Abstract:

Natural gas in Hetianhe Gas Field is mainly sourced from the secondary cracking of liquid hydrocarbon early generated from the Cambrian source rock.In order to investigate the migration and accumulation efficiency and to determine the source area of natural gas,the simulation experiments of hydrocarbon generation from the pyrolysis of source rock in an open system and gas generation from the cracking of crude oil in a closed system were carried out.Based on the experiments,the chemical kinetics models for describing hydrocarbon generation from organic matters and carbon isotope fractionation during methane generation from oil cracking were established,calibrated and then applied to two potential source areas including Bachu Arch and Southwest Depression.The application indicated that both potential source areas have a characteristic of generating aboundant gas in a short period,which is propitious for decreasing gas dissipation during migration and accumulation process.However,two tectonic movements had destroyed the hydrocarbon generated early in Bachu Arch.On the contrary,the tectonic evolvement of Maigaiti Slope dipping to the north and then to the south resulted in the late-generated natural gas in Southwest Depression,because the source rock in this area was at a high tectonic position at early time,which made hydrocarbon accumulate at the high tectonic position of the ancient Maigaiti Slope with a stable tectonic setting before the Himalayan orogeny instead of in the Mazhatage fracture zone located at a low position,avoiding two great tectonic movements.As a result,the natural gas in Hetianhe Gas Field was mainly from the Southwest Depression.

Key words: Hetianhe Gas Field, oil-cracking gas, carbon isotope fractionation, chemical kinetics models, gas migration and accumulation efficiency, gas source area

摘要：

和田河气田天然气主要源自寒武系烃源岩早期所生液态烃的二次裂解。针对其天然气成因类型,设计开展了源岩热解生烃和原油裂解成气模拟实验,在此基础上建立并标定了有机质生烃及原油裂解成甲烷过程中碳同位素分馏的化学动力学模型,进而在和田河气田的潜在源区进行了地质应用。结果表明,和田河气田两个潜在源区均有短期内大量生气的特征,这有利于减小成藏过程中天然气的散失量。但是,巴楚凸起生气期较早,且所生油气先后经历了两次构造运动破坏;而麦盖提斜坡先北倾后南倾的构造格局演化既使西南坳陷烃源岩早期处于构造上倾部位,生气较晚,又使其所生烃类早期在构造相对稳定的西南古斜坡的构造高部位成藏,而不是在其下倾方向的玛扎塔格断垒构造带聚集,避免了和田河地区的两次构造运动破坏。因此,和田河气田天然气应主要源于西南坳陷。

关键词: 和田河气田, 原油裂解气, 碳同位素分馏, 化学动力学模型, 天然气运聚效率, 天然气源区