NORTH SEA DEVELOPMENT Long plagued by HT-HP and economics, Erskine development plan moves ahead
Field platform, to be equipped with temperature and pressure protection,
will operate unmanned
will operate unmanned
The Erskine Field is a joint Texaco/BP property. It is a high temperature, high pressure gas/gas condensate field in the UK North Sea's Central Graben Basin.
Both partners have each had teams working on the field for some years on a multi-staged phased development, and they have also looked at the possibility of working in co-operation with other license holders of HT/HP properties in the area, notably Elf with its Franklin and Elgin fields, in which Texaco also holds an interest.
At times, the prospect has looked good, at others bad, and at times early in its life, close to irretrievable, when the joint partners' program of technical studies and commercial options failed to produce an economically attractive development. But the team pressed on, intent on finding a solution.
Obstacles presented themselves at every stage, some technical, some commercial - at times a combination of numerous obstacles. Problems included two dry-hole appraisal wells in areas for which the team had high hopes.
An early plan for fast-track development through the Phillips Norway-operated Cod/Ekofisk platforms and the Phillips UK-operated Judy platform came to nothing. The outlook was cloudy. Both sides decided that unless a new approach was found, the odds were against development before the year 2000.
Through perseverance and innovation, a new development option was arrived at, based on the Amoco-operated Lomond platform. This solution meant that the field could be developed in a timely manner, cost-effectively, and in such a way that both partners could make enough money to make the project worthwhile.
HP/HT experience
Seen from a North Sea perspective, it is widely regarded that the main factor inhibiting the development of the field is the perceived difficulty of managing the extreme high pressure, high temperature (HP/HT) conditions. For Texaco, however, this was not considered a significant obstacle.
The company had plenty of HP/HT experience already through operating several high pressure fields in the US Gulf area, both on and offshore, with similar reservoir characteristics to Erskine. Experienced people were drafted in to apply that expertise in the context of the North Sea.
It is intended that the development will feature a not-normally-manned platform with control exercised from the Lomond platform 30 km away, which will also provide the route for export of produced fields. Maintenance will be by monthly helicopter visits. Additional unscheduled visits should be kept to a minimum through topsides simplification and reliable instrumentation.
The unmanned platform has numerous advantages, including low cost, compatibility with safety objectives, and general simplification of the operation. This option was selected over a subsea development both for its lower costs and fewer technical problems. Platform cost reduction was achieved by adopting cantilever jack-up drilling and multiphase export. Platform design considerations included pressure protection systems rather than flare booms, chemical storage compatible with a 30-day re-supply and use of chrome material for flowlines.
Field development is controlled by a 3D seismic survey shot in 1989 and re-processed in 1992. This survey contributed towards a 3D reservoir simulation model which allows for advanced analysis of the reservoir features and likely performance in ways which would not have been possible without the use of this technique. The model allows engineers to make predictions about the effects of compaction on permeability and radial local grid refinement near wellbores to simulate condensate banking.
Gas and liquids will be piped, unprocessed, via a 16-in. multiphase pipeline to Amoco's Lomond platform for separation and export. Liquids will then be exported via the Central Area Transmission System (CATS) riser and Forties pipeline system to Cruden Bay, near Aberdeen. Gases will travel, again, through the CATS riser, and on through the CATS pipeline to Teesside.
Pipeline design considerations included corrosion, upheaval buckling, and insulation. The cost of the multiphase pipeline was significantly reduced by qualifying carbon steel instead of solid or clad corrosion-resistant alloy pipe. A high temperature insulation system was needed for the multiphase pipeline to minimize problems with wax deposition and hydrate formation during turndown and later in field life. Operating costs for the pipeline were quantified in order to optimize the cost of insulation on a full field life basis.
Compression retrofit
The host platform was driven by the need to retrofit a dedicated process/compression module to the Lomond platform, which was not originally designed for third party access. This was accomplished by the use of compact heat exchangers, vertically stacked vessels, and reduced metering skid lengths. To minimize offshore hook-up and commissioning, the process module contains all equipment required for Erskine in a single package with only tie-ins to Lomond utilities required.
Both Texaco and BP sides to the team are working to bring the project in on a tight schedule, hoping for DTI Annex B approval early in the second quarter of this year, leading to first gas by fourth quarter 1997. Soon after the granting of UK government sanction, the formal tender document will be issued, and what has for a long time been a complex web of plans, proposals, ideas, and intentions will take concrete form.
According to Robert Shivers, a senior manager on the Erskine team: "So far, it's been rewarding, taking the numbers, the information we have, and putting a deal together that will work. All that's left is to go out there and do it."
Editor's Note:This feature, appearing without an author, was contributed by Texaco.
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