Substantial buildup of CaSO4 and CaCO3 scales downhole contributed to a loss of 10,000 BOPD and the shut-in of 12 of the 70 wells in a Middle East field. The mineral encrustation occurred on electrical submersible pumps (ESPs), motors, and throughout the entire downstream production systems. The root cause was identified to result from water injection of sulfate-containing seawater into calcium-rich formation waters of Burgan and Mauddud reservoirs. This paper presents a case history from scale prediction and laboratory evaluations to the squeeze intervention to demonstrate how an effective scale treatment strategy was set up and implemented.
To mitigate the risk of scale deposition during production, a scale inhibitor squeeze treatment was designed and implemented in the field. The design process started with a comprehensive field survey conducted by a field-experienced technologist. Scaling risks were assessed using water chemistries not only from Upper and Lower Burgan and Mauddud reservoirs, but also under all mixing scenarios with seawater. The systematic performance, fluid compatibility, and stability testing were conducted to formulate a cost-effective, custom scale inhibitor that considered the water chemistry and conditions of the specific horizontal well. A collaborative effort between the chemical supplier and coiled-tubing team engineered an effective application procedure to minimize the loss of squeeze fluid due to refilling in the annulus and to deliver the scale inhibitor to targeted zones. This application technique maximized the effectiveness and lifetime of the squeeze treatment.
The approach to squeeze treatment design combines extensive field experience and application engineering with custom, cost-effective chemistry to meet well-defined key performance indicators (KPIs). In this case, the product candidate demonstrated a superior minimum effective concentration (MEC) of 5 ppm, as determined by dynamic loop tests and static bottle tests, as well as a full range of brine compatibility at any given mixing condition in the reservoirs. Once the intervention was executed, continuous monitoring of the squeeze application demonstrated that the inhibitor residual concentration in the produced brine remained above MEC for ten months, effectively inhibiting scale during that period. A 55% increase in the treatment lifetime was achieved relative to the target of 180 days while recovering the oil production rate of the well, resulting in an increase of 1,000 BOPD. A revisit to the field confirmed that the scale treatment was effective and found no sign of scale deposition in the previous well locations. Modelling simulation was performed before the intervention and matched the field operation results. Future treatment design was also optimized.
The squeeze treatment was carried out for the first time in the field with significant cost savings for the operator in comparison to the previous frequent chemical interventions for the wells involved.