Sediment Source Analysis Of Oil And Gas Objective Strata In The Qiongdongnan Basin

The South China Sea is located in convergence parts of the Pacific plate,Indian-Australian plate and Eurasian plate. Throughout the period of geologicalhistory the South China Sea has main undergone rift epoch from Paleocene to earlyOligocene, Rift fault-depression-squeeze reversed in late Oligocene and thesedimentation period from the early Pliocene to Quaternary. The South China Seastopped expanding from the end of the early Miocene (16.7Ma), and the structuralpattern formed. During the expansion process, the South China Sea developed a widerange of fault and fault-depression basin, which received a large amount of land-sourced material, riching in organic matter, and had good hydrocarbon source rock,transporting and storage of petroleum geological conditions. During the "Ten-Five"and the "Eleven-Five" period, the offshore oil army dominated by CNOOC carried outthe basic geological research about the high precision bio-stratigraphy andsedimentary environmental changes on the shallow waters of Northern South ChinaSea offshore oil. During the "Twelve-Five" period, the State has shifted the focus ofthe work to the oil and gas resource exploration of the deepwater district in NorthernSouth China Sea, the basic geology and Petroleum Geology for the purpose of oil andgas exploration to the deepwater hydrocarbon prospective areas in the Northern SouthChina Sea research has become the focus of current work.This paper is based on major national technology special project " The researchon The evaluation about the potential rich hydrocarbon SAG in deepwater area ofNorthern South China Sea"’ child topics " The research of paleoenvironment andpaleoclimate in deepwater area of Northern South China Sea "(2011ZX05025-002-03), basing on the paleontology information of the oil and gaswell LS22-1-1and LS33-1-1, grain and heavy mineral information of Qiongdongnanbasin and the REE and trace elements information of LS33-1-1, buildingpaleontological stratigraphic section of LS22-1-1and LS33-1-1wells, analysis of thedynamic strength of water in different geological history, general direction of thesource, source type, give help to recover Paleoenvironment and paleoclimate in theQiongdongnan basin in the future. The main conclusions are as follows:Analysing of the LS33-1-1and LS22-1-1well about the seismic interfaceicons of palaeontological fossils data, and then giving paleontological stratigraphic division for the two wells. The seismic interface of Eocene, yacheng group, Lingshuigroup, Sanya group, Meishan group, Huangliu group, Yinggehai group and Ledonggroup are respectively T80T70T60T50T40T30T20, and the geological ageis respectively(T80’ geological age is unknown)28.4Ma.BP.23.0Ma.BP.16.0Ma.BP.11.6Ma.BP.5.5Ma.BP.and1.8Ma.BP.. LS22-1-1well’ completed drillingdepth is3603.0m, and this depth is the interface of T41in Meishan group; LS33-1-1well’ completed drilling depth is4350.0m, and the yacheng group and boundarybetween Eocene seismic interface is T80, and its depth is4356.0m.The depth of LS33-1-1well’ T80T70T60T50T40T30T20is respectively4356.0m3931.0m3672.0m3450.0m3152.0m2692.0m and2214.0m. Yachengformation has a thickness of425.0m; and its internal formation is divided into threesections by seismic interface T71and T72, the T71and T72’ depth is4007.5m and4099.0m and the T71and T72’ geological ages is29.9Ma.BP. and31.5Ma.BP..Lingshui formation has a thickness of259.0m; and its internal formation is dividedinto three sections by seismic interface T61and T62, the T61and T62’ depth is3778.0m and3844.0m and the T61and T62’ geological ages is23.8Ma.BP. and25.5Ma.BP.. Sanya formation has a thickness of222.0m; and its internal formation isdivided into two sections by seismic interface T52, T52’ depth is3519.0m and theT52’ geological ages is25.5Ma.BP.. Meishan formation has a thickness of298.0m;and its internal formation is divided into two sections by seismic interface T41, T41’depth is3331.0m and the T41’ geological ages is13.4Ma.BP.. Huangliu formationhas a thickness of460.0m; and its internal formation is divided into two sections byseismic interface T31, T31’ depth is2955.5m and the T31’ geological ages is8.2Ma.BP.. Yinggehai formation’ internal formation is divided into four sections by T27T28T29. T27T28T29’ depth is respectively2466.0m2491.0m2581.5m andT27T28T29’ geological ages is2.7Ma.BP.3.2Ma.BP.4.2Ma.BP..The depth of LS22-1-1well’ T41T40T31T20is respectively3603.0m3552.0m3336.0m2199.0m. Meishan formation has a thickness of51.0m; Huangliuformation has a thickness of216.0m; Yinggehai formation has a thickness of1137.0m.Yinggehai formation’ internal formation is divided into four sections by T27T28T29. T27T28T29’ depth is respectively2546.0m2817.0m3002.5m and T27T28T29’ geological ages is2.7Ma.BP.3.2Ma.BP.4.2Ma.BP..The analysis of the granularity of BD13-1-1, BD13-3-1, BD19-2-2, ST29-2-1,ST36-1-1and YC26-1-1shows that, the average grain size of sediments is generallydecreasing from yacheng formation to yinggehai formation. The granularity of Yacheng formation and Lingshui formation is bold, and it reflect strong conditions ofdeposit; The particle size from Sanya formation to yinggehai formation is minutely,and not much has changed, it reflects the depositional environments of qiongdongnanbasin during this period are relatively stable.The analysis of the heavy mineral of YC8-2-1, YC21-1-4, BD13-1-1, ST24-1-1and ST29-2-1wells suggests that deposition of minerals are composed of stablemineral, such as zircon, tourmaline, magnetite and titanium ore, the instable heavymineral is rare, and it exists only in the individual layers of the sample.From yacheng group to yinggehai group The Qiongdongnan basin’ depositionenvironment has generally changed from Shore Delta deposition to bathyalenvironment, the water power conditions changed from strong to weak, graindiameter changed from silty sand to mud, the source of the well in NorthernQiongdongnan basin come mainly from Hainan uplift and the corresponding raisedpart near the well, the source of the well in Northern Qiongdongnan basin comemainly from the southern uplift and the corresponding raised part near the well.The average of LREE, HREE and REE is similar to the mainland ofChina, and is much different from deep-sea deposition and the ocean basalt. Ingeneral, it shows the content of light rare earth elements is much more than the heavyrare earth elements. Eu shows negative exception, the distribution curve of earthelement in sediment after ball grain meteorite standardization is similar with Chinaland crust, China loess, land crust and top crust, and it generally reflected the featuresof Chinese "land source".Principal component analysis of trace elements and the changment of its contentshows that, trace elements in sediments of LS33-1-1have a significant relationshipwith the mainland of China, it shows the sources are mainly the weathering anderosional product of the Chinese continental crust, some layers contain components ofvolcanic eruptions and sea.