Preliminary Evaluation Of Carboniferous Sedimentary Characteristics And Hydrocarbon Potential Of Southern Ningxia Region

The study area mainly located at the south of Ningxia Province,across neighboring Shaanxi and Gansu in some areas.Its tectoinc position belongs to the convergence zone between Alashan,Qilian fold and the North China.Carboniferous in the main area is incorporated into Sabina deposition zone.The Carboniferous was sedimented in transitional facies, dark clay,shale and coal is widely distributed.It’s one of the major source rocks in the region.However,the former oil and gas exploration work in the region,mainly focused on the Mesozoic hydrocarbon source rocks,yet,there was little work on the Carboniferous source rocks,the related reseash is weak.In this paper,we carried out a series of geological investigation,typical cross-section measurement and a number of testing and analysis after the system sort and summarize previous results.We get the following key knowledge about Carboniferous strata,sedimentary facies,oil and gas aspects by comprehensive study of geophysics,basin geology,sedimentology,lithofacies paleogeography,petroleum geology and petroleum geochemistry at south Ningxia:(1) Canboniferous can be divided into Qianheishan Group,Chouniugou Group of Lower Carboniferous and Tupo Group,Taiyuan Group of Upper Carboniferous,the Stratigraphic is integrity.The spread range of Qianheishan Group and Chouniugou Group is bounded by Yaoshan-Tanshan to the eastQuwushan to the south,extend to the north and west.partialy missing in Xiangshan.The distribution of Upper Caboniferous relatively expanded. Tupo Group is most widely distribuded,the east boundary overreached Luoshan,reached Weizhou in the west of Ordos Basin,the south boundary arrivaled Nanhushan and Jingning.Taiyuan Group further expanded in the noutheast,while it was denuded relatively serious in the southwest.(2) The main depositional environment of Carboniferous in south Ningxia was transitional facies,and can be divided into carbonate platform,shallow,barrier island-lagoon-tidal and delta sedimentary sestem.Carbonate platform facies appear only in the Early Carboniferous,hereby heavy bedded carbonate rock only developed in Early Carboniferous while not in Upper Carboniferous. Specifically,the main depositional environment of Qianheishan Group were salty lagoon,tidal flat,restricted platform and delta;the main depositional environment of Chouniugou Group were tidal flat,open platform and delta.The main lithology of Tupo Group and Taiyuan Group of Upper Carboniferous is margin clastic rock and clay,with small quantities of carbonate rocks,its main depositional environment was shallow marine,tidal flae and delta.(3) Carboniferous srata in south Ningxia has large thickness and fully developed mudstone,its maximum cumulative thickness thickness is more than500m,in addition to coal, Carboniferous has good hydrocarbon material basis. Carboniferous source rock has high TOC,mostly over2.0%,it’s indicators of good source rocks.However,the sample may be affected by surface weathering and transformation,it’s chloroform bitumen "A"and rock pyrolysis data is poor.Taken together,the abundance of origanic matter reaching the middle-good source rocks standards.Since the Carboniferous is paralic coal-bearing strata,the main carogen type of hydrocarbon source organic material is type Ⅲ,with a small portion of type Ⅱ.Mudstone sample Ro test and pyrolysis Tmax data indicate that the thermal evolution of Carboniferous source rocks are concentrated in the mature-high mature stage.Taking into account the situation of the coverage depth of Carboniferous in study area,we think hydrocarbon source rock maturity dominated by high mature,even over mature.Comprehensive organic matter abundance,type and maturity, Carboniferous source rocks in sourthern Ningxia are good gas source rocks.(4)Multidisciplinary compared strata feature,sedimentary,and source rock feature of Carboniferous in southern and neighboring areas,think southern Ningxia with both good source rocks and good preservation conditions.The features of surface seeps and its reservoir bed rock show that it was occurred hydrocarbon filling when Carboniferous buried.Southern Carboniferous in Ningxia is a good hydrocarbon palys.