RESEARCH AND PREDICTION OF CRACK DISTRIBUTION CHARACTERISTICS OF CHANG 8 FORMATION RESERVOIR IN ZJ AREA OF ORDOS BASIN, CHINA

The ZJ block is located in the southwestern margin of the Ordos Basin, where the tectonic activity is strong, and natural cracks are widely developed. As the main seepage channels of the reservoir, cracks are closely associated with the accumulation of oil and gas. Therefore, it is particularly important to study the distribution of cracks in the area. This study comprehensively used the data of cores, imaging logging, field outcrops, and geophysics to study the genesis and distribution characteristics of those cracks. The data shows that the Chang 8 reservoirs in the study area developed mainly high-angle structural cracks oriented WNW and ENE. Five methods were used to identify and predict the cracks of the Chang 8 reservoir in the ZJ area: coherent volume crack detection, a high precision curvature method, a maximum likelihood method, a structural restoration method, and ant tracking technology. After comparing and analysing the prediction results of the five methods, it was concluded that the prediction results of the structural restoration method were relatively poor, while the maximum likelihood method was more accurate and better at crack detection. The crack detection found that the cracks of the Chang 8 reservoir were distributed primarily in strips oriented ENE and WNW, and oil and gas enrichment is obviously dependent on faults and cracks. The degree of oil and gas enrichment in ENE-oriented tension-torsional fractures was significantly higher than that of WNW-oriented compression-torsional fractures, and oil and gas were more likely to accumulate at the intersections and ends of fractures.