The presence of a complicated, variable-depth oil–water contact (OWC) in the Early Miocene L-III carbonate reservoir of the Mumbai High Oilfield has been well established. The OWC dips towards the SW along a curved profile, but the gas–oil contact (GOC) is flat. Very little is known about the possible mechanisms that could have produced this complex fluid contact. In the absence of a horizontal pressure gradient, gravity should produce a flat OWC. In many fields around the world, where non-flat fluid contacts are observed, the contacts could be described as segmented, tilted or curved OWCs. Commonly believed mechanisms which produce such types of contacts are: fault compartmentalization, hydrodynamic flow, ongoing charge; and reservoir property variation. All these mechanisms fail to explain the tilted OWC of the Mumbai High. This paper proposes that another mechanism – structural adjustments after the migration of hydrocarbons into the palaeotrap – might have resulted in tilting or curving of the originally flat OWC of the Mumbai High. Such a phenomenon is likely to be observed in oil-wet low-permeability carbonate reservoirs. Imbibition-related hysteresis combined with diagenesis-induced property degradation in the water leg are the possible mechanisms that can prevent the OWC from equilibrating even after cessation of structural evolution.

中文翻译：

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油运移后结构变形：印度孟买高油田倾斜油水界面成因的可能机制

孟买高油田早中新世 L-III 碳酸盐岩储层中存在复杂的、可变深度的油水界面 (OWC) 已经得到很好的证实。OWC 沿曲线轮廓向西南倾斜，但油气接触 (GOC) 是平坦的。关于产生这种复杂流体接触的可能机制知之甚少。在没有水平压力梯度的情况下，重力应该会产生平坦的 OWC。在世界上许多观察到非平面流体接触的领域中，接触可以被描述为分段、倾斜或弯曲的 OWC。通常认为产生这种类型接触的机制是：断层划分、流体动力流动、持续充电；和储层物性变化。所有这些机制都无法解释孟买高中倾斜的 OWC。本文提出另一种机制——碳氢化合物迁移到古圈闭后的结构调整——可能导致孟买高地原本平坦的 OWC 倾斜或弯曲。这种现象很可能在油湿低渗透碳酸盐岩储层中观察到。与吸水相关的滞后与水腿中成岩作用引起的性质退化相结合，是即使在结构演化停止后也能阻止 OWC 达到平衡的可能机制。