Explosion Phenomenology and Permeability Enhancement in Earth Media

摘要

Detonation of tamped explosives in a borehole results in a shock wave with a peak stress of about 100 kbars propagating into the rock. The effects of high intensity stress waves on the rock have been deduced from numerical computer calculations which simulate the physics associated with the process and verified by comparison with experimental measurements. The shock wave attenuates as it propagates away from the borehole by fracturing and compacting the rock until at some distance from the borehole the peak stress is below the elastic limit of the earth media and the wave propagates quasi-elastically. Near the borehole the rock is pulverized with exceptionally high fracture frequency but the explosion-produced fracture density decreases rapidly with distance until reduced to a few short isolated tensile fractures. The porosity is severely reduced near the borehole, but increases to near or slightly above preshot value in the tensile fracture region. The rebound of the elastic media creates a compressive hoop stress in the fractured media around the explosive cavity which tends to temporarily close those fractures oriented radially from the borehole. Relatonships describing permeability enhancement using explosives fired in boreholes were derived and are compared with existing field measurements. The degree to which permeability can be enhanced with high explosives depends on material.