Abstract
We report laboratory measurements of electrical resistivity rho , water permeability k, and compressional wave velocity V p for both intact and fractured Berea sandstone samples as functions of temperature from 20 degrees C to 200 degrees C and effective pressure P e from 2.5 MPa to 50 MPa. For the intact sample, V p increases from 3.52 km/s to 4.16 km/s as P e goes from 3 to 50 MPa. With increasing temperature, V p decreases at rates of about 3 percent per 100 degrees C at P e of 5 MPa and about 1.5 percent per 100 degrees C at P e of 38 MPa. Data from the fractured sample are qualitatively similar, but velocities are about 10 percent lower. For both intact and fractured samples, rho increases less than 15 percent as P e increases from 2.5 MPa to 50 MPa. Although both samples show a larger decrease in resistivity with increasing temperature, most of this change is attributed to the decrease in resistivity of the pore fluid over that temperature range. For both samples, k decreases with increasing pressure and temperature. The intact sample permeability varies from 23 mD at 3 MPa and 20 degrees C to less than 1 mD at 50 MPa and 150 degrees C. The permeability of the fractured sample varies from 676 mD at 3 MPa and 20 degrees C to less than 1 mD at 40 MPa and 190 degrees C. The effect of the fracture on k vanishes after several pressure cycles and above about 100 degrees C. These laboratory data are used to demonstrate the possibility of using resistivity and velocity measurements to estimate in-situ permeability of a reservoir.
