Porosity and permeability are key variables that link the thermal-hydrologic, geomechanical and geochemical behavior in rock systems. Recent neutron scattering studies have indicated that the scales of pore sizes in rocks extend over many orders of magnitude from nanometer pores to large open fracture systems (multiscale porosity, cf. Anovitz et al., 2009, 2011, 2013a,b). However, we lack a quantitative understanding of the multiscale porosity regime (i.e., pore size, shape, and volume, pore size distribution, pore connectivity, pore wall roughness) and how porosity is affected by regional variation, thermal changes across the oil window, and, most critically, hydraulic fracturing operations.To begin to provide a quantitative understanding of porosity at nanometer to core scales in these shale formations and how it relates to gas storage and recovery we have used a combination of small and ultra-small angle neutron scattering measurements SEM/BSE and XCT imaging to analyze the pore structure of both clay and carbonate-rich samples of the Eagle Ford Shale. The Eagle Ford Shale is a late Cretaceous unit underlying much of southeast Texas and probably adjacent sections of Mexico. It outcrops in an arc from north of Austin, through San Antonio and then west towards Kinney County. It is hydrocarbon rich, and buried portions straddle the oil window. Several important trends in the rock pore structure have been identified using our approach. Pore distributions are clearly fractal but, as was observed for the St. Peter sandstone (Anovitz et al., 2013a), are composed of several size distributions. Initial porosity is strongly anisotropic, as expected for shales. However, this decreases for shales, and disappears for carbonates with maturity. In both cases significant reduction occurs in total porosity, with most of the change coming at the finest scales (< ~ 10 nm), and an observable decrease at intermediate scales (near 100 nm).

Variations in multiscale (nano to mm) porosity in the Eagle Ford shale as a function of maturity

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.