Slickline Descaling Technology Delivers Cost Savings Over Coiled Tubing

Abstract

Al-Khafji Joint Operations (KJO), a joint operation representing both Saudi and Kuwaiti energy interests in the divided zone, recently encountered obstructions in their offshore field. Routine pressure and temperature surveys revealed that an increasing number of wells were developing scale. The operation required an efficient mechanical tool to clean out extensive accumulated scale bridging within a vertical production string and restore full wellbore accessibility. The well had been previously shut down from operations for five years. The operator considered using a coiled tubing (CT) unit or workover rig to clear the scale but sought a more cost-effective solution. The operator chose a slickline wellbore cleanup and debris breaking tool, which is an impact-driven tool designed to break up scale deposits in a cost-effective, efficient manner. It is jarred down mechanically in the well, each jar applying a short-duration torque via the unique, helically split torque sub. The well's accessible tubing inner diameter was reduced from 2.9-in, nominal to 2-in, at the wireline reentry guide depth. To combat this issue, the slickline technology was deployed with subs increasing in outer diameter (OD) from 1.9-in. to 2.5-in. OD tools. The special features of the wellbore cleanup and debris breaking tool made it better adapted to the well environment and greatly increased the descaling efficiency. Thirty runs enabled the team to clear the scale accumulations down to 3,652 ft (1113 m). The operator confirmed integrity of the tubing at the end of the slickline operation, allowing the slickline team to access the wellbore and run a memory pressure temperature survey to check the well deliverability. The implementation of the wellbore cleanup and debris breaking tool enabled the operator to reduce inventory and overall descaling time. Microscopic and Fourier transform infrared analyses of the scale determined it was calcite (CaCO3) with some small hydrocarbon impurities from either oil or diesel. The descaling rate and cost savings achieved using the wellbore cleanup and debris breaking tool has since resulted in the operator adopting this technology and looking into the feasibility of starting a campaign for scale removal in more than 20 wells. The presence of calcite as a scaling agent is potentially due to the carbonate-saturated formation water and the loss of carbon dioxide from this water to the hydrocarbon phase as pressure decreases. Creating a detailed reservoir characterization that defines fracture orientation, relative aperture produced fluid analysis, and rock properties can help minimize the effect of scale at an early stage. Continuous well monitoring can lead to early identification of scale and determine the need for chemical treatment or further mechanical interventions. This case study demonstrates the benefits of using this wellbore cleanup and debris breaking tool as the first method of mechanical descaling.