TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractExxonMobil has developed two novel reservoir stimulation technologies that enable the rapid delivery of numerous highquality stimulation treatments within a single cased wellbore. These technologies were developed for the purpose of improving, or enabling, economic hydrocarbon recovery from formations that contain multiple stacked reservoir intervals or require the stimulation of long productive intervals. These technologies: (1) enable the stimulation of multiple target zones via a single deployment of downhole equipment; (2) enable selective placement of each stimulation treatment so that they may be designed specifically for each individual zone to maximize well productivity; (3) provide positive isolation between zones to ensure each zone is treated per design and previously treated zones are not inadvertently damaged; and (4) allow for treatments to be pumped at high flow rates to facilitate efficient and effective stimulation.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractExxonMobil has developed two novel reservoir stimulation technologies that enable the rapid delivery of numerous highquality stimulation treatments within a single cased wellbore. These technologies were developed for the purpose of improving, or enabling, economic hydrocarbon recovery from formations that contain multiple stacked reservoir intervals or require the stimulation of long productive intervals. These technologies: (1) enable the stimulation of multiple target zones via a single deployment of downhole equipment; (2) enable selective placement of each stimulation treatment so that they may be designed specifically for each individual zone to maximize well productivity; (3) provide positive isolation between zones to ensure each zone is treated per design and previously treated zones are not inadvertently damaged; and (4) allow for treatments to be pumped at high flow rates to facilitate efficient and effective stimulation.
Effective management of subsea assets requires diligent focus on key performance areas such as productivity improvement, hydrocarbon recovery efficiency, production preservation, and well integrity. Common to all of these key areas is a need to perform periodic interventions on the asset's subsea wells to carry out performance-critical work, e.g., well servicing/repair, production enhancement, reserve additions, and surveillance. Well intervention services on subsea wells have been conventionally performed using large and expensive Mobile Offshore Drilling Units (MODUs). In the North Sea, ship-based light well intervention (LWI) services offer a lower cost solution to conventional MODU based intervention services by using dynamic positioning over the wells and deploying a subsea BOP stack plus fixed-length lubricator that connects as a selfcontained unit to the subsea tree. Tools are conveyed on wireline/slickline from the vessel through the open sea into the selfcontained subsea lubricator/BOP stack. While these LWI services are lower cost, there are more physical and functional limitations that can result in additional technical challenges. One such challenge was encountered when ExxonMobil was evaluating its first LWI on a 5–1/8" x 2" spool/horizontal tree. The target was to pressure test the full TRT/BOP/lubricator stack-up, deploy the pressure tested system as a single unit, and establish hydraulic control of the tree such that separate emergency disconnect devices were not required beyond what was integral to the vessel's proven BOP/lubricator equipment. To achieve this end, ExxonMobil performed quantitative risk analysis on three viable equipment stack-up configurations to determine the safest and lowest cost approach for connecting to its spool/horizontal tree while honoring the 44 ton lifting limits of the particular LWI vessel. The results of this analysis showed that the equipment configuration that was statistically the safest was also the simplest and lowest cost option. Based on the analysis, ExxonMobil modified an 18–3/4" hub style connector for connection between the subsea tree and the vessel's BOP/lubricator and developed a flying stab plate deployment approach, with umbilical slack management, to facilitate stabplate make-up for hydraulic tree control from the vessel. The flying stabplate umbilical leveraged the vessel's BOP/lubricator emergency disconnect to further simplify the system and improve safety. The system has been used twice since development and both deployments were successful. Introduction ExxonMobil Production Company's UK affiliate in the North Sea, Mobil North Sea LLC (MNSL), operates both platform and subsea wells in the Beryl development area. The Beryl Field is located in Block 9/13a of the UK Sector of the North Sea approximately 185 miles (300 km) north-east of Aberdeen. The field was discovered in May 1972, and oil production began in June 1976. The Beryl area includes two manned platforms (Beryl Alpha and Beryl Bravo), two not normally manned Single Point Moorings, and a number of subsea clusters/wells (see Figure 1). The satellite developments shown in Figure 1 are comprised of a mixture of spool/horizontal trees and dual-bore/vertical trees that are tied back to the platforms for gas-lift supply, water injection, and hydrocarbon production. Approximately 40% of the subsea trees are spool/horizontal trees and 60% are dual-bore/vertical trees. Water depths typically range between 350–400 feet with an average reservoir depth of 11,000 feet. The subsea assets currently have 21 active producers that contribute approximately half of the Beryl area production.
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