The
application of electrochemical modification for accelerating
methane extraction in lean coal seams is limited due to the lack of
experimental and theoretical research studies. Therefore, electrochemical
modification with different electric potential gradient values was
selected to modify lean coals in this study; meanwhile, the amount
of methane adsorption and the methane desorption ratio were tested
and analyzed. The results showed that the maximum amount of methane
adsorption in coal samples decreased after electrochemical modification
and the decrease in methane adsorption increased with an increase
in electric potential gradient. The methane desorption ratio increased
from 83.20% up to 87.84 and 86.90% at the anode and cathode zone,
respectively, after electrochemical modification using a 4 V/cm electric
potential gradient. A higher electric potential gradient performs
better in the electrochemical modification. The mechanism of electrochemical
modification using different electric potential gradients was revealed
based on the measurements of Fourier transform infrared spectroscopy
and liquid nitrogen adsorption. It is due to an increase in acid groups
in coal molecular structure and the change of the specific surface
area of coal after modification. The results obtained from this work
contribute to the methane extraction via the electrochemical method
in lean coal seams.
Utilizing the large effective area non-zero dispersion-shifted fiber (LEAF), a multi-parameter optical-fiber sensor has been proposed and experimentally demonstrated for distributed simultaneous temperature and strain measurement, which is based on multiple acoustic modes in spontaneous Brillouin scattering (SpBS) effect. Proof-of-concept experiments demonstrate 3 m spatial resolution over 2.5 km sensing LEAF with 2°C temperature accuracy and 60µɛ strain accuracy. The proposed distributed Brillouin optical fiber sensor allows simultaneously temperature and strain measurement, thus opening a door for practical application such as superconducting cable.
The CO 2 huff-and-puff method has been widely adopted for enhancing CH 4 recovery in shale reservoirs. Revealing the behavior of CH 4 adsorption/desorption in shale during the CO 2 huff-and-puff process clarifies the recovery mechanisms of CH 4 from shale reservoirs. In our work, the question of how CO 2 plays a role in affecting the adsorption/ desorption of CH 4 is investigated using the low-field nuclear magnetic resonance technique. In addition, phase transition of CH 4 is also analyzed to investigate how the existing states of CH 4 transform in shale during this process. Specifically, the states in which CH 4 resides in shale are first recognized by analyzing the measured T 2 spectrum of shale after injecting CH 4 . CO 2 huffand-puff tests are then conducted to investigate how CO 2 impacts the adsorption/desorption behavior of CH 4 on shale samples. Furthermore, the T 2 signals of shale during depressurization are measured to investigate the state transformation of CH 4 in shale during the CO 2 huff-and-puff process. Test results show that three states are observed for CH 4 storage in shale samples, that is, bulk CH 4 , free CH 4 at the pore center, and adsorbed CH 4 on the pore surface. After injecting CO 2 , the adsorbed CH 4 will be desorbed from the shale surface, which thus increases the free CH 4 at the pore center. During depressurization, the free CH 4 is more readily produced from the shale samples, whereas the adsorbed CH 4 is hard to be recovered; more advanced technology should thereby be proposed for enhancing the adsorbed CH 4 from shale reservoirs. This work is expected to inspire new understanding of the mechanisms of CH 4 recovery using CO 2 huff-and-puff methods.
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