Application of a New Interpretation Method for Inflow Oil Tracers at Steady State Conditions

Abstract The Alvheim area is a subsea development comprising several hydrocarbon accumulations produced through long horizontal multilateral wells. Conventional monitoring techniques—such as production logging and downhole intervention-based measurements—are often impractical due to limited wellbore accessibility, high operational complexity, and substantial cost. Consequently, inflow chemical tracers have become a central component of the well and reservoir surveillance strategy. Historically, tracer data have provided clear and reliable information on well clean-up behaviour and zonal inflow of both oil and water. The objective of this paper is to describe the fundamental principles and practical application of a new interpretation methodology for oil tracers under steady-state production conditions. Key elements of tracer-based monitoring include tracer system design, sampling procedures, laboratory analysis, and interpretation of tracer signals. The proposed methodology establishes a direct relationship between tracer mass release and the local presence of the target fluid at each tracer installation point. The core concept involves defining a baseline tracer mass flow trend and interpreting deviations from this trend as indicators of changes in target fluid wetting fraction and indicative of zonal inflow behaviour. The method was applied in the surveillance of the Gekko thin oil-rim development, where long horizontal wells are equipped with autonomous inflow control devices (AICD), swell packers, and both oil and water tracer systems. The new interpretation approach proved essential for identifying the presence of free gas under steady-state conditions, providing critical insight into reservoir behaviour and AICD performance—further discussed in a companion paper. Overall, the paper introduces a novel approach for interpreting tracer signals during steady state production, enabling extraction of additional information and diagnostic value. Practical implementation aspects and potential future developments are also discussed.