Field X is a mature offshore field in the Niger Delta. In 2013, several wells in field X experienced significant production decline and a study conducted by cross-functional team identified fines migration as the primary cause of sandface impairment and acid stimulation was recommended as remediation for the damage. This technical work highlights the strategies and methodology adopted in implementing acid stimulation in field X.

The approach to candidate selection involved screening of historical well test data and pressure transient analyses (PTA) database for impaired/at-risk completions. Typical selection criteria are productivity index (PI) degradation (> 50%), pressure drop due to near wellbore skin (DP skin >500psi), violation of flux constraint, Interval Control Valve (ICV) integrity (dual completion) and water-cut evolution (<5.0%). The team also piloted diversion agents in the field to improve stimulation in wells with high water-cut. A novel method of using dynamic positioning marine vessel with Remotely Operated Vehicle (ROV) and customized dual conduit Coil Tubing (CT) have been deployed to bullhead acid into the formation.

In the last two campaigns executed in 2020 & 2021, this ingenious way of harnessing value from field X has resulted to combined incremental Initial Production (IP) gain of approximately 10,000 bopd and safeguarded completion of a critical oil producer (~11,000 bopd). The total project cost for the two campaigns was ~$25.4 million resulting in significant cost savings (>$51.6 million) compared to rig operations. The use of cross-functional team, robust candidate selection, continuous lookback and adoption of best practices were critical to successful execution. Some challenges being experienced in the field are lack of adequate injectivity, formation lock-up, increasing gas oil ratio (GOR) and increasing water-cut. The team plans to deploy diverters across additional high water-cut wells in future campaigns.

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