Under gauge Hole
Under gauge hole may also be caused by a plastic formation. After being penetrated by the Drilling Bit with a fluid giving a hydro static pressure less than the overburden, which is the usual pressure of the plastic formation, this formation deforms causing the hole to close. One of the formations which most often causes such a situation is moving salt.
The only preventive measure is to use a drilling fluid dense enough to give overburden pressure at the depth of the salt. This will usually be impossible due to the risk of creating fractures elsewhere in the hole. In that case the drilling fluid density should be kept as high as feasible as the flow rate of the salt is proportional to the pressure difference. If the Drill String become Stuck the solution (!) is simple – a pill of fresh water. If this is done the effect of introducing a light fluid on well control aspects has to be taken into account. But here we will talk about the under gauge hole caused mechanically.
So we can summarize when the under gauge hole happens into simple points.
- After using a new Drilling Bit.
- Coring is one method of collecting rock and sediment samples for geological research. Some coring heads are often slightly smaller than bit sizes and will produce under gauge hole so reaming is preferred for the cored sections.
- When changing bits from Roller Cone Bit To PDC Bit in the same section.
- When drilling hard abrasive rocks. The wearing speed of the drilling bit will increase and will lead to drill with worn less diameter drilling bit. So It is a good practice to check your Bit Dullness after POOH.
- By plastic formations (we will not talk about this for now)
Preventative Action To Avoid Under Gauge Hole Stuck Pipe Type.
- Choose the suitably gauge-protected Drilling Bits and Stabilizer according to the formation will be drilled.
- Think about roller reamers. You can check the effect of using under reamer to have in gauge hole case study.
- Always gauge all Bottom Hole Assembly BHA components before RIH and after POOH.
- Ream suspected under gauge sections.
- Tripping Pipe in slowly before the Bottom Hole Assembly BHA enters an under gauge section.
What Is The Indications For Under Gauge Stuck Pipe ?
- As its reason is the under gauge of Drilling Bits and Stabilizers so first thing will be the pulled Drilling Bit or Stabilizers are under gauge.
- And as it will happen after RIH with new in gauge Drilling Bit so the second indicator will be when RIH.
- Sudden set-down weight.
- Circulation is unrestricted or slightly restricted.
- As the under gauge hole may happen after coring operations so Drilling Bit may Stuck at the top of a cored section.