基于电容耦合原理的油基泥浆电成像测井仪特性考察

Investigation on Characteristics of Electrical Imaging Tool for Oil-base Mud Based on Capacitive Coupling

利用有限元法从仪器探测深度和分辨率2个方面研究了基于电容耦合原理的油基泥浆电成像测井仪探测特性,考察仪器结构参数如极板上各钮扣电极尺寸及间距、仪器工作频率、绝缘短节长度、回流电极长度和位置等因素对仪器测井响应的影响.该油基泥浆电成像仪器探测深度约为17.5 cm;随玻璃钢介电常数增加,探测深度变深;随着绝缘短节长度增加,探测深度变浅.识别的最小薄层厚度小于钮扣电极高度;玻璃钢厚度、玻璃钢相对介电常数及绝缘短节长度等因素,几乎不会影响仪器的分辨能力;减小钮扣电极高度,可以提高分辨率.随着纽扣电极的尺寸和间距的增加,视阻抗减小;回路电极高度对正演响应的影响相对较小;随着频率的增加,视阻抗减小;当绝缘短节长度在0.2～1m范围变化时,仪器正演响应变化不明显.

Principally there are two types of electrical imaging tools used for oil-base mud, four- point measurement and capacitive coupling method. The survey characteristics of electrical imaging logging tool based capacitive coupling principle are studied from its depth of investigation （DOI） and resolution with finite element method. The effect of tool structure parameters, such as, button electrode size and spacing, working frequency, length of insulation part, length and position for electrode of return current, on tool logging responses is investigated. The DOI of this oil-base mud electrical imaging logging tool is about 17. 5 cm; the DOI is more deep with bigger fiberglass dielectric constant; the DOI is more shallow with length increase of the insulation part. The minimum distinguishing thickness of thin layer is smaller than electrode height; fiberglass thickness, fiberglass relative dielectric constant, length of insulation part and other factors almost do not affect the distinguishing ability of the tool; decreasing the height of button electrode can increase the tool＇s resolution. With the increasing of size and space of button electrode, appearing impedance decreases; the effect of return electrode height on the forward response is relatively small; with the increasing of resolution, appearing impedance decreases; when the length of insulation part changes in 0. 2-1 m range, the tool forward response change is not obvious.