Quantitative Evaluation of Hydrocarbon Enrichment Controlled by Strike-Slip Faults in Ultra-Deep Carbonate Reservoirs: Insights from the Shunbei F4 Strike-Slip Fault, Tarim Basin

Ultra-deep carbonate reservoirs are increasingly critical to the global energy supply, representing a major frontier in hydrocarbon exploration. While these reservoirs are predominantly controlled by strike-slip faults, hydrocarbon enrichment exhibits considerable spatial variability along these faults, resulting in persistently high exploration risks in the Tarim Basin, China. This paper proposes a quantitative evaluation framework integrating source connectivity, transport capacity, and reservoir quality of strike-slip faults. This multi-parameter quantitative evaluation of the main controlling factors aims to provide a geological basis and an objective reference for hydrocarbon exploration in ultra-deep carbonate reservoirs within the Shunbei area. Utilizing high-precision 3D seismic data and drilling data from 15 exploration wells along the F4 strike-slip fault in the Shunbei area, we identified five distinct kinematic segment types of the strike-slip fault. Subsequently, a comprehensive characterization of source connectivity, transport capacity, and reservoir quality was achieved based on a series of geological parameters, including stratal deformation intensity, gypsum–salt layer thickness, the average value of gradient structure tensor attributes, and the cross-sectional area of fracture–cavity bodies. Principal component analysis was then employed to integrate these geological parameters into a hydrocarbon enrichment index F, quantifying the synergistic coupling effects of multiple geological factors. The results demonstrate a good positive correlation (R2 = 0.78) between the F index and the normalized daily oil equivalent production of each well. To assess predictive performance, a randomized cross-validation with 10 independent trials was conducted. The blind test sets yielded an average predictive coefficient of determination (Q2) of 0.76 and a mean relative error (MRE) of 9.65%, indicating stable predictive performance without major deviations. The spatial configuration of the fundamental parameters for source connectivity, transport capacity, and reservoir quality ultimately determines the enrichment degree of ultra-deep carbonate reservoirs, which is specifically manifested as differential hydrocarbon enrichment models associated with distinct kinematic segment types. Specifically, the high-enrichment model correlates primarily with offset and flexural pull-apart segments; the medium-enrichment model is associated with the flexural pull-apart, transpressional uplift, and weakly transpressive strike-slip segments; whereas the low-enrichment model is confined to the weakly transpressive strike-slip and pure strike-slip segments. This study elucidates fault-controlled hydrocarbon accumulation mechanisms within ultra-deep carbonate reservoirs, providing novel insights for the predictive exploration and quantitative evaluation of ultra-deep energy resources in the Shunbei area.