A lot of assistance was provided by Engineer Gang Chen and Tao Zhang. This work was financially supported by the Major State Research Development Program of China (Grant No.2016YFC0600202) and the China Geological Survey (CGS, Grant No. DD20160183). We thank anonymous reviewers for their constructive comments that greatly improved this paper.

1. Sample Preparation
<ol>
	<li>Sample characterization
	<ol>
		<li>Measure the total organic carbon (TOC) using a TOC apparatus (see Table of Materials) at a temperature of 20 &#176;C and a relative humidity of 65% (per standard GB/T 19145-2003).</li>
		<li>Perform a vitrinite reflectance measurement on polished sections of the shale using a photometer microscope (see Table of Materials).</li>
	</ol>
	</li>
	<li>Sample cleaning and crushing 
	NOT...

<ol>
	<li>Strapoc, D., Mastalerz, M., Schimmelmann, A., Drobniak, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Geochemical+constraints+on+the+origin+and+volume+of+gas+in+the+New+Albany+Shale+(Devonian-Mississippian),+eastern+Illinois+Basin.">Geochemical constraints on the origin and volume of gas in the New Albany Shale (Devonian-Mississippian), eastern Illinois Basin.</a> AAPG Bulletin. 94, 1713-1740 (2010).</li><li>Loucks, R. G., Ruppel, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mississippian+Barnett+Shale:+Lithofacies+and+depositional+setting+of+a+deep-water+shale-gas+succession+in+the+Fort+Worth+Basin,+Texas.">Mississippian Barnett Shale: Lithofacies and depositional setting of a deep-water shale-gas succession in the Fort Worth Basin, Texas.</a> AAPG Bulletin. 91, 579-601 (2007).</li><li>Curtis, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fractured+shale-gas+systems.">Fractured shale-gas systems.</a> AAPG Bulletin. 86, 1921-1938 (2002).</li><li>Montgomery, S. L., Jarvie, D. M., Bowker, K. A., Pallastro, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mississippian+Barnett+Shale,+Fort+Worth+basin,+north-central+Texas:+Gas-shale+play+with+multitrillion+cubic+foot+potential.">Mississippian Barnett Shale, Fort Worth basin, north-central Texas: Gas-shale play with multitrillion cubic foot potential.</a> AAPG Bulletin. 89, 155-175 (2005).</li><li>Jia, C. Z., Zheng, M., Zhang, Y. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unconventional+hydrocarbon+resources+in+China+and+the+prospect+of+explora+exploration+and+development.">Unconventional hydrocarbon resources in China and the prospect of explora exploration and development.</a> Petroleum Exploration and Development. 39 (2), 129-136 (2012).</li><li>Hou, Y. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+pore+structure+on+methane+sorption+potential+of+shales.">Effect of pore structure on methane sorption potential of shales.</a> Petroleum Exploration and Development. 41 (2), 272-281 (2014).</li><li>Chalmers, G. R., Bustin, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+organic+matter+distribution+and+methane+capacity+of+the+lower+cretaceous+strata+of+northeastern+British+Columbia,+Canada.">The organic matter distribution and methane capacity of the lower cretaceous strata of northeastern British Columbia, Canada.</a> International Journal of Coal Geology. 70 (1-3), 223-239 (2007).</li><li>Kang, Y. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+particle+size+on+methane+sorption+capacity+of+shales.">Effect of particle size on methane sorption capacity of shales.</a> Natural Gas Geoscience. 28 (2), 272-279 (2017).</li><li>Wang, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adsorption+influence+factors+and+characteristics+of+adsorption+isotherm+for+shale+to+methane.">Adsorption influence factors and characteristics of adsorption isotherm for shale to methane.</a> Natural Gas Geoscience. 26 (3), 580-591 (2015).</li><li>Ruppel, T. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adsorption+of+methane+on+dry+coal+at+elevated+pressure.">Adsorption of methane on dry coal at elevated pressure.</a> Fuel. 53, 152-162 (1974).</li><li>Zhang, G. D., Han, Y. K., He, Z. P., Gao, X. Y., Chen, H. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+sample+particle+size+on+the+adsorption+capacity+of+the+experimental+study+on+the+effect+of+shale+gas.">The sample particle size on the adsorption capacity of the experimental study on the effect of shale gas.</a> Exploration and Development. 6, 110-116 (2016).</li><li>Ross, D. J., Bustin, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+mass+balance+calculations+on+adsorption+capacities+in+microporous+shale+gas+reservoirs.">Impact of mass balance calculations on adsorption capacities in microporous shale gas reservoirs.</a> Fuel. 86 (17), 696-706 (2007).</li><li>Gasparik, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-pressure+methane+sorption+isotherms+of+black+shales+from+The+Netherlands.">High-pressure methane sorption isotherms of black shales from The Netherlands.</a> Energy &amp; Fuels. 26 (8), 4995-5004 (2012).</li><li>Ji, L. M., Luo, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+sample+size+on+volumetric+determination+of+methane+adsorption+in+clay+minerals.">Effect of sample size on volumetric determination of methane adsorption in clay minerals.</a> Natural Gas Geoscience. 23 (3), 535-549 (2012).</li><li>Wang, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+methane+sorption+capacity+of+Paleozoic+shales+from+the+Sichuan+Basin,+China.">The methane sorption capacity of Paleozoic shales from the Sichuan Basin, China.</a> Marine and Petroleum Geology. 44 (3), 112-119 (2013).</li><li>Zhang, X. D., Sang, S. X., Qin, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isotherm+adsorption+of+coal+samples+with+different+grain+size.">Isotherm adsorption of coal samples with different grain size.</a> Journal of China University of Mining and Technology. 34, 427-432 (2005).</li><li>Wang, Z. X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+discussion+on+the+structural+deformation+and+oil/gas+traps+on+the+western+side+of+the+Xuefeng+Mountain.">A discussion on the structural deformation and oil/gas traps on the western side of the Xuefeng Mountain.</a> Geological Bulletin of China. 31 (11), 1812-1825 (2012).</li><li>Xu, Z. Y., Liang, X., Wang, X. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlling+factors+for+shale+gas+sweet+spots+distribution+in+the+Upper+Yangtze+region:+a+case+study+of+the+Upper+Ordovician+Wufeng+Fm-Lower+Silurian+Longmaxi+Fm,+Sichuan+Basin.">Controlling factors for shale gas sweet spots distribution in the Upper Yangtze region: a case study of the Upper Ordovician Wufeng Fm-Lower Silurian Longmaxi Fm, Sichuan Basin.</a> Natural Gas Industry. 36 (9), 35-43 (2016).</li><li>Chalmers, G. L., Bustin, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lower+cretaceous+gas+shales+in+northeastern+British+Columbia,+Part+I:+geological+controls+on+methane+sorption+capacity.">Lower cretaceous gas shales in northeastern British Columbia, Part I: geological controls on methane sorption capacity.</a> Bulletin of Canadian Petroleum Geology. 56 (1), 1-21 (2008).</li><li>Tan, J. Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shale+gas+potential+of+the+major+marine+shale+formations+in+the+Upper+Yangtze+Platform,+South+China,+Part+II:+methane+sorption+capacity.">Shale gas potential of the major marine shale formations in the Upper Yangtze Platform, South China, Part II: methane sorption capacity.</a> Fuel. 129 (4), 204-218 (2014).</li><li>Zhao, Y. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Study+of+impact+factors+on+shale+gas+adsorption+and+desorption.">Study of impact factors on shale gas adsorption and desorption.</a> Natural Gas Geoscience. 25 (6), 940-946 (2014).</li><li>Xue, H. Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adsorption+capability+and+aperture+distribution+characteristics+of+shales:+taking+the+Longmaxi+Formation+shale+of+Sichuan+Basin+as+an+example.">Adsorption capability and aperture distribution characteristics of shales: taking the Longmaxi Formation shale of Sichuan Basin as an example.</a> Acta Petrolei Sinca. 34 (5), 826-832 (2013).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=U.S.+Shale+Gas:+An+Unconventional+Resource.+Unconventional+Challenges.">U.S. Shale Gas: An Unconventional Resource. Unconventional Challenges.</a> Halliburton Energy Services. , (2008).</li><li>Zhang, L. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adsorption+capacity+and+controlling+factors+of+the+Lower+Silurian+Longmaxi+Shale+Play+in+southern+Sichuan+Basin.">Adsorption capacity and controlling factors of the Lower Silurian Longmaxi Shale Play in southern Sichuan Basin.</a> Natural Gas Industry. 34 (12), 63-69 (2014).</li><li>Gasparik, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Geological+controls+on+the+methane+storage+capacity+in+organic-rich+shales.">Geological controls on the methane storage capacity in organic-rich shales.</a> International Journal of Coal Geology. 123 (2), 34-51 (2014).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Technically+Recoverable+Shale+Oil+and+Shale+Gas+Resources:+An+Assessment+of+137+Shale+Formations+in+41+Countries+Outside+the+United+States.">Technically Recoverable Shale Oil and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside the United States.</a> U.S. Energy Information Administration. , (2013).</li><li>Gao, H. Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isotherm+adsorption+characteristic+of+marine+and+continental+shale+and+its+controlling+factors.">Isotherm adsorption characteristic of marine and continental shale and its controlling factors.</a> Natural Gas Geoscience. 24 (6), 1290-1297 (2013).</li><li>Josh, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laboratory+characterization+of+shale+properties.">Laboratory characterization of shale properties.</a> Journal of Petroleum Science and Engineering. 88-89 (2), 107-124 (2012).</li><li>Li, W. 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U., Stuart, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Gas Adsorption Equilibria: Experimental Methods and Adsorptive Isotherms. , (2005).</li><li>Ji, W. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Geological+controls+and+estimation+algorithms+of+lacustrine+shale+gas+adsorption+capacity:+A+case+study+of+the+Triassic+strata+in+the+southeastern+Ordos+Basin,+China.">Geological controls and estimation algorithms of lacustrine shale gas adsorption capacity: A case study of the Triassic strata in the southeastern Ordos Basin, China.</a> International Journal of Coal Geology. 134-135 (1), 61-73 (2014).</li><li>Liang, M. 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The authors have nothing to disclose.

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 gas13,</s...

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 recognized1,2,3.
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 processes4,5. Natural gas stores in reservoirs are in one of three forms: free gas in pores and fractures, adsorbed gas on the surface of organic matter or inorganic minerals, and dissolved gas in bitumen and water6,7. Previous studies suggest that adsorbed gas accounts for 20 - 85% of the total gas in shale formations6. Therefore, research on the adsorption capacity of shale and its controlling factors are significant to the exploration and development of shale gas resource.
The methane adsorption ability of shale has been widely recognized as significantly varying with temperature, pressure, humidity, maturity, mineral composition, organic matter, and specific surface area1,4,5,6,7; and previous studies have confirmed a larger and clearer correlation between external factors like temperature, pressure, and humidity and methane adsorption.
However, studies on the correlation between intrinsic factors like particle size and methane adsorption are controversial. Kang and Ji suggest that the methane adsorption capacity of the same shale samples increases with a decrease in particle size8,14, whereas Rupple and Zhang believe the relevance between the particle size and adsorption is limited based on the isothermal adsorption curves9,10,11. In addition, without standards for a shale gas adsorption evaluation protocol, laboratories in China typically apply the coal adsorption evaluation protocols for evaluating shale gas adsorption. To clarify the relationship between particle size and adsorption,as well as investigate a prospective exploration zone, we obtained shale samples from the thick marine shale deposits of the Wuling Sag in the Upper Yangtze Plate. A gravimetric sorption analyzer was applied to conduct the isothermal adsorption experimentand obtain the relationship between the particle size and adsorption.
The volumetric and gravimetric methods are the main methods used to test the isothermal adsorption of shale. Volume is the key parameter of the volumetric method, which is easily affected by temperature and pressure12,13,14. Because of uncertainty in the error analysis, the cumulative propagation in direct measurements using the volumetric method for calculating adsorption amounts leads to a large error in the measurement results, which causes an abnormal adsorption isotherm14,15. Compared with the volumetric method, the gravimetric method requires fewer parameters and results in smaller errors: because the mass is conserved, the weight and mass of the gravimetric method are not affected by the temperature and pressure12. It is considered a more scientific and accurate method for measuring theadsorption amount of adsorption at present.
A gravimetric sorption analyzer is used in this experiment, which has a maximum testing pressure of 70 MPa (700 bar) and temperature of 150 &#176;C. The temperature and pressure generated by older apparatus are too low toaccurately simulate the temperature and pressure of the deep underground formation. The key to using a sorption analysis apparatus is reaching the magnetic suspension balance for accurately weighing the sample material, with an accuracy of 10 &#181;g. The apparatus adopts a circulating oil bath heating mode and the temperature range can be controlled for a long time to within 0.2 &#176;C. The accuracy of an old apparatus is low, and thus the error would be larger than that obtained with newer instruments. The experimental operations are performed with the software provided by the apparatus.The operating system will be updated regularly to ensure the analysis is close to the actual underground conditions12.
A magnetic suspension balance (MSB) is used in the gravimetric method to test the methane isothermal adsorption of shale without direct contact between the sample and the equipment, in normal temperature and pressure. The sample is placed in the measuring pool, in which the weight of the sample can be transmitted to the balance through a non-contact suspension coupling mechanism12,13. Under the balance, there is a suspended magnet, controlled by a specially designed controller that allows the free suspension of the permanent magnet below. The permanent magnet connects the position sensor and the sample container&#160;with the coupling frame. The function of the coupling frame is to couple or decouple the sample container to the permanent magnet suspension rod14,15,16.
Our measured samples are black organic-rich shales deposited in marine facies of the Long Maxi formation, Lower Silurian in the Daozhen, Guizhou province. The research area is in the Wuling Sag, upper Yangtze plate, which is bordered by the Sichuan Basin to the northwest and Xuefeng Mountain tectonic zone to the southwest17. The Wuling Sag is a structural transfer and transition zone between the Sichuan Basin and Xuefeng Mountain tectonic zone, which received shallow-deep sea shelf deposits, and marine black shale was widely developed during the early Silurian; the sag was then strongly superimposed by tectonic events like the Indo-China Movement, Yanshan Movement, and Himalayan Movement, which formed multistage folds, faults, and unconformities18. The marine black shale in the Wuling Sag has been significantly influenced by the complex geological conditions, which formed shale gas reserves. As a structural transfer zone, the sag is the sweet spot for shale gas exploration, which is characterized by a weaker deformation, better shale gas generation and preservation conditions, and a better natural fracture matching of the traps19.
High-pressure sorption measurements are conducted based on a standardized procedure with the guidance of the isothermal adsorption apparatus protocol, which has been comprehensively elaborated on in several publications10,11,12,13,14,15,16. The isothermal adsorption experiments were completed in the Key Laboratory of Shale Oil and Gas Investigation and Evaluation of the Chinese Academy of Geosciences. A gravimetric measurement carried out with a magnetic suspension balance (MSB) is performed in four steps: a blank measurement, preprocessing, a buoyancy measurement, and an adsorption and desorption measurement (Figure 1, Figure 2).

<table border="0" cellpadding="0" cellspacing="0" style="width:1587px;" width="1586">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:412px;">XRF D8 DISCOVER X-Ray diffractometer</td>
			<td style="width:427px;">Brook,Germany</td>
			<td style="width:140px;">204458</td>
			<td style="width:608px;">For mineralogy X-ray diffraction</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EBSD three element integration system with spectrum&#160;</td>
			<td>EDAX,USA</td>
			<td>Trident XM4</td>
			<td>For nanoscale imaging (SEM)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mercury injection capillary pressure (MICP)</td>
			<td>USA micromeritics Instrument company</td>
			<td>AutoPore IV 9520</td>
			<td>For the immersion method to measure macropores(Porosity)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Nitrogen gas adsorption at low temperature</td>
			<td>USA micromeritics Instrument company</td>
			<td>ASAP2460/2020</td>
			<td>For the low pressure nitrogen gas adsorption to measure mesopores and micropores(BET)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Finnigan MAT-252 mass spectrometer</td>
			<td>ThermoFinnigan,USA</td>
			<td>TRQ/Y2008-004</td>
			<td>For C isotope</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">LECO CS-230 analyzer&#160;</td>
			<td>Research Institute of Petroleum Exploration and Development</td>
			<td>617-100-800</td>
			<td>TOC apparatus</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">3Y-Leica MPV-SP photometer microphotometric system&#160;</td>
			<td>Leica,Germany</td>
			<td>M090063016</td>
			<td>Ro apparatus</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Magnetic Suspension Balance Isothermal adsorption analyzer</td>
			<td>Rubotherm,Germany</td>
			<td>2015-1974CHN</td>
			<td>For methane adsorption tests</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sieve(20/40/60/80/100/120mesh)</td>
			<td>Sinopharm Chemical Reagent Beijing Co.Ltd</td>
			<td>200*50GB6003.102012</td>
			<td>Used to screen samples</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Absorbent cotton, hammer, tweezers and acetaldehyde</td>
			<td>Sinopharm Chemical Reagent Beijing Co.Ltd</td>
			<td>standard</td>
			<td>Used to clean materials</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Residual gas tight grinder</td>
			<td>Nantong Huaxing Petroleum Instrument Co., Ltd</td>
			<td>TY2013000237</td>
			<td>Sample smasher</td>
		</tr>
	</tbody>
</table>

experimental study of the relationship between particle size and methane sorption capacity in shale

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 &#181;m (60 mesh) in the shale gas fracturing.

<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57705/57705fig1.jpg" /> 
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 fluid bath; (b) the electrical heating device for the electrical heating; (c) the magnetic suspens...

Watch this Scientific Journal Video about Experimental Study of the Relationship Between Particle Size and Methane Sorption Capacity in Shale at JoVE.com

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

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.

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 ...

This method can help answer key questions in the shale gas field about the relationship between particle size and the adsorption capacity of shale. The main advantage of this technique is that the gravimetric method requires fewer parameters and produces better results in terms of accuracy and simulating actual underground structure. First, turn on the magnetic suspension balance computer, and start the magnetic suspension coupling controller.Open the gas two helium cylinder, and roughly adjust it to the appropriate output pressure with the control valve. Next, confirm that the magnetic suspension coupling controller knob is in the Off position. Then, turn on the instrument temperature controller, the oil bath heater, and the vacuum pump.Switch the coupling controller to the Zero Point position, wait one to two minutes, and confirm that the readings are normal and stable. Check the Measuring Point positions in the same way. Then, set the controller to the Zero Point position.Start the System Control Software. Select the Blank Measurement program, and open the configuration window. Name the measurement, select gas two to use helium gas, select other fluid, and select fluid bath.Set the maximum pressure to 70 bars with seven pressure steps, the pressure ramp to two bars per minute, and the oil bath temperature to 50 degrees Celsius. Run the program, and calculate the mass and volume of the empty sample container. After the blank test has finished, set the gas two helium pressure setpoint to one bar.Start gas dosing to fill the sample pool with helium until it is close to atmospheric pressure. Then, stop gas dosing. Next, pull down the temperature sensor.Disassemble the insulating cotton jacket and the double-walled thermostat. Support the double-walled thermostat when the last screw is removed. Unload the double-walled thermostat, being careful not to knock the sensor traverse tube with the wrench.Then, disassemble the sample pool by removing the six screws symmetrically. Carefully open the sample pool. Next, check whether the instrument balance frame is level.To adjust the balance frame, turn the magnetic coupling controller knob to Off, and carefully raise or lower the feet and support screws. Once the system is balanced, take out the sample container, and load a clean, crushed shale rock sample into the sample container. Install the sample container, and then set the coupling to the appropriate position.Then, reinstall the sample pool, being careful to keep the edges within the flange. Install the screws symmetrically, and turn the screws with gentle, uniform force. After installing the sample pool, try installing the double-walled thermostat to ensure that it can be installed smoothly in the later buoyancy measurement.Once this has been confirmed, remove the double-walled thermostat. Next, turn the coupling controller knob to each position to check the balance. Insert the temperature sensor, and install the electrical heating sheath and insulation cover.Connect the electrical heating power supply, and turn on the power. Then, select the Pretreatment program in the instrument software, and open the configuration menu. Name the measurement, choose the vacuum source, and select electrical heating.Set the sample temperature to 105 degrees Celsius, the coupling temperature to 20 degrees Celsius, and the duration to 600 minutes. Then, run the Pretreatment program. Afterwards, turn off the electrical heating, and disconnect the power supply.Remove the electric heating sheath, insert the temperature sensor, and install the double-walled thermostat. Wrap the thermostat with an adhesive insulation cover. Next, in the software, select the Buoyancy Measurement program, and open the configuration window.Set the oil bath temperature to 50 degrees Celsius. Set the maximum pressure to 70 bar, the pressure ramp to two bars per minute, and the number of pressure steps to seven. Then, run the process, which usually takes five to eight hours.After that, select the Sorption Measurement program. If desorption will be evaluated, maintain the oil bath at 50 degrees Celsius, and set 19 pressure points, stepping up from zero bars to 250 bars and back to zero bars. Then, choose gas one instead of gas two for the experimental gas, and run the program.Use a pressurized pump if needed to manually increase the experimental gas pressure to the target value. Let the process finish before removing any components from the instrument. Two shale specimens were crushed and divided by particle size.For all samples, the absolute methane adsorption capacity linearly increased with pressure between zero and 60 bars. After that, the absolute adsorption capacity gradually plateaued. The excess adsorption capacity followed a similar trend at lower pressures, reached a maximum at about 80 to 100 bars, and then decreased with increasing pressure.Shale samples with particle sizes of about 250 micrometers generally had the highest maximum absolute and excess adsorption capacity. This was attributed to the rock being crushed into smaller particles and to micropores and mesopores connecting to form mesopores and macropores, decreasing the total specific surface area of the shale. We first had this idea for this method when we considered how large particles should be used for isothermal adsorption experiments of shale in different regions.Once mastered, this technique can be done in 24 hours if it is performed properly.

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7.4K visualizações.  Chinese Academy of Geological Sciences. This method can help answer key questions in the shale gas field about the relationship between particle size and the adsorption capacity of shale. The main advantage of this technique is that the gravimetric method requires fewer parameters and produces better results in terms of accuracy and simulating actual underground structure. First, turn on the magnetic suspension balance computer, and start the magnetic suspension coupling controller.Open the gas two helium cylinder, and rough...