Coil Tubing Fill Cleanout and Near-Wellbore Acidizing of Plugged Stand Alone Screens: Highly Successful Campaign in Saudi Arabian Gas Wells

Abstract

Gas wells in Field X, south of the giant Ghawar Field, are completed with stand alone screens across a Pre-Khuff sandstone formation as a sand control measure. Although prolific producers, some suffer a severe decline in performance after a period of production, triggering diagnostic work to be performed. Consequently, screen plugging is confirmed and collected samples of present fill are analyzed. Results called for a coil tubing cleanout campaign in order to restore lost productivity. The objective of this paper is to detail the whole operation journey of the fill cleanout jobs that includes fill diagnostic process, assessment of cleanout methods, initial job design, choice of fluids, CT bottomhole assembly tools, execution and field experience, and post-cleanout performance evaluation. A CT wiper trip method has been implemented with either milling or jetting tools. A newly developed rate-activated circulation valve is deployed to aid in lifting solids at high pumping rates as well as jetting acid across the screen interval after fill removal. The fill cleanout campaign has been very successful in restoring well productivity as compared to pre-cleanout and initial post-drilling well performance. A total of 340 MMSCFD of incremental gas rate were restored to-date from 16 cleanout operations. Unprecedentedly, interesting and valuable findings are shared regarding the nature of fill formed inside and/or above the stand alone screens, recommended milling practices to protect CT bottomhole assembly and minimize CT fatigue, the experience of incorporating acid jetting and squeeze in the CT wiper trip method to stimulate damaged formation pack behind the screens, and the preventive measures taken to cope with the fill accumulation issue.