Flow and Heat Transfer along the Boiling Point with Depth (BPD) Zone

Abstract

Boiling Point with Depth (BPD) zones are a common phenomenon within geothermal reservoirs, and their stability is surprising in view of the fact that throughout their depth hot water exists at or close to the boiling point for the local fluid pressure. This poses a problem, because if fluid is not rising towards the surface, conductive heat losses will reduce the temperature below the boiling point, whereas if fluid is moving, continuous stream generation chokes its path through the porous permeable matrix to bring flow to a halt. The solution of this paradox appears to be that heat conduction and fluid velocity are held in balance by steam bubbles locked in place by the rock medium and control the water velocity to less than 1 mm/day by appropriate expanding and contracting. Water and steam therefore coexist throughout the zone with the former being the continuous and moving phase while the latter is both discontinuous and immobile but with a slightly varying volume.