MRCSP Phase I Geologic Characterization Report - Midwest ...

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138 CHARACTERIZATION OF GEOLOGIC SEQUESTRATION OPPORTUNITIES IN THE <strong>MRCSP</strong> REGION a figure perhaps representative of the Waste Gate Formation elsewhere in Maryland. Hansen (1984) noted in the Hammond No. 1 well, the formation is “about 70 percent sandstone (sand); however each unit is relatively thin and rarely exceeds 100 feet in thickness. In Maryland, carbonaceous laminae and calcareous sandstones are present in the Waste Gate, but no coaly seams or limestones have been found.” Hansen (1982) noted rare occurrences of acritarch cysts found within the Waste Gate Formation in the Bethards No. 1 well. A more detailed discussion of the palynology can be found in Doyle (1982) and Hansen (1982). Sandstone porosities estimated from geophysical logs generally range from 19 to 27 percent (Hansen 1982). Based on aquifer tests of a well in Crisfield, Maryland, transmissivities of 340 to 430 gallons/day/foot and hydraulic conductivities of 4 to 5 gallons/day/ square foot were recorded (Hansen, 1984). Based on limited test data, Hansen (1984) suggested that the Waste Gate sandstones are likely to have relatively low permeabilities in comparison to other Coastal Plain aquifers, perhaps on the order of 15 to 150 md. It should be noted that younger units in the Potomac Group include aquifers that are an important source of fresh water supply, particularly in areas west of the Chesapeake Bay in Maryland and in some communities on the Delmarva Peninsula. However, under much of the Delmarva Peninsula, the deep Potomac units, including the Waste Gate Formation, are saturated with salty water ranging from slightly brackish to brines with salinities greater than seawater. DISCUSSION OF DEPTH AND THICKNESS RANGES The top of the Waste Gate Formation ranges from a depth of about 3,500 feet at its up-dip limit to 5,670 feet near the coast (Hansen, 1984) (Figure A17-4). The Waste Gate Formation is estimated to range in thickness from zero feet thick at its up-dip pinchout to about 1,515 feet thick near the Delmarva coast (Hansen, 1984) (Figure A17-5). Hansen (1984) indicate that the Waste Gate Formation thins relatively rapidly by onlap under the Delamarva Peninsula. The location of the up-dip edge of the unit is poorly defined because of a lack of data, but the pinchout line is estimated to trend roughly northeast-southwest through the middle of the Delmarva Peninsula, based the unit’s absence in the few wells in the western part of the Peninsula that penetrate to pre-Mesozoic basement. DEPOSITIONAL ENVIRONMENTS/ PALEOGEOGRAPHY/TECTONISM In early Cretaceous time, Potomac Group sedimentation began to occur as the Piedmont and Blue Ridge provinces were uplifted. These sediments were deposited eastward in a broad, open basin (Glaser, 1969). This basin is referred to as the Salisbury Embayment (formerly referred to as the Chesapeake-Delaware Embayment) (Figure A17-3). Glaser (1969, p. 74) also indicated that deposition probably “ began near or somewhat beyond the present coast line” and then “…apparently migrated slowly westward toward the present day outcrop belt” (Figure A17-2). According to Glaser (1969) by the time Patuxent Formation sediments were being deposited, the Early Cretaceous fall line or basin margin was located, perhaps, only a few miles inland from the present outcrop margin. It should also be noted that the gradient of the surface of the pre- Mesozoic basement appears to vary, apparently increasing from west/northwest to east on the Delmarva Peninsula. The apparent dip of the basement surface between a well on the western side of the Delmarva Peninsula (at Cambridge, Maryland) and the Hammond well (central Delmarva Peninsula) is on the order of 64 feet per mile, whereas the apparent dip between the Hammond well and Bethards well on the eastern edge of the Delmarva Peninsula is roughly 150 feet per mile. Given the paucity of wells that penetrate into pre- Mesozoic basement rocks in the Delmarva Peninsula, the nature of the basement surface is not fully characterized (e.g., the extent to which there is local relief) and it is not clear if this apparent change in surface gradient between the two wells may be the result of pre- Mesozoic erosion (e.g., a canyon), warping, a structural feature, or some combination of the three. Hansen (1978) noted that the change in gradient that occurs within about 10 to 15 miles of the coast, that is, between the Hammond No. 1 and Bethards No. 1 wells, suggests the presence of a tectonic hinge zone that might define the shoreward edge of the Baltimore Canyon Trough (Figure A17-3). Rare occurrences of marine or brackish-water fossils have been noted within the Waste Gate Formation (Hansen, 1984) but, overall, the majority of evidence suggests the formations originated in a high-energy, alluvial setting dominated by fluvial channel facies proximal to the early Cretaceous Fall Line. Hansen (1984) noted that self-potential (SP) log signatures of the sandstones have a blocky aspect, suggestive of braided or stacked sand-channel deposition, rather than the well-defined, fining-upward cycles generally ascribed to deposition by meandering streams. This suggests deposition in a high-energy alluvial complex. In addition, Doyle (1982) reported that samples from the Waste Gate Formation suggest deposition in a humid tropical climatesuch as would be found in the southern Laurasian continent during the Early Cretaceous. SUITABILITY AS A CO 2 INJECTION TARGET OR SEAL UNIT Porosities of the Waste Gate sandstone, as estimated from compensated formation density logs and s electric logs, range from 19 to 27 percent (Hansen, 1982, tab. 4). In general, porosity decreases with increasing depth (Table A17-1). In the shallowest (3,900 to 4,225 feet) of five wells penetrating the Waste Gate in Maryland, direct pumping tests yielded sandstone permeabilities in the range of 75 to 120 md; the Schlumberger method yielded similar results of 63 to 122 md. In general, permeability decreases with increasing depth, falling in the range of 16 to 122 md (Table A17-1). Chemical analyses of the formation waters from two Waste Gate aquifers revealed brines with chloride concentrations of 42,000 mg/l, and salinity (equivalent NaCl concentration) estimates from electric log data ranged from roughly 25,000 to 94,000 ppm (Hansen, 1982, ttabs.. 5 and 6). Salinity increases with depth and are a calcium/sodium chloride type. These waters are at normal hydrostatic pressure and exhibit very lethargic to stagnant flow systems (Hansen, 1984) (Table A17-1). Hansen (1982, 1984) evaluated the Waste Gate Formation for potential for extraction of chemical commodities such as commercial brines, extraction of geothermal heat, and disposal of hazardous/liquid waste. Perhaps most pertinent to considerations for CO 2 injection is the hazardous/liquid waste evaluation. Hansen (1984, p. 18) notes: The fl uvial-deltaic Waste Gate Formation is not ideal for well injection because of its complex sand stratigraphy. Individual aquifers and confining beds are only locally correlative. The geometry of each sand body is complex. With sparse well control, it is impossible to predict unequivocally whether a potential reservoir is laterally connected with an adjacent sand or whether it wedges out within a
APPENDIX A: LOWER CRETACEOUS WASTE GATE FORMATION 139 EXPLANATION M A R Y L A N D 500 ft contours Mean sea elevation (feet) -3500 -5500 U T H E S O -4000 -4500 -5000 -5500 U N I T P I N C 20 10 0 20 40 Miles ³ 20 10 0 20 40 Kilometers Figure A17-4.—Structure contour map drawn on the top of the Waste Gate Sandstone.
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Characterization of Geologic Seques
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ABOUT THE MRCSP The Midwest Regiona
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CONTENTS About the MRCSP ..........
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CONTENTS Figure A14-2.—Structure
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1 CHARACTERIZATION OF GEOLOGIC SEQU
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BACKGROUND INFORMATION 3 (a minimum
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INTRODUCTION TO THE MRCSP REGION’
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GEOLOGIC MAPPING PROCEDURES, DATA S
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OIL, GAS, AND GAS STORAGE FIELDS 27
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CO 2-SEQUESTRATION STORAGE CAPACITY
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CONCLUSIONS AND REGIONAL ASSESSMENT
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REFERENCES CITED 47 National Confer
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49 APPENDIX A Geologic Summaries of
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APPENDIX A: PRECAMBRIAN UNCONFORMIT
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APPENDIX A: CAMBRIAN BASAL SANDSTON
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APPENDIX A: BASAL SANDSTONES TO TOP
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APPENDIX A: UPPER CAMBRIAN ROSE RUN
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APPENDIX A: KNOX TO LOWER SILURIAN
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N T R APPENDIX A: KNOX TO LOWER SIL
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APPENDIX A: MIDDLE ORDOVICIAN ST. P
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-6000 -8000 APPENDIX A: MIDDLE ORDO
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APPENDIX A: LOWER SILURIAN MEDINA G
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