Oil enrichment potential of strike-slip faults and its comprehensive evaluation: a case study of Halahatang buried hill area, Tarim Basin

Oil control and oil enrichment associated with strike-slip faults are an important feature of oil and gas accumulation in petroliferous basins in China. Accurate prediction and evaluation of the oil enrichment potential of strike-slip faults have become one of the core objectives of oil and gas exploration. Using statistical analogy, representative fault dissection, comprehensive analysis, and hierarchical evaluation methods, the study took the Halahatang buried hill area of the Tarim Basin as the study area and conducted systematic research. The results indicated that the oil enrichment potential of strike-slip faults was jointly determined by lateral and vertical oil-controlling effects. The lateral controlling effect constrained the degree of oil and gas migration and accumulation along the fault strike (lateral direction), and the vertical controlling effect constrained the characteristics of oil and gas migration and accumulation along the fault dip direction (vertically upward). The core factors influencing the vertical and lateral oil-controlling effects of strike-slip faults included fault properties, the degree of lateral connectivity between fault strike and source rocks, the effectiveness of fault-fractured reservoirs in forming fracture-vuggy traps, the angle between fault strike during the accumulation period and the regional structural ridge and tectonic stress field of the target layer, and the degree of fault-induced damage to caprock. These factors were attributed to the four core characteristics of faults, i.e., oil supply capacity, connectivity and trap-forming capacity, reservoir-forming capacity, and caprock-preservation capacity, as well as their spatiotemporal matching relationships with fault formation, evolution, and distribution. Previous evaluations of oil enrichment potential in strike-slip faults mostly focused only on oil and gas vertical migration and accumulation along the fault dip direction. This paper supplements that approach by incorporating evaluation concepts and methods for lateral migration and accumulation along the fault strike, and improves the evaluation index system for the controlling effects of vertical migration and accumulation. It proposes a "vertical-lateral, dynamic-static, multi-factor coupled evaluation framework for oil enrichment potential in strike-slip faults". Based on this framework, a comprehensive evaluation of the oil enrichment potential of major faults in the Halahatang buried hill area was conducted. It was clarified that the NWW-near EW-trending faults in the central and southern parts of the buried hill area are the most favorable oil and gas enrichment zones, and the conjugate NNE and NNW-trending strike-slip fault zones in the eastern part are relatively favorable zones. The proposed evaluation framework improves the evaluation concept of oil enrichment potential in areas developed with strike-slip faults, and it has demonstration and referential significance for achieving breakthroughs in hydrocarbon exploration in strike-slip fault belts within petroliferous basins.