Alder is a high-pressure and high-temperature gas condensate field located in Block 15/29a of the UK Continental Shelf. The field lies in a water depth of 492ft (150m) in the central North Sea, approximately 100 miles away from the Scottish coastline and 37 miles away from the UK / Norway median line.
Alder will be developed as a satellite of the operating Britannia field, located 27km east of it in block 16/26.
The offshore project is owned by the operator Chevron (73.68%) and Conoco Phillips (26.32%).
The contracts for major components of the subsea development project were awarded by Chevron in mid 2013. The final investment decision (FID) on the project was taken in January 2014 and approved by the UK government.
Alder field reserves and production
Alder field is estimated to contain approximately 4,820 million standard cubic metres (scm) of gas. It is expected to produce 2.7 million scm of gas and 1,423t of condensate per day. The start of production is expected in 2016.
History of the North Sea field's development
"The offshore project is owned by the operator Chevron (73.68%) and Conoco Phillips (26.32%)."
Alder was discovered in 1975 as an Upper Jurassic reservoir with 9,440 psi of wellhead shut-in pressure and 305°F (15°C) of reservoir temperature with the drilling of 15/29a-2 well.
Four appraisal wells namely 15/29a-3, 15/29a-5, 15/29a-7 and 15/29a-8 were drilled in the field since its discovery, in 1988, 1990, 1993 and 1994 respectively.
Chevron had initially considered developing the field through floating production, storage and offloading (FPSO) solution by using round-hulled Sevan Marine type hull. The subsea development plan was, however, preferred over the FPSO plan in 2010 due to greater environmental risk of the latter.
The field's development plan via subsea tieback to the Britannia platform received initial environmental approval from the Department of Energy and Climate Change (DECC) in August 2013.
Development plan for the Chevron-operated field
The field is due to be developed by tying back up to two subsea wells from Alder to the Britannia Bridge Linked Platform (BLP) through a 28km long production flow line. Production will commence from a single production well initially. The second well will be drilled in the later phase of the field development.
"Alder field is estimated to contain approximately 4,820 million standard cubic metres (scm) of gas."
A conventional semi-submersible drilling rig will be used to drill the wells. The drilling of top-hole sections of the wells will involve riser-less drilling technique using sea water and high viscosity sweeps. Low toxicity oil based mud (LTOBM) will be used for drilling the lower sections of the wells.
The well heads will be connected to a production manifold from where the reservoir fluids will be transferred to the Britannia BLP via a ten-inch and 16-inch pipe-in-pipe system running parallel to an umbilical line.
A dynamically positioned (DP) reel-lay vessel will be used for laying the pipes. Mechanical plough or jetting will be used for trenching and burial of the flowline and umbilical.
The tied back pipe line will use the existing riser and J-tube on the Britannia BLP. The BLP will, however, undergo modification to have a new module, via which the Alder condensate will be transported into the Forties pipeline connecting the Grangemouth oil terminal in the UK. The produced gas will be conveyed through Scottish Area Gas Evacuation (SAGE) pipeline to St Fergus.
Well drilling at Alder is scheduled for completion by the second quarter 2014. The installation of new module on the Britannia BLP and the subsea construction are scheduled to begin in the third quarter of 2014.
Contractors involved with the Alder field
Technip was awarded a contract in July 2013 for engineering, procurement, installation and commissioning of the complete subsea system of Alder. Contractual scope includes the supply of main subsea manifold, subsea isolation valve manifold, pipe-in-pipe flow line, umbilical and the tie-in spools.
The contract will be executed by Technip's operating centre in Aberdeen, UK.
Genesis, a subsidiary of Technip Group, will be responsible for the detailed design under the contract. The pipe-in-pipe will be fabricated at Technip's Evanton spoolbase, Scotland. The umbilical will be manufactured by Technip's subsidiary DUCO in Newcastle, England. Technip's vessels, including the pipelay vessel Deep Energy, will be used for offshore construction.
OneSubsea UK will supply the vertical monobore subsea trees and wellheads for the Alder project.
Aker Solutions was awarded the contract for the design, manufacture and supply of the subsea control system for the oil field development. The contract includes the hydraulic and electrical equipments to be installed at subsea location, as well as on the Britannia BLP.