Characteristics Of Potential Gas Source Rocks And Prospective Evaluation For Gas Hydrates In Muli Depression,South Qilian Basin

At present,the contradiction between economic development needs and energy shortage is becoming more and more obvious,and the research on unconventional energy sources should be accelerated.The investigation and research of gas hydrates in China have mainly focused on the Muli Depression.A large amount of data has been accumulated in the research on the characteristics,conditions and models of accumulation.However,the gas source of gas hydrate and resource prospect is not yet clear.Identify the main contributing strata of the gas source and reveal the resource prospects to provide information for future exploration.This dissertation focuses on research topics.The geological characteristics of those four stratigraphic groups were clarified,and compare the organic geochemical indexes of each stratigraphic group.Furthermore,based on thermal simulation experiments,the gas source conditions provided by different stratigraphic groups for gas hydrate are discussed.And explained the reservoir and accumulation conditions of gas hydrate in this area.Finally,the gas hydrate resources in this area was calculated.The major observations and conclusions from this dissertation include:(1)The lithologic characteristics of Carboniferous and Permian are mainly medium-thick sandstone and thin siltstone,and comprises shallow marine continental shelf,littoral and delta facies.Most of the mudstone layers are missing,presumably caused by fault development.The Carboniferous-Permian organic matter abundance is low,and its hydrocarbon generation capacity is poor.Thus,it is difficult to become a potential source rock of gas hydrate.(2)The lithology of the Triassic is dominated by medium-thin mudstones,medium-thickness sandstones and thin coal seams.The thickness of the mudstones is large,and comprises tidal flat,lacustrine and fluvial facies.The Triassic is dominated by very good and good source rocks.The organic matter type is mainly type ?.Overall,it is in the stage of mature and can be considered as the main potential source rock of gas hydrate.(3)The lithology of Jurassic is mainly composed of medium-thick siltstone,medium-thick mudstone,with thick coal seams,and comprises braided river,delta and lacustrine facies.The Jurassic samples are dominated by very good,good and mediumclass source rocks.The organic matter types are mainly type ? and type ?.Organic maturity is between low and mature,and can serve as the secondary potential source rock for the gas hydrate.(4)Through thermal simulation experiments,it was found that the hydrocarbon gases generated by the Triassic and Jurassic samples in Muli Depression are mainly methane.And the gas production of methane increases with the increase of the temperature set in the experiment.The gas production of heavy hydrocarbons increases first and then decreases.Based on the characteristics of hydrocarbon gas in gas hydrates,the average gas production of methane and total hydrocarbons in the interval of 350? to 400? is used to further explore the hydrocarbon generation capacity of the Triassic and Jurassic source rocks.The results show that the Triassic source rocks have good hydrocarbon generation capacity,followed by the Jurassic.(5)Based on the physical property test of reservoir rock,2D seismic,sections,drilling data and the accumulation pattern of gas hydrate.The method of organic carbon mass balance and volume were used to calculate the geological resources of gas hydrate in Muli Depression.In addition,the resource prospects and favorable exploration strata in this area were analyzed.