Decreasing Coalbed Methane Formation Damage Using Microfoamed Drilling Fluid Stabilized by Silica Nanoparticles
Table 4
Gas permeability test results of original coal core samples.
No.
Length (mm)
Confining pressure (MPa)
(mD)
(mD)
Δ (%)
(mD)
Δ (%)
1#
19.28
0.35
8.19
2.29
72.00
6.61
80.78
0.38
8.22
2.23
72.92
7.38
89.76
0.40
8.37
2.23
73.39
7.22
86.34
Average
8.26
2.25
72.77
7.07
85.63
2#
29.68
0.35
5.45
2.77
49.13
4.43
81.18
0.38
5.41
2.69
50.24
4.19
77.55
0.40
5.44
2.67
50.87
3.88
71.29
Average
5.43
2.71
50.08
4.16
76.68
3#
29.10
0.35
2.32
1.39
40.00
2.03
87.81
0.38
2.28
1.34
40.91
1.92
84.56
0.40
2.25
1.32
41.24
1.92
85.53
Average
2.28
1.35
40.72
1.96
85.97
4#
25.25
0.35
10.59
5.63
46.84
0.38
10.32
5.61
45.64
0.40
10.45
5.73
45.17
Average
10.46
5.66
45.89
5#
21.53
0.35
2.86
1.42
50.35
0.38
2.74
1.38
49.64
0.40
2.78
1.30
53.24
Average
2.79
1.37
50.90
Note: () the confining pressure was 0.9 MPa and the downstream pressure (outlet pressure) was 0.1 MPa (1 atmospheric pressure). () Gas permeability reducing rate was calculated with = [()/] 100%. () Gas permeability recovery rate was calculated with =%. () : the coal core was totally contaminated, so it was not necessary to slice it.
