ASSESSING AUX VASES SANDSTONE HETEROGENEITY IN THE ILLINOIS BASIN FOR POTENTIAL EOR PROJECTS USING CLAY MINERALOGY, POROSITY, AND PERMEABILITY

The Upper Mississippian Aux Vases Sandstone is a significant oil reservoir in the Illinois Basin (ILB), and may be the target of future enhanced oil recovery (EOR) projects. The producing facies is characterized by fine-grained, tidally reworked, elongated sandstone bars. Despite prolific oil production and detailed study of individual oil fields, the spatial distribution of mineralogical heterogeneity within the Aux Vases is poorly understood. Recognizing the spatial variations in clay mineralogy of Aux Vases reservoir rock across the ILB will aid in future discoveries and could improve the overall oil recovery from the formation through proper implementation of EOR techniques.

Past studies characterized the Aux Vases on individual oil field or outcrop belts scales, but those findings have not been integrated into a basin wide model for mineralogical variation within the Aux Vases. Additionally, because of the focus on individual oil fields, mineralogical data gaps exist across the ILB in areas where the Aux Vases exhibits abnormally low chlorite content, anomalous kaolinite and decreased permeability and porosity; all factors that impact oil recovery potential. Due to limited data in the northern ILB there is need for a more regional study to understand the mineralogical changes in the Aux Vases.

New samples have been collected to improve mineralogical data resolution and understand the nature of the spatial distribution of clay minerals within the Aux Vases across the ILB. Semi-quantitative X-Ray diffraction (XRD) methods were used on 30 core samples for clay mineral analysis. Measurements of permeability and porosity of core plugs helped determine how the clay mineralogy is related to those parameters. A synthesis of mineralogical, permeability and porosity data in the north-south trending, tidally influenced sandstone bar facies of the Aux Vases Formation is expected to show spatial variations in diagenetic alteration and deposition with implications for the application of EOR. The mineralogical data should provide new insights and detailed information for understanding how the Aux Vases formed and diagenetically evolved in the ILB.