ESTIMATION OF FRACTURE HEIGHT USING MICROSEISMICITY ASSOCIATED WITH HYDRAULIC FRACTURING

The ratio of horizontal-to-vertical (H/V) particle velocity in backgro und microseismic radiation associated with hydraulic fracturing is sub stantially higher in the dilatant, low-velocity fractured zone than it is outside. This provides a useful diagnostic for determining the hei ght of the fractured zone. Numerical synthesis of guided wave phenomen a within the low-velocity fractured zone accounts for much of the obse rved behavior, but measured H/V patterns are not totally consistent wi th either pure tensile or pure shear sources. A composite model contai ning both tensile-compressional sources and asperity shear failures ap pears to satisfy the main observations better than either source type does alone. This composite is consistent with current models of earthq uake aftershock sequences, which also have different mechanisms at the edges and in the interior of a fracture zone (tensile and shear, resp ectively). The H/V phenomenon is consistent with a predominance of ene rgy with shear-wave polarization traveling at postcritical angles, pro duced either directly by the source or by P-to-S conversion at the edg es of the fracture zone. The H/V ratios are enhanced by increasing dil atancy, which decreases the velocity within the fracture zone.