Researching Of Gas Accumulation Process Of Coal-bearing Source Rock

In order to research the process of gas accumulation of coal-bearing source rock,take the east of the Ordos basin of Shanxi formation as example.Based on the core observation,geo-chemical date,conventional thin section,cathodoluminescence,scanning electron microscope(SEM),Laser Raman spectroscopy and inclusion thermometry experiments,analysis the distribution of source rock and organic matter abundance,type and maturity;combine the basin model to analysis the characteristics of hydrocarbon generation and expulsion in different time.Meanwhile,selects the tight sandstone of Shanxi formation to detailed reasearch the characteristics of petrology and diagenesis.Finally,study on the accumulation period and process.The coal-bearing source rock is the main source rock in the study area,including the dark mudstone,carbonaceous mudstone and coal,which was distributed in Benxi formation,Taiyuan formation and Shanxi formation,the total thickness of the coal is mean 10~12m,the total thickness of with an average of 40~60m,and maximum thickness over 60 m.In vertically,the mudstone and coal of Shanxi formation is widely distributed in study area,which formed the good hydrocarbon source condition.According to the exprimental data,the TOC of coal is 53.48% and the TOC of mudstone is 1.92% in the Shanxi formation.A large number of coal measure source rock in study area,and the kerogen type is mainly ?,the Ro is 1.2%~2.0%,the thermal evolution of maturity of organic matter is high,generally reached the dry gas stage of over mature.The hydrocarbon generation intensity is(4~16)108m3/km2 and the hydrocarbon expulsion intensity is(3.2~12.9)108m3/km2 of coal-bearing source rock of Shanxi formation in study area.The average porosity is 5.4% and the permeability is 0.18×10-3?m2 of the Shanxi formation in the study area,which belong to classic tight sandstone.The homogenization temperature of the brine inclusion,associated with gaseous hydrocarbon,which occurred in first stages quartz overgrowth edges was within the range of 80? to 100? and formative time was speculated at 200~190Ma.The range of homogenization temperature of brine inclusions of the secondary quartz overgrowth edges was within 105?~125?.It can be speculated that the first gas filling time and sandstone densification time was 190 ~ 160Ma;The homogenization temperature of brine inclusions of the third stages aqueous overgrowth edges was 135?~155?,accompanied with quantity of high mature gas filling,speculating the gas reservoir formation and sandstone further densification time was 160~140Ma.According to the palaeogeothermal can beinferred that in I phase the quartz overgrowth edge began to developed in early diagenetic stage B,and developed continuously in late diagenetic stage A.II phase and III phase the quartz overgrowth edge developed in late diagenetic stage A,and kept developing in late diagenetic stage B and C.In the early diagenetic stage A,the reduction of porosity was mainly results of mechanical compaction;and in the late diagenetic stage A,it was mainly leaded by siliceous cementation which was produced by the development of quartz overgrowth edge.These destructive diagenesis jointly leaded to development of the tight density of sandstone in the studying area.Whole with the accumulation characteristics of “reservoir forming later than its densification”.