Drilling and core logging

University of mysore
Department of earth science
DRILLING AND CORE LOGGING

 Introduction
 Diamond core drilling
 Rotary drilling
 Percussion drilling
 Other methods
 Core logging
 Conclusion
 Reference.

 Drilling is a cutting process that uses a drill bit to cut or
enlarge a hole of circular cross-section in solid material.
 There are four main methods for drilling rocks :percussion
drilling, churn drilling, diamond drilling and rotary drilling.
 In percussion-compressed air is used
 In churn(cable tool drilling )- heavy chisel like steel is
repeatedly jerked up and down by a cable wire.
 In diamond – core is cut by rotating annular drilling bit
impregnated with diamonds
 In rotary – a special non coring bit is rotated at the end of a
length of steel rod

 It consists basically of a hammer unit which is
driven by compressed air. This hammer unit
imparts a series of short, rapid, blows to the drill
steel or rods and at the same time slowly rotates
them.
 Two main types of percussion drill:
1. down-the-hole hammer.
2. Top hammer.

 As the name implies the hammer unit is lowered
down the hole at the end of the rods.
 The bit on the end of the hammer unit consists of a
large number of tungsten carbide inserts either
button shaped or chisel ended.
 The percussive action is supplied to the bit by the
hammer unit.
 Rotation of the rod is accomplished by a rotating
unit on the rig itself.
 Mainly used for water well drilling and not
commonly used in mineral exploration.

 In this type of drill both percussive action and rod
rotation are provided by a hammer unit which is
truck mounted on the rig and is moved up and
down by a chain feed.
 The holes drilled by top hammer are smaller varying
in diameter from 38-45 mm.

 First used for drilling oil wells in 1860’s.
 Cheap and reliable way to drill water wells.
 It is a drilling technique in which a sharpened
steel bit attached to rope or cable is repeatedly
raised and lowered at the rate of 30-60 strokes/min and
crushing the rock and making the hole deeper.
 The crushed rock and sludges are removed by a bailer to the
bottom of the hole every 1-1.5 m of advance.
 Pouring of water is required both for drilling and bailing.
 Useful in exploration work for sampling soft formations upto
a depth of 100-150 m.

 Main disadvantage is that churn drilling is very
slow.
 A common fault is that the bailer does not clean out
all the cuttings, and improper bailings may result in
false increase of values with depth
 It is important to case off any overburden to avoid
contamination.

 Designed specifically for mineral exploration
and is the most important type of drilling .
 Recovery of the core drill enables details of
the geology, ground conditions and mineralogy
to be obtained that is not possible with any other
method.
 It was built by a Swiss Engineer in 1862 and by in
1900’s , it became well established technique.
 The sample is cut by a diamond armored bit
recovered in the inner barrel of the core barrel and
brought to the surface.

 The hollow drill rod passes through a tube
in the swivelhead and are held firmly in the
place by a chuck.
 The swivelhead rotates the rod and has a feed
mechanism for advancing the rods as drilling
proceeds.
 The feed mechanism may be achieved by a
screw fed through a system of gears, it may be
hydraulic.
 They have gear boxes so that drilling speed
can be varied according to the rock being drilled.

 Today there are two main types of
diamond drilling; conventional and
wire line.
 In conventional drilling the rods have
to be removed from the hole each time.
It is necessary to recover core from the
Core barrel.
 In wire line drilling the core can be
removed from the hole without withdrawing
the rods.

DIAMOND CORE DRILING MACHINE AT HUTTI
Model-LT575 drilling

 A mechanical device on a drilling rig that
provides clock wise rotational force to the
drill string to facilitate the process of drilling
a bore hole.
 Much like a common hand drill, the spinning
of the drill bit allows for penetration of even
the hardest rock.
 Faster and cheaper than diamond drilling.
 Extremely high rate of penetration and
the larger machines used in oil well
drilling can drill over 100m/hr

 It can obtain sample fragments by chopping its way through
almost any kind of ground- unconsolidated, heterogeneous,
hard, or completely fractured.
 Casing can be driven into the hole a short distance behind
the bit so that walls in loose rock will not cave in.
 The sample is collected in a bailer whenever enough broken
rocks accumulate at the bottom of the hole.

 Jet Drilling: It is a placer sampling method where a casing
and chisel-pointed bit are advanced by percussion while
water is forced ahead to loosen the material and to flush out
and bring the sample to the surface.
 It is replacing churn drilling in many placer mining districts
where minerals other than gold are involved.
 Auger drills: They are important in soil sampling, beach
placer sampling, and in evaluating clay deposits. In any
event, auger drilling stops at the first boulder.

 Core – A cylindrical section of rock, or
fragment thereof, taken as a sample of
the interval penetrated by a core barrel
and brought to the surface for examination
and for analysis.
 All drill hole data gathering is called logging.
 For logging, the geologist will require a
notebook, or logging sheets, pen, tape measure
, penknife, clinometer or protractor, and ruler
for measuring angles.
 For easy identification of rock types its best
to look at wet core

 After the core has been recovered from the core hole and the
core barrel has been opened, the core should be placed in a
core box.
 The core should always be examined in good light, preferably
natural light.
 No other skills are required other than the ability to make
competent mineral and rock identification.

 The core boxes should be laid out in correct order.
 Small wooden blocks with the depth clearly
written on with a marker pen
 The core that has been correctly placed in the
Boxes should run from left to right with the shallow-
est depth in the top left-hand corner and the lowest
Depth in the bottom right hand corner.
 The core samples are then studied carefully and
all the important rocks and structures are noted
along with the depth of formation.

 There are four methods of drilling: percussion drilling, churn
drilling, diamond core, rotary , jet and auger drilling.
 Diamond core is the most efficient method of mineral
exploration.
 There is much confusion in distinguishing between rotary
and diamond drilling as both involve both a purely rotary
action and diamond coring bits are also used in rotary rigs
and non coring bits are also used often in diamond drilling.
 The distinguishing factor is that rotary motion in diamond
drilling is imparted to the rods by a chuck, whereas in rotary,
it is applied by a device called the rotary table.
 Rotary rigs are much bigger and powerful than diamond
drilling machines.

 As drilling is an expensive undertaking , detail study of the
area must be made before starting the project.
 Core logging forms an important aspect of an exploration
geologist job and Important stage in the follow up work to an
exploration target.

 Techniques in mineral exploration- J.H. Reedman.
pg322-371. 1979
 Exploration and mining geology- William C. Peters.
Pg no:431-460.
 en.wikipedia.org/wiki/drilling.
 en.wikipedia.org/wiki/core_drill.
 www.rems.de/diamond-core-drilling.aspx

Drilling and core logging

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