The most significant change this author/mud man
extraordinaire has seen in the last 15 years of experience in the horizontal
directional drilling (HDD) industry is not in the equipment or technology, but
in the capabilities and accomplishments of drilling contractors, especially in
the mini to mid-sized HDD drilling market. Today, contractors with 40,000-pound
drills routinely are completing projects that contractors would not have
attempted without maxi-sized drills just 10 years ago, and it is not uncommon
to see contractors pulling product back in which the static weight of the
product line far exceeds the actual push/pull capacity of the drill. HDD
contractors who are successful in completing large projects with mini to
mid-sized HDD drills are substituting the shear brute strength/horsepower and
pumping capacity of larger drills for brainpower, experience and, last but not
least, patience. Let’s face it: If you’re going to bring a knife to a gunfight
and expect to win, you had better be really good with a
knife!
Attempting larger HDD projects with smaller drilling equipment immediately
narrows one’s margin for success because there is little room for mistakes. One
must realize the shortcomings in utilizing smaller drilling equipment, such as
less rotary torque, less thrust for pushing and pulling, and less mud-pumping
capacity, and understanding how to work within these parameters. Contractors
have to be on top of their game when it comes to matching drilling fluids and
downhole tooling to soil conditions, not only on the final ream/pullback, or
even pre-reaming, but on the pilot hole as well. Failure to control downhole
conditions, such as sticking and swelling clays or fluid-loss control in sand,
while drilling the pilot hole will rob the drill of much needed torque that
could be applied to the reamer. Inadequate drilling fluid gel strength also
will narrow the margin of success by leaving drill cuttings in the borehole to
pack around the drill stem, contribute to differential torque, backpressure
and/or stuck product line. In order to complete large projects with smaller
drilling equipment, it is imperative that the hole is open and free of
obstructions.
Using soda ash is a no-brainer for getting the most out of fluid-loss control
and gel strength in a bentonite drilling fluid. Any time you are mixing Wyoming sodium bentonite
drilling fluid, you should be using soda ash at 1⁄4 pound to 1⁄2 pound per 100
gallons of water, added before mixing bentonite. It is well worth the
investment to utilize a good HDD specialty drilling fluid – which can have up
to three times the gel strength of high-yield bentonite, as well as improved
fluid-loss characteristics – as well as soda ash. PAC (poly anionic cellulose)
polymer will boost fluid-loss control to help maintain borehole stability, and
an xanthan gum-based gel strength enhancer will dramatically increase gel
strength with a minimal increase in viscosity. Remember, viscosity is the
resistance to flow; therefore, the ideal HDD drilling fluid will perform all of
the required functions of a drilling fluid at the lowest viscosity possible.
Grab some of the drilling fluid mix in a clear container, stir in a bit of soil
from the entry or exit pit, and see what happens. If the material settles in
the container, it is going to settle in the hole, leaving cuttings that will
cause an increase in pullback pressure. If the material gets sticky and
thickens up, you will have to add something to take care of reactive clays.
Backreamer designs are especially critical in doing large shots with mini to
mid-size HDD drilling equipment. Backreamers should not block the return flow
from going to the exit side, and when working in reactive (sticking and
swelling) clays, avoid backreamers with large amounts of surface area for clay
to stick to. Back-reamers, such as packer reamers, spiral reamers and/or fluted
reamers, can become completely blocked with clay, create huge increases in
rotary torque and pullback pressure, and are a frac-out just waiting to happen.
A good clay reamer will have a minimal amount of surface area, yet have good
chopping and mixing capabilities, and can mean the difference between a failed
or successful bore.
Drilling technique also is a critical component in expanding the capabilities
of drilling equipment. While drilling the pilot hole, contractors should
closely monitor drilling fluid returns, and note changes in the soil conditions
to avoid surprises or problems during backreaming operations. Contractors also
should avoid creating any bottlenecks in the bore path, which can occur when
drillers do not pull back and rotate the bit through sections of the pilot hole
where push-steering was performed, resulting in reduced annular space around
the drill stem that will block returns and create additional rotational torque.
When tackling large-diameter projects with smaller HDD drilling equipment,
mud-pumping capacity is dramatically less, and because the pullback speed of a
backreamer is limited to the drilling fluid volume delivered to the backreamer,
much more time must be taken for backreaming operations. This is where patience
comes into play, and this is where many contractors fail. A backreamer not only
is cutting soil, but it also is mixing soil with drilling fluid into what
should be a flowable mixture that can be pushed out to the exit side. It takes
two to three times the amount of drilling fluid vs. soil in coarse soil
conditions, such as sand, and four to five times the amount of drilling fluid
vs. soil in reactive clays. Monitoring return flow when backreaming is
essential to success, because the returns will provide a wealth of information,
such as changes in soil conditions, how the drilling fluid is interacting with
the soil conditions, and the adequacy of flow/pumping volume. Contractors
always should have someone monitoring the return flow. That person needs to be
in direct contact with the driller, and can tell the driller if he is
out-running the drilling fluid or if the mixture needs to be adjusted to
changing soil conditions.
When tackling large-diameter HDD projects with mini to mid-sized drilling equipment,
be aware of the shortcomings of the equipment being utilized and the narrow
window of success that comes with this challenge, and take every precaution to
improve one’s chances for success. Remember that you are substituting
brainpower, experience and patience for the lack of horsepower/brute strength
and pumping capacity of larger drilling equipment, and, therefore, you must be
on the top of your game to increase the chances to be successful. As previously
mentioned, if you are going to bring a knife to a gunfight and expect to win,
you had better be really good with a knife.
ND