After developing the Offshore North Sinai (ONS) leases – moving on from the TAO platform – NOSPCO decided to next develop the Kamose gas field, as it had proven reserves. This offshore field is located 50 km north of Rommana, North Western Sinai, in 30 meters of water depth. Due to the small field size, the predicted field life is only four years, with four gas wells producing at a peak rate of 120 million standard cubic feet per day (mscf/d). Because of this, the selected concept for this project, which was initiated in May 2017 and was completed in November 2018, had to be cost effective with a rapid return on investment.
ODE was selected by NOSPCO to perform the concept selection for this development. Four concepts were reviewed, these being: an existing monopod; a partially completed tripod design; an existing conventional jacket; and a Mobile Offshore Production Unit (MOPU) supported by wellhead structure. The MOPU option was further split into assessing the use of either a jack-up barge or a drill rig. In addition to the topside facilities, a 10-inch subsea pipeline, utilizing a hot-tap tie-in to the existing subsea 22-inch TAO to Romanna gas export pipeline, was also required for all options.
Using group workshop techniques, the concept selection evaluated and compared the technical, schedule, safety, operational, risk and commercial (both CAPEX and OPEX) aspects of each option, with a cost accuracy of ±15%. The final output from the study was a detailed concept selection report which identified the jack-up barge MOPU option with an adjacent conductor/wellhead platform as the most cost-effective solution, due to the following numerous benefits.
The jack-up barge, which would be retrofitted to function as a MOPU, has a large deck space area and a suitably sized crane capable of installing the wellhead structure onsite, making this solution self-installing. This would save considerable installation costs typically associated with hiring third party lift vessels.
Equally important, once the Kamose reservoir has been depleted, the wellhead platform shall be made gas safe and have renewably powered navigation beacons installed. The MOPU would then be free to relocate and develop a second field from NOSPCO’s portfolio using an identical wellhead platform structure. Once the second field was depleted, a third could be developed, and so on.
By delaying the full decommissioning of the abandoned platforms until several are ready to be removed, the hire costs of the removal vessel would be consolidated into a single multiple-asset decommissioning project. It is not anticipated that the MOPU will be capable of fully decommissioning the platforms by itself.
The MOPU production and utility facilities, including 230V, 50 Hz power generation, as well as its 45-man accommodation block, navigational aids, fire detection, firefighting systems, lifeboat and helideck, would be reused, significantly reducing the CAPEX of this and future developments. Additionally, as the wellhead platforms used in future developments would be essentially identical to the first, future engineering design costs would be minimal.
Following completion of the concept selection study, ODE was again selected to perform the detailed design for the selected option. This was a highly schedule driven detailed design project to match a fast-track construction and offshore implementation phase. ODE kicked off the detailed design phase by outlining the jack-up vessel selection scope of requirements. After reviewing several vessels, NOSPCO selected the MOSCO-1 barge.
Both the wellhead platform and the MOPU production facilities are fully rated for the maximum gas pressure. Therefore, instead of a blowdown system, only a maintenance vent was necessary. The wellhead platform only contains the wellheads, high-pressure flowlines, the export riser and riser export shutdown valve. All production facilities, including the choke valves, metering and pipeline HIPPS, are located on the MOPU. A maintenance control panel is included on the barge; however, process control will be performed from the main control room at the central processing facility in Romanna.
When first installed, the platform is only supported by connections to the strengthened MOPU hull; however, by the end of the installation process it is fully self-supporting. The installation sequence was designed to minimize offshore construction activities, whilst only requiring the barge facilities, such as its crane.
Following the MOPU’s arrival at the construction location and elevation to the correct height, an extension frame is attached to the front of the barge. This is then extended further by the addition of an installation frame. The mudmat and the first of three jacket substructures are then lowered through the installation frame and temporarily fastened in place.
A central temporary conductor is then lowered down through the installation frame and substructure and attached to the mudmat. Once attached, the mudmat and conductor are lowered together to the sea floor. Two permanent conductors are then lowered through the installation frame and substructure all the way down to the mudmat. They are guided by divers and, following correctly threading through the mudmat, guides are hammered approximately 10 meters into the seabed. Once securely hammered in place, the first substructure is lowered using the crane to the mudmat and bolted in place. The temporary conductor is then removed.
The second substructure is then lowered to the first and bolted. The third conductor is then lowered through the substructures and mudmat before also being hammered into the seabed to a depth of 20 meters. This is followed by the third and final substructure section, and the fourth and final conductor being installed in the same manner, but to a depth of 70 meters. Then, the remaining three conductors are hammered to a depth of 70 meters.
Once hammering is complete, the crown welds are made and the topsides are installed level by level. The four wellheads are installed at the top of the conductors and the riser is also attached and connected to the 10-inch subsea pipeline.
In support of this project, ODE completed all required structural, piping, electrical, instrumentation, process and technical safety deliverables to the ‘approved for construction’ status for the wellhead platform and barge modifications. ODE also provided the engineering required to select a suitable location for a 10” to 22” hot tap tee and the associated subsea pipeline routing between the Kamose asset and the tee’s location within the export pipeline.
All equipment and material specifications were provided together with development of scope of supply for the major contractors, including provision of jack-up barge, mechanical (structural and piping), electrical and pipeline fabricator/installation contractors.
As part of the engineering support scope, ODE undertook technical reviews of vendor submitted materials and equipment tenders, to ensure compliance with specifications and data sheets, making recommendations to the client for technical compliant proposals. ODE is currently supporting NOSPCO by providing assistance during the fabrication and offshore installation.
This project demonstrates ODE’s ability to overcome challenging project and client requirements with inventive, safe and professionally developed solutions. These challenges included creative design modifications to minimize long leads, and to enable the use of materials already held in stock by the client, such as 30-inch conductors with a wall thickness of one inch. The delivered design provides NOSPCO with a valuable solution for developing small fields due to the reusability of both the MOPU and the wellhead platform design.