TY - JOUR

T1 - Acoustic properties of hydrate-bearing coal samples depending on temperature and water saturation type

AU - Dugarov, Geser A.

AU - Duchkov, Anton A.

AU - Manakov, Andrey Yu

N1 - Funding Information: We are grateful to V.G. Smirnov for providing the coal samples. The work was supported by the Russian Science Foundation (grant no. 19-77-00068). Publisher Copyright: © 2021 Society of Exploration Geophysicists.

PY - 2021/3/11

Y1 - 2021/3/11

N2 - We have developed the first experimental acoustic properties measurement during gas-hydrate formation and dissociation in crushed bituminous coal samples. We also compare the results with acoustic properties measurements during freezing and thawing water in the same samples. The results show a more complicated behavior that differs from similar experiments with sand. For the samples with adsorbed water, it does not freeze at anticipated temperatures, but acoustic velocities gradually increase with the decreasing negative temperatures. It is caused by complicated pore surface structures causing partial formation of ice/hydrate from bound water at different temperatures. We also observe that, for the same samples, the acoustic properties change significantly, becoming stronger during gas-hydrate formation than during freezing. We explain it by competitive sorption of methane and water in the coal pore space; methane under pressure replaces part of the adsorbed water from micropores so that this water can easily form hydrate. The difference in the acoustic properties of frozen and hydrate-bearing coal samples is important for developing seismic methods for geophysical characterization of coal seams.

AB - We have developed the first experimental acoustic properties measurement during gas-hydrate formation and dissociation in crushed bituminous coal samples. We also compare the results with acoustic properties measurements during freezing and thawing water in the same samples. The results show a more complicated behavior that differs from similar experiments with sand. For the samples with adsorbed water, it does not freeze at anticipated temperatures, but acoustic velocities gradually increase with the decreasing negative temperatures. It is caused by complicated pore surface structures causing partial formation of ice/hydrate from bound water at different temperatures. We also observe that, for the same samples, the acoustic properties change significantly, becoming stronger during gas-hydrate formation than during freezing. We explain it by competitive sorption of methane and water in the coal pore space; methane under pressure replaces part of the adsorbed water from micropores so that this water can easily form hydrate. The difference in the acoustic properties of frozen and hydrate-bearing coal samples is important for developing seismic methods for geophysical characterization of coal seams.

KW - coal

KW - gas

KW - hydrates

KW - ultrasonic

UR - http://www.scopus.com/inward/record.url?scp=85104327354&partnerID=8YFLogxK

U2 - 10.1190/geo2020-0117.1

DO - 10.1190/geo2020-0117.1

M3 - Article

AN - SCOPUS:85104327354

VL - 86

SP - U31-U37

JO - Geophysics

JF - Geophysics

SN - 0016-8033

IS - 3

ER -