An Integrated Reservoir Evaluation Technique for Dual Structure Reservoir Based on Geomorphic Features and Seismic Anisotropy and its Application to Granite Buried Hill Reservoir in Central Africa

Abstract The basement of Bongor Basin in Chad, Central Africa, is composed of Precambrian granite, gneiss and mixed granite. The basin is a tensile basin formed by the Central African shear strike-slip and tensioning effect. Strong overturning exists in the basin and it suffered long-term weathering and denudation during the Paleozoic and Jurassic periods. Core and drilling data show that both pore and fracture reservoirs are developed in the buried hill, and there are great differences in reservoir patterns and development situation among the buried hills, the reservoir is highly heterogeneous, which have great influence on productivity. This method is based on wide-band, wide-azimuth and high-density seismic data. Combined with logging, core analysis, imaging and production data, this paper firstly summarized the development model of buried-hill reservoir, divided favorable reservoir sections of buried-hill vertically and identified types of reservoir voids, secondly integrated with the results of three-dimensional seismic structural characterization of buried-hill, completed the classification of buried hill morphology, and summarized the reservoir development characteristics of different types of buried hill. On the basis of fully considering the formation, influencing factors and preservation conditions of buried-hill reservoirs, the pre-stack and post-stack prediction are combined to carry out classification prediction of pore and fracture reservoir, among which the prediction method of porous reservoir based on buried hill geomorphological characteristics and seismic sensitive parameters is proposed for the first time. Pre-stack OVT fracture prediction based on seismic wave anisotropy of different azimuth has become a hot spot in fracture prediction in recent years. The study result clarified the distribution characteristics of buried-hill pore and fracture reservoirs, improved the prediction accuracy of buried-hill reservoirs, and provided a set of reliable technology for buried-hill exploration in this area. It is also suitable for exploration and evaluation of other reservoirs with similar seismic and geological conditions.