Reservoir Forming Condition And Exploration Prospect Of Shale-gas In Qijiang-Renhuan Area Of Southeast Sichuan

A thorough study has been performed on shale gases from the Lower CambrianNiutitang Formation and the Upper Ordovician-Lower Silurian Longmaxi Formationin the south-eastern of the Sichuan Basin to understand shale distribution,geochemical characteristics, microstructure, mineral composition, reservoirperformance and preserve conditions.The result shows that fold structures are well developed in the study areas. Thedirection of fold axial has S or reverse S features, which is the result of multiphasetectonic stress. The thickness of the Niutitang shale is in the range of30~90m,generally40~50m. It contains high amount of organic matter with total organiccarbon （TOC） generally above2%and the highest value of9.94%. The thickness ofWufeng-Longmaxi shales varies greatly in the range0~257m. The TOC content isnormally in the range of2~3%, occasionally over4.0%. These shales have mainlytype I kerogen and their thermal maturity reach high-to over-mature stages.The Niutitang shales contain high proportion of brittle mineral with an averagevalue of56.7%. The average clay content is38.7%and other minerals are4.6%. TheWufeng-Longmaxi shales have an average brittle mineral of48.6%, clay minerals of38.1%and other minerals of13.3%. Various pore types occur in shale matrix. Themicropores show an alveolate shape and they are well connected. The poresdistribution is relatively homogeneous and they are mainly dissolution pores. All thisprovide good conditions for hydrocarbon migration and accumulation.The simulated experiments have been performed to test the adsorptive capacity ofshale. The relationship among shale types, organic matter content, thermal evolutiondegree and desorbed gas content has been explored. The proportion of desorbed gasfrom different shale types is in the order of siliceous＞calcareous＞clayey.Resources in place of shale gas in two shale systems are calculated usingvolumetric method in the study area. Shale gas resources in different depths anddifferent structural areas have been refined. Shale gas resources in the NiutitangFormation is mainly distributed in the depths of1,500~3,000m, reaching2.6×1012m3, and shale gas resources in the Wufeng-Longmaxi Formation is mainly distributedin the depths of500~1,500m, reaching0.7×1012m3.In the present study, parameters of optimizing shale gas exploration have beenproposed. Based on my integrated assessment, the favorite shale gas plays in thisstudy area have been identified. The most prospective areas are situated at Chishuitown-Gulin-Guanwen for the Lower Cambrian Niutitang Formation, and the highestpotential areas are Gulin-Tongmin town and Nantong town-Ganshui town–Wenshuitown for the Upper Ordovician Wufeng Formation-Lower Silurian LongmaxiFormation.