Conceptual Design for Maintaining Production of High CO2 Gas in Marginal Field Offshore by Using a Thermoplastic Pipe

摘要

SRA is one of the well platforms in a marginal gas field operated by PT Pertamina Hulu Energi Offshore North West Java (PHE ONWJ). SRA production is evacuated to the SA platform via a 6.3 km 8" Main Gas Line (MGL), which has been in operation since 2002. Changing corrosiveness of the fluids produced at SRA after the MGL integrity and in 2015 several leaks were detected. Repair by conventional means or replacement was deemed uneconomic. 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 sheat. 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 will be using the available Pipe Lay Barge blanket contract for the Pipeline Repair and Replacement Program.. Even though some advantages of flexible pipe cannot be obtained in this project, such as additional weight required and lay barge usage instead of DP2, the selected concept is still the most economic compared to other options. The CAPEX is 10% less than carbon steel pipe. OPEX reductions can be achieved by reducing pigging operations and eliminating In-line Inspection (ILI) and chemical injection.