A simple model has been developed as a scoping tool for transport between an injection well and an abstraction well pumping at the same rate (i.e. a doublet) in a fractured porous rock. This model is aimed primarily at the planning and preliminary interpretation of tracer tests and trial heat exchange using thermal doublets in the Chalk aquifer. The model is essentially a particular case of transport along multiple flow paths and relies on the invariance of double-porosity transport with respect to velocity variations along a flow path. Hypothetical simulations demonstrate that solute tracer tests need to be supplemented by information on fracture porosity in order to be able to predict thermal breakthrough.