油基钻井液环境下电成像仪器对裂缝响应的数值模拟

Numerical simulation of a kind of imaging tool responses on fractures in oil-based drilling fluid environment

基于电磁场理论及三维有限元素法,提出一种用于模拟电成像仪器对裂缝响应的算法。该算法适用于电成像仪器在油基钻井液环境下对裂缝(包括水平裂缝、倾斜裂缝和交叉裂缝)响应的数值模拟。当裂缝张开度大于1 mm时,随着裂缝张开度的减小,裂缝处响应值也相应减小,算法对裂缝有较好的分辨效果;算法对裂缝的识别能力受背景地层与裂缝流体电阻率对比度的影响;仿真结果可以清晰地反映裂缝所处地层位置及方位角,对于倾斜裂缝,通过后续处理还可进一步获取裂缝倾角。

Based on electromagnetic field theory and three dimensional finite element methods,an algorithm for simulating fracture responses of an oil-based drilling fluid electrical imaging tool is presented in detail. This algorithm can be applied to simulate the oil-based drilling fluid imaging tools responses to different types of fractures,including horizontal fractures,inclined fractures and crossed fractures. When the open width of the crack is greater than 1mm,with the decrease of the width,the value of responses declines,and the cracks can be identified perfectly. The ability of the algorithm to identify fractures can be influenced by the resistivity contrast between the background and the fractures. These simulation results clearly reveal the positions and the azimuths of the fractures as well. Fracture dip can also be obtained for inclined fractures through followup treatment.