Reaming & Backreaming Guidelines
Reaming is a high risk operation that accounts for a large proportion of stuck pipe incidents. If reaming operations are conducted too fast, solids from wash-outs and cavings are introduced into the circulating system faster than the hole is being cleaned. This results in a drilling pack off. Do not assume that any resistance is always at the drilling bit; stabilizers and drill collar contact may be indicative of a build up of loose material in the hole and a potential pack-off situation. The
following guidelines are offered as a general list.
Planning For Reaming Operations
- Have a contingency plan for all possible problems. E.g., what to do in case of a leaking swivel packing or leaking saver sub.
- Always pre-plan a trip (check also tripping pipe procedures). Have an up-to-date mud log on the rig floor. Know where high doglegs exist and note troublesome areas from past trips. Utilize the mud loggers’ (Mud logger Job Description) paper model of the BHA and well bore previously mentioned.
- Have singles in the V-door if a downward motion is required to free the pipe after a connection.
- The shakers must be monitored continuously and the volume of solids being removed from the well bore should be recorded.
- While drilling or reaming in problem formations have two people at the console: one man on the brake and the other on the pumps.
- Ensure that the driller (Check also Driller Job Descriptions) knows what actions to take in the event of problems. Are overpull limits, freeing procedures and reaming practices understood? Are written instructions for the driller prepared and updated regularly?
- Mud loggers will record all parameters. Significant changes in trends should be reported immediately to the driller and rig drilling supervisor, then investigated.
Reaming Parameters Used In Drilling
- Use consistent parameters for reaming operations. This assists in identification of changes in torque and pressure trends.
- Any indication of changes in parameters should be addressed immediately. Most drag problems can be reduced by time spent circulating the hole clean.
- An increase in drag, torque or pressure may indicate that the annulus is loaded up, and a pack-off may be forming. Circulate and clean the well bore before continuing reaming.
- If indications of a pack-off Stuck Pipe occur, immediately reduce the pump strokes (e.g. by half ) to reduce the pistoning effect. If, after several minutes the hole does not pack-off, return to the original parameters and be prepared to circulate the hole clean.
- Reaming speed and circulation time should be adjusted if the returning cuttings’ volume rate is excessive.
- If torque becomes erratic or any of the following occurs: a) The rotary is stalling out. b) The cave-in rate increases. c) Torque and pressure readings are increasing, then be prepared to stop, circulate and clean up the hole.
- Prior to heavy reaming, slow rotation (less than 80) should be used in an attempt to “walk” the pipe past ledges.
- Reaming operations should be conducted with the same flow rate as drilling.
- Reaming weight and speed should be kept low (less than 10 – 15 k lbs either up or down). This reduces the chance of sidetracking (check also: sidetrack Drilling) the well and is less damaging to the drill string.
- Control the speed of reaming operations (4 stands an hour can be used as a rule of thumb for the maximum speed). This should also reduce the mechanical damage the drill string does to the well bore.
- Large volumes of settled cuttings or new cavings can be introduced to the hole when reaming. It is critical that this material is circulated out of the hole.
- If the hole packs-off, immediately shut down the pumps and slowly bleed the pressure under the pack-off down to less than 500 psi.
- While reaming in problem formations the hole may need to be wiped at regular intervals, if conditions require it.
- Do not use the Soft Torque while reaming as it may disguise torque trends.
- Make sure the pipe is free before setting the slips.
- After drilling or reaming down, the cuttings should be circulated above the BHA prior to picking up.
- The preferred practice is to always try to work the string past a tight spot as a first option. However, overpull limits must be known and used. Work up to the overpull limit in stages ensuring free movement in the other direction at each stage.
- Limiting overpulls to half the BHA weight has proven to be a successful strategy in avoiding stuck pipe.
- If the top drive stalls out during reaming operations there is a great deal of stored energy in the torqued up drill string, always release this torque slowly.
- When back-reaming do not overpull the pipe into the slips to connect the top drive.
- When washing in, with a drilling mud motor in the BHA, rotate the whole drill string at low rpm.