The Typical Gas Reservoir Anatomy In Central Sichuan Basin And The Optimization Of Favorable Exploration Area

According to the characteristics of hydrocarbon source rocks,reservoir characteristics,distribution of the main controlling factors and favorable exploration areas of Central Sichuan Basin existing gas reservoirs-the Upper Triassic Xujiahe Formation gas reservoir,the Lower Permian gas reservoir,it can be summed up a set of gas reservoir favorable exploration features in Central Sichuan Basin.Especially the main controlling factors for hydrocarbon accumulation of reservoir formation,it is mainly based on the influence of the ancient tectonic setting,the distribution of sedimentary facies and the karstification.These factors all played key role in the formation of gas reservoirs.Reference on results of the Upper and Middle Combinations typical gas reservoir exploration and development,analyze the Lower Combination of typical gas system and summarize their structural features,characteristics of hydrocarbon source rocks,reservoir characteristics and main controlling factors of accumulation etc.,which helps find the Lower Combination developed subsequent favorable area with important guiding significance in Central Sichuan Basin.Therefore,they should be the key research direction of the Sinian Dengying Formation gas reservoir and the Cambrian Longwangmiao Formation gas reservoir research.The Upper Combination Xujiahe Formation gas reservoir system in Central Sichuan Basin is a tectono-lithologic reservoir,which is mainly influenced by palaeostructures and present-day tectonics.The sedimentary microfacies are the key factors for the formation of high-quality reservoirs.The braided delta depositional system is characterized by high quality,especially the reservoir which is in a delta plain and part of the front diversion channel.The favorable exploration area is analyzed on the whole,and the whole reservoir-forming condition is the best in the northern area of Central Sichuan Basin.The Middle Combination Lower Permian gas reservoirs in the Central Sichuan Basin are rich in hydrocarbon source rocks,and several sets of source rocks are located in this area.The porosity and permeability of carbonate rock reservoir matrix in Maokou Formation are very low,which is basically a compact rock mass with no reservoir permeability value,but the cave and fracture are the main reservoir space of natural gas enrichment and percolation channel.The favorable exploration area of the gas reservoir is mainly concentrated in Longnvsi and Guang'an.The hydrocarbon source rocks of the Lower Combination gas reservoirs in Central Sichuan Basin mainly consist of high quality mud hydrocarbon source rocks in the Third Member of Sinian Dengying Formation,Doushantuo Formation and the Third Member of Cambrian Qiongzhusi Formation of.In addition,the algal dolomite in Dengying Formation is also rich-organic.The overall organic abundance is quite rich,but it has been in an over-maturity stage,so the gas generating capacity is relatively limited.The Sinian Dengying Formation in Central Sichuan Basin is restricted platform tidal flat,lagoon and beach facies.The lithology of Dengying Formation is thick layer of grain dolomite,algae dolomite,mudstone and siliceous rock,sand(oolite)crumb grain dolomite interbedded with thin sand.The Dengying Formation reservoir is a typically low porosity and low permeability and highly non-homogeneous pore ~ fractured algae dolomite reservoir.The lateral change of reservoir is larger,and the contrast is poor.The lithology of Cambrian Longwangmiao Formation is mainly psammitic dolomite,oolitic dolomite and crystalline dolostone(including porphyritic micritic dolomite).The main controlling factors for hydrocarbon accumulation of the reservoirs in the Sinian Dengying Formation gas reservoir and the Cambrian Longwangmiao Formation gas reservoir are almost similar in Central Sichuan Basin.These factors are mainly ancient tectonic setting,sedimentary facies distribution,and karstification.They are showed in that the paleo structure had an important controlling function to the oil and gas accumulation,the distribution of sedimentary facies controlled the development of reservoir,and the karstification had further modification of the reservoir.The Sinian Dengying Formation favorable exploration area in Central Sichuan Basin Lower Combination is Yongchuan-Jiangjin – Bishan.This region is a large area in the ancient tectonic slope with good traps;In addition,the Forth Member of Dengying Formation is also well developed in the extension of the N-S steep ridge.The favorable exploration areas of the Cambrian Longwangmiao Formation are mainly in the Leshan-longnvsi paleo uplift core and upper slope.