Two simple models, based on standard analytic solutions for the mechanical behaviour of cracks combined with a simple representation of the frictional properties of fracture surfaces, have been developed. The models describe the stimulation and circulation of HDR reservoirs in naturally fractured basement. The models provide estimates of the rock volume to fluid volume ratios required for stimulations, the injection flow rate for differing injection pressures, and fluid flux/fracture area partitioning, and hence thermal drawdown behaviour.