塔中奥陶系硫化氢成因及寒武系油气探勘潜力

Origin of Hydrogen Sulfide in Ordovician in Tazhong Area and Exploration Potential of Cambrian Oil and Gas

塔里木盆地塔中地区经多次构造抬升、风化剥蚀,存在多套烃源岩,多期生烃,从下寒武统到上奥陶统均含有油气或沥青,且含有大量H2S。H2S分布不受温度或埋深控制,既可随甲烷等天然气一起运移,也可以水溶相态流动,还可由储集H2S的油气藏本身形成。为明确奥陶系储层H2S成因及分布规律,追踪古油气藏分布,探寻寒武系油气资源潜力,从区域油气成藏和演化入手,分析现今流体和古流体化学组成及演变,总结烃类与硫酸盐之间反应(TSR)的控制因素。利用岩心薄片鉴定及野外剖面露头,分析寒武系白云岩储层孔隙类型及成因。研究表明,奥陶系内H2S为原地TSR成因,在上寒武统—下奥陶统内产生,含量高低与埋深或地温没有直接关系,同时受控于走滑断裂注入的寒武系高矿化度、富镁地层水和油气影响。寒武系储层深埋溶蚀孔隙发育,孔隙度普遍为10%左右,具储集油气潜力。因此,预测走滑断层下切的寒武系发育油气藏,这些油气藏中的硫化氢在喜山期并未运移到奥陶系中,仍保存良好。

Tazhong area in Tarim Basin experienced many times of structural uplift,weathering and denudation,and there are many sets of source rocks with multi-stage hydrocarbon generation.From Lower Cambrian to Upper Ordovician,there are oil and gas or asphalt,and there are a lot of H2S.The distribution of H2S is not controlled by temperature or burial depth.It can migrate with natural gas such as methane,or flow in water-soluble phase.It can also be formed by the reservoir itself.In order to clarify the genesis and distribution of H2S in Ordovician reservoirs,trace the distribution of paleo-oil and gas reservoirs and explore the potential of Cambrian oil and gas resources.Starting with regional hydrocarbon accumulation and evolution,the analytical chemical composition and evolution of present and paleo-fluids are analyzed,and the controlling factors of hydrocarbon-sulfate reaction(TSR)are summarized.The pore types and genesis of Cambrian dolomite reservoir are analyzed by core thin section identification and outcrop of field profile.The study shows that H2S in Ordovician is of in-situ TSR origin,which is produced in Upper Cambrian-Lower Ordovician.The content of H2S is not directly related to burial depth or ground temperature,but is controlled by the high salinity,magnesiumrich formation water and oil and gas of Cambrian injected by strike-slip faults.The Cambrian reservoirs have deep buried dissolution pores,and porosity is about 10%.Therefore,it is predicted that there should be oil and gas pools in the Cambrian under strike-slip faults.The hydrogen sulfide in these pools did not migrate to the Ordovician during the Himalayan period and remained well preserved.