oil & gas drilling preliminaries

Drilling Preliminaries

Kartikeya Pandey Prof Anil KumarMBA IFM (HOD Power & Infrastructure 500021353 Management)

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Steps to Drill A Gas/Oil Well1. Complete or obtain seismic, log,

scouting information or other data.

2. Lease the land or obtain concession.

3. Calculate reserves or estimate from best data available.

Steps to Drill A Gas/Oil Well4. If reserve estimates show

payout, proceed with well.

5. Obtain permits from conservation / national authority.

6. Prepare drilling and completion program.

Steps to Drill a Well - cont’d7. Ask for bids on footage, day work,

or combination from selected drilling contractors based on drilling program.

8. If necessary, modify program to fit selected contractor equipment.

9. Construct road, location/platforms and other marine equipment necessary for access to site.

Steps to Drill a Well - cont’d10. Gather all personnel concerned for

meeting prior to commencing drilling (pre-spud meeting).

11. If necessary, further modify program.

12. Drill well.

Introduction

When a suitable structure, sufficiently large, so as to give economically viable reserves of HCs) is discovered for the presence of HCs by geological, geochemical & geophysical methods, a location for drilling of an exploratory / wild cat well is decided.

Classification of Wells

Exploratory Well / WildCat Well: They are drilled purely for exploratory purposes i.e. for gathering information. The well is drilled to find and produce oil or gas in an unproven area,  or to find a new reservoir  in fields,  or to extend a known reservoir.

Classification of Wells

Discovery Well:

If the well does discover a new field, it is called the discovery well for that field.

Classification of Wells

Appraisal Well/ Delineation Well:

After the discovery, the size of the field must be determined. Field size is determined by “step out” or “Delineation” or “Appraisal” well that are drilled to the sides of the discovery well.

Classification of Wells

Developmental Wells:

Wells drilled in the known extent of the field are called Developmental Wells.

Classification of Wells

Infill Wells:

Wells that are drilled in between producing wells in an established field to increase the production rate are called Infill wells.

Classification of Wells

Production Wells:

They are drilled primarily for producing oil and gas, once the producing structure and characteristics are determined.

The well is created by drilling a hole of 5 – 36 inches (127.0 – 914.4 mm) in diameter into the earth with a drilling rig that rotates a drill string with bit attached.

• The cost of drilling is very great. On an offshore rig, it may cost $10,000 for each metre drilled.

• A company incurs vast losses for every “dry hole” drilled.

Drilling A Well

A drilling rig is the machine which creates holes (usually called boreholes) in the ground.

Drilling Rig

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.

Drilling Rig

Drilling rigs can be mobile equipment mounted on trucks, or trailers, or more permanent land or marine-based structures (such as oil platforms, commonly called 'offshore oil rigs).

The term "rig" therefore generally refers to the complex of equipment that is used to penetrate the surface of the Earth's crust.

Primarily in onshore oil & gas fields, once a well has been drilled, the drilling rig is moved off of the well and a service rig ( a smaller rig) for completions is placed for well completion.

This frees up the drilling rig to drill another hole and streamlines the operation.

In early oil exploration, drilling rigs were semi-permanent in nature and the derricks were often built on site and left in place after the completion of the well.

Cable Tool Drilling

Cable Drilling is a pioneer method and the first oil wells in the United States were drilled with cable tools to a depth of 20 mts.

Cable Tool Drilling

An engine , originally a steam engine, causes a wooden beam to pivot up & down.

The bit, is made up of solid steel rod about 4 ft. (1 & 1/3m) long with a chisel point on it.

Drilling Rig

Steam Engine

Walking Beam

Derrick

Drawworks

Pulley

Bit

Drill collar

Drill ing Line

Cable Tool Drilling ( Cont…..)

As the walking beam pivots, it causes the bit to rise and fall.

The bit pounds the well down by pulverizing the rock.

Drilling Rig

Cable Tool Drilling ( Cont…..)

After drilling 3 - 8 ft., (1 – 2 ½ m), the bottom of the well becomes clogged with rock chips.

The bit is raised and a bailer is lowered into the well to remove the rock chips and water.

Drilling Rig

Cable Tool Drilling ( Cont…..)

After the bailer is raised and emptied, the bit is lowered into the well to pound deeper.

Drilling Rig

Cable Tool Drilling ( Cont…..)

Heavy casing ( large diameter pipe) is run down the well to keep water from filling the well and to prevent the sides from caving in.

Drilling Rig

Cable Tool Drilling ( Cont…..)

Cable tool drilling is very slow – 25ft. ( 7 ½ m) per day (average) and 60 ft. (20m) being very good.

Drilling Rig

Rotary Drilling

Today, almost all well are drilled with rotary drilling rigs.

The rotary drilling rig rotates a long length of steel pipe with a bit on the end of it to cut a hole called the well bore.

Drilling Rig

Rotary DrillingThe rotary rig consists of four major systems.

(1) Power System : Diesel Engine

(2) Hoisting System : Derrick / Mast, Draw work

(3) Rotating System : Swivel, Kelly, Rotary table, Drill string, Drill Pipe, Drill Collar, Bit etc.

(4) Circulating system: Mud Tanks

Drilling Rig

Introduction

Derrick

Crown Block

Shale ShakerMud tank

Swivel

Drill Line

BOP

Mud Pump

Motor/ Power Source

Drill Bit

Kelly

Rotary Table

Crown Block: A fixed, steel frame with steel

wheels on a horizontal shaft. It is located at the top of a derrick or

Mast. Is an assembly of pulleys

mounted on beams at the top of derrick

CROWN BLOCKS

Derrick: The derrick or Mast is the tower directly above the well that supports the crown block at the top & provides support for the drill pipe to be stacked vertically as it is pulled from the well.

It is generally 40m in height strong enough to hold the weight of the drill as it goes deeper & deeper into the rock.

The derrick can support a weight of about 50 tonnes or more.

Kelly :

The kelly is a square rod attached to swivel.

The kelly turns all the pipe below it to drill the hole.

To the lower end of the kelly, a 10 m pipe is screwed in.

Kelly

Kelly Bushing

DrillpipePin

Box

DrilPipe: The drillpipe (which, when joined together, forms the drillstring) consists of 30ft. (10m) sections of heavy steel pipe. The pipes are threaded so that they can interlock together.

As the drill goes deeper, a new pipe is added to the end of the first pipe and so on.

Drill Collars

Swivel :

The swivel allows the kelly to rotate freely.

SWIVEL

Rotary Table: The kelly along with the pipe & drilling bit is rotated by a rotor known as “Rotary Table”.

It is a circular table in the derrick floor that is turned clockwise by the prime movers. If it were turned in the opposite direction, the drillpipe would unscrew.

DRAWWORKS DRIVEN ROTARY TABLE

Drill stem:3 main components are Kelly, Drillstring & the Bit.

Drill string: It is made up of steel pipes called drill pipes, drill collars (below the drill pipes are thicker – walled, heavier, stronger pipes to put weight on the bottom of the drills string to drill straight down and prevent the drill pipe from kinking & breaking) and bit in the well.

Drill string: It is made up of steel pipes called drill pipes, drill collars (below the drill pipes are thicker – walled, heavier, stronger pipes to put weight on the bottom of the drills string to drill straight down and prevent the drill pipe from kinking & breaking) and bit in the well.

Drill Bit :

It is located at the bottom end of the drill string. The drill bit is responsible for breaking up and dislodging rock, sediment, and anything else that may be encountered while drilling. There are dozens of different drill bit types, each designed for different subsurface drilling conditions:

1.Steel Tooth Rotary Bits are the most basic type of drill bit used today.

2. Insert Bits are steel tooth bits with tungsten carbide inserts.

Disadvantages of Insert Bit• Inserts dig deeply into formation.

Cones can hit the formation and transmit shock loads to bearings and damage bearings

• Abrasive mud containing sands can erode cutters base and let them fall in the well

• Much more expensive• Can not drill soft to soft-medium hard

formations as fast as steel-tooth bits

3. Polycrystalline Diamond Compact Bits have polycrystalline diamond inserts attached to the carbide inserts found in Insert Bits.

4. Diamond Bits have industrial diamonds implanted in them, to drill through extremely hard rock formations. Diamond bits are forty to fifty times harder than traditional steel bits, and can thus be used to drill through extremely hard rock without dulling overly quickly.

Drilling Mud:

When the drilling goes on , a special type of drilling fluid known as mud is pumped down by a hose through the drilling pipe to keep the bit cool.

(The mud flows just like ink flows out of a pen)

A viscous mixture of clay (usually bentonite) and additives with either water or oil or an emulsion of water with droplets of oil or a synthetic organic fluid.

Drilling Mud ( Cont…..)

The mud squirts out of the drilling bit and flows back through the annular space between the outer side of the pipe and the drilled hole carrying with it chips of rocks that are cut.

Drilling Mud ( Cont…..)

Geologists work day and night to record the sequence in which the different types of rocks come out.

After studying the rocks, the geologists prepare a map showing the vertical distribution of rocks underground.

Drilling Mud ( Cont…..)

From this map, it is possible to find out :

(1) The type of rock

(2) The depths at which different rock types occur

(3) The thickness of the bed of each rock type.

The geologists also note if the rocks give any sign of oil.

3) the mixture of drilling mud and drill cuttings are circulated up the annulusscreens

5) the drill cuttings are removed, and form a cuttings pile. This can be hauled off and disposed of.

4) the mixture iscirculated acrossscreens at surface

1) Clean drilling mud is taken from the steel mud tanks and pumped down the inside of the drill pipe.

2) the mud is circulated through the drill bit into the annulus, lifting the cuttings removed by the drill bit.

6) Clean mud falls through the screens and is returned to the pits

The Drilling Mud Cycle

mud pump

The drilling mud is circulated on a rotary drilling rig to :

1.Cool & lubricate the drillstem.

2. remove cuttings from the hole.

3. control subsurface pressures.

4. Seal permeable formations.

Safety System

Various safety devices are used at the wellhead to cope with dangerous situations that may occur during a drilling operations:

Safety System

Reservoirs penetrated by the drill may contain pressures higher than the mud weight can control and the well may show a tendency to erupt and blowout.

Safety System

When oil is struck, the oil gushes out. Sometimes the oil gushes out with

such tremendous force that it becomes dangerous.

The “Blow – Out” can kill men and damage the oil rig.

To reduce the risk of oil gushing out, there is a strong cap in every well.

The cap is used as a “BLOW OUT PREVENTER” or “BOP”.

WELL COMPLETION

Once a natural gas or oil is drilled , and it has been verified that commercially viable quantities of crudes are present, for extraction, the well must be “completed”.

Completion is done to allow for the flow of crude out of the formation and up to the surface.

WELL COMPLETION ( Cont…..)

Completion includes strengthening the well hole with casing, evaluating the P & T of the formation and then installing the proper equipment to ensure an efficient flow of the crudes.

WELL COMPLETION ( Cont…..)

Completing a well consists of : Installing the well casing Completing the well Installing the wellhead Installing lifting equipment Treating the formation.

Well Casing

Installing well casing is an important part of the drilling and completion process.

Well casing consists of a series of metal tubes installed in the freshly drilled hole.

Objectives of Casing:

1. Supports the walls of the wells.

2. Prevents caving tendencies of unconsolidated formation.

3. Prevents water from entering the oil and gas yielding strata from overlying or underlying formations.

Gas & oil must be confined within the well casing so that they may not escape into overlying / underlying formation.

If the hole is uncased, oil and gas could escape through the well into a permeable horizon having a lower pressure and thus, can be dissipated through them so that desired recovery can never be effected.

In oil well drilling, the cost of casing is usually the greatest single item of expense and selection of pipe weight , size and planning and design of casing installation etc. are amongst the most important problems encountered in well drilling.

WHY???

The casing required to be lowered in the well should be effectively serve the purpose.

It must be of sufficient strength, adequate to withstand the stresses to which it is subjected in the well.

It should be water tight and it should be made of material that resists corrosion or be protected against corrosion (particularly when it is in contact with saline ground water)

The material of which the casing is made should be hard & tough and rigid enough to resist abrasion and distortion by contact with the rock walls of the well or drilling tools.

TYPES OF CASING

Casing types involve the character of the material from which the tubes are made, the method of their manufacture, the design of the joints and especially the method of connecting one individual section to another.

TYPES OF CASING In recent years, economy and safety of

operation at increased depths have necessitated still further changes and improvements in the casing designs.

Resulted in the use of alloy steels having tensile strength of 80.000 lbs / inch2 or more with further changes in thread and coupling designs.

There are four grades of seamless alloy steel casing in use.

 In most wells, the diameter of the well hole decreases the deeper it is drilled, leading to a type of conical shape that must be taken into account when installing casing.

A well commonly has 3 or more concentric casing string.

Shallow wells can have 2 or just 1 casing string.

The largest diam. & shortest length string is on the outside.

The smallest diam. & longest length string is on the inside.

The outside string is cemented first and the inside string last.

A well commonly has 3 or more concentric casing string.

Shallow wells can have 2 or just 1 casing string.

The largest diam. & shortest length string is on the outside.

The smallest diam. & longest length string is on the inside.

The outside string is cemented first and the inside string last.

  There are five different types of well casing:

• Conductor Casing • Surface Casing • Intermediate Casing • Liner String • Production Casing

 Conductor Casing

• Conductor casing is installed first, usually prior to the arrival of the drilling rig.

• The hole for conductor casing is often drilled with a small auger drill, mounted on the back of a truck.

 Conductor Casing

• Conductor pipe is the largest diam. Casing string :

Offshore : 30 – 42 inch. or 76 – 107 cm

Onshore: 16 inch. or 40 ½ cm

• Conductor Casing is usually no more than 20 to 50 feet long. 

 Conductor Casing

• It is installed to prevent the top of the well from caving in & isolates any near surface & fresh water.

• It serves as a route for the drilling mud coming from the well to the mud tanks.

Surface Casing• Surface casing is the next type of

casing to be installed after conductor casing.

• It can be anywhere from a few hundred to 2,000 feet long, and is smaller in diameter than the conductor casing ( 13 ¼ inch or 35 cm.)

Surface Casing

• The primary purpose of surface casing is to prevent soft, near surface sediments from caving into the well.

• It also protects fresh water reservoirs from further contaminating by drilling mud.

Surface Casing

• It also serves as a conduit for drilling mud returning to the surface.

• It helps protect the drill hole from being damaged during drilling.

Intermediate Casing

• Intermediate casing is can be set to isolate problem zones in the well such as abnormal high pressure , lost circulation, or a salt layer.

• It is typically 85/8inch ( 22 cm) .

Production Casing • Production casing, alternatively

called the 'oil string' or 'long string,’ is installed last and is the deepest section of casing in a well.

• This is the casing that provides a conduit from the surface of the well to the petroleum-producing formation.

Production Casing

• The final string of casing is the “Production Casing” or “Oil String” that runs down to the producing zone.

• It is typically 5 ½ inch (14cm) in diameter.

Well casing is a very important part of the completed well.

In addition to strengthening the well hole, it provides a conduit to allow hydrocarbons to be extracted without intermingling with other fluids and formations found underground.

Instead of a casing string, a liner string can be set on the bottom of the well to save money.

While a liner string is very similar to casing string in that it is made up of separate joints of tubing, the liner string is not run the complete length of the well.

A liner string is hung in the well by a liner hanger, and then cemented into place.

It is suspended in the well by a liner hanger and can be cemented in.

The section of the liner in the pay zone may be wire wrapped screen pipe with openings as small as (0.008 inch) or perforated pipe may be used with openings as large as ½ inch or above.

The liner may extend up into the production casing only a short distance and be sealed to the production casing with a packer , or if desired, may be extended to the casing head on the surface, thus forming an inner producing string.

Casing Programs• Sometimes the well is drilled in

stages called a casing program.

• A well is drilled to a certain depth, cased and cemented, and then the well is drilled to a deeper depth, cased and cemented again, and so on.

• Each time the well is cased, a smaller diameter casing is used.

Cementing

After running in the casing string to the desired depth, it is cemented place.

A cement slurry is then pumped down the casing and up around the outside of the casing in the annular space in the hole to the height desired and there the cement is allowed to set & harden to permanently fix the casing in place.

The wall of hardened cement keeps the hole from caving, which might collapse the casing and to make the secure in the hole.

After the casing is installed, tubing is inserted inside the casing, running from the opening well at the top to the formation at the bottom.

The hydrocarbons that are extracted go up this tubing to the surface.

Tubing

Small diameter pipe called tubing is run into the well to just above the bottom to conduct the water, gas and oil ( produced fluids) to the surface.

Tubing protects the casing from corrosion by the producing fluids.

Since the casing is cemented in the wall, it is very difficult to repair the casing.

The tubing string is suspended in the well, so, it can be pulled from the well to repair or replace it during a “work over”

WELL COMPLETIONS

Well completion commonly refers to the process of finishing a well so that it is ready to produce oil & NG.

There are a number of types of completion depending on the characteristics and location of the HC formation to be mined: Open Hole Completion Conventional Perforated Completion• Sand Exclusion Completion• Permanent Completion• Multiple Zone Completion• Drain hole Completion

Open Hole Completion

• Used in very competent formations.

• Consists of simply running the casing directly down into the formation, leaving the end of the piping open.

• There is no production casing over the oil or gas zone.

• This is a very primitive way to complete a well.

Conventional Perforated Completion• A modern well is completed with

steel casing set over the oil zone.

• It consists of production casing being run through the formation.

• The sides of this casing are perforated with tiny holes along the sides facing the formation, which allows for the flow of HCs into the well hole.

Conventional Perforated Completion

• Perforation involves the use of specialized equipment designed to make tiny holes through the casing, & cementing lying in between the formation and the open hole.

Conventional Perforated Completion• In the past, “bullet perforators” were

used which were essentially small guns lowered into the well.

• The guns were when fired from the surface, sent off small bullets that penetrated the casing and cement.

• Today, “jet perforating” is preferred consisting of small, electrically ignited charges that are lowered into the well. When ignited, these charges poke tiny holes through the formation.

Then a device called a "perforating gun" (A) is lowered into the hole at the depth where the oil or gas formation is found.  This may be anywhere from several hundred feet down to tens of thousands of feet. 

After the gun is lined up properly, powerful shaped explosive charges are fired (B) from the control panel in the truck located up at ground level.  These explosives blast a hole in the steel casing and cement, up to several feet out into the rock.  Finally, the oil and gas fluids flow into the holes and up the well to the surface (C).

This method of completion is much better than the old open-hole method shown in the first picture. 

The PG is able to control exactly where the perforations go. 

This helps to limit the amount of undesirable fluids, like salt water, entering the hole, and maximize the amount of hydrocarbons that can be extracted from the well.

Sand Exclusion Completion• Sand exclusion completions are

designed for production in an area that contains a large amount of loose sand.

• This completion is designed to allow for the flow of natural gas and oil into the well, but at the same time, prevent sand from entering the well as the sand inside the well can cause many complications (erosion of casing & other equipment).

Sand Exclusion Completion• The most common method of keeping

sand out of the well hole are:Screening or Filtering system.

• This includes analyzing the sand and installing a screen or filter to keep the sand particles out.

• This filter may either be a type of screen hung inside the casing, or adding a layer of specially sized gravel outside the casing to filter out the sand. Both of these types of sand barriers can be used in open hole & perforated completions

Permanent Completion• In this, the completion and wellhead

are assembled and installed only once.

• The tubing is lowered to the desired depth before perforation and not removed during the life of the well. All other operations are carried out through tubing.

• Completing a well in this way can lead to a significant cost savings.

Multiple Zone Completion • In this practice, the HCs from two or

more formations may be produced simultaneously, without mixing with each other.

• eg. A well may be drilled that passes through a number of formations on its way, it may be efficient in a horizontal well to add multiple completions to drain the formation most effectively.

Multiple Zone Completion • Although it is common to separate

multiple completions so that the fluids from the different formations do not intermingle.

• If the different formations being drilled are close enough in nature to allow fluids to intermingle in the well hole and it is necessary to separate different completions, hard rubber “packing” are used .

Drain hole Completion• It is a form of horizontal or slant

drilling.• It consists of drilling out

horizontally into the formations from a vertical well, essentially providing a “drain” for the HCs to run down into the well.

WELL HEAD

The well head consists of equipments on the surface that:

supports the various pipe strings

seals off the well to prevent leaking of oil or NG out of the well.

controls the flow rates of reservoir fluids.

• Each string of casing usually hangs from a casing head.

• The casing heads consists of heavy steel fitting at the surface.

• It support the entire length of casing that is run all the way down the well.

• “Metal and rubber seals” in the casing head prevent fluids from moving within the wellhead or escaping to the atmosphere.

• Each casing head also has a place for a pressure gauge to warn of leaks.

• This typically contains a gripping mechanism that ensures a tight seal between the head and the casing itself.

• “The Tubing head” is much like the casing head.

• It provides a seal between the tubing , which is run inside the casing.

• It provides connections at the surface, which allow the flow of fluids out of the well to be controlled.

• The tubing head stacks above the uppermost casing head.

• “The Christmas Tree” fits atop the casing & tubing heads.

• It contains tubes and valves that serve to control the flow of HCs and other fluids out of the well.

• It commonly contains many branches and is shaped somewhat like a tree, thus its name, Christmas Tree .

• This is the most visible part of a producing well and allows for surface monitoring & regulation of the HC production from producing well.

“The Christmas Tree” or "tree", is not not "wellhead" as sometimes incorrectly referred to.

• Note that a tree and wellhead are separate pieces of equipment not to be mistaken as the same piece.

• A wellhead must be present in order to utilize a Christmas tree and a wellhead is used without a Christmas tree during drilling operations etc.,

Lifting and Well Treatment

Once the well is completed, it begins to produce.

HCs existing in pressurized formations will naturally rise up through the well to the surface. This is most commonly the case with natural gas and light crude.

Since natural gas is lighter than air, once a conduit to the surface is opened, the pressurized gas will rise to the surface. Thus, once the CT is installed, the NG will flow to the surface on its own

When a well is first drilled, the formation is under pressure and produces O&G at a very rate.

However, as more & more crude is extracted from the formation, the production rate of the well is decreased. This is known as the “decline rate”.

During this time, application of certain techniques including “Lifting Equipment” & “Well Stimulation” can increase the production rate of a well.

Lifting equipment consists of a variety of specialized equipment that are used to help “lift” petroleum out of a formation .

This is most commonly used to extract oil from a formation.

When oil is found as a viscous liquid, it becomes difficult to extract it from underground.

Various types of lifting equipment are available, but the most common lifting method is known as “Rod Pumping”.

Rod pumping is powered by a surface pump that moves a cable and a rod up and down in the well, providing the lifting pressure required in the well, providing the lifting pressure required to bring the oil to the surface.

WELL TREATMENT

Well Treatment or Stimulation is another method of ensuring the efficient flow of HCs out of a formation.

Essentially, this type of well stimulation consists of injecting stimulation consists of injecting acid, water or gases into the well to open up the formation and allow the crude to flow through the formation more easily.

“Acidizing” a well consists of injecting acid (usually HCl acid) into the well.

In Limestone or Carbonate formations, the acid dissolves portions of the rock in the formation, opening up existing spaces to allow for the flow of petroleum.

“Fracturing” consists of injecting a fluid into the well, the pressure of which “cracks” or opens up fractures already present in the formation.

In addition to the fluid being injected,“propping agents” are also used. These propping agents can consists of sand, glass beads, silica sand etc. and serve to prop open the newly widened fissures in the formation.

“Hydraulic Fracturing” involves the injection of water into the formation, while CO2 fracturing uses gaseous .

Fracturing, Acidizing and Lifting Equipment may all be used on the same well to increase permeability.

These techniques are mostly used in oil wells, but have also been used to increase the extraction rate of gas wells.