MRCSP Phase I Geologic Characterization Report - Midwest ...

APPENDIX A: MIDDLE SILURIAN NIAGARA GROUP REEFS
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SUITABILITY AS A CO 2
INJECTION TARGET OR SEAL UNIT
The Niagaran/Lockport through Onondaga Interval is a major
confining unit for CO 2 sequestration in the MRCSP study area.
Because of the thickness and combination of lithologies, it should
prove to be a very effective seal. The carbonates, in general, have
very low porosity and permeability, except in certain units. Similarly,
the great thicknesses of evaporites within this interval have
low permeabilities that should provide an effective seal against
migration of fluids away from lower intervals (such as the Lower
Silurian Medina Group/”Clinton” Sandstone). However, Silurian
and Middle Devonian dolomitized carbonates represent noteworthy
potential sequestration targets in this interval because of significant
porosity development within these units. Some oil and gas fields
have produced from these dolostones, and some Class II injection
wells utilize them. Sandstones in the Lower and Middle Devonian
(Oriskany and Sylvania) could also be important sequestration targets.
The organic-rich Mandata and Needmore shales might also
have potential for sequestration, but this has yet to be determined.
During the MRCSP Phase I study, five potential sequestration units
from this overall interval, the Niagaran Reefs, Mandata Shale, Oriskany
Sandstone, Needmore Shale, and Sylvania Sandstone, were
mapped separately, and each is discussed in more detail in other
sections of this report. During the MRCSP Phase II investigation,
we plan to devote additional study to the Lockport Dolomite and
Bass Islands Dolomite, as both appear to have significant, if local,
sequestration potential.
The Lockport Dolomite has numerous stratigraphic and combination
structural-stratigraphic traps developed in porous patch
reef bioherms or skeletal sand shoals encased in impermeable
argillaceous dolostone (Noger and others, 1996). Local traps also
occur where porosity and permeability pinch out along the flanks
of structures. Porosity development in the Lockport is controlled
primarily by depositional facies and diagenetic history. Patch reef
bioherms and sand shoals have average log-calculated porosities of
8 to 10 percent in producing oil and gas fields, with maximum porosities
as high as 14 percent (Noger and others, 1996). In addition
to moldic, vuggy, interparticle, and intercrystalline porosities, fracture
porosity and permeability enhance production from producing
fields, and should allow for maximum sequestration of miscible CO 2
fluids. Seals for trapping fluids within the formation are provided by
internal impermeable mudstones and the overlying evaporites and
carbonates of the Salina Group.
Caverns within the Salina Group salt units in Michigan and Ohio
may have potential for sequestration of CO 2. Such caverns are currently
used for underground storage of natural gas liquids. In Ohio,
underground storage of hydrocarbons in Salina salt deposits began in
1960. Thirty wells have been permitted for hydrocarbon storage since
1960, but only 11 wells have been used (Tomastik, 2001). Of these
11 wells, only two wells are currently operating. The main products
stored in these wells are butane and propane. There are currently two
active Salina Group salt mines in Cuyahoga and Lake Counties, Ohio
(Figure A8-1) at depths of approximately 2,000 feet. Salt mines in
Michigan and Ohio may also represent some sequestration potential,
although most are not deep enough to achieve supercritical phase.
Approximately 224 salt solution-mining wells have been drilled and
completed in the Salina since the late 1890s in Ohio. Two facilities
with 44 active wells remain open. Depths to the Salina Group
salt beds in these wells range from 1,800 to 3,150 feet (Tomastik,
1997). In West Virginia, there are three solution mining areas: 1) on
the Pleasants/Tyler County line; in southwestern Marshall County;
and 3) in west-central Marshall County (Figure A8-1). Two of these
are currently active (the northern most one in Marshall County is
abandoned). Depths to the Salina range from 6,200 to 6,900 feet in
these wells. One salt-solution well has been drilled in north-central
Pennsylvania with the purpose of using it to store natural gas. However,
solution mining of the salt cavity has not been accomplished to
date because the project is currently tied up in litigation. However,
the great thickness of bedded salt in north-central Pennsylvania, at
depths greater than 7,500 feet, indicates the Salina Group could be a
valuable injection target in this part of the MRCSP study area.
The Upper Silurian Bass Islands Dolomite could also be useful
for sequestering CO 2. Reservoir quality typically occurs where the
dolostone is highly fractured, as in the “Bass Islands trend” of New
York and Pennsylvania (Van Tyne, 1996b). Little is known about the
specifics of porosity and permeability, other than gross generalizations
about fracture porosity. One pool in Erie County, Pennsylvania
provides most of the details on the “Bass Islands trend.” Porosity,
as measured on geophysical logs, ranged from 2 to 15 percent,
averaging 10 percent. Occasionally, however, the Bass Islands
has potential reservoir quality outside of such fractured areas, as
provided by anecdotal information. In the early 1980s, a disposal
well in northwestern Pennsylvania was investigated for problems of
leakage in the annulus. The disposal formation was Upper Cambrian
sandstone (Rose Run), but the fluids were migrating uphole into the
Bass Islands Dolomite where they spread out into the surrounding
region through cavernous porosity within the dolostone. Disposal
fluid was found five miles away, leaking through an old, unplugged
well in Lake Erie. It is unfortunate that the Bass Islands in this area
is very shallow (only 1,700 feet in the disposal well). However, investigation
of the Bass Islands Dolomite at depths below 2,500 feet
would prove valuable in looking for potential sequestration targets
within the dolostone.
9. LOWER SILURIAN NIAGARA GROUP REEFS
The Niagara Group (includes Lockport Dolomite) is early Silurian
(Niagaran) in age and characterized by the development of individual
“pinnacle” reefs and reef complexes along two linear trends,
one in the northern part of the Michigan basin, the other along the
southern part of the basin. Overall, the reef belt both contain pinnacle
and barrier reef complexes, is mostly in the lower peninsula
of Michigan but does extend into northeastern-most Illinois and
northernmost Indiana and Ohio. Individual pinnacle reefs and reef
complexes (averaging 50 to 400 acres in areal extent) are numerous,
extending along linear belts approximately 6 to 15-miles wide
in the northern reef belt and up to 20-miles wide in the southern
part of the Michigan basin. Currently, there are approximately 800
pinnacle reefs and reef complexes (fields) identified in the northern
trend with an additional 400 in the southern trend. Productive reef
intervals range from approximately 50 to 700 feet in thickness.
ORIGIN OF NAMES, TYPE SECTION, SIGNIFICANT
EARLIER STUDIES ON THIS INTERVAL
Hall (1840) named the Niagara for exposures in the Niagara Falls,
New York region. There have been numerous studies discussing the
various stratigraphic aspects of the Silurian reefs in the region (for
examples, see Droste and Shaver, 1985; Shaver and Sunderman,
1989; Shaver, 1991, 1996). Likewise, there have been numerous