Method and application for ultra-deep carbonate reservoir quality evaluation: A case study of the Well X area in the Fuman Oilfield, Tarim Basin, China

The Ordovician ultra-deep carbonate reservoirs in the Tarim Basin are rich in oil and gas resources. However, due to the influence of multiple periods of tectonic activity, their distribution shows strong heterogeneity. In regions characterized by fault-controlled fractures and caves, traditional reservoir quality evaluation methods based on physical property parameters are subject to considerable uncertainty. In contrast, methods incorporating geomechanical parameters show notable advantages. In this study, geomechanical parameters—such as present-day in-situ stress, elastic modulus, and natural fracture density—were quantitatively characterized. A geological model of the carbonate fracture-cavity system was established, and a reservoir quality evaluation factor was defined and calculated to enable a quantitative evaluation of ultra-deep carbonate reservoir quality. The results indicate that: (1) In fault-controlled fracture-cavity ultra-deep carbonate reservoirs, the spatial distribution of geomechanical parameters has strong heterogeneity and significantly affected by fault structure. This distribution is segmented along the fault extension direction. Both the elastic modulus and natural fracture density indicate elevated values near fault zones, while present-day in-situ stresses are relatively lower in these areas. (2) Reservoir geomechanical parameters are strongly responsive to the structural and geological characteristics of fault-controlled fracture-cavity carbonate oil and gas reservoirs. The proposed evaluation methods are effective in evaluating reservoir quality and provide a valuable geological reference and support for the efficient exploration and profitable development of fault-controlled fracture-cavity ultra-deep carbonate reservoirs.