In this paper, we develop a dual-porosity dual-permeability
model
for binary gas migration to explore the permeability evolution in
the matrix and fracture in the process of a gas–water two-phase
flow during CO
2
-enhanced coalbed methane (CO
2
-ECBM) recovery in coal reservoirs. This mechanistic model accommodates
the effects of elastic deformation caused by the effective stress
change in the matrix and fracture, the swelling/shrinkage deformation
of the matrix caused by adsorption/desorption, the convection and
diffusion of gas, and the discharge of water. Specifically, the time-dependent
matrix swelling, from initially completely reducing the fracture aperture
to finally affecting the coal bulk volume, is considered by the invaded
volume fraction involving binary gas intrusion. The model is validated
through laboratory data and applied to examine the permeability evolution
of CO
2
-ECBM recovery for 10 000 days. Furthermore,
we analyze the sensitivity of some selected initial parameters to
capture the key factors affecting CO
2
-ECBM recovery. Our
modeling results show that the permeability evolution can be divided
into two stages during the process, where stage I is dominated by
effective stress and stage II is dominated by adsorption/desorption.
Increasing the injection pressure or initial permeability advances
the start of stage II. The decrease in initial water saturation causes
the permeability to change more drastically and the time of stage
II to appear earlier until a time long enough, after which little
effect is seen on the permeability results.
This work aims to strengthen tunnel construction, optimise construction quality, and improve the life safety of construction personnel and users under the effect that blockchain technology can improve the efficiency of information transmission and information security, and construct a blockchain-based architecture of the construction quality control system and physical architecture. On the premise of ensuring the traceability of the data, the established quality index system shall be used for intelligent evaluation of the construction quality. The test results show that: (1) when the distribution of quality status is abnormal, the probability of the quality assessment value for the qualification of steel bar quality inspection, the welding of the steel coupler and the qualification of constructors' skills all exceed 40%, which requires engineering quality diagnosis. (2) The changes in template quality assessment results under the three conditions are basically consistent with the steel bar quality. (3) The trend of concrete quality assessment results is similar to that of templates and steel bars. The main research contribution is to optimise the tunnel's construction quality control system and control the uncertain factors in the construction quality through the Bayesian network and blockchain technology and optimises the construction quality control system and construction information management.
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