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Jidong Zhang, Zhongwei Chen*
UQ School of Mechanical and Mining Engineering, * [email protected]
Sorption and swelling of coal under unconstrainted conditions
CRICOS Provider Number 00025B
The helium injection results show that volumetric strainincreases linearly with pore pressure, which gives a coalbuck modulus of 9.8 GPa (Figure 3).
The nitrogen injection results show that (a) coal swellingfollows approximately a linear relationship with excessadsorption volume (Figure 4): every cubic meter increasein gas adsorption causes 0.0324% strain increase, and (b)for each step, coal clearly experiences three stages:instant compaction, rapid rebound due to cleat pressureincrease, and slow rebound due to gas diffusion (Figure 3).
Introduction
Experimental apparatus
Results
Figure 1: Experimental apparatus
Figure 2: Pressure and volumetric strain evolution
Figure 4: Langmuir isothermal and swelling measurement
during nitrogen adsorption
References1. Quantachrome Instruments, “high pressure gas sorption system
operating manual”, 2012.
2. Clarkson C R, Bustin R M. The effect of pore structure and gas
pressure upon the transport properties of coal: a laboratory and
modeling study. 2. Adsorption rate modeling[J]. Fuel, 1999,
78(11):1345-1362.
0 1 2 3 4 5 6 7 8 9 10 11 12-500
0
500
1000
1500
2000
0.90
0.93
0.96
0.99
Nit
rogen
pre
ssu
re(M
Pa)
2.95
3.00
3.05
3.10
4.92
4.98
5.04
5.10
6.86
6.93
7.00
7.07
Volu
met
ric s
train
()
Time(h)
Axial strain
Circumferential strain
Volumetric strain
Ⅰ
Ⅱ
Ⅲ
The adsorption capability of coal to different gasses and theinduced swelling are fundamental input parameters for coalseam gas reservoir simulation.
The sorption capacity of coal is usually measured by thevolume method, pressure method or gravity method, wherecoal is normally crushed into powders. Parameters such asthe Langmuir pressure constant and volume are obtained byfitting the adsorption curves. The measurement ofcorresponding deformation of coal is not very common.
In this work, a specially designed sample cell was fitted to theQuantachrome’s high pressure gas adsorption system(20MPa maximum pressure) to measure the adsorptioncapacity of a bituminous coal under different pressures. Atthe same time the system captured the volumetric strain ofcoal during the adsorption process using three strain gaugeTDS-150 (Figure 1). Four pressure values were tested, risingfrom 1 MPa to 7 MPa with an increment of 2 MPa. Nitrogenand helium gasses were used to conduct the work, and theinjection sequence was explained in Figure 2.
The facility offers a reliable experimental capability for directmeasurements of both isothermal curves and sorption-induced strain - important inputs for reservoir modelling.
Figure 3: Volumetric response to helium (left) and nitrogen injection
UQ Centre for Natural Gas
Annual Research Review
2019