基于3D-FEM的洞穴型地层双侧向测井数值模拟及响应特征研究

洞穴型碳酸盐岩储层非均质性强、电测井响应复杂、测井识别和表征难度大，利用数值模拟方法明确该类储层的电测井响应特征，可为洞穴识别与评价提供理论依据.本文基于三维有限元素法（3D-FEM），引入边界局部加密技术，实现对复杂球形洞穴的精细刻画与响应精确计算；对比分析井眼钻穿型洞穴和井旁洞穴的双侧向测井响应特征和敏感性，进而考察双侧向测井对两者敏感范围的差异.结果表明：洞穴的存在导致双侧向测井响应明显降低，受洞穴边界及仪器探测深度等影响，井眼钻穿型洞穴双侧向测井曲线复杂，而井旁洞穴曲线呈“抛物线”型；双侧向测井对井眼钻穿型洞穴的敏感性远大于对井旁洞穴的敏感性，深侧向和浅侧向测井最大可对洞穴边界距井壁0.5 m和0.3 m的井旁洞穴敏感.

Numerical simulation and characteristics analysis of dual laterolog in cavernous reservoirs on the basis of 3D-FEM

Cavernous carbonate formations are characterized by strong heterogeneity, which results in the complex electric logging responses and the difficulty in the logging identification and evaluation. Numerical simulation of electric logging tools is helpful to figure out the logging responses characteristics in these formations and could provide theoretical support for cave recognition and evaluation. In this paper, based on three dimensional finite element method (3D-FEM), local refinement technique is adopted to accomplish the accurate discretization and simulation of complex sphere caves. Then, the response characteristics and sensitivity of dual laterolog to caves around and penetrated by wellbore are analyzed, finally the differences of sensitive scope between deep and shallow laterolog are studied. The results show that the dual laterolog response decreases significantly when cave exists. Affected by cave boundary and the investigation depth of dual laterolog tool, the logging response for caves penetrated by wellbore is very complicated, however it exhibits parabolic-like characteristic for caves around wellbore. Compared with caves around wellbore, the dual laterolog is much more sensitive to caves penetrated by wellbore. For caves around wellbore, the maximum sensitive distance for deep and shallow laterolog between the cave boundary and well wall is 0.5 m and 0.3 m, respectively.