Drilling out accessories differ from component to another related to the type of materiel used in these equipment. In most cases, the casing equipment are PDC drillable, that means they are made of plastic or rubber which make them easier to drill out. Liner accessories are generally made of brass or aluminum which can damage the bit when drilling out resulting in slower penetration rate when drilling the formation.
For drilling out, there are some steps which can be followed for safe operations:
- It has to be noticed that the impregnate bits take longer time than PDC bits to drill out casing accessories.
- Running with washing down at least for the last stand above the theoretical depth of the cement. use maximum possible flow rate.
- Try to tag bottom gently with maximum 2 Tons (4000 lbs) and look out for the nature of cement (green wet cement, medium or hard).
- Apply 50 to 60 rpm while drilling out equipment with PDC. When using the tri-cone bit, the rotation has to be chosen carefully.
- If there is no progress, avoid keeping the bit on bottom, reciprocate the drill string time to time. It is related to the operation to choose adequate pulling time intervals.
- In case of no progress, increasing the weight on bit should not exceed the recommended designed weight on bit of the used drilling bit (with safety factor).
- If the wiper plugs rotate when drilling out, it is necessary to pull out of bottom and tag it without rotation, increase weight to the recommended weight then start rotation till getting to the interval of 60-80 rpm
- This last procedure has to be repeated as necessary as possible till drilling out equipment
- Once the equipment are drilled out, pull out of bottom and circulate to remove the metals debris and junks from bottom.
- Reciprocate the floats intervals several time to avid mechanical stuck pipe when stabilizers pass through them.
- Avoid ceasing the circulation when drilling out equipment.
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| Fig 1- Drilling Bits |
Drilling New Formation
Any drill bit has its designed operating parameters which are chosen for each type of formation, but using these full parameters have to be applied with some guidelines.
- The bottom has to be tagged with maximum flow rate
- Tag bottom gently and start drilling off with 50-60 rpm and no more than 3-4 Tons (6000-8000 lbs)
- Avoid using high level of rotation till getting all the stabilizers out of the casing. This is applied to avoid disturbing cement around the casing shoe which can lead to mechanical stuck pipe with cement junk.
- If no progress is noticed, the weight on bit can be increased gradually without exceeding the recommended parameter.
- It is recommended to use moderate weight on bit till drilling at least the length of the drill bit to have a homogeneous weight on cutters. Overloading cutters can generate premature damage and consequently slow penetration rate.
- Prior to make a connection, it is recommended to keep full flow rate when pulling out of bottom
- After making a connection, start circulating with maximum recommended flow rate, then tag bottom with reduced rotation and weight on bit
- Avoid dropping the string on bottom to do not damage the cutters structures.
- Increase weight to the optimum level, then increase the rotation to the target RPM.
Reaming through open hole
When running a new drilling bit in the hole, the drilling crew tends to running as fast as possible to come back to drilling operations. This behavior can result in damaging the drilling bit, for this reason some precautions have to be followed to avoid such issues:
- Run the drilling bit carefully through diverters, BOPs, well heads and casing shoes.
- Run slowly through the tight spot to avoid damaging the bit cutter structures
- While reaming the tight spots, the flow rate has to be as maximum as possible taking in considerations the problem of washing the formation out.
- Use moderate rotation when reaming around 50 to 60 rpm and monitor the torque closely
- Do not continue reaming the next tight spot till getting steady torque. Leaving tight spot without working on them can lead to mechanical stuck pipe in the next pull out of the hole
- Wash down the two last stands with maximum flow rate and moderate rotation to avoid plugging the nozzles or balling the bit.
- After tagging the bottom, it has to be circulated at least for 5 minutes to clean it.
General Guidelines for Homogeneous Formations
This type of formation is rare because the drilled formation are not homogeneous and they are inter-bedded, but it can be some general rules to be applied when drilling in such cases.
Drilling clean shales can be performed with high RPM. Increasing RPM has more effect than increasing weight on bit on ROP. Drilling through chalk and limestones can be maximized by increasing the weight on bit to fracture the formation. This weight on bit increase has to be combined with moderate rotating. Drilling bit can suffer from abrasive wear when drilling through sandstones. Penetration rate can be maximized by increasing both rotation and weight on bit, but it has to be well monitored to avoid premature damage for the bit by reducing parameters to reasonable level.
NB: Get more information related to drilling and reaming in articles referred below
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