Drill collars

For offshore drilling operations the drill collars given in Table 4.1 will be used.

Table 5.1 Drill collars

OD (“) Body style Connection

9½ 8 6½ 43/4 31/8 Spiral Grooved Spiral Grooved Spiral Grooved Spiral Grooved Flush 7 5/8 Reg 6 5/8 Reg 4 IF NC 35 2 7/8 PAC

• The rotary shouldered pin connections shall all have an API stress-relief groove. The box thread connections shall be provided with a Drilco bore back stress relief groove.

• The spiral grooving (Sine k profile) of the drill collar bodies is a great feature to reduce differential wall sticking.

• For the recommended make up tongue for drill collar connections refer to API torque specifications. These values are the minimum requirements.

• The threads of drill collars not in use must always be equipped with proper steel thread protectors to prevent damaging.

Length of drill collars

The required collar length to achieve maximum desired bit weight can be calculated as follows:

Ldc = Bitwm

(cos of angle) (NP) (BF) (Wc)

where:

Ldc = required collar length, (m) to achieve the maximum bit weight

Bitwm = maximum bit weight, (TONNE)

BF = buoyancy factor, dimensionless Wc = collar weight (in-air),(kg/m)

cos of angle = hole angle from vertical (1 for vertical) NP = neutral point design factor (0.85)

Operators usually run 10-15% more collars than Actual Bit Weight (ABW) would indicate. This gives a safety margin and keeps the buoyancy neutral point within the collars when unforeseen forces move the buckling point up into the weaker drillpipe section.

Adequate collar weight should be available to run 2.0 - 2.5T per inch of bit diameter on bits larger than 61/4” and 1.5 - 1.6T per inch of bit diameter on bits smaller than 6

1

/4”.

Bottomhole assemblies must be designed to compensate for hole inclination. The most effective drill collar force that can be applied to the weight-on-bit is equal to the true buoyant force corrected by the cosine of the hole angle.

Picking up drill collars

Cast steel thread protectors provide a means of dragging the collar into the "V" door and protecting the shoulders and threads. The pin protector must also be left in place to avoid damage to pin threads as the collar is pulled up the ramp into the V-door.

A good grade of drill collar lubricant containing 60% finely powdered metallic lead or 40 to 60% finely powdered metallic zinc should be applied to the threads and shoulders.

Lift subpins should be cleaned, inspected, and lubricated on each trip. If these pins have been damaged and go unnoticed, they will eventually damage all of the drill collar boxes.

Make up of new drill collars

The following should be considered when making up new drill collars:

• A new joint should be very carefully lubricated. Any metal to metal contact may cause a gall.

• Make up hand tight using chain tongs.

• Make up to proper torque with rig tongs.

• Break out connection and inspect for minor damage, or lack of dope adhesion to threads.

• Re-lubricate.

• Make up to proper torque.

Torque control

Use the make up torque recommended for the specific joint size, outside diameter, and bore of collars.

• Torque is the measure of the amount of twist applied to two members as they are screwed together. The product of the tong arm length in metres and the line pull in newton’s is newton metres of torque.

• With a 4ft tong arm and 5 000 lb.line pull at the end of the tong, TORQUE = 4ft x 5 000 lb = 20 000 ft/lbs

• A line-pull measuring device (or torque measuring instrument) should be used in making up drill collars. It is important that line-pull be measured when the line is at right angle or 90 degrees to the tong handle.

• When applying line-pull to the tongs, apply a slow, steady pull rather than jerking the line.

• Drill collars larger than 7” diameter usually require a double-line pull. For example, a pulley at the tong handle is needed to obtain adequate line pull.

Refer to the Drilco Manual or equivalent for recommended makeup torque values for rotary

shouldered drill collar connections (various connection styles) and for commonly used drill collar OD and ID sizes and styles.

How to measure the required drill collar makeup torque:

The proper amount of makeup torque must be measured. There are two steps that must be worked out for all hook-ups:

1. Look in the torque Tables and find the amount of makeup torque recommended for the size drill collars and type of connections.

2. Divide this amount by the number of metres in the effective length of the tong arm. This will give the total line pull at the end of the arm.

Rig maintenance of drill collars

• It is good practice to break different joints on each trip, giving the crew an opportunity to look at each pin and box every two or three trips. Inspect the shoulders for galls, and possible "wash-outs".

• Thread protectors should be used on both pin and box when laying the drill collars down.

Safety clamp (Dog Collar)

The safety clamp is required for handling collars over the hole. It is necessary that the nut is made-up carefully. When not in use, the clamp should be kept in a safe place, free from damage and corrosion.