The paper deals with the handling of liquids in the multi-phase flow pipeline system within Carigali's Duyong Offshore Gas Complex and the Onshore Gas Terminal, in Kerteh, Terengganu. The data and operations experience gathered necessitate changes to the operating procedures originally identified during the design phase. This is to ensure more efficient handling of liquid hold-up in the pipeline during low gas flowrates.
The gas Gathering System, situated at both offshore Terengganu, in the east coast of peninsular Malaysia, comprises the following installations:
Duyong Gas Field Complex
Sotong Collector Platform (SCP)
Onshore Gas Terminal (OGT)
The Duyong Gas Field Complex, situated 200 km offshore, in water depths ranging from 70 to 80 meters, comprises the following platforms:
Wellhead Platform A (WPA)
Wellhead Platform B (WPB)
Wellhead Platform C (WPC)
Central Processing Platform (CPP)
Living Quarters Platform (LQP)
The flow scheme of the entire system is shown in Figure 1. The detailed description of these facilities is described in the next section.
The Duyong Gas Field and the OGT have been operated below the designed production rates, for a period of approximately three years, due to low gas demand by the consumers. The average gas production from the Duyong Field is approximately 0.85 X 10-6 Sm3/day, ranging from a minimum of 0.29 × 10-6 Sm3/day to a maximum of 1.40 × 10-6 Sm3/day. The Duyong gas production contributes approximately 50 percent of the total gas delivered to the OGT. The remaining 50 percent comes from EPMI's field through the SCP.
Production from Duyong is maintained on a rotational basis, from one single wellhead platform at any one time. This is done to monitor the performance of all the wells and the associated facilities on the CPP, and to cater for the low gas demand. Each wellhead platform is allowed to produce continuously for a period of two months.
The low gas flowrate resulted in larger liquid hold-up in the Duyong pipeline system. Handling of liquid hold-up on the CPP during pigging operations, in the early days, had been a major concern to Carigali since it had caused several shutdowns of the offshore facilities.
Initially, handling condensate at the OGT had resulted in discontinuation of gas supply, for short durations, to the Gas Processing Plant (GPP) operated by PETRONAS Gas Sdn. Bhd. (PGSB).
The above mentioned liquid handling problems, however, were overcome by revising the designed operating procedures.
Each wellhead platform is designed to produce 2.80 × 10-6 Sm3/day of gas and 330 Sm3/day of liquid. The produced fluids, comprising gas, condensate and produced water from WPA and WPC are routed to the CPP via two separate 5.6 km and 5-km 14-inch multiphase subseas pipelines respectively. The production from WPB is routed to CPP via a 10-inch production flowline alongside a 30 meter bridge connecting the two platforms.
The CPP, which forms the central hub of the Duyong Gas Field Complex, is designed to receive and treat 7.0 X 10-6 Sm3/day of gas and 1250 Sm3/day of condensate from the wellhead platforms. Three production trains on the CPP ensure continuous production to the OGT.