DRILLING

Collection of geological material.

Samples of geologic materials are collected for three general

purposes:

Measurement of physical and hydraulic properties,

Measurement of chemical and biological properties, and

Identification of lithologic, geologic,mineralogical, and

gross physical properties.

PURPOSE

GEOLOGIC MATERIAL COLLECTED AS

Cores

Cuttings

A core is a cylindrical sample of unconsolidated or

consolidated geologic material obtained in situ by means of a

thick-wall, thin-wall, or rotating coring device.

Cuttings are defined here as small-sized fragments of

unconsolidated, partly consolidated, or consolidated geologic

materials that are transported to the surface by

A stream of air or other fluid used during drilling,

Bailing or grabbing from a drilling,

Sticking to drill bits or auger flights,

Return from auger flights (noncoring methods that use

pocket and spoon, window or door).

DRILLING METHODS

Selection of a drilling method partially is determined by

The type and quality of sample and the sampling device

needed to collect these materials.

Rock properties where drilling takes place.

DRILL BITS AND ROCK PROPERTIES

HardnessDescribes the ability of one mineral to scratch another.

ToughnessDescribes the resistance to fracture that comes essentially

from the tensile strength of rock. Many drill bits are

designed to induce local tensile failure within Rock.

AbrasivenessDescribes the ability of rock fragments to wear away the

drill and polish its cutting edges.

ROCKS GROUPED BY SELECTED DRILLINGCHARACTERS

Igneous:Abrasive: Rhyolite, welded tuffs, granite, pegmetite.

Less abrasive: Basalt, dolerite, gabbro.

Least abrasive: Weathered intrusive rocks.

Etamorphic:Abrasive (and hard): Quartzite, hornfels, gneiss.Quartzite usually the most difficult of common rocks to drill.Less abrasive: Schist.Least abrasive: Phyl ite, slate, marble

Sedimentary:Abrasive (and hard): flint, chert. Quartzite, sandstone,

quartz conglomerate.

Abrasive (less hard): Siltstone, siliceous limestone, many

sandstone.

Non abrasive (hard): Limestone, shale.

Non abrasive (least hard): Mudstone, marl, coal, oolitic

limestone.

DRILL BITS

The hardness of mineral

constituents, the toughness

of the rock, its abrasiveness

should be considered while

choosing drill bits.

Conventional cone bits

Conventional cone bits

VARIOUS BIT DESIGNS – Placement and spacing of studs depends on rock properties.

SITE CHARACTERISTICS AFFECTING DRILLING

Structure Broken rock is more difficult to drill than its intact

equivalent

Energy wasted at each discontinuity.

Joints filled with soft material can be source of delay.

Deviation in penetration.

TYPES OF DRILLING

Percussion drilling

Cable tool

Hammer drill

Air Percussion

Rotary drilling

Three rotary drilling methods are widely used, each

depending on the type of information required and/or the rock

types being drilled.

Air rotary

Mud rotary

Diamond core drilling

CABLE TOOL DRILLING

The objectives of this technology are to limit public

and worker exposure to hazards, obtain representative

geologic samples, and minimize the amount of secondary

waste generated.

PERCUSSION DRILLING

In percussive drilling a chisel-shaped bit is repeatedly struck

against the rock so as to form a hole. It pulverizes the rock to a

fine debris which can be flushed from the hole by drilling fluid.

AIR-PERCUSSION DRILLING

This method is used for penetrating hard rock types to a

depth of around 300m.Rather than a rotating bit, a hammer bit is

forced through the rock by compressed air. As in air-rotary

drilling, rock chips are brought to the surface by the returning air.

ROTARY DRILLING

In rotary drilling the ground is either cut or crushed by tough

blades or points which are rotated against the rock under load.

DIAMOND CORE DRILL BIT

Diamond studded core cutter.

The diamond bit is used in conjunction with a core barrel for

cutting a core out of the rock. The bit is hollow so that as it

cuts into the rock, a core of rock is cut which passes through

the bit and into the core barrel.

AUGUR DRILLING

Solid stem. Hollow stem

AIR-ROTARY DRILLING

This is a quick and economical method of producing a

sample. Compressed air is forced down the drill pipe and, as it

returns to the surface, it carries with it rock chips made by the

rotating bit. This method is used in soft rock materials to about

25m deep, or to drill through the top layer of decomposed rock

and soil to get a fresh rock sample from the bedrock below.

Mud-rotary drilling

This method is used for drilling through soft rocks, sand and clay layers especially in the search for coal, oil or gas. A special mix of clay and water is forced down the drill hole turning a rotary bit, with rock chips returning in the "mud" slurry. This method is used for holes up to 3km deep and can be done from ships or offshore platforms especially in the search for oil and/or gas. A person who collects the chips and identifies the rock type and other information is known as a "mud-logger".

DIAMOND CORE DRILLING

This method involves a pipe encrusted in industrial

diamonds being used to drill through rock layers, with a "core" of

rock being left in the centre of the pipe. This core is recovered

and gives information not only about the rock types, but also

about the relationships between the rock layers in detail.

DIAMOND CORE DRILLING

Thank you