准噶尔盆地烃源岩的热谱分析研究

根据1090热分析系统所得的DTG曲线可区分干酪根类型。用DSC法测定干酪根脂碳率和芳碳率,可研究有机质结构演化并估算生油气量。准噶尔盆地油气源层主要有上二叠系、上三叠系、中下侏罗系和下第三系。以上二叠系最佳,凹陷中部为腐泥型,生气能力为腐殖型的一倍多。侏罗系褐煤生油气量为壳质组>镜质组>惰性组。热谱法用样少,时间短,重复性好,是一种综合性的快速评价方法。

RESEARCH ON SOURCE MATERIALS FOR HYDROCARBON IN JUNGGAR BASIN USING PYROLYTIC ANALYSIS

The DTG(differential thermogravimetry)and TGA(thermo-gravimetric anaysis)curves of various types of kerogens and coal samples from the Junggar basin, Xinjiang, were obtained by using thermogravimetric analyzer connected with 1090 thermo-analytical system made by Du Pont Com. U. S. A. The classification of kerogens can be made based on the alteration stages determined on DTGcurves, in the case of a mixed kerogen, the mixing degree of organic matters from different sources can also be shown. The thermo-alterable characteristics of standard sapropelic kerogen presents a sharp peak which shows that alteration speed in the twinkling of about 450℃ is high, the mixed kerogen presents many peaks, and curve of humic kerogen appears to be swelling circular form. In the Junggar basin, the source materials for oil and gas are mainly distributed in Upper Permian, Upper Triassic, Middle and Lower Jurassic and Eogene deposits, but well developed in Upper Permian deposits. In the central depression, the gas productivity of sapropelic kerogen is twice as high as that of humic kerogen. The oil and gas amount produced from Jurassic brown coal shows: exinite>vitrinite>inertinite. DTA(differential thermal analysis)curves of organic matters show two clearly separated thermodischarging peaks, the first one indicates the burning peak of carbon on fatty texture and the other indicates that of carbon on aromatic skeleton texture. As the temperature increases, the area of the former peak becomes smaller and that of the latter gradually becomes greater. Using F_fa S₁/(S₁+S₂)] for the alterable percentage of fatty carbon and F_arS₂/(S₁+S₂)] for aromatic carbon percentage in total organic carbon and from these values, various types Of organic matters can be distinguished. From the F_ar value, the sapropelic type ranges from 0.1 to 0.3, the mixed type from 0.3 to 0.5 and the humic type is more than 0.5. The rate and productivity of alteration from various types of kerogens to oil/gas are different. The alterable productivity of fatty carbon R_fa=(F_fa^o-F_faⁱ)/F_fa^o] and total alterable productivity, R_t=(F_fa^o-F_faⁱ)/(F_fa^o+F_ar^o)can be used to reflect maturity and a oil-gas production in their evolutional process. After temperature rising up to 390℃, the R_fa value of mudstone(Permian, type-1)in well Zhang-1 in the basin increases obviously, 0.15 at 390-440℃, 0.19 at 440-490℃ and 0.14 at 490-580℃. It suggests that oil/gas released from sapropelic kerogen concentrated in a period of time. However, the oil and gas normally releases from humic kerogen(e. g. in well Chang-141, Lower Jurassic, black mudstone). On the equilibrium theory between aromatic and fatty carbons in the evolutional process of source material, the mass parameter K_c(K_c=F_arⁱ/F_ar^o-1)related to the type and maturity of kerogen could be calculated. In the formula. F_ar^o is primitive aromatic carbon atom and F_arⁱ is that altered to a given stage. A good type of source material of higher maturity has lower F_ar^o and higher F_arⁱ. The greater the K_c value, the larger is the production of oil and gas. Otherwise, for the worse type and/or lower maturity of kerogen, the smaller the K, value, the production would also be lower correspondingly. As the flirty carbon in kerogen is an important contributor to the generation of oil and gas, R_fa and R_rfa(it is F_faⁱ/F_fa^o, the alterable productivity of residual fatty carbon)values in a given stage can reflect the change in amount of expelled. oil/gas and of their potential amount. It can be seen in the diagram of the structural alteration of organic carbon that the K_c value of humic kerogen is less than 1.5, that of mixed type is 1.5-3.0 and that of sapropelic type is more than 3.0. In the well Chai-1 and Chai-2, Junggar Basin, K_c value of the Carboniferous grey-black mudstone are 2-2.43, which has higher production amount of oil and gas, henceforth it is a notable productive series. With increasing temperature, the production of hydrocarbon increases. The thermodegrading curve obtained according to the peak area of fatty carbon on theDSC diagram shows a main peak at 400-450℃, which is different from the result of modelling experiment given the main peak at 300——320^C. This difference may be a result of different rate of increasing temperature. The temperature for alteration of organic matter to hydrocarbon at high speed would be even higher due to short transition time in the alteration experiment using the thermo-analytical method.