The Main Controlling Factors And Quantitative Model Of Gas Content In The Typical Shales Of Guizhou Province

As the outer edge of Sichuan Basin,Guizhou Province has good shale gas potential.The object of this paper are the typical shale in Guizhou Province,which are Niutitang Formation of Lower Cambrian,Wufeng Formation of Upper Ordovician-Longmaxi Formation of Lower Silurian and Longtan Formation of Upper Permian.The study aims to figure out the main controlling factors and build the quantitative model of gas content in these typical shales.Niutitang Shale mostly belongs to the open shelf facies,widely distribute,the thickness of 20-120 m,types of organic matter mainly are?and ?1,the evolution has reached the postmaturity stage,TOC 0.7-14.6%,porosity 0.5-12.0%,brittleness mineral content over 50%,gas content are not high,0.001-1.13 m3 / t,the gas content of he lower part is higher than the upper,and the isothermal absorption experiment result are 2.25m3/t.Wufeng-Longmaxi shale mostly belongs to the shallow sea facies,only distribute in the northwestern Guizhou,the thickness of 15-35 m,types of organic matter mainly are ?,Ro 1.5-3.39%,TOC are high in the bottom part,maximum value is over 7.0%,porosity 0.77-12.0%,brittleness mineral content over 40%,gas content are not high,0.04-3.06 m3 / t,the maximum value shows in the bottom Longmaxi Shale and Wufeng Shale,the upper Longmaxi Shale show the low gas content,and the isothermal absorption experiment result are 3.15m3/t.Longtan Shale mostly belongs to transitional facies,mainly are tidal-flat facies,lagoon facies and swamp facies,the thickness of 15-55 m,small single layer thickness,types of organic matter mainly are ?,Ro reached 2.0-3.0%,TOC mostly larger than 4.0%,porosity 2.0-15.0%,clay mineral content over 40%,gas content show the maximum value of 19.17 m3 / t,the high gas content parts match the distribution of coal,and the isothermal absorption experiment result are 4.5m3/t with the maximum value of 8.8 m3/t.For more systematical study,the main controlling factors of gas content have been classified to first level factors,second level factors and third level factors by rank.The first level factors are tectonism and sedimentation.The second level factors are spatial distribution,organic geochemistry,reservoir characteristics and preservation conditions.The third level factors are thickness,depth,organic matter types,organic matter abundance,maturity of organic matter,reservoir space types,reservoir property,mineral composition and so on.Combined with the typical geological parameters have been mastered,the data should be nondimensionalized for studying their coefficient of correlation with gas content.Based on this,parameters can be selected for multinomial regression method,and the quantitative model can be built by stepwise regression method.The results show: Niutitang Shale has poor preservation condition,gas content is severely affected by tectonic reworking.which makes the main controlling factors of Niutitang Shale are reservoir physical parameters while has poor correlation with organic geochemistry parameters;Wufeng-Longmaxi Shale's gas content main controlling factors are TOC,total pore size volume and feldspar content;Longtan Shale's gas content main controlling factors are TOC,porosity,feldspar content and carbonate mineral content.The quantitative models have been built for each typical shale by stepwise regression method,and the results calculated by these models match well with the actual experiment gas content.