| 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%), typeⅠof 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. |
