Evaluation Of Carboniferous Volcanic Reservoir In The Western Margin Of Junggr Basin

Volcanic rock reservoirs were constantly covered and well studied with the deepening of domestic and international petroleum exploration.Junggar basin is one of China's major petroliferous basins,and significant breakthroughs has been made in its Carboniferous volcanic reservoir exploration.More than 40 reservoirs have been discovered in Wuyiba,Shixi,Chepaizi,hongshanzui,Kelameili and other regions.Years of exploration shows that the Carboniferous volcanic rocks in the western margin of the Junggar Basin region has great potential for oil and gas exploration.However,due to the heterogeneity of volcanic reservoirs are relatively strong,reservoir physical property changes rapidly,recent exploration in that area frequently lost.The main study objects of this paper are the Carboniferous strata in the western margin of Junggar basin.According to a large number of core observation and description,combined with well logging,seismic and geochemical data,We made a detailed analysis to the lithology,lithofacies,ancient volcanoes and weathering crusts of that strata.Furthermore,the formation of Carboniferous reservoirs is described and favorable reservoir development area is forecasted on the basis of the previous research results and latest developments of similar studies in the field.Firstly,according to well data and geochemistry data,lava(70%)and pyroclastic rocks(21%)are widely distributed here.In lava class,Basaltic andesite(35%)and breccia lava(21%)account for the largest share.As to lithofacies,the percentage overflow facies(70%)was higher than that of the explosive facies(19%).The middle and upper subfacies nominate overflow facies.In plan view,the similar explosive subfacies are presented in the east,southeast and north parts of the exploration area,indicating that there are three craters.The residual thickness of the overlying Jurassic indicates ancient Carboniferous landform approximately,places with thicker Jurassic strata represent higher landforms and vice versa.So the place with medium Jurassic strata represents ancient slopes and according to previous researches weathering crusts are well developed here.Secondly,the reservoirs are overall low porosity and especially low permeability based on the analysis of Carboniferous rock samples.The physical property of pyroclastic rocks lower overflow subfacies,volcanic neck subfacies,crater subfacies and weathering crusts are relatively good;that of volcanic sedimentary rocks and pyroclastic sedimentary subfacies are relatively bad.Thirdly,Carboniferous volcanic reservoir in that area formed sequentially through five stages: volcanism,hydrothermal,tectonic,supergene and diagenesis.The third and fourth stages is the key to effective reservoir.Finally,favorable reservoir is predicted on the basis of lithofacies,weathering crust spread and reservoir formation mechanism...