Integrated API Gravity Tracking and Compositional Grading for Dynamic Reservoir Fluid Contact Monitoring in the Niger Delta

Accurate monitoring of reservoir fluid contacts is critical for effective hydrocarbon recovery and reservoir management, particularly in complex and compartmentalized formations such as those of the Niger Delta Basin. Traditional approaches for determining gas–oil and oil–water contacts, including pressure gradient interpretation and repeat formation testing, are costly and require well shut-ins. This study presents an integrated methodology combining API gravity tracking and compositional grading as cost-effective alternatives for monitoring reservoir fluid contact movement. The research incorporates well log interpretation, PVT laboratory data, compositional reservoir simulation (ECLIPSE 100), and comparative analysis with conventional techniques. Results from representative Niger Delta reservoirs show a systematic decrease in API gravity with depth (32° to 28° API between 2,500–2,800 m), confirming gravitational segregation effects. Fields exhibiting higher gas–oil ratios demonstrated improved API values, whereas increasing water cut corresponded with declining API gravity. The integration of compositional grading models with API monitoring provides a thermodynamically consistent and empirically validated workflow for predicting contact migration and improving reserves estimation accuracy. The proposed methodology significantly reduces reliance on costly logging interventions and offers a scalable surveillance solution for both onshore and offshore Niger Delta fields.