The Study On Production Performance And Development Mode Of Near-critical Volatile Bioclastic Dolostone Reservoir

The oil reservoir is in near-critical area when its temperature Tr is between 0.95?1.05 times of the fluid system critical temperature Tc .B near-critical volatile oil reservoir adopted the depletion development using natural energy in the early time and achieved high production. But due to the formation fracture and geological factors, there is lack of connectivity between each well. At present many well blocks are faced with insufficient nature energy and production decreasing rapidly. The situation of production is grim. There are also some special producing features to be explained: the first is producing gas-oil ratio remained stable under bubble-point pressure, which is different from the conventional dissolved gas depletion development theory; the second is the phenomenon of pressure gradient inversion in the wellbore, which conflicts with fluid gravity differentiation.Based on the B oilfield as the research object, several fluid PVT experiments are carried out to confirm the phase characteristics of near-critical fluid. On the basis of bioclastic dolostone reservoir characteristics, the anomaly producing performances are explained clearly.Combined with domestic and foreign similar oilfield development cases and the result of displacement test of different media and numerical simulation results, the late oilfield development mode is confirmed. Conclusions are drawn as follows:(1) Summarize the bioclastic dolostone reservoir geological characteristics and oil reservoir characteristics, conclude the development technical strategy and reservoir development discipline of the similar volatile oil field at home and abroad in order to lay foundation for subsequent research work.(2)The fluid PVT experiments are carried out to confirm the phase characteristics of near-critical fluid and B oil field (Tc-T ?1?) is defined as near-critical volatile oil reservoir.The oil-gas system belongs to low-tension system ( < 1mN/m) when pressure is higher than 25MPa.(3) Summarize the basic production dynamic characteristic, analyse the reason why oil-gas ratio remains stable and the phenomenon of pressure gradient inversion in the wellbore combining near-critical fluid properties and the pore structure characteristics of bioclastic dolostone reservoir.(4) Displacement test of different msdia (water, formation gas, CO2 or N2) are carried out to provide experimental basis for choosing reasonable development model.(5) A component mechanism model is established to compare the oil recovery of different development modes (depletion, water flooding and gas injection) and to optimize conversion time. Associated gas iniection is considered as the most economically and feasible development mode. The oil recovery increases as the gas injection becomes earlier. The results of the study is very important for late oilfield development adjustment.