Effect of Particle Size on Pore Characteristics of Organic-Rich Shales: Investigations from Small-Angle Neutron Scattering (SANS) and Fluid Intrusion Techniques

Yi Shu,Linhao Zhang,Liangwei Sun,Liangfei Bai,Tomasz P Blach,Shu Jiang,Mengdi Sun,Xiang Zhao,Yanran Xu,Qinhong Hu,Zhejun Pan

doi:10.3390/en13226049

Abstract

The sample size or particle size of shale plays a significant role in the characterization of pores by various techniques. To systematically investigate the influence of particle size on pore characteristics and the optimum sample size for different methods, we conducted complementary tests on two overmature marine shale samples with different sample sizes. The tests included small-angle neutron scattering (SANS), gas (N2, CO2, and H2O) adsorption, mercury injection capillary pressure (MICP), and field emission-scanning electron microscopy (FE-SEM) imaging. The results indicate that artificial pores and fractures may occur on the surface or interior of the particles during the pulverization process, and some isolated pores may be exposed to the particle surface or connected by new fractures, thus improving the pore connectivity of the shale. By comparing the results of different approaches, we established a hypothetical model to analyze how the crushing process affects the pore structure of overmature shales. Our results imply that intact wafers with a thickness of 0.15–0.5 mm and cubic samples (~1 cm3) are optimal for performing SANS and MICP analyses. Meanwhile, the 35–80 mesh particle size fraction provides reliable data for various gas physisorption tests in overmature shale. Due to the intrinsic heterogeneity of shale, future research on pore characteristics in shales needs a multidisciplinary approach to obtain a more comprehensive, larger scale, and more reliable understanding.

Highlights

With the commercial development of shale gas in North America and China, the pore characteristics of shale reservoirs have been extensively studied [1,2,3]
This study aims to reveal the influence of particle size on the pore characteristics of overmature organic-rich shales
Previous studies [11,15] have shown that shear and compression forces in the crushing process induce the formation of new fractures and smaller fragments in the shale, generating new porosity, which is consistent with the results of our FE-EM observations

Summary

Introduction

With the commercial development of shale gas in North America and China, the pore characteristics of shale reservoirs have been extensively studied [1,2,3]. Pore characteristics control the hydrocarbon gas storage capacity [4,5], and have an important influence on the gas flow mechanism and producibility [6,7], which can provide basic information for the evaluation of shale reservoirs and Energies 2020, 13, 6049; doi:10.3390/en13226049 www.mdpi.com/journal/energies. Energies 2020, 13, 6049 flow mechanism and producibility [6,7], which can provide basic information for the evaluation of shale reservoirs and shale gas accumulation mechanisms. A series of quantitative and shale accumulation mechanisms.

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