What is Directional Drilling?

Directional drilling is the science of deviating a wellbore along a planned path to a target located at a given lateral distance and direction from vertical. This includes drilling as vertically as possible from a given TVD.

The figure below shows a vertical well and a deviated well.

As a starter one can consider that any well which gets deviated from the vertical axis to achieve the desired target (hydrocarbon reserve in our case) may be termed as deviated well (or Directional well). 

 

Vertical Versus Deviated Wells

What are the applications of Directional Drilling?

1. Side Tracking

Sidetracking is one of the primary uses for directional drilling. Sidetracking is an operation which deflects the borehole by starting a new hole at any point above the bottom of the old hole as in Figure below. 

The primary reason for sidetracking is to bypass a fish which has been lost in the hole; however, there are several other reasons for sidetracking. A sidetrack can be performed so the bottom of the hole can intersect a producing formation at a more favorable position such as up dip above the oil-water contact. A well can be sidetracked to alleviate problems associated with water or gas coning. A sidetrack can be performed in an old well to move the location of the bottom of the hole from a depleted portion of the reservoir to a portion that is productive, such as, across a fault or permeability barrier. 

Most often, a sidetrack is accomplished by setting a cement plug in the hole and dressing off the plug to a depth at which the sidetrack will commence. The sidetrack can be either "blind" or "oriented". In a blind sidetrack, the direction of the sidetrack is not specified and is not considered a directional well. In either case, a deflecting tool is used to drill out the old hole and start a new hole.

 

2. Straight Hole Drilling
straight hole drilling may be a special case of directional drilling where an try is made out to keep the hole vertical. a few reasons for wanting out to keep the hole vertical are :
a. out to keep from crossing lease lines ;
b. out to keep among the specifications of the drilling contract ;
c. out to keep among the well spacing requirements because we are part of a developed field 

 

3. Controlled Directional Drilling

Controlled directional drilling is used when drilling multiple wells from an artificial structure such as offshore platforms, drilling pads, or man made islands. The economics of building one offshore platform for each well would be prohibitive in most cases. However, since wells can be directionally drilled, forty or more wells can be drilled from a single platform. Without controlled directional drilling, most offshore drilling would not be economical.

 

4. Drilling Multiple Sands With One Wellbore
there will be special cases when multiple sands are drilled with one wellbore. where steeply dipping sand zones are sealed by an unconformity, fault, or salt dome overhang, variety of vertical wells might possibly be needed to actually manufacture every sand, which you ll realize are separated by a permeability barrier. in spite of this, all the sand zones often is penetrated with one directionally drilled well thereby greatly reducing the price of production 

 

5. Inaccessible Locations there will be occasions when oil deposits lie beneath inaccessible locations inclusive of towns, rivers, shorelines, mountains, or maybe even production facilities. each time a location can't be constructed directly higher than the manufacturing formation, the wellbore often is horizontally displaced by directional drilling. this allows production associated with an otherwise inaccessible hydrocarbon deposit  

6. Fault Drilling
directional drilling can be applicable in fault drilling. it is typically troublesome to actually drill a vertical well because we are part of a steeply dipping, inclined fault plane. usually, the bit can deflect when passing in the fault plane, and typically the bit can follow the fault plane. to actually avoid the challenge, the well often is drilled upon the upthrown or downthrown side on your fault and deflected into your manufacturing formation. the bit can cross the fault at enough associated with an angle exactly where the direction on your bit can't amendment to actually follow the fault. 

 

7. Drilling Salt Dome Region several oil fields are associated when using the intrusion of salt domes. directional drilling has also been utilized tap a number of oil that has also been trapped by your intrusion on your salt. rather than drilling in the salt overhangs, the wells often is directionally drilled adjacent towards the salt dome and into your underlying traps as shown in figure below. in spite of this, since the event of salt saturated and oil based mostly muds, the level of directional drilling has decreased. it's troublesome to actually drill long intervals of salt with recent water muds. directionally drilling along the salt, alleviates a great deal of the issues related to drilling salt.  

8. Relief Well
a highly specialized application for directional drilling is that the relief well. if a well blows out and is not accessible direct from surface, then a relief well is drilled to actually intersect the uncontrolled well close to the bottom. water or mud are then pumped in the relief well and into your uncontrolled well. since it is typically needed that the relief well intersect the uncontrolled well, the directional drilling has to actually be extremely precise and needs special tools. survey data isn't correct enough to actually intersect a wellbore at depth. proximity logging is needed when drilling relief wells. 

 

9. DRILLING HORIZONTAL WELLS

Horizontal drilling is another special application of directional drilling and is used to increase the productivity of various formations. One of the first applications for horizontal drilling was in vertically fractured reservoirs. In fractured reservoirs, a significant quantity of the production comes from fractures. Unless a vertical well encounters a fracture system, production rates will be low.

Horizontal drilling is used to produce thin oil zones with water or gas coning problems. The horizontal well is optimally placed in the oil leg of the reservoir. The oil can then be produced at high rates with much less pressure drawdown because of the amount of formation exposed to the wellbore.
Horizontal wells are used to increase productivity from low permeability reservoirs by increasing the amount of formation exposed to the wellbore. Additionally, numerous hydraulic fractures can be placed along a single wellbore to increase production and reduce the number of vertical wells required to drain the reservoir.

Horizontal wells can be used to maximize production from reservoirs which are not being efficiently drained by vertical wells.

 

10. Drilling Multilateral Wells

Directional drilling can also be used to drill multilateral wells. Multilaterals are additional wells drilled from a parent wellbore. Multilaterals can be as simple as an open hole sidetrack or it can be more complicated with a junction that is cased and has pressure isolation and reentry capabilities. Multilaterals are used where production can be incrementally increased with less capital costs. Multilaterals can be used offshore where the number of slots are limited. It is also used to place additional horizontal wells in a reservoir.

 

11. Extended Reach Drilling
Another application of directional drilling is what is commonly termed extended reach drilling. As illustrated in Figure below, extended reach drilling is where wells have high inclinations and large horizontal displacements for the true vertical depth drilled. Extended reach drilling is used to develop reservoirs with fewer platforms or smaller sections of a reservoir where an additional platform cannot be economically justified. Extended reach drilling will become more popular as the cost of platforms in deeper water and severe environments becomes more expensive.

 

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1. There Is No Way To save Time

Solution :

Stop concentrating on how to save time. Instead, focus on how to spend time.

- The only way to manage your time better is to spend your time better.

2. Being Busy

Solution :

Spend some time each day thinking about your activities. How much does each of your activities contribute to your objectives? Which activities should be added that you are not presently accomplishing?

- Adequate thought before acting usually leads to much better results

3. Working Smarter Always Beats Working Harder

Solution :

Work Smarter, not Harder. Try finding ways to reduce the number of tasks.

- Make the job easier or quicker and you will probably also make it more efficient

4. Doing It Yourself May Seem Faster and Better in The Short Run, But It Never Faster and Better in The Long Run

Solution :

Recognise that future rewards are closely tied to the performance of your subordinates. Not only are your talents and time limited, but also failing to develop your subordinates is professional suicide. Don’t be fooled by the apparent truth of this assumption in the short run.

5. Filing To Properly Identify The Problem is Perhaps The Greatest Difficulty in Solving It

Solution :

Don’t assume that symptoms are problems. Collect data to understand the exact nature of the problem.

- The solution then become much easier and are more likely to work well.

6. The Ordinary Day-To-Day Activities are The Ones That Most Need To Be Planned If You Want To Control Your Time

Solution :

Identify the patterns involved in your job, then use this information in planning and scheduling every day. Remember to leave room in your schedule for flexibility

 

7. Efficiency does Not Necessarily Lead To Effectiveness

Solution :

Focus first on effectiveness, then on efficiency. Determine first what you should be doing. Then ask how can it be done most efficiently?

- Do the right things right, in the right instance, right place at the right time

8. Many Managerial Short-Cuts Ultimately Cost Vast Amounts of Time

Solution :

Look over all your activities. Which ones are most important relative to your objectives? Which ones are least important? Look for short cuts in the routine, trivial activities.

- Be sure to make sufficient time available for the really important things.

9. Managing The Time Better Involves Spending The Appropriate Amount Of Time On Every Task

Solution :

Review your objectives and your activities. Keep a time log for a week or two. What areas should take less of your time? Where should you increase your time?

- Develop the proper balance for what you’re trying to accomplish

10.Everyone Has All The Time Available

Solution :

Think about whom you are and what you’re trying to accomplish. Write out all your objectives and prioritize them. Rearrange things so that you spend more of your time on he high priority items.

- You will be amazed at how much time you really do have.

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Once the equipment is at the site, the rig is set up. Here are the major systems of a land oil rig:




# Power system

* large diesel engines - burn diesel-fuel oil to provide the main source of power
* electrical generators - powered by the diesel engines to provide electrical power

# Mechanical system - driven by electric motors

* hoisting system - used for lifting heavy loads; consists of a mechanical winch (drawworks) with a large steel cable spool, a block-and-tackle pulley and a receiving storage reel for the cable
* turntable - part of the drilling apparatus

# Rotating equipment - used for rotary drilling

* swivel - large handle that holds the weight of the drill string; allows the string to rotate and makes a pressure-tight seal on the hole
* kelly - four- or six-sided pipe that transfers rotary motion to the turntable and drill string
* turntable or rotary table - drives the rotating motion using power from electric motors
* drill string - consists of drill pipe (connected sections of about 30 ft / 10 m) and drill collars (larger diameter, heavier pipe that fits around the drill pipe and places weight on the drill bit)
* drill bit(s) - end of the drill that actually cuts up the rock; comes in many shapes and materials (tungsten carbide steel, diamond) that are specialized for various drilling tasks and rock formations

Casing - large-diameter concrete pipe that lines the drill hole, prevents the hole from collapsing, and allows drilling mud to circulate.

# Circulation system - pumps drilling mud (mixture of water, clay, weighting material and chemicals, used to lift rock cuttings from the drill bit to the surface) under pressure through the kelly, rotary table, drill pipes and drill collars

* pump - sucks mud from the mud pits and pumps it to the drilling apparatus
* pipes and hoses - connects pump to drilling apparatus
* mud-return line - returns mud from hole
* shale shaker - shaker/sieve that separates rock cuttings from the mud
* shale slide - conveys cuttings to the reserve pit
* reserve pit - collects rock cuttings separated from the mud
* mud pits - where drilling mud is mixed and recycled
* mud-mixing hopper - where new mud is mixed and then sent to the mud pits

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A drilling rig is a machine which creates holes (usually called boreholes) and/or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person.[citation needed] They sample sub-surface mineral deposits, test rock, soil and groundwater physical properties, and also can be used to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or marine-based structures (such as oil platforms, commonly called 'offshore oil rigs' even if they don't contain a drilling rig). The term "rig" therefore generally refers to the complex of equipment that is used to penetrate the surface of the earth's crust.

Drilling rigs can be:

* Small and portable, such as those used in mineral exploration drilling, water wells and environmental investigations.

* Huge, capable of drilling through thousands of meters of the Earth's crust. Large "mud pumps" circulate drilling mud (slurry) through the drill bit and up the casing annulus, for cooling and removing the "cuttings" while a well is drilled. Hoists in the rig can lift hundreds of tons of pipe. Other equipment can force acid or sand into reservoirs to facilitate extraction of the oil or natural gas; and in remote locations there can be permanent living accommodation and catering for crews (which may be more than a hundred). Marine rigs may operate many hundreds of miles or kilometres distant from the supply base with infrequent crew rotation.

History
Until internal combustion engines came in the late 19th century, the main method for drilling rock was muscle power of man or animal. Rods were turned by hand, using clamps attached to the rod. The rope and drop method invented in Zigong, China used a steel rod or piston raised and dropped vertically via a rope. Mechanised versions of this persisted until about 1970, using a cam to rapidly raise and drop what, by then, was a steel cable.

In the 1970s, outside of the oil and gas industry, roller bits using mud circulation were replaced by the first efficient pneumatic reciprocating piston Reverse Circulation RC drills, and became essentially obsolete for most shallow drilling, and are now only used in certain situations where rocks preclude other methods. RC drilling proved much faster and more efficient, and continues to improve with better metallurgy, deriving harder, more durable bits, and compressors delivering higher air pressures at higher volumes, enabling deeper and faster penetration. Diamond drilling has remained essentially unchanged since its inception.

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There are many types and designs of drilling rigs, with many drilling rigs capable of switching or combining different drilling technologies as needed. Drilling rigs can be described using any of the following attributes:

by power used

* mechanical - the rig uses torque converters, clutches, and transmissions powered by its own engines, often diesel
* electric - the major items of machinery are driven by electric motors, usually with power generated on-site using internal combustion engines
* hydraulic - the rig primarily uses hydraulic power
* pneumatic - the rig is primarily powered by pressurized air
* steam - the rig uses steam-powered engines and pumps (obsolescent after middle of 20th Century)

by pipe used

* cable - a cable is used to raise and drop the drill bit
* conventional - uses metal or plastic drill pipe of varying types
* coil tubing - uses a giant coil of tube and a downhole drilling motor

by height

* single - can drill only single drill pipes. The presence or absence of vertical pipe racking "fingers" varies from rig to rig.
* double - can hold a stand of pipe in the derrick consisting of two connected drill pipes, called a "double stand".
* triple - can hold a stand of pipe in the derrick consisting of three connected drill pipes, called a "triple stand".


by method of rotation or drilling method

* no rotation includes direct push rigs and most service rigs
* rotary table - rotation is achieved by turning a square or hexagonal pipe (the kelly) at drill floor level.
* top drive - rotation and circulation is done at the top of the drillstring, on a motor that moves in a track along the derrick.
* sonic - uses primarily vibratory energy to advance the drill string
* hammer - uses rotation and percussive force


by position of derrick

* conventional - derrick is vertical
* slant - derrick is slanted at a 45 degree angle to facilitate horizontal drilling

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Auger drilling

Auger drilling is done with a helical screw which is driven into the ground with rotation; the earth is lifted up the borehole by the blade of the screw. Hollow stem Auger drilling is used for environmental drilling, geotechnical drilling, soil engineering and geochemistry reconnaissance work in exploration for mineral deposits. Solid flight augers/bucket augers are used in construction drilling. In some cases, mine shafts are dug with auger drills. Small augers can be mounted on the back of a utility truck, with large augers used for sinking piles for bridge foundations.

Auger drilling is restricted to generally soft unconsolidated material or weak weathered rock. It is cheap and fast.

Percussion rotary air blast drilling (RAB)

RAB drilling is used most frequently in the mineral exploration industry. (This tool is also known as a Down-The-Hole Drill.) The drill uses a pneumatic reciprocating piston-driven 'hammer' to energetically drive a heavy drill bit into the rock. The drill bit is hollow, solid steel and has ~20 mm thick tungsten rods protruding from the steel matrix as 'buttons'. The tungsten buttons are the cutting face of the bit.

The cuttings are blown up the outside of the rods and collected at surface. Air or a combination of air and foam lift the cuttings.

RAB drilling is used primarily for mineral exploration, water bore drilling and blast-hole drilling in mines, as well as for other applications such as engineering, etc. RAB produces lower quality samples because the cuttings are blown up the outside of the rods and can be contaminated from contact with other rocks. RAB drilling at extreme depth, if it encounters water, may rapidly clog the outside of the hole with debris, precluding removal of drill cuttings from the hole.

This can be counteracted, however, with the use of 'stabilisers' also known as 'reamers', which are large cylindrical pieces of steel attached to the drill string, and made to perfectly fit the size of the hole being drilled. These have sets of rollers on the side, usually with tungsten buttons, that constantly break down cuttings being pushed upwards.

The use of high-powered air compressors, which push 900-1150cfm of air at 300-350psi down the hole also ensures drilling of a deeper hole up to ~1250m due to higher air pressure which pushes all rock cuttings and any water to the surface. This, of course, is all dependent on the density and weight of the rock being drilled, and on how worn the drill bit is.


Air core drilling

Air core drilling and related methods use hardened steel or tungsten blades to bore a hole into unconsolidated ground. The drill bit has three blades arranged around the bit head, which cut the unconsolidated ground. The rods are hollow and contain an inner tube which sits inside the hollow outer rod barrel. The drill cuttings are removed by injection of compressed air into the hole via the annular area between the innertube and the drill rod. The cuttings are then blown back to surface up the inner tube where they pass through the sample separating system and are collected if needed. Drilling continues with the addition of rods to the top of the drill string. Air core drilling can occasionally produce small chunks of cored rock.

This method of drilling is used to drill the weathered regolith, as the drill rig and steel or tungsten blades cannot penetrate fresh rock. Where possible, air core drilling is preferred over RAB drilling as it provides a more representative sample. Air core drilling can achieve depths approaching 300 meters in good conditions. As the cuttings are removed inside the rods and are less prone to contamination compared to conventional drilling where the cuttings pass to the surface via outside return between the outside of the drill rob and the walls of the hole. This method is more costly and slower than RAB.


Cable Tool Drilling

Cable tool rigs are a traditional way of drilling water wells internationally and in the United States. The majority of large diameter water supply wells, especially deep wells completed in bedrock aquifers, were completed using this drilling method. Although this drilling method has largely been supplanted in recent years by other, faster drilling techniques, it is still the most practicable drilling method for large diameter, deep bedrock wells, and in widespread use for small rural water supply wells. The impact of the drill bit fractures the rock and in many shale rock situations increases the water flow into a well over rotary.

Also known as ballistic well drilling and sometimes called "spudders", these rigs raise and drop a drill string with a heavy carbide tipped drilling bit that chisels through the rock by finely pulverizing the subsurface materials. The drill string is composed of the upper drill rods, a set of "jars" (inter-locking "sliders" that help transmit additional energy to the drill bit and assist in removing the bit if it is stuck) and the drill bit. During the drilling process, the drill string is periodically removed from the borehole and a bailer is lowered to collect the drill cuttings (rock fragments, soil, etc.). The bailer is a bucket-like tool with a trapdoor in the base. If the borehole is dry, water is added so that the drill cuttings will flow into the bailer. When lifted, the bailer closes and the cuttings are then raised and removed. Since the drill string must be raised and lowered to advance the boring, casing (larger diameter outer piping) is typically used to hold back upper soil materials and stabilize the borehole.

Cable tool rigs are simpler and cheaper than similarly sized rotary rigs, although loud and very slow to operate. The world record cable tool well was drilled in New York to a depth of almost 12,000 feet. The common Bucyrus Erie 22 can drill down to about 1,100 feet. Since cable tool drilling does not use air to eject the drilling chips like a rotary, instead using a cable strung bailer, technically there is no limitation on depth.


Reverse circulation (RC) drilling

RC drilling is similar to air core drilling, in that the drill cuttings are returned to surface inside the rods. The drilling mechanism is a pneumatic reciprocating piston known as a hammer driving a tungsten-steel drill bit. RC drilling utilises much larger rigs and machinery and depths of up to 500 metres are routinely achieved. RC drilling ideally produces dry rock chips, as large air compressors dry the rock out ahead of the advancing drill bit. RC drilling is slower and costlier but achieves better penetration than RAB or air core drilling; it is cheaper than diamond coring and is thus preferred for most mineral exploration work.

Reverse circulation is achieved by blowing air down the rods, the differential pressure creating air lift of the water and cuttings up the inner tube which is inside each rod. It reaches the bell at the top of the hole, then moves through a sample hose which is attached to the top of the cyclone. The drill cuttings travel around the inside of the cyclone until they fall through an opening at the bottom and are collected in a sample bag.

The most commonly used RC drill bits are 5-8 inches (12.7–20.32 cm) in diameter and have round metal 'buttons' that protrude from the bit, which are required to drill through shale and abrasive rock. As the buttons wear down, drilling becomes slower and the rod string can potentially become bogged in the hole. This is a problem as trying to recover the rods may take hours and in some cases weeks. The rods and drill bits themselves are very expensive, often resulting in great cost to drilling companies when equipment is lost down the bore hole. Most companies will regularly re-grind the buttons on their drill bits in order to prevent this, and to speed up progress. Usually, when something is lost (breaks off) in the hole, it is not the drill string, but rather from the bit, hammer, or stabiliser to the bottom of the drill string (bit). This is usually caused by a blunt bit getting stuck in fresh rock, over-stressed metal, or a fresh drill bit getting stuck in a part of the hole that is too small, owing to having used a bit that has worn to smaller than the desired hole diameter.

Although RC drilling is air-powered, water is also used, to reduce dust, keep the drill bit cool, and assist in pushing cutting back upwards, but also when collaring a new hole. A mud called liqui-pol is mixed with water and pumped into the rod string, down the hole. This helps to bring up the sample to the surface by making the sand stick together. Occasionally, 'super-foam' (AKA 'quik-foam') is also used, to bring all the very fine cuttings to the surface, and to clean the hole. When the drill reaches hard rock, a collar is put down the hole around the rods which is normally PVC piping. Occasionally the collar may be made from metal casing. Collaring a hole is needed to stop the walls from caving in and bogging the rod string at the top of the hole. Collars may be up to 60 metres deep, depending on the ground, although if drilling through hard rock a collar may not be necessary.

Reverse circulation rig setups usually consist of a support vehicle, an auxiliary vehicle, as well as the rig itself. The support vehicle, normally a truck, holds diesel and water tanks for resupplying the rig. It also holds other supplies needed for maintenance on the rig. The auxiliary is a vehicle, carrying an auxiliary engine and a booster engine. These engines are connected to the rig by high pressure air hoses. Although RC rigs have their own booster and compressor to generate air pressure, extra power is needed which usually isn't supplied by the rig due to lack of space for these large engines. Instead, the engines are mounted on the auxiliary vehicle. Compressors on an RC rig have an output of around 1000 cfm at 500 psi (500 L·s−1 at 3.4 MPa). Alternatively, stand-alone air compressors which have an output of 900-1150cfm at 300-350 psi each are used in sets of 2, 3, or 4, which are all routed to the rig through a multi-valve manifold.


Diamond core drilling

Diamond core drilling (Exploration diamond drilling) utilises an annular diamond-impregnated drill bit attached to the end of hollow drill rods to cut a cylindrical core of solid rock. The diamonds used are fine to microfine industrial grade diamonds. They are set within a matrix of varying hardness, from brass to high-grade steel. Matrix hardness, diamond size and dosing can be varied according to the rock which must be cut. Holes within the bit allow water to be delivered to the cutting face. This provides three essential functions; lubrication, cooling, and removal of drill cuttings from the hole.

Diamond drilling is much slower than reverse circulation (RC) drilling due to the hardness of the ground being drilled. Drilling of 1200 to 1800 metres is common and at these depths, ground is mainly hard rock. Diamond rigs need to drill slowly to lengthen the life of drill bits and rods, which are very expensive.

Core samples are retrieved via the use of a lifter tube, a hollow tube lowered inside the rod string by a winch cable until it stops inside the core barrel. As the core is drilled, the core lifter slides over the core as it is cut. An overshot attached to the end of the winch cable is lowered inside the rod string and locks on to the backend, located on the top end of the lifter tube. The winch is retracted, pulling the lifter tube to the surface. The core does not drop out the inside of the lifter tube when lifted because a "core lifter spring," located at the bottom of the tube allows the core to move inside the tube but not fall out.
Once a rod is removed from the hole, the core sample is then removed from the rod and catalogued. The Driller's offsider screws the rod apart using tube clamps, then each part of the rod is taken and the core is shaken out into core trays. The core is washed, measured and broken into smaller pieces using a hammer or sawn through to make it fit into the sample trays. Once catalogued, the core trays are retrieved by geologists who then analyse the core and determine if the drill site is a good location to expand future mining operations.

Diamond rigs can also be part of a multi-combination rig. Multi-combination rigs are a dual setup rig capable of operating in either a reverse circulation (RC) and diamond drilling role (though not at the same time). This is a common scenario where exploration drilling is being performed in a very isolated location. The rig is first set up to drill as an RC rig and once the desired metres are drilled, the rig is set up for diamond drilling. This way the deeper metres of the hole can be drilled without moving the rig and waiting for a diamond rig to set up on the pad.


Direct Push Rigs

Direct push technology includes several types of drilling rigs and drilling equipment which advances a drill string by pushing or hammering without rotating the drill string. While this does not meet the proper definition of drilling, it does achieve the same result - a borehole. Direct push rigs include both cone penetration testing (CPT) rigs and direct push sampling rigs such as a PowerProbe or Geoprobe. Direct push rigs typically are limited to drilling in unconsolidated soil materials and very soft rock.

CPT rigs advance specialized testing equipment (such as electronic cones), and soil samplers using large hydraulic rams. Most CPT rigs are heavily ballasted (20 metric tons is typical) as a counter force against the pushing force of the hydraulic rams which are often rated up to 20kn. Alternatively, small, light CPT rigs and offshore CPT rigs will use anchors such as screwed-in ground anchors to create the reactive force. In ideal conditions, CPT rigs can achieve production rates of up to 250-300 meters per day.

Direct Push Drilling rigs use hydraulic cylinders and a hydraulic hammer in advancing a hollow core sampler to gather soil and groundwater samples. The speed and depth of penetration is largely dependent on the soil type, the size of the sampler, and the weight and power the rig. Direct push techniques are generally limited to shallow soil sample recovery in unconsolidated soil materials. The advantage of direct push technology is that in the right soil type it can produce a large number of high quality samples quickly and cheaply, generally from 50 to 75 meters per day. Rather than hammering, direct push can also be combined with sonic (vibratory) methods to increase drill efficiency.


Hydraulic-rotary drilling

Oil well drilling utilises tri-cone roller, carbide embedded, fixed-cutter diamond, or diamond-impregnated drill bits to wear away at the cutting face. This is preferred because there is no need to return intact samples to surface for assay as the objective is to reach a formation containing oil or natural gas. Sizable machinery is used, enabling depths of several kilometres to be penetrated. Rotating hollow drill pipes carry down bentonite and barite infused drilling muds to lubricate, cool, and clean the drilling bit, control downhole pressures, stabilize the wall of the borehole and remove drill cuttings. The mud travels back to the surface around the outside of the drill pipe, called the annulus. Examining rock chips extracted from the mud is known as mud logging. Another form of well logging is electronic and is frequently employed to evaluate the existence of possible oil and gas deposits in the borehole. This can take place while the well is being drilled, using Measurement While Drilling tools, or after drilling, by lowering measurement tools into the newly-drilled hole.

The rotary system of drilling was in general use in Texas in the early 1900s. It is a modification of one invented by Fauvelle in 1845, and used in the early years of the oil industry in some of the oil-producing countries in Europe. Originally pressurized water was used instead of mud, and was almost useless in hard rock before the diamond cutting bit.[1]. The main breakthrough for rotary drilling came in 1901, when Anthony Francis Lucas combined the use of a steam-driven rig and of mud instead of water in the Spindletop discovery well.[2]

The drilling and production of oil and gas can pose a safety risk and a hazard to the environment from the ignition of the entrained gas causing dangerous fires and also from the risk of oil leakage polluting water, land and groundwater. For these reasons, redundant safety systems and highly trained personnel are required by law in all countries with significant production.


Sonic (vibratory) drilling

A sonic drill head works by sending high frequency resonant vibrations down the drill string to the drill bit, while the operator controls these frequencies to suit the specific conditions of the soil/rock geology. Vibrations may also be generated within the drill head. The frequency is generally between 50 and 120 hertz (cycles per second) and can be varied by the operator.

Resonance magnifies the amplitude of the drill bit, which fluidizes the soil particles at the bit face, allowing for fast and easy penetration through most geological formations. An internal spring system isolates these vibrational forces from the rest of the drill rig.

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Fungsi Casing

Setelah suatu pemboran minyak dan gas bumi mencapai kedalaman tertentu, maka kedalaman sumur tersebut perlu dipasang casing yang kemudian dilanjutkan dengan proses penyemanan. Casing merupakan suatu pipa baja yang berfungsi antara lain : Mencegah gugurnya dinding sumur, menutup zona bertekanan abnormal, zona lost dan sebagainya. Tujuan utama dari perencanaan casing adalah mendapatkan rangkaian casing yang cukup kuat untuk melindungi sumur baik selama pemboran maupun produksi dengan biaya yang murah. Beberapa fungsi casing adalah sebagai berikut :

Mencegah Gugurnya Dinding Sumur

Pada lapisan batuan yang tidak terkonsolidasi dengan baik, maka pada saat pemboran menembus lapisan tersebut dapat menyebabkan terjadinya pembesaran pada lubang bor. Pembesaran pada lubang bor ini adalah akibat runtuhnya dinding sumur, lebih jauh apabila lapisan lunak ini berselang-seling dengan lapisan keras maka akan memberikan efek pembelokan terhadap drill string.

Mencegah Terkontaminasinya Air Tanah Oleh Lumpur Pemboran

Dalam suatu pemboran, untuk mengimbangi tekanan formasi digunakan lumpur pemboran yang memiliki densitas tertentu. Lumpur pemboran ini akan memberikan/mengimbangi tekanan hidrostatik dari formasi. Pada dinding sumur akan terbentuk mud cake sedangkan filtrat lumpur akan masuk menembus formasi. MAsuknya filtrat lumpur ke dalam formasi dapat menyebabkan adanya air. Untuk mencegah terjadinya pencemaran air formasi maka dipasanglah casing.

Menutup Zona Bertekanan Abnormal dan Zona Loss

Zona bertekanan abnormal adalah zona yang dapat menyebabkan terjadinya well kick yaitu masuknya fluida formasi ke dalam lubang bor. Terlebih apabila fluida ini berupa gas dan tidak segera ditanggulangi maka akan terjadi semburan liar (blow out)yang sangat membahayakan. Sedangkan zona loss adalah zona dimana lumpur pemboran menghilang masuk ke formasi.

Membuat Diameter Sumur Tetap

Sebagaimana disebutkan diatas bahwa pada dinding sumur akan terbentuk mud cake. tetapi ketebalan mud cake ini merupakan fungsi dari waktu dan permeabilitas dari batuan yang ditembus.Bila permeabilitasnya besar maka mud cake semakin tebal. Dengan dipasangnya casing maka diameter sumur akan tetap, hal ini terutama akan bermanfaat apabila kita membutuhkan data volume annulus secara tepat.

Mencegah Hubungan Langsung Antar Formasi

Sebagai contoh apabila suatu sumur dapat menghasilkan minyak dan gas dari lapisan yang berbeda dan dikehendaki untuk diproduksi bersama-sama maka untuk memisahkan dua lapisan produktif tersebut dipasang casing dan packer.

Tempat Kedudukan BOP dan Peralatan Produksi

BOP (Blow Out Preventer) merupakan peralatan untuk menahan tekanan sumur yang berada dalam kondisi kick. BOP ini diletakkan pada surface casing. Peralatan produksi yang dipasang pada casing misalnya X-mas Tree dll.

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