Carboniferous Petroleum Resource Assessment In The Eastern Qaidam Basin

The Qaidam Basin is an important petroliferous basin in China,and the Carboniferous is a new series of strata for oil and gas exploration in northern China in the recent years.The large Carboniferous residual thickness in the eastern part of Qaidam Basin has led to favorable exploration prospects,and scientific oil and gas resources evaluation serves as an important basis for further oil and gas exploration.To conduct oil and gas geological exploration and resources evaluation,this thesis carried out in-depth studies centering on such scientific problems as the development mechanism,controlling factors and spatial distribution of hydrocarbon source rocks;geological and thermal background as well as oil and gas accumulation and transport history;and key parameters of oil and gas resources evaluation.Based on geological profile field investigation and sampling as well as drilling core data and laboratory analytical results,this thesis carried out research on the genesis,types and evaluation of hydrocarbon source rocks as well as oil and gas resources evaluation under the guidance of sedimentology,organic geochemistry,organic petrology theories and technical methods.The main achievements are as follows:1.This thesis classified the organic facies of the Carboniferous in the eastern Qaidam Basin based on lithofacies paleogeography classification and organic characteristic studies.The Carboniferous in the eastern Qaidam Basin was mainly classified into four organic facies–the coastal tidal flat-lagoon organic facies?I?,the coastal marsh organic facies?II?,the open platform organic facies 1?III₁?and the restricted platform organic facies?IV?,the coastal tidal flat-lagoon organic facies,coastal marsh organic facies and restricted platform organic facies are favorable for the Carboniferous source rocks in the eastern Qaidam Basin.2.This thesis conducted research on organic source contributions of the Carboniferous hydrocarbon source rocks in the eastern Qaidam Basin on the basis of organic facies classification and biological compound characteristics analyses.There were complicated organic source contributions for the Carboniferous hydrocarbon source rocks and the contributions were varied among terrestrial and marine organic sources.Mudstone,carbonaceous mudstone and coal developed in the coastal marsh organic facies?II?were dominant in higher terrestrial plants and can be classified as terrestrial hydrocarbon source rocks.Mudstone and silty mudstone developed in the coastal tidal flat-lagoon organic facies?I?were the mixture of terrigenous source rocks and can be classified as marine mixed hydrocarbon source rocks.Mudstone,marl mudstone and marl developed in the restricted platform and open platform were mainly marine aquatic organisms and can be classified as marine endogenous hydrocarbon source rocks.Different genetic types have determined varied hydrocarbon generation characteristics of hydrocarbon source rocks.3.This thesis studied on the structural stage and corresponding denudation thickness of the Carboniferous in the eastern Qaidam Basin through balanced profile technologies in combination with apatite fission track analyses.Six large-scale tectonic uplift occurred in the eastern Qaidam Basin from the Hercynian to the Himalayan period,and in the early Jurassic,late Cretaceous,late Eocene,late Miocene and late Pliocene-Pleistocene.The denudation amount was recovered by using the ancient temperature scale method and the seismic stratum trend extension method.In the Hercynian-Indosinian period,the amount of denudation ranged from 2100m to 4300m with the denudation amount being gradually reduced from the southern margin to the northern margin of the basin.In the late Himalayan period,the amount of denudation varied from 200m to 4400m,with large amount of denudation occurring in the basin margin or tectonic uplift areas and relatively small amount of denudation occurring in the depression or less active tectonic areas.4.This thesis studied on the spatial distribution and organic geochemical characteristics of the Carboniferous in the eastern Qaidam Basin through field profile measurement,seismic interpretation,drilling and sample analyses.The spatial distribution of hydrocarbon source rock thickness illustrated that potential hydrocarbon source rocks existed in the Zabu sagasu Formation,the Crook Formation,the Huaitoutala Formation and the Chengqianggou Formation in the eastern Qaidam Basin.Comparatively speaking,the hydrocarbon source rocks of the Crook Formation in the study area were of large thickness?150-400m?and the mudstone hydrocarbon source rocks were dominated with type III organic matter with the vitrinite reflectivity being around 1.3%belonging to the stage of maturity to high maturity,and the TOC of 70%mudstone being greater than 1.0%meeting the standards of high-quality hydrocarbon source rocks,part of which were of extremely high quality.5.This thesis analyzed the development mechanism and controlling factors of Carboniferous hydrocarbon source rocks in the eastern Qaidam Basin based on the analyses of structure,sedimentary facies and organic sources,The hydrocarbon source rocks of the eastern Qaidam Basin were controlled by sedimentary organic facies,organic sources and tectonic evolution.The sedimentary structures controlled the spatial distribution of hydrocarbon source rocks,and the later evolution controlled the residual thickness of hydrocarbon source rocks.The organic sedimentary facies determined the lithology and development characteristics of the hydrocarbon source rocks.The different terrestrial and marine organic contributions controlled the characteristics of the hydrocarbon source rocks being dominant with oil generation or gas generation.6.This thesis calculated the volume of oil and gas resources of the Carboniferous in the eastern Qaidam Basin through the studies of key parameters and by using the petroleum-bearing system simulation technique.The hydrocarbon generation in the Carboniferous in the eastern Qaidam Basin reaches 9.49 billion tons?oil equivalent?,and oil and gas resources generated in the Carboniferous period in the eastern Qaidam Basin reach383.3 million tons?petroleum equivalent?.This thesis found that the Crook Formation generated the highest volume of oil and gas and contributed greatest to oil and gas resources.Mudstone generated the highest volume of oil and gas and contributed greatest to oil and gas resources.7.This thesis divided the Carboniferous strata in the eastern Qaidam Basin into 3accumulation units based on resources potential evaluation,accumulation analysis and basin simulation,namely Ounan prospect area,Olongbluk prospect area and Delingha prospect area.With further analyses on the three accumulation units,this thesis inferred that the Olongbluk structural belt would be the most favorable area for geological exploration,being followed by the Emnik structural belt and the Delingha structural belt.