Fine characterization of internal structure of typical fault-fracture reservoir outcrops in Xunyi area, Ordos Basin

The fault-fracture reservoirs in southern Ordos Basin are characterized by large reserves, high oil abundance, and promising development prospects. However, their internal structures are complex and variable, and existing research cannot adequately support fine characterization of these fault-fracture reservoirs. ObjectiveTo clarify the variation rules of the internal structural characteristics of fault-fracture reservoirs and construct a detailed model of fault-fracture reservoir development, Methodsthis study employed unmanned aerial vehicle (UAV) oblique photography technology for high-precision sampling and modeling of typical fault-fracture reservoir outcrops in Xunyi area. The self-developed software was used to collect and analyze the three-dimensional data from fault-fracture reservoirs, enabling a deeper investigation into their internal structural characteristics and fault-fracture development rules. ResultsThe results showed that: (1) Three types of fault-fracture reservoirs were developed in Xunyi area, namely transtensional type (half-negative flower pattern, graben pattern), pure strike-slip type (closed translational pattern), and compressional-transpressional type (horst pattern). (2) Based on comprehensive parameters such as fault development, rock stratum morphology, and fracture development characteristics of field outcrops, fault-fracture reservoirs were classified into sliding breaking zones, induced fracture zones, and substrate zones. The structural models and quantitative rules of different fault-fracture reservoirs exhibited significant differences, with only fault-fracture reservoirs with the half-negative flower pattern and graben pattern developing wide sliding breaking zones. (3) The fracture density was influenced by the fault-fracture reservoir type, fault separation, fault spacing, fault block location, and sand layer thickness. In general, the highest fracture density was observed in the fault-fracture reservoirs with graben pattern, followed by the fault-fracture reservoirs with half-negative flower pattern, while the lowest density was found in the fault-fracture reservoirs with closed translational and horst patterns. The fracture development increased with larger fault separation, smaller fault spacing, and thinner rock strata. Within the same fault-fracture reservoir, fracture density varied across different fault blocks. ConclusionThis study identifies the models and corresponding quantitative rules of fault-fracture reservoirs with four patterns, summarizes the effects of various factors on fracture density, and provides more geologically accurate quantitative structural characteristics of fault-fracture reservoirs for underground reservoir characterization.