Strategies and Best Practices for Selecting Reservoir Sector Schemes to Manage Offtake in a Waterflood

Abstract

Most reservoirs, especially in carbonate systems, are characterized by heterogeneities in pore systems, permeability, diagenetic imprints, faults and lineaments, fractures, fluid systems and displacement parameters. These variable set of conditions may result in significant differences in in-place volumes as well as life cycle production behavior from different regions of the reservoir when subjected to the same depletion scheme. To guide and control the reservoir life cycle development and management, and to leverage the full benefit of tailoring specific depletion designs suitable for specific areas of the reservoir, the asset owner has instituted a new set of guidelines on reservoir sectorization to govern all operated assets. Reservoir Sectorization could be defined as the process of outlining regions of the reservoir defined by prominent geologic features (structural, stratigraphic, diagenetic, fluid contacts, etc.) that control reservoir and well performance within which production targets can be defined, analyses conducted and surveillance plans designed. A large offshore carbonate reservoir operated by ZADCO, which is the subject of this paper, is impacted in several ways by the aforementioned geological complexities and was deployed as a pilot to test and fully implement the new guidelines on reservoir sectorization. Previously, the existing sector pattern for the candidate reservoir was based on a five-spot flood scheme which is no longer suitable in view of the change to the current field development concept of artificial islands and long MRC wells. Therefore, in addition to compliance with the new guidelines, the key business driver for re-sectorization is to ensure sector geometries that support a line drive system, avoid wells intersecting sector boundaries and provide flexibility to adapt well placement to evolving field development challenges. Advanced integrated workflows (analytical and simulation) were implemented and several sectorization schemes designed (1 or "no" sector, 3 sector, 4 sector, 4 quad, and 5 sector-patterns), assessed and benchmarked against defined criteria for success. Further optimizations through numerous dynamic model sensitivities led to adoption of a particular scheme that best complies with new guidelines on sectorization as well as meet the life cycle production target for the reservoir. This paper highlights the workflows implemented, the challenges encountered and the proposed best practices in working and adopting a reservoir sectorization scheme that best enables sustainable production and maximum recovery within the constraints of the asset owners' guidelines.