沁水盆地山西组致密气成藏条件分析

为了评价沁水盆地山西组的致密气勘探潜力,应用地球化学、流体包裹体、稀有气体和生排烃概念模型等实验技术方法,综合分析了山西组致密气的成藏地质条件。研究结果表明,山西组泥岩和煤岩的总有机碳(total organic carbon, TOC)较大,有机质为Ⅲ型干酪根且达到高-过成熟阶段,以生气为主。泥岩和煤岩的生气潜力巨大,生气量分别达到11.44×10~(12)、39.33×10~(12) m~3,山西组致密气资源量为0.14×10~(12) m~3。稀有气体Ar同位素比值表明泥岩是致密气的主力气源岩,其生成的天然气对致密气的贡献率为70.1%,煤岩的贡献率为29.9%。根据盆地的埋藏-热演化史和流体包裹体的均一温度测试结果,确定山西组致密气存在2个成藏期,对应的成藏时间分别为中-晚三叠世和晚侏罗世-早白垩世。此次研究定量评价了沁水盆地山西组致密气的成藏条件,可为该区致密气的勘探提供有利方向。

Accumulation conditions of tight gas in Shanxi Formation, Qinshui Basin

In order to evaluate the tight gas exploration potential of Shanxi Formation in Qinshui Basin, this paper comprehensively analyzes the accumulation conditions of tight gas in Shanxi Formation by using geochemical, fluid inclusion, rare gas experiments and hydrocarbon generation potential method. The results show that shale and coal have high TOC, with mainly type III kerogen in a high to over-mature stage. Shale and coal have great gas generation potential, with gas generation amount reaching 11.4410_¹² m_³ and 39.3310_¹² m_³, respectively. Ar isotope ratios indicate that shale is the main gas source rock of tight gas, and the contribution of gas generated from shale and coal to tight gas resources is 70.1% and 29.9%, respectively. Based on the burial-thermal history and the homogenization temperatures of fluid inclusions, it is determined that there are two accumulation periods of tight gas in Shanxi Formation, and the corresponding accumulation times are the Middle-Late Triassic and the Late Jurassic to Early Cretaceous, respectively. This study quantitatively evaluated the accumulation conditions of tight gas in Shanxi Formation of Qinshui Basin, which can provide favorable direction for tight gas exploration in this area.