PERMEABILITY OF APACHE LEAP TUFF - BOREHOLE AND CORE MEASUREMENTS USING WATER AND AIR

Field and laboratory methods for estimating and interpreting parameter s obtained from field borehole and laboratory core experiments are exa mined using permeability data interpreted from air and water injection tests in variably saturated fractured tuff at the Apache Leap Tuff Si te in central Arizona. The tuff at the field site has a matrix porosit y of approximately 17.5% and contains numerous near-vertical fractures at an average spacing of 1.3 m. More than 270 m of 6.4-cm-diameter or iented core were collected from boreholes drilled to a maximum depth b elow the surface of 30 m and at a vertical angle of 45-degrees. Labora tory estimates of absolute permeabilities using air and water as the t est fluids were acquired at a range of matric potentials for 105, 5-cm -long core segments extracted at approximately 3-m intervals containin g no obvious fractures. Field scale estimates of fractured rock permea bilities using air and water as test fluids were obtained at ambient m atric suctions and water saturated conditions, respectively. The field tests were conducted along 3-m intervals within boreholes with the in tervals centered on core sampling positions. Borehole and core permeab ilities demonstrate substantial spatial variability, with variations e xceeding three orders of magnitude. Laboratory core data show a strong relationship between permeabilities using saturated water and oven-dr y air injection tests with the latter demonstrating the Klinkenberg ef fect. The influence of matric suction on permeabilities is used to dem onstrate that relative permeabilities do not sum to a constant for a w ide range of matric suction. Only weak relationships exist between per meabilities measured in boreholes versus cores for both water and air. Permeabilities measured in boreholes using air are shown to provide g ood estimates of permeabilities measured using water into initially un saturated, fractured rock at the Apache Leap Tuff Site.