THEORETICAL-STUDY ON THE STABILITY OF A RESERVOIR CREATED BY THE INTERSECTION OF A FLUID-FILLED CRACK WITH AN OBLIQUE JOINT FOR THE EXTRACTION OF GEOTHERMAL HEAT

On the basis of the two-dimensional theory of elasticity, the theoretical analysis of a vertical, fluid-filled crack intersecting an oblique joint has been made for the extraction of geothermal heat from hot, dry rock masses, where the opening of the joint near a point of intersection and the frictional resistance against slips along the joint are taken into account. The stress intensity factors are evaluated for discussing crack kinking at the upper joint tip, and the sufficient conditions on the inclination of the joint and on the length between the upper joint tip and the point of intersection are obtained for keeping a fluid-filled crack stable just beneath a joint. It is also shown that the volume of the stable reservoir created by using a joint is much larger than that of a fluid-filled crack in a jointless rock mass, even if the joint is oblique and is opened up by the fluid pressure.