Harnessing Natural Tracer to Monitor Immiscible Water-Alternate-Gas (iWAG) Breakthrough in Field Offshore Sarawak

Abstract iWAG as an EOR has gained widespread acceptance as an efficient EOR technique based on extensive lab studies and multiple successful field applications. However, even with its broad adoption in the industry, accurately modelling the breakthrough of injected fluids remains challenging due to reservoir heterogeneities and complex dynamics of a three-phase flow in the reservoir. This outlines the importance of continuous reservoir surveillance throughout iWAG implementation. Natural tracer is utilized as a surveillance tool for Field B to verify water breakthroughs through the benefiter wells. Pre-screening analysis was done on 15 gas samples and 6 water samples taken from injection sources and producing wells in Field B, to evaluate the feasibility of using natural tracer in which the fluid is distinguished based on its composition and isotope signature. This study indicates that for Field B particularly, hydrocarbon isotope signature (C1 to C5) shows no significant contrast between the source fluid and the produced fluid thus is not suitable to be used as a breakthrough indicator. However, analysis done on the water chemistry observed significant contrast, especially on the hydrogen isotope between the injected water and produced formation water alongside multiple ionic elements. This paper presents a detailed case study on the pre-screening, implementation, and evaluation of natural tracers for monitoring Water and Gas breakthroughs during the application of the Immiscible Water Alternate Gas (iWAG) Enhanced Oil Recovery (EOR) technique. The study focuses on Field B in East Malaysia, which has adopted iWAG EOR to optimize recovery through a robust FDP. This work highlights the methodologies for natural tracer screening, the surveillance strategy, and key findings from the execution phase.