The Weak Alkali ASP Flooding Research in High Water Cut Shallow Reservoir

Abstract Strong alkali ASP flooding is now the major choice to develop high permeability reservoirs after water flooding in China. The formation was damaged seriously by the component of alkali. Weak alkali ASP flooding technique has become one of the most important research fields in EOR method due to the prevention of side-effects of alkali. The Laojunmiao oilfield has been developed 79 years since 1939. The waterflooding's ineffectiveness was caused by complex reservoir structure and longtime water flooding. The waterflooding remaining oil distribution of Laojunmiao reservoir was analyzed by sealed cores, logging interpretation, fluorescence analyses, numerical simulation and other means. The appropriate EOR technology of high water cut shallow reservoir was selected by laboratory experiments, numerical simulation and single well test. In order to avoid formation damage and protect environment, weak alkali ASP flooding was chosen as the candidate EOR method. The recovery factor of sand body type I and II (high permeability) were higher than type III and IV (low permeability). The main remaining oil type was oil membrane at the particle surface. Membrane remaining oil major distributed at the rock surface between the large grain holes (greater than 10 microns), which was suitable for ultra-low interfacial tension chemical flooding technology. The weak alkali ASP flooding injection parameters were identified by indoor natural core experiments and numerical simulation parameter optimization. Due to the low fracture pressure of shallow reservoir, the pressure rising space of weak alkali ASP was just 1-3MPa. It was necessary to choose the appropriate injection speed, realizing injection pressure control, which avoided dynamic cracks forming. The pressure rose from 4.9 MPa to 7.65 MPa during single well injection test. 6 months later, the water cut of effective wells decreased to 81.3%, the injection system was suitable for Laojunmiao oilfield. The injection process and equipment requirements of weak alkali ASP are simple, which has less effect on the environment. The weak alkali ASP flooding of this paper is different from the conventional chemical flooding, which will provide the necessary support for future applications. The strong alkali ASP flooding will be replaced by weak alkali ASP flooding in the future.