Measurements of the Permeability of the Sheeted Dikes in Hole 504B, ODP Leg 111

Abstract

An inflatable drill-string packer was used to measure the in-situ bulk permeability of two zones deep in Hole 504B, within the sheeted dikes that comprise the deepest 500-600 m of the hole. Previous measurements by Anderson and Zoback (1982), Zoback and Anderson (1983), and Becker et al. (1983a, 1983b) had shown that the upper 200 m of pillow lavas in the hole is fairly permeable, at about I0-14-10~1 3 m 2. In contrast, Anderson et al. (1985a, 1985b) measured a much lower bulk permeability of about 10" 17 m 2 over an interval of >700 m that includes the deeper 400 m of extrusives and the upper 300 m of sheeted dikes. During Leg 111, the packer was inflated first at 936 mbsf, within the transi tion between extrusives and sheeted dikes, isolating the upper 470 m of dikes. Later in the leg, the packer was inflated at 1236 mbsf, isolating over 300 m of deeper dikes. At both depths standard slug tests were conducted, with excellent re sults. These results indicate that the sheeted dikes have bulk permeabilities on the order of 10~1 8 to 10~ n m 2 , compara ble to the value measured by Anderson et al. (1985a, 1985b) in the deeper extrusives and upper sheeted dikes. Thus, ex cept for the permeable upper 200 m of pillow lavas, most of the 1287.8 m of basaltic basement cored in Hole 504B is relatively impermeable.

Site 1256

“…samples recovered from Hole 504B (Becker, Foss, et al, 1992). Figure F38 shows the composition of the deepest borehole fluids collected in Hole 504B at the beginning of DSDP/ODP Legs 83, 111, and 137 (Mottl et al, 1985;Becker, Sakai, et al, 1988;Becker, Foss, et al, 1992) (Table T12) as well as the composition of the uppermost basement fluid estimated from pore water studies during DSDP Leg 69 (Mottl et al, 1983).…”

“…Figure F38 shows the composition of the deepest borehole fluids collected in Hole 504B at the beginning of DSDP/ODP Legs 83, 111, and 137 (Mottl et al, 1985;Becker, Sakai, et al, 1988;Becker, Foss, et al, 1992) (Table T12) as well as the composition of the uppermost basement fluid estimated from pore water studies during DSDP Leg 69 (Mottl et al, 1983). Mg, Ca, K, and Sr concentrations of these deepest fluids are almost constant with depth despite the very large increase in borehole temperature (up to 158°C for the Leg 137 measurement) (Table T12).…”

“…The most detailed studies of the chemistry of basement fluids have been conducted in the region of the oceanic basement reference hole at Site 504 (ODP Sites 501, 504, 677, 678;see Mottl et al, 1983see Mottl et al, , 1985Becker, Sakai, et al, 1988;Mottl and Gieskes, 1990;Becker, Foss, et al, 1992;Alt, Kinoshita, Stokking, et al, 1993) and during ODP Leg 168 and subsequent investigations of young buried basement on the eastern flank of the Juan de Fuca Ridge (Davis, Fisher, Firth, et al, 1997;Elderfield et al, 1999;Mottl et al, 2000;Wheat et al, 2000). These studies have involved both sediment pore water profiles and direct sampling of borehole fluids and have elucidated the main reactions occurring at low to moderate temperatures (<100°C) between buried ocean floor basalts and seawater-derived basement fluids.…”

Site 787

“…Archie's Law, which is empirically derived, may not be appropriate for these samples. However, sampling with a watercooled rock saw and/or uncertainties in the reliability of wet volumes determined by the penta-pyenometer (Becker, Sakai, et al, 1988) also may bias the data (Table 11). In addition, porosity calculations using weights and dry volumes (Becker, Sakai, et al, 1988) are generally within 7% of the values obtained using the wet volumes.…”

“…However, sampling with a watercooled rock saw and/or uncertainties in the reliability of wet volumes determined by the penta-pyenometer (Becker, Sakai, et al, 1988) also may bias the data (Table 11). In addition, porosity calculations using weights and dry volumes (Becker, Sakai, et al, 1988) are generally within 7% of the values obtained using the wet volumes. On the other hand, the porosity results obtained in Hole 787B are comparable to those previously reported for sediments from similar depositional/tectonic environments cored during ODP Leg 125 (Fryer, Pearce, Stokking, et al, in press) and DSDP Leg 60 .…”