渝东南盆缘转换带五峰组—龙马溪组页岩压力体系与有机孔发育关系

四川盆地东南部及其盆缘转换带（以下简称渝东南盆缘转换带）是中国常压页岩气勘探的热点地区。为了厘清渝东南地区页岩气富集规律、优选水平井穿层层段及指导多层系立体开发建设，本文基于扫描电镜的图像定量表征技术，结合三轴力学、液氮吸附等实验分析结果，研究了页岩压力体系与有机孔的发育关系。结果表明：渝东南盆缘转换带五峰组—龙马溪组页岩下部①—②小层有机孔孔径小（1~30 nm），孔隙发育的密集程度高（55.55~808.03个/μm²）；其上部③—⑤小层有机孔孔径变大（30~50 nm），孔隙发育的密集程度低（47.31~466.42个/μm²）；压力系数与有机孔圆度有明显的正相关性。基于液氮吸附实验的孔隙体积分形维数结果表明，研究区龙马溪组页岩孔隙内流体压力的增加，能够对孔隙进行更好的支撑作用，保证孔隙不会因为上覆地层压力而造成变形，使得孔隙能够得到更好的保存。因此，有机孔发育差异是上覆地层压力和孔隙内流体压力共同造成的结果。对于常压区，上覆地层的压力对孔隙发育有着更为重要的影响；对于超压区，孔隙内流体压力的增加会减缓孔隙的变形和消失。三轴力学实验表明，①小层上部观音桥段的存在使得岩石的抗压强度变大，由此在纵向上形成一种压力隔断，引起了上下压力系数的差异，形成了不同的亚压力体系，从而导致了孔隙发育特征的差异。

Relationship Between Shale Pressure System and Organic Pore Development of Wufeng-Longmaxi Formation in Marginnal Conversion Zone of Southeastern Chongqing Basin

Southeastern Sichuan basin and its marginal transition zone (hereinafter referred to as the basin-margin transition zone of SE Chongqing) is the focus of normal-pressure shale gas exploration in China. In order to understand the law of the shale gas enrichment in the southeastern Chongqing, to optimize the rough layers of horizontal well, and further guide the three-dimensional development and construction of the multi-layer system, the relationship between shale pressure system and the development of organic pores was studied by using the image quantitative characterization technology based on scanning electron microscope and the experimental analysis results of triaxial mechanics and liquid nitrogen adsorption. The results show that the organic pore size is small(1-30 nm) in the lower part of Wufeng-Longmaxi Formation shale,but the density of pore development is high(55.55-808.03 count/μm²). The organic pore size is high(30-50 nm) in the upper part,but the density of pore development is small(47.31-466.42 count/μm²). There is a significant positive correlation between pressure coefficient and roundness of organic holes. With the increase of fluid pressure in the pore, the pore will not be deformed by the overburden formation pressure, so that the pore can be better preserved. volume fractal dimension based on liquid nitrogen adsorption experiment show that the increase of fluid pressure in the pore can support the pore better, and ensure the difference of organic pore development is the common result of overburden formation pressure and pore fluid pressure. For the atmospheric pressure area, the pressure of overlying strata has important influence on pore development. For the overpressure zone, the increase of fluid pressure in the pore will slow down the deformation and disappearance of the pore. The realization of triaxial mechanics shows that the existence of Guanyinqiao Formation will increase the compressive strength of rock, thus forming a pressure partition in the vertical direction, resulting in the difference of pressure coefficient between the upper and lower layers, forming different subpressure systems, resulting in the difference of pore development characteristics.