Located in the Philippines, the Malampaya shallow water platform produces gas from the Malampaya and Camago reservoirs, which is then transported 504 km through a 609 mm diameter gas export pipeline (GEP) to the onshore gas plant (OGP) at Batangas. A major shutdown was scheduled to allow for a range of rejuvenation work to take place, including replacement of the main emergency shutdown valve (ESDV) and a neighbouring manual block valve on the GEP.

“Shell Philippines Exploration and Production (SPEX) appreciates that bleeding down an entire GEP is time-consuming and costly, so we chose instead to deploy pressure isolation of the line downstream,” said Sarawak Shell Sdn Berhad/Sabah Petroleum Project Manager Nathan Stephenson.

“This option is made possible by T.D. Williamson’s (TDW’s) SmartPlug technology, a remote-controlled pipeline isolation system. It is designed to withstand maximum allowable operating pressure so that repairs can be carried out while pipeline pressure is maintained.”

The challenge

The ESDV, a 609 mm diameter Class 1500 actuated ball valve on the GEP riser, had to be removed and replaced, along with a nearby manual block valve. Due to the fact that the ESDV and the manual block valve are the primary means of isolating the platform from the GEP, another means of isolation was required.

It was critical that the operation be completed within the 30-day shutdown window, during which other major maintenance procedures would take place. With no room for over-runs or damage to the asset, SPEX trusted TDW to deliver an effective isolation.

A versatile and effective solution

The standard SmartPlug tool is designed to seal against 200 bar (3,000 psi) operating pressure. The highly piggable, bi-directional plug train can travel in either direction inside the pipeline and can operate within any pipeline medium, including gas, crude oil, distillates, treated or untreated water, glycol, and diesel. The two independent plug modules typically travel on a spring-loaded wheel system and can isolate the full pipeline pressure, thus allowing a double-block isolation anywhere in the pipeline system.

The typical isolation plug train is fitted with a pig module at each end. These house the onboard control and communication system, and assist in driving the plug train into and out of the pipeline. The system communicates wirelessly with the external, extremely low-frequency antenna placed on or above the pipeline. A computer system allows the operator onboard the platform or surface support vessel to send and receive commands and data.

Given that the plug modules are self-locking, once they have been expanded against the pipe wall a continued application of differential pressure will maintain or intensify their sealing and gripping ability. Each plug module is designed and tested to seal against the full pipeline differential pressure, thus making it possible to test the sealing and gripping capability of each.

Safety a top priority

Safety is always important in work of this nature. The SmartPlug isolation plug system has received a Type Approval Certificate from Det Norske Veritas (DNV) and confirming compliance with DNV OS – F101. Included in this certification is a detailed Failure Mode, Effects, and Criticality Analysis study based on a Fault Tree Analysis.

The entire Malampaya shutdown team attended ‘Implementation Plan on Paper’ sessions to discuss the operation. Shell also uses a Permit to Work (PTW) procedure at all facilities, including SPEX, and is supported by application of the Task Risk Management Process. All personnel working within the PTW are required to demonstrate full understanding and compliance.

The SmartPlug system is designed to self-lock in the set position, making it fail-safe as long as there is delta pressure across the plugging tool. It will continue to isolate the pipeline pressure, even if communications fail.

To provide the operator with all relevant pressures for both the hydraulic system and the pipeline, delta pressure is constantly monitored through pressure indicators for both the hydraulic system and the pipeline. Alarm switches alert the user if annulus pressure strays from a preset value.

Planning the operation

Given the fixed shutdown window, careful planning of feasibility, tool transportation, customs clearance, provision of pumping services and safety compliance were extremely important to the Malampaya operation.

A year before it was due to commence, TDW carried out an engineering study to analyse the feasibility of SmartPlug technology to this particular problem. Some concerns existed about the piggability of the line, since SPEX had previously encountered a problem when the valve located closest to the launcher failed to open properly, damaging an inline inspection tool. Though the actuator mechanism was later repaired, concerns about obstructions remained. To prepare for this contingency, a gauge pig was run from the platform to the receiver at the OGP to verify piggability along the entire line.

TDW’s piggability study assessed the SmartPlug tool’s ability to negotiate the pipeline to the set location and be retrieved back to the launcher. The study also formulated contingency plans for pigging the SmartPlug tool more than 500 km to the OGP should unforeseen difficulties arise when retrieving the tool. In addition, a pipe stress analysis was performed during which the hoop and von-Mises stresses in the sealing area of the set location on each plug module were checked against permissible utilisation, as defined by the DNV-RP-F113.

Launching and pigging the SmartPlug tool

With everything in place and feasibility confirmed, the pre-launch procedure for launching the SmartPlug tool was executed. The launcher was depressurised and the SmartPlug tool pre-loaded into the launcher barrel. The door was then closed and the launcher pressurised using external pumping services supplied by an oilfield service company. Nitrogen was chosen as the pigging medium because this meant that the gas export could be shut down and be ‘gas free’ while the plug was set. In addition, SmartPlug pigging is better controlled with an external nitrogen pump than with the gas export compressor.

With the launcher pressurised, the launcher valve was opened and the SmartPlug tool pigged to the set location in the riser. Upon reaching that location, both plugging modules of the SmartPlug tool were set at full line pressure, and then depressurised to 50 per cent of the pipeline pressure from the launcher side. After the annulus pressure between the two plugging modules was monitored for four hours to verify the sealing, TDW issued an isolation certificate to SPEX declaring that the situation was safe for valve replacement to commence. The entire launching and set operation was completed in less than 24 hours.

Delivering results

The manual block valve and defective ESDV were successfully removed and replaced, and the integrity safety barrier in the GEP re-established. Following installation and testing of the new valves, the SmartPlug tool was unset and retrieved by running the setting sequence in reverse. Personnel and equipment were then demobilised from the Malampaya platform. The entire operation was completed well within the window established by SPEX.

Restoration of a fully functional riser shutdown valve was an essential requirement for SPEX, as was the need to complete the operation in the shortest possible time. For SPEX, the SmartPlug system offered a quick, effective solution to an otherwise costly, time-consuming and complicated problem.