淡水水淹过程中自然电位基线偏移随含水率变化规律

Relationship between Spontaneous Potential Baseline Shift and Water-Cut in Freshwater Flooding Process

当油层被淡水水淹时,自然电位基线的偏移是定性识别水淹层的重要依据。以测井和油藏工程相关知识为基础,推导出淡水水淹过程中自然电位基线偏移量与含水率的定量关系。研究结果表明:①在含水率相同的条件下,注入水电阻率与原始地层水电阻率的比值越大,基线偏移量越大;②在未水淹期、弱水淹期、中水淹期及强水淹期自然电位基线偏移量随含水率的变化分别表现为基本不变、快速上升、直线上升、缓慢上升。将该方法应用于S油田的含水率及水淹级别的评价时,符合率达82.6%。

In freshwater flooding process,the spontaneous potential baseline shift is an important indicator for qualitative identification of water flooding zone. Based on the spontaneous potential theory, water-cut and relative permeability theory,the quantitative relationship between shale baseline shift and water-cut is deeply studied. The study results show that： （1） if the water-cut of two oil reservoirs is the same,the one which has higher resistivity ratio of injected water and original formation water has bigger spontaneous po- tential （SP） baseline shift; （2） the characteristic of SP baseline shift is different for different water flood- ing grade. In non-water-flooding period, the SP baseline almost has no shift, and in weak water-flooding period,the amplitude of SP baseline shift rises rapidly, and in mid-water-flooding period,there is a liner re- lationship between SP baseline shift and water-cut, and in strong water-flooding period, the amplitude of SP baseline shift rises very slowly. In this paper,the quantitative relationship is applied in S oilfield to de- termine the water flooding grade and the coincident rate reaches to 82.6 %.