渤海湾盆地生物气成因类型与成藏条件

Genetic Types and Accumulation Conditions of Biogas in Bohaiwan Basin

近年来在渤海湾盆地发现了多种成因、零星分布的生物气藏,由于地质条件的复杂性,生物气的成因类型不清、成藏条件不明。为查清生物气的成因类型,分析了生物气的地球化学特征,再结合成藏地质背景,将渤海湾盆地生物气划分为来自烃源岩的生物气和原油降解生物气,前者又包括原生生物气和后生生物气,后者划分为原油厌氧降解生物气和喜氧降解生物气,不同成因的生物气常与热成因气混合成藏。基于上述认识,分析了渤海湾盆地生物气成藏的气源条件、储盖条件、圈闭条件和保存条件,认为渤海湾盆地生物气气源充足、储集空间发育且具有合适的圈闭,盖层封堵能力、东营运动后断层活动性和封闭性成为制约渤海湾盆地生物气成藏的关键。

Great volumes of biogases have been found in the Bohaiwan basin.But they are small and fragmented distribution,with multi-genetic types.In this paper,based on gas geochemical characteristic and geological background,the biogases in the Bohaiwan basin are divided into two types of source rock-and hydrocarbon-derived biogases.The source rock-derived biogases are subdivided into primary and secondary biogases,and the hydrocarbon-derived biogas could be subdivided into anaerobic degradation biogas and aerobic degradation biogases.Complex geological conditions make the genetic types of biogas in the Bohaiwan basin mixing.The coexistence of biogas and thermogenic gas occurs in some of biogas reservoirs.By mean of understanding the conditions of biogas source,reservoir,trap and preservation in the Bohaiwan basin,we consider that the Bohaiwan basin have sufficient source of biogas,developed reservoir and suitable trap.The sealing capacity of cap rock,fault activity after Dongying movement is the key for biogas accumulation.