Measurements and Modeling of Gas Adsorption on Shales

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• 作者：Pongtorn Charoensuppanimit ; Sayeed A. Mohammad ; Khaled A. M. Gasem
• 刊名：Energy & Fuels
• 出版年：2016
• 出版时间：March 17, 2016
• 年：2016
• 卷：30
• 期：3
• 页码：2309-2319
• 全文大小：515K
• ISSN：1520-5029

文摘

Shales have become an important source of natural gas, and the recovery of natural gas from such unconventional reservoirs has increased considerably in the United States. Shale reservoirs may also offer carbon dioxide (CO₂) sequestration potential. Because a large portion of gas in shale reservoirs exists in an adsorbed state, modeling of gas adsorption behavior is needed for generating reliable gas-in-place estimates as well as in evaluating CO₂ sequestration potential. Reliable adsorption data measured at reservoir conditions and an accurate adsorption model are two important requirements for describing gas adsorption behavior on shales. To date, high-pressure gas adsorption data on shales are limited, and this is especially true for CO₂ adsorption at higher pressures. In this work, we have measured adsorption of methane, nitrogen, and CO₂ on three shale samples from the Woodford and Caney shale plays in the U.S. Two of the samples were Woodford shales from Payne and Hancock counties, and the third sample was Caney shale. Pure gas adsorption was measured at 328.2 K and pressures up to 12.4 MPa. Results indicate that, at about 7 MPa, the adsorption ratios of nitrogen, methane, and CO₂ are about 1:2.9:6.1 for the Woodford shale from Payne county, 1:3.0:12.8 for the Woodford shale from Hancock county, and about 1:3.5:30.1 for the Caney shale. Our results also showed that adsorption capacities of each gas appear to be related to the total organic carbon (TOC) content of these shales. In addition, CO₂ preferential adsorption over methane on the shales was stronger for samples with a higher ash content, indicating that mineral matter is an important contributing factor in the CO₂ adsorption capacity of shales. The simplified local density (SLD) model was used to represent the adsorption data obtained in this work. The SLD modeling results indicate that the adsorption data were represented within the experimental uncertainties. Overall, the percentage average absolute deviations for methane, nitrogen, and CO₂ adsorption on the three shales were about 7, 8, and 7%, respectively. In addition, the SLD model surface areas and solid–solid interaction parameters appear related to the TOC content of shales. We note, however, that additional adsorption data on shales as well as detailed surface characterization of such samples will be necessary for developing a generalized, predictive adsorption model for shale gas systems.