菱铁矿对低熟气形成的促进作用

Low-mature gas belongs to unconventional gas, which was proposed in the late 1980s, and the current studies showed a good developing prospect. The formation of low-mature gas was mainly related to coal strata, Jurassic coal strata distributed in western China widely, and siderite is the richest iron-bearing mineral in coal strata. Previous studies from siderite promoting fatty acid decarboxylation have shown that siderite had active effect on low-mature oil formation. However, the effects on the low-mature gas formation have been ignored. Inspired by forefathers’research work, we made exploratory experiments, the results preliminary indicated that siderite had an obvious promoting effect on low-mature gas formation. Based on field investigation and laboratory experiment, this project attempts to find out the abundance of organic acids and the distribution characteristics of siderite in coal strata, as well as their correlation. Hydrocarbon generation by thermal simulation experiment of siderite and low mature coal sample under different combining conditions will be conducted to analyze the gaseous and liquid production and the physicochemical characteristics of solid residue, then to reveal the mechanism of siderite and low mature coal interaction and discuss the promoting effect of siderite on low mature-gas formation.

低熟气是上世纪八十年代末提出的一种非常规天然气，目前的科学研究已显示出良好的发展前景。低熟气主要和煤系地层相关，我国西部侏罗纪煤系地层分布广泛，菱铁矿是煤系地层中最丰富的含铁矿物。前人从菱铁矿促进脂肪酸脱羧角度，探讨了它对低熟油形成的贡献，但未重视菱铁矿对低熟气形成的作用。在前人研究工作的启发下，我们进行了探索性实验，结果初步表明，菱铁矿对低熟气的形成也具有明显的促进作用。本项目拟通过野外考察和室内实验相结合的方法，在查明煤系地层中有机酸丰度和菱铁矿分布特征及其两者相关性的基础上，对不同组合条件下的菱铁矿与低熟煤样开展生烃热模拟实验，分析气液产物及固态残渣物理化学特征，从而揭示菱铁矿与低熟煤相互作用的机理，探讨菱铁矿对低熟气形成的促进作用。

低熟气是上世纪八十年代末提出的一种非常规天然气，主要和煤系地层相关，我国西部侏罗纪煤系地层分布广泛，煤系地层中含有丰富的菱铁矿。为了探索菱铁矿和煤成烃、低熟气的关系，以吐哈盆地为研究区，通过资料调研、野外考察和室内实验，查明煤系地层中菱铁矿分布非常不均一，主体含量在1-5%，最高达近20%。对不同组合条件下的菱铁矿与低熟煤样开展生烃加热模拟实验，结果显示菱铁矿在低温阶段（小于375℃）对气态烃和液态烃均有促进作用，但不显著。菱铁矿添加比例在10-20%时效率最高，若再高反而抑制或延迟生烃。菱铁对碳氢同位素的分馏影响不大。通过改变pH条件发现，偏碱性条件下菱铁矿对煤生烃的促进作用比较明显。通过对固态残渣物理化学特征分析，菱铁矿在400 ℃左右大量地向磁铁矿转化，并产生一定量的氢气，这对有机质成烃过程中的加氢具有重要的意义。