摘要
Abstract
Field investigations have shown that the limestone in Lower Cr etaceous Duoba and Langshan Formation in Cuoqin Basin, a large scale Mesozoic m arine carbonate depositional basin in Xizang municipality of China, are potentia l hydrocarbon resource rock. Initial study indicates that there is a medium abun dance of organic matter, TOC=0.12～0.40%, chloroform bitumen"A"=0.0046～0.0054 , an d the type of organic matter is humic-sapropel. It is difficult to determine the maturity of the organic matter by means of conventional method for its relativ e lower abundance, so biomarker analysis techniques are adopted. In this paper, the geochemical characteristics of aromatic hydrocarbons from the limestone, mainly based on aromatic hydrocarbons analytical data, are discussed in detail.
Various series of aromatic hydrocarbons have been found from the samples: naphth ale ne, phenanthrenes( for example retene and pimantrene), biphenyl，dibenzofuran， fluorene, dibenzothiophen，benzonaphthathiophene，fluoranthene，benzofluoranthen es，pyrene，benzo〔e〕pyrene，chrysene，perylene, tri-aromatic steroids and soo n. . Among them the majority are phenanthrene series,then rectcyclo and pentacyclo aromatic hydrocarbons, and each of the rest has a little quantity. Various ge och emical parameters of these aromatic hydrocarbons are calculated and used to dedu ce the depositional environment, the origin and the thermal maturity of the orga nic matter of the limestone.
Composition of the organic matter and their relative abundance shows that they w ere d erived mainly from lower marine organism, otherwise, the relative high abundanc e of retene，pimantrene and perylene, which are known to be diagnostic biomarker s of terraneous higher plant ,indicates a considerable amount of higher plant input , so a variety of biogenic organic origin of the source rock. The rati o of dibenzofuran/ dibenzothiophen is 2.34～7.74 , shows dominance of dibenzoth io phen among tri-fluorene series and indicates a deoxidized depositional environ ment. Such environment is very favorable for protection of organic material.Methylphenanthrene index (MPI1), sterane C2920S/20(R+S) and hopane C31 22S/22(R+S ) are extensively used geochemical parameters to deduce the thermal evolution stage of the source rock. Other indexes such as the ratio of 2-MN/1-MN, 4- MDB T/∑MDBT, perylene / benzo〔e〕pyrene, benzofluoranthenes/ benzo〔e〕pyrene, TA( Ⅰ)/TA(Ⅰ+Ⅱ) and the like are also reliable parameters to a certain extent. The value of these Indexes of the research area are 0.45～0.57(MPI1) ，0.31～0 .41 ( C2920S/20(R+S)), 0.6(C3122S/22(R+S)) , 1.44～1.83 ( (2-MN)/(1-MN) ), 0.47～0.54（( 4-MDBT)/∑MDBT），0.06～0.12(perylene / benzo〔e〕pyrene) ,1.87～2.52( benzo fluo ranthenes/ benzo〔e〕pyrene），0.14～0.21(TA(Ⅰ)/TA(Ⅰ+Ⅱ), all suggest that th e organic matter have been evolved mature.
Discussions above reaches a conclusion that the organic source, depositional env ir onment and thermal evolution are all advantage for generation of petroleum and t here have developed very potential resource rocks in Cuoqin Basin.关键词
措勤盆地/下白垩统/灰岩/芳烃/地球化学分类
能源科技
