Seven Years' Experience With the First Deepwater SALM

Abstract

Summary This paper describes the performance of the Tembungo single anchor leg mooring (SALM) tanker loading terminal during its first 7 years of operation. This facility, located in 300 ft (91 m) of water, 50 miles (93 km) off-shore Sabah, East Malaysia, has been in continuous service since Oct. 1974. It was designed to moor a 94,000-dead-weight-ton (DWT) (85,000-Mg) storage tanker permanently in maximum wave heights of 39 ft (12 m), winds of 65 mile/hr (29 m/s), and 2-knot (1-m/s) currents.The Tembungo SALM has performed very effectively since start-up. Operational efficiency rates of up to 99.4% 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. 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 also important factors in maximizing operational efficiency. Introduction In recent years the petroleum industry has accepted the concept of using a single point mooring (SPM) as an integral part of an offshore 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 having insufficient recoverable reserves to justify a pipeline. The Tembungo SALM is a good example of an early production application (Fig. 1).The SALM is located 7,000 ft (2134 m) from a fixed separation platform and is connected to the platform by a single 10-in. (254-mm) pipeline. While the SALM was designed to moor a storage tanker permanently that would be offloaded periodically by shuttle tankers moored alongside, it has been used only for shuttle service to date in an operation involving two dedicated 50,000-DWT (45 000-Mg) tankers that each load for 30 to 60 days. 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 proved effective for producing this field and should be equally effective in the production of other similar fields. System Design Criteria The Tembungo SALM has been designed to moor permanently a 94,000-DWT (85 000-Mg) vessel in the 100-year design environment. This environment and other pertinent design criteria are presented in Table 1.The governing parameters for the structural design of an 5PM terminal are the prediction of the statistically most probable peak mooring force and, for hawser-type systems, the selection of the bow hawser. The breaking strength of the hawser assembly will dictate the required structural capacity of the entire mooring facility. Peak mooring forces for the Tembungo SALM facility were determined by means of an empirical technique developed over the past 15 years through a continuing series of model test programs conducted by Exxon Research and Engineering and Exxon Production Research Co. The procedures used have been discussed in the literature by Flory and Poranski and Maddox. Based on the given environmental conditions, the following peak design forces were predicted. JPT P. 1219^