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Two holes have been drilled at Lamont, 450 m apart through the Palisades diabase sill. Well-2 is 229 m deep and Well-3 was drilled to 305 m, both penetrating through the sill and into the underlying Triassic sediments of the Newark Basin. Both holes were logged with downhole geophysical tools, including the BHTV which acoustically images fractures intersecting the well. Using the BHTV logs, 96 and 203 fractures were digitally mapped within the sill in Well-2 and Well-3, respectively. Most fractures appear to dip steeply (76-78º). There is a shift in fracture orientation, however, and these fractures may or may not be continuous over the short lateral distance between wells 2 and 3. The lithology of the sill as identified by drill chips is nevertheless continuous between the holes. Both intersect a 7 m-thick olivine-rich layer about 15 m above the bottom of the sill.

Several fractures identified in Well-2 have large apparent aperture (>6 cm) which correspond to high porosity zones (6-14%) observed in the logs. Resistivity logs were used to compute porosity using Archie’s law and match well with the neutron porosity log in Well-2. We observe a relationship between porosity and fracture aperture within the sill: F= 0.7a +3.8. Using this relationship, we infer the porosity in Well-3. High-porosity, large-aperture zones, including the target olivine layer, are identified in both holes. Changes in the temperature gradient log indicate active fluid flow in the sill, although flow appears to be most active in the sediments. Field tests of bulk permeability will be made in the future to estimate fluid flow potential in isolated intervals and between the wells. In addition, hydrologic modeling of fluid flow, calibration of fracture and log porosity, water chemistry, and chemical analysis of CO2/olivine reactions will be undertaken.

(Text is a summary of "Feasibility Study for CO2 Sequestration in a Natural Olivine-Diabase Aquifer: Preliminary Site Characterization in the Palisades Sill, NY" Katharine Burgdorff, Middlebury College and Dave Goldberg, Lamont-Doherty Earth Observatory)

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Figure 1: Geological map of the Palisades Sill and surrounding regions (Walker, 1969). USGS topography inset map shows localities of the two drill holes (wells 2 and 3) on the Lamont-Doherty Earth Observatory campus with 10ft contours. Elevations and total depths (TD) are marked at each location and the wells are approximately 450 meters apart.



Figure 2: A. Photo of Englewood cliffs where hand samples were collected for chemical analysis. B. Schematic cross-section of Hudson River and Newark Basin sediments south of Palisades. The sill (dark blue) intruded at different stratigraphic levels in the sediments. Wells are shown in yellow (approximated depths) cutting through the sill at different levels of its intrusion into the sediment basin (from Olsen, 1980).



Figure 3: Photo on right shows a digital photo of drill chips sample (820 ft deep) in Well-3. Volume % graphs are shown for each well along with grain size logs and depth below ground level. The sediment types were similar in both holes with an abundance of white sandstone and some pink and gray arkose. Purple siltstone and purple-black shale were more abundant in Well-3 and only a small amount of black shale is found at the bottom of Well-2. Red siltstones are much more abundant in Well-2 and are virtually absent in Well-3. Small intrusions of diabase (dark blue) are observed below the sill contact in both holes at different depths and with varying thickness.



Figure 4: An example of BHTV data in Well-3 from approximately 775 to 825 ft (right). Dotted lines denote a contact between the sediments (darker) and a small diabase intrusion. Digital color photos are used to estimate the average color of samples which also show this contact.




Borehole Research Group at Lamont-Doherty Earth Observatory of Columbia University, 61 RT 9W, Palisades, NY 10964