Improving Offshore Effluent Discharge Quality (EDQ) for High Contaminant Field through Chemical Application and Process Control Tuning
Authors: Lai Vermie Fan Jou , Lee Kok Hock , Mahmud Nurul Syuhada , Kamaruddin Nadia Asshikin , Raja Sahar Raja Nor Rafidah , Rahim Nuramira Ayna , Ain Shabuddin , Robert Willy Bayang , M Sarin M Nizam , Hwang Zi Zin , Chieng Kai Zhen , Abdul Latif Faisal , Zamri Muhammad Syafiq , Abdullah Fathurrahman 
Published: October 2023

Abstract

Objectives/Scope
Field N, located at offshore Sarawak, Malaysia has been identified of gas producing field with high level of contaminants such as mercury, CO2 & H2S. One of major challenges in the development of Field N include the presence of stable emulsion that had caused the oil in water (OIW) reading for the discharge water exceeding the allowable Effluent Discharge Quality (EDQ) limit specified by Malaysia Department of Environment governance. Chemical application i.e., water clarifier with flocculation type was applied in the Produced Water Treatment System (PWTS) to assist in emulsion separation in order to comply with the specification of environmental authority, i.e., OIW ≤ 100 mg/L.
This paper described the multi discipline collaboration efforts between Operation, Process and Production Chemistry on the chemical application and process control tuning on Sludge Receiver’s Level Control Valve (LCV-2031) to promote effective chemical mixing with the fluid and subsequently reduce the OIW reading at the discharge water.

Methods, Procedures, Process
Process control tuning approach starts with controller output% (OP%) and process variable (PV) trending collection based on the default and new tuning parameters (i.e., Proportional Band, Integral and Derivative or PID). The produced water sample at the final discharge point is taken for oil in water (OIW) analysis using accredited method. With the same chemical injection dosage, the LCV controller PID is tuned manually at site in such a way that sustained oscillation is achieved and OIW reading fulfills EDQ limit as per Organization PPGUA Minimum Environmental Specification (MES) of 30 mg/L. Controller behavior verification is necessary during the tuning exercise to ensure the primary control element i.e., Slug Receiver’s level and downstream system process parameters stay within the safe operating limit.

Results, Observations, Conclusions
Based on the field trial program conducted in 2022, it was observed that the OIW reading reduced and improved significantly with the increasing of Slug Receiver LCV-2031 opening% oscillation frequency, which was achieved by providing an optimum Proportional, Integral and Derivative (PID) parameter on the controller. These efforts contributed to the reduction of OIW reading from ≥ 80 mg/L (pre field trial), to below Organization limit of 30 mg/L (post field trial). PID tuning on Slug Receiver’s level control valve controller (LICA-2031) able to provide agitation to the chemical for effective mixing with the produced water, which improves the OIW reading of the effluent discharge without the need of increasing chemical injection dosage.

Novel/Additive Information
This innovative and collaboration efforts contributed to the sustenance of good EDQ performance for Field N and cost saving of chemical required to treat the produced water. With less chemical injected, the HSE impact of flocculants issues encountered at Field N is also minimized.