Interpretation of In-Situ Pressure and Flow Measurements of the Salado Formation at the Waste Isolation Pilot Plant

Abstract

This paper describes preliminary interpretation of in-situ pressure and flow measurements of the Salado Formation at the Waste Isolation Pilot Plant (WIPP). The WIPP facility is located 660 m underground in the Salado, a bedded salt deposit. Shut-in pressure tests were conducted prior to, and subsequent to, the mining of a circular drift in order to evaluate excavation effects on pore pressure, permeability, and host rock heterogeneity. Borehole deformation was measured during these tests and used to correct for changes in the test region volume due to salt creep effects. Preliminary pre-excavation results indicate that the flow properties of this layered host rock are heterogeneous. Resulting pore pressures range from 1 to 14 MPa and permeabilities range from below measurable to about 1 nanodarcy. Normalized borehole diameter change rates were between -4 and 63 microstrains/day. Shut-in pressures and borehole diameters in all test boreholes were affected by the excavation of Room Q coincident with the advances of the boring machine. Preliminary results from post-excavation test results show decreased pore pressures compared to pre-excavation values.

Coupled multiphase flow and closure analysis of repository response to waste-generated gas at the Waste Isolation Pilot Plant (WIPP)

“…In-situ permeability testing indicates a large variability in intrinsic permeability, ranging from less than 10" for anhydrite interbeds Howarth et al, 1991;Beauheim et al, 1993a) …”

“…The extrapolated values have some uncertainty depending on the quality and duration of the tests and may be influenced to some extent by excavation-related depressurization. Based on hydraulic testing performed by and Howarth et al (1991), the undisturbed brine pore pressure at the repository level was assumed to be 12.0 MPa to 12.5 MPa. A best estimate of 12.0 MPa was used in baseline simulations and a range 3-13 of 11.0 MPa to 15.0 MPa was selected for sensitivity analysis.…”

“…A single value of 3E-18 m 2 was reported at ~ 2 m from an excavation and a test of pure halite further (9 m) from the excavation showed no measurable (-zero) permeability . Howarth et al (1991) reported far-field (> 20 m from room) Salado halite permeabilities ranging from 2E-21 m 2 to -zero.For most Salado halite, 1.0E-21 m 2 is considered to be a reasonable undisturbed value for simplified calculations. A range of 1 .OE-19 m 2 to 1 .OE-25 m 2 (approximately zero) has been selected for sensitivity analysis.…”

“…In-situ testing has been performed to determine the hydrologic properties for the halite and the anhydrite interbeds under both undisturbed and excavation-disturbed conditions. The Salado Formation hydrologic parameters are summarized in Section 3, and a complete discussion of parameter selection is contained in Appendix A.In-situ permeability testing indicates a large variability in intrinsic permeability, ranging from less than 10" for anhydrite interbeds Howarth et al, 1991;Beauheim et al, 1993a) …”

Multiphase Flow and Cavern Abandonment in Salt

“…Similarly, permeabilities have been measures as low as 10 -24 m2 at distance fiom mined openings in Germany (Belohlavek et al, 1999). The salt at WIPP is brine saturated with a pore pressure measured at lithostatic (Howarth et al, 1991;Beauheim, Saulnier, and Davies, 1991). Similar to WIPP, Gulf Coast salts are believed to be at lithostatic pore pressure (Kupfer, 1978;Baar, 1961Baar, & 1977 and measurements in the U.S. tend to support pressures approaching lithostatic (Iannacchione and Schatzel, 1985;Molinda, 1988).…”