Abstract:

Reservoir hydrocarbon saturation is the basis of reserve estimate.Rock electricity parameter is one of important factors when using Archie equation to calculate reservoir oil/gas saturation.This article utilizes airdrying and imbibition to establish water saturation of carbonate rock core,compares the experimental method of rock electricity parameters.The porosity of carbonate rock samples used in experiments ranges from 0.5% to 6.2% and the permeability is less than 1×10^-3 μm². Results show that,due to the complexity of pore configuration and the wettability of carbonate rock,the rock will not absorb more water when water saturation reached a critical value,actually the maximum of water saturation always less than 50% by imbibition.Compared the resistivity of lower saturation rock by imbibition with the samples which were full saturated by simulation formation water,the latter R_o  always displays a higher value,on the relationship between resistivity and saturation,most of the resistivity values with full saturation diverge from the extension value which matched from the resistivity point of low saturation samples.The coefficients n and b derived from airdrying and imbibition are quite different,but the change tendency is unanimous,and the coefficient  n has a great correlationship with porosity,that is, n decreases with the increase of porosity.However,it is difficult to set various saturation of carbonate rock with low porosity and permeability in rock-electrical experiment.Due to water/gas migration law of carbonate rock gas reservoir and water/gas equilibrium process within gas reservoir,the rock electricity experimental relationship by airdrying method is better to meet the needs of gas saturation evaluation of carbonate rock gas reservoir.

Key words: carbonate rock, saturation exponent, imbibition, airdrying, Archie equation

摘要：

储层含油气饱和度是储量评价的基础。在以Archie公式为核心的储层含油气饱和度评价方法中，岩电参数是Archie公式应用的基础。通过开展岩电参数研究实验，对利用风干法和自吸增水法建立碳酸盐岩岩心含水饱和度进行了对比。研究结果表明，由于碳酸盐岩岩心孔隙结构、润湿性复杂，依靠自吸水方式，含水饱和度高于一定值后岩心将表现出不再自吸水的现象。自吸增水法所能够达到的最高含水饱和度一般都低于50%，相对于自吸增水建立的岩心低含水饱和度时的电阻率，被模拟地层水100%饱和时的岩心电阻率R_o 普遍偏高，100%饱和状态下的岩心电阻率大都偏离了低饱和度数据点拟合线的延长线。风干法和自吸增水法获得的指数n和系数b数值上具有明显区别，但变化趋势一致，且两种饱和度建立方法获得的指数n都与孔隙度具有较高的相关性，且都随孔隙度增大而降低。对基质孔隙度、渗透率都差的碳酸盐岩储层岩石的岩电研究中，含水饱和度建立十分困难。根据碳酸盐岩气藏成藏后气水运移规律及气藏内部气水平衡过程，风干法所获得的岩电实验关系更符合碳酸盐岩气藏含气饱和度评价的需要。

关键词: 碳酸盐岩, 饱和度指数, 自吸增水法, 风干法, Archie公式