Shale Gas Accumulation Mechanism And Its Application

The paper studied shale gas accumulation mechanism,accumulation conditions, main controlling factors,resource potential analysis,favorable areas and accumulation systems of Lower Paleozoic,Sichuan Basin and its periphery.The conclusions are as follows:（1） Shale gas reservoir is an unconventional gas accumulation,which serves as essential factors of the petroleum accumulation system,such as source rock system, migration system,and reservoir system exist in the same shale bed.Determine the position of shale gas in the hydrocarbon accumulation and distribution spectra.From the geological features and based on the accumulation types,these oil/gas reservoirs can be divided into the "source ended members" and its vicinity（continuous accumulation） and the "reservoir ended members" and its vicinity（discontinuous accumulation）,forming unconventional oil/gas reservoirs（coalbed methane,shale oil/gas,source-contacting oil/gas,water-soluble gas reservoir,etc.） and conventional oil/gas reservoirs respectively,including various types of transitional oil/gas reservoirs.The paper also studied the accumulation mechanisms of shale gas,which includ generation mechanism,migration mechanism,occurrence mechanism and conservation mechanism,etc.and accumulation processes which included the first accumulation and the second accumulation.（2） On the basis of shale gas accumulation theory and accumulation conditions, the controlling factors of shale gas accumulation were analyzed in this paper,which could be divided into internal and external factors.The internal controlling factors are the shale own attributes which include shale geochemical indices,mineral composition,physical indicators,etc.The external controlling factors include depth, temperature and pressure,etc.Among them the total organic carbon type and content, total hydrocarbon content,quartz content,clay mineral content,porosity（fracture）, density,pyrite content and carbonate content of the internal controlling factors are the main factors.Using the multiple linear regression between two parameters,six parameters,eight parameters and gas content to obtain the formula for gas content calculation of the shale,and the gas content between the formula calculation and the measured showed linear fit well.The more parameters using,the better it fits.（3） The favorable areas for developing shale gas reservoirs were predicted by using parameter model.Analogical analysis based on the model suggests that among the marine Lower Paleozoic strata in the Sichuan Basin and its periphery.The most favorable areas of shale gas accumulation of Lower Cambrian are Southern Sichuan-Northern Guizhou-Central Guizhou,Western Hubei-Eastern Chongqing and Northeast Sichuan（Chongqing）,etc.The most favorable areas of shale gas accumulation of Upper Ordovician-Lower Silurian are Southern Sichuan-Northern Guizhou,Western Hubei-Eastern Chongqing and Northeastern Sichuan（Chongqing）-Northwestern Hubei,etc..The indexes of shale in the favorable areas were analyzed to provide reference for early evaluation of shale gas in China.According to the measured gas content,calculate shale gas resource of Lower Cambrian and Lower Silurian by volume method.The shale gas resource in Lower Cambrian is 3.3×10¹²～11.4×10¹² m³,with an average of 7.4×10¹² m³,while the shale gas resource in Upper Ordovician-Lower Silurian is 2.2×10¹²～8.5×10¹² m³,with an average of 5.3×10¹²m³.（4） Study suggested that Western Hubei-Eastern Chongqing is the most favorable areas for the purpose of shallow drilling and sampling in the early stage of shale gas exploration of Upper Ordovician-Lower Silurian.Through five Upper Ordovician-Lower Silurian sections of field observations and sample analysis of Gaogu Pengshui, Xinle Shizhu,Jinfo Mountain of Nanchuan,Baishi Qianjisang and Lianhu Pengshui, suggested that Yuye 1 well should be drilled in Lianhu Pengshui,and the suggestion was adopted.Drilling result showed that not only met the purpose of coring by all well,but also achieved good effects of the gas.（5） General principles of shale gas accumulation system division was proposed in consider of the features of shale gas.The Sichuan Basin and its periphery Lower Paleozoic shale gas accumulation system can be divided into the Lower Cambrian accumulation system and the Upper Ordovician-Lower Silurian accumulation system in vertical.In the plane,the Lower Cambrian accumulation can be divided into Southern-Southeastern Sichuan,Northern-Central Guizhou,Eastern Chongqing, Western Hubei and Hunan,Longmenshan,Micangshan-Dabashan and Central Sichuan accumulation system;the Upper Ordovician-Lower Silurian accumulation system can be divided into Southern-Southeastern Sichuan,Northern Guizhou, Eastern Chongqing,Western Hubei and Hunan,Longmenshan,Micangshan-Dabashan and Central Sichuan accumulation system.Shale gas accumulation system was evaluated by for four levels as follows:the strategic breakthrough area,the strategic expand area,the strategic preparation area and the strategic perspective area.