APPLIED GEOPHYSICS, Vol.14, No.2 (June 2017), P. 216–224, 13 Figures. DOI:10.1007/s11770-017-0620-2
Research of the electrical anisotropic characteristics of water-conducting fractured zones in coal seams* Su Ben-Yu1 and Yue Jian-Hua♦1 Abstract: Water flooding disasters are one of the five natural coal-mining disasters that threaten the lives of coal miners. The main causes of this flooding are water-conducting fractured zones within coal seams. However, when resistivity methods are used to detect water-conducting fractured zones in coal seams, incorrect conclusions can be drawn because of electrical anisotropy within the water-conducting fractured zones. We present, in this paper, a new geo–electrical model based on the geology of water-conducting fractured zones in coal seams. Factors that influence electrical anisotropy were analyzed, including formation water resistivity, porosity, fracture density, and fracture surface roughness, pressure, and dip angle. Numerical simulation was used to evaluate the proposed electrical method. The results demonstrate a closed relationship between the shape of apparent resistivity and the strike and dip of a fracture. Hence, the findings of this paper provide a practical resistivity method for coal-mining production. Keywords: water-conducting fractured zones in coal seams, coalfield goaf, electrical anisotropy, surface roughness, formation water resistivity, formation pressure
Introduction Coal is the main energy resource of China, and the coal-mining industry is highly risk due to frequent accidents. According to statistics, the highest number of coal-mining disasters occurs in China, accounting for 80% globally (Liu and Qin, 2006). Recently, coalmining safety has attracted the attention of the Chinese government and a large investment has been made to
manage this issue (Dong et al., 2011). Although coalmining safety has considerably improved, mining accidents still frequently occur. Flooding is one of the five natural disasters that occur in coal mining. It is well known that water-conducting fractured zones guide water to the mining roadway (Sui, 2015) resulting in flooding that threatens miners’ lives. Therefore, detection of this water could avoid such disasters. Although many geophysical mine-studies (Hagrey, 1944; Yue and Li, 1997; Li, 1999; Liu, 2009; Shen, 2009; Cheng et al.,
Manuscript received by the Editor July 18, 2016, revised manuscript received April 5, 2017. *This work was supported by a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Fundamental Research Funds for the Central Universities 2014QNA88 as well as the National Natural Science Foundation (No. 41674133). 1. Institute of applied geophysics, The school resource and geosciences, CUMT, Xuzhou 221116, China. ♦Corresponding author: Yue Jian-Hua (Email:
[email protected]) © 2017 The Editorial Department of APPLIED GEOPHYSICS. All rights reserved.
216
Su et al. 2015, Chang et al., 2016; Yan et al., 2016) have been performed to address the detection of water conducted through fracture zones and formation fractures, electrical anisotropy is seldom considered in most existing methods. Geological structures of water-conducting fractured zones in coal seams are very complex, and electrical anisotropy is a crucial parameter in geo–electrical models. Incorrect geological conclusions can be drawn from survey data when using an electrical method without considering electrical anisotropy. In order to manage water-conducting fractured zones, we should study electrical anisotropy in detail. Much research has studied the electrical characteristics of coal bearing formations. According to the results of numerical simulations and practical applications (Brace and Orange, 1968), the conductivity of a formation will be high if the formation fractures have high resistivity. In addition, the conductivity attributes of fractures within the entire formation can be described by the roughness of the fracture surfaces and fracture widths (Stesky, 1986). The electrical current path will become complex if the fracture surfaces are rough. In particular, if the roughness is 100%, the fractures are effectively closed (Keller, 1966). Moreover, Power (1987) studied variations in formation resistivity under different formation pressures. Based on the analysis of rock physics and using numerical simulation, we have studied the characteristics of electrical anisotropy in water-conducting fractured zones in detail.
Analysis of the electrical anisotropic characteristics of water-conducting fractured zones We first established a simple geo–electrical model. Furthermore, we modified the model according to research requirement. We discuss the effects of formation resistivity caused by variations of water resistivity and the effects of fracture density, dip angle, and surface roughness on water pressure.
Effect of water resistivity on the electrical anisotropy of water-conducting fractured zones If fractures in coal seams are filled with formation water, the resistivity of the coal seam will be very low due to the low resistivity of the formation water (Li, 2005). In order to analyze the effect of formation water
on a water-conducting fracture zone, a geo–electrical model was established, as shown in Figure 1. For the model, it was assumed that the porosity of the matrix is φ with length, width, and height denoted by L, w, and h, respectively. In addition, the width of the fracture is e and the number of fractures is n. w
L
en e2
.. .. .. . . .
. .. .. .. ..
h
e1
Fig.1 Simple geological model of a water-conducting fractured zone. It is assumed that there are only horizontal fractures and the number of fractures is n. The length, width, and height are indicated by L, w, and h, respectively.
It is assumed that the matrix pore and the fractures are filled with water with the same resistivity ρ f . Additionally, the matrix resistivity can be described by Archie’s equation: ρm = aρf φ–m. Although Archie’s equation was obtained from experiments on sandstone, it has been proved that it can also be applied to other fractured formations (Shen et al., 2010). Note that m (index of pore structure) and a (lithologic factor) are different from those for sandstone. Shen et al. (2010) concluded that for a fractured formation when water saturation Sw = 100%, m = 1.56, and a = 1.0. The resistance of the entire rock can be calculated using parallel and series relationships. If the direction of the current is parallel to the fractures, then the resistance of the model Rh for a unit area can be calculated by equation (1) (Yin and Hodges, 2003) Rh
(
1.0 1.0 1.0 1.0 1 ...... ) , Rhm Rhf 1 Rhf 2 Rhfn
(1)
where Rhm is the resistance of the matrix and Rhfi is the resistance of the ith fracture. According to Ohm’s law, Rhm and Rhfi can be calculated by Rhm
Um L
Um L
S
(h
n
¦e ) w
,
(2)
i
i 1
Rhfi
Uf L
Uf L
S
ei w
.
(3) 217
Electrical anisotropic characteristics of water-conducting fractured zones Hence, the horizontal resistivity of the model ρh can be calculated by
Rh S L
Uh
Rh h w . L
Hence, the vertical resistivity of a water-conducting fracture zone can be computed by
(4)
Uv
If the direction of the current is perpendicular to the fractures, the rock resistance of the model Rv can be computed by Rv
Rvm Rvf 1 Rvf 2 ......Rvfn ,
(5)
O
i 1
Rvm
Rvfi
(a)
Lw
U f e (i ) Lw
ȡh ȡv
1.2×10 3
4 3
2
6.0×10 2
P = 5% n = 10
2 1
3.0×10 2 0.0
(9)
Uh .
(ȡ v /ȡ h 1/2
Ȝ
ȡ 0 (ǜP
(7)
.
(b)
1.5×103
9.0×10
(6)
,
Uv
Figure 2a describes the change of ρ v and ρ h with increasing water resistivity ρf. Figure 2a indicates that with an increase of formation water resistivity, vertical and horizontal resistivities increase linearly. However, the electrical anisotropic coefficient is constant, as shown in Figure 2b. Therefore, it is concluded that the electrical anisotropic coefficient of the rock depends on its pore structure rather than the fluid in the fractures and the matrix porosity.
n
¦ e(i))
(8)
According to the horizontal resistivity and the vertical resistivity, the electrical anisotropic coefficient can be computed by
where R vm is the matrix resistance and R vfi is the resistance of the ith fracture. They can be calculated by
U m (h
Rv L w . h
0
2
4 6 ȡ f ǜP
8
10
0
0
2
4
6 ȡ f (ǜP
8
10
Fig.2 (a) Variations of vertical resistivity ρv and horizontal resistivity ρh with an increase of formation water resistivity. (b) Variation of electrical anisotropic coefficient λ with an increase of formation water resistivity. The porosity of the model matrix P = 5% and the fracture number n = 10.
Effect of fracture density on the resistivity of water-conducting fractured zones The model above was used to study the variation of vertical resistivity, horizontal resistivity, and the electrical anisotropic coefficient with increasing of fracture density using equations (4), (8), and (9). As shown in Figure 3a, with an increase of fracture density, the vertical and horizontal resistivities decrease. Comparing vertical and horizontal resistivity, the vertical resistivity decreases more slowly than horizontal resistivity. In addition, vertical resistivity decreases linearly, while horizontal resistivity decreases irregularly. As shown in Figure 3b, the anisotropic coefficient 218
increases with fracture density.
Effect of matrix porosity on the resistivity of water-conducting fractured zones The variations in vertical resistivity, horizontal resistivity, and electrical anisotropic coefficient were investigated with increasing matrix porosity using the model shown in Figure 1. As can be seen from Figure 4a, with increasing matrix porosity, the vertical resistivity and horizontal resistivity decrease. In addition, the electrical anisotropic coefficient decreases with increasing matrix porosity, as shown in Figure 4b.
Su et al. 1.0×10
3
8.0×10
2
6.0×10
2
4.0×10
2
2.0×10
2
(b)
4
ȡh
P = 5%
ȡv
ȡ f = 5 ǜP
0
2
4
n
6
ȡ f = 5 ǜP
n = 10
2 1 0
0.0
(ȡ v /ȡ h 1/2
P = 5%
3 Ȝ
ȡ 0 (ǜP
(a)
8
10
0
2
4
6
n
8
10
Fig.3 (a) Variation of vertical resistivity ρv and horizontal resistivity ρh with increasing fracture number. (b) Variation of electrical anisotropic coefficient with fracture number. Porosity P = 5% and the resistivity of the formation water ρf = 5 Ω·m. 1.0×10
5
1.0×10
4
1.0×10
3
1.0×10
2
(b) ȡh ȡv
25
ȡ f = 5 ǜP
20
n = 10
ȡ f = 5 ǜP
n = 10
10
1.0×10 0.0 0.0%
(ȡ v /ȡ h 1/2
15 Ȝ
ȡ 0 (ǜP
(a)
5
5.0%
10.0% Porosity (P)
15.0%
20.0%
0 0.0%
5.0%
10.0%
15.0%
20.0%
Porosity (P)
Fig.4 (a) Variation of vertical resistivity ρv and horizontal resistivity ρh with matrix porosity. (b) Variation of the anisotropic coefficient with matrix porosity. The number of fractures n = 10 and the resistivity of the formation water ρf = 5 Ω·m.
Effect of fracture surface roughness on electrical anisotropy
L
The surfaces of natural fractures are usually rough and the conductivity of the fluid in the fracture is affected by the roughness of the fracture surface, as shown in Figure 5. Hence, it is necessary to investigate the effect of fracture surface roughness on rock conductivity and rock electrical anisotropy. Power (1987) proposed an empirical formula to evaluate the equivalent resistivity for a rough fracture filled with conductive fluid (equation (10)). This equation has been confirmed by field and laboratory studies and survey data from the roughness spectrum of the San Andreas Fault (Power, 1987).
Uf ! Uf (
1D ). 1D
(10)
Here α is a roughness ratio of the connected area to the whole area of the fracture surface. For fracture resistivity, we only need to replace the original fluid resistivity ρf by the equivalent resistivity <ρf >. However, formation water resistivity, which is located in the matrix porosity, is still ρf. As shown in Figure 6a, vertical resistivity is nearly invariable with increasing surface roughness. However, horizontal resistivity does increase. The conductive path
e
n
e
.. .. .. . . .
h
w
. .. .. .. ..
2
e
1
Fig.5 Geological model of the water-conducting fractured zone with consideration of the roughness of the fracture surface. It is assumed that there are only horizontal fractures in the model with length, width, and height indicated by L, w, and h, respectively.
of the fluid becomes complex with increasing surface roughness. This reduces the conductivity and increases the resistivity of the fracture. In particular, when the surface roughness a = 100%, the vertical resistivity ρv will be equal to the horizontal resistivity ρh. Figure 6b illustrates the relationship between the electrical anisotropy coefficient and surface roughness. Figure 6b indicates that with an increase of surface roughness, the electrical anisotropy coefficient will decrease. When surface roughness a = 100%, it indicates that the fractures are closed. In this case, the coal seam is isotropic and the electrical anisotropic coefficient is 1. 219
Electrical anisotropic characteristics of water-conducting fractured zones (a)
6.0×10
(b)
2
2.5 ȡh
4.0×10
2
ȡh 2
2.0×10
ȡ f = 5 ǜP
1 (ȡ v /ȡ h 1/2
0.5 0.0 0.0%
20.0%
40.0% Į
ȡ f = 5 ǜP
1.5
n = 10 P = 5%
ȡv
n = 10 P = 5%
ȡv
Ȝ
ȡ 0 ǜP
2
60.0%
80.0%
0 0.0%
100.0%
20.0%
40.0%
Į
60.0%
80.0%
100.0%
Fig.6 (a) Variation of horizontal resistivity ρh and vertical resistivity ρv with fracture roughness. (b) Variation of the electrical anisotropic coefficient λ with fracture roughness. The matrix porosity of the geologic model P = 5%, the number of fractures n = 10, and the resistivity of the formation water ρf = 5 Ω·m.
Effect of formation pressure on the electrical anisotropy of water-conducting fractured zones
al., 1987) dD dp
High pressure exists in the subsurface. Therefore, the width and surface roughness of fractures will vary due to rock elasticity and formation pressure. The relationship between the formation pressure and the width of fractures can be described by (Power et al., 1987) de dp
2T / p.
D D 0 b( p p0 ),
(12)
where θ indicates the standard deviation of roughness distribution, e0 is the initial width of the fracture, and p0 stands for the initial pressure. In addition, the relationship between surface roughness and pressure can be estimated by (Power et
4.0×10 2
2.0×10
P = 5%
ȡ f = 5 ǜP
Į= 10%
n = 10
P = 5%
ȡ f = 5 ǜP Į= 10%
5
2
1.0×10 2 0.0 6 1.1×10
ȡh ȡv
Ȝ
ȡ 0 (ǜP
3.0×10 2
(b) 5.05
n = 10
4.95 (ȡ v /ȡ h 1/2
1.3×10
6
1.5×10 Pressure (pa)
6
1.7×10 6
4.9 6 1.1×10
1.3×10
6
6
1.5×10 Pressure (pa)
1.7×10 6
Fig.7 (a) Variation of vertical resistivity ρv and horizontal resistivity ρh with pressure. (b) Variation of electrical anisotropic coefficient λ with pressure. The matrix porosity of the geologic model P = 5%, the number of fractures n = 10, the resistivity of the formation water ρf = 5 Ω·m, and the roughness of the fracture a = 100%.
220
(14)
where b is a constant related to rock elasticity, p 0 indicates the initial pressure, and α0 stands for the initial surface roughness. Figure 7 illustrates the variation of vertical resistivity ρv and horizontal resistivity ρh with pressure. Figure 7a indicates that horizontal resistivity and vertical resistivity increase with increasing formation pressure. In addition, Figure 7b shows the relationship between the electrical anisotropic coefficient and formation pressure. It is shown that the electrical anisotropic coefficient decreases with increasing formation pressure. Furthermore, Figure 7b also indicates that the effect of formation pressure on horizontal resistivity is more significant than that on vertical resistivity.
Based on equation (11), an empirical formula can be obtained to calculate the width of a fracture, as shown in equation (12) (Brown, 1995)
(a)
(13)
From equation (13), the surface roughness can be obtained as follows
(11)
e e0 2T Ln ( p / p0 ),
b.
Su et al.
Effect of stratigraphic dips of fractures on electrical anisotropy of water-conducting fractured zones The purpose of the research was to study the effect of electrical anisotropy on the apparent resistivity of waterconducting fractured zones. Figure 8 shows a schematic geological model of a goaf. The numerical modeling technique of Yin et al., 1999 is adopted to analyze the effect of electrical anisotropy on measured resistivity. Therefore, we use a numerical model, as shown in Figure 9a, to describe the geologic model of a goaf formation. For the modeling, measurements from a Schlumberger array were performed to simulate the geological behavior of a goaf. Figure 9a shows the geological model and Figure 9b is a schematic of the measurements. Twentyfour values of apparent resistivity around the origin of the coordinates were calculated. These values were used to form an ellipse. The shape of the ellipse can help
A O
M
Loose sediments Bending zone
Fracture zone
Caving zone Coal seams
Goaf
Coal seams
Fig.8 Geological model of a goaf (Sui, 2015).
to analyze the fracture information from the fractured zone. In the modeling, we used models with different stratigraphic dips and strikes to study the relationship between apparent resistivity and the geologic orientations within the fractured zone. Y
Y
N
Ground surface
B ... Homogenous
H1 H2
Homogenous
M A
O
N
4B 3 2 1
X
. 24 ..
Z
Fig.9 (a) Geologic model of a goaf and measurements of a Schlumberger array employed for the modeling. (b) The array of electrodes at the ground surface with 24 values of apparent resistivity around the origin of the coordinate was calculated.
Numerical simulation 1 The purpose of this numerical simulation was to investigate the stratigraphic dips of the fractures in the fractured zone in the goaf. As shown in Figure 10, the fractured zone is sandwiched between the upper and lower homogenous layers. There were three goaf models and the stratigraphic dips of the fractures in the fractured zones were 25°, 55°, and 80°, respectively. However, the stratigraphic strikes were parallel to the y-axis in Figure 10. For the fractured zone, the longitudinal resistivity ρT and the transverse resistivity ρN are 25 ohm-m and 100 ohm-m, respectively. Moreover, for the upper and lower homogenous layers, the resistivity of the upper and lower
homogenous layers was 100 ohm-m and the length of AB was 60 m. According to the principle of the electrical method, it can detect the geological information of fractured zones in the goaf. The numerical modeling results of geological modeling are shown in Figure 11. In Figures 11a, 11b, and 11c, the distributions of apparent resistivity correspond to the geological models in Figures 10a, 10b, and 10c. As described in Figure 11, the shapes of the distribution of the apparent resistivity are significantly different from each other. Hence, these differences can be used to analyze the geological information of the fractured zones.
221
Electrical anisotropic characteristics of water-conducting fractured zones (a)
o
(b)
Y
A
B
N
M
x
o
(c)
Y
A
B
N
M
x
z
o
A
B
N
M
x H 1 = 20 m
H 1 = 20 m
H 1 = 20 m ȡT ȡN ȡT
Y
ȡT ȡN
H 2 = 20 m
ȡT
Į
ȡT ȡN
H 2 = 20 m Į
z
z
Į
ȕ = 0Û Į = 85Û
ȕ = 0Û Į = 55Û
ȕ = 0Û Į= 25Û
H 2 = 20 m
ȡT
Fig.10 Three geologic models of goafs with different stratigraphic dips of 25°, 55°, and 80°, respectively. The stratigraphic strikes are parallel to the y-axis. The resistivities of the upper and lower homogenous layers are 100 ohm-m and for the fractured zone the longitudinal resistivity ρT and the transverse resistivity ρN are 25 ohm-m and 100 ohm-m, respectively.
100
1
2
(b) 200 3 4
21
5 6
20
0 19
Į= 20
7
18
8
17
100
9 16 15
200
200
10 14
13 12
23
22
100
24
1
(c) 200
2
3 4
21
5 6
20
Į= 55
0 19
7
18
8
17
100
9 16 15
11
200 200
100 200 100 0 Apparent resistivity (ǜP)
10 14
11
13 12
Apparent resistivity (ǜP)
23
22
24
Apparent resistivity (ǜP)
Apparent resistivity (ǜP)
(a) 200
22
100
23
1
24
2
3 4
21
5 6
20
0
19
7
Į= 80
18
8
17
100
9 16 15
200
100 200 100 0 Apparent resistivity (ǜP)
200
10 14
13 12
11
100 200 100 0 Apparent resistivity (ǜP)
Fig.11 Numerical modeling results of the geological models of the goafs in Fig. 10. The distribution of apparent resistivity, as shown in (a), (b), and (c), corresponds to the geological models as described in Figs. 10 (a), (b), and (c).
Numerical simulation 2 The purpose of this numerical simulation was to investigate the electrical response to the stratigraphic strikes. As shown in Figure 12, the stratigraphic strikes Y
(a)
o
A
M
x
z
o
H 1 = 20 m
ȕ ȡT ȡN ȡT
ȕ = 0Û Į= 45Û
Y
(b) B
N
Į
A
M
x
z
o
ȕ = 30Û Į= 45Û
Į
A
M
B
N
x
ȕ
H 1 = 20 m ȡT ȡN ȡT
Y
(c) B
N
ȕ
H 1 = 20 m
were 0°, 30°, and 60°, respectively. The stratigraphic dips of the geologic models were all 45°. Moreover, the resistivities of the upper and lower homogenous layers were 100 ohm-m, and for the fractured zone, the
H 1 = 20 m z
H 1 = 20 m ȡT ȡN ȡT
Į
H 1 = 20 m
ȕ = 60Û Į= 45Û
Fig.12 Three geo–electric models (a), (b), and (c) of the goafs with different stratigraphic dips of 0°, 30°, and 60°, respectively. The stratigraphic strikes are parallel to the y-axis. The resistivities of the upper and lower homogenous layers are 100 ohm•m, and for the fractured zone, the longitudinal resistivity ρT and the transverse resistivity ρN are 25 ohm-m and 100 ohm-m, respectively.
222
Su et al. longitudinal resistivity ρT and the transverse resistivity ρN were 25 ohm-m and 100 ohm-m, respectively. The modeling results of the geological models in Figure 12 are shown in Figure 13. In Figures 13a, 13b, and 13c, the distributions of the apparent resistivity correspond to the geological models in Figures 12a, 12b and 12c.
100
22
23
24
1
2
3 4
21
5 6
20 ȕ=0
0 19
7
Į= 45
18
8
17
100
9 16 15
200
200
10 14
13 12
11
100 200 100 0 Apparent resistivity (ǜP)
(c)
200 100
22
23
24
1
2
3 4
21
5
20
6 ȕ = 30
0 19
Į = 45
18
8
17
100
9 16 15
200
7
200
10 14
13 12
11
100 200 100 0 Apparent resistivity (ǜP)
Apparent resistivity (ǜP)
(b)
200
Apparent resistivity (ǜP)
Apparent resistivity (ǜP)
(a)
As described in Figure 13, the shapes of the distribution of apparent resistivity are different from each other due to the difference of the stratigraphic strikes. Hence, the different shapes of the distributions of apparent resistivity can be used to analyze the geological information of the fractured zone. 200 100
22
23
24
1
2
3 4
21
5
20
6 ȕ = 60
0 19 100
7
Į= 45
18
8
17
9 16 15
200 200
10 14
13 12
11
100 200 100 0 Apparent resistivity (ǜP)
Fig.13 Numerical modeling results of geo–electric models (a), (b), and (c) of the goafs in Fig. 12. The distributions of apparent resistivity correspond to the geo–electric models in Figs. 12 (a), (b), and (c).
Conclusions This study discusses the factors affecting the electrical anisotropy of water-conducting fractured zones in coal seams. The factors include formation water resistivity, matrix porosity, fracture density, surface roughness, and formation pressure. After performing numerical simulations, the following conclusions can be drawn: (1) With an increase of formation water resistivity, both vertical resistivity and horizontal resistivity increase. However, the electrical anisotropic coefficient is constant. It is indicated that the electrical anisotropic coefficient depends on the pore structure of the rock rather than the fluid filling the fracture or matrix porosity. (2) With an increase of matrix porosity, both vertical resistivity and horizontal resistivity decrease. In addition, the electrical anisotropic coefficient shows a decreasing trend. (3) With an increase of fracture density, both vertical resistivity and horizontal resistivity decrease. Moreover, the decrease of horizontal resistivity is more significant than that of vertical resistivity, resulting in the increasing trend of the electrical anisotropic coefficient. (4) Fracture surface roughness mainly influences horizontal resistivity rather than vertical resistivity. With an increase of roughness, the horizontal resistivity increases, whereas the electrical anisotropic coefficient decreases. When fracture surface roughness α = 100%,
the fracture is effectively closed and the electrical anisotropic coefficient is λ = 1.0. (5) When formation pressure exits, elastic rock will deform so that the width of the fracture narrows and the surface becomes rough. As a result, the conductive path becomes narrow and complex. Hence, the horizontal resistivity will increase with the increase of the formation pressure. However, the electrical anisotropic coefficient exhibits a decreasing trend with formation pressure. (6) The numerical modeling results show that it is possible to use electrical anisotropy to study the geology of fractures in water-conducting fractured coal seams.
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Su Ben-Yu, graduated from Northeast Petroleum University in Exploration Technology and Engineering in 2006. He received a master’s degree from China University of Petroleum (Beijing) in Earth Exploration & Information Technology in 2009. He pursued his Ph. D. degree from 2009 to 2012 in geophysics in Kyushu University. Currently he is teaching and doing research at China University of Mining and Technology as a geophysical associated professor. His main research field is forward and inverse numerical simulation of mining geophysics.
Yue Jian-Hua, Professor and doctoral supervisor, graduated from the Tongji University in marine geophysics in 1986. He received a master’ s degree in geophysics from the China University of Mining and Technology in 1991 and a Ph. D. degree in coal, oil, and gas geology and exploration in 1997. He pursued post-doctoral studies on mechanics from 1998 to 2001. His main research interests include coal field and mine geophysics.
