Organic Geochemistry Characteristics Of Hydrocarbon Source Rocks In Wan Shou Shan Formation In Northeast Yun Nan And Adjacent Areas

As far as we know,the thickness of strata in the South China Sea transitional environment to the marine environment is large.And this area is one of the main sources of hydrocarbon source rocks.About this paper,the research area is located between the northeast of Yunnan province and the western border of Guizhou province.However,great progress has been made in unconventional oil and gas exploration in this area in recent years.And the Carboniferous Wanshou mountain formation is considered as an important source rock development layer which not only has abundant coalbed methane,but also has good shale gas enrichment.During the Devonian Carboniferous,the southwestern part of the study area was affected by the Tethys ocean activity.Further more,The southern part of the region has a strong orogenic effect.Under the action of regional tectonics,a rift trench has been formed in the Weining area.Generally,the Carboniferous is a large cycle of transgression to regression.The largest scale of transgression is in the Early Carboniferous in the process.During the process of transgression,hydrocarbon source rocks formed under the transition from sea land to marine environment.And The source rocks were acted on long-term evolution and complicated geological structural movements in this area.So it has greatly changed the geochemical characteristics of hydrocarbon source rocks.And traditional organic geochemical indexes,such as organic carbon content,chloroform bitumen "A" content and hydrocarbon generation potential,can not accurately reflect the characteristics of source rocks in the study area.Therefore,based on the study of the traditional organic geochemical characteristics of the source rocks,in order to understand the formation mechanism of the hydrocarbon source rocks in the study area,Characteristics of trace elements and bio marker characteristics of saturated hydrocarbons were used to analyze the characteristics of it in the study area,which has very strong research value and significance.The purpose of this paper is to clarify the regional geological background and tectonic evolution.And it combines the distribution of source rocks and distribution characteristics of sedimentary facies in the Wanshou mountain formation in Northeast Yunnan and adjacent areas.And it utilizes the principles of organic geochemistry and sedimentary geochemistry.And we analyzed the influence of sedimentary environment on source rock enrichment during hydrocarbon generation.So we conclude that it is conducive to the environmental characteristics of hydrocarbon generation in the study area and to predict favorable areas of source rocks.The main achievements and understanding of this article are as follows:The total organic carbon in shale is 1.73%,which is a good source rock.The total organic carbon of carbonaceous mudstone is 18.15%,and the total organic carbon of coal and rock is 45.22%.The main types of organic matter are III type humic kerogen and II2 type humic humic kerogen.The source rock is in the mature and over mature stage,and it is a dry gas generation stage under sufficient organic matter.The sedimentary facies of the Wanshou mountain formation in the study area are mainly riparian facies,tidal flat facies and continental shelf facies.t is formed by the existence of paleo uplift in the direction of NE and NW,forming a semi nimbus like half Bay.The sediment is more affected by the terrigenous debris,and the water circulation in the ancient coast of the East is restricted to a certain extent,and some of the tidal flat swamps and lagoons subfacies are formed in the part of the sediments.Through the analysis of trace elements of source rocks in the study area,the ratio of V/(V+Ni)is reflected as a reduction environment under the condition of anoxia,the circulation of the local water is limited and the increase of salinity leads to a certain level of stratification.And The Rb/K ratio is reflected by salt water and salt water sedimentary environment.And the Sr/Ba ratio reflects that the water body gradually shallower from Weining to Yiliang and approaches to the terrigenous direction.Ceanom values were greater than-0.1,Ce/La > 1.5,all showed anoxic environment.The loss of delta Eu was obviously negative with influence of source rock.The biomarker compounds of the source rocks in the study area indicate that the source of organic matter in the source rocks is a dual biological source,supplemented by organic matter of aquatic organisms as the main source of organic matter such as terrestrial plants.The degree of biodegradation of source rocks is not high as C27 >C29 in sterane.And the ratios of Pr/Ph and Ts to Tm+Ts are all reflected in the background of reducing environment.The shallow water shelf and tidal flat environment in the study area are favorable development areas for hydrocarbon source rocks.The abundance of organic matter is high,and the mother land has dual sources of terrestrial plants and aquatic organisms,which shows it is in the mature and over mature stage of dry gas generation.The water body is modified by a certain degree of fresh water,and the local salinity is relatively high,which is favorable for the generation and enrichment of source rocks,and has good source rock potential.