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Title: Carbon Dioxide Sorption Isotherms and Matrix Transport Rates for Non-Powdered Coal

Abstract

For enhanced coalbed methane/carbon dioxide sequestration field projects, carbon dioxide isotherms and the rate of diffusion of the carbon dioxide from the cleats into the matrix are important parameters for predicting how much carbon dioxide actually will be sequestered under various operating conditions. Manometric (or pressure swing) experiments on powdered coal provide a quick, simple, and relatively inexpensive method for measuring sorption isotherms. However, determination of the rate of transport from cleat into matrix from the rate of gas pressure drop is difficult, if not impossible. (The characteristic time constant for the transport depends on the cleat spacing as well as the rate of diffusion.) Manometric measurements often yield isotherms that are extremely problematic in the region of the carbon dioxide critical point; perhaps even worse, available data seem to indicate that the sorption isotherms measured for powders are much larger than the isotherms of coal cores. Measurements on centimeter-sized samples can take weeks or months to reach equilibrium; for such equilibration times gas leakage rates that would be of no significance in powdered-coal measurements can completely invalidate manometric measurements on coal cores. We have tested and used a simple, inexpensive method for measuring isotherms and carbon dioxide transport ratesmore » in coal cores. One or more cores are placed in a simple pressure vessel, and a constant pressure is maintained in the vessel by connecting it to a gas supply (which contains a very large amount of gas compared to amount that could leak over the course of the experiment). From time to time the gas supply is shut off, the sample is removed, and its weight is recorded at ambient pressure at frequent time intervals for a period of about one hour. The sample is then returned to the pressure vessel, the carbon dioxide pressure restored to its previous value, and the equilibration resumed until the next sample weighing. For a point on the isotherm, the process is repeated until the sample weight reaches a constant value (i.e., typically equilibration times of several weeks). The slope of a plot of sample weight vs. square root of elapsed desorption time gives a measurement for the rate of diffusion. In order to advance all three experimental methods, results from this “ambient-pressure gravimetry” method were compared with data obtained by conventional manometry and by computer tomography. The isotherm and “diffusion” rate measured for the core can be directly used in simulators for reservoir engineering studies of coalseam sequestration and enhanced coalbed methane production.« less

Authors:
; ;
Publication Date:
Research Org.:
National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR (United States)
Sponsoring Org.:
USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
915490
Report Number(s):
DOE/NETL-IR-2007-150
TRN: US200817%%539
DOE Contract Number:  
None cited
Resource Type:
Conference
Resource Relation:
Conference: 2007 International Coalbed Methane Symposium, Tuscaloosa, AL, May 21-25, 2007
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; 02 PETROLEUM; 03 NATURAL GAS; CARBON DIOXIDE; COAL; COAL DEPOSITS; DIFFUSION; ISOTHERMS; METHANE; PRESSURE DROP; PRESSURE VESSELS; RESERVOIR ENGINEERING; SORPTION; TRANSPORT

Citation Formats

Smith, D H, Jikich, S, and Seshadri, K. Carbon Dioxide Sorption Isotherms and Matrix Transport Rates for Non-Powdered Coal. United States: N. p., 2007. Web.
Smith, D H, Jikich, S, & Seshadri, K. Carbon Dioxide Sorption Isotherms and Matrix Transport Rates for Non-Powdered Coal. United States.
Smith, D H, Jikich, S, and Seshadri, K. Tue . "Carbon Dioxide Sorption Isotherms and Matrix Transport Rates for Non-Powdered Coal". United States. doi:.
@article{osti_915490,
title = {Carbon Dioxide Sorption Isotherms and Matrix Transport Rates for Non-Powdered Coal},
author = {Smith, D H and Jikich, S and Seshadri, K},
abstractNote = {For enhanced coalbed methane/carbon dioxide sequestration field projects, carbon dioxide isotherms and the rate of diffusion of the carbon dioxide from the cleats into the matrix are important parameters for predicting how much carbon dioxide actually will be sequestered under various operating conditions. Manometric (or pressure swing) experiments on powdered coal provide a quick, simple, and relatively inexpensive method for measuring sorption isotherms. However, determination of the rate of transport from cleat into matrix from the rate of gas pressure drop is difficult, if not impossible. (The characteristic time constant for the transport depends on the cleat spacing as well as the rate of diffusion.) Manometric measurements often yield isotherms that are extremely problematic in the region of the carbon dioxide critical point; perhaps even worse, available data seem to indicate that the sorption isotherms measured for powders are much larger than the isotherms of coal cores. Measurements on centimeter-sized samples can take weeks or months to reach equilibrium; for such equilibration times gas leakage rates that would be of no significance in powdered-coal measurements can completely invalidate manometric measurements on coal cores. We have tested and used a simple, inexpensive method for measuring isotherms and carbon dioxide transport rates in coal cores. One or more cores are placed in a simple pressure vessel, and a constant pressure is maintained in the vessel by connecting it to a gas supply (which contains a very large amount of gas compared to amount that could leak over the course of the experiment). From time to time the gas supply is shut off, the sample is removed, and its weight is recorded at ambient pressure at frequent time intervals for a period of about one hour. The sample is then returned to the pressure vessel, the carbon dioxide pressure restored to its previous value, and the equilibration resumed until the next sample weighing. For a point on the isotherm, the process is repeated until the sample weight reaches a constant value (i.e., typically equilibration times of several weeks). The slope of a plot of sample weight vs. square root of elapsed desorption time gives a measurement for the rate of diffusion. In order to advance all three experimental methods, results from this “ambient-pressure gravimetry” method were compared with data obtained by conventional manometry and by computer tomography. The isotherm and “diffusion” rate measured for the core can be directly used in simulators for reservoir engineering studies of coalseam sequestration and enhanced coalbed methane production.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}

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