Drilling Engineering – PE311 Rotary System

Introduction to Rotary System The main parts of the rotary system (or the drill string) are: 1. Swivel 2. Kelley 3. Rotary table 4. Drillpipe 5. Drill collars 6. Heavy wall drill pipe Stabilizer Rotary reamers Note: the bottomhole assembly (BHA) is that portion of the drill string between the drill pipe and the drill bit.  

Introduction to 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. As the drill string moves downhole, it is subjected to a variety of stresses, including tension, compression, vibration, torsion, friction, formation pressure and circulating fluid pressure. It is also exposed to abrasive solids and corrosive fluids. The drill string not only must be sturdy enough to withstand this hostile 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".

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.

Drillpipe 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 bottomhole assembly and the drill bit. The drillpipe connects the rig surface equipment with the bottomhole assembly and the bit, both to pump drilling fluid to the bit and to be able to raise, lower and rotate the bottomhole assembly and bit.

Drillpipe 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 has established standards for drill pipe manufacturing practices, dimensions, strengths and performance properties. These standards appear in the following publications: • API Spec 5D: This American Petroleum Institute (API) specification covers seamless steel drill pipe used in the oil and gas industry • API Bul 5C2, Bulletin on Performance Properties of Casing, Tubing and Drill Pipe; 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.

Drillpipe

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.

Drill Collar 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.

Drill Collar To avoid fatigue failures, the drill pipe and uppermost 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 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. http://www.halliburton.com/ps/default.aspx?navid=1736&pageid=4000&prodgrpid=PRG %3A%3AKRMJK0LPT