Gas-bearing Characteristics And Favorable Area Optimization Of The Paleozoic Organic-rich Shale In Northwest Guizhou

The northwest region of Guizhou is located in the northwest Guizhou plateau uplift that in the southwest margin of Yangtze plate,and mainly develop three sets of Marine and transition phase rich organic shale,which has a wide distribution,high abundance of organic matter,high thermal evolution degree,strong reformation in its later stage and big change of gas content.As the main line,paper mainly discusses the geological background of shale development,forming conditions,gas characteristics and hydrocarbon content of the main controlling factors,evaluate the gas-bearing properties of the three sets of rich organic shale,and optimizing favorable zone.The sedimentary facies of study area' Niutitang formation are mainly shallow shelf and deep shelf that consist of dark grey and black shale,the sedimentary facies of Longmaxi formation is given priority to with shallow-deep shelf facies,lithology is black shale and silty shale,that of Longtan formation is given priority to with lagoon-delta-peat,bog-barrier island and tidal flat facies,the lithology is mainly powder sandstone,mudstone and shale of coal seam.Due to the effect of uplift in Guizhou,the Longmaxi formation occurred serious erosion in south of the study area,Niutitang formation and Longtan formation are widely development in the area.Corresponding with sedimentary facies,organic matter type of Niutitang formation and Longmaxi formation are type ? and ?,and type ? for Longtan formation.Organic matter abundance is high,the organic carbon content of Niutitang formation,Longmaxi formation and Longtan formation are 3.47%,3.47%and 6.07%respectively.Thermal evolution degree is generally high,The average vitrinite reflectance of Niutitang formation,Longmaxi formation and Longtan formation are 3.97%,2.67%and 2.45%respectively,all of which belong to a mature stage.Average content of clay minerals of Niutitang,Longmaxi and Longtan formations are 41.9%,41.9%and 41.4%,which mainly are illite/slip layer and Iraq mineral.Porosity distribution of 3 set of rich organic matter shale in between 2%and 10%and permeability main between 0.001mD-0.01mD permeability.Isothermal adsorption shows that the three sets of series of strata shale maximum adsorption capacity are between 0.5m3/t-8.8m3/t.Field analytical experiment shows that cattle hoof pond group gas content is low,the main body between 0.1-0.7m3/t,and peak reached 0.9m3/t.Gas content of Longmaxi formation between 1.0-2.8m3/t,and peak reached 3.4m3/t,high gas content of marine shale concentrated in the bottom of the stratum.Gas content of Longtan formation between 2.50-10.0m3/t,and peak reached 19.6 m3/t,high gas content of transitional shale concentrated in the roof and floor of the coal seam.Based on multi-factor superposition method,study select five favorable areas of three layers:the Lower Cambrian favorable area is located in Zunyi Renhuai and Bijie region.The Lower Silurian favorable area is located in Xishui and Tongzi region.The Upper Permian favorable area is located in the Jinsha,Dafang,Qianxi,and Nayong region,among them the Longtan formation favorable areas featured in high gas content,large distribution area,which is worth further exploration and development potential.