Lecture 1 con't

1.1.3 Applications of Directional Drilling
1. Sidetracking: Side-tracking was the original directional drilling technique. Initially,
sidetracks were “blind". The objective was simply to get past a fish. Oriented
sidetracks are most common. They are performed when, for example, there are
unexpected changes in geological configuration (Figure 1-1).


2. Inaccessible Locations: Targets located beneath a city, a river or in environmentally
sensitive areas make it necessary to locate the drilling rig some distance away. A
directional well is drilled to reach the target (Figure 1-2).



3. Salt Dome Drilling: Salt domes have been found to be natural traps of oil
accumulating in strata beneath the overhanging hard cap. There are severe drilling
problems associated with drilling a well through salt formations. These can be
somewhat alleviated by using a salt-saturated mud. Another solution is to drill a
directional well to reach the reservoir (Figure 1-3), thus avoiding the problem of
drilling through the salt.



4. Fault Controlling: Crooked holes are common when drilling nominally vertical. This
is often due to faulted sub-surface formations. It is often easier to drill a directional
well into such formations without crossing the fault lines (Figure 1-4).



5. Multiple Exploration Wells from a Single Well-bore: A single well bore can be
plugged back at a certain depth and deviated to make a new well. A single well bore
is sometimes used as a point of departure to drill others (Figure 1-5). It allows
exploration of structural locations without drilling other complete wells.



6. Onshore Drilling: Reservoirs located below large bodies of water which are within
drilling reach of land are being tapped by locating the wellheads on land and drilling
directionally underneath the water (Figure 1-6). This saves money-land rigs are much
cheaper



7. Offshore Multiwell Drilling: Directional drilling from a multiwell offshore platform
is the most economic way to develop offshore oil fields (Figure 1-7). Onshore, a
similar method is used where there are space restrictions e.g. jungle, swamp. Here,
the rig is skidded on a pad and the wells are drilled in “clusters".



8. Multiple Sands from a Single Well-bore: In this application, a well is drilled
directionally to intersect several inclined oil reservoirs (Figure 1-8). This allows
completion of the well using a multiple completion system. The well may have to
enter the targets at a specific angle to ensure maximum penetration of the reservoirs.



9. Relief Well: The objective of a directional relief well is to intercept the bore hole of a
well which is blowing and allow it to be “killed" (Figure 1-9). The bore hole causing
the problem is the size of the target. To locate and intercept the blowing well at a
certain depth, a carefully planned directional well must be drilled with great
precision.



10. Horizontal Wells: Reduced production in a field may be due to many factors,
including gas and water coning or formations with good but vertical permeability.
Engineers can then plan and drill a horizontal drainhole. It is a special type of
directional well (Figure 1-10). Horizontal wells are divided into long, medium and
short-radius designs, based on the buildup rates used. Other applications of
directional drilling are in developing geothermal fields and in mining.



Lecture 1

Directional Drilling Training Manual



1 Introduction
1.1 History and Applications of Directional Drilling
Controlled directional drilling is the science of deviating a well bore along a planned
course to a subsurface target whose location is a given lateral distance and direction from
the vertical. At a specified vertical depth, this definition is the fundamental concept of
controlled directional drilling even in a well bore which is held as close to vertical as
possible as well as a deliberately planned deviation from the vertical.
1.1.1 Historical Background
In earlier times, directional drilling was used primarily as a remedial operation, either to
sidetrack around stuck tools, bring the well bore back to vertical, or in drilling relief
wells to kill blowouts. Interests in controlled directional drilling began about 1929 after
new and rather accurate means of measuring hole angle was introduced during the
development of Seminole, Oklahoma field.
The first application of oil well surveying occurred in the Seminole field of Oklahoma
during the late 1920’s. A subsurface geologist found it extremely difficult to develop
logical contour maps on the oil sands or other deep key beds. The acid bottle
inclinometer was introduced into the area and disclosed the reason for the problem;
almost all the holes were crooked, having as much as 50 degrees inclination at some
check points.
In the spring of 1929 a directional inclinometer with a magnetic needle was brought into
the field. Holes that indicated an inclination of 45 degrees with the acid bottle were
actually 10 or 11 degrees less in deviation. The reason was that the acid bottle reading
chart had not been corrected for the meniscus distortion caused by capillary pull. Thus
better and more accurate survey instruments were developed over the following years.
The use of these inclination instruments and the results obtained showed that in most of
the wells surveyed, drill stem measurements had very little relation to the true vertical
depth reached, and that the majority of the wells were "crooked". Some of the wells were
inclined as much as 38 degrees off vertical. Directional drilling was employed to
straighten crooked holes.
In the early 1930’s the first controlled directional well was drilled in Huntington Beach,
California. The well was drilled from an onshore location into offshore oil sands using
whipstocks, knuckle joints and spudding bits. An early version of the single shot
instrument was used to orient the whipstock.
Controlled directional drilling was initially used in California for unethical purposes, that
is, to intentionally cross property lines. In the development of Huntington Beach Field,
two mystery wells completed in 1930 were considerably deeper and yielded more oil
than other producers in the field which by that time had to be pumped. The obvious
conclusion was that these wells had been deviated and bottomed under the ocean. This
was acknowledged in 1932, when drilling was done on town lots for the asserted purpose
of extending the producing area of the field by tapping oil reserves beneath the ocean
along the beach front.

Many legal entanglements developed when it was established through directional surveys
that oil was being removed from a productive zone under the tidelands, the ownership of
which was claimed by both the town of Huntington Beach and the State of California.
The state now supervises the Huntington Beach operations, and subsequently the art of
cylinder drilling or drilling a prescribed “right of way" was developed .
In 1933, during the development of the Signal Hill field in Long Beach, California,
several wells were drilled under the Sunnyside Cemetery from locations across the
streets surrounding the cemetery and even from more distant points to tap a productive
zone underlying the cemetery.
Controlled directional drilling had received rather unfavorable publicity until it was used
in 1934 to kill a wild well near Conroe, Texas. The Madeley No.1 had been spudded a
few weeks earlier and, for a while, everything had been going normally. But on a cold,
wet, dreary day the well developed a high pressure leak in its casing, and before long, the
escaping pressure created a monstrous crater that swallowed up the drilling rig. The
crater, approximately 170 feet in diameter and of unknown depth, filled with oil mixed
with sand in which oil boiled up constantly at the rate of 6000 barrels per day. As if that
were not enough, the pressure began to channel through upper formations and started
coming to the surface around neighboring wells, creating a very bad situation indeed.
Many people felt that there was nothing to do except let the well blow and hope that it
would eventually bridge itself over, and pray that it would do it soon so everyone could
get back to work.
In the meantime, however, a bright young engineer working for one of the major oil
companies in Conroe suggested that an offset well be drilled and deviated so that it
would bottom out near the borehole of the cratered well. Then mud under high pressure
could be pumped down this offset well so that it would channel through the formation to
the cratered well and thus control the blow out. The suggestion was approved and the
project was completed successfully, to the gratification of all concerned. As a result,
directional drilling became established as one way to overcome wild wells, and it
subsequently gained favorable recognition from both companies and contractors. With
typical oilfield ingenuity, drilling engineers and contractors began applying the
principles of controlled directional drilling whenever such techniques appeared to be the
best solution to a particular problem.
Current expenditures for hydrocarbon production have dictated the necessity of
controlled directional drilling, and today it is no longer the dreaded operation that it once
was. Probably the most important aspect of controlled directional drilling is that it
enables producers all over the world to develop subsurface deposits that could never be
reached economically in any other manner.
1.1.2 Technology Advances
The development of reliable mud motors was probably the single most important
advance in directional drilling technology. Surveying technology also has advanced in
great strides. The technologies complement each other.
The development of the steering tool replaced the magnetic single shot instrument as a
means of orienting a mud motor with a bent sub or housing. The tool was lowered by a
wireline unit and seated in the muleshoe orienting sleeve. The wireline was passed
through a circulating head mounted on a drill pipe and had to be retrieved every 90 feet.

Data sent to the surface by the wireline was processed by a surface computer.
Continuous updates were given on azimuth, inclination, temperature and tool face. With
the advent of the side-entry sub, the wireline was passed through the side of the sub thus
eliminating the need to pull the wireline every 90 feet. However, no rotary drilling was
possible with the steering tool.
In the early 1980’s ANADRILL MWD started to gain widespread acceptance as an
accurate and cost-effective surveying tool. Today the MWD has virtually replaced the
steering tool on kick-offs and is used exclusively with the steerable mud motor. A newgeneration
MWD has been developed with the additions of gamma ray, resistivity, and
DWOB/DTOR giving the MWD real time formation evaluation capabilities. Surveys
obtained with the MWD are now widely accepted by both oil industry and regulatory
agencies.
Gyro technology has also progressed. The SRG (Surface Readout Gyro) is the latest
addition to the survey line. It provides fast and accurate surveys electronically,
eliminating the need to read a film base system. Many surveying companies provide their
own tool: "FINDER", "SEEKER”, "GCT”, “FINDS", etc.


Dictionary for the Petroleum Industry free download










AAPG abbr: American Association of
Petroleum Geologists AAPL abbr: American Association of Petroleum Landmen abaft adv: 1. toward the stem of a ship or mobile offshore drilling rig. 2. behind. 3. farther aft than. See aft  abandon v: to cease producing oil and gas from a well when it becomes unprofitable or to cease further work on a newly drilled well when it proves not to contain profitable quantities of oil or gas. Several steps are involved: part of the casing may be removed and salvaged; one or more cement plugs are placed in the borehole to prevent migration of fluids between the different formations penetrated by the borehole; and the well is abandoned. In most oil-producing states, it is necessary to secure permission
from official agencies before a well may be abandoned. abandoned well n: a well not in use because it was a dry hole originally, or
because it has ceased to produce. Statutes and regulations in many states require the plugging of abandoned wells to prevent the seepage of oil, gas, or water from one stratum of underlying rock to another. abandonment n: termination of a jurisdictional sale or service. Under Section 7(b) of the Natural Gas Act, the Federal Energy Regulatory Commission must determine in advance that the "present or future public convenience and necessity" or depletion of gas supplies requires termination. abandonment pressure n: the average reservoir pressure at which an amount of gas insufficient to permit continued economic operation of a producing gas well
is expelled. abd, abdn abbr: abandoned; used in drilling reports. abnormal pressure n: pressure exceeding
or falling below the pressure to be expected at a given depth. Normal pressure increases
approximately 0.465 pow1ds per square inch per foot of depth or 10.5 kilopascals per
metre of depth. Thus, normal pressure at 1,000 feet is 465 pounds per square inch; at
1,000 metres it is 10,500 kilopascals. See pressure gradient.
aboard adv: on or in a ship, offshore drilling rig, helicopter, or production platform.
abrasion n: wearing away by friction. ABS abbr: American Bureau of Shipping.
abscissa n: the horizontal coordinate of a point in a plane obtained by measuring
parallel to the x-axis. Compare ordinate. absolute (abs) adj: independent or
unlimited, such as an absolute condition, or completely unadulterated, such as alcohol.
absolute density n: the density of a solid or liquid substance at a specified temperature.
Sometimes referred to as true density or density in vacuo. See density.
absolute dynamic viscosity n: the force in  dynes that a stationary flat plate with a
surface area of 1 square centimetre exerts on a similar parallel plate 1 centimetre away
and moving in its own plane with a velocity of 1 centimetre per second, the space
between the plates being filled with the liquid in question. It is a measure of the
resistance that the liquid offers to shear. absolute error n: the difference between the
result of a measurement and the true value
of the measured quantity as determined by
means of a suitable standard device.
absolute humidity n: the amount of
moisture present in the air. It may be
expressed in milligrams of water per cubic
metre of air. Compare relative humidity.
absolute kinematic viscosity n: the value
obtained when the absolute dynamic
viscosity is divided by the density
(expressed in grams per cubic centimetre)
of the liquid at the temperature concerned.
absolute mass n: the expression of a fluid's
weight (mass) in terms of its weight in a
vacuum.
absolute open flow n: the maximum flow
rate that a well could theoretically deliver
with zero pressure at the face of the
reservoir.
absolute ownership n: the theory that
minerals such as oil and gas are fully owned
in place before they are extracted and
reduced to possession. Despite this theory,
title to oil and gas may be lost by legitimate
drainage and by the rule of capture. Also
called ownership in place. See rule of
capture.
absolute permeability n: a measure of the
ability of a single fluid (such as water, gas,
or oil) to flow through a rock formation when
the formation is totally filled (saturated) with
that fluid. The permeability measure of a
rock filled with a single fluid is different from
the permeability measure of the same rock
filled with two or more fluids. Compare
effective permeability, relative permeability.
absolute porosity n: the percentage of the
total bulk volume of a rock sample that is
composed of pore spaces or voids. See
porosity.
absolute pressure n: total pressure
measured from an absolute vacuum. It
equals the sum of the gauge pressure and
the atmospheric pressure. Expressed in
pounds per square inch.
absolute temperature scale n: a scale of
temperature measurement in which zero
degrees is absolute zero. On the Rankine
absolute temperature scale, which is based
on degrees Fahrenheit. water freezes at
492' and boils at 672". On the Kelvin
absolute temperature scale, which is based
on degrees Celsius, water freezes at 273°
and boils at 373°. See absolute zero.
absolute viscosity n: the property by which
a fluid in motion offers resistance to shear
and flow. Usually expressed as newton
seconds/metre.
absolute zero n: a hypothetical temperature
at which there is a total absence of heal
Since heat is a result of energy caused by
molecular motion, there is no motion of
molecules with respect to each other at
absolute zero.
absorb v: I. to take in and make part of an
existing whole. 2. to recover liquid hydrocarbons
from natural or refinery gas in a
gas- absorption plant. The wet gas enters
the absorber at the bottom and rises to die
top, encountering a stream of absorption oil
(a light oil) travelling downward over bubblecap
trays, valve trays, or sieve trays. The
light oil removes, or absorbs, the heavier
liquid hydrocarbons from the wet gas. See
bubble-cap tray, sieve tray, valve tray.
Absorbent n: see absorption oil.
absorber n: 1. A vertical, cylindrical
vessel that recovers heavier
hydorcarbons from a mixture of
predominantly lighter hydrocarbons.
Also called absorption tower. 2. A vessel
in which gas is dehydrated by being
bubbled through glycol. See absorb.
absorber capacity n: the maximum
volume of natural gas that can be
processed through an absorber at a
specified absorption oil rate, temperature,
and pressure without exceeding pressure
drop or any oilier operating limitation.
absorption n: 1. the process of sucking
up, taking in and making part of an
existing whole. Compare adsorption. 2.
the process in which short wave
radiation is retained by regions of the
earth.
absorption dynamometer n: a device
that measures mechanical force. The
energy measured is absorbed by
frictional or electrical resistance.
absorption gasoline n: the gasoline
extracted from natural gas by putting
the gas into contact with oil in a vessel
and subsequently distilling the gasoline
from the heavier oil.
absorption oil n: a hydrocarbon liquid
used to absorb and recover components
from natural gas being processed. Also
called wash oil.
absorption plant n: a plant that
processes natural gas with absorption
oil.
absorption-refrigeration cycle n: a
mechanical refrigeration system in which
the refrigerant is absorbed by a suitable
liquid or solid. The most CODlD1only
used refrigerant is ammonia; the most
commonly used absorbing medium is
water. Compare compressionrefrigeration
cycle.
absorption tower n: see
absorber.
abstract-based title opinion n: a title
opinion based on a complete abstract of
title and other relevant documents.
Compare stand- up title opinion.
abstract company n: a private
company in the business of preparing
abstracts of title
and performing related services. Also
called abstract plant.
abstract of title n: a collection of all of
the recorded instruments affecting title to
a tract of land. Compare base abstract.
abstract plant n: see abstract company.
abyssal adj: of or relating to the bottom
waters of the ocean.
Ac abbr: altocumulus.
AC abbr: alternating current.
accelerated aging test n: a procedure
whereby a product may be subjected to
intensified but controlled conditions of
heat, pressure, radiation, or other
variables to produce, in a short time,
the effects of long- time storage or use
under normal conditions. acceleration
stress n: when a crane is hoisting a
load, the additional force the load
imposes on a wire rope or a sling when
the load's speed increases.
accelerator n: a chemical additive that
reduces the setting time of cement. See
cement, cementing materials.
accelerometer n: an instrument that
detects changes in motion or measures
acceleration. accessory equipment n:
any device that enhances the utility of a
measurement system, including
readouts, registers, monitors, and
liquid- or flow-conditioning equipment.
accrete v: to enlarge by the addition of
external parts or particles.
accumulate v: to amass or collect.
When
oil and gas migrate into porous
formations, the quantity collected is
called an accumulation.
accumulator n: 1. a vessel or tank that
receives and temporarily stores a liquid
used in a continuous process in a gas
plant. See drip accumulator. 2. on a
drilling rig, the storage device for
nitrogen-pressurised hydraulic fluid,
which is used in operating the blow out
preventers. See blowout preventer
control unit.
accumulator bottle n: a bottle-shaped
steel cylinder located in a blowout
preventer control unit to store nitrogen
and hydraulic fluid under pressure
(usually at 3,(XK)pounds per square
inch). The fluid is used to actuate the
blowout preventer stack.
accuracy n: the ability of a measuring
instrument to indicate values closely
approximating the true value of the
quantity measured.
accuracy curve of a volume meter n:
a plot of meter factor as a function of
flow rate used to evaluate the meter's
performance. See flow rate, meter
factor:
acetic acid n: an organic acid
compound sometimes used to acidise
oil wells. It is not as corrosive as other
acids used in well treatments. Its
chemical formula is C2~O2' or
CH3COOH.
acetylene welding n: a method of
joining steel components in which
acetylene gas and oxygen are mixed in
a torch to attain the high temperatures
necessary for welding. As an early type
of welding (it was also called
oxyacetylene welding), its primary
disadvantage was the seepage of
molten weld material onto the interior
surface of the pipe, often leading to
corrosion problems. ACGIH abbr: American Conference of Governmental and Industrial Hygienists.
acid n: any chemical compound. one
element of which is hydrogen, that
dissociates in solution to produce free
hydrogen ions. For example,
hydrochloric acid. HCI, dissociates in
water to produce hydrogen ions, H+,
and chloride ions, CI-. This reaction is
expressed chemically as HCI + H+ + CI-
. See ion. acid brittleness n: see hydrogen embrinlement.
acid clay n: a naturally occurring clay
that, after activation, usually with acid, is
used mainly as a decolourant or refining
agent, and sometimes as a desulphuriser, coagulant, or catalyst. acid fracture v: to part or open fractures in productive hard limestone formations by using a combination of oil and acid or water and acid under high pressure. See formation fracturing. acid gas n: a gas that forms an acid when mixed with water. In petroleum production and processing, the most common acid gases are hydrogen sulphide and carbon dioxide. Both cause corrosion, and hydrogen sulphide is very poisonous. acidity n: the quality of being acid. Relative acid strength of a liquid is measured by pH. A liquid with a pH below 7 is acid. See pH.

Produced Water Treatment

INTRODUCTION

Production of water is usually associated with the production of crude oil and natural gas
 
The produced water may be water that exists within the petroleum reservoir as connate 
water
 or bottom water.
Water-flooding operations, water is injected into reservoir to 
 enhance the recovery 
 
Produced and treated water quality 


Produced water always has to be treated before it is disposed or injected into the 
reservoir.
The purpose of the treatment is to remove enough oil from the water such that the
 remaining amount of oil is the water and the oil droplet size are appropriate for the 
disposal or injection of the water.


Produced Water Treating Technology

Suspended Solids Removal
Suspended Oil Removal
Chemical Treating for Control of Bacteria
Chemical Treating for the Control of Scale
Corrosion Control Techniques
Other Chemical Treatment Needs
 
Suspended Solids Removal

suspended solids have a tendency to plug the injection formation thereby tending to
 cause the produced water injection pressure to increase and the produced water 
injection flow rate to decrease.
Suspended solids that are present in the water will exist as distinct particles of varying 
sizes and densities dispersed throughout the water phase.  
 
Particles that are heavier than water will tend to drop to the bottom of the pipe, 
vessel or other type of container at various rates.
Stoke’s Law describes the vertical velocity at which a particle falls through a liquid 
phase. 
 
 Stoke’s Law  
 
 
Where :
Δρ  = difference in density of the dispersed particle
 and the continuous phase,
g     =“g-force” acceleration factor,
gc   = gravity acceleration constant,
dp   = dispersed particle diameter, and
μL  = viscosity of the continuous phase.
  
 
it is clear that the settling velocity can be increased by:
 
 
1. Increasing the size of the solid particles (i.e. by using chemical agents), or
2. Increasing the difference in density between the oil droplet and the water phase, or
3. Lowering viscosity of the water (i.e. by operating at the highest possible temperature), or
4. Increasing the “g-force” imposed on the fluid (i.e. by centrifugal motion)
 
 
 

Fishing Technology (8)

MILLING OPERATIONS

Overview

Junk mills are the surest way to eliminate junk in the hole. There are various
mills that can be used in different circumstances. For example, the insert
type of mill is best suited for milling pipe or tools anchored securely in the
well bore; however, chatter, vibration or loose junk are detrimental to the
inserts.
صورة 15

Types of Mills

1- Insert Type
Can be used for:
• pipe/tools anchored securely in the wellbore.
Caution: Chatter, vibration, or loose junk are detrimental to the
inserts.
2- Crushed Tungsten Carbide Mills
Can be used for:
• almost anything, except in hard abrasive formations.
3- Skirted Flat Bottom Or Concave Type Mill 
Can be used for:
• flared or burred top of fish prior to engagement with an
overshot. Because the skirted mill is stabilized and the
fish is contained within the skirt, it cannot slip off
4- Blade Type Mill
Can be used for:
• junk or cast iron material which will break up.
Features:
• Rugged, durable construction
• Concave, convex, and flat-bottom designs available
• Dressed with tungsten carbide inserts for stationary fish
or junk
• Dressed with crushed tungsten carbide for loose fish or
junk
• Improved cooling during milling
• Increased milling efficiency
5- Pilot Mill/Diamond Point
The Pilot Mill/Diamond Point is used for milling tubing, casing,
liner hangers, liners, drill pipe, drill collars, wash pipe, or
perforated liners.
Using Pilot Mills:
• Select a pilot mill with a blade O.D. ¼ inch larger than
the O.D. of the tool joint or coupling of the fish milled.
The pilot O.D. should be the same as the drift I.D. of the
fish.
• Determine the best rotary speed and weight to run a pilot
mill for each job. Conditions may change from one pilot
milling job to the next in the same well. The change may
require different rotary speeds and weights at different times. In the absence of experience, start with a speed of
between 80 and 100 RPM’s and a tool weight of 2,000
to 6,000 lbs. Vary the speed and weight to obtain the
best results.
• If milling a liner or casing that is gun-perforated,
damaged with a spear, or collapsed, use 60 RPM’s and
2,000 lbs. of weight or less.
• A sudden drop in the milling rate while milling swaged
casing may be caused by a loose ring of steel formed at
a joint or weld, which turns with the pilot mill. Spud the
mill gently to break up the ring and position it for
milling.
• If the milling rate stops or drastically slows down in the
milling of wash pipe, casing or liner without a
noticeable increase in torque, the fish may be turning.
• If so, pull the mill, and retrieve the fish with a spear.
6- Tapered Mills
The Weatherford Standard Tapered Mill is designed for milling
through restrictions. The spiral blades and pointed nose dressed
with crushed tungsten carbide make the mill ideal for reaming
collapsed casing and liners, cleaning permanent whipstock
windows, milling through jagged or split guide shies, and
enlarging restrictions through retainers and adapters. The torque
encountered governs the tapered mill rotary speeds.
• To overcome torque challenges, do not exceed 75
RPM’s.
• Do not rotate a tapered mill resting on a fish. Enter the
fish with a rotary speed of 75 RPM’s ort less.
• Use less weight when running a tapered mill than a junk
or pilot mill. After entering the fish, increase the tool
weight to slowly to 1,000 to 2,000 lbs. Watch for any
torque increase.
7- Watermelon/String Mills
The Weatherford string mill is dressed with tungsten carbide
spiral blades tapered from top to bottom to enable reaming both
up and down in collapsed casing and liners. The lower
connection enables a stinger to be run below the tool to prevent
sidetracking. The mill can also be placed anywhere in a drill or
fishing string. The mill features crushed tungsten carbidedressed
reamer blades.
Can be used for:
• Smooth or rough OD
• Milling out collapsed areas in casing and liners
• Eliminating key seats and doglegs in open hole
• Extending whip stock windows
8- Flat Bottom Cone Buster
Mill
This flat bottom cone buster mill is dressed with crushed
tungsten carbide and is a very aggressive mill used to mill up bit
cones or other pieces of junk. The mill is sturdy enough for
light spudding on the junk to break it up into smaller pieces.
Large circulation ports improve mud circulation for cooling and
for the removal of cuttings. Field reports show these long
lasting mills are safer than using a rock bit because you can’t
lose any bit cones in the hole. Weatherford’s junk mills work
well when milling drillable packers, bridge plugs, retainers, and
cement.
Note: Important characteristics of cone buster mills include that
they can be furnished with:
  •  large circulation ports which improve mud circulation for
cooling and cutting removal.
  •  smooth outside diameter along with stabilizer pads designed
to be run inside casing.
9- Cement Mills
Can be used for:
• Milling cement