Effects of maturation on multiscale (nanometer to millimeter) porosity in the Eagle Ford Shale

摘要: Porosity and permeability are key variables that link the thermal-hydrologic, geomechanical, geochemical behaviorin rocksystemsand arethusimportantinputparametersfor transportmodels. Neutronscattering studies indicate scales of pore sizes in rocks extend over many orders magnitude from nanometer-sized pores with huge amounts total surface area to large open fracture systems (multiscale porosity). However, despite considerable efforts combining conventional petrophysics, neutron scattering, electron microscopy, quantitativenature this porosityintightgas shales, especiallyatsmallerscalesand overlargerrockvolumes, remains largely unknown. Nor is it well understood how networks affected by regional variation rock composition properties, thermal changes across oil window (maturity), and, most critically, hydraulic fracturing. To improve understanding, we have used a combination small- ultrasmall-angle scattering (U)SANS scanning microscope (SEM)/backscattered imaging analyze structure clay- carbonate-rich samples Eagle Ford Shale. This formation hydrocarbon rich, straddles window, one actively drilled gas targets United States. Several important trends been identified using our approach. The results reflected connected (effective) unconnected porosity, as volume occupied organic material. latter could be separated carbon data at all maturities, constituted significant fraction apparent porosity. At lower was strongly anisotropic. decreased increasing maturity, eventually disappearing entirely for samples. In samples, reduction porosity occurred scales, much during initial increases maturity. apparently contradicted SEM observations showed intraorganic increasingmaturity. Organic-rich shales are, however, very complex material fromthe point view studies, more detailed analysis needed better understand these observations.