Deep Investigation by Core Drilling in Mae Mo

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GT-8
5th GEOINDO 2015
23-24 November 2015, Khon Kaen ,Thailand
Deep Investigation by Core Drilling in Mae Mo Basin, Lampang
Province, Thailand
Charlie Pungpanichkul 1, Chawalit Tanomtin 2*
1, 2
Right Tunnelling Co., Ltd., Samutprakarn, Thailand
[email protected]
[email protected]
ABSTRACT
The deep investigation core drilling in Mae Mo basin was conducted during January 2013 - January 2014 by Right
Tunnelling Co., Ltd under supervision of EGAT experienced mine geologist. The 3 rigs of rotary drilling machines were
selected to carry out this project. The drilling program was arranged by EGAT geologist as the site instruction.
Generally, the non-core drilling method has used for the overburden and coring has used for the coal seams and
specified depth of related rock formation. The sandy soil overburden is approximately 30-40 m thick from the ground surface and
whole rock overburden beneath the soil is approximately 350-450 m thick.
Wire line assembly has used for core drilling in deep section including all length of coal seams in order to taken coal
sample. The requirement of the coring is specified more than 95 % of recovery. The drilling has started from the middle part to
the north and turning to the south of the investigation area. The core sample is arranged in metal core boxes in the manner of
their actual depth. After coring has completed, borehole geophysical investigation has started immediately by the owner. The
drilling results and geophysical data were compared at site. The drilled holes are requested to open for the purpose of
monitoring the groundwater level.
The concrete slab supported the drilling machines are removed to the landfill after the investigation drilling has
completed. The drilling report and core sample boxes are submitted to EGAT Mine Geology Department.
Key Words: Mae Mo basin, core drilling, coal seam, red bed
1. GEOLOGY
The typical geological sequence in the investigation area is
consists of 30 m thick of sandy soil overlying 40 m thick of
upper grey mudstone. The red bed siltstone of 260 m thick
is underlying mudstone. The lower grey mudstone is
founded beneath red bed formation and founded from depth
330 m. Two (2) coal seams are intercalated with ligneous
layers within this formation. The fossil layer founded in
siltstone beneath coal seams.
Figure-1. Project Location, Mae Mo basin.
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5th GEOINDO 2015
23-24 November 2015, Khon Kaen ,Thailand
The drill operation is closely monitoring and supervised by
experienced drill foreman and site geologist.
2. DRILLING PROGRAM
The HW casing is installed from ground surface to good
rock strata. Non core drilling is started in sandy soil and
weathered rock overburden. The hard rock overburden is
drilled by wireline Triple tube core barrel with TC bit. The
representative sample is selected and put into core boxes.
Core Drilling is specified by client from the depth of 350450 m, above the upper coal seam about 20-30 m. The final
depth is reached when drilled below lower coal seam 2-3 m
or met the fossil layer in lower red bed siltstone.
Table 1. Drilling Program.
Formation
Thickness
m.
30-40
30-40
200-250
100-150
30-60
Sandy soil
Mud stone
Red bed
Mud stone
Ligneous layer & Coal
Drilling
Method
Non cored
Non cored
Non cored
Non cored
Cored
3. MUD PROGRAM
Circulation mud is prepared by mixing soda ash to raw
water adjusting pH to 8 - 9.5 and then slowly put bentonite
to adjusted water and added 2 chemicals into the mixture.
This mixture is circulating in the storage tank at least 6-8
hrs before using. After curing, this mixture called “mud”,
using as the drilling fluid. In order to take the maximum
advantage of mud properties in drilling operation, the mud
program is prepared.
Drill mechanic are also ready in all drilling time and
mechanical sense is required. The mechanical application is
very important when the drilling machine has some
obstructed or breakdown. The immediately decision and
reparation shall be done to avoid the hole collapses due to
the swelling of the red bed formation.
Three (3) rotary drilling rigs are used to conducting the
investigation. The maximum capacity of the drilling
machines are at least 1.5-2 times of the target drilling
depth. Tungsten carbide drag bits are used in soil and
highly weathered rock overburden. The HQ wire line
coring assembly is used for drilling in harder formation at
deeper section including whole length of coal seams. This
wire line assembly is help to saving the drilling time and
fast enough to avoid the hole collapsing.
The drill rig should be setting on the stable ground during
drilling operation. The concrete slab is proposed to use.
The 20 cm thick of concrete slab is constructed after
compact the original ground surface. The drilling machine
has tied to the concrete by steel wire to fix it and avoids the
movement when pulling drill rods up and prevent hole
deviation.
According to drilling in different rock formation, the mud
should be prepared in different properties. This mud
program is used in the deep investigation in Mae Mo basin.
Table 2. Mud Program.
Formation
Unconsolidated
sediments/loss
circulation
(0-60 m)
Swelling
Mudstone
(60-320 m)
Coal Seam
(> 320 m)
Viscosity
40-45
40-45
45-50
Ingredient
Water: 565 L
Soda ash: 1.0 kg
Bent: 75 kg
DFC: 1.5 kg
Water: 2,449 L
Soda ash: 2.5 kg
Bent: 200 kg
DFC: 4.5kg
CRP: 3 kg
Water: 2,637 L
Soda ash: 2.5 kg
Bent: 225 kg
DFC: 5 kg
CRP: 3.25 kg
Figure 2. Concrete slab for supported drill rig.
Figure 3. Rig Installation on Concrete Slab.
4. DRILLING PREPARATION
Drilling Crews are enough experiences to conducting the
core drilling, especially the driller. More than 10 years
experience drillers are adopted to operate the deep drilling.
GT-8
5th GEOINDO 2015
23-24 November 2015, Khon Kaen ,Thailand
6. DRILLING PROCEDURE
The drilling is started by installation of HW casing in the
soil overburden. The casing is proposed to install as less as
possible. In deep installation of the casing should remove it
out immediately after drilling completed or before 1-2 days
after installed because the skin friction between the swelled
red bed formation and casing surface developed shall
against the pulling force. This skin friction may increase up
to 0.5 ton/m, at this load the casing can’t take and the
rupture of casing is resulted. The best way is use casing as
necessary as possible.
Figure 4. Preparation of wire line core barrel.
Figure 5. Core extruding.
Figure 7. Casing installation.
The non-core drilling should continue below the casing end
by drag bit and TC cored bit. The non core drilling is
continue until reached around 20-50 m above the upper
coal seam, then change to core drilling until completed to
target depth.
Figure 6. Coal Sample.
5. ROLE OF DRILLING FLUID
The mixture of water, bentonite and additive chemicals,
called mud, were used as drilling fluid for whole length of
drilling operation. The mud is very important when drilling
at deep section. It’s help to cooling and lubricating the drill
bit and drill rod from abrasion of wall rock. The drill
cutting have transported from bottom of the hole to the hole
collar by mud circulation. According to circulation of the
mud, it forming mud cake at the hole wall to protecting the
hole collapse and circulation loss.
Figure 8. Non- core samples from overburden.
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5th GEOINDO 2015
23-24 November 2015, Khon Kaen ,Thailand
logging are not allowed. Coal samples were brought to
laboratory for chemical properties testing.
Figure 9. Core samples.
The drilling revolution used is rather low when using drag
bit due to drill rods shank and become higher when conduct
core drilling. Normally, the revolution used in drilling with
TC bit is between 150-300 RPM and the circulation of
drilling fluid is about 11 GPM or 42 LPM. The WOB is not
specified, applied up on the rock formation. Too much
WOB should induced clogging at the drill bit. The pressure
of circulation fluid should be controlled. Too high
circulation pressure should increase the up hole velocity but
also induced hole collapse. The adjusting of these factors is
very important and should effect to drilling rate and may
lead to some drilling problems.
Figure 11. Coal sample.
9. SITE REMEDIAL
When the investigation drilling has completed without any
suspecting, the site remedial is required to its original. The
concrete slab should be removed by hydraulic jacking and
transport concrete to the permitted landfill. The drilled hole
after remove casing is leave to open for monitoring the
groundwater depth as long as possible. Some casing and
drill rods that obstructed in drilled hole should be noted and
inform to the client because they effecting to the
excavation.
7. GEOPHYSICAL SURVEY
The borehole geophysical investigation is immediately
starting after the drilling has completed. The gamma ray
logging, density and ATV survey are conducted by EGAT,
Geophysical Section. The interpretation of geophysical
logging data should be done at site and compare to the core
samples at whole depth. The conflict of results should be
solved by re-surveying until founded the conclusion.
Figure 12. Site Re-habitation.
10. CONCLUSION
Figure 10: Borehole geophysical survey
8. CORE SAMPLE
All core samples from drilled holes are arranging to actual
depth in metal core boxes, wrapped by plastic sheet and
submit to EGAT, Mine Geology Section. The photos and
Deep investigation by non-core and core drilling has
conducted at the middle area in Mae Mo basin. The
investigation is carrying by 3 rotary drilling machines.
These investigation depths are between 400-600 m from
existing ground surface. There are founded 2 coal seams
from depth of 400-550 m. The core drilling fluid is used
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5th GEOINDO 2015
bentonite with 2 chemicals mixing to adjust it properties to
meet the requirement.
The total of 10,010 m was drilled consisting of non-core
drilling 7,176 m and core drilling of 2,834 m. The average
total drilling rate is approximately 35 m/day. The drilling in
red bed formation is hardest due to its swell property. The
major problems during drill operation are hole collapse and
circulation loss especially in coal seams at the deepest
depth.
The drilling machine and equipment condition, experiences
of drilling crews and drilling method are the most
important.
The project completion is reached by
cooperation of site geologist, driller, drill assistants, drill
mechanic and drill supervisor.
11. REFERENCES
Rotary Drilling Accessories Catalogue, Boart Long Year.
Horizontal Directional Drilling Information Guideline,
Drilling Fluid, Straightline, 2006.
Formulas and Calculations for Drilling Production and
Work Over, Norton J. Lapeyrouse, Elsevier Science,
2002.
Closure Report of the Mae Mo Investigation Project, Right
Tunnelling Co., Ltd, 2014.
23-24 November 2015, Khon Kaen ,Thailand
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