APPLICABLE IN BOULDERY FORMATION AND SUBSTIYTUTE OF PERCUSSION METHOD

1. Drilling Technique in Himalayan Region
By
H. K. BEHERA
ASSISTANT EXECUTIVE ENGINEER
CGWB, DIV-XVII, DHARAMSHALA

2. Contents
1. Introduction
2. Procedure
3. Requirement of tools
4. Construction of wells
5. Pros & Cons

3. Introduction:
As much as 90% of the land surface of the earth is covered with
loose, unconsolidated material such as soil, clay, silt, sand,
gravel and boulders, which varies in depth from a few
centimetres to hundreds of meters.
The Himalayan region is one of the most problematic region for
drilling through such unconsolidated formation due to the
tendency of the earth to cave in behind the drill bit. This makes
it difficult to retrieve the drill string after the hole has been
drilled. In practice, the bore hole is often lost before a casing
tube can be inserted to support it.

4. Other problems are caused by cavities or porous ground, which
interfere with the circulation of the flushing medium and
prevent the drill cuttings from being flushed out of the hole.
In places where overburden strata are mixed, or when the
drillability is unknown, it is difficult for the driller to decide what
tools to be used in order to get the best overall results without
risking the loss of equipment in the hole.

5. The best solution for dealing with such problematic
unconsolidated formation is to use either
(a) Percussion drilling method
(b) Latest Odex Method and
( c) dual rotary method.
Drilling method in unconsolidated formation

6. Percussion drilling Method
Percussion drilling technique is the oldest drilling technique. It was adopted in India at the
beginning of using of mechanical tools in Ground Water Drilling.
The percussion drilling technique employs the principle of lifting and dropping of
heavy string of tools suspended on a cable with a bit at the bottom to deliver rhythmic blows
against the bottom of the hole so that the formation is broken and crushed. Drilling is
accomplished with a tight line so that the bit strick in the formation when the cable is
stretched. The reciprocating motion of the drilling tool mixes the loosen material and the
sludge is removed from the hole periodically by bailer or sand pump. This drilling is applied in
unconsolidated formation and casing is used to prevent the hole from caving. In cased hole
drilling technique, the drilling and casing are simultaneously proceeded till the completion of
depth of drilling target. Till 1991 the percussion drilling was to mean only drilling with casing,
but in 1991, a new technique adopted from Japan in Indian Drilling field to drill in percussion
technique without casing pipe. This technique is called Open Hole Percussion Drilling
Technique (i.e. without casing).
So in open hole drilling technique, the use of drive pipes is limited and are avoided,
thus it saves cost of casing pipes as well as time from driving of casing pipes, which helps to
increase the drilling progress. The Open Hole Drilling is the method to drill a borehole using
clay and mud to prevent collapse of the borehole.
Now the percussion drilling method has been discarded by CGWB due to slow rate
penetration , huge expenditure in construction of wells and time taking cumbersome drilling
technique

7. Odex method
The best solution for dealing with such problems is to use ODEX
equipment in unconsolidated formation.
• ODEX equipment enables you to drill and case deep holes
simultaneously in all types of formation, even those with large
boulders. Casing diameters from 89 mm (ODEX 76) to 273 mm (ODEX
240) can be used.
The method is based on a pilot bit and eccentric reamer, which
together drill a hole slightly larger than the external diameter of the
casing tube. This enables the casing tube to follow the drill bit down
the hole.
• When using ODEX, part of the impact energy is diverted to the casing
tube via a shoulder on the guide device, which in turn impacts a
special casing shoe at the lower end of the casing.

9. Procedure :
• In this method of drilling the casing is drived simultaneously with
advance of drilling.
• After completion of targeted depth, the drilling string is retrieved
from the bore bore hole leaving the casing string in the bore hole.

10. Requirement of Tools and Machineries:
• High torque rating top head drive DTH drilling Rig
• Adequate capacity Air Compressor
• Odex drilling attachments :
i) Guide device
ii) Pilot Bit
iii) Reamer bit
Iv) Cashing Shoe

11. Construction of wells
• After completion of the drilling, the drilling string is pulled out from
the bore hole leaving the casing in the bore. The slotted pipe is
lowered to the water bearing zone and the casing pipe is pulled out
exposing the slotted portion of casing pipe.
• Well assembly is lowered from top to the desired depth and odex
casing is pulled out completely and gravel packing is done.

12. Pros & Cons
• It is time effective and cost effective than the conventional
percussion drilling method.
• In this method of drilling larger dia. Tube wells can not be
constructed.

13. .
Thanks.

14.  As much as 90% of the land surface of the earth is covered with loose, unconsolidated material such
as soil, clay, silt, sand, gravel and boulders, which varies in depth from a few centimetres to
hundreds of meters.
 Drilling through this so-called overburden is often problematic, due to the tendency of the earth to
cave in behind the drill bit. This makes it difficult to retrieve the drill string after the hole has been
drilled. In practice, the bore hole is often lost before a casing tube can be inserted to support it.
Other problems are caused by cavities or porous ground, which interfere with the circulation of the
flushing medium and prevent the drill cuttings from being flushed out of the hole.
 In places where overburden strata are mixed, or when their drillability is unknown, it is difficult for the
driller to decide what tools to use in order to get the best overall results without risking the loss of
equipment in the hole.
 The best solution for dealing with such problems is to use ODEX equipment.