渝东南地区阳春沟构造带五峰组—龙马溪组页岩构造裂缝特征及形成期次解析

渝东南地区阳春沟构造带是页岩气勘探有利区，构造裂缝发育特征和期次研究有助于评价该地区页岩气储层物性和保存条件。以渝东南地区阳春沟构造带五峰组—龙马溪组页岩构造裂缝为研究对象，通过岩心观察、成像测井解释、包裹体测温、磷灰石裂变径迹测年和区域构造运动演化等手段，对页岩构造裂缝发育的特征及形成期次进行研究，进而分析构造裂缝形成与页岩气成藏过程的匹配关系。研究结果表明，阳春沟地区五峰组—龙马溪组页岩中的构造裂缝非常发育，被方解石充填，多处呈现不同期次裂缝交错切割形成复杂缝网，并可见揉皱、微断层等现象。这些裂缝形成于3期构造运动：第一期为北北西向、北西西向和北东向裂缝，以方解石和黄铁矿全充填为主，形成于燕山运动中期，磷灰石裂变径迹测年为82~95 Ma，包裹体测温为190~210 ℃；第二期为北北东向、北东东向平面剪切缝和北西向剖面剪切缝，以方解石充填—半充填为主，形成于燕山运动晚期，磷灰石裂变径迹测年为68~78 Ma，包裹体测温为165~185 ℃；第三期为北北东向、北东东向平面剪切缝和北西向剖面剪切缝，并对前期裂缝进行改造，裂缝以方解石充填为主，形成于燕山末期—喜马拉雅期，磷灰石裂变径迹测年为30~62 Ma，包裹体测温为135~155 ℃。第一期构造裂缝形成于页岩最大埋深—开始抬升期，有利于改善页岩储层物性。第二期和第三期构造裂缝形成于页岩气藏调整期，该期的抬升运动会增加页岩气的逸散量，破坏页岩气的保存条件。抬升时期开始的越早，页岩气藏经历的调整破坏时期越长，单井含气量和测试产量就越低。

Characteristics and genesis of shale fractures in Wufeng-Longmaxi formations of Yangchungou structural belt in Southeast Chongqing

The Yangchungou structural belt in southeast Chongqing is a favorable area for shale gas exploration. The study on the development characteristics and stages of structural fractures is helpful to evaluate the physical properties and preservation conditions of shale gas reservoirs in this area. Taking the Wufeng-Longmaxi formations shale structural fractures in Yangchungou structural belt in southeast Chongqing as the research object， the characteristics of shale structural fractures development and their formation stages were studied by means of core observation， imaging logging interpretation （FMI） fracture staging， inclusion thermometry， apatite fission track dating and regional tectonic evolution. The results show that the structural fractures in the shale of Wufeng-Longmaxi formations in Yangchungou area are well developed and filled with calcite. In many places， complex fracture networks are formed by staggered fractures of different periods， and the phenomenon of corrugation micro-faults can be seen. These fractures were formed in three stages of tectonic movement： the first stage is NNW， NWW and NE trending fractures， mainly filled with calcite and pyrite， formed in the middle Yanshan movement， apatite fission track dating is 82-95 Ma， and inclusion temperature is 190-210 ℃； the second phase consists of NNE-NE trending plane shear fractures and NW trending section shear fractures， mainly calcite filling and semi-filling， formed in the late Yanshan Period， apatite fission track dating of 68-78 Ma， inclusion temperature of 165-185 ℃； the third stage is the NNE-NE trending plane shear fracture and the NW trending section shear fracture， and the previous fractures are reformed. The fractures are mainly filled with calcite and formed in the Late Yanshan to Middle Himalayan. The apatite fission track dating is 30-62 Ma， and the inclusion temperature is 135-155 ℃. The first stage tectonic fractures are formed in the period of shale maximum burial depth and the beginning of uplift， which is beneficial to improve the physical properties of shale reservoir. Tectonic fractures of the second and third stages are formed in the period of shale gas adjustment， which will increase the amount of shale gas escape and destroy the preservation conditions of shale gas. The earlier the uplift period begins， the longer the shale gas reservoir experiences the period of adjustment and destruction， the lower the gas content and test production per well.