Comparisons of SEM, Low-Field NMR, and Mercury Intrusion Capillary Pressure in Characterization of the Pore Size Distribution of Lacustrine Shale: A Case Study on the Dongying Depression, Bohai Bay Basin, China

Abstract

This work investigates the use of scanning electron microscopy (SEM), low-field nuclear magnetic resonance (NMR) relaxation, and mercury intrusion capillary pressure (MICP) to reveal the pore size distribution (PSD) characteristics of shales. The comparisons were conducted using six shale samples from the Dongying Depression, Bohai Bay Basin, China. The results show that SEM can effectively reveal the PSD of shale but cannot detect micropores (<100 nm in diameter) smaller than the imaging resolution or selected macropores if a smaller region of interest (ROI) with a higher resolution is used. Two limitations of MICP were addressed. First, high-pressure intrusion by mercury might either deform or destroy the skeletal porous structure of shale due to the compressibility of the clay minerals and the nanopore system. Second, pore-shielding effects can induce high uncertainty in the MICP PSD results. The large pores are shielded by access to small pores, and thus, the volume of small pores obtained from the MI...