seepage resistance build-up effects at two activator injectors. There are apparent deviations in Hall plots after the activator injection. Activator flooding enables uniform water injection profiles for different layers. The PI tests show that the pressure drop speeds get lowered during the injection period. As for the oil incremental effect evaluation, the theoretical waterflooding characteristic curve function gives an estimation of the incremental oil production to be 1.77×104 m3 during the evaluation period. CRM analysis indicates that the connectivity between injector I2 and producer P4 is higher than that of other wells, and the time lag of getting a response by the activator fluid is smaller than other wells, which is an indication of potential fluid channeling in the flow path. It is validated by the high concentration of produced agent from P4 during HAF. The successful implementation of the activator flooding pilot trial proves that the lab results of amphiphilic polymers can be scaled up to field scale and it plays an important role in the de-risking of full-field implementation. Besides, it shed light upon the effective displacement of heavy oil with a viscosity greater than 150 mPa·s in offshore reservoirs by amphiphilic polymers.