川东北碳酸盐岩气藏岩石渗透率变化实验

地应力变化是一个三轴方向上的综合应力变化,传统的应力敏感性实验与地层真实情况存在较大误差。为了研究超高压碳酸盐岩气藏储层渗透率与有效应力的关系,针对实际井获取的岩心,设计了不考虑岩石中孔隙流体压力的三轴应力变形实验和考虑岩石中流体压力的变形实验方案,推导了由三轴应力实验数据计算渗透率变化的数学模型,在此基础上分析了川东北碳酸盐岩超高压气藏岩石渗透率变化与有效应力的关系。结果表明:在同样的有效应力条件下,考虑孔隙中流体压力时渗透率下降幅度更大。3号岩心有效应力达到50 MPa时,无因次渗透率下降幅度为57.48%。对于天然裂缝发育的岩心,使用考虑岩心中流体压力的变形实验能更好地获取渗透率的变化规律;对于天然裂缝不发育的岩心,使用不考虑岩心中孔隙流体压力的三轴应力实验能更好的获取基质渗透率的变化规律。对比国内外异常高压气藏,认为研究区气藏渗透率的应力敏感性较强。实验研究为气藏科学、高效开发提供了科学保障。

Experiments on permeability change of carbonate gas reservoirs in the northeastern Sichuan Basin

The terrestrial stress variation is a comprehensive triaxial change in nature.The traditional stress sensitivity experiment results do not match well with actual situation.In order to establish the relations between permeability and effective stress of carbonate gas reservoirs with ultra-high pressure,we designed two triaxial deformation experiments by using cores,one with and another without pore fluid pressure being con-sidered.Through experiments we established mathematical model for calculating permeability change based on experiment data and analyzed the relations between permeability and effective stress of carbonate gas reservoirs with ultra-high pressure in northeastern Sichuan Basin.The results show that the permeability declines more quickly in the experiment with pore fluid pressure being considered than that without pore fluid pressure being consi-dered under the same effective stress.The dimensionless permeability reduces by 57.48% for the No.3 core sample when the effective stress reaches 50MPa.For cores with well developed fractures,the experiment with pore fluid pressure being considered can better reveal the changing patterns of the permeability.In contrast,for those with poorly developed fractures,the experiment without pore fluid being considered works better for understanding the permeability variation of the matrix.Compared with other ultra-high pressure gas reservoirs both domestic and abroad,the reservoirs in the study area have higher stress-sensitivity.The experimental study provides a solid basis for highly efficient development of the gas reservoirs in the study area.