Analysis On The Sedimentary Environment And Hydrocarbon Source Rock Characteristics Of Black Shale In Dawuba Formation Of Early Carboniferous In Huishui,Guizhou

The black shale is a kind of rock assemblage that is widely deposited in the crust,which is rich in organic fine-grained sediments.Due to its formation in a specific marine sedimentary environment of hypoxia-poor oxygen,so the black shale plays an important role in sedimentology,paleoecology and geochemistry research.In addition,black shale,as a source rock,has a direct relationship with fossil energy,so the black shale has become one of the hot spots in the field.In recent years,with the progress of science and technology and the strong support of the government,China has continuously strengthened the research on the black shale of the southern sea,shale gas exploration has been carried out successively in Chongqing,Sichuan,Guizhou and Yunnan.Guizhou province as one of important provinces that shale gas,shale gas resources in the province within the scope of evaluation and exploration,divided into the four good workspace and seven sets of potential shale gas formation.Dawuba Formation is one of the seven potential shale formations,its main distribution in Weining-Liupanshui in the southwest of Guizhou and Ziyun-Changshun-Luodian-Huishui area in the south of Guizhou,long deposited a set of typical black shale rich in organic matter.In view of the significant discovery and successful exploitation of the shale gas in Weining-Liupanshui in the southwest of Guizhou province,this paper will focus on the study of the black shale in south of Guizhou.This study selected two sections of Wangyou and Duanshan Wuliqiao in Huishui area,and conducted field reconnaissance and sample collection.By means of sedimentology,petrology,elemental geochemistry and organic geochemistry,the sedimentary environment and hydrocarbon potential of black shale in the study area are analyzed comprehensively.This paper discusses the sedimentary environment and the formation and enrichment of organic matter of source rocks,and provides scientific guidance for the exploration and development of shale gas in Guizhou province.The main achievements and recognition of this thesis are as follows:1.According to the field outcrop observation and the analysis of indoor rock,the black shale of the early carboniferous series in the research area is mainly carbonaceous shale and mudstone,lamellation development,and some of its layers can be seen with a large amount of polished mirror?asphaltenes?and brachiopods,and the fine grained pyrite veins and carbonaceous shale interlayer appear,it reflects the depth of the water.The upper or lower strata of the section are mainly mudstone and limestone,and the calcium content increased,it reflectsthe shallow water.From the perspective of lithology combination,rock color and paleontology characteristics,the sedimentary facies of the study area belong to shallow water shelf facies.2.According to the analysis of field petrology and geochemical characteristics,the sedimentary environment of black shale in Dawuba formation of early carboniferous in Huishui,as a whole is an suboxic-anoxic sedimentary environment.Among them,the water body of the Wuliqiao is deeper than that of Wangyou in Huishui.It indicates that the sea water depth of Wangyou-Duanshan Wuliqiao in Huishui is gradually deepened from north to south,and the offshore distance is further and further away.Wuliqiao is close to deep water shelf area,while Wangyou is closer to shallow water platform area.3.Through the test of the organic matter abundance?TOC?of the black shale in the two sections of the study area,the average value of the black shale were 1.23%and1.73%respectively,which were more than 1%,which reached the level of"good^excellent".Kerogen type belongs to?₁^?₂,indicated its origin parent material includes both aquatic and terrestrial creatures,for the hybrid,it can be concluded that due to the reproduction of aquatic plants such as algae and organic matter degradation process of oxygen consumption caused by the suboxic-anoxic depositional environment,as the study area the preservation of organic matter and transformation provides the necessary conditions;According to the maturity of source rocks?Ro?,the hydrocarbon source rocks in the study area belong to the early stage of the mature stage,which is the dry gas phase.At the same time according to the vitrinite reflectance and paleogeothermal relationship can be concluded that the study area of black shale experienced after the normal water deposition caused by geological events or buried deep geothermal late hydrothermal?170?²10??.4.Through the study of black shale sedimentary facies change characteristics,elemental geochemistry characteristics and organic geochemistry characteristics in the study area,it shows that the water body of Wangyou is relatively shallow,and closer to the middle Guizhou ancient land,which has a great influence on TOC and organic matter type.At the same time,it affects shale gas exploration.It is also the reason why Guizhou province has not achieved the ideal result in the development of Ziyun 1well of shale gas in Guizhou province in recent years.5.By studying the regional sedimentary characteristics and geochemical parameter analysis,it is believed that the sedimentary environment in the study area is in a weak oxidation-weak reduction environment.Combined with sedimentary facies change characteristics,the phase change of Huishui-Ziyun region becomes stronger and stronger.Shallow water slope facies carbonate rocks are often sandwiched in black shale,resulting in thin shale thickness and the ability to affect shale gas.Therefore,the favorable area of the potential shale formation of Dawuba formation in south of Guizhou is compared with the previous conclusions.Compared to the northern limit,Wangyou needs to move southward to the south of the Wuliqiao area,south to Luodian,or to the southeast of Ziyun.