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油气生成受控于动力学。因而取决于时间和温度,但和岩石的类型基本无关。最终形成受温度、压力和古地矿物学控制的一种热力学稳定组合的成分。本文选用了一种最低自由能值的计算程序,计算地下3048～12192m深的碎屑岩储层中各种矿物组合的热力学平衡的气体组分。在纯净砂岩储层中,甲烷浓度随深度增加而降低,大约在7620m深处消失。但是,如果还存在石墨残渣,则甲烷可继续生成,一直持续到12192m。看来气体组分受石墨与水反应生成的甲烷,与甲烷被水氧化形成的二氧化碳和氢气之间的平衡所影响。在有含铁矿物存在的情况下,当甲烷被氧化时,地层中的赤铁矿减少,而磁铁矿增加。随着地层埋深的增加,高温使地层中的方解石胶结物热分解成二氧化碳,冲淡了甲烷的浓度,形成无经济价值的气体组合。当储层矿物组合中有含硫矿物时,如黄铁矿和硬石膏,会生成硫化氢。这对深部研究很有意义。另外,热力学计算表明,地下深度达到平衡的气体组分与储层矿物之间存在极大的相关性。
Hydrocarbon generation is controlled by kinetics. It is therefore dependent on time and temperature, but has little to do with the type of rock. Eventually forming a thermodynamically stable combination of components controlled by temperature, pressure and paleo-mineralogy. In this paper, a calculation program of minimum free energy is selected to calculate the thermodynamically balanced gas components of various mineral assemblages in clastic reservoirs of 3048 to 12192 m underground. In pure sandstone reservoirs, the concentration of methane decreases with depth and disappears at a depth of about 7620m. However, if graphite residue still exists, methane can continue to be generated until 12192m. It appears that the gas component is affected by the balance between methane and water, which is formed by the reaction of graphite with water, with the balance between carbon dioxide and hydrogen formed by the oxidation of methane with water. In the presence of iron-bearing minerals, when methane is oxidized, the amount of hematite in the formation decreases and magnetite increases. As the depth of the formation increases, high temperatures pyrolyze the calcite cement in the formation into carbon dioxide, diluting the concentration of methane to form a gas mixture of no economic value. Hydrogen sulfide is formed when sulfur minerals, such as pyrite and anhydrite, are present in the mineral assemblages of the reservoir. This makes sense for deep research. In addition, thermodynamic calculations show that there is a significant correlation between the composition of the gas at a subsurface depth of equilibrium and the reservoir minerals.