On the Visibility of Non-Intersected 'Nearby' Fractures in Inter-Well Tracer Tests: Scoping Simulations, I

Abstract

In past scoping simulations (2013a), we illustrated the parameter uncoupling between heat and solute (tracer) transport in a geothermal well doublet within a five-fracture reservoir model, and the use of thermosensitive tracers to restore the correlation between thermal lifetime (as a prediction target) and tracer signals (as an early predictor). In the present technical note, we look into the effects of non-intersected fractures inside or outside the reservoir on inter-well tracer test signals. Unlike in the past study, where fracture parameters were varied uniformly for the whole set of fractures, we now switch fractures on and off individually. Preliminary scoping simulations on this greatly simplified five-fracture geometry indicate that tracer signals before ~two reservoir turnover time units exhibit slight influences from fracture presence or absence, yet not sufficient sensitivity to enable detecting the presence of non-intersected fractures, neither outside nor inside the reservoir. Though the fracture sensitivity of tracer BTCs generally increases with observation time, late tailings of tracer signals still cannot provide a sensible method for fracture detection. Nonetheless, it still seems worthwhile attempting to provide a tracer BTC type-curve framework for such systems, given that the tracer-based inversion of some of the matrix-fracture system parameters can sometimes be constrained by other methods.