Utilizing Chelating Agent System Fluid to Remove Scale Buildup from Stuck ESP Shaft in Offshore Saudi Arabia

Abstract Saudi Aramco’s first offshore field produced by electrical submersible pumps (ESPs) has completed a nine year operating cycle, sustaining the field production rate with an acceptable ESP run life in most cases. Recently, a well in this field has experienced a stuck pump shaft shortly after installation. In the past, similar failures in the same well had led to ESP replacement through workover operations. To avoid the same outcome, an effort was initiated to regain operation of the ESP stuck shaft, and realize the production target without a workover. After the first failure, a scaling tendency analysis exhibited this well to have tendency for carbonate scaling. The Dismantle Inspection and Failure Analysis (DIFA) and laboratory testing of samples taken from the pump stages confirmed the presence of predominantly calcium carbonate scale. The impellers and diffusers of the ESP pump were discovered to be totally blocked with solid precipitation, which had been the cause of frequent pump trips and decreasing production rate. Using parts from the third failed ESP, a chelating-agent-based treatment fluid was designed to dissolve the scale buildup in the stuck ESP shaft without adversely affecting the tubular and downhole equipment. After the treatment, to avoid the reoccurrence of pump failure, scaling indices and thermodynamics of the scale precipitation tendency of the formation water associated with its crude stream were studied. Results indicated that scale inhibitors, such as polyacrylic acid (PAA) or polyphosphinocarboxylic acid (PPCA), bullheaded into the formation may be used to control scale in this well in the future. With a stuck pump shaft, this well would normally have been worked over to replace the ESP, thereby consuming 10 days of rig time and sustaining potentially avoidable production losses. The goal of the project was to remove the scale accumulation, regain operation of the stuck ESP shaft, and reestablish the production of 5 MBOD. Consequently, a costly workover was avoided and the life of the ESP was increased without compromising the completion. The successful treatment for this stuck ESP shaft, which was carried out by bullheading the treatment fluid is a reference treatment design for similar cases. The history of the well, laboratory studies, and recommendations to avoid scale precipitation in the future are detailed.