Integrated reservoir Modeling and reservoir Characterization to optimize production and ultimate recovery for the complex reservoir in the coastal basin of Mauritania

Abstract

Naturally fractured reservoirs are inherently heterogeneous and anisotropic due to faulting and tectonic complexity, which makes reservoir characterization highly challenging. Additionally, these reservoirs deplete quickly, causing exacerbated productivity decline over time. Fracture modeling is therefore a key development issue for naturally fractured reservoirs and requires an integrated approach from geology to reservoir simulation and from micro- to field-scale modeling and field planning. Moreover, as fractures are below the limit of seismic resolution, the static fractures models are mainly constrained by borehole data (i.e., core images or image logs) using conventional structural geology techniques. Due to the importance of the Mauritania, Senegal, Gambia, Guinea-Bissau, and Guinea-Conakry basin (MSGBC basin) in the offshore of West Africa MSGBC basin, which was developed as a tectonically developed basin, including the naturally fractured Chinguetti oil field, and to address these challenges, a comprehensive approach has been proposed, including detailed statistical analyses for the fractures, identifying the fractures’ trends, and correlating them with the geological and production data. Following the production decline of the Chinguetti oil field, primarily driven by pressure depletion, no other Miocene reservoirs in the region despite significant resources such as the Tiof field (~288 MMbbl, nearly twice Chinguetti) have been effectively developed, largely due to severe Chinguetti reservoir compartmentalization. Fracture models were developed to predict and characterize the various fracture sets, their 3D spatial distribution, and their impact on the reservoir behavior. The Chinguetti field’s production history illustrates the technical and operational challenges of managing a compartmentalized turbidite reservoir in a deepwater environment. It stands as a valuable case study in adaptive reservoir management, waterflood optimization, and probabilistic development planning in structurally complex offshore settings. The results demonstrate that structurally induced heterogeneities lead to hydraulic isolation, multiple fluid contacts, and inefficient pressure support, ultimately controlling production performance and contributing to early decline in the field. Production peaked at 75,000 BOPD shortly after start up and declined rapidly during the initial months, before stabilising to a gradual decline from June 2006. The field has underperformed since start up, with the reservoir more complex than originally thought. Production has also been affected by operational issues. The applied secondary recovery strategies include water and gas injection from five injection wells along with five producing wells, which are highly recommended to maintain the reservoir pressure. These scenarios may be extended to further offshore fields in West Africa and elsewhere.