Challenge of Produced Water Treatment on Offshore Unmanned Wellhead Platform in Aung Sinkha Field
Authors: Suebsook Jiranoot 
Published: February 2024

Aung Sinkha (ASK) is presently in the development phase, situated in the Gulf of Moattama, Myanmar. The two wellhead platforms (WPA-1 and WPA-2) are positioned 90 km from ASK onshore processing facilities. Through engineering studies and cost evaluations in the conceptual phase, it was determined that the Produced Water Treatment (PWT) method is chosen to separate, treat, and dispose of produced water at the offshore wellhead platform.

The design challenges of Offshore Unmanned PWT Facilities encompass various critical aspects, including:

the extremely varying of produced water profile over the field life, the offshore unmanned facilities located far from shore, the reliability and performance of water treatment, the enhancing alternatives for PWT separation efficiency, the Produced Water Disposal facilities constraints (i.e. Caisson length vs. shallow water depth, Caisson Vent location) and the layout and structural design to support Water Treatment Package.

PWT technology underwent thorough in-house evaluating and screening, considering cost and time constraints, before advancing to Basic Engineering to ensure that all key design parameters are incorporated in the study.

The ASK offshore PWT facilities is located at WPA-2 and adhere to disposal specification less than 29 ppmv of Oil in Water (OIW) as per Myanmar regulation. The primary treatment unit employs De-Oiler Hydrocyclone, while secondary treatment unit involves a Degasser. These technologies are selected Due to their maturity, proven efficiency mature with proven efficiency, simple control, high reliability of static equipment, alignment with the treatment specifications, and cost effectiveness.

The unit is capable of handling a wide range of flowrates from 0 to 5,500 BPD with flexible operating and control philosophy. Skim Vessel is installed upstream of PWT Units to ensure stable flowrate, enhancing separation performance. To achieve the challenging disposal specification, pressure drop across De-oiler Hydrocyclone and Degasser's retention time are key design parameters. To address the challenges of unmanned operation, online monitoring of both inlet and outlet stream is implemented, and operating conditions are adjusted remotely. Chemical injection facilities are provided as back-up for separation improvement. For produced water disposal, Caisson length is specially designed for shallow water depth and the dedicated Caisson Vent is required to meet safety design criteria. To allow flexible for future de-bottlenecking, the Degasser is designed with provision for upgrading to Horizontal Induced Gas Floatation (IGF).

It is highly challenging to consistently achieve water treatment specifications give the wide range of produced water rate, fluid properties, operating conditions, layout/structural constraints, and the need for high reliability with optimal investment. All aspects and options have been studied and evaluated thoroughly during Basic Engineering to ensure the development of a robust design for PTTEP's first offshore unmanned PWT facility. The intention is to create a design that not only serves the needs of this project effectively but also provides meaningful insights and applicability to future projects.