WHY CHOOSE CLEAR-BORE FOR
HORIZONTAL DIRECTIONAL DRILLING

• Superior Rheology: The rheological (flow properties) characteristics of Clear-Bore have been proven in both the laboratory and job site as providing better drilled cutting removal from the bore hole than the types of high yield bentonite typically used in HDD operations.
• High Gel Strength: The gel strength (cuttings suspension capacity) of Clear-Bore slurry is greater than that of most HDD bentonite based drilling fluids – you do not need to add expensive additions of Xanthan Gum to increase the gel strength.
• Excellent Fluid Loss Control: Clear-Bore provides a tight thin filter cake which provides excellent bore hole stability. Clear-Bore polymers are unique in their ability to actually bind drilled cuttings together to provide an even tighter filter cake than bentonite based drilling fluids – no additional fluid loss additives are required.
• Ultra High Yield: With a typical dose rate of only 2.5-5kgs of Clear-Bore per 1000liters (m3) of water. One 5kg bag of Clear-Bore yields the equivalent volume of drilling fluid to that of 30-50Kgs of high yield bentonite or 70-120Kgs of standard drilling grade bentonite. In effect 1 metric tonne of Clear-Bore produces as much drilling fluid as 7 -10 metric tones of high yield bentonite. Additionally the Clear-Bore fluid exhibits superior drilling fluid properties.
• The Product is UNIVERSAL – i.e. one-sack-does-all. Whether you are drilling through sand, rock, gravels or boulder clay etc, no additional polymers or products are needed. Very little technical support is required if you have the correct concentration. Clear-Bore exhibits excellent shale and clay inhibitition as well as “anti-bit-balling” properties making it ideal for drilling sticky clays as well as sands and gravels.
• Salt Water Tolerant: Clear-Bore will mix in both salt water and fresh water and can be used to drill below the water table through difficult salt-water contaminated formations.
• Non-toxic and Completely Biodegradable: Clear-Bore is ideal for environmentally sensitive sites (EPA tested).
• Dramatically Reduces Drilling Fluids Disposal Costs: By adding of a small dose of Calcium Hypochlorite to a full pit or tanker full of used Clear-Bore slurry it will break down overnight to approximately 20-30% semi-solid material and 70-80% water. Thus disposal costs are dramatically reduced by up to 90%.
• Zero Percent Sand Content: Clear-Bore does not contain any minerals so it does not contain any grit (bentonite typically contains 0.5 – 4.0% grit). Clear-Bore fluid is proven to reduce mud pump wear and reduce associated operating costs.
• Versatile: Clear-Bore is fully compatible with bentonite slurry. Added to hydrated bentonite slurry Clear-Bore provides an extremely cost effective one-bag additive for increasing the Gel strength and fluid loss control characteristics of bentonite whilst also creating clay and shale inhibition.
• Reduced Storage, Transport and Handling Costs: Because of the small volumes required (one tenth of that of bentonite) there are reductions in storage and transport costs as well as manual handling benefits. The ease of use is perfect for operators.
• Easy Mixing with Reduced Down Time: Unlike most drilling fluids Clear-Bore mixes quickly and easily through a standard venturie hopper, typically reaching optimum drilling fluid properties within 5 minutes (most drilling fluids which take at least 20 minutes to fully hydrate).
• Recycles: unlike most polymer based drilling fluids Clear-Bore is easily recycled through standard recycling units.
• Stable: For long and large diameter bores Clear Bore can be ordered with an added stabilizer which will increase its operating life from 3 – 4 weeks to well over 3 months.

Loss of
returns, flow or circulation can be a problem in HDD installations. Zones of
high porosity/permeability, natural fractures, rubble zones, gravel and natural
voids can all cause loss of drilling fluid to the formation.

In these cases,
bentonite and standard fluid additives may not be sufficient to seal the
borehole. Some sort of coarser bridging agent may be required. Lost circulation
material (LCM) may be necessary.

LCM is found in
three forms: fiber, flake and granular. The fiber types of LCM are usually made
from shredded paper, cane fiber, wood fiber or spun mineral fiber. The flake
types of LCM are usually made from mica, ground Formica or cellophane. The
granular materials are made from ground nut hulls, granular bentonite or water
swellable, non-soluble, crystalline polymers. Additionally, each type of
material can come in different sizes: fine, medium and coarse.

The choice of
LCM to use can depend on several factors, including the type of loss. In
seepage situations in sand, fine flake or fiber material may be of benefit. In
fractures in rock, coarser material may be needed to plug and seal the
fracture. If natural voids are encountered, water swellable crystalline
polymers or granular bentonite may help fill and seal the void. Combinations of
these materials can also be beneficial. Blends of all three types of LCM are
available in fine, medium and coarse. The blends take much of the guesswork out
of choosing a certain type and the only decision to make is the required size.

The rig pump
can also be a factor in choosing the LCM to use. Large river crossing rigs,
having larger pumps, will normally be able to pump a much larger variety of LCM
than the smaller utility rigs. Smaller utility rigs with smaller pumps may be
limited to the finer size LCM. Regardless of pump size, all screens in the
fluid system must be removed before using LCM. A properly working LCM will plug
any screens left in the fluid system. Larger nozzles in the bit and reamer may
also be necessary.

Availability
can be a limiting factor in LCM choice. These materials may be readily
available in active oilfield areas but most HDD work is performed outside these
areas. If losses are anticipated because of geotechnical information, local
knowledge or any other reason, a supply of LCM should either be on the job site
or located in advance as a contingency plan.

A research
project was performed at the University of Alberta in Edmonton, Alberta, in a
commercial gravel pit with three 200-ft installations of 4-in. SDR 17 high
density polyethylene (HDPE) made at depths of 5 ft. The first installation
required 3,500 total gal of fluid during the pilot bore and pullback. The fluid
used consisted of soda ash, bentonite (50 lbs per 100 gal water) and a
suspension enhancer. Good slurried flow was maintained for 110 ft. On the first
pilot bore, flow was lost at 110 ft and inadvertent returns occurred.
Inadvertent returns continued through the rest of the pilot bore and throughout
the reaming process.

The second
installation used the same fluid with the addition of a fibrous suspension
agent at a concentration of 0.5 lbs per 100 gal of fluid. Flow was maintained
for 150 ft at which time returns were lost and inadvertent returns occurred.
Inadvertent returns continued through the rest of the pilot bore and throughout
the reaming process. A total of 3,000 gal of fluid was used.

The third
installation used the same fluid as the second but a fine, fibrous LCM (N-Seal)
was added at a concentration of 4 lbs per 100 gal of fluid. A total of 2,200
gal of fluid was used and flow was maintained on both the pilot bore and during
the reaming process. A higher concentration of the LCM would probably have
reduced the fluid usage even more.

LCM can be a
valuable, cost-effective tool in reducing fluid losses and preventing
inadvertent returns.

Frank
Canon, Baroid Industrial Drilling
Products, a Halliburton company, is a member of the Drillmaster Advisory Board.
All Drillmaster Reports are reviewed by the Drillmaster Advisory Board: Canon,
Mike Dvorak, The Charles Machine Works Inc.; Ron Lowe, Myers-Aplex, a Pentair
Pump company; Dan Miller, American Augers Inc.; and Ed Savage, Vermeer Mfg.

Tips for Keeping Swivels in Top Form

It’s well known that preventative maintenance will reduce costs in your operation — the challenge is making the time to maintain your equipment before there’s a problem. Pullback swivels for horizontal directional drilling (HDD) can be relatively easy to maintain if a simple routine is adopted on the site and in the yard.

Preventative maintenance begins in purchasing the appropriate swivel for your rig. Swivels rely on bearings to function, and the load ratings for those bearings are not linear. Simply use a swivel at 10 percent below its working load limit and you will increase bearing life by 40 percent.

On the jobsite, the machine operators can make a huge contribution to equipment maintenance in just a few minutes by following a simple clean-up procedure:

At the end of each pull, continue rotation of the string and hose down the swivel.

Pay particular attention to the gap in the swivel. Wash all the mud and dirt from the split line groove of the swivel, until clean water runs out.

Once it’s clean, rotate the swivel a couple turns while squirting 20W machine oil into the groove to keep the seal cavity from drying out.

If fine particulates accumulate in the gap and dry out, they can cement the seals, locking them solid. Start up the rotation in a week or two, and there is a real danger that the seal will tear and be rendered useless. Torn seals are the beginning of the end for a swivel.

Once the swivel is washed clean, inspect the swivel for damage. Stubborn dirt can hide substantial damage — make sure you’re looking at base metal.

Check clevis pins for wear and be sure to check the clevis lugs around the pins for gouges or other damage. Clevis pins are designed specifically for this application and contribute to the strength of the swivel. Never substitute with unapproved parts.

Between jobs, keep the swivel clean. Protect it from the elements and keep it oiled to prevent unnecessary corrosion. Always fit a thread protector to the API threads.

Pump a little grease into the swivel to ensure the bearings remain packed. On many swivels, the grease can flow easily out through the gap between the swivel halves. On these swivels, really pump the grease through while rotating the swivel to ensure that contaminants are flushed out.

On large swivels, grease will typically exit through a relief valve — review the owner’s manual. Always make sure the valve is clear; failure of grease to exit through the relief valve may mean the valve is faulty or no longer operational. Adapters on the box connection can render the relief valve invisible. Take extra precautions if you cannot see the relief valve functioning. Do not remove the relief valve or replace with a second grease nipple.

Use only the factory recommended grease for your swivel. Mixing grease with different formulations could seriously diminish the expected properties and damage the bearings beyond repair.

Ensure that there is no loose feeling when the swivel is rotated by hand — listen for grinding sounds, which may mean the bearings have become contaminated. A well-maintained large swivel should rotate smoothly using a pry bar between the clevis ears. Checking rotation on the string can’t tell you anything: a drill rig can generate more than enough torque to rotate a worn or damaged swivel.

If the swivel is starting to hitch or grind, it must be serviced immediately. Most manufacturers offer service kits for their products; the swivel’s serial number will identify exactly which parts are required. Servicing a swivel onsite saves transportation costs, but this option should be approached with caution. Swivels are built to exacting tolerances with the appropriate tools in clean environments — don’t compromise the integrity of your equipment if you’re not prepared to do the job right.

A better option is to schedule a service visit between jobs at a factory authorized repair facility.

Assessments and repairs can be made quickly — typically in two to three weeks. You’ll get a complete inspection, good advice and a reconditioned swivel that can return to service with confidence.

Don’t risk a job on a piece of equipment that’s not functioning smoothly. Invest in a little preventative maintenance and you’ll see the benefits.

Jon Twidale, P.E., is project manager for DCD Design & Mfg. Ltd. Article was co-written with INROCK Drilling Systems.

Drilling fluid properties for rock formations are fairly straightforward with  carrying capacity and  lubrication being the most important factors.

The fluid must carry cuttings from the bore hole and also provide lubrication to prevent excessive wear on the tooling. Maintaining viscosity high enough to carry cuttings from the bore is critical in maintaining penetration rates. Too little viscosity will allow cuttings to fall out of the slurry and be deposited behind the drill head. Too high of viscosity increases pumping pressures and limits flow properties that in turn will reduce penetration rates.

Generally, marsh funnel viscosities of 50 to 60 seconds or slightly higher seem to work quite nicely. Rock drilling fluids for horizontal directional drilling (HDD) applications are generally fresh water, bentonite based. High-yielding, extended sodium bentonites are the most common product in HDD applications. These extended bentonites are formulated to provide fast hydration and high yields at low concentrations (generally ± 3 percent). Usually expressed as “barrel yield,” these products would fall in the category of 200 bbl/ton. “Barrel yield” is an oilfield term for measuring the viscosifying capability of a bentonite clay and is defined as the number of oil field barrels (42 gal) of ~35 second mud that one ton of bentonite will produce. In other words, one ton of 200 bbl bentonite will produce ~8,400 gals of 35 second slurry. This is important to know as contractors may come across other materials that may easily double the application rate.

Some addition of polymer additives will aid in lubrication and flow properties. Polymers are shear thinning, thus allowing higher viscosity fluids to be pumped without a corresponding increase in pumping pressure. This allows the contractor to maximize the flow patterns in the annular space while maintaining higher viscosities and reasonable pumping pressures. It is important to remember that “polymer” is a generic term, in this case describing a category of products. Polymers can exhibit very different properties when introduced to a bentonite drilling fluid. Understanding the desired properties and choosing the appropriate polymer is a key factor.

In this application, we are interested in the ability of the polymer to increase viscosity and add lubrication to the drilling fluid. On the surface, the polymer choice would be a long chain PHPA (such as Wyo-Vis, EZ Mud, Insta-Vis Plus, Poly-Plus). These long chain polymers are effective viscosifiers and provide excellent lubrication at low concentrations. The contractor must consider all facets of the project, which will probably include mud cleaning.

Long chain PHPA polymers can become an issue with blinding of the screens during the cleaning process. With this in mind we may want to look toward a short chain PHPA (such as Wyo-Vis LVP, EZ Mud Gold, Poly-Plus LV) or a branch type polymer such as a PAC (Uni-Drill, Liqui-Trol, Super Pac). While the application rate may be slightly higher to achieve the same viscosity, the increased material will provide better lubricity in the system.

Always take care to introduce polymers to the system slowly to prevent the formation of “fisheyes” or lumps of non-hydrated polymer. Once fisheyes form, they usually only come out one way and that is usually off the shaker. While they look like nice shinny crystals in the sunlight, they are really your wasted dollars.

Gel Strength
We have discussed viscosity as one of the most important factors in rock drilling fluids but we have not mentioned gel strength yet. We target viscosity because it one of the easiest properties to measure on the jobsite. Even the greenest of hands can master the marsh funnel test. We must remember that viscosity is only a measure of resistance to flow and does not measure carrying capacity or gel strengths.

While viscosity of a new drilling fluid is a good indication of the ability of the fluid to carry and suspend cuttings, it may not be the same for a recycled drilling fluid. Suspended solids in a drilling fluid will also increase the viscosity. When a mud engineer comes to the jobsite to test a drilling fluid, you will note they always use other testing equipment to get a more complete picture of what the true properties of the mud.

Direct indicating viscometers also measure viscosity but give us much more information. We can generate PV (Plastic Viscosity), AV (Apparent Viscosity), YP (Yield Point) and gel strength properties for the drilling fluid. With these numbers, we can get a good handle on the carrying capacity of the fluid at rest and when moving. Add in a density, filtrate and sand content test, and we have a lot of information from which to make responsible decisions.

Because of the volume of drilling fluids used, a rock drilling job usually involves a mud cleaning system. A simple example of mud cost-savings by using a mud cleaning system usually convinces the contractor pretty quickly. (Example:  45 min. per stem at 10 gal./min. equals 450 gal. so a 2,000-gal. mix would last only four stems) This does not mean the drilling fluid can be used forever without adjustments. Drilling fluids need to be “sweetened” on a regular basis during the drilling operation. As cuttings are removed from the system, some of the drilling fluid is lost due to encapsulation of the cuttings. Small particles also tend to build up in the drilling fluid, reducing the carrying capacity of the system and some or all may need to be disposed of. As drilling progresses, the requirement for increased volume allows for the addition of water and fresh additives. This constant refreshment usually keeps the system in good working order.

In closing, we look for a mud system that has low density, a viscosity of 60 plus and very low entrained solids. Slight adjustments in viscosity will allow for different cutting sizes to be removed from the borehole. Remember only drill with as much viscosity as you need to clean the hole!

When using a new string of pipe, make sure the Drive Chuck/Sub Saver is new as well to prevent damage to the new threads on the pipe. A Drive Chuck/Sub Saver that has worn threads can damage the new ones easily. Also, check proper alignment of the pipe and the Drive Chuck/Sub Saver and adjust if necessary. Good alignment will greatly reduce thread wear.

Break-in the pipe threads on the first bore. This consist of lubing the threads (preferably with a copper flake lube such as Jet-Lube) making up the joint to full torque, breaking the joint and re-applying more lube. Repeat this process 3 times. This will ensure that the threads are burnished and will prevent galling and seizing.

Make sure to maintain the alignment of the pipe in the ground and the pipe in the rig. This prevents side loading the threads and unnecessary wear and possible cross threading. Keeping the rig stake downs from moving is important.

When making up the threads use slow rotation to reduce heat and prevent over running the thread shoulders.

Always make up the joints to full torque. Having good vice jaw inserts or properly fitting sliding wrenches is a must.

Keep the distance from the rig to the entry hole as close as possible. Lack of entry hole support will make it easy to buckle the pipe when thrusting to steer in hard conditions.

Keep the initial entry angle as low as possible and smoothly transition to the desired depth.

Never exceed the recommended maximum bend radius (less bend radius is better and will greatly extend the life of your drill pipe). Many operators tend to level out the bore to quickly from the entry hole or surface too quickly when exiting. This causes extra bending stress on the pipe and shortens the life substantially.

Rotate the pipe regularly. This means moving the lead pipe to the end of the string continually. This prevents the first few pipes from seeing all of the footage on pilot and pull back every time.

If all of the above recommendations are followed you will get an excellent return on your drill pipe investment.