Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractAn inter-laboratory study of high-pressure gas sorption measurements on two carbonaceous shales has been conducted in order to assess the reproducibility of the sorption isotherms and identify possible sources of error. The measurements were carried out by seven international research laboratories on either in-house or commercial sorption equipment using manometric as well as gravimetric methods. Excess sorption isotherms for methane, carbon dioxide and ethane were measured at 65°C and at pressures up to 25 MPa on two organic-rich shales in the dry state. The samples were taken from the immature Posidonia shale (Germany) and from the over-mature Upper Chokier formation (Belgium). Their total organic carbon (TOC) and vitrinite reflectance (VRr) values were 15.1% and 4.4% and 0.5% and 2.0%, respectively. The objective of the study was to assess the inter-laboratory reproducibility of sorption isotherms as would be expected with each laboratory following its own measurement and data reduction procedures. All labs were asked to follow a predefined sample drying procedure prior to measurement in order to minimize any effects related to moisture. The reproducibility of the methane excess sorption isotherms was better for the high-maturity shale (within 0.02 -0.03 mmol/g) than for the low-maturity sample (up to 0.1 mmol/g), similar to observations in earlier inter-laboratory studies on coals. The reproducibility for CO2 and C2H6 sorption isotherms was satisfactory at pressures below 5 MPa, however,the results deviate considerably at higher pressures. Artefacts in the shape of the excess sorption isotherms were observed for CO2 and C2H6 and these are explained as being due to a high sensitivity of gas density to temperature and pressure close to the critical point as well as from a limited measurement accuracy and possibly uncertainty in the equation of state (EoS).The low sorption capacity of carbonaceous shales (as compared to coals and activated carbons) sets very high demands on the accuracy of pressure and temperature measurement and precise temperature control. Furthermore, the sample treatment, measurement and data reduction procedures must be optimized in order to achieve satisfactory inter-laboratory consistency and accuracy. Unknown systematic errors must be minimized first by calibrating the pressure and temperature measurement sensors to high-quality standards. Blank sorption measurements with a non-sorbing sample (e.g. steel cylinders) can be used to identify and...

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