Horizontal
Drilling Techniques, Directional Drilling Methods
Mud Motor
Used In Directional Drilling. (note the slight bend to facilitate turning the
bit slightly in a particular direction)
Horizontal drilling, often called
directional drilling has revolutionized the way that oil and gas wells are
drilled. The reason that horizontal drilling in changing the oil and gas
business is that a well drilled sideways through a zone of oil and gas bearing
rock, will produce many more times what a vertical well would. This is because a
vertical oil or gas well only penetrates a few feet of the oil or gas zone
whereas a well drilled horizontally may penetrate several thousand. This also
means that previously unproductive rock formations such as the Barnett shale and
Bakken oil shale can be productive.
A Continental Resources
Rig Drilling a Horizontal Well In The Bakken Formation
Because these formations have poor
porosity not much natural gas or oil could flow out, but with horizontal
drilling a lateral, or directional hole can be drilled at around ninety degrees
for a few thousand feet and hydraulic fracturing or "fracking" could be done. A
frac job involves the pumping of high pressure fluid and a material such as
rounded beads to act as a proppant and keep the fissures that are broken by the
high pressure open and allow gas or oil to flow out.
Glass Beads Used As Proppant To Hold Fractured Fissures Open
The two technologies, horizontal drilling
and hydraulic fracturing were made for each other. In addition to new wells such
as in the Barnett shale, older wells can be drilled horizontally and stimulated
with hydraulic fracturing. Once drilling has been finished and casing has been
set in the well bore a service company such as Halliburton sets up dozens of
large frac tanks and trucks with high pressure pumps pump thousands of gallons
of fluid and proppant, under extreme pressure, into the oil or gas well. This is
called a frac job, since the pressure of the fluid fractures the underground
rock formation, and fissures and channels for oil and natural gas to seep out
are increased.
Here is a photo of Halliburton
equipment set up for a hydraulic fracturing or frac job.
Multiple pumping units are often
used in stages to pump thousands of gallons of fluid held in frac tanks down the well bore after casing has been set,
to fracture the formation.
For more on how hydraulic fracturing is done see:
What Is A
Frac Job
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Other Applications Of Horizontal
Drilling
In addition to
conventional oil and gas, directional drilling is being used to recover
coal bed methane. Coal bed methane, which is essentially a more methane
rich form of natural gas, is found throughout much of the country. This
low volume, low pressure gas has been known about for years and farmers
in some parts of the country as it bubbled from water wells but until
horizontal drilling came along there was no way to get enough gas from
a single well to make drilling for it profitable. Coal bed methane is
now a growing source of natural gas thanks to horizontal drilling.
Recent estimates are that coal bed methane accounts for over nine
percent of total natural gas production in the U.S. Horizontal drilling
is the primary method being used for shale gas deposits, coal bed
methane and shale oil such as contained in the Bakken formation of
North Dakota.
Illustration Of Coal Bed Methane
Horizontal Drilling.
Horizontal
Drilling For Coal Bed
Methane
Illustration Of Directional Drilling
The methods shown above are
similar to that which is used in horizontal drilling for oil and gas. The
illustration on the left incorporates Drill String Radar along with the LWD -
MWD to detect the boundaries of the coal seam. The MWD or LWD
equipment ( LWD if logging sensors are used) typically consists of sophisticated
electronics including accelerometers to measure gravity and determine
inclination, and magnetometers which detect the earth's magnetic field and
provide compass direction of azimuth of the drilling assembly. In order for these instruments to read the
earth's magnetic field, they are placed in nonmagnetic drill collars or "monel"
collars behind the mud motor. The directional drilling assembly consists of the
bit,
mud motor, MWD -LWD sensors and nonmagnetic drill collars. LWD or Logging While
Drilling instruments often read gamma radiation given off by the formation. This
information is interpreted at the surface to determine if the drilling assembly
is still within the shale or coal bed since each type of rock has a different
signature based on it's emitted gamma radiation.
Having a reliable signal from these
sensors is vital to horizontal drilling since they tell the driller at the
surface which direction and at what angle he is drilling the well. Radio
telemetry, which uses ultra low frequency radio waves that are picked up from an
antenna on the surface, provide very fast updates of where the tool face, or
bend in the mud motor is and compass direction or azimuth. This type of system
is often used in shallow coal bed methane drilling but is often impractical at
extreme depths that are often encountered in horizontal drilling for oil and
gas.
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When depth prevents using radio telemetry
a mud pulse system is used. Data from the MWD equipment is sent up hole in the
form of pressure pulses inside the drill pipe. A transducer at the surface
decodes these pressure spikes and the information from the sensors is displayed
on a rig floor display that shows inclination and azimuth.
How A Mud Motor Works In Horizontal
Drilling
The key component of horizontal drilling
is the mud motor. This device is powered by the force of drilling fluid or "mud"
that is pumped down the drill pipe. A mud motor contains a rotor, which is a
spiraled shaft that turns the bit. It is surrounded by a fixed chamber called a
stator. See the illustration below.
Illustration Of Mud Motor Used In Horizontal Drilling
The mud motor above appears
straight but actually has a slight bend of two degrees to facilitate directional
drilling. Often mud motors are adjustable to that directional drillers can make
adjustments in te field according to how much angle they need to build. Often a
rock bit will be used while building angle and then a PDC or polycrystalline
diamond compact will be used for the lateral section.
Photo of a PDC or Polycrystalline Diamond
Compact bit. 
Photo of a rock
bit.
PDC bits are often used in shale
and sometimes limestone. Rock bits are very effective for drilling in sandstone.
Since the mud motor can turn the bit
without the drill pipe moving, and because there is a slight bend in the mud
motor (often adjustable) the mud motor can be turned in a particular direction
so the bit can chew away at the rock and slide forward. By knowing what
direction the bent motor is sliding in, thanks to MWD or measure while drilling
technology, horizontal drilling is possible.
This explanation of horizontal drilling as
used in the oilfield was intended to describe the basics of how horizontal wells
are drilled.. There are other new technologies in directional drilling such as
rotary steerable that are revolutionizing the industry. Utilizing a system of
sensors and kick pads, the drill string can be rotated from the surface and the
kick pads bump the drilling assembly and bit in the desired direction. This
allows a well to be drilled horizontally much faster since more weight and
torque can be applied to the drill bit.
Other advances in horizontal drilling and
MWD include hot hole tools. Hot hole tools are specialized MWD equipment and mud
motors that can withstand temperatures of over 300 degrees Fahrenheit as is
found in many locations.
For more on horizontal drilling techniques
see the next page.
How Wells
Are Drilled Horizontally
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