电导率异常检测裂缝识别方法与应用——以鄂尔多斯盆地延长组深层低渗透砂岩为例

Application of conductivity anomaly detection technique for fracture identification: a case study on deep low-permeability sandstone in Yanchang Formation, the Ordos Basin

受构造作用与地应力影响,鄂尔多斯盆地局部地区延长组深层低渗透砂岩储层裂缝发育。为了系统识别与评价裂缝,对倾角测井电阻率与极板方位曲线进行处理,阐述了电导率异常检测的直观成图法,并通过与电成像解释结果对比,总结不同类型裂缝的响应特征,进一步探讨了该方法的适用条件。通过实际资料处理,认为在低渗透砂岩地层,裂缝开度越大,钻井液侵入造成的高导(低阻)特征越明显,电导率异常检测可直观识别开度大于45μm的裂缝,并可准确判断裂缝走向、裂缝高度、裂缝倾角及地层最大水平主应力方向等信息;对于开度小于45μm的裂缝,识别精度较低。对裂缝发育的低渗透储层研究区,该方法可有效识别裂缝及评价裂缝参数。

Due to impacts of tectonic activities and crustal stresses, deep low-permeability sandstone reservoir formations of Yanchang Formation in certain parts of the Ordos Basin contain well-developed fractures. To identify and assess these fractures, dipmeter logging conductivities and polar plate orientation plots were processed to generate direct mapping technique for detection of conductivity anomalies. Through comparison with electric imaging interpretation results, responses of various fractures were identified to further clarify application conditions of the technique. Through processing of actual data, it is determined that higher fracture apertures in the low-permeability sandstone formations may lead to more obvious features of high conductivity （low resistance） induced by drilling fluids. By way of conductivity anomaly detection, fractures with apertures over 45 um can be identified directly. In addition, orientations, heights, dips and directions of maximum horizontal stresses in such formations can be determined accurately. As for fractures with apertures below 45um, the technique reveals lower accuracy in identification. Generally, the technique can be deployed in low-permeability reservoir formations with fractures developed to identify fractures and assess fracture parameters effectively.