STUDY ON THE RESONABLE HORIZONTAL DRILLING TECHNOLOGY TO RECOVER METHANE GAS IN MAO KHE UNDERGROUND COAL MINE

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MINISTRY OF EDUCATION AND TRAINING
HANOI UNIVERSITY OF MINING AND GEOLOGY






Nguyen Tran Tuan






STUDY ON THE RESONABLE HORIZONTAL
DRILLING TECHNOLOGY TO RECOVER METHANE
GAS IN MAO KHE UNDERGROUND COAL MINE

Major: Petroleum Engineering
Code: 62.52.06.04




SUMMARY OF DOCTORAL THESIS IN ENGINEERING

HANOI - 2014


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The research has been accomplished at
Department of Drilling and Production, Faculty of Oil and Gas,
Hanoi University of Mining and Geology

Supervisors:
1. Assoc.Prof. Dr. Tran Dinh Kien
2. Dr. Nguyen Xuan Thao

Examiner 1: Assoc.Prof.Dr Truong Bien
Vietnam Aschnology
Examiner 2: Dr Khuou Huu Bo
University of Transport and Communications
Examiner 3: Dr Nguyen Xuan Toan
Vietnam National Oil and Gas Group







This thesis is going to be defended at the committee of
doctorate thesis examiners of Hanoi University of
Mining and Geology on date month year 2014

This thesis can be found at Hanoi National Library or
Library of Hanoi University of Mining and Geology


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Introduction
1. The necessity of thesis
In recent years, a number of mines in Quang Ninh has
occurred the large gas explosion causing percussionage to people and
property such as Mao Khe Coal Company in 1999 which killed 19
people, two consecutive gas explosion at Khe Cham II coal
Enterprise and 909 coal exploitation Enterprise in 2002 that killed 13
people. March 2006, the Thong Nhat coal Company had happened
coal methane explosion that killed 8 people and the most recent gas
explosion at Khe Cham Coal Company December 9, 2008 in which
there were 11 deaths.
Along with the application of traditional methods of
ventilation to reduce the concentration of methane gas in the mine to
a safe level; Mao Khe mine has also started to apply the methods of
drilling boreholes in different directions to remove methane in the
coal seams in the mining production areas as well as in cover stone.
In fact, drilling long horizontal boreholes are low effect and it is not
reach to the design length, the reasons are mainly due to lack of
choice of drilling method and drilling technology which is suitable
with the purpose of removing mine methane. Therefore, the study in
the choice of drilling method, appropriate horizontal drilling
technology to remove gas through the boreholes in Mao Khe mine in
accordance with the geological and exploitation conditions in the

mine to ensure the safety of Mao Khe, pollution reduction is needed
with scientific and practical to meet the production demand of Mao
Khe mine in particularly as well as in other mines in Vietnam.
2. The purpose of this study


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The study is the research in methods and choice of
horizontal drilling technology to remove methane in Mao Khe mine
to ensure safety in production operating. The results of this study
will be scientific and practical basic application in remove gas in
other coal mine in Vietnam.
3. The objects and margin for research
- The object of study: selection in horizontal drilling
technology of rotary – percussion drilling equipment RPD-130SL-
F2W and the kits of sample threading drilling PS-89 to drill
horizontal boreholes for removing gas in accordance with geological
and exploitation conditions in Mao Khe coal mine.
- The sphere of study: study in the characterization of
horizontal drilling technology; rotary – percussion drilling
technology in the geological conditions of the Mao Khe coal mine,
the influence of these technologies to drilling rate.
4. Detail of the study
- Study from the technical documents which relate to global
and domestic drilling for remove gas.
- Study on the characterizations of horizontal and rotary –
percussion by sample threading drilling technology for horizontal
boreholes for methane removing in coal pit mines.
- Testing of rotary – percussion drilling of horizontal
boreholes in actual conditions of the Mao Khe mine.

Base on the theoretical and testing results to select the
appropriate value of parameters in horizaontal rotary – percussion
drilling for methane removing as well as define the efficiency of this
method in the Mao Khe coal mine.



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5. Research methods
- Collect, research, and analysis of data related to the field of
study;
- Experiment in real conditions; monitoring and collecting
real data about rotary - percussion drilling technology in horizontal
drilling for gas escape in Mao Khe mining conditions;
- Application of statistical mathematic methods to analysis
the actual monitoring data for selection of appropriate horizontal
drilling technology.
6. Scientific and practical meaning
- Scientific meaning: The study on application of rotary –
percussion drilling technology using RPD -130SL – F2W drilling
equipment and the kit of sample threading drilling tool PS -89 to
drilling horizontal boreholes for gas off in Mao Khe coal mine is not
only overcome the disadvantages of rotary drilling methods but also
improve the drilling rate and the gas removable. The results are the
scientific basic as well as justification for the selection of gas
removing technology in coal pit mine in Quang Ninh.
- Practical meaning: the selection of appropriate drilling
parameters in horizontal drilling using RPD – 130SL – F2W and PS
– 89 for in Mao Khe mine that increase the efficiency of rotary
drilling and gas removing are necessary and respond promptly to the

current demand in methane remove.
7. The new conclusion of thesis
The study proposed the application of horizontal drilling
technology to remove methane in pit coal mines in Mao Khe by
rotary – percussion drilling method and sample threading pipe
drilling technology instead of conventional rotary drilling.


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Experiment in production conditions, selection of reasonable the
rotary – percussion drilling parameters to drill horizontal boreholes
for removing methane in Mao Khe mining conditions.
8. The protective contentions
- Application of rotary - percussion drilling technology by
RPD-130SL-F2W and kits of sample threading drilling pipe PS-89 to
remove gas from horizontal boreholes in Mao Khe mine is
reasonable and it is suitable with the geological conditions as well as
the current demand of gas removed.
- Horizontal drilling with rotary – percussion drilling
equipment - RPD-130SL-F2W and kits of sample threading drilling
pipe PS-89 has the average speed of a mechanical increasing from
1.45 times to 1.7 times and reducing the energy for rock destroyed
from 70% to 51% in cooperation to rotary drilling method in the
same conditions.
9. The database of thesis
The thesis bases on the final report documents the geological
exploration and the coal production documents of Mao Khe Coal
Company, Vietnam Coal and Minerals Group as well as the member
companies. The study also uses the technical documents which relate
to the content of research as well as the articles and scientific studies

of the authors published in the domestic and international journals.
10. The content and structure of thesis
The thesis consists of an introduction, four chapters study
the content, conclusions, recommendations and a list of publish
articles of author and the references. The entire contents of the thesis
is presented in 138 pages of A4, font size of 14 in Time New Roman,
Unicode, including 58 figures, 27 tables and appendices.


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CHAPTER 1
OVERVIEW OF GAS REMOVE IN PIT COAL MINE
TECHNOLOGY IN OVER THE WORLD AND IN VIETNAM
1.1. The requirement of methane recovery from pit coal mine in
over the world.
Today, science has confirmed the released methane gas from
coal mines entering the atmosphere is one of the main causes the
environmental pollution and the greenhouse effect. However, in
positive perspective, the methane itself is energy resource for human,
for the chemical industry, boilers, and industrial furnaces, used for
production power. Thus, in the coal mining industry, if the
technology of methane recovery is suitable methane will be a
precious energy resource, and the recovery of methane released
during mining will contribute actively eliminate fire hazards and
minimize mining causing environmental pollution.
1.2. The technology of methane removable drilling in the pit coal
mine in over the world.
Today, there are two technology mainly used for removing and
recovery methane from the coal mine: through the boreholes which
is drilled from the surface and through the boreholes drilled from the

pit mine.
1.3. The status of research and application of methane removing
drilling technology.
The research and application of methane removing drilling
technology in Vietnam in general and in Khe Cham, Mao Khe in
particular is just in beginning period, there is no scientific work
published. Thus, the study of selection appropriate drilling
technology for gas removing in Mao Khe geological conditions as


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well as other mines in Quang Ninh province is necessary in science
and practical.
CHAPTER 2
GEOLOGICAL CHARACTERIZATIONS, MINING STATUS
AND POTENTIAL FOR METHANE GAS
IN MAO KHE COAL MINE
2.1. Geology, physic and chemical characterizations
2.1.1. Geology structure.
Geology structure of Mao Khe coal mine is in Quang Ninh
sedimentary strata and divided into two clearly block North – South
by a fault [15].
2.1.2. Constructive characterization and faults system.
The constructive characterization of the mine is rips and faults. There
are totally 18 faults along the direction of the mine and some of them
in South West direction
2.1.3. Physical characterization of rocks.
The research of strata has showed that the geological structure of the
Mao Khe is quite similar with Quang Ninh mine area. The magma is
distributed in right general layers. Coal, claystone and siltstone near

the coal reservoir form walls, coal pillars. On the other side,
sandstone and others are far from the reservoir.
2.2. Characteristic and the nature of Mao Khe coal mine.
The coal seams in Mao Khe coal mine were highly degenerated and
the color of coal change between black and dark grey. Coal is
relatively hard, and the hardness in drilling levels from III-V;
hardness f-level is usually greater than 2; density from 1.55 to 1.70
g/cm3. Common minerals in coal samples are arghilit, silica oxit.


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2.3. Current status of coal exploitation and the potential of
methane in Mao Khe.
2.3.1. Current status in exploitation of Mao Khe.
Today, Mao Khe is in production from two wings which
includes 9b West, level -80/25, V8 West, level -80/+30, V8 East,
level -150/-80, V7 Đ.TR, level -80/-25; V6 W level -80/-25; V6
Đ.TR level -80/-25; V6 ĐMR level -80/-25 in the North side and
8CN-ĐN II, level -80/LV; V.8 CB-ĐN I, level -80/+25 in the South.
2.3.2. Methane potential in Mao Khe coal mine.
According to the results from the research of experts [1, 4,
12, 22, 35, 36], the classification of gas existing in coal seams and
side walls depends on the forming conditions of the mine as below:
- Gas in free form exists in the fractures, pores of the
reservoir
- Gas exists in the form of adhesion, sustainability chemical
and physical link and usually coming out from the coal when under
external force such as beating, crushing, etc.
- Gas exists in connate water in the reservoir.
2.3.3. Safety solutions to prevent methane appearance in pit.

In the current period, along with the application of
appropriate ventilation system, Mao Khe mine has been studying the
application of drilling technology to remove methane from coal
seams, or areas containing methane and other toxic gases.

Chapter 3
Study in selection of appropriate technology
of horizontal drilling to remove methane in
Mao Khe coal mine


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3.1. Characteristic of horizontal drilling
3.1.1. The lost of axial load on rock destroying




Figure 3.1 Shape of drilling pipe is compressed in
drilling horizontal boreholes
The axial load on drill bit is actually defined as below:
P
k
= P
o
- P
c
- P
t
(3.4)

Where: P
k
: actual axial load on drill bit, N; P
o
: maximum allowance
load of drilling head, depends on technical characteristic of drilling
machine, N; P
c
: weight of drilling pipe, N.
3.2.1. Curving and oblique of horizontal boreholes.













3.1.3. Difficulties in horizontal drilling.
o
Figure 3.4. Curving borehole due to
eccentric drilling equipment

Figure 3.5. Direction of curving borehole

Figure 3.6. Ability of borehole deflected
when meet rock in different hardness

Figure 3.7. Deflection of borehole when
drilling in coal zone



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




1
In general, the difficulties in horizontal drilling are similar
with vertical drilling.
Boreholes in horizontal drilling do not actually have water
column and rarely using clay based mud in drilling. It therefore
always prone to collapsing along the upper boreholes.






In the static state, the upper part of the horizontal borehole in
depth of Z, with in distance from borehole center (Figure 3.9) and
subjected to the force:
Z

Z 0


(3.10)
Where:

o
- rock density, N/m3; Z – distance from borehole
to surface,m
Horizontal stress at the wall of drilling hole is defined as
below:

r
=
Z
z 0


(3.11)
Where: wall force factor,;

- Poisson factor.

The value of depends on type of rocks, clay from 0,35 - 0,4;
sandstone 0,15 - 0,20; Carbonate from 0,25 - 0,30.
In horizontal boreholes, side grooves and cavities often
occurs in the lower borehole while drilling through the weak
stratigraphy such as the clay-acgilit layer, the coal seams. The main
reason is due to the weight of drill pipe always prone to tend on the
Figure 3.8. Shape of upper boreholes

in horizontal drilling in fracture zone.

Figure 3.9. Cover rock status in
horizontal drilling boreholes.



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underside of borehole while tripping. Grooving diagram in borehole
is described as in Figure 3.10.








3.2. Study on the appropriate selection of horizontal drilling
technology for removing methane in Mao Khe mine.
3.2.1. Status of methane removing drilling in Mao Khe.
Base on the development plan as well as the potential
methane of 9Đ coal mine there are some long horizontal boreholes
will be located along the side of longwall for removing gas before
production time. The borehole will be drilled at the drilling station
which is about 350m away from the longwall (figure 3.12). All
boreholes will be designed in the shape of paper fan with the
direction to the longwall. The first borehole is 30 degree with escape
wind line; the second is 15 degree with the first one. The next
borehole is continuously designed in that way and gas recovery at

coal seam and the side wall before producing. The space of the
longwall đã phá hỏa đánh sập after production time. The position and
the structure of gas off horizontal holes in 9Đ level -80 is showed in
figure 3.12 and 3.13.
a
1
2
Figure 3.10. Grooving diagram in
horizontal borehole

Figure 3.11. The effect of drilling
pipe on the lower side of borehole
while drilling.



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MT
Q
Q
n 








Figure 3.12: Position of the holes in preparation

for mining at 9Đ seam










Figure 3.13: Boreholes structure for gas recovery in 9Đ seam
The number of the boreholes in production area will be
defined as below:
(3.19)
Q: volume of gas in production area of longwall
Q
MT
: volume of recovery methane flow at the long wall,
m
3
/month
Mining directional
Ventilation way
Ventilation way


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3.2.2. The basis of horizontal drilling technology for methane
removing in Mao Khe.

3.2.2.1. The views of appropriate horizontal drilling
3.2.2.2. The views of enhance mechanical drilling rate base on the
basis of energy lost when destroying rocks
According this view, to increase the mechanical drilling rate
it needs: increasing the energy of rock destroying by increase the
drilling rate and the axial weight on the drill bit; decreasing the
energy of destroying rocks by using suitable bit and appropriate
drilling technology; decreasing the contact area of bottom hole by
drilling small holes.
3.2.2.3. The view of increase mechanical drilling rate base on
appropriate drilling parameters.
According to this view, the mechanical drilling rate is
defined by drilling parameters: axial load, rotation rate, circulation
rate, and physical characteristic of rocks and technical characteristic
of bits.
3.2.3. The selection of drilling method and technology for gas
removing in Mao Khe
3.2.3.1. The selection drilling method.
Base on the characteristic of horizontal drilling as well as the
requirement of gas removing in Mao Khe; this study has the
selection of rotary – percussion drilling technology for methane of in
Mao Khe coal mine. The equipment will be used for drilling is RPD
– 130SL – F2W by Koken from Japan; and the sample threading
drilling tool PS-89.
3.2.3.2. The selection of drilling parameters.


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D
).P0038,064,3(91,1

n
s


tb
y
πD
δn
n 
The axial load on drilling bits in rotary – percussion
horizontal drilling is defined as below [31, 33, 39]:
P
0
= k..S
t
.P
S
(3.30)
Where: k - friction factor between the bit and rock. This
factor k varies on the nature of the stone, washing water and
structure drills. In the same rocks, the same drill bit with clay base
drilling mud, the factor k = 0,5 – 0,3; with natural water k = 0,35 –
0,2; = 0,17 – 0,23; the factor presents for the change in the contact
area of the cutting and rocks; S
t
- area of the cutting particles, cm
2
;

đ

- compression resistance of rock stress, N/cm
2
.
Rotation rate is selected by using O.V. Ivanov equation [33]
as below:
(3.31)
Where: n – tốc độ vòng quay rpm, round/m; D – diameter of
drilling bit, mm
The relation between rotation rate and percussion frequency
is defined as below [27, 31]:

(3.33)
The selection of Khoảng dịch chuyển bases on the physical
characteristic of rocks as well as percussion frequency. For rock at
VI-VIII in drilling,

= 70mm - 90mm; For rock at VIII-IX in
drilling,

= 60mm - 80mm; For rock at IX-XI in drilling,

= 40mm
- 60mm.
Drilling fluid is water with the flow of 40-60l/m when
drilling by sample threading tool.
According to the experience of experts [27, 31, 39], is
selected as table below:


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Table 3.1. Many rotary – percussion drilling regime properties
Rock types
P
0
, N
n, v/ph
Q, l/ph
n
đ
,
time/m
Siltstone, VI-VII in
drilling
3000-
5000
200-
250
40-50
800-
900
Siltstone, sandstone,
VIII-IX in drilling
7000-
9000
200-
300
40-50
1000-
1200
Siltstone, sandstone,

gravel, IX-XI in drilling
7000-
13000
200-
300
40-50
1000 -
1600
CHAPTER 4
EXPERIMENT RESULTS OF HORIZONTAL ROTARY –
PERCUSSION DRILLING TECHNOLOGY FOR REMOVING
METHANE IN MAO KHE COAL MINE
4.1. Tested drilling equipment.
The tested drilling equipment is RPD – 130SL – F2W by Koken
from Japan which is the combination of two methods of rotary
drilling and percussion drilling technique. RPD-130SL-F2W is
arranged two actuators for axial load to drill bit: hydraulic system in
combination with the transmission chain and energy of percussion by
percussion system installing at the top of drilling equipment. Thus,
when we drill into hard rocks there is the combination of two forces:
and axial load and the power percussion from percussion system.
Drilling tool includes the kits of horizontal sample threading
PS-89; drill pipe, sample kits, bit.
4.2. Experiment results of horizontal drilling parameters effects
to mechanical drilling rate.
The experiment was operated at gas off borehole in 9Đ East
wing level 80 in Mao Khe mine, drilling in sandstone sized IX-X,


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32
34
24
0
5
10
15
20
25
30
35
40
%
40
20
13
0
5
10
15
20
25
30
35
40
45
%
Ảnh hưởng của tải tr ọng chi ều tr ục
Ảnh hưởng của tốc độ vòng quay
Ảnh hưởng của lưu l ượng nước r ửa

hardness in 5000 – 7000 Mpa according to Sreiher P, siltstone sized
VII – VIII, hardness 2000 – 3000 MPa according to Sreiher P by
using PS – 89, the drill bit diameter of 101 mm, HS-C style. The
calculation of the effect of drilling parameters to drilling rate is
showed as below.









Figure 4.3: Effective of drilling parameters to penetration rate of
horizontal drilling by PS – 89
a) Dark grey siltstone: P
s
= 2000 – 3000 MPa
b) Sandstone: P
s
= 5000 – 7000 MPa
Axial load effect
Effect of rotary rate
Effect of fluid flow rate
4.3. Experiment result of the selection of rotary – percussion
drilling.


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Table 4.18. The comparision of drilling parameters between rotary and rotary percussion drilling in rocks
with hardness of P
s
= 2000 - 3000 MPa
Properties
Rotary
Rotary - Percussion
n
đ
= 800times/m
n
đ
= 1000times/m
n
đ
= 1200times/m


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Penetration rate, m/h
Energy of destroy, kW.h/m
Penetration rate, m/h
Energy of destroy, kW.h/m
Rotary rate, v/ph
Table 4.20. The comparision of drilling parameters
between rotary and rotary percussion drilling in rocks
with hardness of P
s
= 2000 - 3000 MPa; P
0

= 9000N
Table 4.21. The comparision of drilling parameters
between rotary and rotary percussion drilling in rocks
with hardness of P
s
= 2000 - 3000 MPa; Po = 11.000N
1. V
m
General rotary drilling; 2. E General rotary drilling; 3. V
m
with n
đ
=1000times/m;
4. E with n
đ
=1000times/m; 5. V
m
with n
đ
=1200times/m; 6. E with n
đ
=1200times/m.
Rotary rate, v/ph


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Table 4.19. The comparision of drilling parameters between rotary and rotary percussion drilling in rocks
with hardness of P
s
= 5000 - 7000 MPa

Properties
Rotary
Rotary - Percussion
n
đ
= 800times/m
n
đ
= 1000times/m
n
đ
= 1200times/m


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Penetration rate, m/h
Energy of destroy, kW.h/m
Penetration rate, m/h
Energy of destroy, kW.h/m
Rotary rate, v/ph
Rotary rate, v/ph
Table 4.22. The comparision of drilling parameters
between rotary and rotary percussion drilling in rocks
with hardness of P
s
= 5000 - 7000 MPa; P
0
= 9000N
Table 4.23. The comparision of drilling parameters
between rotary and rotary percussion drilling in rocks

with hardness of P
s
= 5000 - 7000 MPa; Po = 11.000N
1. V
m
General rotary drilling; 2. E General rotary drilling; 3. V
m
with n
đ
=1000times/m;
4. E with n
đ
=1000times/m; 5. V
m
with n
đ
=1200times/m; 6. E with n
đ
=1200times/m.


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According to the results of experiment, we select the
appropriate regime of rotary – percussion equipment RPD – 130 SL
– F2W and the PS – 89 wireline barrel to drilling long horizontal
holes for gas off in Mao Khe as be showed in Figure 4.20
Figure 4.20. The comparision
Rock type
Axial
Load

KN
Rotation
rate,rpm
Percussion
frequency
tpm
Circulation
rate lpm
Siltstone VII-
VIII, P
s
= 2000 -
3000 MPa
7-9
160-180
900-1100
50-60
Sandstone IX-
X, P
s
= 5000 -
7000 MPa
9-11
160-200
1000-1200
50-60
4.4. The effective of drilling for gas off in 9 East swing level – 80
According to the results of monitoring methane
concentrations appear in the ventilation of the longwall before
removing gas 9D at the highest of 1.62 % , averaging 0.73 %, and the

lowest at 0.54 % , often exceeded the warning level, power
interruptions. After removing gas by horizontal drilling holes, the
highest methane concentration is 0.9 % (decrease nearly 50 % from
the highest levels of methane before gas off operation), the average
was 0.66 % and the lowest is 0.50 % . Methane concentration is
relatively stable, rarely exceeds the warning level (CH4 = 1 %) ,
there was no case exceed the power cut-off (CH4 = 1.3 %).
Therefore, it increases efficiency of production time from 5 % - 10 %
due to reduce stopping times for warnings or power, that increases
production of longwall mining up to 33.4 %. At the same time, the


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costs for longwall ventilation decreased 30.4 % compared to the non
application of the system for gas removing [6, 7].
CONCLUSION AND RECOMMENDATION
CONCLUSION
According to the results of the study, I am going for some
below conclusion:
1. Stratigraphy of Mao Khe coal mine is sedimentary with
coal seams, clay, sitlstone, coal. Complicated structure includes
many faults… Those effect to the selection of drilling technology.
Mao Khe Coal Mine mine kind of dangerous methane
escaped with about 15.58 m3/day. Methane drainage process in
production operation is complicated and depends on the type of
longwall, mining technology, coal seam structural features, structure
of surrounding rocks, and permeability and the characteristic of gas
storage in coal seams as well as in the rock surrounding. Therefore,
the choice of appropriate research methods to remove gas with the
geological conditions, the mine operation conditions in Mao Khe to

ensure safety in mining and environmental protection is necessary,
with scientific meaningful and practices.

2. The selection of rotary – percussion drilling technology by
RPD – 130SL – F2W and PS – 89 to drilling horizontal boreholes for
removing methane is appropriate and suitable with the conditions of
production operation as well as the demand of gas off.
The results of experiments in Mao Khe show that mechanical
drilling rate of RPD and PS in horizontal borehole increase 1,45 to
1,7 time and the energy for rock destroyed decrease from 70% to
51% compared to rotary drilling in the same conditions.


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From the results of experiment in real, I have selected
appropriate parameters of rotary – percussion drilling by RPD –
130SL – F2W and PS – 89 for horizontal drilling for gas off in Mao
Khe coal mine as follow: axial load for drill bit from P = 9000 –
11000N, rotary rate = ; fluid flow =; percussion frequency =, when
drilling in sandstones, homogeneous, grain size of VIII – IX, P = ,
axial load transmit to drill bit from 7000 – 9000 with rotary rate = ;
percussion frequency.
3. The efficiency of methane remove in longwall mines 9Đ
Mao Khe mine by drilling horizontal holes is averagely at 36.2%.
Thus increasing efficiency production time from 5% - 10%, resulting
in production in longwall has increased to 33.4%. And the costs for
longwall ventilation decreased 30.4% compared to the non
application of the system for gas off.
RECOMMENDATION.

Recommendation of application of rotary – percussion
drilling technology and sample threading drilling as well as the
results of this study to drilling horizontal boreholes for methane off
in some pit mine need removing methane which has the same
conditions with Mao Khe.
In application process, it need to research to complete rotary
– percussion drilling technology, equipment selection, drilling
parameters which is suitable with each drilling conditions and the gas
off requirement.


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LIST OF WORKS OF THE AUTHOR
1. Phan Xuan Duong, Nguyen Xuan Thao, Nguyen Tran Tuan
(2004), Study on the application of gas drainage drilling
technology for increasing safety efficiency at Quangninh
underground coal mines, Proceeding of the 16
th
Scientific
Conference, Hanoi University of Mining and Geology, Hanoi,
pp. 220-227.
2. Phan Xuan Duong, Nguyen Xuan Thao, Nguyen Tran Tuan
(2008), Study on the drilling technology of large developing
boreholes for underground coal gasification, Proceeding of
the 18
th
Scientific Conference, Hanoi University of Mining
and Geology, Hanoi, pp.74-78.
3. Tran Đinh Kien, Nguyen Tran Tuan (2009), Some problems on the
selection of drilling methods for methane gas recovery

boreholes at underground coal mines, Proceeding of the 20
th

Scientific & Engineering mining, Vung Tau, pp.182-186.
4. Nguyen Xuan Thao, Nguyen Tran Tuan (2004), Study on the gas
drainage drilling technology to recovery Methane gas and
prevention of explosion in Quang Ninh underground coal
mines,Bulletine of Mining Science and Technology, Vol. 7, Ha
Noi, pp.22-25.
5. Nguyen Xuan Thao, Nguyen Tran Tuan, Nguyen Tu Vinh (2004),
Study on the water drainage drilling technology in Quang Ninh
underground coal mines, Bulletine of Mining Science and
Technology, Vol. 3, Ha Noi, pp.16-18.
6. Nguyen Xuan Thao, Nguyen Tran Tuan, Nguyen Tu Vinh (2004)
Some problems on the selection of exploration drilling