Tender-Supported Operations at the Odin Field
Authors: Smith E.L. , Dixon W.P. 
Published: December 2007

The first North Sea tender-supported drilling operations were successfully completed at the Odin field in Feb. 1985. Tender-supported operation was chosen to minimize investment in this marginal field. The operations were very successful and the actual lost time resulting from support vessel disconnection was significantly lower than predicted. The tender support vessel (TSV) provided mud storage, mud pumps, and mud treating facilities; a cement pump; cement bulk storage; materials lay-down area; additional quarters; and other services during the drilling operations. During platform hookup and commissioning, the TSV provided additional accommodation. This paper describes the tender-support concept, major tender-support components, and operational experience at Odin.

Introduction

Odin is a gas field in the North Sea located in Block 30/10, which is approximately 178 km [96 naut miles] from Bergen. Norway, and 240 km [130 naut miles] from Stavanger, Norway. Fig. 1 identifies the Odin field and some of the surrounding North Sea oil and gas fields. The Block 30/ 10 license was awarded to Esso in 1969 as part of the second Norwegian licensing round. The license is operated and held. 100% by Esso, with a 17.5 % net profit interest belonging to the Norwegian government. The profit interest belonging to the Norwegian government. The Odin field discovery well, 30/10-2, was spudded in late Dec. 1973 in 103 m [338 ft] of water. The well was tested and abandoned in early 1974. A confirmation well, 30/10-3, was drilled later in 1974. While Esso was evaluating the discovery, at Odin, the Petronord Group was developing the much larger Frigg Petronord Group was developing the much larger Frigg field 22 km [12 naut miles] south of Odin. Initial evaluation of Odin indicated that a fully integrated drilling, production, and processing platform could not be justified production, and processing platform could not be justified because of the limited hydrocarbon resources. Studies conducted in 1977 and 1978 indicated that the Odin field might be developed economically if surplus capacity in the Frigg field facilities could be used. (Fig. is a diagram of the Odin/Frigg system.) This utilization minimized the size of the platform and the capital investment required. Key factors that enabled this to be done were the existence of available platform space and spare processing and transportation capacity in existing or processing and transportation capacity in existing or expandable infrastructure, the low number of wells required (11), and the short drilling period (19 months). Excess capacity meant space for two 28 337-kW [38,000-hp] compressors on Platform MCP-1 (a booster platform on the pipeline to St. Fergus), as well as space for the installation of a new metering and separation module on Platform TCP-2 (a platform in the Frigg field complex) Platform TCP-2 (a platform in the Frigg field complex) and space on Platform TCP-2 for additional compression when required. Spare capacity in existing compression and separation facilities on Platform TCP-2 was available initially. With the use of the Frigg installations for the compression, dehydration, metering, processing, and transportation activities. the drilling facilities became the dominating factor in determining the Odin platform space requirements. A study of various marginal field alternatives, including a subsea development similar to the Northeast Frigg field, identified the tender-support concept as a viable option. When evaluating the economic alternative of tender-supported operations for a field like Odin, one must compare the incremental cost of a larger platform, including possible delays in sales revenues resulting from a longer possible delays in sales revenues resulting from a longer construction period, vs. total costs for the support vessel over the expected drilling period, including possible positive effects if the support vessel can also be used for positive effects if the support vessel can also be used for additional accommodation and shop facilities during the hookup phase. Other factors-such as the company's tax paving position, local regulations regarding capitalizing and expensing costs, the competitiveness of the rig market at the time of contracting, depth and areal extent of the reservoir, and potential drilling problems that must be overcome-contribute to making each decision very field-, company-, and country-dependent. An analysis indicated that up to 16 wells could be drilled under the Odin field conditions before a tender-supported system lost its financial attractiveness. Although tender-supported drilling operations had not been conducted previously in the North Sea, the concept had been used for many years in the Gulf of Mexico. Furthermore, tender-supported accommodation units were readily available in the North Sea and had demonstrated an ability to remain on station at a platform during the most severe winter weather. The use of a TSV moved load and space requirements for the installation of major equipment from the platform to the support vessel. The equipment included mud and cement bulk tanks, mud pits and mud pumps, and the cement pumping unit.

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