Experimental Study of the Relationship Between Particle Size and Methane Sorption Capacity in Shale

Summary

We use an isothermal adsorption apparatus, the gravimetric sorption analyzer, to test the adsorption capacity of different particle sizes of shale, in order to find out the relationship between particle size and the adsorption capacity of shale.

Abstract

The amount of adsorbed shale gas is a key parameter used in shale gas resource evaluation and target area selection, and it is also an important standard for evaluating the mining value of shale gas. Currently, studies on the correlation between particle size and methane adsorption are controversial. In this study, an isothermal adsorption apparatus, the gravimetric sorption analyzer, is used to test the adsorption capacity of different particle sizes in shale to determine the relationship between the particle size and the adsorption capacity of shale. Thegravimetric method requires fewer parameters and produces better results in terms of accuracy and consistency than methods like the volumetric method. Gravimetric measurements are performed in four steps: a blank measurement, preprocessing, a buoyancy measurement, and adsorption and desorption measurements. Gravimetric measurement is presently considered to be a more scientific and accurate method of measuring the amount of adsorption; however, it is time-consuming and requires a strict measuring technique. A Magnetic Suspension Balance (MSB) is the key to verify the accuracy and consistency of this method. Our results show that adsorption capacity and particle size are correlated, but not a linear correlation, and the adsorptions in particles sieved into 40 - 60 and 60 - 80 meshes tend to be larger. We propose that the maximum adsorption corresponding to the particle size is approximately 250 µm (60 mesh) in the shale gas fracturing.

Introduction

Shale is a clay rock with a thin sheet of bedding structure, which serves as both a shale gas source rock and a reservoir. Shale has a strong anisotropy consisting of nano- and micron-scale pores, and graptolite fossils are commonly recognized^1,2,3.

Shale gas is commercially exploited in the Yangtze Plate, Southern China. As an unconventional gas system that serves as both a source rock and a reservoir for methane, shale gas is derived from the organic matter within the shale through biogenic and/or thermogenic processes⁴

Protocol

1. Sample Preparation

1. Sample characterization
   1. Measure the total organic carbon (TOC) using a TOC apparatus (see Table of Materials) at a temperature of 20 °C and a relative humidity of 65% (per standard GB/T 19145-2003).
   2. Perform a vitrinite reflectance measurement on polished sections of the shale using a photometer microscope (see Table of Materials).
2. Sample cleaning and crushing
   NOTE: To avoid the influence of various internal and external factors as well as the inhomogeneity of shale as much as possible, select a large shale roc....

Results

Figure 1: Experimental set-up for gravimetric gas adsorption at high temperatures and pressures. This figure shows the set-up for the isothermal adsorption experiment: (a) the oil bath heating device for the.......

Discussion

The materials used in this experiment are shown in the Table of Materials. Before the sample pool is removed, it must be confirmed that the temperature and pressure in the sample pool are at normal pressure and normal temperature; otherwise, there is a danger of injury. If the temperature is too high, wait for the temperature to drop and then removethe sample pool. If the pressure is too high or too low, manually set the air pressure on the software and use an inert gas^13,

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
XRF D8 DISCOVER X-Ray diffractometer	Brook,Germany	204458	For mineralogy X-ray diffraction
EBSD three element integration system with spectrum	EDAX,USA	Trident XM4	For nanoscale imaging (SEM)
Mercury injection capillary pressure (MICP)	USA micromeritics Instrument company	AutoPore IV 9520	For the immersion method to measure macropores(Porosity)
Nitrogen gas adsorption at low temperature	USA micromeritics Instrument company	ASAP2460/2020	For the low pressure nitrogen gas adsorption to measure mesopores and micropores(BET)
Finnigan MAT-252 mass spectrometer	ThermoFinnigan,USA	TRQ/Y2008-004	For C isotope
LECO CS-230 analyzer	Research Institute of Petroleum Exploration and Development	617-100-800	TOC apparatus
3Y-Leica MPV-SP photometer microphotometric system	Leica,Germany	M090063016	Ro apparatus
Magnetic Suspension Balance Isothermal adsorption analyzer	Rubotherm,Germany	2015-1974CHN	For methane adsorption tests
Sieve(20/40/60/80/100/120mesh)	Sinopharm Chemical Reagent Beijing Co.Ltd	200*50GB6003.102012	Used to screen samples
Absorbent cotton, hammer, tweezers and acetaldehyde	Sinopharm Chemical Reagent Beijing Co.Ltd	standard	Used to clean materials
Residual gas tight grinder	Nantong Huaxing Petroleum Instrument Co., Ltd	TY2013000237	Sample smasher