Drilling Rig Systems Functioning - Research Paper Example

Name Course Tutor Date Drilling Rig Systems Introduction Rig is a complex tool or equipment that is used in creating holes on the ground. Drilling rig are machines that are majorly used in drilling of water wells oil wells, and natural gas extraction. These machines can be used to install sub-surface fabrications like underground utilities, tunnels, instrumentation, and wells. Most of them are mechanically driven while others are small enough and can be handled by a single person. Most of the drilling rigs are mobile hence movable by use of tracks and trailers (Roughnecks). However, there are those that are installed permanently especially offshore oilrigs. Drilling rigs used in drilling water wells and mineral explorations are small and portable. Huge drilling rigs can also be used in extracting natural gas in remote conditions. Drilling rigs have been the cause of most oil spillages in the oceans and therefore drilling detecting problems should be identified before engaging this machine. Past historical problems in addition to preliminary information from the engineers and supervisory personnel can aid in the success of this machine. Components of a Rig A rig contains four main systems, which are the power, hoisting, rotating, and circulating systems. The power system Most of the rigs constructed are utilizing internal combustion engines as their primary source of power. In order to operate the engines, the rigs use diesel fuel as their source of power. Power from the diesel engines is usually converted to electrical power which helps in circulating the rotors while the switch control the gears. The following illustration shows a rotary drilling rig. Figure 1: Rotary Drilling Rig Hoisting System It is important to affirm that the work of a rig is just to make a hole regardless of its source of power and in order to conduct the exercise successfully it must be helped by a hoisting system. The hoisting system comprises of crown block, derrick, travelling block, and a rope as indicated in the figure above. Heavy pieces of machinery form the drawback as can be seen from figure 1 above. The drawback also consists of a revolving drum and a wire rope which is known as a drilling line which is wrapped around it. A cat shaft on the drawback is used to mount catheads, which is also another component of the drawback. Because of the tough operation and rotating function of the hoisting system there must be a means of reducing friction and this is assisted by a spool shaped device known as a friction cathead. While drilling two types of friction catheads can be used in both ends of the drawback. The friction catheads are meant to make or break the drilling string while it is inserted in the hole. In addition to this, the other mechanical cathead an also be used when the length of the drilling pipe is being extended during the drilling process. The following figure shows the components of a hoisting system Figure 2: Hoisting system From the figure, we can see that the drilling lines are thin and the reason for their thinness is for efficiency. Generally most of the drilling lines measure about one and one eight inches and one and half inches in diameter. Wire ropes can be used in place of a drilling lines but this is discourages since most of them are made up of steel hence complex for this work. However, adjustments can be made to ensure that wire ropes arrive at the rig in a wrapped form on a large supply reel. Installation of the drilling begins with taking one end to the top of the derrick where a large multiple pulley is normally located. The large set of pulley is therefore identified as the crown back as can be seen from figure 2 above while the collection of the pulley is known as sheaves. The travelling block, which rests on the rig floor, consists of large sets of pulleys and sheaves. Fastline is a part of the drilling line, which comes out of the draw work directly to the crown block when the travelling block is raised or lowered using the derrick. The other end of this line is known as a deadline since it is considered secure. It is secure because it runs from the wire rope to the supply reel hence considered very secure. Another reason why it is considered is because it does not move and it is mounted on the rig substructure by deadline anchor. Circulating system During the drilling process, rocks and other cuttings are formed and this need to be removed hence the function of the fluid circulating system. The fluid as commonly known is made up of a clay suspension and water forming a drilling mud. During the drilling process, the mud travels from the steel tanks to the pump. From the pump, the mud is forced through high-pressure surface connections to the drill string. From here, the mud flows slowly to the drill bit. The bit contains nozzles that release the mud as it drills. The mud also performs a function of cooling off the bit as it drills and this helps in reducing friction. However, if the mud is left to accumulate on the drill it may hinder the drilling process and therefore needs to be recycled. Because of it expensive nature, the drilling mud must be circulated back to the steel tanks and therefore from the nozzles of the drill it passes through the annular spaces and back to the drillstring and hole to the surface. Before heading back to the tank, impurities, and other substances must be removed hence a contaminant removal is necessary at this stage. From here, the mud goes to the suction tank. The major and principal components of a rig circulating system includes mud pumps, mud pits, mud mixing equipment and contaminant removal equipment as already discussed above. The following image shows a circulating system of a rig Figure 3: Circulating system of a rig Duplex and triplex cylinders are common in most circulatory systems as they are used in reciprocating positive displacements pistons in the mud pumps. Pumping strokes in a back and forth direction is a mechanism that is mostly utilized by the duplex pumps. However, looking at the functionality and mechanisms applied by the triplex pumps it is worth noting that these pumps are more compact since their output pressure pulsation is not so much while they are also so cheap to operate compared to the duplex pumps. A close looks at the majority of the pumps contain triplex pump design. In addition to this, the triplex pump has the advantage of moving high solids content fluids lade with abrasives in addition to pumping larger particles. As already indicated these pumps are simple to operate and maintain since they are cheaper hence very reliable. Another distinct advantage of triplex pump is that it is able to operate wider rangers of pressure and flow rates by involving changes in the diameters of the pump liners and pistons. Components of a rig circulating system From figure 3 it is evident that the rig circulating system consists of many items. To begin with, the standpipe receives discharges of the mud picked from the mud pump in the mud pits through a discharge line. The standpipe is usually located vertically on the derrick on one leg mast. From the standpipe the mud is usually deposited into a flexible and strong reinforced rubber hose known as the rotary hose or Kelly hose which is connected to another component known as the swivel. The swivel receives mud from the Kelly and directs the mud through the drill pipe and collars to the drill bit. From here the mud heads back to the annulus after taking a very sharp U-turn. A space found between the outer side of the drill and the wall of the hole is what we are referring to as the annulus. The steel pipe will eventually led back the pump to the shale shaker which is a vibrating screen like device. Using agitators, which helps in, maintain a proper mix of the liquids and solid in the mud, the mud is recycled. During the drilling process, if many silt and sands are drilled a de-silter or de-sander is added in order to reduce the concentration of sand and silt in the mud. It is important to notice that the quality of the mud is very important since its efficiency is equal to the volumetric efficiency of component drilled. The product of a volumetric and mechanical efficiency is the overall efficiency of a mud-circulating pump. In mechanical engineering, mechanical efficiency of the pumps is assumed to be 90% and its relative efficiency with linkages to the pump drive shaft. However, volumetric efficiency is always at 100% hence Em, of 90% and a volumetric efficiency, Ev,of 100%. In most cases, two circulating pumps are mounted on the rig. Deeper wells are always worked on using one rig while shallow wells can comprise of both pumps operating parallel to each other in order to deliver larger portions of flow rates that is necessary. Drilling pipes are also measured in terms of their diameter, weight per foot, their length, and the steel grade. The second range of drilling pipe, which measures about 27-30 feet in length, is the most common. It is length on each joint is usually accurately measured and recorded while finding out the total depth of the well while conducting drilling operations. The joints of the drill pipes are usually enclosed on the tool joints using the drill strings. Rotary System All big equipment’s used during drilling in a drill rig to obtain a big rotation is what is referred to as a rotary system. Major components of the rotary system include a swivel, Kelly, rotary drive, rotary table, drill pipe and the dip collars. Some of these parts have already been discussed in our sub topics above in this paper. Without the swivel, a drilling rig cannot obtain support and weigh for rotation since the swivel is responsible for holding stings, which assists in rotation. The swivel supports itself on a bail, which is attached by a hook to the travelling block. The swivel contains a gooseneck which offers a downward pointing connection to the rotary hose. Engineers categorize swivels on their ability to support weight and on their load and carrying capacity. The following image shows a rotary system of a rig Figure 4: Rotary System of a Rig The Kelly is usually hexagonal or square in shape to assist in giving a firm grip for turning since. The Kelly also consists bushes, which helps in avoiding friction and are rubber in nature. The bushes fit into master bushing and they help in transmitting torque to the Kelly during operations. During this time it is very important that the Kelly remains as straight as possible for maximum efficiency and also to avoid destruction of bush components. However, this is avoided further as the Kelly saver sub is placed between the Kelly and the first joint of the drilling pipe. Engineers and other operators dealing with this system must permit enough space for passage of the largest bit within the rotary table that accepts Kelly bushings. The drilling pipe is also identified in terms of male and female. The male part is known as the box while the female part is the pin. The female part is the one attached due to its thicker wall (upset) compared to the rest of the drill pipe and this is meant to provide a stronger joint. Drill collars form the lower parts of the rotary drill as can be seen from our figure 4 above. The walls of the collars are also thick and made of heavy steel tubular meant to increase the weight of to the bit. This weight is important during drilling as it applies the necessary force to the ground. A small distance is normally left between the borehole and the drill collars, which assists in efficiency of the drill as well as maintaining the collar as straight as possible. Subs in form of stabilizers an also be applied in order to keep the drill collars in a centralized manner. Well control systems The well control system helps in detecting the kick, closing the well at the surface in addition to rotting the well to remove the formation fluids under a pressure while increasing the mud density. The rotation of the drill under the pressure is also a function of the control system in addition to diverting the flow away from the personnel and equipment to avoid spillage and spillage. Well control system is a component of the drilling rig and it is necessary for preventing the uncontrolled flow of formation fluids from reaching the well bore. Cases of the formation fluid displacing the drilling fluid are usually common while drilling. This is because the bit penetrates a permeable formation, which contains fluid pressure in excess. When formation fluids flow and fill the drilling fluid, we call it a kick. If the control system fails to control, fluid formation there will be a blowout. This has happened over several occasions and resulted to a lot of oil spillage in the ocean leading to huge losses. For example, in January 2000 a failure of the gas gasket on the interface detector resulted to approximately 100 barrels of jet fuel in Virginia. Escravo spill of 300,000 barrels in 1978, SPDC Forcados terminal tank failure in 1978 leading to a spill effect of 580, 000 barrels, Texaco Funiwa -5 in 1980 leading to spills of 400,000 barrels and many others. The control system is therefore more important especially in controlling environmental damage. However, due to safety concerns engineers have come up with annular preventers that stop flow from the well with the help of synthetic rubber springs, which helps in contracting the fluid passage. The preventers can handle and prevent pressures of up to 10,000 psi. During certain situations the rubber packing may fail to take the shape of the hole leading to the hydraulic system of the ram an annular failure. However, a screw that locks the device in place is used as a precautionary measure that encloses the system just in case the annular preventers fail in their functioning. This is also closely monitored using computers and a close change in pressure is easily detected and corrected. Well Monitoring system Monitoring a drilling rig is the most technical and automated bit of drilling especially in oil wells since they are considered more dangerous and have many detrimental effects. Computer systems have been installed with software to detect parameters such as the depth of drilling, penetration rate. The hook load is monitored while the rotary speed is also checked. Rotations from the rotary speed, torques and pumping rate are also monitored. Pumping pressure and the mud density is checked in order to increase the efficiency of drilling. Other factors such as mud density, salinity, and temperature must also be monitored since this can easily lead to explosions if not well regulated. The accumulation of gas content, which is normally toxic, should also be monitored while the pit level and flow rate should also be checked to avoid further damages. Worked examples Example 1 Oil flows at the rate of 3 l/s through a pipe of 50 mm diameter. The pressure difference across a length of 15 m of the pipe is 6 kPa. Determine the viscosity of oil flowing through the pipe. Using Hagen-Poiesuille equation-1.8.5 , ΔP = (32 μuL)/d2 u = Q/(πd2/4) = 3 × 10–3/(π × 0.052/4) = 1.53 m/s μ = Δ P × d2/32uL = (6000 × 0.052)/(32 × 1.53 × 15) = 0.0204 Ns m2 Example 2 Determine the power required to run a 300 mm dia shaft at 400 rpm in journals with uniform oil thickness of 1 mm. Two bearings of 300 mm width are used to support the shaft. The dynamic viscosity of oil is 0.03 Pas. (Pas = (N/m2) × s). Shear stress on the shaft surface = τ = μ (du/dy) = μ(u/y) u = π DN/60 = π × 0.3 × 400/60 = 6.28 m/s τ = 0.03 {(6.28 – 0)/ 0.001} = 188.4 N/m2 Surface area of the two bearings, A = 2 π DL Force on shaft surface = τ × A = 188.4 × (2 × π × 0.3 × 0.3) = 106.6 N Torque = 106.6 × 0.15 = 15.995 Nm Power required = 2 π NT/60 = 2 × π × 400 × 15.995/60 = 670 W. (check using eqn. 1.9.2, P = μ π3 N2LR3/450 h = 669.74 W) Example 3 Determine the oil film thickness A single acting reciprocating water pump of 180 mm bore and 240 mm stroke operates at 40 rpm. Determine the discharge if the slip is 8%. What is the value of coefficient of discharge. If the suction and delivery heads are 6 m and 20 m respectively determine the theoretical power. If the overall efficiency was 80%, what is the power requirement. Theoretical discharge = A L N60= π × × × 01840 244060. 2. = 4.0775 × 10– 3 m3/s = 4.0715 l/s = 4.0715 kg/s Slip = 8% ∴ Actual flow = 4.0715 ×92100= 3.746 l/s or kg/s Coefficient of discharge =3 746 4 0715..= 0.92 Theoretical power = mgH = 3.746 × 9.81 × 26 = 955.45 W Actual Power = 955.45/0.8 = 1194.3 W or 1.1943 kW References Roughnecks. Rock Bits And Rigs: The Evolution Of Oil Well Drilling Technology In Alberta, 1883-1970 By Sandy Gow,. New York: University of Calgary Press, 2005. Read More

The following figure shows the components of a hoisting system Figure 2: Hoisting system From the figure, we can see that the drilling lines are thin and the reason for their thinness is for efficiency. Generally most of the drilling lines measure about one and one eight inches and one and half inches in diameter. Wire ropes can be used in place of a drilling lines but this is discourages since most of them are made up of steel hence complex for this work. However, adjustments can be made to ensure that wire ropes arrive at the rig in a wrapped form on a large supply reel.

Installation of the drilling begins with taking one end to the top of the derrick where a large multiple pulley is normally located. The large set of pulley is therefore identified as the crown back as can be seen from figure 2 above while the collection of the pulley is known as sheaves. The travelling block, which rests on the rig floor, consists of large sets of pulleys and sheaves. Fastline is a part of the drilling line, which comes out of the draw work directly to the crown block when the travelling block is raised or lowered using the derrick.

The other end of this line is known as a deadline since it is considered secure. It is secure because it runs from the wire rope to the supply reel hence considered very secure. Another reason why it is considered is because it does not move and it is mounted on the rig substructure by deadline anchor. Circulating system During the drilling process, rocks and other cuttings are formed and this need to be removed hence the function of the fluid circulating system. The fluid as commonly known is made up of a clay suspension and water forming a drilling mud.

During the drilling process, the mud travels from the steel tanks to the pump. From the pump, the mud is forced through high-pressure surface connections to the drill string. From here, the mud flows slowly to the drill bit. The bit contains nozzles that release the mud as it drills. The mud also performs a function of cooling off the bit as it drills and this helps in reducing friction. However, if the mud is left to accumulate on the drill it may hinder the drilling process and therefore needs to be recycled.

Because of it expensive nature, the drilling mud must be circulated back to the steel tanks and therefore from the nozzles of the drill it passes through the annular spaces and back to the drillstring and hole to the surface. Before heading back to the tank, impurities, and other substances must be removed hence a contaminant removal is necessary at this stage. From here, the mud goes to the suction tank. The major and principal components of a rig circulating system includes mud pumps, mud pits, mud mixing equipment and contaminant removal equipment as already discussed above.

The following image shows a circulating system of a rig Figure 3: Circulating system of a rig Duplex and triplex cylinders are common in most circulatory systems as they are used in reciprocating positive displacements pistons in the mud pumps. Pumping strokes in a back and forth direction is a mechanism that is mostly utilized by the duplex pumps. However, looking at the functionality and mechanisms applied by the triplex pumps it is worth noting that these pumps are more compact since their output pressure pulsation is not so much while they are also so cheap to operate compared to the duplex pumps.

A close looks at the majority of the pumps contain triplex pump design. In addition to this, the triplex pump has the advantage of moving high solids content fluids lade with abrasives in addition to pumping larger particles. As already indicated these pumps are simple to operate and maintain since they are cheaper hence very reliable. Another distinct advantage of triplex pump is that it is able to operate wider rangers of pressure and flow rates by involving changes in the diameters of the pump liners and pistons.

Components of a rig circulating system From figure 3 it is evident that the rig circulating system consists of many items.

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