Rotary Drilling System Components PDF

Rotary System The rotary system is the heart of the rotary drilling rig; its function involves transmitting rotating function to the drillstring and consequently the bit. including tension, compression, vibration, torsion, friction, formation pressure and circulating fluid pressure. It is also exp...

Rotary System The rotary system is the heart of the rotary drilling rig; its function involves transmitting rotating function to the drillstring and consequently the bit. including tension, compression, vibration, torsion, friction, formation pressure and circulating fluid pressure. It is also exposed to abrasive solids and corrosive fluids. environment, but it must be lightweight and manageable enough to be efficiently handled within the limits of the rig's hoisting system. At the same time, it must: provide weight to the bit; allow control over wellbore deviation; and help ensure that the hole stays "in gauge". The main parts of the rotary system (or the drill string) are: 1. Swivel 2. Kelley 3. Rotary table 4. Drill pipe 5. Drill collars 6. Heavy wall drill pipe 7. Stabilizer 8. Rotary reamers Note: Drillstem = Kelly + drillpipe + drill collar + bit Drillstring = Drillpipe + drill collar + bit Note: the bottom hole assembly (BHA) is that portion of the drill string between the drill pipe and the drill bit. Swivel The rotary swivel connects the circulating system to the rotary system while providing a fluid seal that must absorb rotational wear while holding pressure. The swivel is hung under the traveling block and directly above the Kelley. It provides the ability for the Kelly to rotate while the traveling block to remain in a stationary rotational position while simultaneously allowing the introduction of drilling fluid into the drill string. Kelley The Kelley is of square or hexagonal cross-section that screws into the drillstring while providing a flat surface for applying torque to rotate the pipe. The main function of a Kelly is to transfer energy from the rotary table to the rest of the drill string. Top-end is connected to swivel while the bottom is to rotary table. Rotary Table and Master Bushing The rotary table has two main functions:  To rotate the kelly and hence the drillstring  To support the weight of the drillstring when it is not supported by the hoisting system. The table consists of a disc which is located in the middle of the drilling rig floor. It is being driven from an electric motor connected via a gear box to the rotary table. The centre of the rotary table is a hole which accommodates a master bushing that the kelly bushing is fitted. The rotation of the table transmits the motion to the kelly and drill string. Top Drive Drilling Now day modem rigs have rotation and circulation hydraulically powered device “Top Drive” which is basically a combined rotary table and Kelly. The top drive consists of a DC drive motor that moves in a track along the derrick and connects directly to the drillstring without the need to a rotary table. The top drive is mounted on the rig's swivel, the swivel attaches to the travelling block and supports the drillstring weight. Top Drive features: 1. Replaced Kelly and Kelly bushing and it rotates the string. It is an alternative to the rotary table and Kelly drive. 2. Drilling to be carried out stand by stand instead. A rotary table type rig can only drill 30’ sections of drill pipe while a top drive can drill 90-feet drillpipe. Therefore, there are fewer connections of drill pipe and hence improving time efficiency. 3. Top drive is not removed during trips.  Top Drive system Rotary Table drive system Compression between Kelly Drive System and Top Drives System: Kelly Drive System Top Drive System Rotary table provide rotation. String is rotated with TDS motor Cheaper , slow , inefficient, unsafe. Expensive, Fast, efficient, safe. Kelly capable to drill with one TDS is capable to drill with drill pipe single drill pipe. stand. Take longer time to make Take less time to make connection. connection. TDS keep hanging all time with For tripping (RIH/POOH), Kelly travelling block& hook while must be rack back with swivel in rate tripping. hole on rig floor. TDS is new drive system. Kelly is old drive system. In TDS drill pipe are completely Kelly is not round pipe reduce life round, better for BOP element. of BOP rubber element. In case of TDS we need only mouse Kelly need two case hole on rig hole on rig floor. floor, Rate hole & mouse hole In Kelly crew have to operate TDS have hydraulic system to move elevator manually, less safety. links and elevator, more safety. In Kelly system, bit is off bottom In TDS bit almost on bottom, when equivalent to Kelly length when make new connection. connect another pipe for drilling. Drill pipe The longest portion of the drill string consists of connected lengths of drill pipe. The primary purposes of drill pipe are to provide length to the drill string and transmit rotational energy from the Kelly to the bottom hole assembly and the drill bit. The drill pipe connects the rig surface equipment with the bottom hole assembly and the bit, both to pump drilling fluid to the bit and to be able to raise, lower and rotate the bottom hole assembly and bit. Hole size, well depth, casing and cementing requirements, subsurface pressures, circulating system and drilling mud parameters, hoisting capacity, pipe availability and contract provisions are among the factors that influence drill pipe selection. The American Petroleum Institute (API) has established standards for drill pipe manufacturing practices, dimensions, strengths and performance properties. These standards appear in the following publications: The Minimum Yield Stress is referred to in the name of the grade; thus E75 grade steel has a Minimum Yield Stress of 75,000 psi, G105 has a Minimum Yield Stress of 105,000 psi. API-standard drill pipe is available in three length ranges: Range 1(18-22 ft), Range 2 (27-30 ft) and Range 3 (38-45 ft). Range 2 is the length most commonly used, making the "average" length of a drill pipe joint about 30 feet. Drill Collar The drill collars provide weight and stability to the drill bit, maintain tension on the drill pipe and help keep the hole on a straight course. Drill collars are thick-walled tubular pieces machined from solid bars of steel. The bars of steel are drilled from end to end to provide a passage to pumping drilling fluids through the collars. To accurately control the amount of force applied to the bit, the driller carefully monitors the surface weight measured while the bit is just off the bottom of the wellbore. Next, the drillstring (and the drill bit), is slowly and carefully lowered until it touches bottom. After that point, as the driller continues to lower the top of the drillstring, more and more weight is applied to the bit, and correspondingly less weight is measured as hanging at the surface. Downhole MWD sensors measure weight-on-bit more accurately and transmit the data to the surface. To avoid fatigue failures, the drill pipe and upper most drill collars need to be kept in tension at all times. Tension can be maintained by running an adequate number of collars in the bottomhole assembly to ensure that the neutral point (that is, the point below which the drill string is in compression, and above which it is in tension) will always be below the drill pipe Heavy Wall Drill Pipe Serves as an intermediate-weight drill string member between the drill pipe and the much heavier drill collars, thereby reducing fatigue failures, providing additional hole stability and aiding in directional control. The most important drill string application for heavy wall drill pipe is in the so- called zone of destruction — the area above the topmost drill collars where drill pipe fatigue failure is most likely to occur. To reduce fatigue failures in this area of the borehole, 18 to 21 joints of heavy wall drill pipe should be run above the drill collars. This provides a gradual change in stiffness between drill collars and drill pipe. Also, the ability of the heavy wall drill pipe to bend (unlike drill collars) serves to relieve high stresses at the connections. Heavy wall drill pipe was first used in directional drilling, which generally requires flexibility in the drill string. It is now widely used in vertical and horizontal drilling as well. With less wall contact than would be experienced with drill collars, its usage reduces torque and wall-sticking tendencies. Its smaller degree of wall contact, together with its greater stiffness relative to regular drill pipe, results in increased stability and better directional control. Heavy wall drill pipe is also useful in reducing hook loads, making it ideal for smaller rigs drilling deeper holes. Stabilizer Centralize the drill collars, help maintain the hole at full-gauge diameter and aid in directional control. Stabilizers, by centralizing the drill string at selected points in the borehole, can be used to: Ensure that the weight of the drill collars is concentrated on the bit; Reduce torque and bending stresses in the drill string; Prevent wall-sticking or key-seating of the drill collars; Maintain constant bit direction in straight-hole drilling. Reamer The Rotary Reamer is designed for various reams in drilling operation. In very hard formations, the outside cutting structure of a bit gradually wears away if it is not protected. This results in a hole diameter that becomes smaller with increasing depth. When a hole is severely undergauge, it is necessary to ream each new bit back to bottom before drilling can resume. This not only costs rig time and reduces bit life, but it increases the possibility of sticking the drill string. Other Rotary Components Hole openers: Used for drilling large diameter holes. They have replaceable cutters and serve the same function as an underreamer except they are not collapsible and can only be used when there is no restriction smaller than the hole size they drill. Shock sub (Vibration Dampener) A shock sub is normally located above the bit to reduce the stress due to bouncing when the bit is drilling through hard rock. The shock sub absorbs the vertical vibration either by using a strong steel spring, or a resilient rubber element. JARS: The purpose of these tools is to deliver a sharp blow to free the pipe if it becomes stuck in the hole. Hydraulic jars are activated by a straight pull and give an upward blow. Mechanical jars are preset at surface to operate when a given compression load is applied and give a downward blow. Jars are usually positioned at the top of the drill collars. Axial Tension/Compression Stress The largest tension load exists at the top of the drill- string because of the weight of the drill collars, stabilizers, drill-pipe, and other string components. The bottom of the string is subjected to axial compressive force because of the hydrostatic pressure acting at the bottom of the pipe.