低渗透气藏介质变形评价参数研究

Astudy of parameters for evaluating deformation of low permeability gas reservoirs

目前中国低渗透气藏的储量占未动用气藏储量的比重越来越大,而低渗透气藏一般都采用衰竭式开采,在生产过程中地层压力逐渐下降,导致储层岩石变形,使得孔隙度和渗透率降低,从而导致低渗透气藏开发效果变差。在对苏里格低渗透气藏岩心进行大量应力敏感性实验的基础上,通过对实验数据的分析,比较了线性、指数和乘幂3种典型渗透率随有效压力变化的关系模型。分析结果表明:乘幂变异模型较其他两者与实验数据更为吻合,在此基础上,推导了考虑应力敏感性时的低渗透气藏产能公式。由此提出了刻画岩石介质变形的新参数——岩石变形系数,用此参数可以很好地表征低渗透气藏介质变形的变化特征及其对低渗透气藏产量的影响,并依据该系数对低渗透岩心的变形程度进行分类,得到了比较好的分类效果。

The proportion of reserves of lowpermeability gas reservoirs to non-producing reserves is larger andlarger in Chi-na at present. And the depletion way of productionis used in low permeability gas reservoir currently ,so the gradual drop of formation pressure during the exploitation will result in the deformation of rocks ,which makes the reservoir porosity and per-meability decline. And that will lead to the development of low permeability gas reservoir deteriorate.Based onthe experiments of stress sensitivity to Sulige cores and the analysis of the data ,a comparision was made among the three classical models (line-ar ,exponential and power) about the relationship between the effective pressure and the permeability. The results indicate thatthe curves of power are more similar to the experimental data than that of the other two. And the productivity and pressure dis-tribution equations of a low permeability gas reservoir were deduced with consideration of stress sensitivity. Hence ,rock de-formed coefficient ,a new parameter of depicting deformation,was given.It can be used to represent the characteristics of de-formation in low permeability gas reservoirs. And sorting of the deformation degree of low permeability cores by the coefficients had good results.