Preliminary Carbon Dioxide (CO2) Sequestration Characterization, Dare, Tyrrell and Hyde Counties, North Carolina
Preliminary assessment of saline aquifers potentially suitable for carbon dioxide (CO2) sequestration in North Carolina’s Coastal Plain (Dare, Tyrrell, and Hyde counties) was undertaken on Lower and Upper Cretaceous strata from -3,000 feet to -6,100 feet below sea level. National assessment criteria by the USGS, USEPA, and the USDOE for CO2 injection into geologic formations are a depth greater than -3,000 feet, and formation waters with over 10,000 ppm dissolved solids.
The prime target area, Dare Co., is near several large industrial CO2 emitters. The sparsely populated area has extensive federally-owned lands including the Navy-Air Force electronic bombing range and qualification range (Dare Bombing Range).
About 153 line miles of 1970’s-era 2D seismic data along with paper geophysical logs from 19 oil exploration wells and sub-surface structural maps (circa 1980’s) were converted from paper to digital formats (.sgy, .las, and .shp) respectively for geographic information system (GIS) and modern seismic software.
Analysis indicates a potentially continuous 150- to 200-foot-thick sand at a depth of -4,500 to -6,600 feet along a coast parallel strike line for ~35 miles. This sand is above the crystalline basement. An overlying stratigraphic sequence has sand units beginning at a depth of about -3,500 feet extending downward to the top of the lower sand. Some structural closure is present and these sands could be a potential natural gas storage reservoir.
The M2-6600 sand (depositional unit #1 of Almy 1987a,b) of Lower Cretaceous age underlies most of Dare Co. at a depth of -3,000 feet or more and has estimated salinities that are close to the 10,000 ppm total dissolved solids (TDS) criterion, and in many cases exceed that value. There are well-to-well variations in the estimated salinity content. The spontaneous potential (SP) salinity estimates of formation water resistivity used to determine TDS tend to be more saline (NaCl) than those determined by the induction log method supplemented by a few resistivity logs.
The M2-3950 sand in depositional unit #2 (Almy 1987a,b), is shallower and in the northern half of Dare Co. where it appears to be too shallow (e.g., above -3,000 feet) for CO2 sequestration. Continuity of sand units is somewhat less clear; however the seismic-stratigraphy approach of Coffey and Sunde (2009) provides clarity on the sand distribution.
Estimated salinities are generally well above the 10,000 ppm TDS criterion; there are well-to- well variations in the estimated salinity content. The SP salinity estimates tend to be more saline than those determined by the induction log method.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012