水驱油地层电阻率变化规律数值模拟及拐点影响因素分析

Numerical simulation of formation resistivity variation in water drive process and analysis of influence factors of inflection point

为确定水驱过程中地层电阻率与含水饱和度之间的关系,提出变倍数多倍注入水物质平衡理论模拟方法,模拟分析淡水水淹时各种地质因素对地层电阻率变化规律和拐点含水饱和度的影响,并与岩心水驱试验数据进行对比。结果表明:数值模拟方法精度较高;地层物性越好、注入水与原始地层水电阻率比值越大,拐点含水饱和度越小,水淹进程就越快越强;束缚水饱和度越高、残余油饱和度越低,饱和度指数n越大,拐点含水饱和度就越大,水淹进程就越慢越弱;大部分拐点出现的注入水倍数k通常为1.4～2.0;地层孔隙度越小,残余油饱和度越大,地层水和注入水矿化度比值越大,地层水淹后电阻率增大现象越加显著,地层强水淹后电阻率就会越大于水淹初期油层的电阻率值。

A theoretical simulation material balance method of variable multiple injected water was proposed to confirm the relationship between formation resistivity and water saturation.Through the theoretical simulation method,the influence factors of formation resistivity and water saturation of inflection point were analyzed.Comparison with the data of core displacement experiment proved that the numerical simulation method has high precision.The better the formation physical property or the bigger resistivity ratio of injected water to original water,the lower the water saturation of inflection point,the faster the process of water drive.The higher the irreducible water saturation,the lower the irreducible oil saturation or the bigger the saturation exponent,the higher the water saturation of inflection point,the slower the process of water drive.The inflection point usually appears when the injection water multiple is 1.4-2.0.The smaller the porosity,the higher the irreducible oil saturation or the bigger salinity ratio of injected water to original water,the bigger the waterflooded formation resistivity.And the waterflooded formation resistivity is even bigger than the reservoir resistivity.