基于地应力校正的变胶结指数饱和度计算方法——以库车前陆盆地A井区为例

Saturation calculation method of variational cementation index corrected based on geostress:a case study of A block in Kuqa foreland basin

库车前陆盆地巴什基奇克组裂缝性致密砂岩储层埋藏深、厚度大、物性差、地应力强,复杂的储层特征导致地层电阻率随埋藏变深而异常升高,出现低阻气层和高阻水层,全井段应用统一的岩电参数计算含气饱和度会产生认识性错误。基于测井、测试资料及粒度、铸体薄片等实验资料,深入分析了储层物性、岩性、储集空间类型、流体类型、裂缝和水平主应力差对地层电阻率的影响,建立了随水平主应力差变化的胶结指数计算模型,提高了饱和度计算精度,为储层流体识别和储量评估提供可靠依据。研究表明,地层电阻率随水平主应力差异常增大有明显的幂指数增大关系;构造应力产生的裂缝是地层电阻率增大的重要原因;在一定范围内,胶结指数随水平主应力差异常增大呈二次幂函数增大关系,且增大趋势逐渐变缓。

The tight sandstone formation of Bashijiqike Formation,Kuqa foreland basin is characterized by deep burial depth,large thickness,poor physical property and strong geostress.These complex reservoir characteristics lead to an abnormal increase in the formation resistivity with the depth,which may cause low-resistivity gas reservoirs and high-resistivity water reservoirs.Cognitive errors will occur when using the unified rock-electro parameters to calculate the gas saturation of all well sections.Based on logging data,test data,granularity,casting thin-sections and other experimental data,the influences of various factors,such as physical property,lithology,reservoir space types,fluid type,fracture and horizontal principal stress difference,on the formation resistivity are analyzed thoroughly.Then,a new calculation model of cementation indexes varying with the horizontal principal stress difference is established to improve the precise calculation of saturation and provide a reliable basis for reservoir fluid identification and reserves evaluation.The results show that the formation resistivity abnormally increases with the horizontal principal stress difference,shown as an increasing power exponent relationship.The fractures caused by tectonic stress is one of the dominating factors for an increase in formation resistivity.In a certain range,the cementation index abnormally increases with the horizontal principal stress difference,shown as an increasing quadratic power function relationship,whereas the increasing trend gradually slows down.