X凹陷A构造低阻气层成因机理分析

Genetic mechanisms of low-resistivity gas zones in structure A of sag X

经勘探开发证实,X凹陷A构造H组地层Q_(3)c上部层段存在大量低阻气层。针对该层段地质沉积环境认识不清、储层微观认识不深入、气层低阻成因尚未明确等问题,以研究区3口井的测井资料为基础,结合钻井、录井资料和大量岩石物理实验资料开展相关研究。对研究区开展了基于薄片鉴定资料的岩石学、物性特征分析;通过连井剖面、特殊测井资料并结合大量岩石物理实验对低阻气层成因机理开展研究;基于数字岩心技术构建多组分导电模型,从微观可视化尺度证实了低阻气层成因机理,开展有限元电性模拟定量分析各低阻成因对电阻率降低的贡献。研究结果表明,由于高阳离子交换容量粘土矿物的存在以及良好物性基础上发育复杂孔隙结构,共同导致了研究区Q_(3)c上部气层的低阻响应。其中,粘土附加导电性对低阻响应的贡献为35.63%,良好物性条件下的复杂孔隙结构对低阻响应的贡献达到64.37%,电性模拟结果与测井电性特征吻合,证实了Q_(3)c上部低阻气层成因机理。

As confirmed by exploration and development,many low-resistivity gas zones exist in the upper portion of layer Q_(3)c of the H Formation in structure A of Sag X.Given the problems such as unclear understanding of the geological sedimentary environment,insufficient microcosmic knowledge about the reservoirs,and unclear causes of the low resistivity of the gas zones,this study conducted extensive research based on the log data of three wells in the study area,as well as the data on drilling and many petrophysical experiments.Specifically,the petrological and physical property characteristics of the study area were studied using the thin-section identification data;the genetic mechanisms of low-resistivity gas zones were studied using the well tie sections and the special log data,as well as the data of many petrophysical experiments;the formation mechanisms of low-resistivity gas zones were confirmed from the microscopic visualization scale by constructing a multi-component conductivity model using the digital core technique,and the contributions of various low-resistivity geneses to the decrease in resistivity were quantitatively analyzed through the finite element-based electrical simulations.As indicated by the study results,the low-resistivity response of the gas zones in the study area is caused by the presence of clay minerals with high clay content and high cation exchange capacity and also results from the complex pore structure formed under the favorable physical property conditions in the anomalous high-pressure depositional setting.The contributions of the clay additional conductivity and the complex pore structure to the low resistivity are 35.63%and up to 64.37%,respectively.The electrical simulation results are consistent with the log-derived electrical characteristics,verifying the genetic mechanisms of the low-resistivity gas zones in the upper portion of the Q_(3)c.