The Role of Chemicals Loss in Sandstone Formation in ASP Flooding Enhanced Oil Recovery

Abstract

Chemical combination flooding technique especially alkali/surfactant/polymer (ASP) flooding has proven to be an indispensable way to enhance oil recovery (EOR). The progress of this flooding technique in Daqing Oilfield (China) shows that it is promising to keep production from falling and help oil companies make profit in a low-oil-price era. However, the ASP chemicals chromatographic separation and loss in sandstone formation are still the weaknesses in the promotion of ASP flooding. Laboratory investigations for characterizing the behavior and distinction of chemicals loss in sandstone reservoir with strong base (NaOH) and weak base (Na2CO3) ASP flooding were recently carried out. The experiments were designed to pointedly study the chromatographic separation, and consumption loss behaviors of alkali and surfactant in sandstone reservoirs with ASP flooding. Furthermore, the incremental oil recovery factor in heterogeneous sandstone reservoirs with strong base (NaOH) and weak base (Na2CO3) ASP flooding process was evaluated and compared. The loss rates of chemicals and the permeability damage degree in various experiments were determined respectively, the consumption loss mechanism and influencing factors were discussed, and the formulation composition and slug combination patterns were also optimized. Then, the role of ASP chemicals loss in sandstone formation during ASP combination flooding EOR process was worked out. The results indicated that the chemicals loss behaviors could be weakened and the chemicals chromatographic separation phenomenon could be alleviated in weak base (Na2CO3) ASP flooding, and the average loss rate of alkali and surfactant could drop 9.61% and 15.67% respectively in heterogeneous sandstone reservoirs comparing to strong base (NaOH) ASP flooding. The profitable EOR effect could also be obtained with weak base (Na2CO3) ASP flooding, and the enhanced oil recovery could still reach 20% or more. Moreover, an approximately 15% reduction in permeability damage rate could be realized in the weak base (Na2CO3) ASP flooding instead of strong base (NaOH) system, and the reservoir flow assurance issues related to chemicals loss behaviors could be addressed. The optimal design of ASP formulation and slug combination pattern could technically and economically achieve high oil recovery in sandstone reservoirs with weak base (Na2CO3) ASP flooding. The results are beneficial to well understand the chemical combination flooding mechanism and can contribute to the existing knowledge in the chemicals super additive effects during EOR process, and it is also significant to further improve the oil displacement efficiency and reduce the injection cost in heterogeneous sandstone reservoirs with weak base (Na2CO3) ASP flooding process.