A LABORATORY INVESTIGATION OF PERMEABILITY IN HEMISPHERICAL FLOW WITHAPPLICATION TO FORMATION TESTERS

We use borehole and laboratory measurements with a probe to obtain loc al permeability estimates. Under ideal conditions sufficiently far fro m the probe, the flow induced is hemispherical. We describe an experim ental apparatus that can flow fluids through a probe under isotropic c onfining stresses and present an analysis to deduce the optimal dimens ions of a finite cylindrical rock to simulate hemispherical flow like that in a semi-infinite medium. We derive equations for permeability i nterpretation of laboratory measurements. We made pressure measurement s on a number of synthetic and natural rocks as functions of confining stress, probe size, flow rate, and flow direction. For synthetic rock s, the calculated permeability shows little dependency on these factor s. For natural media, however, flow direction appears to have a major effect at high rates that increases with decreasing probe size. On the basis of these data, we propose a fines-migration mechanism. As expec ted, permeabilities show a hysteretic dependence on confining stress. Hemispherical flow measurements with homogeneous porous media indicate that fluid injection would yield permeability close to the true value . Furthermore, sequential injection of multiple phases shows that endp oint effective permeabilities may also be obtained.