drilling methods and equipment

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DRILLING METHOD AND EQUIPMENT MODULE No. PTDR 6001 LEARNING OUTCOME When you complete this module you will be able to... Discuss drilling methods, identify the equipment components for each method and possess a basic knowledge of drilling safety and techniques. Learning Objectives Here is what you will be able to do when you complete each objective. 1. Describe the arrangements that must be made prior to moving drilling equipment onto a lease. 2. Describe the tools and components used in cable tool drilling. 3. Describe the tools and components used in rotary drilling. 4. Describe the safety measures to be followed and discuss the techniques used in properly drilling a well. INTRODUCTION A well is drilled with the object of tapping underground reservoirs of oil or gas. It is an expensive and risky procedure that may or may not make a profitable return. The discovery of the Leduc field in Alberta, for example, was made on well No. 134; the previous 133 wells were dry holes. It is to be expected that such an undertaking would develop considerable technical skill in order to reduce the risk and to overcome the many difficulties encountered. This module describes some of these techniques very briefly. The drilling methods used for oil and gas wells are classified under two headings: 1. Cable tool drilling (churn drilling) 2. Rotary drilling OBJECTIVE ONE When you complete this objective you will be able to... Describe the arrangements that must be made prior to moving drilling equipment onto a lease. Learning Material LEASE ARRANGEMENTS One of the first steps in exploring for oil or gas is drilling on the recommended site to determine whether hydrocarbons are present in commercial quantities. 1

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Driling Equipment and Methods

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Page 1: Drilling Methods and Equipment

DRILLING METHOD AND EQUIPMENT MODULE No. PTDR 6001

LEARNING OUTCOME

When you complete this module you will be able to...

Discuss drilling methods, identify the equipment components for each method and possess a basic knowledge of drilling safety and techniques.

Learning Objectives

Here is what you will be able to do when you complete each objective.

1. Describe the arrangements that must be made prior to moving drilling equipment onto a lease.

2. Describe the tools and components used in cable tool drilling.

3. Describe the tools and components used in rotary drilling.

4. Describe the safety measures to be followed and discuss the techniques used in properly drilling a well.

INTRODUCTION

A well is drilled with the object of tapping underground reservoirs of oil or gas. It is an expensive and risky procedure that may or may not make a profitable return. The discovery of the Leduc field in Alberta, for example, was made on well No. 134; the previous 133 wells were dry holes.

It is to be expected that such an undertaking would develop considerable technical skill in order to reduce the risk and to overcome the many difficulties encountered. This module describes some of these techniques very briefly.

The drilling methods used for oil and gas wells are classified under two headings:

1. Cable tool drilling (churn drilling)

2. Rotary drilling

OBJECTIVE ONE

When you complete this objective you will be able to...

Describe the arrangements that must be made prior to moving drilling equipment onto a lease.

Learning Material

LEASE ARRANGEMENTS

One of the first steps in exploring for oil or gas is drilling on the recommended site to determine whether hydrocarbons are present in commercial quantities.

However, before drilling commences, certain other arrangements and decisions have to be made. These may include:

1. Leasing of the land.

2. Building of roads.

3. Moving the equipment in.

4. Drilling method.

5. Depth and size of well.

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A mineral lease is a contract between the Exploration Company and landowner. It allows the operator the rights to drill for and produce oil, gas or condensate in exchange for certain royalties paid by the operator.

The payment of royalties commences with the beginning of production and it is commonly around 1/8 of the production, but may run as high as 1/5 of the production.

When two or more companies have rights to a given field, a unitized operation is generally formed. In such a practice, the groups involved agree upon an operating formula and a single operator is generally designated to process all gas from the field.

The depth of a hole is dictated by the exploration objectives and the depth of the target formation, which can range from less than 300 to more than 7000 meters.

The size of the borehole depends on the depth, the type of completion and to a lesser extent, on the geology and the capacity of the available drilling equipment. Borehole sizes range from 89 to more than 660 mm.

OBJECTIVE TWO

When you complete this objective you will be able to...

Describe the tools and components used in cable tool drilling.

Learning Material

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 meters.

The basic operation of cable tool drilling consists of punching a hole in the subsurface by repeatedly lifting and dropping a heavy cutting tool suspended from the end of a cable. Every 30 to 50 cm, the bit is pulled up and the loosened material is removed from the borehole using a bailing apparatus suspended from a wire rope.

Cable tool drilling is an outmoded method of "digging" a wetland therefore; a discussion of the parts and operation of the rig will be brief. Figures 1 and 2 should be studied carefully while reading the following description of the cable tool rig.

1. Underground Tools

The standard tools (string of tools) used under the ground consist of a bit, drill stem, several jars and the rope socket to which the cable is attached. Figure 1 illustrates these tools.

Bit - the bit is the actual cutting tool and is usually 1.8 to 2.4 meters long, chisel shaped and attached to the lower end of the string.

Drill Stem - is a steel bar, which supplies weight necessary for the operation and serves as a guide.

Jars - or bar link, imparts a jarring impact to the tool and is included as a safety feature to loosen stuck cutting tools.

Bailer - is a bucket with a non-return valve in the bottom used to remove cuttings from the well bore.

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Figure 1 Cable Drilling Tools

2. Surface Equipment

The essential surface parts of a cable rig are: the prime mover, the derrick, the walking beam, the band wheel, sand reel, calf wheel, bull wheel and various other auxiliaries as pulleys and sheaves - all shown in Figure 2.

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Figure 2 Cable Tool Drilling Rig

Prime Mover - internal combustion engines or steam engines used to provide power.

Cellar - an excavation under the rig floor, dug before drilling to provide space for equipment at the top of the well bore. The cellar serves to collect drainage water and other fluids, which are jetted at intervals.

Walking Beam - raises and drops the string of tools providing the motivating force to dig a new hole.

Bull Wheel - is a drum or reel to which the drilling line is affixed, and is used to pull the tools from the hole or lower them into the hole.

Calf Wheel - is a drum or reel used to lower casing into the borehole.

Sand Line - the line, which raises and lowers the bailer. The sand line is affixed to the sand reel.

Crown Block - the sheaves at the head of the derrick for the drilling cable, casing line and sand line.

Casing - a large diameter steel pipe run in the borehole to protect the hole from caving and seepage. Casing is cemented in place.

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Control Head - this is bolted to the top of the casing and is equipped with valves to control fluids rising to the surface from the well bore.

The drive to the walking beam, in the rig illustrated, is transmitted from an engine to the band wheel, crank and pitman. Downward motion of the walking beam is limited in the event of failure of any of these parts by the headache post (an emergency stop).

As the hole deepens, the driller lowers the tools so as to maintain precisely the right amount of impact. Too slow a rate of lowering will reduce drilling speed; too fast a rate will make the drilling line slack, reduce the lift and impact and introduce a risk of the well being drilled away from the vertical.

If water keeps seeping into the well, interfering with the operation, a second casing of smaller size is lowered into the well and cemented in place.

A cable tool installation is simple and requires little power. Two men per shift can operate the rig and daily costs are low.

3. Advantages and Disadvantages

This method has the advantages of requiring less initial capital outlay and giving a continuous record of the formations being drilled. It is a slower method than rotary and often requires more casing. Moreover, it is limited to shallower depths than the rotary. It finds application in small drilling programs or possible wildcat wells.

Spudding in

This is a common term in the petroleum industry and simply means to commence actual drilling operations on the well. The term is handed down from cable tool operations in the early days of the oil industry.

In order to drill a hole with a cable tool rig, it is necessary to have sufficient clearance beneath the walking beam to hang the string of drilling tools. Fifteen to thirty meters may be required and it is therefore necessary to make this depth of hole by some other means before commencing the cable rig drilling. The procedure is termed "spudding" in and is carried out using a short, heavy spudding bit with its own cable run through the crown block.

Today portable-spudding rigs may be used to drill the conductor hole, run the conductor pipe and have all preparatory work completed for the big rig to move in and immediately commence drilling. Depending on the size, these may be truck, trailer or skid mounted and driven by diesel or gasoline engines. Generally, all are fitted with telescoping masts.

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OBJECTIVE THREE

When you complete this objective you will be able to...

Describe the tools and components used in rotary drilling.

Learning Material

ROTARY DRILLING

Oil and gas drilling today is done almost exclusively with the rotary rig. The portability and operational characteristics of the rotary rig make it superior for petroleum exploration.

The normal rig operating in Western Canada requires the services of sixteen full-time employees. Three, five-men crews are made up from the sixteen employees and each crew marks an 8 hour tour. A crew consists of a driller, derrickman, motorman and two floor hands. The three crews are supervised by the toolpusher who is in charge and responsible for the safe, efficient operation of the rig.

Rigs are owned by individuals or companies known as drilling contractors, whereas the wells are owned by oil and gas explorers, often referred to as operators. The Oil Company or operator hires or contracts the drilling contractor to drill the well at a given location to a specified depth. A rig may be contracted by the meter drilled, by the day or on a turnkey basis.

1. Drilling Rig Components

Types of drilling bits are shown in Figure 3 from left to right are: a three-cone hard formation rock bit, soft formation drag bit, hard formation core head and a worn rock bit.

Figure 3 Types of Drilling Bits

The major components of a rotary rig are shown in Figure 4. The rotary rig performs three main functions: hoisting, circulating and rotating.

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Figure 4 Diagrammatic View of Rotary Drilling Rig Standard Derrick

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Figures 5, 6and 7 illustrate the jackknife rig with mast laid down, the mast partially erected and the mast fully erected.

Figure 5 Jackknife Rig - Mast Down

Figure 6 Jackknife Rig - Mast Partially Erected

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Figure 7 Jackknife Rig - Mast Partially Erected

a. Derrick or Mast

The mast (or derrick) rises 29 to 50 meters above the rig floor and is the most obvious component of a drilling rig.

Derrick and mast are used interchangeably even though technically there is a fundamental difference between the two terms. To be moved, the derrick (also called the standard derrick) has to be dismantled piece by piece and erected piece by piece at the new location. In contrast, the mast can be moved without disassembling and as a consequence, it replaces the derrick in most drilling operations. Today, use of the standard derrick is limited to offshore drilling rigs and some extremely deep (on land) wells.

The mast or derrick is erected on a substructure, which serves to:

1. Support the rig floor and rotary and to provide working space.

2. Provide space under the floor for blowout preventer (valves for controlling an overpressured well).

The substructure supports the rotary table, the mast and the full weight of the drill stem, whether suspended from the crown block or rotary table.

Drill pipe is pulled and racked in stands when it is necessary to change the bit or to come out of the hole for other evaluations. A stand normally consists of 3 joints of pipe, called a thribble and has a length of about 27.4 meters.

The mast is an integral part of the hoisting system. By means of the traveling block, wire line, crown block and drawworks, it supports the hook and elevators. The drill stem is raised and lowered by the drawworks, which is powered by up to four engines.

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b. Drawworks

Drawworks is the hoisting mechanism on a drilling rig that consists of a large winch that spouts off or takes up the drilling line to lower or raise the drill stem and bit. Most drawworks are equipped with at least a two-brake system. One brake is hydraulic or electric and is used to control the speed of descent of the loaded traveling block. This brake is not capable of bringing the loaded traveling block to a complete halt, but the other brake, a mechanical brake, can bring the load to a complete stop.

Hoisting speeds of the drawworks can be varied over a wide range through the use of a multirange transmission system. It is necessary, when pulling pipe, to control the speed at which pipe is hoisted to avoid swabbing the well in.

Generally, the drawworks has a drive sprocket to drive the rotary table through a heavy duty chain. On some rigs, the rotary is driven by an independent engine or electric motor.

Catheads are an extension of a shaft of the drawworks that is used to lift heavy equipment around the rig and to tighten and loosen drill pipe joints. The make-up or spinning cathead is on the driller's side of the drawworks and the breakout cathead is on the opposite side.

Figure 8 View of Rotary Drawworks for Medium Depth Drilling Up to 3100 meters

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Figure 9 Components of a Heavy Rig Capable of

Drilling to 6200 Meters Assembled in the Factory

c. Blocks and Wire Line

The blocks and wire line, like the derrick and drawworks, are components of the hoisting system. Heavy loads of pipe and drill stem can be controlled and easily handled by means of the mechanical advantage provided by the crown block, traveling block and wire line.

During drilling operations, the load consists of drill pipe and drill collars, with the bit attached to the bottom drill collar. This is collectively referred to as the scroll string. At other times, the load may be a string of casing, which is often heavier than the drill string. Casing is lowered and cemented in the hole for protection. In most casing operations, the load on the hoisting system is approximately the weight of the casing string. However, where problems occur in running casing and the casing has to be worked in tight spots, the load on the hoisting system can substantially exceed the deadweight of the casing string.

The traveling block carries the hook and elevators and each is designed for a specific job. Elevators are clamps or latches, which secure the drill pipe when hoisting or lowering the pipe in the well, bore. The hook latches into the swivel bails at the top end of the kelly and carries the drill string load (less the weight on the bit) during the drilling operation.

d. Rotary System

Main components of the rotating system include: the bit, drill collars, drill pipe, kelly and kelly bushing, rotary table and engines.

e. Rotary Drilling Bits

The bit is the only part of the rig equipment that actually makes a hole.

Various types of bits are available for the different types of formations encountered where the principle of operation is the crushing or grinding of the resisting surface. Fishtail bits are useful in soft formations (sandstone or shale), while a brag or rock bit may be ideal in limestone or rocky formations. (The latter is also called a roller cone type). The fish-shaped bit

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cuts like the carpenter's auger with its two hardened cutting edges. The rock bit grinds the rocky subsurface with its three-toothed rollers.

All bits have passages to allow the flow of drilling mud to assist in the operation. The drill bit is connected to a pipe 9 to 12 meters long called a drill collar. Drill collars are heavier and much sturdier than drill pipe, and their function is to supply weight on the bit as well as keep the bit from wandering. Several drill collars may be used on the drilling operation depending on the weight desired.

f. Drill Stem

The drill stem consists of the drill collars (mentioned previously), drill pipe and a kelly. Drill collars are heavy, thick-walled, hollow steel tubes, drill pipe is a hollow steel or aluminum tube much lighter than the drill collar and a kelly is a square or hexagonal steel tube. These three components are collectively referred to as the drill stem. The drill stem performs both as a drive shaft and a pipeline.

Principal functions of the drill stem are:

1. To raise and lower the bit from or into the hole.

2. Transfer the rotation from the rotary to the bit downhole.

3. Conduct the drilling fluid from the surface down the hole to the bit to cool, lubricate and flush drill cuttings back to surface.

4. Apply weight to the bit through the mass of the drill collar(s).

g. Kelly and Swivel

A kelly is a square or octagonal-shaped steel tube and is the upper terminus of the drill stem. Kellys are equipped with a kelly bushing (a drive bushing), which during drilling operations is engaged in the rotary and transfers power from the rotary to the drill stem. The kelly is permitted to move vertically in the bushing, which allows continuous drilling of 9 to 10 meters - the length of a single joint of drill pipe.

The swivel supports the load of the drill stem during drilling, it allows rotation of the drill stem, but it does not rotate and finally, it provides a passageway for the drilling fluid to enter the drill stem.

h. Circulating System

The circulating system is the third major component of a drilling rig. For the drilling system to function on a rotary rig, fluid must circulate downward through the drill stem, around the bit, up the annulus (space between the drill stem and the wall of the hole), over the shaker and into the pits to be recirculated.

The circulating fluids' main functions are:

1. Clean the bottom of the hole.

2. Cool the bit.

3. Flush cuttings from the hole.

4. Prevent entry of the formation fluid's into the hole.

5. Support the walls of the well to prevent a cave in.

The normal drilling fluids are muds, which have special chemical and other additives to give them specific desired properties.

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Drilling fluid may also be air or gas, in which case the mud pump is replaced with air compressors.

The art of mud control has developed rapidly and it is one of the most complex subjects the drilling crew deals with. Special clays are used to give substance to the mud and heavy minerals, such as barite, are added to increase the mud's weight. Chemicals control the thickness or viscosity and the ability to form a mud cake on the borehole wall.

The flow of the mud system can be traced through on Figure 4 and Figure 10.

Rotary drilling needs less casing in the hole since the plastering of walls with mud also seals off any flow of water. On the other hand, the mud may shut off any oil or gas producing formation.

For this reason, in exploratory wells, the drilling is performed with more consideration given to making sure that oil and gas producing formations are not bypassed. When it is necessary to insert casing into a rotary-drilled hole, it is done in a similar way as in cable tool drilling.

Figure 10 Diagrammatic Section Showing Equipment Below the Derrick Floor,

the Borehole and Drilling String

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2. Advantages and Disadvantages

One of the advantages of rotary type drilling is that this method is a faster operation and therefore more economical. Also, it is a method adaptable to wells reaching 9000 meters or more. In rotary drilling, it is possible to control the gas pressure and the size of the hole is quite uniform along the entire depth.

The drawbacks of this method, however, are the expensive equipment needed and the increase of crewmembers required per shift.

Modern rotary rigs are mobile with a type of derrick which folds to a horizontal position. They can be moved to a new location and brought into service with minimum delay.

OBJECTIVE FOUR

When you complete this objective you will be able to...

Describe the safety measures to be followed and discuss the techniques used in properly drilling a well.

Learning Material

SAFETY MEASURES

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

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. When a blowout occurs, the entire operation may be ruined and therefore, means must be provided to prevent it. Figure 10 shows the installation of two large bore valves, called blowout preventers, which are hydraulically operated. Their purpose is to shut the hole off with a device called an accumulator, which is set apart from the rig. The top preventer is of different construction from the bottom one and is operated when the drill pipe is in the hole. The bottom one may be shut off when no drill pipe is in the hole.

A dangerous situation is most likely to arise in new areas where a reservoir is penetrated containing gas or oil under a higher pressure than had been estimated. The first symptom of a blowout may include the sudden increase in the drilling fluid returning to the mud pits. In such a case, the operator should close the blowout preventer, add weighting material to the drilling fluid and apply back- pressure to the fluid returning to the surface through the annular space.

PROPER DRILLING TECHNIQUES

Drilling operations require trained crews, thoroughly experienced in all methods and techniques used in the field, to maintain a straight hole and to avoid wasting time and effort in fishing out broken or twisted pieces of equipment.

The techniques used may be summarized as:

1. Good spudding in work.

2. Good condition of drilling equipment.

3. Good quality drilling fluid.

4. Constant surveying of the well.

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As was mentioned earlier, spudding in is the preparatory work when drilling a wetland unless it is properly performed, it may cause deviation from the vertical.

The drill bit should be sharp enough and the proper type of bit should be used for the type of formation drilled. If a bit breaks, the pieces must be fished out of the hole using equipment available for this purpose. Figures 11 and 12 illustrate some of the fishing tools used by the industry.

Figure 11 Typical Fishing Tools

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Figure 12 Typical Fishing Tools

The success of rotary type drilling may depend, to a large extent, on the control of the mud weight and quality, as well as on the proper functioning of the mud circulating equipment. The fluid should be dense enough and should be capable of adhering to the hole walls to prevent caving. The hydrostatic pressure maintained by the mud should be in excess of the gas pressure of the formation to prevent blowouts.

Holes have a tendency to deviate, particularly when being drilled through inclined strata. There are several instruments to detect crooked holes and control the operating procedures. Recording instruments are available to measure the angle of deviation during the operation by either dropping them into the drill stem or running them into the pipe on a wire line.

Deviations can be corrected by using special equipment called whipstocks, which maintain the lower end of the stem rigid until the hole is established in the desired direction.

Figure 13 shows the equipment and procedure used. In Figure 13(a), the whipstock is placed in position. In Figure 13(b), a short length of deviated hole is drilled. In Figure 13(c), the whipstock is pulled. In Figure 13(d), the deviated hole is reamed, and drilling is eventually continued.

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Figure 13 Directional Drilling

 

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Learning Module: 027-31-95-08 PTDR 6001 Self-Test

[ Print Self-Test ]

Directions:

Answer the following questions.

Compare your answers to the enclosed answer key.

If you disagree with any of the answers, review learning activities and/or check with your instructor.

If no problems arise, continue on to the next objective or next examination.

1. A contract, which allows a well to be drilled, is called a _____________.

2. A _______________ operation is formed when more than one company has rights to a given field.

3. _________________ drilling is a pounding or percussion method of making a well bore.

4. Borehole casing is ________________ in place.

5. Hoisting, circulating and rotating are functions, which are performed by a _______________.

6. A drilling rig that can lay down the mast in one piece is called a ______________.

7. A standard derrick must be ____________________ before moving the rig.

8. The main hoisting mechanism on a drilling rig is called the _______________.

9. ___________ bits are used for drilling in soft formations such as sandstone or shale.

10. The ___________ component of a drilling rig consists of drill collars, drill pipe and a kelly.

11. The sturdy, heavy pipe connected to the drill bit is called a ______________.

12. The circulating fluid used on a rotary drilling rig is called ___________, occasionally ______ or _______ may be substituted.

13. Two large bore valves called _________________ are used to stop the drilling fluid from being forced out of the well bore if over pressuring accidentally occurs.

 

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Learning Module: 027-31-95-08 PTDR 6001 Answer Guide

1. mineral lease

2. unitized

3. Cable tool

4. cemented

5. rotary drilling rig

6. jackknife rig

7. dismantled

8. drawworks

9. Fish-tail

10. drill stem

11. drill collar

12. drilling mud, air, gas

13. blowout preventers

 

Learning Module: 027-31-95-08 PTDR 6001 Assignment

[ Print Assignment ]

1. What information must be known by the engineer before he commences drilling for oil or gas?

2. Explain the cable method of drilling.

3. Name the string of tools, as used in the above method, in their proper sequence.

4. Define in your own words:

a. rig

b. casing

c. control head

d. spudding in

5. Would you consider the rotary type of drilling more efficient and reliable than the cable method? Discuss the main points of difference between the two methods.

6. Explain the reasons for using drilling fluid in rotary drilling operations.

7. Outline the safety equipment in rotary drilling and measures taken to safeguard property and life.

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