The Characteristics of the Layer‐Bound Faults and Their Effects on the Ordovician Fracture‐Cavity Reservoirs in Tahe Area of the Tarim Basin

ABSTRACT In the Lower‐Middle Ordovician strata of the Tahe area, Tarim Basin, faults of different scales and phases play a crucial role in the development of karst reservoirs in the Yingshan Formation. While numerous studies have focused on the controlling effects of faults on karst reservoirs in the Tarim Basin, the characteristics of lower‐order strike‐slip faults within the Ordovician and their specific control over fracture‐cavity reservoirs have rarely been discussed. Based on seismic profile and outcrop interpretation, this study finds that Ordovician lower‐order strike‐slip faults exhibit layer‐bound characteristics and are associated with the development of karst cavities. These layer‐bound faults, to some extent, control the distribution of the fracture‐cavity systems. Consequently, this paper first delineates the distribution characteristics of layer‐bound faults within the Ordovician seismic stratigraphic framework of the Tahe area. By analysing 3D seismic data and outcrop profiles, the layer‐bound fault interpretation model is finely characterised, introducing the concepts of mechanical interfaces and mechanical units to establish a model for layer‐bound faults in Ordovician carbonate rocks. Subsequently, by investigating the characteristics of the fracture‐cavity systems, the relationship between layer‐bound faults and these systems is elaborated, the controlling effect of layer‐bound faults on fracture‐cavity reservoirs is discussed and a development model for such reservoirs under the influence of layer‐bound faults is established. The controlling effects are primarily manifested in three aspects: Firstly, layer‐bound faults are extensively developed within induced fracture zones, which coincide with favourable development areas for fracture‐cavity reservoirs. Secondly, the distribution trends of layer‐bound faults and fracture‐cavity reservoirs are generally consistent, indicating a degree of control over the spatial distribution of the fracture‐cavity systems. Thirdly, in areas where layer‐bound faults develop, they act as fluid conduits, enhancing dissolution processes and consequently promoting the development of fracture‐cavity reservoirs. This demonstrates that layer‐bound faults, functioning as conduits and local barriers for subsurface fluids within the strata, play a significant role in the development of fracture‐cavity reservoirs. These findings provide certain guidance for the exploration and development of carbonate ‘fault‐karst reservoirs’ in the Tahe area.