Packer Experiments During IODP Expedition 301 to Assess Upper Crustal Permeabilities in 3.4 Ma Crust on the Eastern Flank of the Juan de Fuca Ridge

During IODP Expedition 301, a single-element drillstring packer was used to determine upper crustal permeabilities in two new holes drilled ~30 m apart into a sediment-buried ridge in 3.4 Ma crust on the eastern flank of the Endeavour Segment, Juan de Fuca Ridge. In Hole 1301A, the packer was inflated in casing in Hole 1301A to assess permeability averaged over the open-hole section spanning 93 m of uppermost basement. Hole 1301B penetrated deeper into basement (318 m), with stabler hole conditions, allowing the packer to be inflated at three open-hole positions to assess average permeabilities over the intervals 207-318, 177-318, and 152-318 m into basement. Constant-rate injection tests were run of longer duration (1-2 hrs) than the 20-30 min tests typically run in previous experiments in other crustal holes. The experiments were designed to provide results complementary to previous packer and CORK results indicating both a spatial-scale and age-dependence of permeability in shorter sections of uppermost basement in four holes drilled during Leg 168 on a transect in crust of ages 0.9 to 3.4 Ma. The results in Hole 1301A may be ambiguous because of the likelihood that the outside of the casing string was not properly sealed; but if the response is real, preliminary interpretation is consistent with a permeability on the order of 3-5 x 10-11 m2 averaged over the 93 m open hole zone. The results from Hole 1301B indicate a slightly lower permeability deeper into basement, ~1 x 10-11 m2. These results are noteworthy in several respects. First, the estimated bulk permeability in upper basement is considerably greater than that calculated from packer experiments in nearby Holes 1026B and 1027C during ODP Leg 168, which penetrated only the upper 40-50 m of basement. Also, the combination of results from Holes 1301A and B suggests only a modest reduction in permeability with depth over the uppermost 318 m of basement at the site. Planned cross-hole experiments using these and other holes over days to years will allow assessment of the scale dependence of permeability in the upper crust.