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腐泥型有机质在成烃演化过程中以先生成原油再裂解成气已有共识,但有多大的比例是由干酪根直接降解生成以及如何鉴别尚存异议。选取华北地区下马岭组低成熟腐泥型页岩,采用高温高压黄金管体系及常规高压釜热模拟实验装置,对同源于该页岩的原始干酪根、残余干酪根和原油开展了生气模拟实验。结果表明:(1)腐泥型有机质生油高峰期后,干酪根直接降解成气量占总生气量的20%左右;原油裂解主成气期为422~566℃(R_O=1.3%~2.5%),生气量占裂解气总量的85.5%。(2)干酪根降解气和原油裂解气Ln(C_1/C_2)值与Ln(C_2/C_3)值均随演化程度增高而增大,但受原油和干酪根结构差异、裂解生气速率及所需活化能大小的影响,过成熟阶段,干酪根降解气Ln(C_2/C_3)值逐渐增大,原油裂解气Ln(C_2/C_3)值基本稳定,且低升温速率的Ln(C_1/C_2)值比高升温速率的值大。(3)新建考虑演化阶段的裂解气判识图版,认为四川盆地震旦系—寒武系天然气主要为原油裂解气。研究成果进一步明确了腐泥型烃源岩发育区,高演化阶段以寻找原油裂解气为主要目标,而非烃源岩晚期干酪根降解气,并可为有机质全过程生烃演化轨迹曲线的确定提供重要依据。
There has been consensus that sapropelic organic matter can be remelted into gas by the first generation of crude oil during the process of hydrocarbon generation and evolution. However, what percentage of the total amount of sapropelic organic matter is generated by the direct degradation of kerogen and how to identify the remaining objections? The low-mature sapropelic shale from Xiamaling Formation in North China was selected to simulate the original kerogen, residual kerogen and crude oil from the shale using high-temperature and high-pressure gold tube system and conventional autoclave thermal simulation device experiment. The results showed that: (1) The kerogen directly degraded to about 20% of the total gas production after the peak of sapropelic organic oil generation; the main gas cracking period of crude oil was 422-566 ℃ (R_O = 1.3% -2.5% ), Angry gas accounted for 85.5% of the total amount of cracked gas. (2) Ln (C 1 / C 2) and Ln (C 2 / C 3) values of kerogen degradation gas and crude cracked gas both increase with the evolution degree, but due to the difference of crude oil and kerogen structure, cracking gas rate and the required Ln (C_2 / C_3) value of kerogen degradation gas gradually increases, Ln (C_2 / C_3) value of crude cracked gas is basically stable, and Ln (C_1 / C_2) value of low heating rate Larger than the rate of heating rate. (3) A new cracked gas identification plate considering the evolutionary stage is proposed, which shows that Sinian-Cambrian natural gas in Sichuan Basin is mainly crude oil pyrolysis gas. The results further clarify the development of sapropelic source rock, the high evolution stage to look for crude oil pyrolysis gas as the main target, rather than the source rock late kerogen degradation gas, and can be the whole process of organic matter evolution of hydrocarbon generation trajectory to determine the curve Provide important basis.