STUDY ON HYDROCARBON GENERATION AND GAS-STORAGED CAPACITY OF DIFFERENT COALBEDS IN SAME RANK IN HUAINAN COALFIELD

Abstract: Coalbeds B_11b and B₁₀ from the lower Shihezi formation of Permian are a pair of adjacent coalbeds at Xiejiaji coal district in Huainan Coalfield. Both coalbeds are of same rank ( Ro= 0. 80-0. 82% ) and under the same geological conditions. However, their gas-bearingness and gas-compositions are quite different. B11b is rich in coalbed gas and heavy hydrocarbon compositions, whereas B₁₀ is poor. According to their coal petrology and organic geochemistry, the reasons on gas- bearingness and strong coal- generated hydrocarbon are studied in this paper. 1. Under optical and fluorescence microscopy, there exist many kinds of hydrocarbon-rich macerals and microindicators in coal-generated hydrocarbon in B_11b, such as bituminite-filling, resinite-filling, exudatinite, suberinite, oil drops and oil film, and micrinit.es with many shapes and occurences. Some of these macerals are also the microindicators in migration of coal-generated oil and gas. 2.The information in organic geochemistry shows that both coal beds might form in different sedimentary evironments. Their OEP parameters are roughly same, i.e. they are in the same maturity. However, the parameters, such as Pr/Ph, Pr/nC₁₇, Ph/nC₁₈, are quite different. These parameters show that the reducibility of B_11b is stronger than that of B₁₀. The author has considered that B_11b is mainly composed of herbaceous plant and hydrophyte and form in an environment of "open waters" or "swamp water land", while B₁₀ is maed up of wood plant and form in an environment of "forest swamp". The thermal analysis shows that B_11b is of higher thermal weight-loss than B₁₀ and greater potential in coal-generated hydrocarbon. 3.The porosity and gas-storing capacity of both the coal beds has also been studied by author. The theory and experiments have indicated that the porosity in B11bis favourable for gas storage, diffusion and migration.