湖北鹤峰地区二叠系大隆组页岩气储层特征及评价

Characteristics and evaluation of shale gas reservoir of Upper Permian Dalong Formation in Hefeng Area, Hubei Province

根据6条露头剖面和HD1井薄片的详细观测,并借助偏光显微镜、X射线衍射、场发射扫描电镜和有机碳含量(TOC)分析,常规孔隙度和渗透率分析,以及比表面积和孔径分析等,对湖北鹤峰地区二叠系大隆组黑色岩系的储层进行了研究。结果表明,研究区大隆组具备发育页岩气的基本地质条件:岩石类型以富有机质的泥页岩为主,局部夹碳酸盐岩和薄层状硅质岩,脆性矿物含量较高,这有利于后期成岩流体的改造和页岩气开发阶段的水力压裂改造;有机质含量多大于2%,热演化程度较高(Ro平均为2.38%),且为利于生成油裂解气的Ⅰ型干酪根,富有机质的黑色岩系沉积厚度较大(介于30.3～38.0 m),具有较高的生烃能力;储集性能在纵向上变化不大,总体表现为低孔—特低孔、特低渗特征,有机质孔隙和矿物基质孔中的微孔和中孔是页岩比表面积的主要贡献者,它们构成了气体吸附的主要场所。HD1井大隆组埋藏较浅,断裂复杂且较发育,这可能是造成大隆组生烃条件优异而含气量相对较少的原因。因此,保存条件应是控制鹤峰地区大隆组页岩气含气量的主要因素,保存条件较好的鹤峰向斜发育区应为页岩气有利区。

Based on detailed observation of the 6 outcrop profiles and thin sections of well HD1, and in combination with polarizing microscope, X-ray diffraction, field emission scanning electron microscopy, and the analysis of total organic carbon content and reservoir physical property, the reservoir characteristics of black rock series of Upper Permian Dalong Formation in Hefeng Area, Hubei Province, is studied. It has excellent basic geological conditions for shale gas of Dalong Formation in the study area. The main rock type is the mud shale rich in organic matters with intercalated carbonate and thin-layer siliceous rock, and high content of brittle minerals, which is conducive to the later diagenetic fluid transformation and the forming of hydraulic fracturing in the stage of shale gas development. It has higher hydrocarbon generation ability of black rock series of Upper Permian Dalong Formation in Hefeng Area, due to the high TOC(most of >2%) and high thermal evolution degree(average Ro=2.38%), type Ⅰ of kerogen, and relatively large deposition thickness(between 30.3 ~38.0 m). The reservoir is generally characterized with low-ultra-low porosity and low permeability with approximately uniform physical properties in vertical. Micropores and mesopores in the organic matter and mineral matrix are the main contributors to shale specific surface area,which forming the main places of gas adsorption. Dalong Formation in well HD1 buried shallowly with complex faults developing nearby, which may be the reason why the hydrocarbon generation conditions are such excellent but the gas content in Dalong Formation is relatively low. Hefeng syncline with better preservation condition is the favorable area for shale gas,because preservation condition may be the main factor to control shale gas content of Dalong Formation in the study area.