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.
Two holes drilled into the Cascadia accretionary prism during Ocean Drilling Program (ODP) Leg 146 were instrumented with borehole seals ("CORKs") for long-term monitoring of temperatures and pressures at in situ conditions. We report the results obtained during submersible data recovery operations at the sites in September, 1993, 9.5 months after the CORK instruments were emplaced. The installation at Hole 889C off Vancouver Island was severely damaged during a deployment made very difficult by poor weather and unstable hole conditions; no useful data were recovered there. In contrast, the installation at Hole 892B in the accretionary prism off Oregon produced excellent thermal and pressure data that provide constraints on the hydrogeology at that site. Site 892 is located over the hanging wall of a hydrologically active thrust fault that is penetrated at a depth of about 100 m in the 146-m-deep Hole 892B. In addition, there is a well-defined regional bottom-simulating reflector (BSR) whose depth shoals about 8 m to 72 mbsf at the site, presumably because of the thermal effects of fluid flow in the fault zone. Results of numerical modeling demonstrate that the local shoaling of the BSR is consistent with the effects of recent up-dip fluid flow that initiated roughly 400 yr ago at an average flux per meter along strike of 1 × 10~6 m 3 s"'; steady-state flow is precluded. Hole 892B was sealed with a pressure gauge and a 10-thermistor chain extending to a depth of 122 mbsf. Temperatures in the CORKed hole define a generally uniform gradient of about 68 mK m" 1. At the depth of the regional BSR, this gradient gives a temperature identical to that on seawater-methane-hydrate phase boundary at the equivalent pressure. The gradient is significantly greater than that defined by shipboard temperature measurements made in exploratory holes about 200 m to the southwest. The disagreement can be explained if the exploratory holes intersected fault-controlled zones of fluid upflow at shallower depths than the CORKed hole. The gradient defined by the shipboard measurements may reflect locally diminished heat flow in the footwall of the fault. CORK temperatures also define a distinct thermal anomaly at the depth of the fault zone, which is consistent with results of numerical simulations of a transient fluid flow event. The up-dip fluid flux is constrained to be approximately 6 × I0" 5 m 3 s~1, nearly two orders of magnitude greater than the average rate inferred from the shoaling of the BSR. Pressures in the sealed hole decayed from an initial ("shut-in") superhydrostatic value of 70 kPa to a low, relatively stable value of 13 kPa within a few months after drilling (lithostatic pressure at 100 mbsf in this hole is about 630 kPa). The initial superhydrostatic value may have been caused by charging of the formation during drilling, although it is more likely that high pressures were present in the fault zone initially and drained after the fault was penetrated, probably to the surrounding formation spanned by the open section of...
During the 1993 Alvin dive series to the TAG hydrothermal field, 50 measurements of conductive heat flow were attempted at the 50-m-high, 200-m-diameter TAG active mound. The 43 successful stations included gradient and thermal conductivity measurements made with the 5-thermistor, 0.6-or 1-m-long A/v/« heat flow probes, which with a few exceptions could be pushed into most locations on and off the sulfide mound. The stations were made in a variety of characteristic environments on and off the mound, and were transponder-navigated to an estimated accuracy of ±5 m relative to the 10-m-diameter central complex of black smokers. The distribution of these stations allows a reasonable mapping of coherent patterns in the conductive heat flux from the mound. As might be expected, conductive heat flow values are extremely variable (0.1-86 W/m ) within a few meters of the black smokers, where the station environments were generally pockets of sulfide debris amid larger sulfide rocks with widespread shimmering water indicative of diffuse hydrothermal flow. On the west side of the sulfide rubble plateau that surrounds the central black smoker peak, a coherent belt of very low heat flow (<20 mW/m ) is present 20-50 m west of the smokers, suggestive of local, shallow recharge of bottom water. On the south and southeast side of the mound, very high heat flow exists (>5 W/m 2 ) on the sedimented terraces that form the slope down from the "Kremlin" area of white smokers, suggesting an extension of the fluid flow processes responsible for the white smokers. Heat flow is also high (0.3-3 W/m 2 ) in the pelagic carbonate sediments on the surrounding seafloor within a few tens of meters of the southwest, northwest, and northeast sides of the mound. The distribution of these areas of high and low heat flow in general supports a possible schematic model of subsurface patterns of heat and fluid flow within the active mound (Tivey et al., 1995), and was used to guide placement of several of the holes drilled during Leg 158.
An inflatable drill-string packer was used at the end of Leg 118 to measure the bulk in-situ permeability of four intervals within the 500 m of 12-m.y.-old gabbros of oceanic layer 3 cored in Hole 735B. The packer was inflated six times successively, at depths of 49,47, 389, 299, 223, and again 223 mbsf, to determine the average permeabilities of the respective intervals between the respective inflation depths and the bottom of the hole. Two of these inflations were essentially repeated tests to verify the packer seal and apparent indications of relatively high permeability below 49 and 223 mbsf. The inflation depths of the packer were chosen on the basis of the dual laterolog resistivity log, which clearly distinguished the six major lithologic Units observed in the recovered core. Thus, the inflation at 389 mbsf essentially isolated the olivine-rich gabbros and troctolites of Unit VI; the inflation at 299 mbsf isolated Unit VI plus most of the olivine gabbros of Unit V; the inflations at 223 mbsf isolated Units V and VI plus the iron-titanium oxide-rich gabbros of Unit IV; and the inflations at 49/47 mbsf isolated Units IV, V, and VI plus the olivine gabbros of Units II and III. At each inflation, several standard slug tests and/or constant-rate injection tests were conducted, with good, repeatable results. Measured interval permeabilities decrease by two orders of magnitude with depth, ranging from about 24 to 0.2 × 10~1 5 m 2 , similar to the range in permeabilities measured in the basaltic sections of Holes 395A and 504B. The permeabilities of the intervals between packer inflation depths were estimated from the differences in measured transmissivities, showing that Unit IV is the most permeable section, averaging about 80 × 10~1 5 m 2. The log analysis of Goldberg et al. (this volume) shows that most of the permeability found above 299 mbsf, in Units II, III, and IV, can be attributed to a few zones of isolated fractures; the hydraulic conductivities of these fractures are probably much greater than the average permeabilities reported here. These fractures probably resulted from tectonic processes associated with the uplift of the fracture-zone transverse ridge in which the hole is located; thus, the relatively low permeability measured deeper in Hole 735B may be more representative of oceanic layer 3 gabbros in situ.
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