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

Lawrence Michael Anovitz, David Robert Cole, Julia Meyer Sheets, Alexander Swift, Harold William Elston, Susan Welch, Steve James Chipera, Kenneth Charles Littrell, David Francis Raymond Mildner and Matthew John Wasbrough
Effects of maturation on multiscale (nanometer to millimeter) porosity in the Eagle Ford Shale (in Geoscience follow-up papers from URTeC 2013 and 2014, John O'Brien (prefacer), Ken Beeney (prefacer), Troy Beserra (prefacer), Mike Kendrick (prefacer), Marc Marshall (prefacer), Gene Sparkman (prefacer) and R. Randy Ray (prefacer))
Interpretation (Tulsa) (August 2015) 3 (3): SU59-SU70


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

ISSN: 2324-8858
EISSN: 2324-8866
Serial Title: Interpretation (Tulsa)
Serial Volume: 3
Serial Issue: 3
Title: Effects of maturation on multiscale (nanometer to millimeter) porosity in the Eagle Ford Shale
Title: Geoscience follow-up papers from URTeC 2013 and 2014
Author(s): Anovitz, Lawrence MichaelCole, David RobertSheets, Julia MeyerSwift, AlexanderElston, Harold WilliamWelch, SusanChipera, Steve JamesLittrell, Kenneth CharlesMildner, David Francis RaymondWasbrough, Matthew John
Author(s): O'Brien, Johnprefacer
Author(s): Beeney, Kenprefacer
Author(s): Beserra, Troyprefacer
Author(s): Kendrick, Mikeprefacer
Author(s): Marshall, Marcprefacer
Author(s): Sparkman, Geneprefacer
Author(s): Ray, R. Randyprefacer
Affiliation: Oak Ridge National Laboratory, Chemical Sciences Division, Oak Ridge, TN, United States
Affiliation: Anadarko Petroleum Corporation, Houston, TX, United States
Pages: SU59-SU70
Published: 201508
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 46
Accession Number: 2016-006914
Categories: Economic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
Secondary Affiliation: Devon Energy, USA, United StatesLumina Technologies, USA, United StatesR3 Exploration Corporation, USA, United StatesOhio State University, USA, United StatesChesapeake Energy Corporation, USA, United StatesNational Institute of Standards and Technology, USA, United States
Source Note: Online First
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 201604
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