Prediction and research of fracture distribution characteristics of the Chang 8 reservoir in Zhenjing area, Ordos Basin

Abstract

The Zhenjing area is on the southwestern margin of the Ordos Basin where the tectonic activity is strong, and natural fractures are widely developed. As the main seepage channels of the reservoir, fractures significantly affect the accumulation of oil and gas. Therefore, it is crucial to study the distribution of fractures in this area. This study comprehensively used cores, image logging, field outcrops, and geophysical data to study the genesis and distribution characteristics of these fractures. The results indicate that the Chang 8 reservoirs in the study area primarily developed high-angle structural fracture-oriented northwest-west and northeast-east. We used five methods to identify and predict the fractures of the Chang 8 reservoir in the Zhenjing area: coherent volume fracture detection, a high-precision curvature method, a maximum likelihood method, a structural restoration method, and ant-tracking technology. After comparing and analyzing the prediction results of the five methods, it was concluded that the structural restoration method performed relatively poorly, whereas the maximum likelihood method was more accurate and better at fracture detection. It was found that the distribution direction of the fractures of the Chang 8 reservoir was primarily northeast-east and northwest-west, showing a strip shape. Oil and gas enrichment is obviously dependent on faults and fractures. The degree of oil and gas enrichment in the northeast-east-oriented tension-torsional fractures was significantly higher than that of northwest-west directional compression-torsional fractures, and oil and gas were more likely to accumulate at the intersections and tails of these fractures.