DTH Drilling Method

COOL AND CLEAN WATER is a precious gift of nature. Not only human, but all living being depends on it. Except underground water, no water anywhere is cool and clean. Nor is any other supply of fresh water is plentiful. More than 97% of earth's fresh water is ground water. Generally, drilled wells can protect the purity of underground water more easily and more securely. Today's water well driller is both the provider and protector of ground water resources. Different drilling methods are used to tap different ground water formations. Due to earth's different geologic formations, the formation under our feet differs from one place to the next. Hence, drilling problems provide the challenges of water well work. To start the work with, then, driller must know something about the places and soil formation, where ground water occurs and how it got there in order to make it available for proper use.

Rotary Mud Drilling

The principle of Rotary Mud Drilling is based upon a rotating hollow drill stem and has a fluid of mud or other substance flowing through it. The purpose of circulating the fluid through drill stem is for the removal of the cutting, cooling of the drill stem rotating in the bore hole and sealing of formation walls to prevent caving and water loss.

The Rotary Mud Drilling Rig, which consist of a mast with sheave pulley mounted at the top for the purpose of operating a hoist mechanism. A square or keyed drive called a Kelly, hanging in the mast by a block assembly. A water swivel is connected at the top of the Kelly, which is connected a rubber hose or steel with flexible joints as pressure dictates. This Kelly is driven by a rotary table drive assembly which has inserts or blocks to fit the Kelly. The length of the Kelly is larger than the drill rods in order to drill down a few feet below to enable a section of drill pipe to be added as the hole drilled deeper. Hollow drill rods and rotary bit are attached by the use of sub at the bottom of the Kelly. Additional drilling rods are added to the string just below the Kelly, as drill goes deeper. The drill bit has holes in the bottom through which the fluid can flow. Draw works, which is attached on the rotary table drive, which operates the hoisting mechanism. Mud pump mounted on the rig, which forces the drilling fluid through the lines to the swivel down the Kelly and out the bottom of the bit.

Various types of drill bits are used for Rotary Mud Drilling. Star type drag bit is used in soft unconsolidated formation such as clay and sands. It has fluid courses which tend to jet the formations and the blades are very effective for sticky clays. The cone type roller bits have two to four cone type cutters mounted on the roller bearings, which have teeth in varying lengths. The bits having long teeth cutters are use for soft formation to short intermeshing cutters which tend to chip in very hard material. Harder the formations, cone teeth are shorter. Thumb rule to rotate soft formation bits at higher speeds and have much lower bit weight. Suitable RPM for soft formation drag bits are from 50 − 150. Suitable RPM for very hard formation roller bits are from 30-50.

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