Deptt. of Irrigation and Drainage Engineering, Dr. PDKV, Akola Well Drilling Methods M. U. Kale Assistant Professor Deptt. of Irrigation and Drainage Engineering, Dr. PDKV, Akola

Tube Well Drilling Equipments Tube well drilling equipment involves three distinct operations – Drilling the bore hole Installing the casing and well screen Developing the well to ensure sand-free operation at maximum yield. If artificial gravel packing is required, the operation is considered as a part of well screen installation. Tube wells may be bored, jetted, driven or drilled.

Tube wells Bored well – excavation is carried out by hand or power augers Jetted tube wells – excavation is done with high velocity jet of water Driven well is constructed by driving a pointed screen into the ground and adding casing pipes to the drive point as it is being driven into the ground. Drilled well – excavation is done either by percussion or rotary drills. Classification of water well drilling equipments Percussion or Cable Tool Drills Rotary Drills – direct rotary, reverse rotary and air rotary Down the hole hammer drills Classification on the basis of capacity rating Shallow Medium Heavy

Drilling Methods On the basis of type of drilling equipment used, tube well drilling methods are classified as

Mechanical Percussion Drilling

Mechanical Percussion Drilling Commonly known as Cable Tool Drilling Drilling – by operating the tool in up & down motions The Drill bit crushes the hard foundation into small fragments. To form slurry, water is added to this crushed material. Slurry is removed from bore hole at intervals by sand pump or bailer. Formation of sludge slows down the penetration of tool. Standard equipment for cable tool drilling – portable rig mounted on truck chasis. Portable rig consist of Mast (derrick) Two or Three line hoist A Spudder for raising and dropping the tools Diesel engine to provide power

Portable rig In three line hoist One line for operating drilling tools (drilling reel) For operating bailer or sand pump (sand reel) Third for operating boring pipes (casing reel)

Bailer Used to remove drill cuttings from time to time. Consist of section of pipe 2-5 m long with valve at bottom and hook at the top. Generally equipped with flap or dart valve. Sand Pump Similar to bailer except that it is equipped with a piston for the purpose of drawing the drilled cuttings from a well. Used for removal of heavy cuttings More effective than bailer.

Adaptability of Cable Tool Drilling Method Used in all type of formations Better suited for drilling in consolidated formations containing large rocks and boulders. Disadvantage Slow rate of drilling Need to case the hole as drilling progresses

Advantages of Cable Tool Drilling Accurate well log Water quality and yield of different water bearing strata can be estimated during drilling Much less water is needed as compared to hydraulic rotary and jetting methods. Any encounter with water bearing formations is readily noticed as water seeps into the hole. Highly skilled labour is not required Suitability for drilling in hard foundations.

Hydraulic Rotary Drilling

Hydraulic Rotary Drilling consist of Cutting a bore hole by means of rotating drill bit Removing the cutting by continuous circulation of drilling fluid. Types of Hydraulic Rotary Drilling Direct Circulation Drilling Reverse Circulation Drilling

Direct Circulation Drilling Drilling fluid i.e. drilling mud – pumped down through the drill pipe Drilling fluid passes out through the nozzles in the drill bit and flows upward in the annular space. Cuttings carried in suspension to ground with upward moving fluid.

Reverse Circulation Drilling Drill fluid used is clear water. Drilling fluid flows by gravity into the annular space between the hole and drill pipe. Drill fluid along with cuttings is recovered through drill pipe generally by means of centrifugal pump. The bore hole is not cased during drilling. Water required at the rate of 3-9 lit/sec. Mud is added to water if formation starts to cave in. The drilling operation has to be carried out round the clock. For holes more than 300 m depth, compressed air is used as circulating drilling fluid.

Air Rotary Drilling Compressed air is used as drilling fluid rather than drilling mud. It is recent well drilling method. Compressed air escape out through holes in drill bit and moves upward in annular space carrying drill cuttings to the surface. Advantages Air rotary method results in faster penetration in hard rock formations, as compared to conventional hydraulic rotary drilling methods. Loss of circulation does not prevent drilling. Accurate data sampling is possible.

Air Rotary Drilling Limitations Air Rotary drilling is limited to consolidated materials. Large quantity of air is required for drilling Difficult in caving formations.

Thank you