Integrated deepwater fields development
The Appomattox Deepwater Development project involves the initial development of the Appomattox and Vicksburg deepwater fields, which are located approximately 129km (80 miles) offshore Louisiana, US, at a water depth of approximately 2,195m (7,200ft).
The Appomattox field is primarily situated in Mississippi Canyon block 392 and straddles Blocks 391 and 348, whereas the Vicksburg discovery is situated in Mississippi Canyon block 393.
The final investment decision (FID) for the project was taken in July 2015, leading to the start of construction. Production from the project is scheduled to start by 2020.
The deepwater fields are owned by Shell (79%) and its partner Nexen Petroleum Offshore (21%), a wholly-owned subsidiary of CNOOC. Peak production from the fields is estimated to be approximately 175,000 barrels of oil equivalent (boe) a day.
The Appomatox field was discovered in March 2010 by drilling the discovery well at Mississippi Canyon block 392. The well was drilled to a depth of 7,643m (25,077ft) and encountered approximately 162m (530ft) of oil pay.
It was followed by drilling an appraisal sidetrack well that same year to a depth of 7,910m (25,950ft), which encountered approximately 116m (380ft) of oil pay. The field was further appraised in February 2012 by drilling an appraisal well in Mississippi Canyon block 348, at a water depth of approximately 7,257ft and to a total depth of 25,851ft. The well encountered approximately 150ft of oil pay.
The Vicksburg field was discovered in July 2013 by a discovery well at Mississippi Canyon Block 393 that was drilled at a water depth of 2,269m (7,446ft), to a total depth of 8,042m (26,385ft). The discovery well encountered more than 152m (500ft) of net oil pay.
The two fields are together estimated to hold recoverable reserves amounting to 650 million barrels of oil equivalent (MMboe) approximately.
The reservoirs of the Appomattox and Vicksburg fields are located in the Jurassic period (between 150 and 200 million years ago) Norphlet play, a geological formation that extends from onshore to the deep waters, characterised by high pressures and well temperatures.
The third major discovery in the Norphlet play, named Rydberg, was made in July 2014. The field is located within MC Block 525. The Gettysburg prospect in the Desoto Canyon Block 398 is also being explored currently. These two prospects are located approximately 16km (ten miles) from the Appomattox field.
The development plan primarily entails the installation of a semi-submersible, four-column production host platform, a subsea system featuring six drill centres, and the drilling of 15 production wells and five water injection wells. The infrastructure at the project site will have a design capacity ranging between 120,000boe/d and 200,000boe/d.
The new production platform will be Shell’s eighth and biggest floating platform in the Gulf of Mexico. Shell was able to reduce the project cost by approximately 20%, based on the experience gained from the development of the previous four-column production platforms in the Gulf of Mexico, such as the Olympus tension leg platform.
Crude oil produced from the project will be conveyed via a new 24in-diameter pipeline, named the Mattox Pipeline, to an existing offshore structure in the South Pass area and further supplied onshore using an existing pipeline. The Mattox Pipeline, which will be fully owned and operated by Shell Pipeline Company, will feature pre-installed subsea connection points to accommodate future interconnections.
The Gettysburg and Rydberg prospects are currently being reviewed for a possible connection to the Appomattox infrastructure, which will further increase the total estimated discovered resources in the area to more than 800MMboe.
In 2013, Delmar performed the mooring design engineering services for the floating platform, which included global mooring analysis verification using its nonlinear polyester stiffness method and mooring analysis software. Some of the exploratory and appraisal wells in the area were drilled employing the Deepwater Nautilus rig.
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