Two tools. One decision.
Two distinct tools, two distinct purposes - understanding the difference is the first step to choosing the right BHA configuration.
Side by side. Drag to explore.
Most people use the terms “hole openers” and “underreamers” interchangeably without knowing the difference. While both products are used to enlarge a pre-existing well bore, one is fixed diameter and the other is expandable. The type of application and certain parameters will tell you which tool to use. The biggest factor is what restrictions there are in the well bore.
Underreamer
Expandable blades. Opens below restrictions.
Diameter
Expandable - opens downhole
Best for
Enlarging below casing or restrictions
Run
Through the restriction, then expand
Restriction passing
Yes - collapsed OD passes through
| Attribute | Hole Opener | Underreamer |
|---|---|---|
| Diameter | Fixed - set by tool body and cutter gauge | Expandable - opens downhole |
| Best for | Top-hole enlargement, riserless intervals | Enlarging below casing or restrictions |
| Run | After or with the pilot bit | Through the restriction, then expand |
| Restriction passing | No - full gauge from surface | Yes - collapsed OD passes through |
Understanding the difference.
Knowing which to deploy can mean the difference between a clean, on-time job and unnecessary rig time.
Hole Opener
A hole opener is a fixed diameter tool that is commonly used in drilling larger top hole sections where there are no restrictions. Hole openers are used in all facets of drilling a well for actually enlarging the hole, to act as a stabilizer, or to use for a wiper trip (ensure hole is to gauge). Hole openers usually are run with roller cones but as the hole sizes get smaller, some people prefer to use a bladed hole opener which does not use roller cones. Most people consider a hole opener “dumb iron” because there are no moving parts, when in fact there is a considerable amount of engineering that goes into them. Although hole openers have not changed in appearance very much since their inception, the roller cone cutters have gone through many changes to increase the drilling life of the tool. HOC manufactures both custom roller cones and proprietary bodies under the Viper and RHO product lines.
- Fixed diameter, no moving parts
- Used in larger top hole sections without restrictions
- Enlarges the hole, acts as stabilizer, or wiper trip
- Roller Cone or Drag Type cutters
- Custom roller cones and proprietary bodies - Viper & RHO lines
Underreamer
Underreamers are hydraulically expandable tools that are used for a completely different reason. Underreamers are a much more complex tool than a hole opener and require careful engineering and planning. They are used to expand the wellbore beyond the pre-existing hole, which may be below a restriction. Most of the time the restriction is casing and good cement jobs are necessary to hold the casing in place. Because a larger bit or hole opener cannot fit through smaller casing, an underreamer is needed to sit just below the casing shoe so that the tool can expand beyond the inside diameter of the casing. Once you underream to the desired depth, the pumps are disengaged and the tool’s hydraulic cutting structure collapses into the body, allowing you to pull back through the casing and out of the hole. Cutting structures span a full range from roller cones to PDC, suited to Concurrent or Dedicated drilling applications.
- Hydraulically expandable
- More complex, requires careful engineering and planning
- Used below restrictions - typically casing
- Sits just below the casing shoe to expand beyond its ID
- Collapses to pull back through casing when done
“The biggest factor is what restrictions there are in the well bore.”
Hole Opener Corporation manufactures both - and our team members have guided this decision on wells worldwide. Contact us for a recommendation.
Which tool is right for your program?
Our team members can help you weigh restrictions, run sequence, and cutting structure against your wellbore program. To find out more about underreamers, visit our underreamer products page or contact us.
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