Rotary Drilling

This book was written for use as a college textbook in a petroleum engineering curriculum. The material was organized to present engineering science fundamentals first, followed by example engineering applications involving these fundamentals. The level of engineering science gradually advances as one proceeds through the book.

Chap. 1 is primarily descriptive material and intended as an introduction to drilling engineering. It is suitable for use as a text in a freshman- or sophomore-level introductory petroleum engineering course. Chaps. 2 and 3 are designed for use in a drilling-fluids and cements laboratory course and are aimed at the sophomore or junior level. Chaps. 4 through 7 are suitable for a senior-level drilling engineering course. Chap. 8 provides additional material that could be covered in a more advanced course at the senior level or in a masters-degree program.

Because the text was designed for use in more than one course, each chapter is largely independent of previous chapters, enabling an instructor to select topics for use in a single course. Also, the important concepts are developed from fundamental scientific principles and are illustrated with numerous examples. These principles and examples should allow anyone with a general background in engineering or the physical sciences to gain a basic understanding of a wide range of drilling engineering problems and solutions.

Contents

1. Rotary Drilling

1.1 Drilling Team

1

5.3 Bit Selection and Evaluation

209

1.2 Drilling Rigs

3

5.4 Factors Affecting Tooth Wear

214

1.3 Rig Power System

5

5.5 Factors Affecting Bearing Wear

219

1.4 Hoisting System

7

5.6 Terminating a Bit Run

220

1.5 Circulating System

12

5.7 Factors Affecting Penetration Rate

221

1.6 The Rotary System

17

5.8 Bit Operation

236

1.7 The Well Control System

21

Exercises

240

1.8 Well-Monitoring System

26

1.9 Special Marine Equipment

27

6.

Formation Pore Pressure and

1.10 Drilling Cost Analysis

32

Fracture Resistance

Exercises

37

6.1 Formation Pore Pressure

246

Drilling Fluids

6.2 Methods for Estimating

Pore Pressure

252

2.1 Diagnostic Tests

42

6.3 Formation Fracture Resistance

285

2.2 Pilot Tests

53

6.4 Methods for Estimating

2.3 Water-Base Muds

54

Fracture Pressure

287

2.4 Inhibitive Water-Base Muds

72

Exercises

294

2.5 Oil Muds

75

Exercises

82

7.

Casing Design

Cements

7.1 Manufacture of Casing

301

7.2 Standardization of Casing

302

3.1 Composition of Portland Cement

85

7.3 API Casing Performance Properties

305

3.2 Cement Testing

86

7.4 Casing Design Criteria

330

3.3 Standardization of Drilling Cements

89

7.5 Special Design Considerations

339

3.4 Cement Additives

90

Exercises

348

3.5 Cement Placement Techniques

103

Exercises

110

8.

Directional Drilling and Deviation Control

8.1 Definitions and Reasons for

Drilling Hydraulics

Directional Drilling

351

4.1 Hydrostatic Pressure in

8.2 Planning the Directional

Liquid Columns

113

Well Trajectory

353

4.2 Hydrostatic Pressure in Gas Columns

114

8.3 Calculating the Trajectory of a Well

362

4.3 Hydrostatic Pressure in Complex

8.4 Planning the Kickoff and

Fluid Columns

115

Trajectory Change

366

4.4 Annular Pressures During Well

8.5 Directional Drilling Measurements

377

Control Operations

119

8.6 Deflection Tools

402

4.5 Buoyancy

122

8.7 Principles of the BHA

426

4.6 Nonstatic Well Conditions

127

8.8 Deviation Control

443

4.7 Flow Through Jet Bits

129

Exercises

453

4.8 Rheological Models

131

4.9 Rotational Viscometer

135

Appendix A: Development of Equations for

4.10 Laminar Flow in Pipes and Annuli

137

Non-Newtonian Liquids in a

4.11 Turbulent Flow in Pipes and Annuli

144

Rotational Viscometer

4.12 Initiating Circulation of the Well

154

Bingham Plastic Model

474

4.13 Jet Bit Nozzle Size Selection

156

Power-Law Model

476

4.14 Pump Pressure Schedules for Well

Control Operations

162

Appendix B: Development of Slot Flow

4.15 Surge Pressures Due to Vertical

164

Approximations for Annular

Flow

Pipe Movement

for Non-Newtonian Fluids

4.16 Particle Slip Velocity Exercises

173 183

Bingham Plastic Model

477

Power-Law Model

481

Rotary Drilling Bits

5.1 Bit Types Available

190

Author Index

484

5.2 Rock Failure Mechanisms

200

Subject Index

Rotary Drilling Process

The objectives of this chapter are (I) to familiarize the student with the basic rotary drilling equipment and operational procedures and (2) to introduce the student to drilling cost evaluation.

1.1 Drilling Team

The large investments required to drill for oil and gas are made primarily by oil companies. Small oil companies invest mostly in the shallow, less-expensive wells drilled on land in the United States. Investments in expensive offshore and non-U.S. wells can be afforded only by large oil companies. Drilling costs have become so great in many areas that several major oil companies often will form groups to share the financial risk.

Many specialized talents are required to drill a well safely and economically. As in most complex industries, many different service companies, contractors, and consultants, each with its own organization, have evolved to provide necessary services and skills. Specialized groups within the major oil companies also have evolved. A staff of drilling engineers is generally identifiable as one of these groups.

A well is classified as a wildcat well if its purpose is to discover a new petroleum reservoir. In contrast, the purpose of a development well is to exploit a known reservoir. Usually the geological group recommends wildcat well locations, while the reservoir engineering group recommends development well locations. The drilling engineering group makes the preliminary well designs and cost estimates for the proposed well. The legal group secures the necessary drilling and production rights and establishes clear title and right-of-way for access. Surveyors establish and stake the well location.

Usually the drilling is done by a drilling contractor. Once the decision to drill the well is made by management, the drilling engineering group prepares a more detailed well design and writes the bid specifications. The equipment and procedures that the operator will require, together with a well description, must be included in the bid specifications and drilling contract. In areas where previous experience has shown drilling to be routine, the bid basis may be the cost per foot of hole drilled." In areas where costs cannot be estimated with reasonable certainty, the bid basis is usually a contract price per day. In some cases, the bid is based on cost per foot down to a certain depth or formation and cost per day beyond that point. When the well is being financed by more than one company, the well plan and drilling contract must be approved by drilling engineers representing the various companies involved.

Before the drilling contractor can begin, the surface location must be prepared to accommodate the specific rig. Water wells may have to be drilled to supply the requirements for the drilling operation. The surface preparation must be suited to local terrain and supply problems; thus, it varies widely from area to area. In the marshland of south Louisiana, drilling usually is performed using an inland barge. The only drillsite preparation required is the dredging of a slip to permit moving the barge to location. In contrast, drillsite preparation in the Canadian Arctic Islands requires construction of a manmade ice platform and extensive supply and storage facilities. Fig. 1.1 shows an inland barge on location in the marsh area of south Louisiana and Fig. 1.2 shows a drillsite in the Canadian Arctic Islands.

After drilling begins, the manpower required to drill the well and solve any drilling problems that occur are provided by (1) the drilling contractor, (2) the well operator, (3) various drilling service companies, and (4) special consultants. Final authority rests either with the drilling contractor when the rig is drilling on a cost-per-foot basis or with the well operator when the rig is drilling on a cost-per-day basis.

Fig. 1.3 shows a typical drilling organization often used by the drilling contractor and well operator when a well is drilled on a cost-per-day basis. The drilling engineer recommends the drilling procedures that will allow the well to be drilled as safely and economically as possible. In many cases, the original well plan must be modified as drilling progresses because of unforeseen circumstances. These modifications also are the responsibility of the drilling engineer. The company representative, using the well plan, makes the on-site decisions concerning drilling operations and other services needed. The rig operation and rig personnel supervision are the responsibility of the tool pusher.

Barge Drilling Rigs Louisiana

Fig. 1.1 - Texaco drilling bärge Gibbens on location in Fig. 1.2 — Man-made ice platform in deep water area of

Lafitte field, Louisiana. the Canadian Arctic Islands.

Fig. 1.1 - Texaco drilling bärge Gibbens on location in Fig. 1.2 — Man-made ice platform in deep water area of

Lafitte field, Louisiana. the Canadian Arctic Islands.

Drilling Rig Component

rig crew

Fig. 1.3-Typical drilling rig organizations.

rig crew

Fig. 1.3-Typical drilling rig organizations.

Jacknife Mobile Rotary Drilling

Fig. 1.4-The rotary drilling process.

rotary drilling rigs marine land bottom support. floating conventional mobile semisubmersible drillship jacknife portable mast platform barge jackup self contained tendered

  1. 1.5-Classification of rotary drilling rigs.
  2. 1.4-The rotary drilling process.
  3. 2 Drilling Rigs

Rotary drilling rigs are used for almost all drilling done today. A sketch illustrating the rotary drilling process is shown in Fig. 1.4. The hole is drilled by rotating a bit to which a downward force is applied. Generally, the bit is turned by rotating the entire drillstring, using a rotary table at the surface, and the downward force is applied to the bit by using sections of heavy thick-walled pipe, called drill collars, in the drillstring above the bit. The cuttings are lifted to the surface by circulating a fluid down the drillstring, through the bit, and up the annular space between the hole and the drillstring. The cuttings are separated from the drilling fluid at the surface.

As shown in Fig. 1.5, rotary drilling rigs can be classified broadly as land rigs or marine rigs. The main design features of land rigs are portability and maximum operating depth. The derrick of the conventional land rig must be built on location. In many cases the derrick is left over the hole after the well is completed. In the early days of drilling, many of these standard derricks were built quite close togethei^as a field was developed. However, because of the high cost of construction, most modern land rigs are built so that the derrick can be moved easily and reused. The various rig components are skid-mounted so that the rig can be moved in units and connected easily. The jackknife, or cantilever, derrick (Fig. 1.6) is assembled on the ground with pins and then raised as a unit using the rig-hoisting equipment. The portable mast (Fig. 1.7), which is suitable for moderate-depth wells, usually is mounted on wheeled trucks or trailers that incorporate the hoisting machinery, engines, and derrick as a single unit. The telescoped portable mast is raised to the vertical position and then extended to full height by hydraulic pistons on the unit.

The main design features of marine rigs are portability and maximum water depth of operation. Submersible drilling barges generally are used for inland water drilling where wave action is not severe and water depths are less than about 20 ft. The entire rig is assembled on the barge, and the unit is towed to the location and sunk by flooding the barge. Once drilling is completed, the water is pumped from the barge, allowing it to be moved to the next location. After the well is completed, a platform must be built to protect the wellhead and to support the surface production equipment. In some cases, the operating water depth has been extended to about 40 ft by resting the barge on a shell mat built on the seafloor.

Offshore exploratory drilling usually is done using self-contained rigs that can be moved easily. When water depth is less than about 350 ft, bottom-supported rigs can be used. The most common type of bottom-supported mobile rig is the jackup (Fig. 1.8). The jackup rig is towed to location with the legs elevated. On location, the legs are lowered to the bottom and the platform is "jacked up" above the wave action by means of hydraulic jacks.

Semisubmersible rigs that can be flooded similar to an inland barge can drill resting on bottom as well as in a floating position. However, modern semisubmersible rigs (Fig. 1.9) are usually more expensive than jackup rigs and, thus, are used mostly in water depths too great for resting on bottom. At present, most semisubmersible rigs are anchored over the hole. A few semisubmersible rigs employ large engines to position the rig over the hole dynamically. This can extend greatly the maximum operating water depth. Some of these rigs can be used in water depths as great as 6,000 ft. The shape of a semisubmersible rig tends to dampen wave motion greatly regardless of wave direction. This allows its use in areas such as the North Sea where wave action is severe.

A second type of floating vessel used in offshore drilling is the drillship (Fig. 1.10). Drillships are usually much less costly than semisubmersibles unless they are designed to be positioned dynamically. A few drillships being planned will be able to operate in water depths up to 13,000 ft. Some are designed with the rig equipment and anchoring system mounted on a central turret. The ship is rotated about the central turret using thrusters so that the ship always faces incoming waves. This helps to dampen wave motion. However, the use of drillships usually is limited to areas where wave action is not severe.

Offshore development drilling usually is done from fixed platforms. After the exploratory drilling program indicates the presence of sufficient petroleum reserves to justify construction costs, one or more platforms from which many directional wells

Portable Mast Rig
Fig. 1.7-Portable mast being transported. Fig. 1.9-A semisubmersible drilling rig on location.

can be drilled are built and placed on location. The platforms are placed so that wellbores fanning out in all directions from the platform can develop the reservoir fully. The various rig components usually are integrated into a few large modules that a derrick barge quickly can place on the platform.

Large platforms allow the use of a self-contained rig-i.e., all rig components are located on the platform (Fig. 1.11). A platform/tender combination can be used for small platforms. The rig tender, which is a floating vessel anchored next to the platform, contains the living quarters and many of the rig components (Fig. 1.12). The rig-up time and operating cost will be less for a platform/tender operation. However, some operating time may be lost during severe weather.

Platform cost rises very rapidly with water depth. When water depths are too great for the economical use of development platforms, the development wells can be drilled from floating vessels, and the wellhead equipment installed on the ocean floor. Underwater completion technology is still relatively new and experimental.

Although drilling rigs differ greatly in outward appearance and method of deployment, all rotary rigs have the same basic drilling equipment. The main component parts of a rotary rig are the (1) power system, (2) hoisting system, (3) fluid-circulating system, (4) rotary system, (5) well control system, and (6) well monitoring system.

1.3 Rig Power System

Most rig power is consumed by the hoisting and fluid circulating systems. The other rig systems have much smaller power requirements. Fortunately, the hoisting and circulating systems generally are not used simultaneously, so the same engines can perform both functions. Total power requirements for most rigs are from 1,000 to 3,000 hp. The early drilling rigs were powered primarily by steam. However, because of high fuel consumption and lack of portability of the large boiler plants required, steam-powered rigs have become impractical. Modern rigs are powered by internal-combustion diesel engines and generally subclassified as (1) the diesel-electric type or (2) the direct-drive type, depending on the method used to transmit power to the various rig systems.

Diesel-electric rigs are those in which the main rig engines are used to generate electricity. Electric power is transmitted easily to the various rig systems, where the required work is accomplished through use of electric motors. Direct-current motors can be wired to give a wide range of speed-torque characteristics that are extremely well-suited for the hoisting and circulating operations. The rig components can be packaged as portable units that can be connected with plug-in electric cable connectors. There is considerable flexibility of equipment placement, allowing better space utilization and weight distribution. In addition, electric power allows the use of a relatively simple and flexible control system. The driller can apply power smoothly to various rig

Eugene Island Offshore Rig
Fig. 1.10-An offshore drillship.
Eugene Island Offshore Rig
Fig. 1.11 - A self-contained platform rig on location in the Eugene Island area, offshore Louisiana.
Eugene Island Offshore Rig
Fig. 1.12 —A tendered platform rig.
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