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低渗透油藏由于天然能量不足、岩性致密和压力传导能力差,导致开发过程中地层压力下降幅度较大。地层压力的下降会造成岩石变形而影响其物性和渗流能力,岩石表现出应力敏感性特征。借助室内岩心流动实验,模拟再现地层压力的下降过程,研究了低渗透油藏有效上覆压力对岩石启动压力梯度的影响。结果表明,当地层压力下降时,启动压力梯度随着岩石骨架承受的有效上覆压力的增加而增加,即启动压力梯度具有应力敏感性;且岩石的渗透率越低,当地层压力下降幅度相同时,启动压力梯度的增幅越大,即启动压力梯度的应力敏感程度越强。因此,在根据启动压力梯度计算低渗透油藏合理井距时,要充分考虑地层压力保持水平对启动压力梯度的影响。
Low permeability reservoir due to lack of natural energy, tight lithology and poor pressure conductivity, resulting in the development process of pressure drop larger strata. Decreasing formation pressure can cause rock deformation and affect its physical properties and seepage ability. Rocks exhibit stress-sensitive characteristics. By means of indoor core flow experiment, the descending process of formation pressure is simulated and the effect of effective overburden pressure of low permeability reservoir on the pressure gradient of rock initiation is studied. The results show that the starting pressure gradient increases with the increase of the effective overburden pressure on the rock framework when the formation pressure decreases, ie, the starting pressure gradient is stress-sensitive. The lower the permeability of the rock, At the same time, the larger the increase of the starting pressure gradient, the stronger the stress sensitivity of the starting pressure gradient. Therefore, when calculating the reasonable well spacing of low permeability reservoirs based on the starting pressure gradient, the influence of formation pressure holding level on the starting pressure gradient should be fully considered.