International energy contractor Petrofac is to use what it describes as "an innovative mobile offshore production unit (MOPU)" for opening up the Cendor offshore field, 140km off the east coast of Malaysia.

The MOPU will be a converted Bethlehem mat-type jack-up drilling rig with production and water-injection facilities installed.


The use of the unit in place of permanent offshore facilities is deemed the most suitable because it offers the most flexible approach given the marginal nature of the field's first phase of development.

According to Richard Hall, Petrofac's Malaysia general manager, the field development has been classified as marginal because of reservoir uncertainties rather than volume of oil in place.

"Given that uncertainty, we looked at five development concepts, of which the mobile production unit was one," said Hall.

"When we tested the various scenarios of reservoir performance being worse or better than expected, the MOPU approach was superior in terms of risk management and project economics.

"This approach also means that early production experience will allow us to optimise the placement of subsequent wells."

One obvious option for exploiting this field was to use a conventional jack-up rig equipped with production facilities, but drilling markets are now so tight that nothing is available.

What opened the door to the mat-type jack-up at Cendor was seafloor conditions.

Said Hall: "We determined that the seabed conditions at our field location are virtually flat, so we could use mat-type units which are far less marketable for drilling due to their limitations."

Bethlehem mat units offer a large deck space with substantial load-bearing capabilities, allowing for installation of the different oil and gas processing facilities, well intervention and the space to retrofit other process equipment depending on reservoir performance.

Drilling will be through triple splitter wellheads that will allow the drilling of three wells through a single conductor.

"Not only does this reduce the wave loadings on the MOPU structure, but the overall structural member - 36in outside diameter conductor with three cemented inner 13in diameter casing strings - is of such integrity that it can be unsupported from the seabed up to the support deck on the MOPU," said Hall.

"Use of this innovative technique renders the MOPU concept feasible in our water depth."

Depending on future reservoir performance, a fourth conductor will be installed to make room for additional wells.

The wells will be drilled with vertical top hole sections, gradually building angle to reach a maximum depth of just over 3km.

Additional flexibility will be provided by jet pump technology incorporated in the design for use if inherent reservoir pressure proves to be insufficient for natural flow.

Rory Edwards, Petrofac Resources vice-president business development, says the major advantage of the MOPU concept is the long-term flexibility.

He said: "The unit sits freely on the seabed and can thus be mobilised and demobilised in a short period of time. Depending on field performance and further development planning, a more permanent structure may be installed to which the existing conductors can be attached.

"Petrofac is pioneering this approach in Malaysia.

"The Cendor team is already assembled and work on the field development plan is on track."

Tenders for the main contracts for the MOPU - and for the field's floating storage and offloading unit (FSO) and mobile offshore drilling unit (MODU) - have been called and contracts will be awarded in June/July.

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Source: The Press & Journal
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