Ground Water Well Drilling - Admission/Application Essay Example

Table of Contents Introduction…………………………………………………….…………………………..3 Cable Tool Drilling………………......................……..………...……………………….3 Mud Rotary Drilling...................................................................................................4 Reverse Rotary...................................................................................................…...5 Air Rotary Method....................................................................................................7 Conclusions and Recommendations....................................................................8 References…...........................................................................................................9 Introduction The report discusses the procedures of different drilling techniques and gives the advantages and disadvantages of these techniques with special reference to the types of strata in which a particular method is suitable or not suitable. Cable Tool Drilling The chipping and cutting of earth by lifting and dropping a heavy solid chisel-shaped bit, suspended cable from a truck-mounted rig is called cable-tool drilling. Steel casing is used to keep the hole open during drilling in unstable soil, the purpose of casing is also to isolate the potentially contaminated strata. The cable-tool method is unrestricted as to dept, diameter and ability to penetrate geological materials when it comes to monitoring well-drilling. Whether drilling below or above water table the method is very much suitable. Small volumes of easily contained cuttings are produced. Little or no outside drilling fluids are needed normally and fluids which are used are primarily to facilitate cuttings removal by a bailer or sand pump. Sufficient annular space has to be maintained between the drilling casing and monitoring-well casing to allow effective placement of filter and sealing material. The size of test holes or steel casing around the well casings should be 3 to 5 inches greater in diameter than the monitoring-well casings. 2 inch diameter monitoring well should be installed within 5.5 inch diameter or larger test hole or drilling casing. Advantages Cable tool drilling surpasses all other techniques in detection and isolation of water fluid bearing intervals and ease of development of drilling surface. It helps to easily obtain excellent sediment samples while drilling for water, this helps in testing the site when drilling for obtaining water to check whether the use of water from the site is hygienic or not. Successively smaller casing may be easily telescoped within previously installed casing to avoid carrying shallow contaminated materials into lower strata units. Cable tool drilling is very useful as the sampling of soil and water during drilling and the installation of monitoring equipment is easily accomplished during cable-tool drilling. The rigs used in cable tool are very much simple with very few lubricated parts at positions likely to contaminate test hole or monitoring well. There are other cable tool rigs which are dual purpose rigs which can also be used in rotary drilling techniques. Cable tool technique is applicable in all kinds of strata. Disadvantages The primary disadvantage of cable-tool drilling is its relatively slow rate of penetration. It varies from 10 ft per day to 45 ft per day depending on the type of strata. This the reason behind the cable tool rigs are becoming relatively rare. Secondly sufficient annular space has to be maintained between drilling casing and the monitoring well casing to allow effective placement of filter and sealing materials. Mud-Rotary Drilling In mud-rotary method the bore hole is advanced by rapid rotation of a drill bit mounted upon the end of drill rods. Drilling mud, a water-based drilling fluid that can be composed of all sorts of materials is pumped into the drill pipe and escapes through the bottom of the bit. The mud settles in a settling pit after being carried out to surface along with the drill cuttings. The mud is added at regular intervals along with the re-circulation of the mud that has been used and comes to the surface. In this way as the depth of the hole increases the mud is added. Mud rotary drilling is carried out in un-consolidated and semi-consolidated formations. After the borehole is drilled to the desired depth, the screen and the casing for the well are installed in the hole. Pumping of mud from the well/borehole is done. After that gravel pack, bentonite plug and grout seal are added in the well. Advantages It is suitable in unconsolidated soils. Mud rotary excels all other drilling techniques when it comes to drilling in unconsolidated framework. The mud provides effective cuttings removal and stabilizes the walls of the boreholes at the same time. Mud rotary drilling offers a number of advantages. It is very fast and efficient means of drilling. Efficient rigs can produce several hundred feet of hole per day. The mud rotary method can reach to several thousand feet in depth and create hole diameters to greater than 48 inches. The method is adaptable to a wide range of geological conditions. Sediment sampling is broadly supported in direct-rotary method. Hydrologic conditions have little effect on mud rotary drilling and the operations are not hindered by the presence of ground water. Disadvantages Mud rotary drilling is sometimes very slow as its pace is determined by the type of soil in which the drilling process is done. A tri-cone roller bit that excels at quick drilling in sands is not suitable for drilling in hard limestone. An engineer can also not change the bits very frequently as it increases the costs of the work and thus an optimum solution is required which comes with experience. If drilling mud is not carefully engineered, drill fluids may invade permeable zones, compromising the validity of subsequent monitoring well samples from those intervals. The mud cake necessary for hole stability will usually interfere to some unknown extent by ionic exchange with the analysis of monitoring well water samples. Reverse Rotary The reverse rotary method operates by the same general principles as direct- mud rotary except that compressed air is pumped down the drill rods and returns with the drill cuttings up through the annulus. The reverse rotary method is best suited to drilling in relatively stable to consolidated formations. Casing is sometimes used to prevent caving in poorly consolidated formations. Reverse rotary drilling is a very fast and efficient means of drilling. Rigs that are properly equipped and staffed can drill several hundred feet of hole per day. The reverse rotary method can reach to several thousand feet in depth and create hole diameters up to approximately 17 inches. Reverse-air rotary rigs are unrestrained by karst (cavernous) terrain. Sediment sampling is supported both in poorly lithified materials (by split-barrel samplers) and in consolidated rock (by coring). Advantages Reverse rotary drilling supports the telescoping of casings to successively smaller sizes to isolate drilled intervals and protect lower geologic units from contamination by previously drilled contaminated upper sediments. Reverse- rotary rigs are sometimes fitted with a casing driver to overcome bore hole instability problems in unconsolidated sediments. When so equipped, reverse-air rotary rigs minimize the potential for inter-aquifer contamination. Reverse rotary rigs are available at several locations in the state. Disadvantages Reverse-air rotary drilling presents some disadvantages. In contaminated formations, the use of high-pressure air may pose a significant hazard to the drill crew due to rapid transport of contaminated material up the bore hole during drilling. Large volumes of hazardous gases may be discharged at the surface, posing an immediate hazard to the drill crew and others in the vicinity. Introduction of air to ground water could interfere with chemical analyses primarily by oxidation and by vigorous agitation and mixing. Concentrations of volatile contaminants are very likely to be reduced in ground water adjacent to holes drilled using the reverse-air rotary method. The air discharged from air compressors normally contains finely atomized lubricating oil. To help prevent this oil from contaminating monitoring well drill holes, compressor discharge filters must be installed (and maintained during regular intervals) on rigs used to drill monitoring wells. Air-discharge samples should be collected as reference samples for future comparison where hydrocarbon contamination is being studied. These samples are a necessity in applications where lubrication of down-the-hole hammers or other tools is essential. The use of foam additives to aid cuttings removal can also introduce organic contaminants into the monitoring system. These should be avoided, but where necessary, samples of the foaming agent must be taken as reference samples. Cuttings above the water table are usually very fine and hard to interpret. Also, the drying effect of the air in the annulus may reduce or eliminate any natural moisture in the cuttings, thereby masking low yield water producing zones. Conversely, when high- yield aquifers are encountered, large volumes of water may be produced during drilling, a definite disadvantage if the water is contaminated and requires special handling and disposal. When reverse-air rotary methods are used, hole diameters should be 3 to 5 inches larger than the outer diameter of the well casings to allow effective placement of filter and sealing materials. Two- inch diameter monitoring wells should therefore be installed within 5.5- inch diameter or larger holes. Air Rotary Method Air rotary drilling is similar to direct mud rotary drilling except that compressed air is used to transport the cuttings to the surface. An air-operated downhole casing advancement system is sometimes used. This casing advancement system consists of an air-operated down-the-hole hammer drill that is fitted with a specialized bit that has an eccentric reamer that cuts the hole large enough for the casing to follow. The hammer drill is designed to be used inside and the drill casing bottom so that the bit and eccentric reamer are below the casing. By the use of compressed air the hammer pulverizes the material below the casing and it is then blown back through the casing to the top of the hole. As the hammer drives through material it also reacts against an interior shoulder beveled on the drill casing shoe, which pulls the casing down the hole as the hammer drill is advanced. Advantages The major advantage of this method is that that it is well suited for drilling through difficult material such as rock fills. Disadvantages The major drawback is the high air pressure and large air volume required for the operation and it is prohibited on the embankment of a dam. Button Bit vs Rotary Bit There is not much difference between a button bit and a rotary bit but the button bit is more suitable for use in soft strata mainly clayey strata while the rotary bits are useful in hard rocks and sandy strata. Conclusion and Recommendations All the methods have certain advantages and disadvantages and the strata condition is the deciding factor for adopting any specific method for drilling. Cable Tool method is very conservative approach and is becoming obsolete but it has certain advantages when it comes to testing of soil and ground water. Reverse Rotary method is a relatively better approach than the air rotary if drilling has to done near water storage facilities. Mud Rotary technique is by far the most appropriate one with very little disadvantages. Works Cited A. M., Michael, Khepar S. D., and Sondhi S. K. Water Wells and Pumps. N.p.: McGraw Hill Professional, 2008. Print. Alth, Max, Charlotte Alth, and Blackwell Duncan, Sr. Wells and Septic Systems. N.p.: McGraw Hill Professional, 1991. Print. Crush, Mark, Sr. Portable Water Well Drilling Rig Plans Book. N.p.: Aardvark Global Publishing, 2005. Print. Crush, Mark, Sr. Water Well Drilling Trouble Shooting Guide. N.p.: Aardvark Global Publishing, 2005. Print. Gordon, Raymond. Water Well Drilling with Cable Tools. N.p.: Bucyrus-Erie Co,, 1958. Print. Ragunath, Hari. Ground Water. N.p.: New Age International, 2007. Print. Read More