MODELLING TRACER BREAKDOWN UNDER GEOTHERMAL CONDITIONS

Abstract

Geothermal tracer tests are widely used in the industry to identify flow pathways between production and reinjection zones. The results of these tests are often used to predict the potential for thermal breakthrough of cooler reinjection fluids. This is usually done
by using the tracer test data to constrain the flow paths through which reinjection fluids travel in numerical reservoir models.
Recent experimental studies by Mountain and Winnick, and Sajkowski et al have shown that naphthalene sulfonates that are widely used in the geothermal industry as tracers have temperature limits. These studies have measured the rates of the thermal breakdown reactions that these compounds undergo. These breakdown rates have been shown to depend on temperature and pH.
This paper presents work to model the breakdown of different types of geothermal tracers and incorporate the reactions into transport models of tracer flow in a geothermal reservoir. The ultimate purpose is to estimate temperatures along the paths that tracers flow within the reservoir. We will present models of the reaction kinetics of some naphthalene sulfonate and alcohol tracers and the findings of incorporating these reactions into numerical models of reservoir tracer tests.