中国生物气-低熟气藏形成条件与潜力分析

Reservoir formation and resource potential of biogenic-low maturity gases in China

根据文献资料统计分析,生物气低熟气资源约占世界天然气资源的14.5%。生物气低熟气气藏的形成与分布的特点为①气藏分布符合“源控论”,气藏距气源岩较近。②有机质以腐殖型为主并保存良好,时代新、沉降幅度较大并具还原水介质条件的沉积盆地有利于生物气形成,气候寒冷、水介质微咸对有机质保存有利。③盆地内构造活动相对平静、盖层稳定发育、不整合面少的区块有利于形成生物气低熟气气藏。④气藏有多种圈闭类型,以古隆起或同沉积构造最为有利。⑤三角洲—滨海相、滨浅湖(海)相沉积生储盖层组合优越,有利于形成生物气低熟气气藏。对比中国及世界的地质条件,推测中国的生物气低熟气资源量约为6万亿m3,是具重要价值的找气新领域。根据中国4个生物气低熟气气田的勘探实例,认为中国的中、新生代陆相沉积盆地生成生物气低熟气资源潜力巨大,应加强相应的研究和勘探工作。

According to the literature statistics, biogenic-low maturity gases account for 14.5% of the natural gas reserves in the world. The formation and distribution of biogenic-low maturity gas reservoirs are characterized by the following facts. The gas reservoirs are close to the source rocks. The organic matters are mainly humus, and conserved well. The sedimentary basins developed in the near era with large subsidence and reducing water conditions are favorable for the generation of biogenic gases. And the cold weather and subsaline aqueous medium condition is favorable for the conservation of organic matters. Biogenic-low maturity gas reservoirs prefer to develop in the areas with relatively quiet tectonic movement, stable cap rock and few unconformity surfaces. Paleo-uplifts and syndeposit structures are the best ones among multi-types of gas reservoir traps. The source-reservoir-cap combinations in deltaoffshore and shallow lake areas are favorable for the formation of biogenic-low maturity gas reservoirs. Comparing the geologic conditions in China with those in other countries in the world, the paper predicts that the biogenic-low maturity gas resources are about 6 trillion cubic meters in China. The exploration of the 4 biogenic-low maturity gas fields in China suggests that the great resource potential of biogenic-low maturity gas exists in the Mesozoic and Cenozoic continental sedimentary basins.