The Kentucky Geological Survey (KGS) operated and drilled the 1 Hanson Aggregates stratigraphic research well to assess the subsurface CO₂ storage capacity in deep saline reservoirs of the Middle Cambrian–Lower Ordovician Knox Group and underlying strata in the Central Appalachian Basin in eastern Kentucky (Bowersox et al., 2013; Bowersox et al., 2013; Bowersox et al., 2017; Greb et al., 2017; Bowersox et al., 2018). All depths in the well were measured from the drilling rig kelly bushing (KB) which was 227.5 m above the sea level (2 m above the ground-level elevation of 225.5 m). It was drilled in northern Carter County, Kentucky, United States (Figure 1), at a location where all potential reservoir and confining strata and Precambrian basement could be penetrated at a total well depth (TD) less than 1,525 m below the surface (Bowersox et al., 2013; Bowersox et al., 2017; Bowersox et al., 2018). The 1 Hanson Aggregates well reached a TD of 1,474 m in Precambrian Grenville gneiss and successfully tested reservoir and in situ rock properties in both the Knox and underlying Middle Cambrian strata (Bowersox et al., 2017, Bowersox et al., 2018, Bowersox et al., 2019a; Bowersox et al., 2019b; Greb et al., 2017; Figure 2).

The focus of this report is the Rose Run Sandstone formation of the Knox Group, an important reservoir for oil and gas production and liquid waste disposal in the U.S. Midcontinent (Rike, 1992; Riley, 1992; Riley, 1994; Battelle Memorial Institute, 2015) and candidate deep saline reservoir for CO₂ storage. Previous tests of the Rose Run’s capacity for storing CO₂ were conducted in the Battelle Memorial Institute (Battelle) 1 American Electric Power (AEP) well at the Mountaineer Power Plant on the Ohio River at New Haven, West Virginia (Gupta et al., 2006; Lucier et al., 2006; Gupta, 2008a; Gupta, 2008b; Lucier and Zoback, 2008), 118 km northeast of the 1 Hanson Aggregates (Figure 1, location 2), and in the Ohio Division of Geological Survey CO₂ No. 1 well near Port Washington, Tuscarawas County, Ohio (Wickstrom et al., 2011), about 250 km northwest of the KGS 1 Hanson Aggregates well (Figure 1, location 3; Figure 3).

This study reports the results of tests and analyses of the Rose Run reservoir properties conducted in the KGS 1 Hanson Aggregates well. We provide an estimate of the CO₂ storage capacity of the Rose Run in the KGS 1 Hanson Aggregates well and the surrounding region that contributes to the evaluation of subsurface CO₂ storage along the Ohio River industrial corridor (Gupta et al., 2006; Lucier et al., 2006; Gupta, 2008a; Gupta, 2008b), although there are no plans for its development in foreseeable future.

KGS collected a robust dataset of geophysical log data and conventional whole core and rotary sidewall core analyses from the KGS 1 Hanson Aggregates well (discussed in detail in Bowersox et al., 2018) to conduct this evaluation of the Rose Run. The Rose Run was a primary zone of interest in the KGS 1 Hanson Aggregates well for testing reservoir properties and estimating CO₂ storage capacity. This study reviews the reservoir properties of the Rose Run interpreted from geophysical electric and nuclear logs (electric logs or logs), formation imaging logs, analyses of conventional whole-diameter cores (Figure 2, Test 3) and rotary sidewall cores, and in situ reservoir properties determined from step-rate testing to estimate its CO₂ storage capacity in northeast Kentucky. All geophysical logs used in this evaluation, as well as core photographs, are available free to the public through KGS’s Oil and Gas Records Database at https://kgs.uky.edu/kygeode/services/oilgas/, KGS Record Number 143577. Core analyses are available on request from the KGS at Contact Kentucky Geological Survey, University of Kentucky (uky.edu).

The geology of the Rose Run Sandstone in the northeast Kentucky study area and adjacent Ohio and West Virginia is summarized from Bowersox et al. (2021). The Rose Run lies near the Cambrian–Ordovician boundary throughout much of the Central Appalachian Basin in the study area. The KGS 1 Hanson Aggregates well lies on the eastern flank of the Waverly Arch (Woodward, 1961; Ettensohn, 1980; Figure 1), a low-relief forebulge of the Appalachian foreland basin associated with the Taconic Orogeny (Root and Onasch, 1999). In the mapped study area (Figure 3), the Rose Run is near-horizontal, occurring as a single sand body overlying the Copper Ridge (Figures 2, 4), that thins south of the KGS 1 Hanson Aggregates (Figures 4, 5). Well cuttings, rotary sidewall cores, and whole cores from the Rose Run in the KGS 1 Hanson Aggregates well showed it to be a white to green–gray, fine-to medium-grained sandstone with subrounded to rounded grains and dolomitic cement (Bowersox et al., 2021). North of the study area, in the Battelle 1 AEP well and in the Ohio Division of Geological Survey CO₂ No. 1 well (Figure 1); the Rose Run occurs as thin sands interbedded with dolomite (Figure 6), whereas in central Ohio along the Waverly Arch (Figure 1); the Rose Run may consist of as many as four distinct sandstones with significant porosity and permeability (Riley, 1992; Riley et al., 1993; Riley et al., 2002) separated by dolomites (Riley et al., 2002; Wickstrom et al., 2005; Gupta, 2006).

The 9.8 m-thick section of Rose Run was penetrated in the KGS 1 Hanson Aggregates well at drilled depths of 1,000 m–1,009.8 m kB and was cored at depths from 1,005.8 m to its base at 1,009.8 m (Figure 2). The cored section was consisted of thin-bedded dolomitic quartz arenite with thin clay beds near the base. XRD analysis of a core plug near the base of the Rose Run at 1,008.1 m found 71.1% quartz, 20.9% dolomite, and a total of 7.5% potassium feldspar, illite/smectite clays, and mica. Dolomite volume in the Rose Run section was determined from a crossplot of formation bulk density and photoelectric factor from the density log (Schlumberger, 1987) normalized to the mineralogy from the XRD analysis (Bowersox et al., 2021). The average dolomite volume in the Rose Run above 1,006 m (3,300.5 ft) drilled depth was 6.8%, whereas the average dolomite volume below 1,006 m averaged 15.3% (Bowersox et al., 2021). Porosity of the Rose Run was calculated from the formation density log (Alger et al., 1963; Schlumberger, 1972). The matrix density of the Rose Run was most affected by the dolomite content, and averaged 2.67 g/cm³ (Bowersox et al., 2021). The formation fluid density of 1.06 g/cm³ was determined from a water sample collected from the Rose Run before the step-rate test (Bowersox et al., 2021). Porosity calculated in the Rose Run averaged 11.2% in the KGS 1 Hanson Aggregates well (Bowersox et al., 2021). At the industry-standard 7% porosity cutoff used for evaluating CO₂ storage reservoirs (Medina et al., 2011), the average Rose Run porosity in the 1 Hanson Aggregates was 12.3% and the net reservoir thickness was 8.5 m. In the mapped 2,146 km² evaluation region (Figures 3, 5), the average porosity was 11.4% in 23 wells and average net reservoir thickness was 6.2 m.

The reservoir volume required to store a volume of supercritical CO₂ (hereinafter CO₂ or supercritical CO₂, depending on context) in a deep saline reservoir requires five data points: reservoir height, porosity, temperature, pressure, and formation-water salinity. The CO₂ temperature/pressure phase-change boundaries (adapted from Freund et al. (2005)) at expected depths were estimated from bottomhole temperatures and pressures measured wells in the region surrounding the KGS 1 Hanson Aggregates well and the three step-rate tests in the well (Bowersox et al., 2021). However, the depth to the CO₂ critical point for subsurface storage can usually be estimated from reservoir hydrostatic pressure and regional geothermal gradients, ubiquitous underpressured reservoirs in Kentucky (Takacs et al., 2010) and with the low geothermal gradient (see the discussion in Bowersox et al. (2013)) push the depth to the CO₂ critical point much deeper in the subsurface. The top of the Rose Run was penetrated in the KGS 1 Hanson Aggregates well at a depth of 1,000 m (−772 m subsea elevation). The CO₂ critical pressure and temperature (7.39 MPa, 1,072 psi; Freund et al., 2005) reached at a drill depth of 795 m (−567 m subsea elevation) in the KGS 1 Hanson Aggregates well. The critical temperature, however (31.1; C; Freund et al., 2005), is not reached until a drill depth of 942 m (−714 m subsea elevation), or 58 m above the top of the Rose Run in the KGS 1 Hanson Aggregates well (Figure 10). Thus, the depth required to reach the CO₂ critical point temperature limits the reservoir area available for CO₂ storage in the northeast Kentucky evaluation region.

Average porosity and net reservoir thickness (h_net) in the Rose Run in the 1 Hanson Aggregates well and 2,145 km² (828 mi²) evaluation region (Figure 10) were calculated using the industry-standard 7% porosity cutoff (Medina et al., 2011) to compute the CO₂ storage capacity. At the 7% porosity cutoff, average porosity in the evaluation region is 11.6% and h_net is 6.2 m (20 ft). The density of supercritical CO₂ under Rose Run reservoir conditions of temperature and pressure is 768 kg/m³ (Peace Software, 2017). Supercritical CO₂ storage capacity in a deep saline reservoir was calculated using the methodology of Goodman et al. (2011). G C O 2 = A t φ T h g ρ C O 2 E s a l i n e , (3) where G_CO2 is the estimated supercritical CO₂ storage volume (kt/km²), A_t is the surface area of the storage reservoir (km²), φ_T is the average regional reservoir porosity (fractional) at the 7% porosity cutoff, h_g (m) is the average net reservoir thickness (Figure 10), ρ_CO2 is the density of supercritical CO₂ under reservoir conditions of pressure and temperature (kg/m³), and E_saline is the reservoir lithology-weighted CO₂ storage efficiency factor. The reservoir pore volume (φ_Th_g) at the 7% porosity cutoff was calculated for 27 wells in the evaluation region, and then the total reservoir volume calculated in Petra.

Although the CO₂ storage efficiency factor accounts for unsuitable reservoir rock by lithology (Goodman et al., 2011), applying a 7% porosity cutoff ensures a conservative evaluation of storage capacity. The storage efficiency factor, in practice, is applied as a range of probable storage efficiencies which vary for different reservoir lithologies (U.S. Department of Energy, Office of Fossil Energy, National Energy Technology Laboratory, 2015). P₁₀ and P₉₀ values provide a nominal range of efficiency values defining the lower and upper bounds of plausible supercritical CO₂ storage volumes about a most-likely P₅₀ value. The estimated P₅₀ supercritical CO₂ storage volume for the Rose Run in the northeast Kentucky evaluation region (Figure 10) is 77.2 kt/km² (220,000 short tons/mi²), 165.7 Mt (1.8 × 10⁸ short tons) in the 2,145 km² (828 mi²) evaluation region, with a P₁₀–P₉₀ range of 40.8 kt/km² (116,500 short tons/mi²) to 132.4 kt/km² (378,000 short tons/mi²), or 87.6–284.1 Mt (9.7 × 10⁷—3.1 × 10⁸ short tons) in the evaluation region. The surface area required to store the estimated P₅₀ supercritical CO₂ volume in the Rose Run is 12.9 km²/Mt (−4.5 mi²/million short tons), or 388.4 km² (150 mi²) of surface area to store 30 Mt (33 million short tons) of CO₂ generated during the life span of a coal-fired electrical generating plant.

As a known saline reservoir in parts of Ohio and Kentucky, the Rose Run Sandstone has been a regional target for potential carbon sequestration (Zerai et al., 2006; Greb et al., 2009; Venteris et al., 2009; Greb and Solis, 2010; Greb et al., 2012). Wickstrom et al. (2010) estimated 11 Gt (12.1 B short tons) of volumetric CO₂ storage potential in deep saline reservoirs in eastern Kentucky, of which the Rose Run, assuming 10 m of net sand with 8% average porosity, was estimated to have potential CO₂ storage capacity of 5.4 Gt (−6 B short tons). Throughout the area evaluated for CO₂ sequestration by the Midwest Regional Carbon Sequestration Partnership (MRCSP), fracture porosity was the least common type of porosity observed in Rose Run cores (Wickstrom et al., 2010), consistent with observations of this study.

The Rose Run in the KGS 1 Hanson Aggregates well and surrounding evaluation region has good porosity and permeability (Figure 8) and good injectivity (Bowersox et al., 2021), but does not have sufficient reservoir volume to serve as a large-volume (30-million ton) CO₂ storage reservoir (Figure 10). The Beekmantown and overlying strata have sufficient geomechanical strength, about double that of the Rose Run (Bowersox et al., 2021), and low porosity and permeability as measured in core plugs and rotary sidewall cores from the Battelle 1 ARP well (Joel Sminchak, Battelle, unpublished data) averaging 1.25% porosity and <0.001 mD permeability, respectively, to ensure confinement of stored CO₂, thus the Rose Run could contribute to a stacked-storage reservoir (discussed in Hovorka, 2013; Raziperchikolaee et al., 2019).

The comparison of Rose Run CO₂ storage capacity in the KGS 1 Hanson Aggregates well and the Battelle 1 AEP well and Ohio 1 CO₂ well tests.

Gupta (2008a) found the Rose Run to be unsuitable for CO₂ storage downdip at the Battelle 1 AEP test well site in West Virginia where there are three primary differences when compared to the KGS 1 Hanson Aggregates well: i. The Rose Run in the Battelle 1 AEP well lies at a much greater drilled depth (2,365–2,387 m), about 1,364 m deeper than in the KGS 1 Hanson Aggregates well (Figure 6), and would thus require much greater injection pressure (Lucier et al., 2006), ii. The logs through the 22 m Rose Run stratigraphic interval show 13.1 m of net sand (as used in this study) interbedded with thin dolomite beds (Figure 6) versus a single sand body as found in the KGS 1 Hanson Aggregates well, and iii. The Rose Run in the Battelle 1 AEP well has much lower porosity (Figure 7) compared to the KGS 1 Hanson Aggregates well. Analysis of 31 plugs (Figure 7) from conventional whole cores from the Battelle 1 AEP well shows average porosity in the Rose Run of 6.3% and average permeability of 12 mD (Gupta, 2008b), and one core plug at 2,369.8 m with 10.4% porosity and 49 mD permeability (Gupta 2006). Average permeability calculated from a “straddle packer” test of the Rose Run in the Battelle 1 AEP well, assuming a 10.7 m composite productive sandstone section, is 8.2 mD (Spane et al., 2006) versus 57.4 mD calculated from the step-rate test in the KGS 1 Hanson Aggregates well (above). Average porosity calculated from the density log in the 25 m Rose Run section in the Battelle 1 AEP well is 4.1%, and average porosity is 8.5% in the 6.1 m of net sand with porosity ≥7% (as used in this study). CO₂ storage capacity was calculated for the Rose Run in the Battelle 1 AEP well using the methodology of Goodman et al. (2011), with supercritical CO₂ density adjusted for reservoir temperature (this study) and pressure (Lucier et al., 2006) at an average depth of 2,375 m. P₅₀ CO₂ storage capacity of the Rose Run in the Battelle 1 AEP well was 59.2 kt/km² (290,000 short tons/mi²), or about 77% of the supercritical CO₂ storage capacity of the KGS 1 Hanson Aggregates well (above).

The Rose Run in the Ohio 1 CO₂ well was penetrated in the interval of 2,247–2,288 m (Wickstrom et al., 2011), depths only slightly shallower than in the Battelle 1 AEP well. The Rose Run in the Ohio 1 CO₂ well is equally unsuitable as the Battelle 1 AEP well, with the same reservoir issues: depth, thin sands (Wickstrom et al., 2011), and low porosity (Figure 6). The review of the formation density log in Wickstrom et al. (2011, figure three0) shows only 5.5 m of net sand with porosity >7% in the 40.8-m Rose Run section. Analysis of 10 rotary sidewall cores from sandstones in the Rose Run interval of the Ohio 1 CO₂ well yielded an average of 7.0% porosity, with a range of 3.3%–10.7%, and average permeability of 5.1 mD in a range of 0.0034–31.6 mD, respectively (Wickstrom et al., 2011). Thus, the Rose Run in the KGS 1 Hanson Aggregates well, Battelle 1 AEP well, and Ohio 1 CO₂ well all lack sufficient CO₂ storage capacity to support stand-alone large-volume CO₂ storage (see the discussion in Bowersox et al., 2019a), but could serve as part of a stacked-storage reservoir.

The tests of the Rose Run in the KGS 1 Hanson Aggregates well demonstrated that its reservoir properties are suitable for long-term CO₂ storage and vertical confinement by the overlying Beekmantown. Reservoir properties, Rose Run and Beekmantown geomechanical properties, and injectivity tests were all favorable for using the Rose Run for CO₂ storage, although there are no plans to carry out this in foreseeable future. Because the Rose Run is thin and would require a large reservoir area to have sufficient capacity to store CO₂, it would only provide a CO₂ storage contribution as part of a stacked-reservoir project. The lack of an updip, lateral reservoir trap, however, appears to preclude supercritical CO₂ storage in the Rose Run in the northeast Kentucky evaluation region. Additional research and modeling will be necessary to determine if the Rose Run is entirely excluded from supercritical CO₂ storage in the Central Appalachian Basin of northeast Kentucky.