Kathrin Ann Lewis's thesis
by
Kathrin Ann Lewis, MSE
University of Texas at Austin, 2001
Supervisor: Mukul M. Sharma
Laboratory experiments were performed to determine whether existing NMRI equipment could (1)
detect methane either adsorbed on, or present in, pores of coal and/or carbon, (2) quantify
the signal contributions from methane, and (3) distinguish between methane and water when both
are present. Such data could be used in continuing research for diffusion studies, imaging or
logging correlation, if a data set could be assembled which mimics conditions encountered in coalbed
methane production. Most of the research literature reviewed has not dealt with coal on a
macroscopic scale, nor has it dealt with adsorption in the pressure ranges found in coalbed
methane reservoirs. The expectation was that some baseline measurements could assist in mapping the scope and
direction of future research.
The first imaging trials were done on a coal core plug sample from the San Juan basin. Short
imaging experiments were run at various pressures in an attempt to monitor coal/gas interactions.
There were problems with strong contrasting signals from free methane in the dead spaces of the holder;
consequently, most tests had to be run with glass beads packing the remaining volume of the holder.
Additional trials used 100-mesh charcoal (both wet and dry) to examine the relative signal contributions
of methane and water.
Coal image experiments suggested that there would be a contribution from the broad signal of the
coal matrix, which will require a baseline subtraction technique in any further work. As methane
pressures increased, there was some alteration of the NMR signal, but no trend emerged relating
signal strength to pressure. It was not clear whether "free" methane signal contributions
(such as might come from coal cleats) could be isolated and quantified. Charcoal work indicated that
further study at higher methane pressures might yield more information. Bloch decay experiments
hinted that methane signal contributions may possibly be distinct from those of water and solids.
Interestingly, even methane introduced at these relatively low pressures appeared to depress the overall
signal intensity of the wet charcoal samples. Further work could be done to confirm and expand
the initial data set, as well as develop data at higher methane pressures.
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