Scale buildup in sour gas is increasing in Saudi Arabia.Clean out with foam,especially for a depleted reservoir,is known and proven as an effective method to solve the problem.With more complex well completion and trajectory,heavier and harder scale materials and high hydrogen sulfide(H2S)content,the foam descaling job encounters more challenging conditions,which apparently create unexpected problems during operation.After several failures,mainly caused by lost circulation and uncontrolled gas(H2S),due to dynamic bottom-hole changes during operation and alternation of foam properties,coiled tubing(CT) foam clean out was suspended for further investigation for almost 3 years. The well subject discussion was selected to relaunch the foam descaling after the suspension period. Completed horizontally with 7 liner,4tubing and 578 open hole,the well was selected to be sidetracked to enhance the productivity on the lower carbonate reservoir.Several gauge cutter runs were performed to check the well accessibility prior to drifting the well with the dummy whipstock and tag above the target depth.The obstruction was suspected to be a thin layer of scale.As the well condition is depleted,descaling using foam is proposed. This paper will discuss the lessons learned from the previous failure and the correction while preparing the foam descaling design and flexibility to overcome dynamic operation on the field.This operation result opens the window to bring back foam clean out as the most efficient option to descaling or clean out in a depleted well.
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