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Mud Rotary Drilling. Rotary drilling with mud is the most widely used method for water-well construction. A rotary drill rig has three functions: rotating the drill string, hoisting the drill string, and circulating the drilling fluid. A bit is rotated against the formation while mud is pumped down the drill pipe, through ports in the bit, and back to the ground surface through the well bore hole.This why larger drill pipe and mud pumps make drilling faster. . Rotary drilling is sometimes called mud rotary drilling. Drill pipes or rods are joined to a bit to form the drill string. The drill pipe is the link transmitting torque from the rig to the bit, and the pipe carries the drilling fluid down the hole. The best top-head drives are powered by hydraulic motors capable of variable speeds like our R-77 rig, rather than positive constant rotation like post hole diiger conversion rigs..Smaller drilling rigs hydra drill type (or what ever is the new garage made brand of the week online.), work best with smaller bits, because of the small water course swivel and drill pipe , then re-drilling well bore with larger hole opening bit later. Drill bit types 1) Tricone Roller Bits.For use with larger rigs with hydraulic power and more available torque.Small rigs don't have the power or weight to use these properly. These bits bit consists of three cone-shaped rollers are best suited for brittle or friable materials. The tricone with steel teeth milled into the surfaces. Tooth locations are designed so that as the cone rotates, each tooth strikes the bottom of the hole at a different location. Drilling fluid is jetted on each roller to clean and cool it. The cutting action is a progressive crushing under the point load of each tooth. Roller bits designed for rock, rocky soil (gravel), and soft formations (shale) have long teeth. The bits for harder formations have smaller, stronger teeth. The gauge teeth on bits designed for very hard rock are reinforced with webs. For extremely hard formations, milled teeth are replaced with connected carbide buttons. (2) Drag Bits.Work fairly well with smaller lighter rigs. These bits are used in SOFT OR HARD soils and other unconsolidated materials. The blades are designed so that they cut into the formation with a carving or scraping action. Drag bits may have multiblade, hardened-steel, finger-shaped teeth or may have connected carbide-reinforced cutting edges. Bit weight required to cut rock depends on the design of the bit and the strength of the rock. Before drilling hard rock, add drill collars (heavy thick wall pipe for weight) instead of drill pipe until the load is sufficient for reasonable cutting.Smaller rigs the drill collars are to heavey for the gear case to hold ( THEY DONT HAVE WEIGHT BEARING SWIVELS.). As you dig deeper and add drill pipe, you may have to hold back on the drill string. Regulate mud-pump pressure by varying the RPM of the pump. Pressure from the weight of the fluid column in the annulus or from a restriction in the annulus caused by an accumulation of cuttings indicates insufficient cleaning. This type of pressure can cause formation damage, resulting in lost circulation and wall damage Drilling Fluids. Drilling fluid (bentonite clay) is circulated in rotary drilling to cool, clean, and lubricate the drill string, to flush cuttings from the hole, and to stabilize the borehole wall. Water is the basic fluid and is satisfactory for lubricating and cooling the tools. However, water has limited abilities to carry cuttings and stabilize the borehole wall.To solve this add bentonite clay to drilling water . Mud cools and lubricates through heat absorption from the bit and reduction of drill-string abrasion against the borehole wall. Heat is generated as the bit scrapes and grinds. Without the cooling fluid, the bit would overheat and be useless. Research indicates that removing the cuttings around and under the bit is the most important factor in keeping the bit cool. Requirements for cooling fluid are less than those for removing the cuttings. Therefore, if you keep the borehole clean with the fluid as you drill, you also cool and lubricate. This is true with clay muds and polymer fluids.Bentonite Clay muds suspends cuttings and flushes them up to top and to mud pit.. . (1) Lost Circulation. Lost circulation refers to a loss in volume of drilling fluid returning to the surface. The implication is that some fluid pumped down the drill pipe is entering the formations. The mud pit will lower,( watch your mud pit water level for water level). since some of the mud is used in forming a mud cake on the borehole wall; however, increased lowering can indicate circulation loss. Losses can occur through open-graded sand or gravel or open joints in rock. A loss can occur when cuttings are not washed out and the borehole annulus becomes restricted, resulting in increased down- hole pressure. Spudding (raising and lowering the drill string is IMPORTANT!) the hole too violently can cause loss also. Spudding helps wash cuttings, but down-hole pressures increase momentarily. Experienced drillers can estimate when spudding is safe. When fluid cumulation is lost and a driller continues to drill, he is drilling blind. An experienced driller with larger rig knows the rig can often drill blind successfully, but reestablishing circulation is always safer,especaially with smaler hydra drill type rigs. (2) Fall-In. Fall-in is material that accumulates in the bottom of the borehole after you stop drilling and connect another drill pipe.this is why once you get to bottom and need to add more drill pipe it is a good practice to run bit up and down 2 feet in both directions to ensure all cuttings are washed up well. This material is borehole-wall material that results from sloughing or caving or cuttings previously carried in suspension. Fall-in occurs when you encounter a loose, unstable formation and the drilling-fluid weight is insufficient to stabilize the formation. If you anticipate or suspect fall-in, raise the drill bit off the bottom of the hole (20-foot minimum) each time drilling is interrupted. This will prevent the cuttings and fall-in from settling back around the bit until the problem is solved. (3) Stuck Drill String. The drill bit and any collars just above the bit are larger in diameter than the drill pipe. The string becomes stuck when cuttings collect on the bit and collar shoulder. This condition is called sanded in. Be careful because you can break the drill pipe while trying to remove the drill string. Regaining circulation and working the sand out are seldom successful. If the formation will not take the fluid when you engage the pump . Little can be done to free the drill string except to wash a small pipe down the annulus to the bit and jet the settled sand back into suspension. When the annulus is too small to pass a jet pipe, a part of the drill string may be lost When the annulus is small, excessive up-hole velocity can promote erosion of the filter cake in granular zones and allow caving against the drill pipe. If this occurs, try to maintain circulation and rotation, even if circulation is slight. Where the grains are angular, the drill pipe can become locked while being rotated. This situation is similar to a sanded-in bit. With smooth pipe (not upset), hammering up and down will sometimes dislodge the string. You can reestablish circulation and continue drilling. Be careful because hammering up and down can produce unfavorable compacting of the sand. In a hole of fine-grained soil or shale, where the alignment has significantly deviated(crooked hole) and the drill pipe has wallowed into the wall, the pipe can become wall stuck. Pipe friction and relatively high borehole pressure can move the pipe tighter into the wallowed groove as you pull the string. An alert driller should recognize early stages of deviation and take measures to realign the hole. (4) String Failure. When the drill string parts, leaving a portion in the borehole, the drill string is rung off. this happeneds more with larger powerful rigs, smaller rigs with 6hp and less usually don;t have the power to do this.The portion in the borehole is a fish and attempts to retrieve the portion is fishing. Fishing tools include a tapered tap and an overshot die or homemade tools . Ringing off is normally fatigue failure in the drill-rod joints caused by excessive torque or thrust (repeated flexing and vibration that crystallizes heat-treated tool joints) or by borehole deviation (with flexing of the string). Examine drill rods for signs of failure. (5) Deviation. A deviated borehole is called going crooked. If you make the initial setup without plumbing and leveling the rig. you can expect the borehole to go crooked. A crooked borehole usually amplifies other problems later and can make a borehole unsuitable for a well. You should always anticipate deviation, since the borehole naturally tends to spiral from bit rotation. Variations in the formation badness may start deviation. Excessive bit load magnifies minor initial deviation. Use all available guides and collars and a reduction in bit load to minimize deviation. Driller's Log. Prepare a driller's log for every well drilled. The log contains data, such as water-bearing-strata information, you use to locate and drill a well.an example of a well driller's log Changes in circulation, color, and consistency of drilling fluid. Observations of the cuttings carried to the surface. Depth to material contacts. Size and apparent classification of the cuttings. Fluid loss or gain. Penetration rate. Soil description (fine or coarse, clay or sand). Soil Sampling. Try to obtain good material samples, and log the depth from which the samples came. Cuttings continuously wash to the surface during drilling. Heres a drilling log sample. Using 10ft drill pipe.
1. 0-10ft top soil
2. 10ft- 20ft sandy clay.
3. 20ft-30ft red clay.
4.30ft-40ft red clay.
5. 40ft-50ft some rock and sand.
6. 50ft -60ft course water bearing sand.
7. 60ft -70ft course water bearing sand.
8. 80ft -90ft black clay.
This is a good place to stop. you have 20ft of water bearing sand and a clay bottom means water can't get below it.
Set casing with well screen as close and inline with water bearing sand as possible. use end cap on bottom of casing.
For more drilling tips please check out our Troubleshooting Water well book. |
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