Acid stimulation and scale squeezing are generally well-established hydraulic well intervention practices,rnalthough methods for delivering such treatments specifically to deepwater, subsea wells are a less maturernarea of application. A rig-less intervention alternative provides a more economic option for interveningrnon subsea wells, in comparison to traditional rig-based methods. This technical paper describes thernplanning and execution of a multi-service vessel (MSV)-based hydraulic intervention campaign atrnChevron’s Tahiti field in the U.S. Gulf of Mexico.rnChallenged with early-life well productivity decline and imminent injected seawater breakthrough, thernTahiti asset formed a multi-disciplinary team to develop a fit-for-purpose solution to remediate andrnmitigate these concerns. Acid stimulation was selected to arrest and recover well productivity, while scalernsqueezing was required for protection against barium sulfate scaling from the mixing of formation waterrnand injected seawater. These treatments were to be delivered to subsea production wells in water depthsrnof ~4,200 ft.rnThe design basis of this hydraulic intervention system involved dual, open-water coiled tubing stringsrndeployed from the MSV to a subsea stimulation module. This module is landed and secured subsea on arnmodified suction pile, allowing structural isolation from the horizontal subsea production trees. In turn,rna flexible jumper from this module to a valve package and modified choke insert on the tree enabledrnaccess to the wellbore for delivery of the treatments. De-coupling the stimulation module from the treerninterface alleviated the risk and complexity of removing crown plugs and imparting load forces on therntree, and denotes the ‘hybrid’ nature of the system.rnDesign and operational phases required overcoming challenges such as coiled tubing fatigue management,rnunexpected loop current conditions, and deployment sequence optimization. Given the first-timerndeployment of this hybrid system, detailed front-end engineering and design was required for validationrnof an enhanced well control and emergency disconnect system, to accommodate safe execution. Thern5-well campaign was executed incident-free during 2015, delivering a total treatment volume of almostrn30,000 bbls, resulting in 8,500 BOPD gross initial production uplift, and cost savings of 85% inrncomparison to traditional rig-based methods.
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