HR: 1340h
AN: U43C-1400    [Abstracts]
TI: Laboratory and Simulation Investigation of Gas Adsorption, Transport, and Carbon Sequestration in Coal
AU: * Kovscek, A A
EM: kovscek@stanford.edu
AF: Stanford University, Energy Resources Engineering 367 Panama St., Stanford, CA 94305-2220, United States
AU: Lin, W
EM: wenjuanl@pangea.stanford.edu
AF: Stanford University, Energy Resources Engineering 367 Panama St., Stanford, CA 94305-2220, United States
AU: Tang, G
EM: ttcv@chevron.com
AF: Chevron Energy Technology Center, 100 Chevron Way, Room 61-1613, Richmond, CA 94802, United States
AU: Jessen, K
EM: jessen@usc.edu
AF: University of Southern California, Chemical Engineering and Materials Science, 925 Bloom Walk, HED 311, Los Angeles, CA 90089-1211, United States
AB: Deep coalbeds are attractive for sequestering CO2. Injection of CO2, or mixtures of CO2 and N2, enhances CH4 recovery from the coalbed and at the same time sequesters CO2. Powder River Basin (WY) coals, as studied here, adsorb about three times as much CO2 as CH4. Thus, sequestration in coalbeds has the potential for carbon neutrality. We study gas flow and adsorption within coal using experiments and numerical modeling. Coal samples are characterized by porosity, CH4/ CO2/ N2 sorption isotherms, and permeability. This coal exhibits significant hysteresis among adsorption and desorption isotherms. Coal permeability is a function of the injected gas composition, pore pressure (at constant effective stress), and pressure history. Displacement experiments are conducted with N2, CO2, and various mixtures of CH4, CO2 and N2. Most interestingly, the coal exhibited ability to separate N2 from CO2 due to the preferential strong adsorption of CO2. Injection of a mixture rich in CO2 gives slower initial recovery of CH4, increases breakthrough time, and decreases the volume of gas needed to sweep out the coalbed. Injection gas rich in N2 leads to faster recovery of CH4, earlier breakthrough of N2, and a significant fraction of N2 in the produced gas in short time. We develop a two-phase (gas and solid), dual continuum model to rationalize and explain the experimental trends. The dynamics of gas movement through coal are determined in large part by the sorption behavior of mixtures of CH4, CO2 and N2 on the coal surface. These ternary gas mixtures are best described by a real adsorbate solution model in comparison to the commonly used extended Langmuir equation. According to the multicomponent adsorption isotherms, sorption and the selectivity of a particular gas species for a coal surface is a function of pressure and the mixed-gas composition. Reproduction of transient binary flow behavior is characterized as excellent and the dynamics of ternary systems are predicted with acceptable accuracy. For these coals, the most sensitive simulation input parameter was the multicomponent sorption isotherms, including scanning loops. On a practical note, accurate tools for performance prediction in coalbeds are instrumental in design and implementation of sequestration schemes. The results and analysis garnered demonstrate that models substantially more sophisticated than the state of the art are needed when mixtures of CO2 and N2 are injected into coalbeds containing CH4.
DE: 3919 Equations of state
DE: 5114 Permeability and porosity
DE: 5139 Transport properties
SC: Union [U]
MN: 2007 Fall Meeting