实验研究洞穴地层的双侧向测井响应特征

Investigating dual laterolog responses of cavernous formation by physical simulation

基于数值仿真构建缩小比例的双侧向测井实验平台,实现典型洞穴地层的深浅侧向电阻率测量及响应特征分析。研究洞穴尺寸、充填性质、发育位置和形状等参数对双侧向测井响应的影响,总结洞穴地层的双侧向测井响应规律,为洞穴地层的识别与评价奠定基础。研究表明:双侧向测井视电阻率随洞穴尺寸增大而减小;洞穴的电阻率与基岩对比度越大,双侧向视电阻率越低,响应特征越明显;洞穴离井眼越远,对双侧向测井响应贡献越小,视电阻率增大;球型洞穴和方型洞穴的双侧向测井响应差异大,球型洞穴对双侧向测井的径向贡献大于方形洞穴,但纵向贡献小于方形洞穴,基于测井曲线形态能大致反映洞穴形状。

A downscaled platform for dual laterolog experiment is established based on numerical simulations. Typical dual laterolog responses of the cavernous formation are conducted via the platform. Influential factors such as the cave size, infilling materials, caves position and shape are investigated to recognize the dual laterolog responses, aiming at discrimination and evaluation of the cavernous formation. The results show that the apparent resistivity of the dual laterolog decreases when the cave size increases. The apparent dual laterolog resistivity is negatively correlated with the ratio between the resistivity of the cave and the bedrock. In addition, the apparent resistivity is directly proportional to the distance between cave and wellbore. There is a significant difference in the laterolog response between the ellipsoidal cave and the square cave. Generally, the radial contribution of the ellipsoidal cave is larger than that of the square cave. However, the vertical contribution of the ellipsoidal cave is smaller than the radial contribution of the square cave. The cave shape can be roughly determined by the dual laterolog curves.