基岩油气藏是目前柴达木盆地油气勘探的重点领域,前期勘探程度低,储盖组合认识不清。研究发现,柴达木盆地基岩油气藏主要发育在山前带,基岩储层岩性复杂多样,共钻遇花岗岩和变质岩两大类岩性,储层具有孔隙+裂缝的双重介质储集空间,裂缝以构造裂缝和溶蚀缝为主,孔隙以溶蚀孔隙为主。受沉积环境和干旱气候影响,柴达木盆地基岩发育2种类型盖层:其一是基岩上覆的含膏泥岩、泥岩区域盖层;其二是咸水下渗,方解石和膏岩类胶结于基岩顶部储层的孔隙和裂缝中,形成的顶封式局部盖层。由于构造运动和剥蚀作用的影响,基岩储层和上覆盖层在时间上是不连续的,但在空间上是直接接触,含膏泥岩和泥岩盖层直接覆盖在基岩层之上,储盖组合配置好,形成大范围的面—面接触,对油气起到良好的遮挡作用。
Research on basement hydrocarbon reservoir is a new hot point in the Qaidam Basin now.During the previous oil-natural gas exploration,the scale of oil-gas reservoirs in the basement is underestimated due to the lack of systematic assessment of reservoir-caprock assemblage.The study found that the basement reservoirs in the Qaidam Basin are mainly developed in the piedmont zone.The lithology of the basement reservoirs is complex and diverse,and granite and metamorphic rocks are encountered.The reservoir has a double-medium reservoir space with fractures and pores.The fractures are dominated by structural fractures and dissolution joints,and the pores are dominated by dissolved pores.Influenced by the sedimentary environment and arid climate,the basement reservoirs of the Qaidam Basin develops two types of caprocks,one of which is the anhydrite-bearing mudstone cover and mudstone cover above the basement reservoir,and the other is a top-sealed partial cover which is mainly formed by salty water seepage,leading to calcite and anhydrite filled and cemented in the pores and cracks in the top reservoir of the basement rocks.As being affected by tectonic movement and stratigraphic erosion,the underlying basement rock reservoir and the overlying anhydrite-bearing caprock assemblage are temporally discontinuous,but they contact in direct spatial.The anhydrite-bearing mudstone and mudstone caprocks are directly covered on the basement reservoir,and the reservoir-caprock assemblage is well configured to form a wide range of face-to-face contact,which has a good shielding effect on oil and gas.
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