Geological Characteristics Of Shale Gas From Upper Ordovician Wufeng Formation To Lower Silurian Longmaxi Formation In Changning Block

The research object of this paper is Upper OrdovicianWufeng-Lower SilurianLongmaxi formation in Changning area.In this paper,the field profile and drilling cores,laboratory test data,combining with the previous research,are used.The characteristics of shale formation,reservoir characteristics and organic geochemical characteristics in this area are systematically studied,and making the comprehensive prediction of shale reservoir at last.Through the analysis of rock color,mineral composition,rock structure characteristics and biological content of the single well coring,2 subfacies(Inner shelf and Outer Shelf)with 6 microfacies(organic rich siliceous mud shed,organic rich silty clay,silty mud shed shed deep,shallow silty clay,silty sand plaster shed shed,gray powder sandy mud)are clarified in the study area.According to the outcrops,drilling cores,logging data,combined with the sea level and sedimentary cycle,identified the top and bottom layer and its interface of Wufeng-Longmaxi formation,and divided a substrata of Longyi memberfinelyin Changning area.By using the X diffraction analysis showed that the mineral composition,the Wufeng-Longmaxi formation clastic minerals contain silica,feldspar,pyrite and carbonate,brittle mineral clay minerals is greater than 55%,much less than 30%,with characteristics of high brittle mineral content,clay mineral content moderate proportion.Thin section and scanning electron microscope observation showed that the types of reservoir spacesof shale are mainly micro pores and cracks in Wufeng-Longmaxi formation in Changning area;The porosity is mainly distributed in 0.71%?10.3%,average 5%,permeability between0.00016×10-3?m29.9×10-3?m2,the average is2.21×10-3 ?m2;Study on adsorption isotherm showed that the Gas content is higher overallin Wufeng-Longmaxi formation.According to a series of geochemical analysis of outcrop and core,showing that the organic matter types of shale are mainly ?-? 1 in Wufeng-Longmaxi formation,the average TOC is 2.36%,the average Ro is 2.60%,generally achievinghigh-over mature stage,mainly productingdry gas.Finally,according tothe distribution characteristics of the shale mineral,TOC,porosity,gas content,and the evaluation standard of shale reservoir classification,deemed that ?+?reservoir thickness in N212 well area reached the maximum in Wufeng-Longmaxi formation in the study area.