Reservoir Management at Dunlin

Abstract

Summary Dunlin field in the U.K. North Sea has been developed using reservoir simulation as a valuable tool in optimizing its exploitation. Simulation studies have been applied routinely to evaluate alternate development plans as well as to help understand the complex fluid movements in the reservoir. The paper presents examples of these applications. Introduction The Dunlin field, located in the northern North Sea, is owned jointly by Shell U.K. Exploration and Production, Esso Exploration and Production U.K., British Natl. Oil Corp., Gulf Oil Corp., and Conoco (U.K.) Ltd., and is operated by Shell. Since discovery in 1973, the field has been the subject of a flexible and continuously adaptable development plan. The initial plan was based on limited reservoir description from only a few wells and relatively widespread seismic data. Recognizing the limitations of the data, the development plan called for updating and improving the reservoir description as part of the initial steps of field development. The data from this early development needed rigorous evaluation to produce a final plan near optimum. One of the tools that has been very useful both in the data evaluation phase and the optimization phase of reservoir management is reservoir simulation. This paper includes major results of some of Esso E and P U.K. simulation studies of the Dunlin reservoir. Water encroachment into the highly stratified Brent (Middle Jurassic) reservoir can be understood best in terms of simulation studies. The extent and effect of restrictions to vertical flow in the reservoir are difficult to predict from geological studies, but use of history matching by reservoir simulation can quantify the hydraulic effect of these restrictions. The model then can become a useful tool on which to base management decisions for field development. The Esso reservoir simulation program has been used successfully to match the pressure and water cut performance at Dunlin. The cross-sectional model developed for the Main Fault Block at Dunlin has been used to understand how to manage the field effectively. Background Reservoir simulation has proved a valuable tool in management of the Dunlin reservoir. Dunlin, like other North Sea Viking Graben fields, presents a challenge to the reservoir manager trying to optimize field development and operation. The fields are, without exception, highly faulted and geologically complex. They require very large initial capital investment, which must be optimized relative to the development of the reservoir. Reservoir simulation enables the engineer to try out various development schemes before commitment to install a platform. It also can assess the sensitivity of the ultimate recovery to various unknowns in the early reservoir description. Ultimately, the simulation model can become an operational tool, regularly updated, to help understand the complexities of fluid movement within the reservoir. This paper addresses Esso's experience in evaluations of the Dunlin field development as an example of the use of reservoir simulation both for development planning and as a working tool in reservoir management. These studies have been undertaken by Esso to assist in decisions regarding the Dunlin Unit. JPT P. 227^