Drilling & Production

Leonard LeBlanc Houston The first spar-shaped production floater was ordered by Oryx-CNG for the Neptune prospect in Viosca Knoll Block 826 in the US Gulf of Mexico. The water depth is 2,000 ft. The 700-ft, 72-ft diameter long cylinder is surrounded by spiral ridges, which prevent vortex-induced vibration. Production is expected in 1997. J-lay and S-lay pipe installation speeds and repair rates are compared. The figures were obtained for similar water depths laying 12-in. diameter pipelines for

Jan 1st, 1995

Leonard LeBlanc
Houston

  • The first spar-shaped production floater was ordered by Oryx-CNG for the Neptune prospect in Viosca Knoll Block 826 in the US Gulf of Mexico. The water depth is 2,000 ft. The 700-ft, 72-ft diameter long cylinder is surrounded by spiral ridges, which prevent vortex-induced vibration. Production is expected in 1997.

J-lay pipe installation rate competitive with S-lay methods

  • J-lay and S-lay pipe installation speeds and repair rates are compared. The figures were obtained for similar water depths laying 12-in. diameter pipelines for the deepwater Auger and Enserch GB388 Fields.

Experience obtained on both J-lay and S-lay methods by McDermott International using the same pipe size in the same water depth indicates close parity in installation speed and repair rates. The experience, derived from pipelay operations for the deepwater Auger and Enserch BG388 fields in the US Gulf of Mexico, was presented at McDermott's Deepwater Symposium, held in November in Houston.

The S-lay method experienced an average 1.67 miles/day lay rate, about 18% faster than J-lay, which achieved an average speed of 1.41 miles/day. On balance, however, J-lay methods required 16% fewer repairs. A repair requires cutting out a defective weld and re-welding the joint. J-lay repairs averaged 0.9% of the joints welded, versus 1.07% of joints welded for S-lay (see table).

Among the advantages presented for the new J-lay methods over conventional S-lay are the following:

  • Use of a smaller pipe installation crew
  • Use of conventional welding
  • Reduced pipeline touchdown distance
  • Reduced bottom tension
  • Quick abandonment and recovery
  • Closer monitoring of welding and coating quality
  • Possible to store large amounts of pipe
  • Ease of remounting J-lay assembly on other units.

Among the disadvantages noted during the J-lay pipe installation process are:

  • Quad joints must be assembled ashore
  • Single work station is crowded.

Mobil's tension leg riser combines low cost, compliancy

A group headed by Mobil Research and Development of Dallas has developed a tension leg riser design that eliminates most fatigue concerns and provides flexible jumpers where significant dynamic loading is anticipated. The design can eliminate the large costly conventional risers that are required to bring a large volume of commingled production or gas from the seabed.

The design calls for a large subsurface buoy that is tethered to the seabed and supports steel risers from the seabed. Spanning the remaining 100-150 meters between the buoy and surface production vessel are flexible risers arrayed in a catenary fashion to isolate the buoy from floater motions. The flexible jumpers are not subjected to high tensile loads or hydrostatic pressure.

Infill drilling predictive model now on TORIS

The infill drilling predictive model (IDPM), which simulates incremental oil recovery by infill drilling with waterflooding is now operational in the TORIS (tertiary oil recovery information system) database.

The model simulates water and oil movement in 3D and provides a method of calculating pay continuity and permeability variations using the history match of production data. The model requires downhole information on pay continuity and permeability variation among the various layers.

Scientific Software-Intercomp developed the model for the US Department of Interior, which operates the TORIS database. The model was first devised 10 years ago to assess enhanced oil recovery efforts and is being made available widely now to calculate the impact of infill drilling programs.

Additional information on the IDPM program is available in the SPE/DOE 27761 technical proceeding, presented at the Ninth Symposium on Improved Oil Recovery held in Tulsa, Oklahoma last year.

Mooring systems used to export rare product in Mideast - water

Twin single point mooring systems to be installed off Turkey's Manavgat River mouth will be used to load and ship an increasingly rare commodity in the Mideast - fresh water. The water is destined for eastern Mediterranean countries.

A water volume of 500,000 cm/d - half treated and half raw - will be transported from a water production facility positioned on a hill onshore through four 1,200 mm submarine pipelines. Two single point mooring systems 1,300 meters offshore will be used to moor water tankers and load the water. Intec Engineering of Houston is providing consultant and construction management services for Turkey's State Hydraulic Works.

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