Undergauge Hole In Drilling Problems & Consequences

Undergauge Hole in drilling is a miracle that means that the drilled hole periphery is lower than the used Drilling Bit periphery. It always happens after the Drilling Bit and the Stabilizers needles got worn while drilling abrasive gemstone, so the following section using the same Drilling Bit will produce lower periphery hole or under hand hole. And if it was decided to run new in hand Drilling Bit after that, it'll have difficulty to run in the last undergauge section and reaming will be needed to pass this undergaugesection.However, the Drilling Bit can jam in the undergauge hole and come Stuck, If it was decided to run snappily without reaming.

Undergauge hole may also be caused by a plastic conformation. After being entered by the Drilling Bit with a fluid giving a hydrostatic pressure lower than the overburden, which is the usual pressure of the plastic conformation, this conformation deforms causing the hole to close. One of the conformations which most frequently causes such a situation is moving swab.


The only preventative measure is to use a drilling fluid thick enough to give overburden pressure at the depth of the swab. This will generally be insolvable due to the threat of creating fractures away in the hole. In that case, the drilling fluid viscosity should be kept as high as doable as the inflow rate of the swab is commensurable to the pressure difference. If the Drill String becomes Stuck the result(!) is simple – a lozenge 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 then we will talk about the undergauge hole caused mechanically.

When Undergauge Hole Happens While Drilling

So we can epitomize when the undergauge hole happens into simple points.

*After using a new Drilling Bit.
*Coring is one system of collecting gemstone and deposition samples for geological exploration. Some coring heads are frequently slightly lower than bit sizes and will produce undergauge 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 jewels. The wearing speed of the drilling bit will increase and will lead to drill with worn lower periphery drilling bit. So It's a good practice to check your Bit Dull Grading after POOH.
*By plastic conformations( we won't talk about this for now)

Precautionary Action To Avoid Undergauge Hole

*Choose the suitably hand- defended Drilling Bits and Stabilizer according to the conformation will be drilled.
*Suppose about Roller Reamers. You can check The effect of using under reamer to have in hand hole case study.
*Always gauge all nethermost Hole Assembly BHA factors before RIH and after POOH.
*Ream suspected undergauge sections.
*Tripping Pipe in sluggishly before the Bottom Hole Assembly BHA enters an undergauge section.

What Is The suggestions For Undergauge Hole?

*As its reason is the undergauge of Drilling Bits and Drilling Stabilizers so first thing will be the pulled Drilling Bit or Stabilizers are undergauge.
*And as it'll be after RIH with new in hand Drilling Bit so the alternate index will be when RIH.
*unforeseen set-down weight.
*Rotation is unrestricted or slightly confined.
*As the under hand hole may be after coring operations so Drilling Bit may Stuck at the top of a cored section.

Freeing Procedure For Stuck Caused By Under Gauge Hole

*You can consider the following tips while freeing similar type of Stuck Pipe
*Jarring up with maximum trip cargo.
*Don't Jar down.
*Consider the use of an acid lozenge.
*Consider applying necklace as a last resort. But put in your considerations that Drill Pipe, Heavy Weight Drill Pipe HWDP yield strength will be affected with similar necklace and will be dropped.

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