Minimum-Cost Platform Designs--Cook Inlet, Alaska
- Robert C. Visser (Belmar Engineering)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- September 2007
- Document Type
- Journal Paper
- 1 - 8
- 2007. Society of Petroleum Engineers
- 4.2.4 Risers, 4.2 Pipelines, Flowlines and Risers, 3 Production and Well Operations, 1.10 Drilling Equipment, 4.5.5 Installation Equipment and Techniques, 4.5.2 Platform Design, 4.5 Offshore Facilities and Subsea Systems, 1.6 Drilling Operations
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The paper describes two minimum-cost, self-erecting platform designs and one caisson structure design that can be installed in Cook Inlet, Alaska, without the need for heavy lifting equipment. The Cook Inlet environment is characterized by 30-ft tides and during the winter months by fast-moving ice floes. The area is remote from other offshore operating areas, and there is no heavy lifting equipment. One of the designs has been built: Platform Osprey was installed in Cook Inlet in 2000. The paper will describe how it was designed, constructed, and installed. A second, different design concept allows platform installation in deeper water, again without the need for heavy lifting equipment. The third design concept is an outrigger caisson design that can be installed with a jackup drilling unit. It would be applicable as a satellite platform structure.
Use of these minimum-cost platform and caisson designs would enable development of marginal fields in Cook Inlet that heretofore could not be developed because the high cost of mobilizing and demobilizing heavy lifting equipment to and from Cook Inlet would have made development uneconomical.
In the period from 1964 to 1968, four oil fields and one gas field were developed in Cook Inlet, Alaska, from 14 platforms (Visser 1992). During this period of high activity, there were several mobile drilling units, derrick barges, and pipeline lay barges in the Inlet. At the completion of development, however, the equipment departed, and Cook Inlet became a backwater as far as offshore oil activities were concerned. Yet there were still undeveloped discoveries and identified prospects. However, the high cost of mobilizing and demobilizing mobile drilling rigs and heavy lift equipment discouraged operators from pursuing these potential opportunities.
One such undeveloped discovery, the Redoubt Shoal field in Cook Inlet, Alaska (Figs. 1 and 2), was found by Amoco (now BP, then PanAm) in 1969 but not deemed commercial at the time. Forest Oil Corporation (then Forcenergy) took over the acreage in 1996 and, following a 3D seismic survey, concluded that the field could be commercial. To confirm this, however, would require the drilling of at least two and possibly four appraisal wells. This is usually done by drilling one or more expendable appraisal wells with a mobile drilling unit. For remote Cook Inlet, the cost of a single appraisal well was estimated to be USD 25 to 30 million including the cost of mobilization and demobilization. Installing a platform in Cook Inlet the "conventional?? way was also cost-prohibitive without the ready availability of heavy lifting equipment, and the cost of such a platform was estimated to be USD 60 to 80 million.
As an alternative, Forest decided to investigate the possibility of installing an "exploratory?? drilling structure. Requirements for such a minimum structure were:
- Capability to support a 20,000-ft modular drilling rig
- Installation without heavy lifting equipment
- Feasibility of conversion into a permanent platform
- Easy removal in case the prospect did not pan out
- Possibility of moving the structure to another Cook Inlet location.
Several platform concepts were developed by a Redondo Beach, California, consultant, Belmar Engineering (Visser and Carlson 2002). The selected concept requires no heavy lifting equipment and uses the tide to install the platform.
|File Size||2 MB||Number of Pages||8|
Bhat, S.H. and Cox, G.F.N. 1995. Ice Loads on Multi-Legged Structures inCook Inlet. Proc., Port and Ocean Engineering under Arctic Conditions(POAC-95), Murmansk, Russia.
Blenkarn, K.B. 1970. Measurement andAnalysis of Ice Forces on Cook Inlet Structures. Paper OTC 1261 presentedat the Offshore Technology Conference, Houston. 22-24 April, 1970.
Visser, R.C. 1992. ARetrospective of Platform Development in Cook Inlet, Alaska. JPT44 (2): 146-150, 202-203. DOI: 10.2118/19160-PA.
Visser, R.C. 1995. Reassessment ofPlatforms in Cook Inlet, Alaska. Paper OTC 7781 presented at the OffshoreTechnology Conference, Houston, 1-4 May, 1995.
Visser, R.C. and Carlson, G.E. 2002. Osprey Project: Designand Installation of a Novel Platform in Cook Inlet, Alaska. Paper OTC 14221presented at the Offshore Technology Conference, Houston, 6-9 May.