近井眼洞穴型地层双侧向测井敏感因素分析

洞穴、裂缝及缝洞组合体是火成岩、碳酸盐岩储层的重要存储空间，具有各向异性明显、非均质性极强的特点，测井识别及定量评价难度大。为了给洞穴型地层测井识别与评价提供理论依据，基于有限元法，采用数值模拟方法分析了井径、钻井液电阻率、基岩电阻率、洞穴半径、洞穴填充物及洞穴与井壁的距离等因素对双侧向测井响应的影响。结果表明:在近井眼洞穴型地层中，由于洞穴的存在使双侧向电阻率明显减小，且随着洞穴半径增大，双侧向电阻率的减小幅度也增大；洞穴中心处的双侧向电阻率最小，随着洞穴半径增大，深、浅侧向电阻率都减小；双侧向电阻率随着洞穴与井壁的距离增大而增大，且浅侧向电阻率的增大程度明显高于深侧向电阻率。研究结果可为洞穴型地层双侧向测井资料的解释提供理论指导。 

Analysis of Sensitive Factors in Dual Laterologs for Cavernous/Karst Formations Near the Borehole

Igneous and carbonate reservoirs consist of formations characterized by containing extensive fractures, caverns (karst), and fractured karst. The challenges exist in the fact that there is obvious anisotropy and strong heterogeneity, resulting in huge difficulty in logging identification and quantitative evaluation. In order to provide a theoretical basis for the logging identification and evaluation of karst/cavernous formations, the numerical analysis has been used to analyze the effects of hole diameter, drilling fluid resistivity, matrix resistivity, cave size, cave fillings. Further, the distance between cave and borehole is calculated based on the response of dual laterolog using the finite element method. The results showed that the dual laterolog resistivity was significantly reduced due to the existence of near-borehole cave formation. With an increase of cave size, the reduced amplitude of dual laterolog resistivity could be increased as well. The dual laterolog resistivity is the smallest at the center of cave, and as the cave radius increases, both the deep and shallow lateral resistivity decrease. The dual laterolog resistivity increases with the increase of distance between the cave and the well wall, and the increase rate of shallow lateral resistivity is significantly faster than that of deep lateral resistivity. The research results can provide theoretical guidance for the interpretation of dual laterolog data in cavernous/karst formation.