Drill string
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The document discusses the components and functions of a drill string. It describes the main components as the kelly, drill pipe, drill collars, and drilling bit. It explains the drill string provides functions like imposing weight on the bit, transmitting rotation, providing a fluid conduit, and allowing tools to be run in the hole. It also discusses calculating the neutral point where there is no compression or tension in the pipe, using factors like weight on bit, pipe weight, mud density, and differential pressure. The document concludes by covering selection considerations for drill pipes based on tension loading, collapse resistance, and torsional strength needed for deviated holes.
Drill string
- 1. DRILL STRING by: Jarugula Bhavya Sri (14008012) 1 Department of Petroleum Engineering KL University , Guntur
- 2. Introduction • The drill string constitutes the connection between the rig and the drill bit. • The main components of the drill string are: (1) kelly (2) drill pipe (3) drill collar and (4) drilling bit • heavy-weight drill pipe, jars, stabilizers, reamers and various subs (kelly sub, bit sub, shock sub, cross-over sub, etc.) 2Department of Petroleum Engineering ,KL University , Guntur
- 3. The drill string provides multiple functions like: 1. Imposes required weight on the bit 2. Transmits rotary motion from the kelly to the drill bit 3. Provides a two way fluid conduit from the rig to the drill bit 4. Medium to lower and raise the drill bit in the hole 5. Stabilizes the bottom hole assembly (BHA) and minimizes vibrations 6. Permits pressure and formation fluid testing through the drill string 7. Allows through-pipe running of formation evaluation tools when they can not be run in the open hole 3 Department of Petroleum Engineering ,KL University , Guntur
- 4. Neutral point • The neutral point occurs a at the depth where there is no compression or tension in the pipe. You can calculate it dividing the flotation force by the nominal weight per foot of pipe. • Long slender columns like DP, have low resistance to bending and tend to fail by buckling if -Force at bottom causes neutral point to move up. 4 Department of Petroleum Engineering ,KL University , Guntur
- 5. Calculation Of Neutral point • Total length of the drill string is under tension due to its own weight(partly counterbalanced by the buoyancy). • Part of destruction force is obtained by a certain amount of weight on bit (WOB) which forces the bit against the rock. • lower part of the drill string is set under compression. • Due to the geometrical shape of the drill string (length/diameter ratio), it has a tendency to buckle. To reduce this buckling tendency, it is aimed to design the drill string in such a way that the neutral point is located inside drilling collars Department of Petroleum Engineering ,KL University , Guntur 5
- 6. Department of Petroleum Engineering ,KL University , Guntur 6
- 7. The neutral point can be calculated for different scenarios as: • In the absence of mud (drilling with air as drilling fluid): Ln =WOB/12.Ws • In the presence of drilling mud: Ln =WOB/12. (Ws − ρs.As) • When differential pressure is considered as well, the neutral point is found at: Ln =WOB/12. (Ws − ρe.Ae + ρi.Ai) Department of Petroleum Engineering ,KL University , Guntur 7
- 8. 8 Department of Petroleum Engineering ,KL University , Guntur
- 9. Selection Of Drill Pipes • Generally subjected to 3 types of loadings. (1)Tension Loading : If the drill string is to consist of more than one size the pipe having the lowest capacity should be placed just above the drill collars Department of Petroleum Engineering ,KL University , Guntur 9
- 10. (2) Collapse Loading: An external pressure which is greater than the internal pressure resulting in collapse of drill pipe . 10 Department of Petroleum Engineering ,KL University , Guntur
- 11. (3) Torsional Strength: It is critical when drilling in deviated holes, deep holes, reaming or when the pipe is stuck. • T=(725.4*HP)/RPM Where, T=torque applied on drill pipe(kg-m). HP=horse power used to rotate the pipe. RPM=revolutions per minute. Department of Petroleum Engineering ,KL University , Guntur 11
- 12. ANY QUERIES…? Department of Petroleum Engineering ,KL University , Guntur 12