多孔介质中甲烷水合物的微观分布对电阻率的影响

电阻率测井技术是天然气水合物储层资源量估算的重要手段,明确储层电阻率与水合物在沉积物孔隙中微观分布的关系对准确估算水合物饱和度有重要意义。使用自主研发的天然气水合物计算机断层扫描（CT）技术-电阻率测量装置,开展多孔介质中甲烷水合物生成实验,同时进行CT观测与电阻率测试,得到了反应过程中扫描图像和电阻率数据,讨论了孔隙中水合物在不同微观分布模式下电阻率与水合物饱和度的关系。结果表明：水合物饱和度低于10.50%时,水合物以接触分布模式为主,与水合物对孔隙的填充效应相比,排盐效应更加显著,电阻率随水合物饱和度增大略有下降;水合物饱和度为10.50% ~ 22.34%时,水合物为悬浮与接触共存分布模式,悬浮分布模式下的水合物对孔隙水连通截面的阻塞作用较大,电阻率随水合物饱和度的增大急剧升高;水合物饱和度为22.34% ~ 27.50%时,水合物仍然为悬浮与接触共存分布模式,在大部分孔隙已被堵塞的情况下水合物的填充作用对电阻率影响较小,电阻率随水合物饱和度增大而升高的趋势逐渐变缓。可见,电阻率响应特性在不同的水合物饱和度范围下明显不同,与水合物的微观分布有关。

Effect of Microscopic Distribution of Methane Hydrate on Resistivity in Porous Media

The resistivity logging technology is an important mean for estimating natural gas hydrate reservoir resources. It is important to determine the relationship between reservoir resistivity and microscopic distribution of hydrate in sediment pores for accurate estimation of hydrate saturation. The methane hydrate formation experiment in porous media was carried out and CT observation and resistivity test was performed based on the independently-developed experimental device with CT-resistivity measurement, and image and resistivity data were obtained during methane hydrate formation. The relationship between resistivity change and hydrate saturation in different microscopic distribution model of methane hydrate was discussed. The experimental results showed that the hydrate distribution was mainly in contacting mode, compared with the filling effect of hydrate on pores, the salt-removing effect was more significant, therefore the resistivity decreased slightly with the increase of the hydrate saturation when the hydrate saturation was lower than 10.50%. The hydrate distribution was between floating and contacting mode, and the hindrance effect of hydrate on the pore-water connected section in the floating distribution mode was greater, so the resistivity increased sharply with the increase of hydrate saturation when the hydrate saturation ranged between 10.50% and 22.34%. When the hydrate saturation was 22.34%-27.50%, the hydrate still in a coexistence distribution mode of floating and contacting; in the case that most of the pores have been clogged, the effect of hydrate on the resistivity was small, hence the rate of resistivity growth reduced as the hydrate saturation increase. It can be seen that the resistivity response characteristics are significantly different under different hydrate saturation ranges, which is related to the microscopic distribution of hydrate