洞穴型地层双侧向测井响应数值模拟与特征分析

基于有限元素法,采用边界局部加密技术,实现对球形、椭球形洞穴的精确剖分与双侧向测井响应快速数值模拟,分析不同洞穴尺寸、填充类型及不同填充程度条件下双侧向测井响应特征,对比纵向、径向延伸椭球形洞穴与球形洞穴响应异同,从而研究洞穴发育形状对双侧向响应影响。结果表明:洞穴的存在导致双侧向测井响应明显降低且存在正差异,深侧向受洞穴尺寸及围岩影响严重,一定程度上可反映洞穴发育规模与填充情况,浅侧向测井可较好反映洞穴内填充物电阻率;椭球形洞穴的长轴若沿纵向延伸,其响应由球形洞穴过渡为类似侵入带特征,若沿径向延伸,其响应由球形洞穴过渡为类似薄层特征。

Numerical simulation and corresponding characteristic analysis of dual laterolog for cave reservoirs

Finite element method was utilized to fast simulate logging responses with the help of local refinement mesh generation. Caves with different sizes, infill material, and various infill level were simulated and analyzed. In addition ellipsoids with different radial and vertical distribution were simulated to further study the effects of cave structure on the dual laterolog response. The results can be summarized as follows:the dual laterolog response decreases significantly when cave exists; although the deep laterolog is affected by the cave size and surrounding bed, in some degree it can indicate the cave size and infill condition; the infill resistivity of the cave can be derived with the help of shallow laterolog response; lastly, when the ellipsoidal cave develops in the major axis direction, dual laterolog response converts to invasion zone response; if ellipsoidal cave develops along the minor axis, dual laterolog response converts to folium layer response gradually.