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沁水盆地南部地区上古生界海陆过渡相煤系碎屑岩中气测异常现象极为普遍,具有较好含气显示的致密砂岩及泥岩段与裂缝发育程度密切相关,该类含气储层应定义为裂缝性致密碎屑岩储层。受特殊构造演化及复杂成岩作用的综合影响,该区煤系碎屑岩中裂缝发育特征具有一定特殊性和复杂性,且研究程度较浅。基于该现状,综合利用钻井、岩心、测井、压裂、薄片及力学测试等资料,对该地区山西组碎屑岩地层裂缝发育特征进行了综合研究。结果表明,所研究碎屑岩地层普遍经历了强压实及强胶结作用,孔隙度普遍低于5%。裂缝的存在能显著提高不同类型孔隙间的连通性,显著改善储层物性,提高渗流能力。砂岩中以发育构造缝为主,包括张性缝、剪切缝及少量挤压缝,非构造裂缝主要包括溶蚀缝;泥岩中构造缝和非构造缝均较为发育,构造缝包括剪切缝及少量张性缝及滑脱缝,非构造缝包括层理缝、溶蚀缝及成岩收缩缝。砂岩中裂缝要比泥岩中裂缝更为发育。目的层碎屑岩中以中—低角度缝为主,裂缝充填类型以未充填及半充填裂缝为主,均为有效裂缝。较好的裂缝有效性与该地区特殊的构造演化特征密切相关,喜马拉雅运动期强烈的隆升剥蚀对煤系进行了强烈的改造,主要体现在应力大幅度卸载、地层温度的强烈降低及张性应变量的产生3个方面。该改造作用一方面可使煤系原本紧闭的裂缝重新张开成为有效缝;另一方面可产生一些新的张性裂缝,这是研究区煤系碎屑岩中张性裂缝较为发育的重要原因。这些张性缝的形成时期较晚,多未充填,有效性好。基于以上认识,加强裂缝发育层段的精细解释及裂缝发育“甜点区”的准确预测对实现裂缝性致密碎屑岩储层天然气突破具有现实意义。
The anomalous gas measurements in the coal-clastic rocks of the Upper Paleozoic in the southern part of the Qinshui Basin are extremely common. The tight sandstone and mudstone segments with good gas display are closely related to the degree of fracture development. Such gas-bearing reservoirs should be It is defined as a fractured clastic rock reservoir. Due to the special tectonic evolution and complicated diagenesis, the characteristics of the fractures in the coal-clastic clastic rocks in this area have some particularities and complexities, and the studies are shallow. Based on the current situation, the comprehensive utilization of drilling, core, well logging, fracturing, flake and mechanical testing and other data to comprehensively study the fracture development characteristics of the clastic rock strata in Shanxi area of this area. The results show that the clastic rocks under study generally experienced strong compaction and strong cementation, with porosity generally below 5%. The existence of cracks can significantly improve the connectivity between different types of pores, significantly improve reservoir physical properties and improve seepage ability. Sandstones are dominated by structural tectonic fractures, including tensility fractures, shear fractures and a few extrusion fractures. Non-structural fractures mainly include dissolution fractures; structural fractures and non-structural fractures are well developed in mudstone, and structural fractures include shear fractures and A small amount of tension and slippage seam, non-structural joints, including layering joints, dissolution cracks and diagenetic contraction joints. Cracks in sandstone are more developed than cracks in mudstone. Middle-low angle seam is the main type of clastic rocks in the target layer, and the types of fracture filling are mainly unfilled and semi-filled fractures, all of which are effective fractures. The better fracture effectiveness is closely related to the special tectonic evolution characteristics of the area. The intense uplift and erosion during the Himalayan campaign strongly reformed the coal measures, mainly due to the significant unloading of stress, the strong decrease of formation temperature and the tensor strain Produce three aspects. On the one hand, this reforming effect can make the originally closed fractures of coal measures reopen into effective fractures; on the other hand, some new tensile fractures can be produced, which is important for the development of tensile fractures in coal measures in the study area the reason. The formation of these tension joints later, more unfilled, effective. Based on the above understanding, it is of practical significance to enhance the fine interpretation of fractured development intervals and the accurate prediction of fracture development “sweet spot ” to achieve natural gas breakthrough in fractured clastic rock reservoirs.