| Low permeability volatile oil reservoir fluid property is complex,the crude oil property is prone to unstable changes in the development process,development is difficult.At present,there are few cases of gas flooding for volatile oil reservoirs in China,and the experience is not enough.The research object of this thesis is the lowpermeability volatile oil reservoir under Kenkyak salt,which was developed by water flooding in the early stage.Due to poor reservoir physical properties,the development effect of water flooding is poor,and the current formation pressure level is 40%,which makes it difficult to comprehensively tap potential and stabilize production of oil and gas reservoirs.In this thesis,the pre-salt reservoir is taken as the research object,phase balance theory,seepage mechanics,reservoir numerical simulation methods are used to carry out studies on the mechanism of volatile oil injection,oil displacement law,development technology policy and so on,and develop a set of gas injection development strategy suitable for the target area.The results are as follows:(1)The mechanism of volatile oil miscibility: based on the phase equilibrium theory and the mixed cell grid method,the flash calculation method is modified to solve the unstable problem of the volatile oil phase equilibrium calculation at the critical point.The mass transfer coefficients of different gas injection components in oil and gas phases were defined,and the mass transfer coefficients of different gas injection components in oil and gas phases were compared.Based on the improved calculation method of minimum miscible pressure combined with the phase balance calculation model,the dynamic evaluation chart of minimum miscible pressure in the target area was constructed,so as to realize the dynamic evaluation of minimum miscible pressure at different pressure holding levels and different development stages.(2)The analysis method of gas drive percolation development law of volatile oil reservoir is established,and the dynamic law of phase permeability curve under different gas injection is analyzed.The composition mechanism model is established: to analyze the difference of oil displacement efficiency and sweep ability under different miscible state of injected gas and crude oil,and the influence of oil and gas gravity differentiation on enhanced oil recovery by gas injection is emphasized.The life-cycle analysis method of gas flooding miscible flooding and immiscible flooding is put forward,and the oil displacement law of different miscibility degree is defined,which provides theoretical guidance for the design of field gas flooding development program.(3)Completed the formulation of gas injection development plan of sub salt reservoir: from the perspective of miscibility and enhanced oil recovery,select the produced gas as the best injected gas in the target area.On the basis of history fitting,typical well groups are divided.The injection volume of the injection wells of the initial well group in Block H is optimized to be determined by the injection production ratio of1.15.When the local formation pressure recovers to 48%,the injection production ratio is changed to 1.0,and the shut in gas oil ratio of the production well is set to1500m~3/m~3.The gas injection mode is that the continuous gas drive is changed to water gas alternating 1:2;The injection volume of the injection well of the initial well group in block L is optimized to be determined by the injection production ratio of 0.6.When the local formation pressure drops to 46%,the injection production ratio is changed to1.0,and the shut in gas oil ratio of the production well is set to 1400m~3/m~3. |
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