Rotary drilling is the most popular well drilling method. Mud rotary is widely used in the Lower Byland where substantial overburden exists, while air rotary rigs are found primarily in the Upper Byland and the few high bedrock areas across the world.
The principle of rotary drilling method is based upon a rotating drill stem made of lengths of drill pipe about 15 feet long. A bit is attached to a heavy stabilizer or drill collar at the end of the column of drill pipe. The extra weight and larger outside diameter of the stabilizer just above the bit helps to maintain a straight drill hole. The drill stem is hollow and has a drilling fluid of either mud or air circulating down the drill stem out through the nozzles in the bit and up along the outside of the drill stem. The rotating action of the bit breaks up the material and the drilling fluid carries the cuttings to the surface where they settle out in a mud tank.
In rotary drilling, the borehole size is larger than the casing size. In drift formation, the entire hole is completed before casing is installed. In rock wells, the length of hole to be cased is drilled, the casing is installed, then the bit size is reduced and the rock portion of the well is completed.
Use of the down hole air hammer with rotary equipment provides a combined percussion-rotary method that penetrates rapidly in consolidated formations. Test holes are usually 6 inches in diameter when using this method. In most cases, however, conventional water-based drilling fluids must be used with a roller bit when drilling through unconsolidated overburden above bedrock. Exceptions to this occur when an air hammer is used to drive the casing after materials are blown out of the casing or when the rig is equipped with a casing driver.
This method allows contractors to drill more wells, and be able to drill them deeper and faster. Instead of using a mud pump, they use compressed air.
In this method, the drill pipe and bit are joined and advanced simultaneously. The conventional top drive drills the open hole and the lower rotary drive is used to set casing without any requirement for casing hammers, under-reamers, or drilling mud. Advantages of this drilling method are: ability to drill in tough conditions, quicker penetration rates, straighter holes, and a large compressor is not needed because the lower drive operates on hydraulics.
Either air or water can be used as the drilling fluid in this modification of reverse circulation technique. There is usually no grinding of cuttings, and the drilling fluid, if not air, can be clear water.
This section covers the major water well components used when installing a water well.
Borehole is a vertical boring to reach aquifer (water bearing geologic material). In a well terminating into rock, an open borehole will extend beyond the bottom of the well casing.
Well seal is a mechanical device to prevent contamination from entering well casing that is installed after well completion. All well caps and seals shall be weathertight, tightly secured, and vermin proof.
Well casing is steel or plastic pipe installed to keep borehole wall from collapsing and houses the submersible pump and drop pipe.
| PVC | Vs | Steel |
|---|---|---|
| Non-corroding | Corroding | |
| Lower strength | Higher strength | |
| Fewer water quality complaints | Rusty water | |
| Rotary construction only | Suitable for any drilling method |
Grout is impermeable cement or clay placed in annular space between borehole and casing to prevent well contamination, maintain separation of aquifers, and preserve artesian aquifers.
