Single and cross-hole experiments indicate very high permeability in young ocean crust

Author(s): Fisher, A. T.; Becker, K.; Davis, E. E.
Author Affiliation(s): Primary:
University of California at Santa Cruz, Department of Earth and Planetary Sciences, Santa Cruz, CA, United States
Other:
University of Miami, United States
Geological Survey of Canada, Canada
Volume Title: AGU 2006 fall meeting
Source: Eos, Transactions, American Geophysical Union, 87( Fall Meeting Suppl.); American Geophysical Union 2006 fall meeting, San Francisco, CA, Dec. 11-15, 2006. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0096-3941 CODEN: EOSTAJ
Note: In English
Summary: IODP Expedition 301 was part of a multidisciplinary program designed to evaluate formation-scale hydrogeologic properties within young oceanic crust on the eastern flank of the Juan de Fuca Ridge. This expedition focused on sites located in an area between basement outcrops (former seamounts) that are known to be hydrogeologically active. Expedition 301 completed single-hole drilling, coring, logging, and packer tests, and installed three long-term subseafloor observatories (CORKs) for use in future cross-hole experiments. Two new basement holes, 1301A and 1301B, extend 110 m and 320 m into basement, respectively, below 260 m of sediment. Drillstring packer experiments were conducted in basement in Hole 1301B, with the packer set at three depths, to isolate the lowermost 166, 141, and 111 m of open hole. Two or three constant rate injection tests lasting one hour were conducted at each setting depth. Pressures recorded at depth during fluid injection were interpreted using conventional methods, yielding near-hole permeabilities on the order of 10-11 m2. CORKs were set in Holes 1301A and 1301B after completing packer experiments, but both holes were sealed incompletely. As a result, negative differential pressures established by the pumping of cold seawater during drilling, coring, and other operations were sustained by the continued flow of cold bottom water into the holes following the end of Expedition 301 operations. Borehole pressure data recovered from ODP Hole 1027C, 2.4 km to the east of Site 1301, one year later show a distinct rise in pressure associated with the flow of water into the new holes, and have been interpreted as a cross-hole pumping test. The greatest unknown in interpreting the cross-hole response between Sites 1301 and 1027 is the rate at which water flowed into the new holes during the year following Expedition 301, but possible flow rates can be constrained within a finite range based on operational and hydraulic considerations. Cross-hole permeability indicated by the pressure response in Hole 1027C is on the order of 10-13 to 10-11 m2, and corresponding formation compressibility is about 0.2 to 100 times that of seawater, respectively. Controlled cross-hole hydrogeologic experiments lasting several years will begin in Summer 2008, following sealing of Holes 1301A and 1301B and installation of three additional subseafloor observatories.
Year of Publication: 2006
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Crosshole methods; Crust; East Pacific; Expedition 301; Experimental studies; IODP Site U1301; Integrated Ocean Drilling Program; Juan de Fuca Ridge; Leg 168; North Pacific; Northeast Pacific; ODP Site 1027; Ocean Drilling Program; Ocean floors; Oceanic crust; Pacific Ocean; Permeability; Pumping; Sea water; Well-logging
Coordinates: N474524 N474524 W1274351 W1274351
N474500 N474600 W1274600 W1274600
Record ID: 2007061580
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