Porosity and Fractal Characteristics of Shale across a Maturation Gradient
Received date: 2015-02-08
Revised date: 2015-05-04
Online published: 2015-09-10
This study employed low pressure gas adsorption porosimetry to investigate the evolution of meso-and micro-pores in a suite of 11 New Albany shale samples(the Illinois Basin,Devonian/Mississippian,U.S.)across a wide range of thermal maturity corresponding to vitrinite reflection Ro values from 0.35% to 1.41%.Meso-and micro-pore volumes follow a nonlinear evolutionary path with thermal maturity,which is constricted by the transformation of kerogen during the early mature stage and secondary cracking of bitumen/oil at the late mature stage.Fractal dimensions of pore walls derived from Frenkel-Halsey-Hill(FHH)and thermodynamic models range from 2.47-2.61,indicating that pores in shales express fractal characteristics in terms of shape and size.This study also finds the fractal dimension of pore walls to be positively correlated with meso-and micro-pore volumes,and negatively related to average pore size in shale,with only the least mature and the two most mature samples behaving as outliers.Enhanced fractal dimension leads to growing pore wall heterogeneity and increasing adsorption sites and gas adsorption capacity of shale.Therefore,the fractal dimension of pore walls may serve as a quantification indicator of pore heterogeneity and thus a valuable predictor for the gas adsorption capacity of shale.
Key words： Shale; Pore structure; Fractal characteristics; N2 adsorption; CO2 adsorption
CHEN Yan-yan，ZOU Cai-neng，Maria Mastalerz，ZHU Ru-kai，BAI Bin，YANG Zhi . Porosity and Fractal Characteristics of Shale across a Maturation Gradient[J]. Natural Gas Geoscience, 2015 , 26(9) : 1646 -1656 . DOI: 10.11764/j.issn.1672-1926.2015.09.1646
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