An Integrated Approach To Efficiently Unlock the Resource Potential in a Large Cluster of Fields

Abstract

An integrated study on a cluster of 23 fields in South Oman was performed in the Petroleum Development Oman (PDO) Study Center, in order to derive a coherent view on the cluster development as well as to write (waterflood) FPDs for the individual fields. The study combined conventional and state-of-the-art workflows and was conducted by a large integrated team over a period of three years. The study was conducted in four phases: screening, full field modelling, infra-structure development and FDPs for the 6 large fields and the writing of appraisal / development plans for the remaining 17 fields. This paper describes the workflow and learnings of the study. Introduction The cluster of fields in South Oman holds a significant near-term growth potential through active waterflood implementation and later, through polymer flood recovery (Fig.1). The cluster development strategy addresses 23 clastic fields with a significant STOIIP base. A large integrated team of PE staff have spent 3 years to address and progress the major fields therein to FDP. The Cluster consists of green and brown fields characterised by high gross liquid production, rapid watercut development (>80%), variable well performance and marked pressure decline. The fields are medium to small salt withdrawal-related structures often with stacked reservoirs, varying oil quality (7–400cP) and low to medium fault density. To date, only a small percentage of the STOIIP has been recovered. This marks the cluster with high development potential for large-scale waterflood. The study was undertaken to support further development decisions, to identify the value of remaining reserves including growth and SFR opportunities and to create life cycle development plans. Key challenges to unlock the value of the cluster was to provide a clear scope maturation plan for each field by understanding surface and subsurface controls leading up to a development concept selection and culminating later with the roll out of 23 field development plans. The study started in Oct 2003 and by end 2005 delivered 6 value-assured FDPs for the large fields in Phase 1 covering 2/3rd of STOIIP. The remaining satellite fields were pursued in Phase 2, and delivered 17 FDP's by the end of 2006 covering the remaining 1/3rd of STOIIP. For evaluation of capital intensive waterflood developments the operating asset team required that the subsurface models be robust with relatively long shelf life. Workflows and synergies were built across the asset-study team interface, to not only deliver quality FDPs but also through embedment, ensuring successful execution. Fig.2 shows the cluster study work flow. The study clearly demonstrates that a blend of conventional methodology and state-of-the-art stochastic techniques can efficiently model waterflood behaviour. The Screening Phase In the early stage of the study it was essential first to get a high level overview of the fields and their underlying uncertainties in order to focus more in-depth work at the subsequent stages of the project. Some of the fields had been studied in the years before, but these studies were performed by different teams, at a different maturity level of the fields and with different objectives. The current study provided the first cluster wide attempt for development planning. A multi-disciplinary effort went into the screening phase to help identify data gaps and formulate clear appraisal strategies. This was built upon the following steps: Seismology: Existing seismic interpretations were inventorised and QC'd. Obvious problems and inconsistencies were fixed and a first pass estimate of the top structure map uncertainty was provided for all fields.