MRCSP Phase I Geologic Characterization Report - Midwest ...

4 CHARACTERIZATION OF GEOLOGIC SEQUESTRATION OPPORTUNITIES IN THE MRCSP REGION
2002). Such large volumes of gas storage capacity strongly suggest
that CO 2 gas can be successfully managed in subsurface reservoirs
within the region.
In active oil fields, it has been demonstrated that CO 2 can be
used for enhanced oil recovery (EOR). In this process, some of the
oil that remains in reservoirs after primary production is recovered
by injecting CO 2 that either (1) repressurizes the reservoir and displaces
and drives the remaining oil to a recovery well (immiscible
flooding) or (2) directly mixes and chemically interacts with the
remaining oil as it pushes it to the producing well (miscible flooding).
Approximately 70 oil fields worldwide currently inject CO 2
for EOR (U.S. DOE, 2004) demonstrating the effectiveness of this
value-added sequestration option. Moreover, enhanced oil recover,
while sequestering CO 2, could provide an economic incentive to
storage in several parts of the MRCSP region where CO 2 sources
are near oil fields.
Unmineable Coal Beds
The MRCSP region includes the Appalachian basin, which contains
the second- (West Virginia), third- (Kentucky), fourth- (Pennsylvania)
and fourteenth- (Ohio) leading coal-producing states in
the nation (EIA, 2005). Unmineable coal beds offer an alternative
option for geologic sequestration in the region because, unlike the
previously described reservoir types, CO 2 injected into a coal bed
would not only occupy pore space, but would bond, or adsorb, onto
the carbon in the coal itself. The adsorption ratio for CO 2 in coals
is approximately twice that of methane; thus, in theory, the injected
CO 2 would displace methane, allowing for the potential of enhanced
gas recovery (Reznik and others, 1982; Gale and Freund, 2001;
Schroeder and others, 2002). Because of the adsorption mechanism,
concerns of miscibility that occur in oil and gas reservoirs are not an
issue. Thus, the injection of CO 2 and resulting enhanced recovery of
coalbed methane could occur at shallower depths than for depleted
oil reservoirs. Hydrogeologic flow, water chemistry, coal thickness
and quality, and subsurface temperature-pressure conditions are
some of the variables that control the potential use of coal beds for
CO 2 sequestration and enhanced coalbed-methane recovery (Pashin
and others, 2003). Although there is currently only limited coalbed
methane production in the MRCSP region, rising gas prices have
led to growing interest in this energy resource in the last decade, and
secondary recovery of methane may provide an economic incentive
for sequestration of CO 2 from sources in the coal fields.
Carbonaceous Shales
The MRCSP region also contains widespread, thick deposits of
carbonaceous shales. These shales are interesting in that they are
often multifunctional—acting as seals for underlying reservoirs, as
source rocks for oil and gas reservoirs, and as unconventional gas
reservoirs themselves. Analogous to sequestration in coal beds, CO 2
injection into unconventional carbonaceous shale reservoirs could
be used to enhance existing gas production. As an added bonus, it
is believed the carbonaceous shales would adsorb the CO 2 into the
shale matrix, permitting long-term CO 2-storage, even at relatively
shallow depths (Nuttall and others, 2005a).
INTRODUCTION TO THE MRCSP REGION’S GEOGRAPHY AND GEOLOGY
GEOGRAPHY
The seven-state MRCSP partnership is an enormous and economically
diverse area of the United States that excess of 255,000 square
miles in size (>662,000 square kilometers). The area considered for
geologic sequestration (excluding the upper peninsula of Michigan
and the Illinois basin portion of Indiana and Kentucky) contains
over 201,000 square miles (501,000 square kilometers). The diverse
topography, hydrology, and bedrock geology of the region present
a variety of geologic sequestration options. Additionally, numerous
environmental considerations will be needed in different parts of the
seven-state region. The MRSCP region encompasses three major
physiographic regions: 1) Atlantic Plain, including the Continental
Shelf and Coastal Plain (Maryland); 2) the Appalachian Highlands,
including the Piedmont Province (Maryland), Blue Ridge Province
(Maryland, West Virginia), Valley and Ridge Province (Maryland,
Pennsylvania, West Virginia), and Appalachian Plateaus Province
(Kentucky, Ohio, Pennsylvania, West Virginia); and the 3) Interior
Plains, including the Interior Low Plateaus (Kentucky, Ohio) and
Central Lowland (Indiana, Michigan, Ohio) (Figure 2).
Bedrock is at or near the surface in much of the Appalachian
Highlands and is covered by Quaternary-age sediments in the Atlantic
Plain and in parts of the Interior Plains north of the Ohio River.
Variable surface topography, climate, and sediment and bedrock
types covering the area result in varied land uses, surface water, and
ground water conditions across the seven states.
GENERAL GEOLOGY, MAJOR STRUCTURAL
FEATURES AND TARGET AREAS
Because the four reservoir classes being considered under this
task all occur in sedimentary rocks, only those areas within the seven
states with thickness of sedimentary rocks considered adequate
for CO 2 sequestration were evaluated for their geologic sequestration
potential. This differs from the terrestrial sequestration portion
of the MRCSP project, which examined the entire land-surface area
of the seven-state region. Also, although sedimentary rocks of appropriate
thickness occur in a large part of the MRCSP region, the
types and depths of potential CO 2 reservoir strata vary. Figure 3 is a
generalized map of the geologic units at or near the surface that also
shows the major geologic structures of the region. Figure 4 is a cross
section across the map illustrating the sedimentary rocks thicken
into geologic basins and thin above structural arches.
Much of the Appalachian highlands, from the Piedmont on the
east to the Allegheny front on the west, were not included in this
investigation because they are dominated by folded and faulted
metamorphic and igneous rocks. Additionally, it was not possible,
within the scale of this project, to map most of the local sedimentary
deposits within this folded section of the Appalachian Mountains
because of a lack of data on the depth and thickness of individual
units. Likewise, the Upper Peninsula of Michigan was not included
in the geologic assessment of CO 2 sequestration potential because
it consists mostly of metamorphic and igneous rocks. Although
a small area of sedimentary rocks, considered to be a part of the
Michigan basin, does exist in the Upper Peninsula, these rocks do
not obtain depths great enough for consideration as a geologic sequestration
target and were not included in this study.
The eastern limit of MRCSP geologic investigations is the Maryland
shoreline. Although many offshore sedimentary rocks may
have a potential for sequestration, they were not investigated in
this project. The western boundary for geologic mapping within the
MRCSP region is a multi-county boundary that represents the ap-