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Introduction Study Area Objectives Literature review Methodology Results Conclusions 2

Coal bed methane production and CO 2 sequestration are the promising technology being developed as a win–win process to reduce global warming and produce a valuable energy resource. Manik (2002) used the PSU-COALCOMP reservoir simulator to understand the influence of sorption isotherms. 3

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To study the influence of sorption isotherms. To predict the efficiency of coal seam sequestration by sweep efficiency and variable pressure distribution. 5 (

The basic well pattern is based on plans for the newest available coal seam sequestration project. (Cairns, 2003) 6 Well site AWell site B Well site C (Cairns, 2003) Fig 2. 3D well pattern in coal seam. Fig 1. Horizontal well pattern in coal seam. 915m 183m Horizontal Methane Production Wells Vertical Methane Production Well Vertical CO 2 Injection Well Horizontal CO 2 Injection Wells

Coal seam fluids generally consist of water, methane, and small amounts of other hydrocarbons, H 2 S, and carbon dioxide. These fluids can be found both in the bulk coal matrix and in the coal cleats. Fig 3. Mechanisms for flow of methane in coal seam. (Remner et al., 1984) 7 CH 4 CO 2

Simulator : PSU-COALCOMP Isotherm model : The Langmuir is a two-parameter model of the following form: c: the amount of gas that is sorbed to the solid matrix (mmol/g) λ Vλ V : the Langmuir volume constant (mmol/g) λ Pλ P : the Langmuir pressure constant (kPa) P: the pressure of the gas (kPa) 8 (Langmuir, 1918)

In an actual coal bed methane production and carbon sequestration project, kinetics can play a significant role. (Sams et al., 2003) Lumped-parameter model : 9 τ: the sorption time constant (s) D mi : the micropore diffusion coefficient(ft 2 /day) R mi : the cleat spacing(ft)

Porosity : For CBM production, the porosity is in reference to the cleat porosity and not to the matrix. cleat porosity=0.1% correction : CO 2 → mmol/g-coal CH 4 →0.0026mmol/g-coal 10 (Source :

11 (Carroll and Pashin, 2003) Fig 4. Sorption isotherms: (a)a sampling of Langmuir isotherms used in the model (b)the measured values from 26 samples within the Black Warrior Basin

12 Calculate the maximum amount of CO 2 Estimate how much would actually be sequestered Predict the changes with coal sorption properties

Production well Injection well (Cairns, 2003) Steps in the simulated production/sequestration process are as follows: Shut in the central wells for a day Inject CO2 into the coal seam stop injection CO 2 CH 4 Water Shut in 13

14 Fig 5. Thermodynamic maximum amounts of carbon dioxide that can be sequestered in coal at a gas pressure of 3500 kPa (500 psi). Langmuir Isotherm model: Table 1 Coal seam properties PropertyValue Sorption volume constant (CO 2 ) a mmol/g-coal Sorption pressure constant (CO 2 ) a kPa

Fig 6. Amount of carbon sequestered as a function of the Langmuir pressure constant and the Langmuir volume constant. Solid lines : theoretical maxima Points : simulations (psi) 15

The values from simulations < theoretical maximum, because : (1) CO 2 can not infiltrate a portion of the coal seam because of sweep inefficiency. (2) The pressure within the seam is not uniform. mole fraction of carbon 60-70% gas pressure (in psi ; 1 psi=6.89 kPa) 16

Carbon dioxide sequestered Methane produced Simulate result Theoretical maxima 50% - 70%80% - 97% Langmuir volume Direct proportionInverse proportion Langmuir pressure Inverse proportionDirect proportion 17

Langmuir volume constant (V L ) : The maximum amount of gas that can be adsorbed on a piece of coal at infinite pressure. Langmuir Pressure constant (P L ): This parameter affects the shape of the isotherm. 18 ( media/webhelp/c-te-concepts.htm)

For sequestration, the amount of CO 2 was between 50~70%. The amount of methane produced was between 80~97%. As the Langmuir volume increases and the Langmuir pressure decreases, the amount of CO 2 sequestered goes up, and the amount of methane produced decreases. 19

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