New Field Simulation Strategy With Detailed Element Models and Flux Boundary Conditions: Statfjord Field Case Study

Abstract

SPE Members Abstract Full field reservoir simulation has been adequate for reservoir management purposes for more than a decade long production history of the Statfjord Field in the North Sea. At the present stage, the beginning of production decline, the simulation strategy needs to be changed. A full field model would be unmanageably large if the geological detail needed to understand the issues relevant to further recovery enhancement is included. Most of the remaining reserves will be recovered by sidetracking and infill drilling. The remaining oil has then to be mapped carefully using both the geological information obtained during these years together with a reliable history matching. In this paper, a methodology has been developed for history matching regions with very detailed geology, while taking into account the interaction with the whole reservoir. The method involves writing to a history file the fluxes between the cells at the boundaries of the regions of interest and the rest of the reservoir. This methodology has been tested for the Statfjord Field. The CPU-time was reduced by 35 percent compared to a conventional method. The insights obtained were achieved in a shorter time. The fluid flow processes are better represented and the reservoir description obtained is more representative. Furthermore, the element model is now run in prediction mode as a tool for reservoir management and planning well activities. Thus a new simulation strategy, based on history matched, geologically detailed element models and preserving the interaction with the whole reservoir, has been proved useful. Introduction The Statfjord Field has produced oil for a period of 11 years with three offshore platforms, called A, B and C, draining the middle, southern and northern parts of the field. A full field reservoir simulation model have been found adequate for reservoir management purposes in this period. The Statfjord Field consists of three separate reservoirs : Upper Brent, Lower Brent and Statfjord. The Brent reservoirs are produced by water flooding, while the Statfjord reservoir is produced by miscible gas flooding. At the present stage, when the majority of the wells have experienced either gas or water breakthrough, the simulation strategy needs to be changed. The remaining reserves in the field will to a great extent be recovered by side tracks and infill drilling in the future. An important issue is therefore to map the remaining oil and evaluate different strategies to recover these reserves. When a field is on production decline, detailed models are necessary to do reservoir management, evaluate and determine optimized well activities on the field to maximize the production. The new simulation strategy will be to use more detailed element models where a detailed reservoir description can be implemented. P. 51^