Low-frequency (<100 Hz) Dynamic Fracture Compliance Measurement in the Laboratory Available to Purchase

Although the mechanical compliance of fractures can have a large impact on estimation of oil and gas reservoir stress state and fluid contents, only a limited number of fracture compliance measurements are available, particularly in the sub-kilohertz frequency range relevant to the field seismic measurements. Also, most laboratory measurements are for the normal fracture compliance, and measurements for the shear fracture compliance are rather rare. For this reason, a laboratory device was developed which allows us to measure both normal and shear specific compliances of an interface (fracture) simultaneously, in the frequency range of ~1 Hz–100 Hz. Using this device, dynamic fracture compliances of a sheared, water-saturated and drained fracture were measured, under small fracture-normal stress. For the saturated fracture, the normal fracture compliance was clearly frequency dependent, with the relaxation frequency at 10~20 Hz. This result, however, did not agree well with an analytical model which predicted much larger compliance changes and a higher relaxation frequency than the experiment. Observed normal to shear fracture stiffness ratio ranged from 1.8–2.8 for the saturated fracture and 1.7 –1.9 for the drained fracture, both decreasing with increasing normal stress on the fracture. Interestingly, for a fracture containing a thin rubber membrane, the normal-to-shear compliance ratio increased with the stress, apparently exhibiting the opposite behavior.