Drilling and Producing Operations Utilizing a Tension-Leg Platform
- R.E. Irelan (Conoco U.K. Ltd.) | C.G. Alldredge (Conoco U.K. Ltd.) | W.A. Downie (Conoco U.K. Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- October 1986
- Document Type
- Journal Paper
- 383 - 389
- 1986. Society of Petroleum Engineers
- 2.2.2 Perforating, 4.2 Pipelines, Flowlines and Risers, 1.14 Casing and Cementing, 1.3.1 Surface Wellheads, 4.2.4 Risers, 4.2.3 Materials and Corrosion, 5.5.2 Core Analysis, 1.6 Drilling Operations, 4.1.5 Processing Equipment, 1.3.2 Subsea Wellheads, 6.1.5 Human Resources, Competence and Training, 1.14.3 Cement Formulation (Chemistry, Properties), 2 Well Completion, 1.7.5 Well Control, 4.5 Offshore Facilities and Subsea Systems, 4.5.5 Installation Equipment and Techniques, 4.5.4 Mooring Systems, 5.6.4 Drillstem/Well Testing, 1.10 Drilling Equipment
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The Hutton field, discovered in 1973, is located in U.K. Block 211/28 about 275 miles [440 km] off the Shetland Islands in 485 ft [148 m] of water. The 1979 decision to proceed with field development was significant because the structure selected would become the world's first commercial tension-leg platform (TLP). This operational review covers the predrilling and completion of the first 10 wells from a semisubmersible predrilling and completion of the first 10 wells from a semisubmersible drilling rig, their subsequent tieback to the TLP, and the startup activity from an integrated-deck philosophy with production operations from a platform with moving trees, flexible flowlines, and production riser platform with moving trees, flexible flowlines, and production riser tensioners.
The TLP is a buoyant structure moored to the seafloor by tethers held in tension. It responds to the forces of wind and wave, though the motion is primarily in the horizontal plane. As a result, wells must be drilled through a seabed template and terminated with a wellhead at the mudline. A riser system is then required from the wellhead to the TLP. In the Hutton application, each riser has a dedicated tensioner with Christmas trees and process equipment on board the TLP. Much of the equipment was uniquely designed for Hutton and had not been field-tested. The platform was towed to the field in July 1984. First oil was produced on Aug. 6, 1984, just 22 days after installation, and by mid-Sept. 1984, field production was near the design plateau rate of 90,000 BOPD [ 14 300 ml/d oil].
Predrilling Phase Predrilling Phase The Hutton template has 32 drilling slots on about 8.5-ft [2.6-m] centers. Four of the slots double as template pile slots. A leveling feature was also incorporated in the design to ensure that the wellheads would be level to facilitate tieback to the TLP. The template was installed by a crane barge, and 30-in. [76-cm] piles were set by a conventional semisubmersible drilling rig. The rig then began the drilling program.
A conventional casing program of 30 x 20 x 13 % x 9% in. [76 x 51 x 34 x 24 cm] was used and 7-in. [ 18-cm] liner was required on only long-stepout wells. The 30-, 20-,and 13 3/8-in. [76-, 51-, and 34-cm] casings were all cemented to the mudline with the 9 5/8-in. [24-cm] casing cement designed to overlap the 13 3/8-in. [34-cm] shoe by 500 ft [152 m]. The 36- and 26-in. [91- and 66-cm] hole sections were drilled with seawater by taking returns at the mudline. Below the 20-in. [5 1 -cm] casing, diesel-oil-emulsion mud was used. A total of 10 wans plus two sidetracks for reservoir definition and well relocation were drilled with hole inclinations up to 58 degrees. A 7-in. [18-cm] liner was set in two wells, five were cored, and four were drillstem tested. All wells were temporarily plugged and abandoned in preparation for subsequent platform installation.
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