吐哈盆地低熟气评价的化学动力学方法及其应用

Chemical kinetic method of evaluating low-mature gas and its application in Tuha Basin

针对目前尚无公认的有效方法评价低熟气生成量的难题,本文从低熟气的(低温)热成因机理出发,认为被广泛、成功应用于成熟的热成因天然气生成量评价的化学动力学理论仍然应该是评价低熟气生成量的有效方法。在此基础上,建立并标定了吐哈盆地代表性泥岩、煤岩干酪根成气的化学动力学模型,与可能部分成为低熟气先质的非烃、沥青质的化学动力学模型一起,构成了评价低熟气生成量的方法。标定结果表明,盆地内有机质成气的平均活化能低于其成油的活化能,而且成气过程中低活化能组分的含量也高于成油过程。这可能正是吐哈盆地的有机质在大量生油之前的低成熟阶段,能开始规模性地生成低熟气、从而导致工业性的低熟气聚集的内因所在。应用表明,吐哈盆地低熟气的总生成量可观,达到632.15×1011m3,而且生气强度较高,最高达到100×108m3/km2以上。吐哈盆地低熟气资源量约为3.16×1011～12.62×1011m3。可见,盆地内低熟气具有可观的勘探潜力。本文所建立的方法应该可被推广应用到其他含低熟气盆地的低熟气的评价当中。

In view of the fact that so far there is no an effective method to evaluate the generation amount of low-mature gas quantitatively, this paper deduces, based on the formation mechanism of low temperature thermal genesis of low-mature gas, that the chemical kinetics theory, which has been applied widely and successfully to evaluating generation amount of normal thermal genesis natural gas, still remains to be an effective method of evaluating the generation amount of low-mature gas. On this basis, the chemical kinetic models of representative samples of kerogen both in mudstone and coal are constructed and calibrated, in accompany with the kinetic model of resine and asphahene, which may be the precursor of low-mature gas partly, constitutes the evaluation method of low-mature gas. The results show that the average activation energy of organic matter to gas are lower than that of the organic matter to oil, and the abundance of component with low activation energy during the process of organic matter to gas are more rich than that of organic matter to oil. These may be the inner causes that result the generation of low-mature gas in large amounts during the low-mature stage before oil generated in large amounts and the commercial accumulation of low-mature gas. The initial application indicates that total generation amount of low - mature gas is about 632.15×10^11 m^3 in Tuha Basin and with intensity of gas generation as high as 100×10^8m^3/km^2 In case of 1% of migration and accumulation coefficient, the resource amount of low-mature gas is between 3.16×10^11～12 and 62×10^11 m^3. This suggests that considerable exploration potential of low-mature gas in Tuha Basin. And it is workable to evaluate the generation amount of low-mature gas using the chemical kinetic models and it can be also to popularize to other basins rich in low-mature gas.