Petroleum Geology Evaluation And Favorable Area Optimization In Liaoyuan Basin

The Liaoyuan basin is located on the west side of the basin group in the eastern part of Jilin province.It is a residual fault depression coal bearing volcaniclastic sedimentary basin,basin area is 630km2,the maximum thickness of the sedimentary cover is 2400 m,oil has been seen in partial coalfield drilling which indicates Liaoyuan basin possess a good prospect for oil and gas exploration.But the poor understanding of petroleum geology at the present stage restricts the demand of following exploration.Basing on the digesting of original data and achievement,combined with drilling,core,test data and seismic data,with the guidance of theoretical analysis of basin structure,petroleum geology,sedimentology,volcanic petrology,the research has made clear the stratigraphic division of Liaoyuan basin,the structural form and tectonic evolution.Identified sedimentary facies and volcanic facies and establishing section of sedimentary cycles and volcanic eruption batches.Stablished the lithofacies distribution in the Liaoyuan Basin,clearing basin source reservoir caprock assemblage conditions,revealing the main control factors of petroleum accumulation,selected the favorable area of oil and gas accumulation to give suggest for further exploration.Through the observation of two new drilling geological wells' core in the Liaoyuan basin,we have made clear the characteristics of lithologic combination in different areas,and redefined the stratification boundary between geological wells and coalfield wells.On this foundation,combined with the existing results of gravity-magnetic-electric and time-frequency electromagnetic,we possessed horizons tracing and fault interpreting on 2D seismic,revealing the structural zoning characteristics of Liaoyuan basin,finally resuming the3 period and 7 stage tectonic evolutions of the basin and the "two concave and one convex" long term succession structural pattern.Through core observation,we reckon the delta facies and lacustrine facies are the two main facies types in Changan formation,and 4 types of subfacies and 8 kinds of microfacies are identified.Based on sedimentology and sequence stratigraphy,the Changan formation is divided into four layers vertically.According to analytical data such as palaeo-geomorphology,sandstone percent,it is know that the provenance of Changan formation is from North West and Southeast,and present the plane distribution of sedimentary facies in each layer;Anmin Formation to Deren Formation in the research area is majorly dominated by intermediate-basic volcanic rock,3 types of volcanic facies and 8 types of volcanic subfacies identified through core and log data,and according to the characteristics ofgravity-magnetic-electric,the seismic reflection characteristics,the distribution characteristics of different lithofacies in the research area have been revealed.Through the analysis of sedimentary evolution and volcanic eruption cycle,three sets of hydrocarbon source rocks are separately developed at Jiuda Formation,1st of Changan,3rd of Changan in the Liaoyuan basin.Through core test data analysis,the organic matter abundance of thick mudstone in Jiuda Formation is excellent,source rock belong to Type III kerogen,stay in over mature evolution stage and experienced hydrocarbon expulsion threshold,it's the chief source rock in Liaoyuan basin;The organic matter abundance of mudstone in 1st of Changan is excellent,source rock is mainly type II kerogen,which stay at maturity stage,can also be considered as potential source rock for oil and gas supply.The scale and geochemical test results of hydrocarbon source rocks confirm that Liaoyuan basin has rich resource potential.There are two categories of reservoir classification in the Liaoyuan basin,the clastic reservoir is mainly ultra-low porosity and ultra-low permeability,developed in the 2nd of Changan formation;Volcanic flooding facies of volcanic rocks develop microcrack,which is type II volcanic reservoir.volcanic deposit facies of volcanic rocks develop intergranular pores,which is type II volcanic reservoir.There are two sets of source-reservoir-caprock assemblages in the basin,the volcanic source-reservoir-caprock assemblages of the Amin Formation and the clastic source-reservoir-caprock assemblages of the Changan Formation.Based on the results of oil and gas exploration in Liaoyuan basin,the main controlling factors of hydrocarbon accumulation are beneficial source rock hydrocarbon supply,high quality reservoir,advantageous matching of time-space relationship between Reservoir forming conditions.Based on the comprehensive analysis of hydrocarbon accumulation conditions in Liaoyuan Basin,We predicted the advantageous zone of oil and gas accumulation,identify five effective traps and provide suggestions for the next step of exploration..