致密油藏气驱最小混相压力预测

Minimum miscibility pressure prediction of gas flooding in tight reservoirs

为了明确致密储层微观孔隙结构是否影响流体的最小混相压力,探索适合该类储层的气驱最小混相压力预测方法,通过理论计算分析对其开展了系统研究。结果表明:当孔喉半径小于50 nm时,孔喉会对流体的临界性质及相态产生重要影响。孔喉半径越小,影响程度越大,且流体临界温度和临界压力均随孔喉半径的减小而降低,相图区域随孔喉半径的减小而向左缩小。进一步,孔喉半径对重质组分的临界温度影响较大,对临界压力的影响较小,而其对轻质组分的影响则相反。纳米级孔喉的存在可以明显降低气驱的最小混相压力。因此对于存在纳米孔的致密储层,已不能再用常规方法确定其流体最小混相压力,可以由流体临界参数偏移计算模型联立PR状态方程预测该类储层的气驱最小混相压力,这样的计算结果具有信服力。该研究成果对同类盆地致密储层孔喉对流体相态最小混相压力的影响研究具有一定指导意义。

In order to clarify whether the micro-pore structure of tight reservoir affects the minimum miscible pressure of fluid, a prediction method of the minimum miscible pressure of gas flooding suitable for this kind of reservoir is explored, and a systematic study is carried out through theoretical calculation and analysis. The results show that when the pore throat radius is less than 50 nm, the pore throat will have an important influence on the critical properties and phase state of the fluid.The critical properties and phase states of fluids are greatly affected by nano-scale pore throat. The smaller the radius of pore throat is, the greater the influence is. The fluid critical temperature, pressure and phase diagram area decrease with the decrease of radius of pore throat. Furthermore, the radius of pore throat has a greater influence on the critical temperature of heavy components and a smaller impact on the critical pressure, while it has the opposite effect on the light components. Tight pore, especially nano-scale, can significantly reduce the minimum miscibility pressure of gas flooding. Therefore, for tight reservoirs with nano-scale pore, conventional methods are no longer possible to determine the minimum miscibility pressure of fluids. The minimum miscibility pressure of gas flooding in this type of reservoir can be predicted by the fluid critical parameter migration calculation model and PR equation of state. The calculation results are convincing. The research results have certain guiding significance for the influence of pore throat on the minimum miscible pressure of fluid phase in tight reservoirs of similar basins.