碳同位素动力学模拟及其在天然气评价中的应用

The modelling of carbon isotope kinetics and its application to the evaluation of natural gas

天然气碳同位素动力学模拟是国际油气地球化学界的前沿性研究方向。它和盆地沉积埋藏史、受热史结合起来,对于评价天然气的成因和成藏历史是一种新而且有效的手段,正逐渐为人们所接受。介绍了天然气形成的碳同位素动力学模拟,以及其在评价天然气的成熟度、气源、运移-聚集史和油气比研究等方面应用的新进展,充分展示了其具有良好的应用价值。天然气碳同位素特征不仅受母源、成熟度的影响,而且与运聚条件、沉积盆地增温速率有关。瞬时聚集气与累积聚集气在碳同位素特征存在明显差别。碳同位素分馏动力学模型在不同含油气盆地会存在差异,不仅取决于气源条件,还与运移-聚集史、沉积-构造史有关。中国叠合型盆地天然气藏成因复杂,具有多期、多源的特点,本研究对这类天然气的研究与评价提供了新思路。

The modelling of carbon isotope kinetics of natural gas is a leading research direction in oil and gas geochemistry at home and abroad. Combined with basin sedimentary burial and geothermal histories, the modelling of carbon isotope kinetics provides a new and effective means for evaluating the origin and aceumulation history of natural gas pools. In this paper, we briefly introduce the modelling of carbon isotope kinetics of natural gas formation and its applications to the assessment of natural gas maturity, the determination of gas source, the history of gas migration and accumulation, and the oil-gas ratio. We show that this approach is of great value for those applications. The carbon isotopic characteristics of natural gas are not only affected by gas source and maturity, but also are related to accumulation conditions and the geothermal gradient in a basin. There are obvious differences in the characteristics of carbon isotope ratios between instantaneous gas and cumulative gas. The kinetic model of carbon isotope fractionation may be different for different basins, which depends on gas source condition, accumulation history and sedimentary tectonic history. Since the origin of natural gas pools in the superposed basins of our country is very complicated, and because natural gas pools have features of multiphase and variable gas-sources, this paper may provide new thoughts for the study and evaluation of natural gas.