An offshore well-platform namely "xyz" is in a marginal gas field operated by Pertamina Hulu Energi Offshore North West Java (PHE ONWJ). "xyz" production is transported to the "xy" platform via a 6.3 km 8" Main Gas Line (MGL), which has been in operation since 2002. In 2015 several leaks were detected and it was known that well ‘xyz-1’ produced high CO2. A Repair by conventional means i.e. replacement with the same steel material was deemed uneconomic due to the high CO2 content. A study was therefore initiated to evaluate the technical and economic feasibility of low capital cost and low maintenance cost technologies to rehabilitate pipelines in marginal fields with high CO2 content without increasing safety or environmental risks.

In the appraisal stage, several technology options were considered and a thermoplastic pipe was selected as the preferred alternative compared to traditional rigid carbon steel pipeline. The assessment process started with a pipeline technology review, followed by technical compatibility/acceptance study, a check of commercially available pipe sizes and a comparison of total installation cost, installation schedule, and operation-maintenance considerations. The decision was facilitated by Expected Value Decision Analysis. The expected value of each option included CAPEX, OPEX, NPV, and all quantified aspects and risk.

The thermoplastic plastic pipe assessed is a flexible pipe for shallow water consisting of polyethylene (PE) internal liner, annular ring steel strip armor, and PE outer sheet. The PE inner liner is nearly hermetic, but allows traces of gases such as CH4, CO2, H2S, and H2O to permeate through. These permeants tend to accumulate in the flexible pipe annulus. A slight overpressure above atmospheric develops in the pipe annulus driving the gases to the end fittings where they are vented, preventing excessive pressure build up.

Additional weight is required for on bottom stability of thermoplastic pipe to be laid in Offshore North-West Java area. The installation spread was using the available Pipe Lay Barge blanket contract for the Pipeline Repair and Replacement Program. Even though different technical approach needed to accomplish the work, such as the need of additional weight and using lay barge instead of DP2, the selected concept is still the most economic compared to other options. The CAPEX spending was competitive compared to carbon steel pipe one. In addition, OPEX reductions can be achieved by reducing pigging operations and eliminating In-line Inspection (ILI) and chemical injection.

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