Analysis Of Late Paleozoic Sedimentary Environmental Evolution And Its Source Rock And Reservoir Stratum Characteristics In Sanjiang Area, Heilongjiang Province

IIIThe Sanjiang area is mainly comprised of Jiamusi block and Nadanhada terrane,which is located in the eastern part of Heilongjiang province,an important tectonic metallogenic region.In recent years,it has made an important breakthrough in oil and gas exploration of Paleozoic Marine strata in China.Since the late Paleozoic strata in Sanjiang area are widely distributed and stable,it is expected to be a new series for oil and gas exploration.However,recent research in this area was mainly focused on plate tectonics,rather than lithofacies paleogeography,and the analysis or evaluation of hydrocarbon source rocks and reservoir characteristics were relatively weak,which restricts the development of late Paleozoic resource.This study focused on Jiamusi block and took Nadanhada terrane as the important object of tectono-stratigraphic analysis.Based on previous studies,this study analyzed the lithology and lithofacies characteristics,provenance characteristics and paleogeographic evolution of the key strata in Late Paleozoic in Sanjiang area by using field survey combined with indoor analysis.Furthermore,the key source rock strata and reservoir characteristics in study area were analyzed by laboratory test for favorable exploration direction,area and horizon,which provided reference for future resource exploitation and related work.The results are as follow:(1)Heitai formation,Zhenzishan formation and Erlongshan formation of the Late Paleozoic of the Sanjiang area were mainly comprised of five types of rocks,that are limestones,clastic rocks,volcanic clastic sedimentary rocks,pyroclastic rocks and igneous rocks.It can be further divided into seven subclasses involving sndstones,sandstones,siltstones,mudstones,tuff conglomerates,tuff sandstones,tuff and extrusive rocks and other twenty-one kinds of basic rock types.Heitai formation,Zhenzishan formation and Erlongshan formation can be recognized as four sedimentary facies: neritic facies,delta facies,lacustrine facies and volcanic facies,four kinds of sedimentary subfacies involving carbonate platform,delta front,delta plain and shallow lake,and eleven kinds of sedimentary microfacies including bioherm,open platform,organic reef,estuary dam,channel,swamp,static cement,turbidity current,underwater fan,thermal debris flow and eruption facies.(2)The middle Devonian Heitai formation mainly developed neritic facies;the late Carboniferous Zhenzishan formation mainly developed deltaic-lacustrine facies;the early Permian Erlongshan formation mainly developed volcanic facies.The evolution of sedimentary environment was related to the Late Paleozoic plate tectonic movement in this region.(3)The provenance analysis by Dickinson diagram indicated that the middle Devonian Hetai formation was dominated by limestone with its sediment provenance coming from the basin.The samples of the late Carboniferous Zhenzishan formation had higher quartz content,but less lithic and feldspar content,which was greatly affected by terrigenous detrital deposition,and the sediment provenance came from the re-cycled orogenic belt.The early Permian Erlongshan formation had a relatively low quartz content and a relatively high content of lithic and feldspar.The lithic content was mostly volcanogenic and rarely sedimentary,which was characterized by near-source deposition,indicating that the sediment source came from the magmatic arc source area.The transformation of the provenance region proved that the eastern source of the Late Paleozoic Jiamusi block was transformed from passive continental margin to active continental margin.(4)The organic matter evolution of limestone in Hetai formation had entered the over-mature stage,and the organic matter abundance was in the range of poor-medium,which made it difficult to form favorable source rocks.The organic matter type of carbonaceous mudstone and coal in Zhenzishan formation was ? kerogen with organic matter evolution transferring into over-mature stage and organic matter abundance being in the range of good-very good;The organic matter type of mudstone is ? kerogen with organic matter evolution transferring into high mature stage and organic matter abundance being the best.The Zhenzishan formation had a widely distribution in the study area with stable formation occurrence and large source rock thickness with good quality,that were potential for gas generation.(5)The test samples of reservoir rocks from Zhenzishan formation and Erlongshan formation were poor porosity and permeability conditions,indicating that they were tight reservoirs with ultra-low porosity and ultra-low permeability.But the coal seam of Zhenzishan formation was well developed with stable formation,level without deformation;the main coal seam was the high coal rank bright type coal with its thickness in 6m or so,and it had single component with large brittleness;coal body structure belonged to native-fragmented type,which can be conservative defined as?class gas block standard.It had the advantageous condition of coalbed methane reservoir and conformed to the characteristics of self-generation,self-storage and self-sealing.(6)According to research results above,the late Carboniferous Zhenzishan formation in Mishan-Baoqing area,east edge of Jiamusi block,Sanjiang area,Heilongjiang province,was the optimal region and key stratum.In addition,the high work degree of its surrounding geology-geophysics as well as its perfect infrastructure make it more potential for further work.