This paper describes the performance of the Tembungo Single Anchor Leg Mooring (SALM) tanker loading terminal during its first seven years of operation. This facility, located in 300 feet of water, 50 miles (93 km) offshore Sabah, East Malaysia, has been in continuous service since October 1974. It was designed to permanently moor a 94,000 DWT storage tanker in maximum wave heights of 39 ft. (12 m), winds of 65 mph (29 m/s), and 2 kt (1 m/s) currents.
The Tembungo SALM has performed very effectively since start-up. Operational efficiency rates of up to 99.4 percent on an annual basis have been achieved, with an average of 95%. A major factor in the high utilization of this terminal has been the very low level of maintenance required on the SALM components. Pre-planning the annual inspection and maintenance program with the diving contractor and developing detailed procedures for tanker change-out and for hose and hawser replacement were procedures for tanker change-out and for hose and hawser replacement were also important contributors toward maximizing operational efficiency.
In recent years the petroleum industry has accepted the concept of employing a Single Point Mooring (SPM) as an integral part of an offshore production facility. The SPM, which provides direct tanker loading, may production facility. The SPM, which provides direct tanker loading, may allow a field to be brought on-stream earlier than with a pipeline to shore and it may allow the development of those fields which have insufficient recoverable reserves to justify a pipeline. The Tembungo SALM, described herein, is a good example of an early production application.
OTC Paper No. 3804, copyrighted and presented at the 1980 Offshore Technology Conference, described the performance of the Tembungo Single Anchor Leg Mooring (SALM) during its first five years of service. With permission from the OTC, portions of that paper will be incorporated permission from the OTC, portions of that paper will be incorporated herein.
The SALM is located 7,000 ft (2,134 m) from a fixed separation platform and is connected to the platform via a single 10-in. (9254 mm) pipeline. While the SALM was designed to permanently moor a storage tanker, which would be periodically offloaded by shuttle tankers moored alongside, it has only periodically offloaded by shuttle tankers moored alongside, it has only been used for shuttle service to date in an operation which employs two dedicated tankers. While one tanker is loading, the other tanker departs to discharge its cargo. In this service, with prolonged periods of berth occupancy, the two shuttle tankers effectively become temporary storage facilities. This type of operation requires periodic production shut-in while the loaded tanker departs the SALM and the empty tanker comes on. These operational procedures have proven to be very effective for producing this field and should be equally as effective in the production of other similar fields.
The Tembungo SALM has been designed to permanently moor a 94,000 DWT vessel in the 100-years design environment. This environment and other pertinent design criteria are presented in the following tables:
Design Criteria for the Tembungo SALM
Water Depth 296 ft (90 m)
Tanker Size 94,000 DWT
Significant Wave Height 21.0 ft (6.4 m)
Maximum Wave Height 39.0 ft (11.9 m)
Maximum Wind Velocity 65 mi/hr (29.5 m/s)
Maximum Current Velocity 2.0 kt (1.0 m/s)(perpendicular to waves)
Product Transfer Piping 10 in. (254 mm) Product Transfer Piping 10 in. (254 mm) Maximum Operating Pressure 200 psig (1.38 MPa)
Maximum Surge Pressure 400 psig (2.76 MPa)
Peaking mooring forces for the Tembungo SALM facility were determined by Peaking mooring forces for the Tembungo SALM facility were determined by means of an empirical technique which has been developed over the past fifteen years by Exxon Research and Engineering and Exxon Production Research Company. The procedures have been discussed in the literature by Flory, Poranski and Maddox. Based on the given environmental conditions, the predicted Maximum Bow Hawser Load was 840 kip (3,736 kN), and the Maximum Anchor Leg (axial) Load was 1,200 kip (5,338 kN), and the Maximum Anchor Leg Deflection was 37 ½ degrees from vertical.
The SALM mooring buoy is anchored through a single pretensioned anchor leg to a gravity-type mooring base at the sea floor. To minimize diver time and underwater work, the universal joint attachments between riser and base and buoy and riser were designed to be hydraulically latched (or unlatched) from the surface.
Basic components of the SALM are the Mooring Base, the Riser Shaft, the Anchor Leg Assembly, the Hose Arm and Loading Hose System, the Mooring Buoy, the Mooring Hawsers, and the Pipeline End Manifold (PLEM).
The Tembungo Field has produced continuously since October 1974 at quarterly average rates which have varied from 2000 BOPD to 16000 BOPD. For this seven year period, the average overall operational efficiency, i.e. total days minus total downtime days divided by total days, has been 95%. Operational efficiency is categorized below and is shown graphically in Figure 8.