东营凹陷沙四段滩坝砂油藏耗水作用与成藏机制探讨

Discussion on Beach-Bar Sandstone Reservoir Water Consumption and Reservoiring Mechanism of Fourth Member in Shahejie Formation,Dongying Depression

通过对储集体内充填孔隙的主要蚀变矿物-伊利石的研究确认,东营凹陷沙四段滩坝砂大面积含油的原因是前成岩期长石高岭石化引发的耗水作用所致,而现今的伊利石则是耗水期高岭石在后期碱性环境下进一步蚀变的二次产物。滩坝砂体中的耗水作用减少了储层内同沉积地层水的含量,在相对封闭的油藏体系内降低了地层压力,增加了空孔体积,形成了烃源岩与储层之间的压力势差,为油气成藏提供了动力来源。依据埋藏成岩演化规律和有机质热演化剖面的对比分析,确定了晚成岩A期是主要的耗水作用阶段,与烃类聚集高峰期相对应。提出了"耗水降压、负压充注"的成藏模式,揭示了滩坝砂大面积含油的成藏机理。通过对长石含量、蚀变程度和单位摩尔分子耗水量的计算,得出东营凹陷滩坝砂体的总耗水量约为20亿t,即相当于提供了等量的原油储集量,展示了该地区滩坝砂油藏的勘探潜力。

Through the study and identification of illite-a main altered mineral filled pores in reservoir, the causation of large area oil-bearing beach-bar sandstone in the Fourth Member of Shahejie Formation is water consumption initiated by feldspar kaolinization during early diagenetic period. While the illite today is original kaolinite under later alkaline environment further altered secondary product. The water consumption within beach-bar sand mass has reduced reservoir synsedimentary strata water content, in the relatively closed reservoir system reduced strata pressure, increased pore volume and formed pressure potential difference between source rock and reservoir, provided energy source for oil and gas reservoiring. According to buried diagenetic evolution pattern and organic matter thermal evolution section comparative analysis have considered the later diagenetic period stage A is the main water consumption stage, corresponding to hydrocarbons accumulation peak stage. The paper has put forward a reservoiring model of “water consumption pressure reduction, negative pressure filling”, thus revealed beach-bar sandstone large area oil-bearing reservoiring mechanism. Through the computation of feldspar content, alteration degree and specific molar molecule water consumption, worked out the Dongying depression beach-bar sand mass total water consumption is about 2 billion tons, amount to provide equivalent crude oil storage capacity, thus have shown the beach-bar sandstone oil reservoir exploration potential.