The importance of lithofacies control on fluid migration in heterogeneous aeolian formations for geological CO2 storage: Lessons from observational evidence and modelling of bleached palaeoreservoirs at Salt Wash Graben, Utah

Electrical Imaging of a Shallow Free-Phase Stray Gas Plume from an Abandoned Exploration Well

“…An interbedded series of "red sandstone" and "red shale" between 8.8 and 32.6 m (107 ft) is interpreted to be the redbrown Earthy Member silty sandstone. At 38.1 m (125 ft) and below, thick metre-scale beds of "hard white sand" and "white sandstone" were observed, which are diagnostic of the bleached aeolian cross-bedded sandstones of the Slick Rock Member [15,26]. Sandstone bleaching occurs from the acid-reductive dissolution of sand grain hematite coatings by CO 2 -charged groundwater, commonly observed for the Entrada Formation's transmissive sections [3,13].…”

“…To correlate tomogram resistivity bodies with lithology, the tomogram results were compared to existing borehole records and geological maps. The original cable tool drill cutting descriptions of Crystal Geyser/Ruby 1-X [12] were separated into geological units based on established lithology descriptions of the travertines and the Earthy and Slick Rock Members of the Entrada Formation [13,15,26,30]. The Crystal Geyser drilling log was also compared to the recovered core log and lithological interpretations of scientific exploration well CO2W55, drilled by Kampman et al [13].…”

“…The presence of subsurface FPG near Crystal Geyser is well-supported, and near-surface FPG accumulations may exist. The broad spatiotemporal distribution of subsurface CO 2 fluids (free-phase, dissolved-phase, and supercriticalphase) and surface free-phase CO 2 efflux is well-documented along the Green River Anticline and intersecting fault zones [3,13,14,16,[24][25][26]. "Shows" of FPG were observed in the Crystal Geyser drilling log at multiple depths, as shallow as 39 m [12,20].…”

“…Furthermore, a FPG accumulation within the Entrada Formation was inferred to be the source of erupted gas during Crystal Geyser's most powerful (or "major" [21]) eruptions because the CO 2 discharge and duration were too large/lengthy to be solely supplied by degassing inside the well conduit [27]. Consequently, numerical modelling studies simulated the large-scale lateral spreading and development of FPG plumes beneath low permeability strata in the Green River Anticline [26,28,29]. Despite the few drilling observations and modelling efforts of FPG, the actual location and greater spatial extent of such speculated FPG accumulations remain uncertain.…”

“…The exposed stratigraphic unit of the footwall is the Earthy Member of the Entrada Formation (Figure 3) [14]. The outcropping Earthy Member is red-brown siltstone to silty sandstone with nodular to irregular bedding [15,26]. The pale brown Curtis Formation overlies the Earthy Member with a local dip of 9 °N (Figure 3) [3].…”