The Research On Shale Gas Bearing Characteristics Of Wufeng Formation-Long Maxi Formation From Southeastern Region Of Chongqing

The thesis is aim at investigating shale formation located at southeastern region of Chongqing,which belongs to Wufeng formation of Upper Ordovician to Long maxi formation of Lower Silurian.According to the analysis via experimental data measured by real core samples and outcrops and gas content data tested on site,investigation of characteristic of gas content in shale formation is performed.Combining the feature of organic geochemistry,distribution of shale structure and character of formation development,discussion on main parameters that control the gas content in study region is conducted.Moreover,favorable area of gas content in the study region is determined.Southeastern region of Chongqing is located on Yangzi paraplateform of Yangzi depression,where experienced plenty of tectonic movements,which results in complex structure deformation in this region.Wufeng formation-Long maxi formation is deposited in shallow shelf facies environment.It mainly develops three sub-facies as deep sandy shelf facies,shallow muddy shelf facies and shallow sandy shelf facies.The thickness of rich organic shale in the target layer is controlled by depth of sedimentary water,which reduces from northwest to southeast direction and mainly distributed between 40 to 120 meters.The depth of formation is determined by structure distribution,which has lower depth in the region of axial anticline and higher depth in the region of core syncline.The distribution of depth is the range of500 to 4000 meters.The type of shale matrix in Wufeng formation-Long maxi formation majorly belongs to type I and seldom type II.It contains high amount of organic carbon?average 1.4%?,high maturity of organic matter?average 2.56%,all of them reach high or over maturity,which pass peak of hydrocarbon generation?.High brittleness material?higher than 60%?,low porosity?average 1.25%?and low permeability(mainly less than 0.01×10^-3?m²)are characteristic of this formation.Types of storage space are micro-fractures,intergranular pores and organic pores.Experimental results of adsorption isotherm indicate that rich organic shale in Wufeng formation-Long maxi formation has strong adsorption capacity,the value of maximum adsorption capacity V_L is distributed between 0.46 to 7.63 m³/t with average value 2.90 m³/t.Based on gas content from on site desorption,the gas content Wufeng formation-Long maxi formation is between 0.09 to 5.32 m³/t with average value 1 m³/t,which basically reaches minimum standard of industrial production.Vertically,target layer can be separated into three intervals.Bottom sub-member I has highest gas content from on site desorption,then top sub-member III is less and middle sub-member II is the worst.Horizontally,gas content gradually declines from southwest to northeast direction.Gas content in the block type structure tectonic zone is better than the middle and south regions.Gas content is determined by organic carbon content,quartz content,development of fracture and reserve conditions.On basis of evaluation standard for favorable area of shale,superposition is utilized for every coefficient for the target layer in study region.In addition,combining reservoir forming condition and surface feature,one type I favorable area and five type II favorable areas are figured out for Wufeng formation-Long maxi formation in southeastern region of Chongqing.