Ordos Basin, Permian Depositional Systems And Coal-derived Gas Into The Study Of Tibetan Relations

AbstractOrdos Basin is the second basin of China, which is a cratonic basin shaped by the combinationwith palaeozoic pIatform and Mesozoic inland sag basin. The area of Ordos is 25 X l04km2. Theresearch of depositional system is the basis and premise for oil and gas exploration. Through indetail observing the cores of 98 cored wells, 24 field profiles and analyzing the log data of morethan 380 wells, author obtain the characteristic of the depositionaI system, palaeogeography andprovenance. On this basis, author want to find out the relationship of dePOsitional system and humicgas pools. It is a profitabIe to attempt.This thesis discuss in detail the aIlocation of depositional system and migration of streamchannel during the different times, discover the characteristic and evoIution of palaeogeograPhy indifferent times, and point out that there mainly were five delta systems in the north, west and southof the basin on the basis of compiling stratigraphic isopach map, sand body isopach map andpalaeogeograPhic maP of TaiyUan and Shanxi stages in lower Dias epoch, lower Shihezi and upperShihezi stages in middIe Dias epoch and Shiqianfeng stage in upper Dias epoch. So author putforward that the basin developed the depositional system of meandering river delteepicontinentalsea in Taiyuan stage, the depositional system ofoffshore lake --braided channel in Shanxi stage andthe depositional system of in1and lake --delta in middle and upper Dias epoch.In this thesis, author analyze the provenance first time by utilizing the characteristic of regionstructural settings, the rock combination of denuded region, the frame of palaeogeography, sandbody distribution, the types of lithic fragment, cathodoluminescence, the analysis of heavy mineraland palaeocurrents. Author point oUt that Ordos basin has the favorabIe conditions for larse-scalegas field by analyzing and researching the vitrinite reflectance(Ro), the intensity of producinghydrocarbon, the sealing conditions, the stages of producing hydrocarbon, the isopach map of coalbed and dark mud, the distribution of induStrial producing gas wells.According to the research to coal bad and peat bad of predecessor sand author, author point outthe characteristic of the peat deposition, and on this basis, build up the peat depositional system andits mbdel of producing coal. At the same time, author point out that the larse-sca1e peatformingswamp correspond to the transforming stage between the high system tract and transgress systemtract of sequence. Combination with the research of predecessors and by studying the developinghistory of geodynamic of the basin, aUthor restore the geothermal history and divide three stages ofthe migration of humic gas in Dias, and reach the conclusion that the last producing gas pools ofDias is developed in Miocene. TherefOre the last producing pools in Ordos basin is late, time ofproducing gas is long, and the volume is lnye, all these are the favorable faetors for larpe-sca1ehumic gas field.The Dias humic gas pools inside of the basin are lithologic gas poo1s with stractigrPgy traP, thedistribution of reservoirs are mainIy controlled by depositional system, especially the reservoirs ofS2stage and H9stage are controlled by the river-delta depositional system. They are the main gasreservoirs in the basin. On the basis of discussing in detail the combination of producing-reservoir-cover and the characteristic of migration and accumulation, author get the model of forming Dias humic gas pools in Ordos.