Unlocking Potential: Re-Accessing Left-Behind Potential in GS365 Field GoS, Egypt: Navigating Through Challenging Historical Data, Compositional Gradient Reservoir, Multi-Layer Stacked Reservoir, and Complex Structure Setting

Abstract GS365 oil field sits in the southern Gulf of Suez faced significant challenges in development plan: limited historical data, restricted accessibility, and single mudline producer from thin oil rim overlain by a sizeable gas cap. This presented challenges for both geological and reservoir engineering teams, including defining reservoir geobodies, estimating fluid contacts, optimizing well spacing, infill drilling, and maximizing recovery. Well engineering faced the additional challenge of managing gas cusping and maximizing reserves through trajectory and perforation design. To overcome these challenges, this study employed a comprehensive approach integrating static and dynamic reservoir modeling. Key uncertainties addressed included reservoir pressure, fluid contacts, reservoir quality variations, and aquifer description. Lack of dynamic data due to limited accessibility necessitated utilizing surface parameters like wellhead pressures and temperature as model control points. Production uncertainties from limited surveillance data were addressed through historical data analysis, Prosper modeling, fluid characterization and PLT interpretation. A 3D model was built and history matched to refine the estimated oil initially in place (STOIIP) range. This integrated approach yielded valuable insights for infill drilling and optimizing target location selection to manage uncertainties. A slanted well design was chosen to maximize reservoir contact and minimize gas cusping while maintaining low drawdown pressure. Post-drilling results exceeded expectations: encountered pressures were on the high side, and new sands with virgin pressure were discovered, indicating untapped potential in the reservoir of interest. Revisiting the initial gas-oil contact (GOC) with updated pressure data and detailed fluid characterization revealed a shallower GOC by +100 ft, leading to an increase in STOIIP estimates. Accessing the shallower reservoirs was as prognosis, highlighting its importance in field development and potentially influencing future infill well strategies. This study demonstrates the successful reviving of untapped potential in mature field through a data-driven approach addressing uncertainties in historical data, reservoir characterization, production performance, and pressure assessment. By integrating deep analysis, 3D simulation modeling, and cross-checking with analytical methods, this study validates the effectiveness of the applied methodologies and strategies. This approach offers valuable insights for maximizing recovery from similar challenging reservoirs, contributing to long-term production sustainability in aging fields.