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)
Additional information on the specifications
of the Lamont Test Facility.
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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. |
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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). |
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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. |
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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.
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