Structure Evolution And Oil-Gas Exploration Prospects Of Liuhe Basin,Jilin Province

In recent years,due to the new development of oil and gas resources development direction,small and medium-sized fault basin groups in the southeastern part of Songliao Basin have been paid more and more attention by researchers.The Liuhe Basin is mainly located in Liuhe County,Jilin Province,from the north to the Shengshui Town of Liuhe County,and from the west to the Xinbin Town of Liaoning Province.It is about 80 km long,with a width of 10-20 km and an area of about 1100 km²,whose trend is about 50°northeast.The basin is mainly filled with a set of Mesozoic strata,and good source rocks have been found,which has certain exploration prospects.However,due to the low level of exploration,research work of it is urgently needed.The field geological survey and the fine interpretation of the seismic section indicate that Liuhe Basin is an asymmetrical double-fault narrow graben controlled by the northwest margin fault in the early stage,the southeast margin fault in the late stage and the eastern basin fault in the present.Along the long axis of the basin,the dumbbell-shaped structural framework of the central uplift and the depressions on both sides have been formed.The development and evolution of the basin is mainly affected by the subduction of the Farallon plate,the Izenaiqi plate and the Pacific plate to the Eurasia continent repeatedly.It has been experienced six construction periods and four distinct tectonic movements so far.Through detailed field geological observation and core observation of exploration wells,the sedimentary facies model of Liuhe Basin is established.Three types of sedimentary facies are identified in the study area:fan-delta facies,lacustrine facies and sublacustrine fan facies,and 7 sedimentary subfacies and 12 sedimentary microfacies are divided.Among them,the sedimentary period of the Houjiatun Formation and the Dashatan Formation is a semi-deep lake-fan delta sedimentary system dominated by northwest source supply.The upper Xiahuapidianzi Formation and Hengtongshan Formation are semi-deep sublacustrine fan-fan delta systems are characterized by the development of sublacustrine fans and the supply of southeast and northwest provenances.While the strata in the area are from bottom to top,the sedimentary center is also characterized by migration from west to east as well as from south to north.Dark mudstones are developed well in the basin,and the test results are shown that the organic matter abundance of the Xiahuapidianzi Formation is in medium to good source rocks with the II₁-II₂ kerogen type,and the evolution stage is mature to high maturity stage,which is the most favorable source rock horizon in the basin.The organic matter abundance of the Dashatan Formation is mainly medium to poor source rocks with II₁-II₂ and in the stage of high maturity to maturity,which is the favorable source rock layer in the basin.The organic matter abundance of Hengtongshan Formation is mainly shown as medium source rocks,and the kerogen type is type III,which is in the stage of low-maturity to over-maturity evolution and is the source rock with low potential in the basin.Most of the reservoirs are characterized by ultra-low porosity,low permeability and ultra-low permeability,and belong to tight sandstone reservoirs.There are three types of source-reservoir-cap assemblages in the basin.The self-sourcing and self-reservoiring,lower-sourcing and upper-reservoiring,upper-sourcing and lower-reservoiring assemblages are formed in the basin.The favorable exploration target areas of the Liuhe Basin are mainly the volcanic dome tectonic area in the central part of the Hengtong sag and the deep depression in the eastern part of the Xiangyang sag.Moreover,the advantaged exploration target zoon in the central volcanic dome of the Hengtong sag mainly develops the volcanism puncture reservoirs,the fan-delta front lithologic reservoirs and the lenticular sublacustrine-fan lithologic reservoirs;The deep depression in the eastern part of the Xiangyang sag mainly develops the uplifted lithologic reservoirs of the fan-delta front and the lenticular lithologic reservoirs of the sublacustrine-fan.