莺歌海盆地底辟流体动态平衡体系及气藏模式

Diapiric Hydro-Dynamic Balance System and Gas Reservoir Model in Yinggehai Basin

中央底辟带是莺歌海盆地天然气的主产区,底辟的物质构成及活动方式,直接控制着天然气的成藏过程与特点。为探索莺歌海盆地底辟构造带天然气成藏过程和气藏特征,阐述了底辟的主要侵入方式,重点总结并剖析了底辟流体的动态平衡形式,分析了流体动态平衡控制下的气藏特点。依据物质构成和侵入方式,可将研究区底辟群分为缓慢挤入型、持续刺穿型、周期塌陷型及混合突破型,前3种分别属于泥底辟主导的层递扩散体系、流体前锋诱导的刺穿碎裂体系、流体柱主导的周期性宣泄动态平衡体系。在动态平衡体系下,气藏为多期充注的混合气,气藏多层叠置,充注程度不一;同构造层结构复杂,多个含油气系统并存;天然气地球化学组分具分层性,碳同位素值倒置。气藏勘探中,区分底辟侵入方式尤其必要,应综合从目标圈闭的类型、砂体与底辟的关系及邻近相关气藏等进行综合分析,以判断圈闭的含气性。

The central diapir zone is the key gas-producing area in Yinggehai basin. Material compositions and activities of the diapir directly control the natural gas accumulation course and features. For probing the course and features, this paper demonstrates the main intrusion pattern, emphasizes and summarizes the diapiric hydro-dynamic balance system and analyzes the gas reservoir characteristics under the control of dynamic balance of fluids. According to material compositions and intrusion pattern, diapirs in the study area can be classified into 4 types such as slow wedging, continuous penetrating, periodic collapsing and mixed breakthrough. The former 3 types belong to stepping diffusion system dominated by mud diapir, penetrating fragment system induced by fluid front and periodic collapsing dynamic balance system dominated by fluid column, respectively. In a dynamic balance system, gas reservoirs are charged with multi-stage mixed gas and overlapped with each other in different charging degrees. The structure of syntectonic stratum is complex and several petroleum systems can coexist. Petrochemical components of natural gas exhibit delamination and inversion of carbon isotope value could be found. It is necessary to distinguish intrusion pattern of diapirs during gas reservoir exploration. Integrated analysis should be conducted regarding target trap type, relationship between sand body and diaper and the neighboring gas reservoirs to identify gas-bearing properties of the traps .