Simultaneous Hydraulic/Physical Parameter Measurement on Rock Specimens Subjected to Triaxial Conditions

The apparatus described provides for laboratory studies of stress-coupled parameters, with simultaneous measurement of mechanical deformation, permeability, electrical resistivity, and compressional wave velocity in 10- by 20-cm (4- by 8-in.) cylindrical test specimens with pore fluid pressure and subjected to triaxial test conditions. The compact collar-coupled design facilitates specimen installation and apparatus mobility. Axial and volumetric strains are determined using external linear displacement transducers, and differential axial stress is determined by a load cell which is an integral part of the loading column. Hydrostatic pressures in the confining fluid and in the pore fluid reservoirs up- and downstream from the test specimen are measured with pressure transducers. Data acquisition and servocontrol of the confining pressure and axial loading are performed by a microcomputer system, and test results are cross-correlated with the applied differential axial stress. Transient pulse techniques are used to determine the permeability of specimens in the range of 10⁻²⁰ to 10⁻¹⁶ m² (10 nanodarcies to 100 microdarcies). The electrical resistivity measurements incorporate phase-sensitive detection with a four-terminal configuration. Transducers in the specimen end caps generate and detect mechanical pulses for wave velocity measurements. The apparatus is designed to operate with corrosive pore fluids such as brine. System performance is illustrated by representative results from tests on a specimen of domal salt during equilibration, and during and after deformation.