Sticking Mechanism Categories and Preventation actions

•  Solids Induced Pack-off

 Packing Off - First Actions
a) At the first signs of the drill string torquing up and trying to pack-off, the pump strokes should be reduced by half. This will minimise pressure trapped should the hole pack-off. Excessive pressure applied to a pack-off will aggravate the situation. If the hole cleans up, return flow to the normal rate.

b) If the string packs off, immediately stop the pumps and bleed down the standpipe pressure [NB not possible with a non-ported float valve]. When bleeding pressure down from under a pack-off, control the rate so as not to "U" tube solids into the drill string in case they plug the string.

c) Leave low pressure (<500 psi ) trapped below the pack-off. This will act as an indicator that the situation is improving should the pressure bleed off.

d) Holding a maximum of 500 psi on the standpipe and with the string hanging at its free rotating weight, start cycling the drill string up to maximum make-up torque. At this stage do not work the string up or down.

e) Continue cycling the torque, watching for pressure bleed off and returns at the shakers. If bleed off or partial circulation occurs, slowly increase pump strokes to maintain a maximum of 500 psi standpipe pressure. If circulation improves continue to increase the pump strokes.

f) If circulation cannot be regained, work the pipe between free up and free down weight. DO NOT APPLY EXCESSIVE PULLS AND SET DOWN WEIGHTS AS THIS WILL AGGRAVATE THE SITUATION (50k lb max). Whilst working the string continue to cycle the torque to stall out and maintain a maximum of 500 psi standpipe pressure.

g) DO NOT ATTEMPT TO FIRE THE JARS IN EITHER DIRECTION.

h) If circulation cannot be established increase the standpipe pressure in stages up to 1500 psi and continue to work the pipe and apply torque.

i) If the pipe is not free once full circulation is established, commence jarring operations in the opposite direction to the last pipe movement. Once the pipe is free rotate and clean the hole prior to continuing the trip.

•  Unconsolidated formations

 Description

An unconsolidated formation falls into the well bore because it is loosely packed
with little or no bonding between particles, pebbles or boulders. Video clip of sand sloughing
The collapse of the formation is caused by removing the supporting rock as the well is drilled. This is very similar to digging a hole in sand on the beach, the faster you dig the faster the hole collapses. It happens in a well bore when little or no filter cake is present. The un-bonded formation (sand, gravel, small river bed boulders etc.) cannot be supported by hydrostatic overbalance as the fluid simply flows into the formation. Sand or gravel then falls into the hole and packs off the drill string. The effect can be a gradual increase in drag over a number of metres, or can be sudden. This mechanism is normally associated with shallow formations. Examples are shallow river bed structures at about 500m in the central North Sea and in surface hole sections of land wells. This mechanism normally occurs:
· While drilling shallow unconsolidated formations.
 Preventative Action

These formations need an adequate filter cake to help stabilise the formation. Seepage loss can be minimised with fine lost circulation material. If possible, avoid excessive circulating time with the BHA opposite unconsolidated formations to reduce hydraulic erosion. Spot a gel pill before POOH. Slow down tripping speed when the BHA is opposite unconsolidated formations to avoid mechanical damage.
Start and stop the pumps slowly to avoid pressure surges being applied to unconsolidated formations. Control-drill the suspected zone to allow time for the filter cake to build up, minimise annulus loading and resultant ECD’s. Use sweeps to help keep the hole clean. Be prepared for shaker, desilter and desander overloading. A method successfully used in the North Sea is to drill 10m, pull back to the top of the section and wait 10 minutes. Note
any fill on bottom when returning to drill ahead. If the fill is significant then ensure the process is repeated every 10m. It may be impossible to prevent the hole collapsing. If so let the hole stabilise itself with the BHA up out of harm’s way.
Rig site indications
· Increase in pump pressure.
· Fill on bottom.
· Overpull on connections.
· Shakers blinding.
 Freeing
Follow First Actions but be aware that the pressures (i.e. 500 psi, 1500 psi) will probably not be achievable in shallow
formations.

• Mobile Formations

 Description
The mobile formation squeezes into the well bore because it is being compressed by the overburden forces. Mobile formations behave in a plastic manner, deforming under pressure. The deformation results in a decrease in the well bore size, causing problems running BHA’s, logging tools and casing. A deformation occurs because the mud weight is not sufficient to prevent the formation squeezing into the well bore. This mechanism normally occurs: · While drilling salt.

 Preventative Action

Maintain sufficient mud weight. Select an appropriate mud system that will not aggravate the mobile formation. Plan frequent reaming/wiper trips particularly for this section of the hole. Consider bi-centre PDC bits. Slow trip speed before BHA enters the suspected area. Minimise the open hole exposure time of these formations. With mobile salts consider using a slightly under-saturated mud system to allow a controlled washout.

 Rig site indications

· Overpull when moving up, takes weight when running in.
· Sticking occurs with BHA at mobile formation depth.
· Restricted circulation with BHA at mobile formation depth.

 Freeing

Spot a fresh water pill if in a salt formation. (Consider the effect on well control and on other open hole formations ). If moving up, apply torque and jar down with maximum trip load. If moving down, jar up with maximum trip load. Torque should not be applied while jarring up.

• Fractured & Faulted Formations

 Description
A natural fracture system in the rock can often be found near faults. Rock near faults can be broken into large or small pieces. If they are loose they can fall into the well bore and jam the string in the hole. Even if the pieces are bonded together, impacts from the BHA due to drill string vibration can cause the formation to fall into the well bore. This type of sticking is particularly unusual in that stuck pipe can occur while drilling. When this has happened in the past, the first sign of a problem has been the string torquing up and sticking. There
is a risk of sticking in fractured / faulted formation when drilling through a fault and when drilling through fractured limestone formations.
This mechanism can occur:
· in tectonically active zones.
· in prognosed fractured limestone.
· as the formation is drilled.

 Preventative Action

Minimise drill string vibration. Choose an alternative RPM or change the BHA configuration if high shock vibrations are observed. Slow the trip speed before the BHA enters a suspected fractured/faulted area. Generally, fractured formations require time to stabilise. Be prepared to spend time when initially drilling and reaming prior to making significant further
progress. Circulate the hole clean before drilling ahead. Restrict tripping speed when BHA is opposite fractured formations and fault zones. Start / stop the drill string slowly to avoid pressure surges to the well bore. Anticipate reaming during trips. Ream fractured zones cautiously.
 
 Rig site indications.

· Hole fill on connections.
· Possible losses or gains.
· Fault damaged cavings at shakers.
· Sticking can be instantaneous.

 Freeing

If packed off while off bottom then follow First Actions. Otherwise JAR UP in an effort to break up formation debris. Use every effort to maintain circulation. Circulate high density viscous sweeps to clean debris. Spot acid if stuck in limestone

• Naturally Over-Pressured Shale Collapse

 Description
A naturally over-pressured shale is one with a natural pore pressure greater than the normal hydrostatic pressure gradient. Naturally over-pressured shales are most commonly caused by geological phenomena such as under-compaction, naturally removed overburden (i.e.
weathering ) and uplift. Using insufficient mud weight in these formations will cause the hole to become unstable and collapse.
This mechanism normally occurs in:
· Prognosed rapid depositional shale sequences.
 Preventative action
Ensure planned mud weight is adequate. Plan to minimise hole exposure time. Rigorous use of gas levels to detect pore pressure trends. Use of other information to predict pore pressure trends (for example Dexp ). Once the shale has been exposed do not reduce the mud weight. It may also be the case that the mud weight will need to be raised with an increase in inclination See Well bore stability Section of SP KB 1997 Guidelines.
 Rig site indications
· Cavings (splintery) at shakers.
· Increased torque and drag.
· Gas levels, D exponent.
· Circulation restricted or impossible.
· Hole fill.
· An increase in ROP.
· Cuttings and cavings are not hydrated or mushy.
 Freeing
Follow First Actions.

•  Induced Over-Pressured Shale Collapse

 Description
Induced over-pressure shale occurs when the shale assumes the hydrostatic pressure of the well bore fluids after a number of days exposure to that pressure. When this is followed by no increase or a reduction in hydrostatic pressure in the well bore, the shale, which now has a higher internal pressure than the well bore, collapses in a similar manner to naturally over-pressured shale. Video clip - Unstable Shale in WBM
This mechanism normally occurs:
· In WBM.
· After a reduction in mud weight or after a long exposure time during which
the mud weight was constant.
· In the casing rat hole.
 Preventative action
Non water based muds prevent inducing over-pressure in shale. Do not plan a reduction in mud weight after exposing shale. If cavings occur, utilise good hole cleaning practices. See Hole Cleaning Section
 Rig site indications
· Cuttings / cavings show no sign of hydration.
· Cavings (splintery) at shakers.
· Tight hole in casing rat hole.
· Increased torque and drag.
· Circulating restricted or impossible.
· Hole fill.
1.2.6.4 Freeing
Follow First Actions.

• Reactive Formations

 Description
A water sensitive shale is drilled with less inhibition than is required. The shale absorbs the water and swells into the well bore. The reaction is ‘time dependent’, as the chemical reaction takes time to occur. However, the time can range from hours to days.
This mechanism normally occurs:
· When using WBM in shales and clays in young formations.
· When drilling with an incorrect mud specification. Particularly, an
insufficient concentration of inhibition additives in OBM and WBM such as
salts (KCl, CaCL), glycol and polymer.
 Preventative action
Use an inhibited mud system. Maintain the mud properties as planned. The addition of various salts (potassium, sodium, calcium, etc. ) will reduce the chemical attraction of the water to the shale. Various encapsulating (coating) polymers can be added to WBM mud to reduce water contact with the shale. Monitoring mud properties is the key to detection of this problem. Open hole time in shale should be minimised. Regular wiper trips or reaming trips may help if shales begin to swell. The frequency should be based on exposure time or warning signs of reactive shales. Ensure hole cleaning is adequate to clean excess formation i.e. clay balls, low gravity solids etc.
 Rig site indications
· Hydrated or mushy cavings.
· Shakers screens blind off, clay balls form.
· Increase in LGS, filter cake thickness, PV, YP, MBT.
· An increase or fluctuations in pump pressure.
· Generally occurs while POOH.
· Circulation is impossible or highly restricted.
Freeing
POH slowly to prevent swabbing. See First Actions.

• Hole Cleaning

 Description
In deviated wells cuttings and cavings settle to the low side of the hole and form layers called solids beds or cuttings beds. The BHA becomes stuck in the solids bed.
OR Cuttings and cavings slide down the annulus when the pumps are turned off and pack-off the drill string. Avalanching can also occur while the pumps are on.
Good hole cleaning means removal of sufficient solids from the well bore to allow the reasonably unhindered passage of the drill string and the casing.
There are several main reasons for solids not being cleaned out of the well bore.
These are:
· A low annular flow rate.
· Inappropriate mud properties.
· Insufficient circulation time.
· Inadequate mechanical agitation.
If any of the above are missing good hole cleaning will be very unlikely. In 40-65 degree wells the cuttings bed will slide down the low side of the hole. This can happen while pumping, not just when the pumps are off. In highly deviated wells of 65 degrees or more cuttings settle very quickly in spite of high flow rates. This is known as
avalanching. A cuttings bed of 10% of the hole diameter (1.75 inches in 17.5 inch hole) looks harmless enough. Add a drill string and the situation looks very different.
Cuttings beds can also increase drag in the well and cause problems with applying WOB in horizontal holes.
Preventative Action
· Maximise the annular velocity.
- Consider the use of a third mud pump.
- Consider using larger drill pipe.
· Ensure circulation times are adequate.
- Consult the hole cleaning charts for confirmation.
- Monitor the cuttings returns at the shakers.
· Maximise mechanical agitation of cuttings beds.
- Rotation.
- Reciprocation.
· Optimise mud properties.
- increase YP in near vertical wells.
Rig site indications· Overpulls increasing while POOH from TD in deviated hole (7-10 stands).
· Erratic pump pressure.
· Poor weight transfer to bit.
· Difficulty orienting toolface.
· Absence of returns at shakers.
· Presence of re-ground cuttings (LGS).
· Overpulls inside casing.
 Freeing
See First Actions
Refer to Hole Cleaning section for more information.

• Tectonically Stressed Formations

 DescriptionWell bore instability is caused when highly stressed formations are drilled and there exists a significant difference between the near well bore stress and the restraining pressure provided by the drilling fluid density. Tectonic stresses build up in areas where rock is being compressed or stretched due to movement of the earth’s crust. The rock in these areas is
being buckled by the pressure of moving tectonic plates. When a hole is drilled in an area of high tectonic stresses the rock around the well bore will collapse into the well bore and produce splintery cavings similar to those produced by over-pressured shale. In the tectonic stress case the hydrostatic pressure required to stabilise the well bore may be much higher
than the fracture pressure of the other exposed formations
This mechanism usually occurs:
· in or near mountainous regions.
 Preventative action
Plan to case off these formations as quickly as possible. Maintain mud weight within planned mud weight window. Well bore instability shows itself as a hole cleaning problem. If possible drill these formations in smaller hole sizes. This will minimise the impact of a hole cleaning problem. Ensure that the circulation system is capable of handling the additional volume of cavings often associated with this mechanism. If hole problems do occur, Ref Hole Cleaning section. Use offset data to establish optimum inclination and azimuth as these are key factors in reducing the extent of the problem. Ref Wellbore Stability section in  Rig site indicators
· Pack-offs and bridges may occur.
· Cavings at the shakers (splintery).
· Increase torque and drag.
· If stuck, circulation is likely to be impaired or non-existent.
· Increase in volume of returns at the shakers relative to the hole volume drilled.
 Freeing
See First Actions

Air Drilling

is used through primarily nonhydrocarbon bearing zones to optimize drilling performance. Our air drilling systems eliminate nonproductive time caused by sticking or lost circulation and are well known for providing record ROPs, which ultimately lead to:

• Decreased costs
• Minimized deviation tendency in faulted formations
• Minimized lost circulation compared to conventional fluid systems

Drilling with air requires additional equipment and fluids to guarantee the safety of the job:

• Downhole equipment: percussion hammers and PDC air hammer bits
• Surface equipment: air compression equipment, rotating control devices, and two-phase separation equipment
• Fluids, chemicals, and related services

Horizontal wells –Underbalanced Equipment

•Specialized equipment is required to run an underbalanced well •Compressors •Mist pumps •Gas separators •Pressure boosters
•Rotating BOP •Closed loop system

Horizontal wells – Underbalanced

Horizontal wells – Underbalanced

•Under balanced drilling can reduce lost circulation, minimize differential sticking, increase drilling rates, and, most importantly, create higher productivity completions because formation damage is minimized. •To maximize benefits, extreme care must be taken to keep drilling and completion operations underbalanced at all times. •The rate of return from wells drilled underbalanced is typically higher. •Techniques for drilling underbalanced include –Lightweight drilling fluids, –Gas injection down the drill pipe, –Gas injection through a parasite string –Foam injection. •Nitrogen is typically used because of its relatively low generation cost, scale control and low potential for downhole fires. •Nitrogen injection down the drill pipe is the most cost effective when electromagnetic measurement-while-drilling (MWD) is used. •Despite added cost and time, parasite injection of nitrogen is the preferred method when electromagnetic MWD is not possible. •Foams are more stable than aerated systems, but they are more costly

Horizontal wells – Underbalanced Mud Systems

•Lightweight Drilling Fluids. –The simplest mechanism to reduce hydrostatic pressure in the wellbore is the use of lightweight drilling fluids, such as fresh water, diesel or lease crude. –The primary problem with this approach is that hydrostatic pressure can not be reduced enough to remain underbalanced in many reservoirs. Gas Injection Down Drillpipe. –With this technique, air or nitrogen is added to the drilling fluid and it is pumped directly down the drill pipe. –Advantages of this technique include: •Hydrostatic advantage gained over entire vertical depth, •Wellbore does not have to be specifically designed for underbalanced condition, •Less gas is required to achieve given pressure compared to parasite injection •Penetration rate may be improved. •Gas Injection Down Drillpipe Cont –Disadvantages of this technique include: •an overbalanced condition may occur if the well is shut down •exotic MWD systems are required. •Gas Injection Via Parasite String. –With this technique, a second pipe is run outside of the intermediate casing. –Advantages of this technique include: •No operational differences, •Constant bottom hole pressure is achieved, and •Standard MWD equipment can be used. –Disadvantages of this technique include: •Additional costs are incurred, •Additional time is required, •Larger diameter surface casing is required. •Foam Versus Two Phase Flow. –A nitrogen foam system is less damaging to water sensitive formations and has been used on a limited basis. –The additional nitrogen requirements to generate stable foam have made this cost prohibitive in most cases. –Aerated systems with gas/liquid ratios varying from 10-to-1 to 50-to-1 are simple and flexible, but pressure control/gas surging can be a problem. –The margin of safety for aerated systems is typically larger than for more stable systems, such as foams. –Foams also exhibit some sensitivity to hydrocarbons, so large inflows of hydrocarbons can destabilize them. –Temperature limits of current foams, about 180°F, restrict the use of foam to depths less than 12,000 ft.

Taking a Kick-Lost Circulation

Horizontal wells –Taking a Kick

•Most horizontal wells are development wells, this means that the reservoir should have already be well understood. –The chances of taking a kick in a horizontal well are reduced –Surge and swab pressures are still a factor •Well control procedures –Well control procedures are identical to vertical wells –Remember only the vertical component of the well will give you hydrostatic pressure –Drill bit should be on bottom when killing the well

Horizontal wells –Lost Circulation

•Lost circulation is treated similar in horizontal well as in vertical wells issues include: –Sensitivity of the formation to LCM material –Difficulty in spotting pills –Chances for differential sticking while dealing with losses are much higher •Curing lost circulation in horizontals –Always pull out to the first available casing string, mix enough LCM to fill the HZ section –Mix LCM as reservoir and hole conditions dictate •Particle size distribution •Fibers •Gunk squeeze

Horizontal wells -Overbalanced

•Most horizontal wells are completed without cementing or perforation –May have slotted liners –Open Hole completion –Gravel Pack completion Horizontal wells – Overbalanced Mud Systems •A horizontal mud system should have the following characteristics: –Formation damage control: •The horizontal mud system should not contain clays or acid-insoluble weight materials which can migrate into the formation and plug pores. •It should be formulated with breakable or acid-soluble viscosifiers, fluid-loss materials and properly sized plugging agents, all of which limit fluid loss to the formation and assure good clean-up. •The filtrate should be formulated to prevent clays in the producing zone from swelling, migrating or plugging the formation. –Formation damage control cont. •The filtrate should be formulated to prevent clays in the producing zone from swelling, migrating or plugging the formation •The filtrate should be compatible with formation fluids so that it will not precipitate mineral scales. •The fluid and filtrate should not change the wetting characteristics of the formation from either water-wet to oil-wet or from oil-wet to water-wet. •The filtrate should not form emulsions with formation fluids and block the formation. –Drillability: •The horizontal mud system should provide good hole-cleaning, lubricity and inhibition. •It should minimize hole enlargement and provide wellbore stability. –Compatibility with completion equipment and procedures: •Particles should be sized for formation pore throat bridging yet be small enough to pass through completion equipment. •The fluid should be formulated with acid-soluble, water-soluble, oxidizer-degradable or solvent soluble materials, which will not cause precipitates or emulsions. •Breakers should be compatible with formation fluids and horizontal mud system filtrate. •Susceptibility to different types of formation damage varies greatly and is dependent on the formation type and well conditions. •Some formations tolerate a wider range of horizontal mud system composition more than others. •When production is from carbonate fractures, significant amounts of insoluble materials can be tolerated without a significant reduction in productivity. –Usually, fluids which invade these types of formations can be produced back from the well •Lower permeability sandstones and depleted or unconsolidated sandstone reservoirs do not tolerate fluid and particle invasion without causing extensive damage. –Detailed knowledge of the formation, permeability, pore pressure, mineralogy and formation fluid composition must be called upon to assist in selecting the proper horizontal mud system

Multilateral Wells

•Like horizontal wells, multilateral wells justify their existence through their economics. •Defined as a single well with one or more wellbore branches radiating from the main borehole, they can be an exploration well, an infill development well or a re-entry into an existing well. –They all have a common goal of improving production while saving time and money. •Multilateral-well technology has not yet evolved to the point of horizontal-well technology. •The complexity of multilateral wells ranges from simple to extremely complex. •They may be as simple as a vertical wellbore with one sidetrack or as complex as a horizontal extended-reach well with multiple lateral and sublateralbranches. •While existing techniques are being applied and fresh approaches are being developed, complications remain, and the risks and chances of failure are still high.

Horizontal Wells

Why Drill Horizontally:-
•Increasing Production and Reducing Overall Drilling and Completion Costs
•Cost experts agree that horizontal wells have become a preferred method of recovering oil and gas from reservoirs in which these fluids occupy strata that are horizontal, or nearly so,
–they offer greater contact area with the productive layer than vertical wells
–While the cost factor for a horizontal well may be as much as two or three times that of a vertical well, the production factor can be enhanced as much as 15 or 20 times,
•Applications for horizontal wells include the exploitation of thin oil-rim reservoirs, avoidance of drawdown-related problems such as water/gas coning, and extension of wells by means of multiple drainholes.
•During the 1950s, the Soviet Union drilled 43 horizontal wells, a considerable effort with respect to the equipment available then.
•Following their foray into horizontal drilling, the Soviets concluded that while horizontal wells were technically feasible, they were economically disappointing or, in other words, not profitable.
–As a result, they abandoned the method.
•Unlike a directional well that is drilled to position a reservoir entry point, a horizontal well is commonly defined as any well in which the lower part of the wellbore parallels the pay zone.
•The angle of inclination used to drill the well does not have to reach 90°for the well to be considered a horizontal well.

Directional Drilling

•Sometimes wells must be drilled at high angles or even horizontally•Economic, environmental and technical reasons sometimes require that the well be dilled directionally•Deviated wells can sometimes access more of the reservoir than vertical ones •Large expensive offshore platform act as a central point for several deviated wells and can make these wells economical to drill •Specialized BHA’sare required to drill these wells –Include MWD (Measurements will drilling) tools –Mud motors –Stabilizers •Wells can be drilled in almost any direction now: S or U shaped, Horizontal

Blow Out Preventers

•
A large valve used to control wellbore fluids

•In this type of valve, the sealing element resembles a large rubber doughnut that is mechanically squeezed inward to seal on either pipe (drill collars, drillpipe, casing, or tubing) or the openhole.
•The ability to seal on a variety of pipe sizes is one advantage the annular blowout preventer has over ram-type blowout preventers Most blowout preventer (BOP) stacks contain at least one annular BOP at the top of the BOP stack, and one or more ram-type preventers below
•While not considered as reliable in sealing over the openholeas around tubulars, the elastomericsealing doughnut is required by API specifications to seal adequately over the openholeas part of its certification process

Drilling Rig Components

1
.Crown Block
2.CatlineBoom and Hoist Line

3.Drilling Line

4.Monkeyboard

5.Traveling Block

6.Top Drive

7.Mast

8.Drill Pipe

9.Doghouse

10.Blowout Preventer

11.Water Tank

12.Electric Cable Tray

13.Engine Generator Sets

14.Fuel Tank

15.Electrical Control House

16.Mud Pumps

17.Bulk Mud Component Tanks

18.Mud Tanks (Pits)

19.Reserve Pit

20.Mud-Gas Separator

21.Shale Shakers

22.Choke Manifold

23.Pipe Ramp

24.Pipe Racks

25.Accumulator

Exploration-Geophysics

Definition:•In hydrologic terms, the study of the physical characteristics and properties of the earth; including geodesy, seismology, meteorology, oceanography, atmospheric electricity, terrestrial magnetism, and tidal phenomena•We will only be briefly covering some surveying techniques

Knowing about the geology and the most likely traps that include hydrocarbons is important! Actually finding those traps is another thing altogether.
•Many methods have tried and failed to locate these reservoirs. The most important today are:
–Geological Exploration
–Ariel surveying
–Physical (Seismic) exploration
–Exploratory drilling

Geological Exploration•Actual surface observations by trained geologist can help to identify possible targets for exploration–Rock out crops–Canyon walls, road cuts, modern day structures•Geological maps can be made from these observations leading to the next phase of exploration

Aerial and satellite survey•High altitude surveys give a good picture of large anticlines or faulted regions that may be of interest•These surveys (either from aircraft or satellite) will help close in on further areas of interest.

Seismic Exploration
•The is the most common geophysical exploration method
•Shockwaves are aimed downwards into the rock strata and reflect back to sensitive surface equipment
•Different densities and hardness of the rocks reflect the waves at different rates of speed, seismologists interpret the variance in reflections and can model the strata below with the aid of complex computer programs

Seismic Exploration•New techniques such 3D seismic increase the success rates of finding reservoirs•Other geophysical exploration techniques include variations of gravity and magnetic properties to help detect subsurface formations.

Drag BITS

what is drag bit?

A drag bit is a drill bit usually designed for use in soft formations such as sand, clay, or some soft rock. However, they will not work well in coarse gravel or hard rock formations. Uses include drilling water wells, mining, geothermal, environmental and exploration drilling. Whenever possible, they should be used to drill pilot holes because they produce cuttings that are easiest to log

Historically there were two types of drill bits used in or natural gas drilling rigs , a drag bit and a rock bit:

1.a polycrystalline diamond compact hammer bit( pdc bits) is used for soft rocks, like sand and clay. The drill string is rotated along with pneumatic pressure, and nibs on the bit shear the rock.

2.a deep hole (also called a roller bit ) consists of teeth on wheels which turn as the drill string is rotated. These teeth apply a crushing pressure to the rock, breaking it up into small pieces.

In today's modern industry the two main types of drill bits are now classed as PDC (polycrystalline Diamond Compact) and Roller Cone; although the tri-cone dominates, bi-cone and mono cone bits do exist. Natural and synthetic diamonds are used in coring bits, as well as for very hard rock drilling with mud motors and turbines.drag bit type bits are used for mining and construction and also for oil and gas work over wells.

What PDC bit?

A drilling tool that uses polycrystalline diamond compact (PDC) cutters to shear rock with a continuous scraping motion. These cutters are synthetic diamond disks about 1/8-in. thick and about 1/2 to 1 in. in diameter. PDC bits are effective at drilling shale formations, especially when used in combination with oil-base muds.

Advantages of PDC bits:

Bit Brokers International introduces PDC bits to their line-up of products. These bits are designed for high speed drilling in shale, limestone, and sandstone formations. Unlike roller cones, these PDC bits are a one piece matrix bodies with no moving parts. The fixed-cutters shave away the rock, making it possible to operate with higher rotation speeds more efficiently in consolidated formations.

Bit Brokers offers PDC bits in a variety of sizes and number of blades.

Variables affected PDC bits design

1.Bit body material.

2.Bit profile.

3.Grave protection.

4.Cutter shape.

5.Number of concentration of cutter.

6.Locations of cutter.

7.Cutter orientation.

8.Cutter exposures.

9.Hydraulics.

Roller cone bit

A roller-cone bit is adrill bit used for drilling through rock, for example when drilling for oiland gas.

There are three types of roller cone bit:

1.The two cone bit: is used for soft formation only.

2.The three cone bit: is the most widely used.

3.The four cone bit: is used for drilling large hole size.

oil traps

There are three basic forms of a structural trap in petroleum geology:

• Anticline Trap
• Fault Trap
• Salt Dome Trap

The common link between these three is simple: some part of the earth has moved in the past, creating an impedence to oil flow.
Anticline Trap

An anticline is an example of rocks which were previously flat, but have been bent into an arch. Oil that finds its way into a reservoir rock that has been bent into an arch will flow to the crest of the arch, and get stuck (provided, of course, that there is a trap rock above the arch to seal the oil in place

Fault Trap

Fault traps are formed by movement of rock along a fault line. In some cases, the reservoir rock has moved opposite a layer of impermeable rock. The impermeable rock thus prevents the oil from escaping. In other cases, the fault itself can be a very effective trap. Clays within the fault zone are smeared as the layers of rock slip past one another. This is known as fault gouge

Salt Dome Trap
Salt is a peculiar substance. If you put enough heat and pressure on it, the salt will slowly flow, much like a glacier that slowly but continually moves downhill. Unike glaciers, salt which is buried kilometers below the surface of the Earth can move upward until it breaks through to the Earth's surface, where it is then dissolved by ground- and rain-water. To get all the way to the Earth's surface, salt has to push aside and break through many layers of rock in its path. This is what ultimately will create the oil trap

Stratigraphic Traps

A stratigraphic trap accumulates oil due to changes of rock character rather than faulting or folding of the rock. The term "stratigraphy" basically means "the study of the rocks and their variations". One thing stratigraphy has shown us is that many layers of rock change, sometimes over short distances, even within the same rock layer. As an example, it is possible that a layer of rock which is a sandstone at one location is a siltstone or a shale at another location. In between, the rock grades between the two rock types. From the section on reservoir rocks, we learned that sandstones make a good reservoir because of the many pore spaces contained within. On the other hand, shale, made up of clay particles, does NOT make a good reservoir, because it does not contain large pore spaces. Therefore, if oil migrates into the sandstone, it will flow along this rock layer until it hits the low-porosity shale. Voilà, a stratigraphic trap is born!

Combination Traps

As the name implies, a combination trap is where two (or more) trapping mechanisms come together to create the trap. In reality, many successful oil traps are combination traps.