Experimental Study on the Effect of Coal Particle Size on the Mechanics, Pore Structure, and Permeability of Coal-like Materials for Low-Rank Coalbed Methane Reservoir Simulation

Abstract

Coal-like materials have been widely used to simulate low-rank coalbed methane (CBM) reservoirs to develop fracturing stimulation technology since the transportation and preparation of low-rank coal produce easily secondary damages, causing large dispersion of test results. However, the coal particle sizes have a significant effect on the performance of coal-like materials among many factors. Hence, to accurately simulate lowrank CBM reservoirs for promoting the development of reservoir stimulation technologies, cement, gypsum, pulverized coal, and sand were selected as similar materials to make coal-like samples with different coal particle sizes to study the influence law of coal particle size on the mechanics, pore structure, and permeability of samples. The ultrasonic wave velocity, dynamic parameters, uniaxial compressive strength, elastic modulus, and uniaxial tensile strength of samples increased with increasing coal particle size in the range of 0−2 mm. However, these parameters suddenly decreased when the coal particle size increased to 2−3 mm. The porosity and permeability of the samples exhibited an opposite trend compared to the above parameters. The fracture occurred in cementing materials, and the crack extension direction was affected by the coal particle sizes. The fracture complexity of the coal-like samples decreased with increasing particle size under uniaxial compressive testing. The failure mode was mainly a tensile failure, supplemented by shear failure. The coal-like materials can well meet the performance requirements of low-rank CBM reservoirs.

Effects of Proportion of Anhydrous CaCl2 on the Expansion Properties of Soundless Cracking Agents

“…During the hydration of SCA, its hydration properties varied with the hydration time. Therefore, the initial setting time of SCA is the time required from when SCA is mixed with water until the slurry begins to lose plasticity. , The hydration state corresponding to the initial setting time of SCA is the initial setting state. When the hydration temperature of the SCA was completely reduced to room temperature, it indicated that the SCA slurry no longer undergoes the hydration exothermic reaction, that is, the SCA hydration process ended, and the complete hydration state was reached.…”

Comparative Experimental Study of Fracture Mechanisms and Characteristics of Coal-like Materials under Quasi-Static and High-Pressure Air Blasting Fracturing

“…All of these factors can significantly impact the accuracy of the experimental results. Therefore, this study employs similar materials instead of raw coal for air fracturing experiments, as previously done in related research. , …”

“…Therefore, this study employs similar materials instead of raw coal for air fracturing experiments, as previously done in related research. 31,32 To ensure the safety of operators and the stability of the experimental system, the maximum blasting pressure is set not to exceed 10 MPa. Therefore, to elucidate the changes in the fracturing mechanism of air blasting with varying blasting pressure, it is necessary to use similar materials that can reflect the characteristics of coal samples and reduce the strength of coal-like materials as much as possible.…”

Experimental Study on Differential Thermal Response and Pore-Fracture Structure Evolution Characteristics of Coals under Microwave Irradiation: A Case Study of Five Different Rank Coals

“…4−6 Meanwhile, the promotion of CBM development and utilization is also consistent with China's strategic goals of "peak carbon dioxide emissions" and "carbon neutrality". 7 However, due to the characteristics of low porosity and low permeability of CBM reservoirs and the gradual increase in mining depth, 8 the mining difficulty of CBM is increasing. 9,10 At present, in order to increase the mining efficiency of CBM, common methods for increasing fractures and permeability include hydraulic fracturing, 11,12 thermal stimulation (heat injection), 13−15 gas injection displacement, 16 solvent extraction, 17 liquid nitrogen freeze−thaw, 18 etc.…”