LEARNING OBJECTIVES
Having worked through this chapter the student will be able to: General:
• Describe the basic components and the function of each component in the drillstring.
Drillpipe:
• Describe the components parts of a joint of drillpipe.
• Describe the way in which drillpipe is classified in terms of size, weight and grade
• Describe the stresses and wear mechanisms to which the drillstring is exposed.
• Describe the techniques used to inspect drillpipe and the worn pipe classification system.
Tooljoints:
• Describe a tooljoint and identify the major characteristics of a tooljoint HWDP:
• Describe HWDP
• Describe the reasons for running HWDP.
• Describe the reasons for using Drillcollars.
• Describe the loads to which Drillcollars are subjected.
• Describe the function of: conventional; Spiral; Square and Monel Drillcollars. BHA Components:
• Describe the function of: Stabilisers; Roller Reamers; Shock Subs; Subs; and Drilling Jars.
• Describe the ways in which the above are configured in the BHA.
• Calculate the dry weight and buoyant weight of the drillstring.
• Calculate the length of drillcollar required for a drilling operation.
• Calculate the Section Modulus of component parts of the drillstring.
The term drillstring is used to describe the tubulars and accessories on which the drillbit is run to the bottom of the borehole. The drillstring consists of drillpipe, drillcollars, the kelly and various other pieces of equipment such as stabilisers and reamers, which are included in the drillstring just above the drillbit (Figure 1). All of these components will be described in detail below. The drillcollars and the other equipment which is made up just above the bit are collectively called the Bottom Hole Assembly (BHA). The dimensions of a typical 10,000 ft drillstring would be :
Component Outside Diameter (in.) Length (ft)
Drillbit 12 1/4”
Drillcollars 9 1/2” 600
Drillpipe 5” 9400
The functions of the drillstring are:
• To suspend the bit
• To transmit rotary torque from the kelly to the bit
• To provide a conduit for circulating drilling fluid to the bit
It must be remembered that in deep wells the drillstring may be 5-6 miles long.
Kelly
Drill Pipe
CO
Q
Bottom Hole Assembly
Collars, Reamers; Stabilisers, Jars
Bit
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