Technology Application And Oil Displacement Mechanisms Of In-situ Combustion After Steam Injection In Heavy Oil Reservoirs

In the middle and late stage of development of heavy oil reservoir by steam injection,oil steam ratio is falling sharply,water cut is increasing,and economic benefit is poor.Although most oil fields have stopped most of the steam injection thermal recovery projects becuase of the sharp decline of oil prices,there are still a lot of crude oil remaining in the reservoirs.Therefore,it is urgent to exploit a highly efficient and economical develop way to exploit this kind of heavy oil reservoirs.In this paper,aiming at the problems existing in the late stage of steam injection in heavy oil reservoirs,based on the subjects of petrophysics,reservoir engineering,thermo engineering theoretical basis,seepage mechanics and thermal recovery etc,technology application and oil displacement mechanisms of in-situ combustion after steam injection in heavy oil reservoirs is studied.The main research methods applied in the dissertation include investigation,physical simulation,reservoir engineering computation and reservoir numerical simulation.Summing up the reservoir characteristics and existing problems in the late stage of development of heavy oil reservoirs by steam injection,oil displacement efficiency of different replacement methods was studied,and recovery rate of different development methods was predicted.The main research methods applied include investigation,physical simulation,example analysis,parameter analogy.Based on these research,it is determined that the in-situ combustion is the most widely used and optimal development technology after steam injection in the process of heavy oil reservoir development.By conducting a midway fire extinguishing experiment on a combustion tube,oil saturation and temperature field,fluid distribution and combustion of oil sands type characteristics along combustion tube is analyzed.The combustion zone is divided by these characteristics and flue gas flow regularity.By comparing the combustion characteristic parameters of different combustion tube experiments,the effects of existed secondary water formed during steam injection on the development effect and geological model of in-situ combustion are studied.Through physical simulation experiments,the PVT properties of the oil-gas mixtures（including CO₂、N₂、mixture gas） under different temperatures and pressures are tested.On this basis,visualization experiments of high temperature and high pressure of flue gas flow characteristics of is carried out.Further,the mechanism of highly efficient development of heavy oil reservoirs during in-situ combustion is studied from the aspects of chemical reaction mechanism,PVT characteristics,and microscopic flow characteristics of flue gas.Aiming at a block in Shengli oilfield,Through the research of the development status and the distribution of the remaining oil of the target block,in-situ combustion is is determined to be the following development technology.The basic characteristic parameters of crude oil combustion reactionin the block were studied by physical simulation.Then,the optimal well pattern and injection production parameters are determined by reservoir numerical simulation.These research achievements in this paper improve oil displacement mechanisms of in-situ combustion after steam injection in heavy oil reservoirs.It plays an important role for the expanding process of in-situ combustion after steam injection in heavy oil reservoirs.