Geomechanical properties will constrain CO2 injection into the lower Ordovician Rose Run sandstone deep saline reservoir, Appalachian Basin, Kentucky, USA

Abstract

The Kentucky Geological Survey (KGS) 1 Hanson Aggregates stratigraphic research well, Carter County, Kentucky, USA, was drilled to a total depth of 1474 m as a field-scale test of potential CO 2 storage reservoir properties in the Central Appalachian Basin. Geomechanical properties of the Rose Run sandstone (upper Ordovician Knox group) were tested for its suitability as a storage reservoir. A 9.8-m thick section of the Rose Run was penetrated at 1000 m drilled depth and a whole-diameter core and rotary sidewall cores were taken. Average porosity and permeability measured in core plugs were 9.1% and 44.6 mD, respectively. Maximum vertical stress gradient calculated in the wellbore was 26 MPa/km. Wellbore fractures in dolomites underlying and overlying the Rose Run follow the contemporary N53°E Appalachian Basin stress field. The Rose Run elastic geomechanical properties were calibrated to values measured in core plugs to evaluate its fracturing risk as a CO 2 storage reservoir. Mean Young's modulus and Poisson's ratio values of the Rose Run were 45 GPa and 0.23, respectively, whereas Young's modulus and Poisson's ratio values were 77.1 GPa and 0.28, respectively, in the overlying Beekmantown dolomite, suggesting the Rose Run may fracture if overpressured during CO 2 injection but be confined by the Beekmantown. Triaxial compressive strength measured in core plugs found the Rose Run and Beekmantown fractured at mean axial stresses of 156.5 MPa and 282.2 MPa, respectively, confirming the Beekmantown as suitable for confining CO 2 injected into the Rose Run. A step-rate test was conducted in a mechanically-isolated 18.6-m interval bracketing the Rose Run. Static Rose Run reservoir pressure was 9.3 MPa, and fracture gradient under injection was 13.6 MPa/km, suggesting step-rate testing before CO 2 injection, and subsequent pressure monitoring to ensure confinement. As the region around the KGS 1 Hanson Aggregates well is underpressured and adjacent to faulted Precambrian basement, further research is needed to evaluate its induced seismicity risk during CO 2 injection.