四川盆地东南部页岩气同位素分馏特征及对产能的指示意义

Methane isotope fractionation characteristics of shale gas and its significance as a productivity indicator

高玉巧 高和群 何希鹏 丁安徐 张培先 何贵松

GAO Yuqiao GAO Hequn HE Xipeng DING Anxu ZHANG Peixian HE Guisong

中国石化 华东油气分公司 勘探开发研究院, 南京 210011

Research Institute of Petroleum Exploration & Development, East China Branch Company, SINOPEC, Nanjing, Jiangsu 210011, China

页岩气甲烷碳同位素是研究页岩气同位素分馏特征及产出过程的重要指标。选取四川盆地东南部及盆缘转换带内6大区块10口页岩气井上奥陶统五峰组-下志留统龙马溪组页岩，通过现场含气量测试过程中页岩气甲烷碳同位素变化，研究不同压力系统、不同小层下甲烷碳同位素分馏特征，探讨页岩气同位素与物性、含气性关系，并结合实际排采数据，对典型页岩气井产出阶段进行划分。页岩气解吸过程中，逐渐升高，甲烷碳同位素逐渐变重；超压页岩气甲烷碳同位素整体较小，从盆缘外部向内部，甲烷碳同位素逐渐变轻。纵向上，随着深度的增加，甲烷同位素整体变轻；页岩孔隙度越大、游离气含量越高、页岩保存条件越好，甲烷碳同位素分馏作用就越不明显。最后，选取武隆向斜L井岩心现场解吸气样，通过甲烷同位素分馏，对页岩气解吸阶段进行划分，并将排采气同位素与现场解吸气同位素进行比对。该井排采气的δ13C1值对应现场岩心连续解吸0.9 h释放气体的δ13C1值，其采收率约为24.8%，尚处于初期排采阶段。

Carbon isotopes of methane in shale gas provide an important index for studying isotope fractionation characteristics and the gas production process. The carbon isotope variation of shale gas during in situ gas content measurement was studied for 10 shale gas wells of Wufeng-Longmaxi formations in 6 large blocks in the southeastern Sichuan Basin and the basin margin transition zone (the basin margin-transition zone of southeastern Chongqing). The fractionation characteristics of methane under different pressure systems and different subformations were studied, and the relationships between the isotopes of shale gas and its physical and gas-bearing properties were discussed. The production stages of typical shale gas wells were divided by drainage data.δ13C1 gradually increased during shale gas desorption, while the carbon isotope of methane in overpressure shale gas was smaller. From the outside of the basin margin to the inside, the carbon isotope of methane gradually became lighter, and in the longitudinal direction, with the increase of depth, the methane isotope becomes lighter. Greater porosity of shale, higher content of free gas and better preservation conditions of shale correlate with less fractionation of carbon isotopes. Finally, the desorption stage of shale gas was divided by methane isotope fractionation, and the isotopes of production gas was compared with that of core desorption gas of well L in the Wulong syncline as an example. The δ13C value of gas released corresponded to that of core sample after continuous desorption of 0.9 h, and its recovery rate was about 24.8%, which was still in the initial stage of drainage production.

国家科技重大专项"彭水地区常压页岩气勘探开发示范工程"（2016ZX05061）和中国石化科技部项目"渝东南盆缘转换带页岩气富集主控因素研究"（P18057-2）联合资助。

https://doi.org/10.11781/sysydz201906865