Source Rock And Cap Rock Evaluation Of Well Qijia 1 In Qaidam Basin

The Qaidam Basin is full of natural gas because of its special geological factors.The Sanhu depression is the Quaternary sedimentary center of the Qaidam Basin,but also the country's largest biological field.Well Qijia 1 is a all coring exploratory well located in the southwest of Salt Lake structure which is in the north slope of the Sanhu region.The study of this well will provide a scientific basis for choosing correct exploratory direction,meanwhile,lay the foundation for the further exploration and development of natural gas in Salt Lake region,Sanhu depression.This paper studys the organic matter abundance?the organic matter type?the maturity of organic matter and the gas productivity of well Qijia 1 based on geochemical analyses?Rock pyrolysis analysis and CH₄ simulation experiment of samples;Basing on drilling cores?mud logging and well logging,we use various parameters,such as breakthrough pressure?breakthrough time?mudstone porosity-permeability?specific surface area?the diameter of hole and so on,to evaluate the cap rock of well Qijia 1 from both macroscopic and microcosmic levels;We also study the accumulation mechanisms of biogas of the Salt Lake region,and point out the reasons why well Qijia 1 had no gas during drilling.The study shows that the organic matter of Shizigou formation and Qigequan formation of well Qijia 1 is not very high and belongs to non to poor grading chiefly,the organic matter type is?₂ and?basically.The organic matter of Qigequan formation is in the immature stage,and the organic matter of Shizigou formation enters to mature stage in 2850m.The microorganism live well in the 35⁵5?on the basis of the CH₄ simulation experiment,and the biogas is mainly produced around 1300m of this well,but the gas generation intensity of this well is small.The well Qigequan and Shizigou formation mudstone has seal ability which becomes higher with depth.The Shizigou formation cap rock is in?^?grading mainly,mainwhile the Qigequan formation is mostly in?^?grading.Physical sealing and gas concentration sealing is the main sealing mechanisms in this well.In the Salt Lake region,the trap is reliable,and the source-reservoir-seal assemblage as well as the spatio-temporal allocation of the three is well,so the biogas can accumulate in the synsedimentary anticlinal trap by constant dynamic balance.Through the study,we think the reasons of well Qijia 1having no gas are that this well locates in the structure lower and its Shizigou formation source rock is not well.