页岩裂缝成因及其对含气性影响——以渝东南地区阳春沟构造带五峰—龙马溪组为例

doi:10.13809/j.cnki.cn32-1825/te.2020.03.020

摘要/Abstract

摘要：

以渝东南地区阳春沟构造带上奥陶统五峰组—下志留统龙马溪组龙一段页岩裂缝为研究对象,通过地震—地质解释剖面、岩心观察、成像测井解释（FMI）、薄片鉴定、氩离子抛光扫描电镜等宏观、微观综合研究手段,对页岩裂缝发育特征、形成主要控制因素及其有效性对含气性影响进行分析。研究发现,阳春沟构造带五峰组–龙马溪组页岩中发育剪切缝、层理缝、滑脱缝、解理缝、收缩缝等多种裂缝。裂缝产状受地层产状影响,页理缝和层间滑动缝呈现为中高角度—垂直裂缝,剪裂缝反而呈现为水平—低角度缝。多处呈现多期裂缝交错切割形成复杂缝网,并可见揉皱、微断层等现象。影响该构造带裂缝发育程度和分布形态的主控因素有构造地质作用、页岩矿物成分和力学性质、斑脱岩出现频次。构造地质作用是裂缝发育的外因,阳春沟构造带呈现为断展褶皱构造样式,受到多期构造作用的影响,剪切缝、网状缝、复杂缝网带及揉皱带等非常发育。页岩矿物成分和力学性质是裂缝发育的内因,控制解理缝、晶间缝和收缩缝等微观裂缝及层理缝的发育,阳春沟地区龙一段页岩泊松比较小,杨氏模量较大,脆性指数较高,有利于各类裂缝形成。页岩层内斑脱岩出现越频繁、越靠近五峰组与临湘组之间的主滑脱面,滑脱现象越明显,相应的层间滑脱缝越发育。虽然阳春沟构造带天然裂缝非常发育,但是该地区保存条件并未遭受严重破坏,仍具备较好的页岩气勘探潜力。钻探揭示龙一段页岩总含气量与邻区相当,气测全烃优于邻区,游离气占比也高于邻区,说明本地构造裂缝的形成扩展了页岩气中游离气的储集空间,有利于页岩气成藏。

关键词: 页岩, 裂缝, 五峰—龙马溪组, 渝东南地区, 阳春沟构造带, 成因分析

Abstract:

By the macro and micro comprehensive research methods of seismic-geological interpretation profile, integrated core, imaging log interpretation（FMI）, thin sections authentication, and argon ion polishing scanning electron microscope, the characteristics, main controlling factors of the properties of the shale of Wufeng Formation-Longmaxi Formation in the Yangchungou structural belt of southeast Chongqing and their influence on shale gas-bearing properties are analyzed. The study shows that there are many fractures such as shear fractures, bedding fractures, slip fractures, cleavage fractures, and shrinkage fractures developing in the shale of Wufeng Formation-Longmaxi Formation in the Yangchungou structural belt. The integrated analysis shows that shale fractures and interlayer sliding fractures there are vertical with middle-high-angle, whereas shear fractures are horizontal with low-angle. Most of the fractures are formed in multiple stages resulting in fracture nets, creases, micro faults and other phenomena. The development and distribution of these fractures are controlled by the tectonic activity, shale mineral composition and mechanical properties, and development of bentonite. Tectonic geology is the external cause of fracture development. The Yangchungou structural belt presents a fault-folding fold structure and is affected by multi-stage tectonic movements. Shear fractures, reticulate fractures, complex fracture network belts, and crumple belts are very developed. Shale mineral composition and mechanical properties are the internal causes of fracture development, controlling the development of micro-fractures and bedding fractures, such as cleavage fractures, intergranular fractures and shrinkage fractures. The Poisson ratio in 1st Longshan member of Yangchungou area is relatively small, the Young’s modulus is large, and the brittleness index is high. All those are good for the formation of various cracks. The more frequently the porphyry in the shale layer is, the closer it is to the main slip surface between the Wufeng Formation and the Linxiang Formation, the more obvious the slip phenomenon is, and the more developed the interlayer slip fractures are. Although the natural fractures in the Yangchungou structural belt are very developed, the preservation conditions have not suffered serious damage, so the shale gas exploration potential is still good in the study area. Drilling revealed that the total gas content of the shale is equivalent to that of the adjacent area, and the total hydrocarbon measured by gas is better than that of the adjacent area. The proportion of free gas is also higher than that of the adjacent area. It indicates that the formation of local structural fractures has expanded the storage space of free gas in shale gas, which is beneficial to the rock gas accumulation.

Key words: shale, fracture, Wufeng-Longmaxi Formation, Southeastern Chongqing, Yangchungou structural belt, controlling factors

中图分类号:

TE37

马军. 页岩裂缝成因及其对含气性影响——以渝东南地区阳春沟构造带五峰—龙马溪组为例[J]. 油气藏评价与开发, 2020, 10(3): 126-134.

MA Jun. Origin of shale fractures and its influence on gas-bearing properties: A case study of Wufeng-Longmaxi Formation in Yangchungou structural belt in southeast Chongqing[J]. Reservoir Evaluation and Development, 2020, 10(3): 126-134.

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