137 Copyright © 2013 by The American Association of Petroleum Geologists. DOI: 10.1306/13391710M1023588 12 Comparison of Porosity Distribution within Selected North American Shale Units by SEM Examination of Argon-ion-milled Samples James M. Rine, Erin Smart, William Dorsey, Kultaransingh Hooghan, and Michael Dixon Weatherford Laboratories, 5200 N. Sam Houston Parkway West, Suite 500, Houston, Texas, 77086, U.S.A. (e-mails: james.rine@weatherfordlabs.com, erin.smart@weatherfordlabs.com, will.dorsey@weatherfordlabs. com, bobby.hooghan@weatherfordlabs.com, mike.dixon@weatherfordlabs.com) ABSTRACT The distribution of nanometer-size pores in ten selected Eagle Ford Group, Haynesville, Marcellus, and Barnett shale samples was similar when comparing relative numerical abun- dances of maximum pore diameters but not when comparing relative abundances of pore areas (pore sizes). Differences also existed between units in the association of pores with or- ganic material. Pores were measured on argon-ion-milled (AIM) samples and examined with a field emission environmental scanning electron microscope (SEM). One Haynesville sample was also evaluated using a focused ion beam (FIB) SEM to compare to the AIM results. With the AIM samples, pore types were subdivided into three categories—organic pores, mixed matrix/organic pores, and matrix pores—based on the amount and type of material (organic or inorganic) surrounding the pores. Organic pores are pores generally associated with kero- gen macerals, whereas mixed matrix/organic pores are pores that are probably associated with bitumen or pyrobitumen. Matrix pores are not associated with any organic matter. Within the sample set studied, only the Barnett samples contained pores almost exclusively within organic particles. The majority of the maximum pore diameters were less than 100 nm within all the samples examined. Only the Barnett samples, however, had a majority of their pore areas (or porosity) comprised of pores less than 10,000 nm 2 (which is the area of an equi- dimensional pore with the maximum pore diameter of 100 nm). James M. Rine, Erin Smart, William Dorsey, Kultaransingh Hooghan, Michael Dixon, 2013, Comparison of porosity distribution within selected North American shale units by SEM examination of Argon-ion-milled samples, in W. Camp, E. Diaz, and B. Wawak, eds., Electron microscopy of shale hydrocarbon reservoirs: AAPG Memoir 102, p. 137–152. INTRODUCTON Electron microscopic examination of pores within mudrocks (shales and mudstones) has become much more sophisticated over the last few years, driven not only by the intense economic interests in shale gas and oil but also by the technological improve- ments that allow characterization of nanometer-scale features. Since 2007, electron microscopy techniques have evolved sufficiently to allow researchers to 13835_ch12_ptg01_hr_p137-152.indd 137 7/3/13 3:10 AM