First international inter-laboratory comparison of high-pressure CH 4 , CO 2 and C 2 H 6 sorption isotherms on carbonaceous shales

Abstract

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...

Characterization of methane adsorption on overmature Lower Silurian–Upper Ordovician shales in Sichuan Basin, southwest China: Experimental results and geological implications

“…As expected from Eqs. (1) and (2), the n excess will approach zero when the pressure is high enough and the density of methane in free state approaches the density of adsorbed methane; this inference has been verified by experiments with CO 2 adsorption on activated carbon and shales under very high pressures (Gensterblum et al, 2009;Chareonsuppanimit et al, 2012;Gasparik et al, 2014b).…”

“…At present, it is hard to evaluate which model is more accurate because the uncertainty of experimental data becomes greater at high pressures (Gasparik et al, 2012(Gasparik et al, , 2014b) and all models can fit experimental data fairly good within the experimental errors at high pressures (Gasparik et al, 2012(Gasparik et al, , 2014aGensterblum et al, 2013). Therefore, much work has to be carried out in the future on the reduction of experimental errors at high pressure ranges (Gasparik et al, 2014a).…”

“…Then the excess adsorption of methane at a given temperature was calculated using the routine methods reported in the literature (Krooss et al, 2002;Zhang et al, 2012;Gasparik et al, 2012Gasparik et al, , 2014a. The uncertainty of calculated excess adsorption increases with pressure and varies among samples under different temperatures (Gasparik et al, 2012(Gasparik et al, , 2014b. The maximum error derived from the uncertainty of the void volume is estimated to be about 0.2 cm 3 /g rock at 15 MPa when reported under STP conditions (temperature = 0°C and pressure = 0.1 MPa), close to that reported by Gasparik et al (2012).…”

Geological models of gas in place of the Longmaxi shale in Southeast Chongqing, South China

“…For all samples, the experimental temperature was 60 C. Five extra temperature points (40,80,100,120, and 150 C) were measured for Sample 8 to construct the relationship between adsorbed gas capacity and burial depth. The detailed experimental procedures for the magnetic suspension balance equipment have been well documented in previous publications (Giovanni et al, 2001;Ottiger et al, 2008;Pini et al, 2006Pini et al, , 2010Gasparik et al, 2014b).…”

“…The precision of the magnetic suspension balance is 0.01 mg, and the maximum values of pressure and temperature are 35 MPa and 200 C, respectively. The temperature of the sample container is controlled using a heating oil bath cycle with an accuracy of 0.01 C. The mass change of a sample exposed to the sorptive gas (methane in this study) at a definite temperature and variable pressures is directly measured by the equipment, and the excess adsorption amount is then calculated by the blank and buoyancy corrections at the given temperature (Gasparik et al, 2014b). For all samples, the experimental temperature was 60 C. Five extra temperature points (40,80,100,120, and 150 C) were measured for Sample 8 to construct the relationship between adsorbed gas capacity and burial depth.…”