Case History: Sand Handling and Hydrocarbon Containment During a Coiled Tubing Cleanout of a Live Deepwater Well

Abstract

Procedures, photographs, diagrams, results and recommendations are shared from an operation to remove sand plugs from a high pressure deepwater well with a failed lower completion. Specific recommendations minimize risk and provide for the safe handling of sand on the surface as the oil passes below bubble point pressure and undergoes rapid expansion. This paper includes photos, diagrams and lessons learned from an operation conducted during the month of December 2011.Removing sand plugs from a live well entails multiple risks. As the hydrocarbon is circulated to surface gas will evolve and expand rapidly, increase the velocity of the mixture and pose the risk of loss of containment due to erosion, especially if sand is entrained within the mixture. Any interruption to surface handling of wellbore fluids and sand creates the risk of stuck coiled tubing. Coiled tubing stuck inside production tubing in a live well would result in an unwelcome and probably difficult fishing job. Literature ReviewA number of papers on coiled tubing cleanouts are provided in the attached references. However none of the papers specifically address the safe handling of sand on surface. SPE 166531 Risks and Mitigations.Risks and mitigations are outlined below. RiskMitigations Flammable Hydrocarbon Gas Equipment layout allowed all liquid flowing out of the well to be contained in pressurized tanks with venting to the production platform vapor recovery unit or flare. Hydrocarbon ContaminationAll liquids were contained in pressurized tanks. The well was maintained hydrostatically overbalanced by use of the coiled tubing choke to keep the well from flowing. Sticking the Coiled TubingMultiple flow paths and redundant equipment minimized the chance of shut-in. The rate of penetration of sand plugs was synchronized with purging of the sand buster.Provisions were made to inject additional liquid (drill water) upstream of anticipated plugging points such as the sand busters. Erosion of Surface Equipment.The well was never allowed to flow, so the maximum rate was dictated by the circulation rate of the coiled tubing. Much of the sand was removed upstream of the bubble point. Multiple vessels allowed for multiple pressure steps. We had multiple spare chokes as well as a complete spare choke manifold (on a standby boat). Damage of CT Pumps by Solids 800 barrels of brine (4 times tubing volume) were on hand to allow us to dispose of used liquids. Extra tanks were provided for settlement of solids for recycle of brine. Planning.The same contractor, Schlumberger, operated the coiled tubing unit and the flow-back equipment. This helped ensure close communication during planning and execution. Bronco provided sand buster equipment and personnel. Emphasis was placed on the need for close communication and coordination. Extra supervisors were hired to ensure the operation went smoothly and folks had adequate rest. Schlumberger modeled flow in the surface equipment to ensure rates would stay below erosive velocities at the planned circulation rates. All con...

Separating Solids First - Design and Operation of the Multiphase Desander

“…The multiphase desander is used in both permanent and temporary applications (Hagemeijer and Jagernath 2003;Peruzzi et al 2013;Dreher et al 2014). Fixed systems integrate the WHD components into the flow scheme just off the wing valve of the choke.…”