Geomechanical and Structural characteristics of a paleoreservoir -caprock sucsession; sandstones of Humbugflats, Central Utah

Different horizons within an exposed deformed sedimentary sequence can, along with the fracture pattern, potentially be utilized by reducing fluids, in turn altering the mineralogical composition of the unit. Potentially resulting in discoloring (bleaching) and changes to the mechanical integrity of an entire layer, exemplified by a paleo-reservoir in an exposed sequence of the Entrada Sandstone in Utah, USA. The main focus of this study has been to investigate the mechanical strengths of the different units and map the fracture patterns in order to provide detailed data on the different lithologies. Further trying to find patterns in the collected data, in both the fracture patterns, supplemented with data on the deformation bands within the paleo-reservoir, and within the mechanical properties of the different units. Detailed mapping of the fractures has been conducted on the studied outcrop, situated at Humbugflats on the north end of the San Rafael Swell. In total 82 tests have been conducted to get constraints on the mechanical differences of the units. The data gathered on the fractures generally concur with previous studies conducted in the area, with minor differences. The fractures and deformation bands can be populated into two main fracture populations and three deformation band populations. The mechanical data reveal that the mechanical strength of the units is related to the porosity of the rock within, in consensus with earlier studies. The mechanism for the proposed bleaching in the paleo reservoir is thought to be a reducing fluid, saturated with CO2 driven by buoyancy. Causing fluid migration along fractures and into the paleo-reservoir, increasing the fluid pressure in the reservoir causing it to extensively deform. The results of this study provide a summary for geomechanical differences caused by bleaching and fluid saturation of a paleo-reservoir.