A typical HDD system usually has two main components: drill bit and reamer, which are referred to as: “The Tooth” and “The Wings”, respectively.
The drill bit is the rotating part of the system. It drills through the hard strata and creates a hole for the reamer to push through.
The reamer, on the other hand, is an “elbow” pipe with a conical point that has the same external diameter as the drill pipe to which it connects. It is named after its shape that resembles an oversized drill bits used in directional drilling. But it looks like something between a drill bit and a pipe with wings.
It allows the drilling of large diameter bores that are not possible with conventional single bitpoint bits without requiring multiple passes and time-consuming tripping back to surface between passes, especially in hard rock.
Types of HDD Reamers
Reamers come in a variety of shapes and sizes. The type of reamer used is determined by the project’s requirements and soil conditions.
Drilling tasks might be difficult on sandy soil. Soft soil is prone to collapsing in on itself, necessitating the use of some kind of support system. Compaction reamers are the best choice for reaming boreholes dug in this sort of ground.
To drive drilling fluid into the surrounding soil, this reamer design relies on a bentonite filter cake. The slurry injection provides much-needed support and prevents the hole from collapsing. The cutting heads are usually shaped like a cone and grow in size over time. The slurry mixture is forced into the soil by the tapered design.
Hole openers are used to enlarge pilot holes for large applications, as the name implies. These cutters operate with ground formations that regular reamers can’t penetrate. They ream rock formations with rolling cutters.
These reamers frequently require multiple passes to safely open the hole. With each pass, the hole gets a little bigger. Workers must stabilize each successive size in order to achieve this without destroying the reamer.
A mixing reamer is suitable for reaming a borehole in clay or tougher ground conditions.
Rippers, fly cutters, and beaver tails are examples of these types of reamers. They aid in the breaking up of soil particles and mixing them with drilling fluids to aid in the removal of cuttings from the hole. Workers must use a certain type of drilling fluid with these reamers since clay and water have a tendency to clog the bore.
While all three types of mixing reamers function effectively in tougher soils, the fly cutter works best in highly compacted settings. Larger rocks can slide through the reamer of a fly cutter as it travels through the hole because of its open design. As a result, the fly cutter is frequently preferred over other options when working with hdd projects that involve drilling through sandstone and siltstone.
Maintenance of HDD Reamers
The three components of any type of HDD rig must function properly and in conjunction with each other. Failure of just one component can greatly affect the performance of an entire rig. Therefore, all components must be properly maintained and replaced when needed to ensure longevity in a drilling system.
A driller can take care of small problems before they become big ones that could potentially shut down a well. All these components should be checked frequently for quality and wear, and problems should be addressed immediately. Take your cue from the following:
Tools break, tips crack, and crowns chip, drill out insert and inspect for damage. If an insert breaks while drilling, clean it off quickly! Insert can get caught in HDD casing as it’s being retrieved from a bore hole ruining it.
Check for chips in food.
Chips will be small and black. If you see them, they are close to the surface and removal of drill is needed ASAP.
Prolonged exposure in high temperature.
Surface of insert can develop cracks if running too hot for a long period of time, especially near a drill face or shoulder. Chips will be small and black like the ones that come from H2S gas.
High vibration (abrasive) drilling.
Excessive vibration can reduce the life of an insert.
Rigidly holding drill and not following recommended RPMs can cause damage to components.
Reducing rotation per minute or RPM will increase tool life and is a more cost effective alternative than replacing the inserts often.
The direction of vibration is critical when using an HDD Reamer.
Vibrating in reverse (counter-clockwise rotation on the tool’s cobalt type drill bits) will extend the life of your inserts and increase the amount of usage you can achieve before replacing them.
Do not overheat your drill bit while drilling a straight hole. High temperature changes metal properties which leads to cracking, pitting and premature wear of inserts.
The correct speed for drilling a straight bore is 80-100 RPM per inch of diameter. Never run faster than this unless you are a highly skilled operator.
Pitting, caused by debris and carbon solids in the drilling mud that are not completely flushed out of the bore hole.
Using a clean coolant will help prevent premature wear of drill bits.
Bring drill back to surface if casing sticks during drilling process.
The spec sheets for each manufacturer’s tool recommend this action as well. The casing may be weakened or damaged.
Worn out bits are often misused in HDD and will cause premature wear on your Reamers if continued to be used with worn out cutters.
Always replace them when recommended (usually near 8-12mm).
Do not run tool very fast when drilling into hydrocarbon bearing zones (Joint Injections). This situation causes pressure to build up behind the cutting edge more than in formations the tool is designed to drill.
A clean casing during the drilling process will help prevent premature wear on HDD reamers and reduce vibration that causes high speed pitting if casing sticks in the bore hole.
Do not run your drill at a slower RPM than recommended on drill insert manufacturer spec sheets.
This will cause premature wear of inserts and have a negative impact on the boring tool’s life span.
Although the cost of maintaining a drilling rig may seem expensive to an individual or company, if it is done properly, it can ensure longevity in each hole drilled. This will result in greater productivity from each rig and in the end, more profits to those involved in the hdd projects.
Extending the lifespan of a drilling rig is beneficial not only to the owner or individual leasing it, but also for the environment. The longer a surface rig stays on location without being moved, the less wear and tear is done to that area. This can be a great benefit in preservation and sustainability of the ecosystem around drilling rigs.
To ensure quality and longevity in directional drilling systems, maintenance must be performed on the rotary table, slips, and pipe string. Each component is vital for the overall efficiency of each rig system. All components should be checked regularly for wear and replaced when needed.