Evaluation of Nanoscale Accessible Pore Structures for Improved Prediction of Gas Production Potential in Chinese Marine Shales

Published

December 20, 2018

Author(s)

Yang Wang, Yong Qin, Rui Zhang, Lilin He, Lawrence M Anovitz, Markus Bleuel, David F. Mildner, Shimin Liu, Yanming Zhu

Abstract

The lower Cambrian Niutiang and Lower Silurian Longmaxi shales in the Upper Yangtze Platform (UYP) are considered as the most promising strata for shale gas exploration in China. To shed light on the study of evaluation of nanoscale pore structure for improved prediction of gas production potential in Chinese marine shales, systematic investigations of pore accessibility and its impact on methane adsorption capacity were conducted using various techniques including geochemical and mineralogical analyses, field emission scanning electron microscopy (FE-SEM), helium porosimetry, small angle neutron scattering (SANS) and methane adsorption techniques. The results show that organic matter (OM) pores with various shapes are the most important type dominating the pore system of the Chinese marine shale. Partial OM tended to mix with clay minerals and converted to organo-clay complex with developing plentiful micro-/mesopores. A unified fit model with different structure levels was used to model the experimental SANS data to characterize the heirarchical pore structure of Chinese marine shales. Both surface and mass fractals were identified by SANS ranging between 2.41 and 2.85 for the six tested Chinese marine shales. Porosity and specific surface area ranged between 2.31% and 14.94% and between 0.50x10⁵ cm²/cm³ and 9.86x10⁵ cm²/cm³, respectively. Futhermore, the fraction of accessible pores has been evaluated by comparing the porosities estimated by He porosimetry and SANS techniques. It was found that most of the fraction of accessible pores is greater than 70% for these shales. When pore radius is greater than 5 nm, the fraction of accessible pores is greater than 90%. In addition, the high percentage of accessible pores may reduce methane adsorption capacity in shale rocks, while low pore accessibility could reduce methane production at a certain pressure difference, indicating pore accessibility could become an essential impact factor for methane production in shale gas reservoirs.

Citation

Energy & Fuels

Volume

32

Issue

12

Pub Type

Journals

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Keywords

Pore structure, pore accessibility, FE-SEM, SANS, He porosimetry, methane adsorption, Chinese marine shale, Upper Yangtze Platform

Citation

Wang, Y. , Qin, Y. , Zhang, R. , He, L. , Anovitz, L. , Bleuel, M. , Mildner, D. , Liu, S. and Zhu, Y. (2018), Evaluation of Nanoscale Accessible Pore Structures for Improved Prediction of Gas Production Potential in Chinese Marine Shales, Energy & Fuels, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=924884 (Accessed December 14, 2024)