川东南DS地区龙马溪组页岩裂缝发育特征及期次解析

Shale Fracture Characteristics and Its Application of the Longmaxi Formation in DS Area, Southeast Sichuan

裂缝发育特征和期次对页岩气储集空间的研究非常重要。以川东南DS地区龙马溪组为例,通过对地表及岩心裂缝观测分析和样品采集,开展了裂缝分期配套、构造反演、磷灰石裂变径迹测年和包裹体测温,确定了裂缝的发育特征和期次。研究表明,川东南DS地区龙马溪组页岩内发育了2套平面剪切缝和1套剖面剪切缝,这些裂缝形成于3期构造运动。第1期为NNW、NWW向和NE向裂缝,以方解石和黄铁矿全充填为主,形成于燕山运动中-晚期,磷灰石裂变径迹测年为67.8～58.6 Ma,包裹体测温为295～325℃;第2期为NNE向、NEE向平面剪切缝和NW向剖面剪切缝,以方解石半充填为主,形成于燕山末-喜山中期,磷灰石裂变径迹测年为58.6～18.2 Ma,包裹体测温为297～309℃;第3期为NNE向、NEE向平面剪切缝和NW向剖面剪切缝,并对前期裂缝进行改造,裂缝以未充填为主,形成于喜山运动末期以来,磷灰石裂变径迹测年为18.2～7.8 Ma,包裹体测温为189～232℃。

The characteristics and phases of fracture development are very important for the study of shale gas reservoir space. Taking Longmaxi Formation of DS area in the southeast Sichuan Basin as an example, based on the observation and analysis of outcrops and cores, the fracture stages, structural inversion, this paper discusses apatite fission track dating and inclusion temperature measurement to determine the development characteristics and period of cracks. The research shows that two sets of plane shear fractures and a set of profile shear fractures develop under the action of the three-phase tectonic movement in the study area. Those in the first phase formed in the middle and late period of Yanshan tectonic movement. The directions of the fractures include NWW,NNW and NE, maninly filled by the calcite and pyrite. The homogeneous temperature of inclusions is 295-325℃, and the apatite fission track age ranges from 67.8 to 58.6 Ma. The tectonic fractures in the second phase emerged at the end of Yanshan tectonic movement and the middle period of Himalayan tectonic movement. The directions of the fractures include NNE, NEE and NW, mainly half filled by calcite. The homogeneous temperature of inclusions is 297-309℃, and the apatite fission track age ranges from 58.6 to 18.2 Ma. The tectonic fractures in the third phase shaped at the end of Himalayan tectonic movement. The directions of the fractures include NNE, NEE and NW, and the fractures are mainly unfilled. The third stage is to transform the earlier fractures, when the homogeneous temperature of inclusions is 189-232℃, and the apatite fission track age ranges from 18.2 to 7.8 Ma.