Cost reduction of subsea gas production systems using emerging hydrate remediation technology
Henry Sheil A , Peter Young A and Martin Richardson BA Peritus
B Poyry Pty Ltd
The APPEA Journal 51(1) 201-214 https://doi.org/10.1071/AJ10014
Published: 2011
Abstract
Gas flowlines are presenting flow assurance challenges in hydrate management resulting from low ambient seawater temperatures in an increasing number of deepwater developments. When the equilibrium hydrate temperature of the produced fluid is above the minimum seabed temperature, and the hydrate inhibition system fails, there is a risk of hydrate blockage in the subsea system.
The industry-preferred approach for hydrate blockage remediation is dual sided depressurisation (DSD). The objective is to depressurise the flowline below hydrate onset conditions, thus allowing hydrate dissociation and safe disposal of the gas inventory. This is generally performed by one of two methods: installation of a dual flowline system for facility-based depressurisation (CAPEX impact) or by connecting a mobile offshore drilling unit (MODU) to an appropriate wellhead or christmas tree (XT) to allow simultaneous depressurisation at the MODU and the facility (OPEX impact).
It is recognised that both methods incur significant costs. Typically the cost, schedule and availability uncertainties of bringing in a MODU to solve these production stoppages are too high. Consequently, subsea developments often select the increased CAPEX option.
An optimisation of the MODU-based intervention method is the subject of this paper. The feasibility of using a lightweight intervention vessel (e.g. an offshore support vessel) in place of the MODU is investigated. In discussing this optimisation, this paper also presents an introduction to hydrate remediation theory, some practical challenges, case studies and vessel requirements.
Henry has 28 years of oil and gas facilities experience. He has worked for both operating companies and consultants/service providers, initially in the North Sea sector, the in the Asia Pacific region since 1991. His initial professional experience was gained working in oil and gas production and facilities, and gas turbines. He is a generalist practitioner in the area of subsea production systems, with particular interest in subsea trees, control systems, flowline connection systems, flexible flowlines and umbilicals, subsea hydraulic and electrical distribution, and subsea construction and intervention using remote (i.e. diverless) technology. Henry holds a first class honors degree in mechanical engineering from NUI (Dublin) in Ireland, attained Chartered Engineer status in 1988 through the Institution of Engineers of Ireland (C.Eng.MIEI), and graduate diploma of business from Curtin University, WA. Member: SPE and SUT–UK and Australia. henry.sheil@peritusint.com |
Peter Young is a senior pipeline engineer with more than six years oil and gas experience in both the upstream and downstream sectors of the industry, having been employed by Shell, BP, JP Kenny and Peritus International. Working in all engineering phases, Peter has knowledge of pipeline design, pipeline repair, pre-commissioning, pipeline installation contingency planning, reliability, maintenance and operations. Peter has worked on significant projects including the Woodside Browse, Sunrise and Pluto LNG Projects on the Australian North West Shelf, and the BP Harding Area Gas Project on the UKCS. Author of two papers, Peter is presenting them both nationally and internationally. Further, Peter has practical field experience aboard a diving support vessel, an oil platform and at an oil refinery. Peter holds an MSc(res) in Advanced Mechanical Engineering from University of Sheffield, and a BEng(Hons) in Mechanical Design and Technology from Northumbria University, UK. peter.young@peritusint.com |
Martin is a senior project engineer with Pöyry Pty Ltd. He has more than 18 years of international office and site-based engineering experience, including oil and gas (onshore and offshore platforms, FPSO), LNG, petrochemical, pharmaceutical and aluminium manufacturing facilities. His project engineering experience includes instrument engineering, procurement, vendor management and factory and site testing. Site experience includes management and supervision of installation and construction contractors, cost and schedule management, progress reporting, inspection of site installations, and technical support for client organisations. Martin holds an HNC in industrial measurement and control from the University of Teeside, and an ONC in engineering from Longlands College of Further Education, England. martin.richardson@poyry.com |
