Modelling Challenges of a Low Permeability Clastic Reservoir – A Case Study from the Ravn Oil Field Offshore Denmark

Abstract

Wintershall took on the challenge and developed a low permeable Upper Jurassic oil reservoir in the Greater Ravn Area offshore Denmark. A new depositional model was created based on core studies and the results of two hydraulically stimulated horizontal production wells. The reservoir consists of very fine to coarser grained storm-influenced lower shoreface sediments. Intervals of conglomerates within the background shoreface deposits appear to be mainly matrix supported, but occasionally also clast supported. The reservoir quality is controlled by the matrix grain size, which has a major impact on permeability, but to a lesser extent on porosity. Increasing matrix grain size enhances the permeability. Conglomerates are therefore not indicative for the reservoir quality. Predicting and modelling the occurrence and distribution of the coarser grained matrix with the better reservoir quality as sheet-like deposits is essential. An updated static model has been created and used for dynamic simulation, history matching and production forecasts. The production wells proved producibility with initial flow rates better than predicted. Long term production behavior is essential to decide on the overall potential for further development of the Greater Ravn Area.