Study on expansion of heating chamber by chemical steam flooding in offshore heavy oil reservoirs

Abstract After multiple rounds of cyclic steam stimulation(CSS), the thermal recovery performance becomes worse. Steam flooding is needed to further improve the recovery rate. However, there is no experience in multi-media composite steam-flooding in offshore heavy oil reservoirs. The research show that good formation and expansion of the steam chamber is very important for steam flooding. Therefore, it is necessary to study steam chamber expansion characteristics of multi-medium composite steam flooding, so as to further improve the thermal recovery. In this paper, experiments and numerical simulation methods are used. Firstly, taking a typical heavy oil sample in Bohai offshore as the target, experimental research on the synergistic mechanism of composite steam with different agents were carried out. The synergistic mechanism of different media was analyzed, and the medium combination mode of the target oilfield was clarified. The expansion process and expansion characteristics of the heating chamber with different media combinations were analyzed by two-dimensional displacement visualization experiments. According to the experiment results, the remaining oil is analyzed. Through the image processing software, three kinds of of remaining oil distribution characteristics are clarified. Finally, the injection parameters of multi-media composite steam flooding in the target oilfield were optimized, and the effect was predicted. Through the above research, three meaningful understandings are obtained. Firstly, the enhanced-effect mechanism of chemical composite thermal media was clarified, that is viscosity reducer reducing viscosity, gas dissolved & reducing viscosity, and foam’s plugging effect. Secondly, it’s clear that in the steam swept area, the remaining oil is mainly flake oil, which is mainly distributed in the swept front, accounting for about 70 %, the columnar oil is in the swept area, accounting for about 17 %, and the membranous oil is in the near wellbore area, accounting for about 13 %.The first two are mainly enhanced by viscosity reducer and foam, and the membranous oil is mainly enhanced by oil displacement agent. Thirdly, the research results have successfully guided the comprehensive adjustment plan of L2 oilfield. The 3 injection 10 production well group predicted that the recovery rate was increased to 30.7 %, while it’s 15.6 % before. Multi-media composite steam flooding has opened up a new development mode, which can improve the exploitation of reserves effectively and so as the recovery rate after multiple rounds of CSS. It is of great significance to developing offshore bottom-water heavy oil reservoirs.