川东南五峰组—龙马溪组页岩气录井碳同位素特征及其地质意义

为了更详尽地分析不同深度段五峰组—龙马溪组页岩气的碳同位素特征以及页岩气的成藏富集规律，选取川东南地区3口典型页岩气评价井开展了页岩气碳同位素录井工作。在钻探现场连续取样并检测泥浆气的碳同位素值，并以DY5井为例检测了岩屑释气过程中的碳同位素变化。基于碳同位素录井数据，综合分析了五峰组—龙马溪组页岩气的碳同位素平面分布及纵向变化特征、碳同位素倒转特征和岩屑释气过程中的碳同位素分馏特征。综合分析认为：四川盆地五峰组—龙马溪组页岩气碳同位素值由盆地周缘向中心逐渐变轻，这一变化规律主要受控于页岩的热演化程度；川东南3口井的泥浆气碳同位素的纵向变化及倒转特征具有一定共性，表明其具有相近的页岩气富集规律；DY5井的岩屑罐顶气越靠近地质甜点区域同位素分馏越明显且岩屑释气量越大，反映该段页岩气具有初始地层压力高、含气量大、纳米孔隙更发育等特征。

Mud gas isotopic logging of Wufeng-Longmaxi shale in southeastern Sichuan Basin

In order to analyze the carbon isotope characteristics of shale gas from the Wufeng-Longmaxi formations at different depths in more detail, and research the shale gas accumulation, three typical shale gas evaluation wells in southeastern Sichuan Basin were selected to carry out carbon isotope logging. The carbon isotope of mud gas was continuously sampled and measured with drilling, and the carbon isotope change during the gas release from cuttings was also measured. Based on data obtained from the isotope logging, the carbon isotope distribution and vertical variation, as well as the carbon isotope reversal and carbon isotope fractionation of shale gas are comprehensively analyzed, which reveals that the carbon isotope value of Wufeng-Longmaxi shale gas in the Sichuan Basin gradually decreases from the margin to the center of the basin, and this change is mainly controlled by the maturity of the organic matter. The carbon isotope characteristics of shale gas of these three wells have certain commonality, which indicates that shale gas accumulation rules were similar in this area. In sweet point, the carbon isotope fractionation of the top gas of the cuttings jar is much greater, and the amount of gas released from the cuttings is higher, reflecting this section has high initial pressure, large gas content, and more nano pores.