Field experiences

Iwafune-Oki Project

Offshore Platform

Drilling Work

Receiving Site

Japex Offshore Co., Ltd. (JPO)
July 1983 - December 1990

With this project, JOE provided a multi-disciplined team of its most highly experienced senior engineers to conduct the necessary feasibility study, prepare and organize bid packages, and eventually assisted JPO from bid evaluations, project management, procurement, construction, installation, and until the commissioning of the Iwafune-Oki field facilities.
The Iwafune-Oki Oil-Gas Field is situated approximately 30 km at the North East of Niigata-City, and 4 km offshore off Arai-Hama, Nakajyou-Machi, Kita-Kanbara-Gun, Niigata Prefecture, Japan. The platform is located at Latitude N38°07’46”7, Longitude E139°20’29”6 with a water depth of 36.2 m.

The Iwafune-Oki platform is a self-contained drilling and production platform with 20 slots (5 x 4 layout). The platform is designed to withstand a 100-year return storm condition (wind speed 52.7 m/s, wave height 18.4 m, currents 1.33 m/s) and a seismic loading greater than the famous Niigata earthquake in 1964. The platform design life is 25 years and design fatigue life is 50 years.

The platform comprises of a Jacket (Jacket weight: 1,810 t, Piles weight: 1,480 t, Conductors weight: 1,000 t) and a Topsides (Lower Deck: 1,780 t, Drilling Substructure weight: 980 t, Mud Pump Module weight: 1,190 t and Accommodation and Utility Plant Module weight: 1,290 t).

The platform is made up of a steel template–type jacket supported on a system of distributed 8 main piles and 4 skirt piles. The jacket dimensions are 26.7 mW x 55.7 mL at mud line, 18 mW x 47 mL at the top of jacket and 44 m total height. The skirt pile sleeves extend from above the horizontal frame at elevation -9.5 m to below the horizontal frame at the mud line. The 54” diameter main and skirt piles extend approximately 60 m below the seafloor. The main piles are driven through legs and the skirt piles are driven through guides located at the upper horizontal levels through the lower bay sleeves. Loads are transferred from the jacket to the main and skirt piles by grouting the legs and sleeves to the piles. The 20 conductor piles with 30” diameter are driven through conductor guides at elevation +5m to approximately 50 m below the seafloor.

A National 110-M drilling rig with a top drive system is installed on the platform. A top drive is a mechanical device usually mounted on a drilling rig so as to provide the necessary torque to the drill string as well as to enable drilling of a borehole. It is a system similar to rotary table but located at the swivel place in order to facilitate vertical movement up and down the derrick. Compared to other drive system, a top drive is more advantageous because it allows the drilling rig to drill longer sections of a stand of drill pipe as it can drill 27 m stands (triple drill pipe connections) against a rotary table type rig which is limited to only 9m (single drill pipe) section of drill pipe. A longer section of drill pipe not only allows the drilling of a deeper section of the wellbore, it also has fewer connections of drill pipe resulting to time efficiency. The savings in time also reduces the risk of a string being stack due to annulus clogging.

The production fluids from Iwafune-Oki platform is transferred to the existing onshore terminal at Niigata Higashi Port via a 12 inch diameter submarine pipeline with a total length of 21.6 km. The fluid is separated into crude oil and gas in a slug catcher and separators. The produced crude oil is stored in oil tanks in the onshore terminal and is then sent to export tanker or pipeline. The produced gas is dehydrated and desulfurized before sending to export pipeline.

JOE received an award from JPO with the acknowledgement of the superior technology applied to the platform.

* The specification of platform is quoted from the construction drawing.

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