Study On The Geological Characteristics Of Shale Gas From Wufeng Formation To Longmaxi Formation In Changning Area

This paper aims at the marine shale of upper Ordovician Wufeng formation and lower Silurian Longmaxi Formation in the southern margin of Sichuan basin,Changning demonstration plot and surrounding area.In this dissertation,depend on field outcrops,drilling core,logging data,seismic exploration and interpretation data,various geochemical data,using the basic theory of Sedimentology,Petroleum geology and Unconventional oil and Gas geology as Theoretical Foundation,forward research of the geological characteristics,find out the relationship between the geologic features and the shale gas,also conclude the main geological factors which are beneficial to form the shale gas reservoir.This paper provides theoretical basis and technical support for shale gas exploration and development in this research area and the surrounding area.The stratigraphic preservation of Wufeng-Longmaxi formation is complete,and the top and bottom boundaries are quite clear,which is conducive to division identification and horizontal tracking.Based on the detailed analysis of the drilling log data,the characteristics of the rocks,logging curves and paleontology,and combing the sea level changes,this paper laying the Wufeng-Longmaxi shale into two parts,the distribution of stratigraphic thickness is north-thick and south-thin.Wufeng-Longmaxi formation is in a restricted shelf sedimentary environment.According to their deposit sediment,it can be further divided into two subfacies and six micro-facies.Among them,the mud sheds micro-facies and the siliceous sheds micro-facies are the most benefit to enrichment of shale gas.The main types of organic matters are Type ? and Type ?1.The TOC of target stratum is 0.07%?8.35%,the average is 1.4%,the average of bottom's TOC is highest.Organic matter maturity in this area have already reached maturity and over-maturity stages.The average thickness of rich organic shale in the study area is over 20m,which shows the great potential of hydrocarbon source and shale gas accumulation conditions.The main mineral constituents is clay minerals and quartz.The high content of quartz in the bottom make the rock brittle and it is benefit to fracturing development.The reservoir space in the research area is dominated by micro pore and fractures.And the penetration rate is 0.01?10Md,it should be typical low porosity and low permeability reservoir.The gas volume at the bottom of the target layer is higher and between 1.849?2.175m3/t,with an average of 1.921m3/t.which means it has the great value to exploitation.The analysis of the regional cover,stratum and regional tectonic background shows that,the objective layer has good conditions for burial depth,structural development,roof and effective shale thickness,which is good for shale gas preserved.From above,clarified the geological factors conducive to the enrichment of shale gas.The enrichment of shale gas is controlled by the sedimentary environment,which is far away from uplifted and deposit in deep water,and the sedimentary environment is the basic conditions for form organic-rich shale.The Shale reservoir has the characteristic of low porosity and low permeability,however,the micro-pore and micro-fractures would be the reserving space for shale gas.The quality of preservation is the key to the formed the high quality of shale gas reservoir.According to this standard,in Gongxian-Julian-Qilin-Shuanghe area may have the good potential of commercial shale gas exploitation.