attached to the bottom of the first length of casing to protect it from damage. The upper
Hydraulic drilling is fast becoming one of the most popular well drilling methods in
Michigan. Mud rotary is widely used in the Lower Peninsula where substantial
overburden exists, while air rotary rigs are fo und primarily in the Upper Peninsula and
the few high bedrock areas of Lower Michigan.
The principle of rotary drilling is based upon a rotating drill stem made of lengths of drill
pipe about 15 feet long. A bit is attached to a heavy stabilizer or drill collar at the end of
the column of drill pipe. The extra weight and larger outside diameter of the stabilizer
just above the bit helps to maintain a straight drill hole. The drill stem is hollow and has
a drilling fluid of either mud or air circulating down the drill stem out through the nozzles
in the bit and up along the outside of the drill stem. The rotating action of the bit breaks
up the material and the drilling fluid carries the cuttings to the surface where they settle
out in a mud tank.
Several types of bits are available to the rotary driller. The bit most generally used in
Michigan is the tri-cone roller bit. The type and number of cutting teeth on the bit cones
vary depending upon the type of formations to be penetrated.
The upper end of the drill stem is attached to a kelly on a table drive rig and swivel
which are mounted on a large mast. Hydraulic controls lower or raise the drill stem and
operate the rotary motion. When a hole has been drilled the full length of the kelly, the
drill stem is raised, the joint between the kelly and drill pipe is broken, and an additional
length of drill pipe is added. The drive mechanism for the drilling operation is provided
either at the rotary table (table drive) or at the swivel (top head drive). The rig also
contains a cable called a casing line which is used to raise and lower sections of drill
pipe and casing.
In rotary drilling, the borehole size is larger than the casing size. In drift formation, theentire hole is completed before casing is installed. In rock wells, the length of hole to be
cased is drilled, the casing is installed, then the bit size is reduced and the rock portion
of the well is completed.
Mud rotary utilizes a drilling fluid of bentonite clay and water. The mud serves several
purposes: (1) remove cuttings from the drillhole, (2) prevent collapse of the drillhole
and reduce water loss to the formations by forming a filter cake on the borehole wall,
(3) suspend cuttings when drilling is stopped, (4) cool and clean the drill stem and bit,
and (5) lubricate bit bearings and mud pump parts. After the cuttings are allowed to
settle in the mud tank, the mud is recirculated via a mud pump to the swivel at the top of
the kelly, then down through the drill stem. The mud tank is usually rectangular in
shape with a mud volume of 200-800 gallons and may contain several baffles to aid in
separation of cuttings from the drilling mud before it enters the pump intake for
recirculation. A device known as a sand separator may be used to further remove
sands and other "parasites" from the drilling mud. Samples of cuttings may be obtained
directly from the borehole before the fluid and cuttings spill into the mud tank.
Most larger rotary rigs have an air compressor to enable the contractor to also use air
as the drilling fluid. The high velocity of the air as it exits the bit is sufficient to blow the
cuttings away from the bit and carry them up to the surface where they settle out around
the borehole. Air rotary is used primarily for drilling in consolidated (rock) formations. In
rock wells with substantial overburden, mud will be used for drilling through the drift, and
after the casing is set the drilling operation will be converted to air rotary for completion
of the rock portion of the well. Clean water is often used for drilling the rock portion of
the hole after setting the casing.
Air hammer drilling, sometimes referred to as down hole drilling, is used extensively in
Michigan's hard rock areas. The bit used in this drilling method is essentially a
pneumatic hammer operated at the end of the drill stem. Compressed air operates a
piston which strikes the top of the bit at a very rapid rate. The cutting tips on the bit are
made of tungsten-carbide which are extremely resistant to abrasion. The combined
hammering and rotation of the bit results in penetration of hard rock at a rate faster than
any other drilling method.
Reverse-circulation is another form of rotary drilling. It differs from conventional
hydraulic rotary in that the drilling fluid travels in the opposite direction. The drilling fluid
travels up the inside of the drill stem with cuttings, through the pump and is dischargedinto the settling pond or tank. After cuttings are settled, the drilling fluid flows into the
borehole and down to the bit. The pressure of the fluid against the bore hole wall
prevents caving. The few reverse-circulation drilling rigs found in Michigan are used
primarily for drilling large diameter municipal, industrial, and irrigation wells.
CABLE TOOL DRILLING
Cable tool drilling, also known as percussion drilling or spudding, is a widely used well
drilling method in Michigan. Michigan has more cable tool rigs than any other type of
drilling machine. Some rigs are combination rotary-cable tool, enabling the operator to
use the rotary along with the casing driving ability of the cable tool. Although it is a
slower drilling method, the cable tool is less costly and simpler to operate than a rotary
drill rig and is suitable for most geologic conditions.
The cable tool operates by raising and dropping a heavy drill string in the drillhole. The
drill string, with bit on the lower and rope socket (or swivel socket) on top, is suspended
in the hole with a cable. The cable is threaded over the crown sheave located at the top
of the mast, down to the walking beam, and onto the cable drum where it is stored. The
up-and-down drilling action imparted to the drill stem and cable by the walking beam.
The walking beam is pivoted at one end, has a cable sheave at the other end and is
connected to the crank gear with a pitman. Rotation of the crank gear causes the
walking beam to move up and down. Additional cables called sand lines or casing lines
are used to raise and lower casing, bailers, plungers, or other tools.
The rhythmic raising and dropping of the bit loosens up sand or clay and breaks up rock
into "cuttings" and mixes them with water added by the driller to form a slurry. The
cuttings are then removed from the hole with a dart-valve baile r or other type of bailing
device. Formation type is determined by visual inspection of cuttings from the bailer and
the drilling contractor's knowledge of the rig's operation, such as the difficulty or ease of
drilling the particular formation. The up-and-down motion combined with the left-lay
cable and rope socket cause the drill stem and bit to rotate slightly on each vertical
stroke. This rotation helps maintain drillhole roundness.
The portion of the drillhole above the bedrock must be cased to preve nt caving. Casing
is driven into the drillhole with the use of heavy drive clamps bolted onto the drill stem.
The drill stem is lowered into the casing until the drive clamps strike the top of the
casing. The raising and dropping of the heavy drive clamps and drill stem drives the
casing into the drillhole. Prior to driving, a drive shoe of hardened, tempered steel is
end of the casing is protected by inserting a temporary drive cap. The usual cable tool
drilling operation involves drilling past the end of the casing, bailing the hole to remove
cuttings, driving casing, cleaning the hole, then resuming drilling. Generally, a few feet
of open hole is drilled beyond the casing before casing is driven. The driving, drilling,
and bailing operations are repeated until the desired depth is reached.
In screened wells, the pull-back method is generally used. This involves driving casing
to the bottom of the portion to be screened. A screen of smaller diameter than the
casing is placed into the casing. The top end of the screen is fitted with a K-packer or
other device which seals between the screen and casing. The screen is pushed to the
bottom of the casing, then the casing is "bumped" up to expose the screen to the
formation. The bailer is then used to begin development of the screen.
Continuous-flight, spiral auger well drilling rigs are found in those parts of western,
central and northern Lower Michigan where sand is the predominant glacial drift
material. In some areas, augers are used to drill the upper portion of the well and then
the well is completed with the cable tool method. In other areas of the state, augers are
used to drill the entire well.
The auger method utilizes spiral augers, usually in 5 foot lengths. The auger stem is
turned by a hydraulically-controlled rotary drive head. After drilling the length of an
auger, the auger joint is broken and another 5 foot section is added. Cuttings spiral
their way up to the surface where they appear around the borehole, making formation
identification relatively simple. If enough clay is present in the formation, the drillhole
will remain open when augers are removed. Dry sands and other caving formations
may be a problem for the auger driller and will occasionally result in the loss of long
flights of augers. When the auger encounters saturated sand (the water bearing
formation to be screened), drilling generally can be continued for a short distance but
the hole will not remain open in the saturated formation when the augers are removed.
The auger flight is then broken down and removed from the drillhole after drilling the
depth of the well or when changing to another type of drilling operation.
Casing is then placed into the drillhole. Some driving of the casing may be necessary
because of caving of portions of the drillhole or lack of straightness of the drilled hole. A
drillable plug is generally placed in the end of the casing prior to placement in the
drillhole. After placement of the casing, it is then filled with water and the screen driven
out through the plug and exposed to the water bearing formation. Keeping the casing
filled with water prevents heaving of sand into the casing when the plug is knocked out.
Another method used by some drillers (but not recommended) is to thread the screen
directly to the well casing, thereby installing the screen and casing in one operation.
The well is than pumped to remove the fine material from around the screen and to
determine if water quality and quantity are suitable.
As the well is being test pumped with a plunger or surge block, the discharged water
should be used for washing cuttings into the annulus to seal those parts of the annulus
that have not collapsed. Granular bentonite should be added to the cuttings in a
proportion of 1 part bentonite to 4 parts cuttings. Whenever the borehole penetrates a
clay layer, bentonite shall be used as the grouting material.
Driven wells are common in many areas of Michigan, especially around lakes where
groundwater may be close to the surface. Simple installation methods and the low cost
of materials make them attractive to homeowners or cottage owners who wish to install
their own water supplies. However, since the well point and casing are driven into the
ground, soil conditions are a major factor in suitability of the site. The site must be
generally sandy and free of boulders or bedrock to be suitable for a driven well. Hard
clay, silt, and very fine sand are generally difficult to drive through.
The installation of a driven well often begins by angering a hole with a hand auger or
posthole digger as far as possible. A drive point, consisting of a reinforced well screen
with a steel point on the end, is coupled to a 5 foot length of galvanized casing. The
most common casing size for driven wells is 1-1/4 inch inside diameter. A drive cap is
placed an the top of the casing and a heavy weight is used to strike the top of the drive
cap, driving the point into the ground, When the drive cap is driven close to the ground
and driving cannot be continued, another length of casing is added and driving is
resumed. Special drive couplings are used to join sections of casing,
Hand driving is usually accomplished by using a weighted driver consisting of a 3 or
4 foot piece of 3 inch diameter pipe capped on the top end. Extra weight is placed in the
top portion of the driver. The driver fits over the casing and is guided by it. Ano ther
type of driver has a steel rod on the bottom that slides into the casing through a hole in
the drive cap. Raising and dropping the driver is done with the use of handles welded
on the sides of the driver. The weighted driver may also be suspended from a tripod
and tackle arrangement. The use of a sledge hammer for driving is not recommended
since it may result in bent or broken casing from glancing blows.
As driving progresses, penetration becomes increasingly difficult due to friction between
the drive point/casing and the soil. Depths beyond 40 feet become difficult when driving
to settle, the water is recirculated through the pump, swivel, drill pipe and down to the
by hand. Driving a well is always a gamble since a boulder can easily damage the well
point or completely stop the driving. When a driven well attempt is aborted, the casing
and well point must often be left in the ground since retrieval is difficult without
A weighted string is used periodically during driving to determine if water has been
encountered. When water has been reached, the string will come up wet. The well
screen must then be developed to remove the fine material. This is accomplished by
pumping and surging. A pitcher pump or shallow well jet pump may be used for
development. Pumping and/or surging is continued until the water, which at first is full
of sand and silt, runs clear. If an auger was used to start the hole, it is necessary to
grout the annular space between the drillhole and casing. Bentonite or neat cement
(cement and water mixture) may be used for this purpose.
The major disadvantages of driven wells are as follows: (1) they are generally shallow,
therefore more vulnerable to surface or near surface contamination; (2) the screens
tend to encrust with carbonates at a faster rate due to their small diameter; and (3) their
yield is limited (< 10 gallons per minute [gpm]), since they can be pumped only with a
shallow well jet pump or hand pump.
Jetting is a drilling method suited for the sandy areas of southwestern Michigan. Jetting
remains a popular method for drilling small diameter wells due to its simplicity and
inexpensive cost of equipment. Many of the portable, do-it-yourself drilling machines
advertised in magazines utilize the jetting method.
Jetting and hollow-rod equipment are quite similar except that drilling water is pumped
with the jetting method and the direction of water flow is opposite. The jetting method
involves using a high velocity stream of water to break up the formation material and
wash the cuttings away. A chisel-shaped bit with holes to serve as nozzles is attached
to the end of a string of hollow drill pipe. Water pressure is provided to the nozzles by
using a high pressure pump. Water exits from the nozzles and loosens the material
being drilled while keeping the bit clean. The bit is raised and lowered and rotated
slightly to maintain a round hole. The cuttings are washed to the surface on the outside
of the drill pipe and flow into a settling pit or tank. Cutting samples are easily obtained
at this point. A 55 gallon drum is o ften used for this purpose. After cuttings are allowed
bit. Jetting can also be done without recirculation of the drilling water; however, a
removed from the hole. The drill rods are then reassembled, casing is driven, the drive
continuous supply of water must be available at the site.
The casing is usually installed as the drilling proceeds. A drive shoe is attached to the
bottom end of the casing and a drive cap inserted in the top. A drive block clamped to
the drill pipe is used to force the casing into the drill hole. The depth of the open hole
drilled before casing is installed depends on the type of formation and whether bentonite
has been added to the water as a drilling fluid to keep the hole open. The drilling/driving
sequence is extremely time consuming in caving formations, especially at greater
depths, since the drill string must be disassembled and removed from the well before
driving casing and must be reassembled before resuming drilling.
Hollow-rod, sometimes referred to as the hydraulic-percussion drilling method, is used
throughout Michigan's Lower Peninsula, with the largest concentration of hollow rod rigs
being found in the central and southern portion of the state. The hollow-rod is an old
drilling method that can be time consuming in some situations, but remains popular due
to its simplicity and relatively low cost of equipment. Most hollow-rod wells are 2 inch
diameter, but 4 inch casings are installed occasionally. This method is well suited for
sand and soft clay formations with relatively few boulders. It can also be used for
drilling rock wells, but progress is slowed considerably. Wells several hundred feet in
depth have been completed by the hollow-rod method.
The drill string used in hollow-rod drilling is similar to that used in jetting, except that the
chisel bit has a ball check valve in it. Water or a clay-water mixture is kept in the
annular space between the drill rods and well casing to help prevent the uncased
portion of the hole from collapsing. The water is supplied to the annulus by gravity
intake from a small mud tank. A 55 gallon drum is often used as a settling tank.
Drilling is done by lifting and dropping the drill stem and bit. The drill pipe used has
triple wall thickness to add weight to the drill string. The drill string is also rotated
slightly by hand during each stroke to maintain a round drill hole. As the bit drops, the
ball check opens and mud and cuttings enter the hollow drill rods. On the upstroke, the
check valve closes and keeps the cuttings in the drill rods.
Eventually the drill rods fill up and the slurry is discharged into the mud tank at the
surface where the cuttings settle out. Samples of cuttings can easily be obtained from
the mud tank. The continuous reciprocating drilling motion maintains circulation of the
drilling fluid from the bit, up the drill rods to the mud tank, from the mud tank into the
annulus, and down to the bit. The direction of flow is opposite that in the jetting
operation and no pressure pump is required.
Casing is driven as drilling progresses by clamping a weighted drive block to the drill
rods. When another length of casing is added, the drill rods must be disassembled and
block is removed and drilling is resumed. Close observation of formation samples and
COMPARISON OF WATER WELL DRILLING METHODS
water/drilling fluid circulation by the drilling contractor is essential to determine when
groundwater has been encountered. When a water-bearing strata is reached, drilling
fluid is usually lost to the formation. At this point, it is necessary to install a well screen,
if in an unconsolidated formation, and begin the well development process. Hollow-rod
rigs are equipped with walking beams, thus a plunger is most generally used to develop
OTHER DRILLING METHODS
DUAL TUBE ROTARY
Use of the down hole air hammer with rotary equipment provides a combined
percussion-rotary method that penetrates rapidly in consolidated formations. Test holes
are usually 6 inches in diameter when using this method. In most cases, however,
conventional water-based drilling fluids must be used with a roller bit when drilling
through unconsolidated overburden above bedrock. Exceptions to this occur when an
air hammer is used to drive the casing after materials are blown out of the casing or
when the rig is equipped with a casing driver.
This method allows contractors to drill more wells, and be able to drill them deeper and
faster. Instead of using a mud pump, they use compressed air.
In this method, the drill pipe and bit are joined and advanced simultaneously. The
pulled through the hole.
conventional top drive drills the open hole and the lower rotary drive is used to set
casing without any requirement for casing hammers, under-reamers, or drilling mud.
Advantages of this drilling method are: ability to drill in tough conditions, quicker
penetration rates, straighter holes, a nd a large compressor is not needed because the
lower drive operates on hydraulics.
Either air or water can be used as the drilling fluid in this modification of reverse
circulation technique. There is usually no grinding of cuttings, and the drilling fluid, if not
air, can be clear water.
A sonic drill uses high frequency mechanical oscillations, developed in the special drill
head, to transmit resonant vibrations and rotary power through the drill tooling to the drill
bit. The operator controls the frequencies to suit the specific conditions of the geology.
An air spring in the drillhead isolates the vibrations from the rest of the rig. The
vibrations fluidize the soil particles at the bit face, allowing fast and easy penetration in
most geological formations including bolders and rock.
One of the main advantages of the sonic drill is its ability to produce continuous core
samples of both unconsolidated and consolidated formations with detail and accuracy.
The core samples can be analyzed to provide a precise and detailed stratigraphic profile
of any overburden condition including dry or wet saturated sands and gravels, cobbles
and boulders, clays, silts and hard tills.
Directional drilling is the technique of drilling at an angle from the vertical by deflecting
the drill bit. Directional wells are drilled for a number of reasons: to develop and
offshore lease from one drilling platform; to reach a payzone beneath land where drilling
cannot be done, e.g., beneath a railroad, cemetery or lake, or to drill around a blockage
in an existing wellbore.
A pilot hole is drilled under the natural feature and then backreamed to make the hole
large enough to accommodate the pipe. Once the hole is large enough the pipe is