Unlocking First Deepwater Sarawak Sour Gas Molecule Towards Sustainable Future
Authors: Goh T. , Mash'al H. , Loh R. , Lee T. , Teh A. , Tay W. , Mion F. , Subramaniam S. , Kumar S. 
Published: February 2024

Rosmari & Marjoram (R&M) Development Project aims to unlock first deep-water, sour gas fields in Sarawak to fill the ullage of feed gas to Sarawak LNG production demand. However, due to the remote location of the wells about ~220 km from Bintulu shore and significant Hydrogen Sulphide (H2S) contaminant level, it demands significant sour gas processing as well as flow assurance and corrosion management which introduces significant safety, operability, and both CAPEX and OPEX challenges.

The Project started off with a few conventional Offshore concepts, where the bulk majority of the gas processing units are located on either integrated Central Processing Platform (iCPP), Floating Production Storage and Offloading (FPSO) or subsea tie-ins concept into existing sour gas processing hub riding on maximizing synergy of CCS technology within the area. These concepts have been assessed with various sour gas processing and sour gas disposal methods before the treated gas can be evacuated to either existing hub or a new dry gas export trunkline, to minimize both corrosion and flow assurance risk.

Throughout the concept selection process, the conventional Offshore concepts were found to be associated with significant challenges of sour gas disposal method where the Project has assessed Acid Gas Re-injection, Sea Water Scrubbing to allowable limit for seawater disposal as well as SRU to produce molten Sulphur to be stored and exported from a FPSO. On top of significantly high CAPEX, each respective Offshore concept comes with high complexity on both technical safety and operating solutions, as well as uncertainty on License To Operate due to its potential environmental impact. The Project has then stepped out from the norms by proposing the iCPP to be Normally Unmanned iCPP (NUI) to reduce risk exposure on offshore personnel by moving bulk of processing units including the sour gas processing and disposal to a new Onshore Gas Plant (OGP) by transporting dry sour gas through a new trunkline.

Due to residual risks from the proposed NUI concept, the Project went through series of Competitive Scoping and structured engineering decision making process to further minimize offshore processing scope. This has resulted into a simplified Wellhead Platform (WHP) with minimum functional requirements to enable the "Normally Unmanned" philosophy to be integrated with a multiphase trunkline and a full fledge OGP. This introduces new flow assurance and corrosion challenges which the Project team managed to overcome with robust design for hydrate and corrosion management.

The safety and operability of the Project have further improved by minimizing Offshore scope and integration with a full fledge OGP provides higher capability for robust and reliable designs and safe separation distance/material handling between different processes due to larger space available onshore. Lower landing pressure onshore and large slug handling capability enables the operations of multiphase trunkline as well as free flow from WHP enhancing ultimate recovery from the fields.

With this integrated concept, the Project has also able to reduce ~20% of the GHG emissions which enables it to surpass internal performance standard and GHG intensity target by replacing conventional fuel gas combustion via gas turbine offshore with power import from local grid that is made up by significant amount of renewables. The GHG journey for this Project has then reached another significant milestone by partnering with Sarawak Energy in adopting Renewable Energy Certificates (RECs) to source 100% hydropower from the grid, contributing to further reduction of 15% of its GHG emission.

The conventional Offshore concept requires robust structural design to support the heavy weight from the processing equipment on the topside, which contributes to a remarkable capital expenditure. The Project CAPEX reduces substantially with the selection of an integrated concept, making the Project economically feasible to be sanctioned to Final Investment Decision (FID).