Abstract
Aung Sinkha (ASK) is a new development field located in the Gulf of Moattama, Myanmar. The two wellhead platforms (WPA-1 and WPA-2) location is 90 km from ASK Onshore Processing Facilities. Based on engineering study and cost evaluation in Conceptual phase, the Produced Water Treatment (PWT) is selected to separate produced water, treat and dispose at offshore wellhead platform. The scope of Basic Engineering (BE) is to design Offshore PWT to achieve disposal specification.
The design challenges of Offshore Unmanned PWT are including various aspects as following.
Extremely varying of produced water profile over the field life
Offshore unmanned facilities and locates far from shore
Reliability and performance of water treatment
Enhancing alternatives of PWT separation efficiency.
Produced Water Disposal facilities constraints i.e. Caisson length vs. shallow water depth, Caisson Vent location
Layout and structural design to support Water Treatment Package
PWT technology has been evaluated intensively and pre-screened in-house with cost and time constraints prior to preceding Basic Engineering to ensure that all key design parameters are incorporated in the study.
The offshore PWT of ASK is located at WPA-2 with disposal specification less than 29 ppmv of Oil in Water (OIW) as per Myanmar regulation. The primary treatment unit is De-Oiler Hydrocyclone. The secondary treatment unit is Degasser. These technologies are selected as they are mature with proven efficiency, simple control, high reliability of static equipment, fit for purpose to the treatment specification and low investment cost.
The unit is capable to handling wide range of flowrate from 0 to 5,500 BPD with flexible operating and control philosophy. Skim Tank Vessel is installed upstream of PWT Units to ensure stable flowrate enhancing separation performance. To achieve the challenge disposal specification, pressure drop across De-oiler Hydrocyclone and Degasser's retention time are key design parameters. To fill the gap of unmanned operation, OIW at both inlet and outlet stream are online monitoring and operating conditions are remote adjusting. 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 be flexible for future de-bottlenecking, the Degasser is designed with provision for upgrading to Horizontal Induced Gas Floatation (IGF).
It is very challenging to achieve water treatment specification steadily with wide range of produced water rate, fluid properties, operating conditions, layout/structural constraints, required high reliability with optimum investment. All aspects and options have been studied and evaluated thoroughly during Basic Engineering in order to accomplish the good design for the first Offshore Unmanned PWT of PTTEP that could be beneficial and applicable to other projects meaningfully.
