Mapping and Quantifying the Clay Aggregate Microporosity in Medium- to Coarse-Grained Sandstones Using the 14C-PMMA Method

Abstract Microporous aggregates of kaolin minerals and illite are common products filling the intergranular volume (IGV) of deeply buried sandstones. Using BSEi (backscattered electron imaging), a full analysis of IGV is difficult and time consuming since it necessitates a two-step process, at the scales of (1) macroporosity between the detrital grains, and (2) microporosity within the clay aggregates. The 14C-PMMA method permits the mapping and quantification of the connected porosity in sandstone core samples across scales. This method is based on the complete impregnation of the connected porosity by 14C-labeled MethylMethAcrylate (MMA) monomer, and its subsequent in situ polymerization. Imaging the spatial distribution of the radioactive tracer within a section of an impregnated sample allows an integrated analysis of IGV from the core scale to the nanometer scale. This technique is illustrated through analysis of the clay cement of a medium- to coarse-grained sandstone from the Athabasca Basin (Canada). The measured connected porosity distributions of kaolin mineral aggregates (average porosity 42%) and illite fillings (average porosity 70%) are in accordance with Gaussian distributions. This method also permits quantification of the relative volumetric amounts of the both illite and kaolin aggregate.

[1]  Jean Serra,et al.  Image Analysis and Mathematical Morphology , 1983 .

[2]  S. Morad,et al.  Clay minerals in sandstones; controls on formation, distribution and evolution , 2009 .

[3]  V. Bense,et al.  Assessing Textural Variation in Laminated Sands Using Digital Image Analysis of Thin Sections , 2003 .

[4]  P. Sardini,et al.  The 14C-polymethylmethacrylate (PMMA) impregnation method and image analysis as a tool for porosity characterization of rock-forming minerals , 2005, Geological Society, London, Special Publications.

[5]  A. Cerepi,et al.  Pore microgeometry analysis in low-resistivity sandstone reservoirs , 2002 .

[6]  David A. Budd,et al.  Quantification of Porosity and Permeability Reduction Due to Calcite Cementation Using Computer-Assisted Petrographic Image Analysis Techniques , 1996 .

[7]  R. Ehrlich,et al.  Petrographic Image Analysis, I. Analysis of Reservoir Pore Complexes , 1984 .

[8]  S. Okayama,et al.  Penetration and energy-loss theory of electrons in solid targets , 1972 .

[9]  Dimitri Prêt.  Nouvelles méthodes quantitatives de cartographie de la minéralogie et de la porosité dans les matériaux argileux : application aux bentonites compactées des barrières ouvragées , 2003 .

[10]  D. Rubin.  A Simple Autocorrelation Algorithm for Determining Grain Size from Digital Images of Sediment , 2004 .

[11]  A. Hurst,et al.  Clay Microporosity in Reservoir Sandstones: An Application of Quantitative Electron Microscopy in Petrophysical Evaluation , 1995 .

[12]  A. Meunier,et al.  Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review , 2002, Clay Minerals.

[13]  Richard H. Worden,et al.  Sandstone Diagenesis: The Evolution of Sand to Stone , 2009 .

[14]  Pierre Francus,et al.  An image-analysis technique to measure grain-size variation in thin sections of soft clastic sediments , 1998 .

[15]  Malcolm C. Thomas,et al.  Sand grain analysis—image processing, textural algorithms and neural nets , 1998 .

[16]  O. Amiri,et al.  Distribution spatiale de la porosité des matériaux cimentaires , 2007 .

[17]  A. Lindberg,et al.  Study of porosity and migration pathways in crystalline rock by impregnation with 14C-polymethylmethacrylate , 1993 .

[18]  Robert I. Ferguson,et al.  INFORMATION ON GRAIN SIZES IN GRAVEL-BED RIVERS BY AUTOMATED IMAGE ANALYSIS , 2003 .

[19]  Alain Meunier,et al.  An Imaging Method for the Porosity of Sedimentary Rocks: Adjustment of the PMMA Method--Example of a Characterization of a Calcareous Shale , 2002 .

[20]  Stuart N. Lane,et al.  Automated extraction of grain-size data from gravel surfaces using digital image processing , 2001 .

[21]  M. Cooper.  The use of digital image analysis in the study of laminated sediments , 1998 .

[22]  N. Clauer,et al.  Mineralogy and Geochemistry of the Host-Rock Alterations Associated with the Shea Creek Unconformity-Type Uranium Deposits (Athabasca Basin, Saskatchewan, Canada). Part 1. Spatial Variation of Illite Properties , 2006 .

[23]  D. Beaufort,et al.  On the connected porosity of mineral aggregates in crystalline rocks , 2006 .