Geological modeling of excellent fracture-vug carbonate reservoirs: A case study of the Ordovician in the northern slope of Tazhong palaeouplift and the southern area of Tabei slope, Tarim Basin, NW China

Abstract

Based on the reservoir characteristics of individual wells, the combined main controlling factor of fracture-vug reservoir and reservoir space synthesized modeling was adopted to establish geological models for the Ordovician reservoirs in the northern slope of the Tazhong palaeouplift and the southern area of the Tabei slope. Geological models for six types of wells were established: (1) cavity + fracture-vug controlled by sequence boundary; (2) cavity + fracture-vug on the top of cavity controlled by fractures; (3) cavity in the surface layer + fracture-vug under the cavity controlled by the sequence boundary and faults; (4) single fracture-vug controlled by the sequence boundary and faults; (5) single vug controlled by deep hydrothermal fluids along faults and fractures; (6) single fracture controlled by faults and fractures. Two types of synthesized geological models were established under the tectonic background of cuesta, namely, platform type slope of the Tazhong area and the gentle slope of the Tabei area. Type 1 and 2 reservoirs are common in the Yijianfang-Yingshan Formation of the HA6-Xinken Region, and type 3 and 5 reservoirs are common in the Yingshan Formation of the ZG8-ZG43 Region. A comprehensive evaluation shows that the reservoir of cavity + fracture-vug on the top of cavity controlled by the sequence boundary is the best, followed by cavity + fracture-vug on the top of cavity controlled by faults. So the areas that meet configuration of cavities and fracture-vugs and single vug controlled by deep hydrothermal fluids along faults and fractures are important targets for exploration and development. Key words: carbonates, fracture-vug reservoir, geological model, main controlling factors, Ordovician, Tazhong-Tabei area