Abstract

Both inert and reactive Tracers have been used to further the understanding ofthermal recovery applied to heavy oils and bitumen. They can be used to gain anunderstanding of process conformance. recovery mechanisms or even reservoirheterogeneities. Tracers are commonly transported in The water phase which isthe continuous phase in a water-wet porous medium. Inert aqueous tracers willfollow the primary flow paths of the liquid water while reactive aqueoustracers can dissolve/precipitate away from these regions. This paper discussesinert tracers and reactive geochemical tracers as they have been used bothindependently or together in analysis of steamflood processes.

Introduction

Classical analysis of tracer dispersion has involved examination of diffusion.capacitance or differential mixing mathematical models. In this paper themechanisms of dispersion are examined by modelling the physical dispersionmechanisms rather than by examining the dispersion/diffusion coefficient.

Use of tracers to aid in steamflood analysis is discussed at two dimensionscales. First the use of inert tracers is discussed at the laboratory scale.These tracers are used to infer details about bed capacitance. i.e. the abilityof the oil sand matrix to retain and disperse an injected tracer pulse.

Secondly, the use of reactive. geochemical tracers is discussed at the fieldscale and is compared to the behaviour of inert tracers at the same scale inorder to derive further information about the field process.

The water phase, being the continuous phase in a water-wet sand medium. is usedto convect the inert or reactive tracers. Discussion of bed capacitance is thuscentred on flow properties of the water as it leaves the injection well andflows to the production we II. Produced concentrations of tracer can Then beused to discern details of the water-phase streamlines. The multiphaseenvironment (oil, water, gas) causes the tracer to be diverted by movement ofboth the oi I and gas phases. A further complication arises when the gas phaseis steam because condensation of water vapour will dilute the concentration oftracer.

A geochemically reactive tracer such as silica introduces a new dimension. Inaddition to the dependence of tracer concentrations on flow path of the waterphase, oil and gas saturations and condensation of the gas. temperature of thewater phase is important since solubility of silica in water is a strongfunction of temperature. Use of an inert tracer together with this type ofreactive tracer is proposed In order to decouple some of the flow pathcharacteristics thereby highlighting the contribution of the steam-front as acontributor to produced silica concentrations.

First, pulse injection of a tracer in a physical simulation of a steam-additivedrive process will be discussed. A numerical reservoir simulator is used tocapture the dispersion mechanism of dead-end pore volume.

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