考虑拟时间的页岩气压裂水平井生产数据分析方法

Production data analysis method of shale gas horizontal well fracturing considering pseudo time

由于没有相关计算模型,页岩气压裂水平井通过生产数据分析解释压裂改造参数时,没有考虑页岩气藏存在的吸附气解吸及地层压力变化的影响。根据页岩气藏物质平衡方程,推导出考虑吸附气解吸的页岩气藏物质平衡拟时间计算模型,改进了变产变压生产数据特征分析方法流程通过Blasingame图版拟合诊断边界流动阶段、评价动态总储量;通过规整化拟压力(RNP)与物质平衡拟时间平方根图版拟合线性流段斜率,识别线性流结束时间,解释地质、压裂参数。研究表明,不使用拟时间时,RNP与物质平衡时间平方根图的线性流拐点不是真实的线性流结束时间,解释的渗透率偏低、裂缝半长偏高。四川盆地某页岩气井动态参数解释结果证明,本方法能综合考虑吸附气解吸、地层压力变化对RNP曲线物质平衡拟时间的影响,提高了线性流结束时间诊断精度和参数解释结果的准确性。

Because there is no relevant calculation model,the influence of adsorbed gas desorption and formation pressure change in shale gas reservoir is not considered when interpreting fracturing parameters through production data analysis in shale gas horizontal well fracturing.According to the material balance equation of shale gas reservoir,this paper deduces the material balance pseudo time calculation model of shale gas reservoir considering desorption of adsorbed gas and improves the process of production data characteristic analysis method of variable production and variable pressure.That is,the Blasingame chart is used to fit and diagnose the boundary flow stage and evaluate the dynamic total reserves;the normalized pseudo pressure(RNP)and the square root chart of material balance pseudo time are used to fit the slope of linear flow section,identify the end time of linear flow and interpret the geological and fracturing parameters.The results show that the inflection point of linear flow in the square root diagram of RNP and material balance time is not the real end time of linear flow when pseudo time is not used,and the interpreted permeability is low,and the fracture half-length is high.The dynamic parameter interpretation results of a shale gas well in Sichuan Basin show that this method can comprehensively consider the influence of adsorption gas desorption and formation pressure change on the material balance pseudo time of RNP curve,and improve the accuracy of diagnosis of linear flow end time and parameter interpretation results.