Exploration Potential Analysis Of M Well Area'S Shanxi Formation In Western Jingbian

The study area is located in the central Yishan Slope of Ordos Basin,surround by the Jingbian Gas Field(in the east)and the southern part of Sulige Gas Field(in the west).The exploration in the study area shows that the oil and gas of Shanxi Formation are relatively active.Shanxi Formation is one of the main hydrocarbon reservoirs in the Upper Paleozoic in this area.It has a significant research value whether as a replacement layer for the Lower Paleozoic or as a major gas layer for development.Therefore,this study takes Shanxi Formation as the research object.Through drilling,coring,geochemical logging,logging interpretation,core observation and microscopic thin section analysis etc.,this thesis analyses the stratigraphic development features,sedimentary facies,reservoir and source rocks,etc.On this basis,this thesis evaluated the exploration potential of the Shanxi Formation objectively.By researching the sedimentary facies,we found that subaqueous distributary channel is the main sand supplyment of the Shanxi Formation.Shan 1 and Shan 2 formation have undergone multi-stage deposition.The thickness of sand body is controlled by the sediment supply and depositional environment.The areas which are in the main channel and well supplied have a large cumulative thickness of sand bodies.The thickness of the sand body is gradually decreasing from the rich parts to the poor supply of margins and provenance.The Shanxi Formation reservoir is a typical low—ultra-low porosity,low—ultra-low permeability tight sandstone gas deposit,by studies and researches on reservoir characteristics.The lithology of the Shan 1 Formation is chiefly medium-coarse litharenite and lithic quartz sandstone.Shan 2 Formation is mainly medium-coarse lithic sandstone.Medium-coarse-grained quartz sandstone and lithic quartz sandstone are effective reservoirs for gas in the study area.Based on the analysis of geochemical data of source rocks,it is shown that source rocks such as coal,dark mudstone and argillaceous limestone are mainly developed in the study area.As high-quality hydrocarbon source rock,the coal beds'average thickness is 9.1m.The argillaceous source rocks has the characteristics of multi-layer development and wide-cover distribution,the average thickness is 75 m,the vitrinite reflectance Ro is more than 2.0%.In the mature-dry gas stage,the organic matter types of coal and dark mudstone are mainly humic,and the gas generation intensity is about 24×10⁸m³/km².The Shanxi Formation gas reservoir in the study area is a tight sandstone lithologic gas reservoir.The natural gas components of the Upper Paleozoic gas reservoirs are chiefly CH₄,with an average content of 91.34%.And the non-hydrocarbon components are mainly CO₂ and N₂.The formation water is weakly acidic,which is medium to high salinity formation water.The average unobstructed flow of the Shanxi Formation is 5.8×10⁴m³/d.The result of gas production test is exceptional.The source-reservoir-seal combination of the tight sandstone gas reservoirs in the Shanxi Formation is a self-generated,self-storage and self-capped type.The main source rocks are coal and carbonaceous mudstone in the marsh microfacies in the bay of Shanxi Formation and mudstone in the underwater distributary bay microfacies.The natural gas reservoir is sandstone deposited in underwater distributary channels.The direct cap rocks are mudstone and silty mudstone deposited in the underwater distributary bay microfacies.And the regional caprock is the underwater distributary bay microfacies of the Shihezi Formation Mudstone.The comprehensive research shows that the geological conditions of Shanxi in the research area are superior,the test gas effect is also very ideal,and the prospect of exploration and development is good.Among them,the I,II area is the favorable target area of Shanxi group in the research area.