Identifying Additional Opportunities From a Mature Oil Reservoir Having Significant Production Challenges
Authors: Alsane A. , Al-bahar M. A. , Thakuria C. , Dhote P. , Bora A. , Dharanidharan B. , Nalla G. , Koyassan Veedu F. 
Published: January 2023

The paper describes the challenging task of identifying additional production opportunities from a matured oil reservoir with significant production history, commingled production,zones with varying rock properties, and drive mechanisms. The reservoir is having more than 40 years of production history and is currently in a stage of decliningoil production with water breakthroughs in many areas of the reservoir.

A new, improved workflow comprisinga classical approach and sector model review wasapplied to understand the recovery efficiency and identify any additional potentials on top of the base profile. The study resultsprovidedan interesting insight into the recovery mechanism and possible additional opportunities in the reservoir. Several recovery ideas like identifying undrained areas, improved completion strategy, the intervention of existing sick wells, and application of EOR processes were applied to estimate the improvementof recovery over the existing field development plan.

All components of recovery efficiencies like pore-scale displacement (Ep), drainage (Ed), volumetric sweep (Es), and cut-off (Ec) were reviewed, and the scope for improvement was identified using sector models of the reservoir. The next stage was a fully integrated reservoir study to diagnose the ongoing water flood process and examine strategies to improve areal and verticalsweep. Significant reservoir insights were gained from detailed water influx and reservoir pressure maps and identifying bypassed oil by zone. The last stage was constructing a representative sector model incorporating the latest data for IOR and EOR, which were screened based on the economics criteria. The number of recovery options was evaluated and optimized in the reservoir sector model to select potential opportunities and estimate incremental recovery.

Four opportunities were identified that show incremental recovery by improvements in Ep, Ed, and Es for each reservoir zones. The target areas with bypassed oil have been identified for improvement in Ed and Es. Changing from commingled to dedicated completions in a specific shallow, relatively less depleted zone show improvement in Es. Implementing a regular 5-spot pattern water flood instead of random spot water injection in a major shallow zone improves Ed and Es. Lastly, Alkaline Surfactant Polymer (ASP) flooding improves Ep. A detailed roadmap was generated for each recovery option. New polymer-based gels such as preformed particle gels (PPGs), microgels, swelling micron-sized polymers (Bright Water), and pH-sensitive polymers were recommended to mitigate excess water production due to wellbore and reservoir-related challenges. This workflow identified a significant improvement in expected ultimate recovery (EUR) in the mature brownfield and will be applied to other reservoirs in the KOC portfolio.

The novelty of the work is an innovative approach to characterizing the existing recovery plan into its underlying efficiencies (Ep, Ed, Es, Ee) and a detailed breakdown of the recovery factor, which led to practical guidance on implementing recovery ideas to improve recovery from the mature oil reservoir.