Abstract: 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 μm 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 45 μm, 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.

Key words: dipmeter logging, conductivity anomaly detection, low-permeability sandstone, fracture identification, dipmeter logging, conductivity anomaly detection, low-permeability sandstone, fracture identification