Some of the standard drilling tools commonly used in drilling are briefly described here, together with procedures for, and information on, their use. More detailed descriptions and specifications of particular tools are to be found in the relevant manufacturer's literature.
1. Float Sub
Float subs are always used when drilling pilot holes, and can also be used when drilling 36", 26" (or 22"), and 17 1/2" (or 16") hole sections.
When using float subs, the following procedures shall be carried out:
1. When running in hole, break circulation as soon as all the drill collars and one stand of drill pipe are in the hole. This checks the correct operation of the float sub.
2. Fill up the drill pipe every ten stands.
3. Run in slowly and carefully to avoid excessive surging as the drill pipe has effectively a closed end.
2 Circulating Sub
Circulating subs can be used when drilling 12 1/4" or smaller holes, and are used for circulating lost circulation material and for pumping cement in an emergency when the nozzles in the bit are plugged, or considered to be too small; (i.e. less than 16/32"). Circulating subs can also be used in connection with downhole motors to avoid tripping wet pipe.
Note: Normally, circulating subs are not used when survey barrels are to be dropped, because of the possibility of the barrel shifting the sleeve. If a survey is required, run the instrument barrel on a slick line, so that it passes through the circulating sub in a controlled manner.
When using circulating subs the following procedures apply:
1. Always ensure that it is possible to pass the ball (used to shift the sleeve and open the circulation ports) through the drill string, the drop-in sub and the drilling jars.
2. To establish circulation through the circulating sub, the ball is dropped in the drill string and pumped down. By applying pressure when the ball has seated, a pin will be sheared that consequently allows the sleeve to shift and hence open the circulation port(s).
3 Drop-In Check Valve
Drop-in check valves are used as a means for closing the drill string from well flow, by means of dropping (or pumping) a check valve down to its recess in the drop-in sub. It is different from an ordinary float valve in that it does not work as an check valve assembly until the Check Valve is set in the drop-in sub. It is used on all wells as soon as the BOP stack is in place. Drop-in subs are usually installed one or two singles above the drill collars.
Ensure that it is possible to pass the Check Valve (dart) through the kelly cock and if possible through the circulating head for kick control.
If both a circulating sub and a drop-in sub are used in the drill string, ensure that it is possible to pass the ball through the drop-in sub.
4 Kelly Cock
The right-hand kelly cock is used at all times when drilling (including diverter drilling). During mud motor drilling a second right-hand kelly cock is positioned one single below the kelly to allow the use of drill pipe screens. (Such screens should be of the retrievable type; i.e. with a wireline fishing neck).
There should be a spare kelly cock on the drill floor ready for use at all times.
5 Inside BOP
An inside BOP (Gray valve) is used when hanging off the drill string in the well head and is installed one single below the hang-off tool. It shall not be installed when the string is hung off with the bit in open hole, (so that wireline tools may be run). An inside BOP will also be used when stripping in pipe. It should always be available on the drill floor ready for use.
6 Junk Sub
Junk subs may be used when drilling out 9 5/8" and 7" casing shoes, and on the last roller bit run prior to drilling or coring with a diamond bit.
The main body diameter of a junk sub is relatively small, and it is not as rigid as a drill collar or stabiliser. Consequently its use can lead to hole angle or directional problems.
7 Fast Shut Off Coupling
Fast shut-off couplings are used for emergency shut-off purposes when running in or pulling out tubing, casing, or drill pipe. They are currently used by the Company in sizes to suit 3 ½" and 5" drill pipe. The fast shut-off coupling is designed to be dropped over the drill pipe with an open kelly cock attached. The coupling automatically latches under and seals off around the tool joint (or collar). The kelly cock can then be closed, to stop the flow through the string.
A fast shut-off coupling corresponding to the size of pipe in use with an open kelly cock made up on it shall be available on the drill floor at all times.
Note: Check that the seals are correct for the pipe size in use.
8 Safety Joint
A safety joint is used to provide a readily releasable connection in a wash-over string. The design should:
- allow transmission of full torque loads in the normal direction
- allow transmission of moderate torque loads in the reverse direction
- enable the safety joint to be broken with no more than half the torque required to break a normally made up tool joint of corresponding size.
9 Drilling Jars
Drilling jars should be used in all drilling assemblies of 17 ½" and smaller. In certain circumstances, consideration can also be given to using them in tophole sections.
The jars should be suitable to be run in compression, and have the same connections as the drill collars.
The intention in general is to place the jar just above that part of the assembly which is most likely to stick, and generally in top part of the drill collars assembly.
If the jar does not seem to be working, make sure that the overpull applied to the string is "worked down" to the jar. Another option that may be used is a surface jar.