# Introduction to Drilling Engineering **An Open-Source Textbook for Undergraduate and Graduate Petroleum Engineering Students** *Roman Shor, Ph.D., P.Eng.* *Harold Vance Department of Department of Petroleum Engineering* *Texas A&M University* --- ## About This Book The subsurface holds a wealth of natural resources, and drilling a well is the primary way of accessing resources deeper than a few hundred feet. Whether the target is hydrocarbons, geothermal energy, reservoirs for carbon storage, or a water table, a hole must be drilled — and drilling that hole safely, efficiently, and economically requires a rigorous engineering foundation. This textbook was developed for the drilling courses in the petroleum engineering curriculum at Texas A&M University: an introductory sophomore-level drilling course (PETE 225), an advanced senior-level course (PETE 355), and a general graduate-lvel course (PETE 661). It is released as an open educational resource so that students, instructors, and practicing engineers anywhere in the world can use, adapt, and improve it. The book emphasizes engineering judgment over recipe-following. Drilling is a discipline where the conditions change with every foot drilled — the rock, the fluid, the pressure, the temperature — and where the consequences of a wrong decision can be severe. The goal of this textbook is not to produce engineers who can look up an answer, but engineers who understand *why* the answer is what it is and can reason about situations they have not seen before. --- ## A Note on the Text This ebook is being written and finalized during the Fall 2026 semester, with chapters being actively added. Figures in many cases are placeholder images from relevant slides utilized in PETE 225 and PETE 355. The target release of the completed book is December 2026. --- ## How to Use This Book ### Sophomore-Level Course (PETE 225: Introduction to Drilling Engineering) PETE 225 provides a broad introduction to the drilling process across the following chapter sequence: **Chapters 1–2** establish the context: the petroleum engineering discipline, the exploration and production industry, how a well is drilled from surface to target, and general drilling operations. **Chapter 3** covers the drilling rig itself: rig types, the five rig systems (hoisting, rotary, circulating, power, and well control), fundamental rig equipment, rig operations, and how a rig is selected for a drilling program. **Chapters 4–7** cover drilling fluids: their functions and types (Chapter 4), property measurement (Chapter 5), the calculations used to design and adjust mud systems (Chapter 6), and borehole hydraulics (Chapter 7). **Chapters 8 and 9** introduce well control (Chapter 8) and well control calculations (Chapter 9). Basic calculations are included in the sophomore level course and then revised in the senior level course. **Chapter 11** introduces directional drilling. Detailed directional drilling calculations and well planning are covered in the senior level course. **Chapter 17 and 18** introduce casing, the reason we case wells, typical casing programs, and how we choose casing setting points. Details around casing design, and drillstring design are covered in the senior level course. ### Senior-Level Course (PETE 355: Drilling Engineering) PETE 355 assumes completion of PETE 225 and covers quantitative well design. The course follows a different sequence than the chapter order, organized by design workflow: The course usually begins **Chapters 14 - 16** with an introduction to geomechanics (Chapter 14), hoop stress (Chapter 15), and wellbore stability (Chapter 16). This information, along with information about the pore pressure and fracture gradient are then used in **Chapter 18** to determine casing setting depths. **Chapters 17, 19 and 21** provide the background for casing, casing design, and cementing given the pore pressure, fracture gradient, geology and insitu stresses. **Chapters 19 and 20** cover drillstring design. At this time, directional drilling and well planning from **Chapter 11 and 12** are reviewed. The course concludes with a final project covering **Chapter 22 and 23** where the students create a DWOP for a sample well planning scenario. --- ## Chapter Overview ### Part I: Foundations --- #### Chapter 1 — Introduction to Petroleum Engineering This chapter establishes the industrial, geological, and economic context for everything that follows. Students are introduced to the origin of hydrocarbons — from the deposition and transformation of organic matter through kerogen types and the oil and gas windows — and to the geological structures (traps) that allow hydrocarbons to accumulate in commercial quantities. The chapter then follows the full exploration and production (E&P) lifecycle from initial exploration through appraisal, development, production, and ultimately plugging and abandonment. The role of drilling within this lifecycle is examined, as is the broader value chain connecting the wellbore to the consumer. The chapter closes with a discussion of drilling applications beyond oil and gas: geothermal energy, carbon capture and storage, and water wells. **Key topics:** Hydrocarbon origins · Kerogen types and maturation · Structural and stratigraphic traps · E&P lifecycle · Well types (wildcat, appraisal, development, infill) · Casing program overview · Beyond O&G applications --- #### Chapter 2 — Drilling Operations This chapter covers the practice of drilling a well — from how the industry evolved to where it is today, to the engineering decisions made before a bit touches the ground. Students learn the five-step drilling process (target selection, site preparation, surface hole, drilling to total depth, and completion), the concept of Drilling a Well on Paper (DWOP) as a structured planning methodology, and how pore pressure and fracture gradients define the drilling window within which every decision must be made. The chapter also addresses liability: the distinct roles of operators, drilling contractors, service companies, and regulators, and why understanding these relationships is essential for practicing engineers. **Key topics:** History of rotary drilling · Well types across the E&P lifecycle · The five-step drilling process · DWOP · Pore pressure and fracture gradients · The drilling window · Operator/contractor/regulator relationships --- #### Chapter 3 — Drilling Rigs This chapter covers the machine at the center of every drilling operation: the drilling rig. It begins with the four fundamental rig functions, hoisting, rotating, circulating, and maintaining well control, and the operations a rig performs over the life of a well. Rig types covered are onshore (singles through quads, self-erecting masts, walking rigs) and offshore (jackups, semi-submersibles, drillships). Each of the five rig systems is described with its component equipment: the hoisting system, the rotary system, the circulating system, the power system including grid-connected and hybrid rigs; and the well control system. The drillstring is then covered, and how it transmits energy from the rig to the downhole equipment in the bottom hole assembly and drillbit. The chapter closes with rig selection: technical decision factors derived from the well design, contractor evaluation criteria, and contract types. **Key topics:** Four rig functions · Rig operations and time split · Land rig classification (single/double/triple/quad) · Offshore rig types · Block-and-tackle mechanics · Fast line tension and derrick load · Drawworks and braking · Elevators and bails · Deadline anchor and hookload accuracy · Top drive vs. kelly · Slips and connections · Iron roughneck · Circulating flow path · Triplex pump output calculation · Shale shakers and solids control · Power systems and hybrid rigs · BOP stack · Choke and kill manifold · Drillstring components · PDC and tri-cone bits · Rig selection criteria · Day-rate, footage, and turnkey contracts --- ### Part II: Drilling Fluids --- #### Chapter 4 — Drilling Fluid Functions and Classification Drilling fluid, typically called mud, is the lifeblood of the drilling operation. This chapter presents the functions of mud and explains the physics underlying each. The chapter then surveys the full classification of drilling fluids: gas-based systems, the major families of water-based mud, and oil- and synthetic-base systems. Filter cake formation and fluid loss control, the mechanisms by which mud seals permeable formations, are treated in depth. The chapter closes with a practical decision framework for mud selection. **Key topics:** Eight functions of drilling fluid · Well control and pressure barriers · Gas-based systems · Water-based mud families · Oil-based and synthetic-base mud · Mud composition and additives · Filter cake and fluid loss · Mud selection criteria --- #### Chapter 5 — Drilling Fluid Characterization To manage a mud system, engineers must be able to measure its properties precisely and interpret what those measurements mean. This chapter covers the suite of standard mud tests to measure key properties, and the four standard rheological models used to describe mud behavior. Time based behavior of mud is covered, including thioxotropy and gel strength. The chapter closes with a systematic survey of mud contaminants and their signatures. **Key topics:** Mud monitoring objectives · Density measurement · Fann VG/35 viscometer · Marsh funnel · Rheological models (Newtonian, Bingham Plastic, Power Law, Herschel-Bulkley) · Shear thinning and thixotropy · Gel strength · Fluid loss measurement · Solids analysis · Chemical analysis · Contaminants (salt, calcium, CO₂, H₂S, drill solids) --- #### Chapter 6 — Drilling Fluid Calculations This chapter translates the concepts of Chapters 4 and 5 into the quantitative tools used in daily engineering practice. The ideal mixing model, the foundation of all mud density design, is derived from first principles and applied to the three fundamental mud adjustment problems: weighting up with barite, diluting with water or base oil, and simultaneous dilution and re-weighting. The critical limitation of the ideal mixing model (it does not apply to dissolved salts) is explained, and brine density is addressed through tabulated data for common oilfield salt systems. The chapter then introduces equivalent circulating density (ECD) as the operating pressure concept that bounds every circulating operation within the drilling window. **Key topics:** Oilfield unit conversions · Ideal mixing model · Weighting agents and their properties · Brine density from dissolved salts · Barite addition calculations · Dilution calculations · Simultaneous dilution and weighting · Temperature and pressure effects on downhole density · Hydrostatic pressure · ECD --- #### Chapter 7 — Drilling Hydraulics Drilling hydraulics governs the flow of fluid through the drill string, bit, and annulus, and sets the limits on penetration rate, cuttings transport efficiency, and equivalent circulating density. This chapter covers pipe and annular flow in laminar and turbulent regimes for Newtonian and Bingham Plastic fluids, pressure loss calculations throughout the circulating system (drill string, bit nozzles, annulus), pump output and standpipe pressure, ECD factors, and field calibration of hydraulics models. **Key topics:** Laminar and turbulent flow · Reynolds number · Fanning friction factor · Pipe and annular pressure losses · Newtonian and Bingham Plastic hydraulics · Bit nozzle pressure loss · Standpipe pressure · Pump output calculations · Equivalent circulating density · Eccentric annulus correction ### Part III: Well Control --- #### Chapter 8 — Introduction to Well Control Well control is the set of equipment, procedures, and engineering practices that keep formation fluids from entering the wellbore uncontrolled — and that manage an influx safely when one occurs. This chapter builds the conceptual foundation. It defines primary, secondary, and tertiary well control and the barrier philosophy that underlies them, then develops formation pressures in detail: normally pressured, sub-normally pressured, and over-pressured formations, the gas effect, and depleted zones. Primary well control is presented as maintaining overbalance within the drilling window, bounded by the leak-off test and the maximum allowable annular surface pressure (MAASP). Temporary reductions in bottomhole pressure — swabbing during trips and the trip margin that guards against it — are analyzed. The well is then modeled as a U-tube, allowing shut-in drill pipe and casing pressures (SIDPP and SICP) to be interpreted together to characterize an influx. The chapter closes with kick detection, blowout preventers and secondary equipment, shut-in procedure, and an introduction to the two principal kill methods: the Driller's Method and the Wait-and-Weight Method. **Key topics:** Primary/secondary/tertiary well control · Well control barriers · Formation pressure mechanisms · Normal, subnormal, and overpressured formations · The gas effect · Depleted zones · Overbalance and the mud density trade-off · Leak-off test · MAASP · Swabbing and trip margin · The well as a U-tube · SIDPP and SICP interpretation · Trip tank and kick detection · BOP equipment · Shut-in procedure · Driller's Method · Wait-and-Weight Method --- #### Chapter 9 — Well Control Operations and Procedures This chapter covers the operational execution of well control, from the pre-kick data collection that makes a kill possible to the step-by-step procedures for shutting in and killing a well. Preparation comes first: slow circulating rate (SCR) pressures, pump output, and wellbore geometry must all be known before a kick happens. The kill sheet — the central document that organizes well data, kick data, and calculated kill parameters before any pump is started — is developed in full, including construction of the choke pressure schedule. Shut-in procedures are covered operationally: kick indicators, soft versus hard shut-in, and the special hazards of tripping operations. The Driller's Method, Wait-and-Weight Method, and Volumetric Method are then walked through in operational detail. Gas behavior during kill operations — migration, expansion during circulation, solubility and bubble point, and the underground blowout — receives dedicated treatment. The chapter closes with special situations: horizontal wells, deepwater well control, and barite plugs and bullheading. **Key topics:** Slow circulating rate (SCR) pressure · Pump output · Kill sheet completion · Choke pressure schedule · Kick indicators · Soft vs. hard shut-in · Tripping and swabbed kicks · Driller's Method operations · Wait-and-Weight Method operations · Volumetric method · Gas migration and expansion · Gas solubility and bubble point · Underground blowouts · Horizontal well considerations · Deepwater well control · Barite plugs and bullheading --- #### Chapter 10 — Well Control Calculations This chapter develops the quantitative framework underlying all kill methods. Starting from the constant bottomhole pressure principle, it derives the circulating pressures that govern a kill: slow circulating rate pressure, initial circulating pressure (ICP), and final circulating pressure (FCP). The evolution of drill pipe and casing pressure is traced through both circulations of the Driller's Method and through the single circulation of the Wait-and-Weight Method, including step-by-step construction of the choke pressure schedule. Four extended worked examples anchor the chapter: a complete kill sheet, a shoe integrity comparison between the two kill methods, a negative-MAASP scenario, and kick fluid identification from SIDPP, SICP, and pit gain. A dedicated section on common calculation errors — and how to recognize them from pressure behavior during a live kill — closes the quantitative treatment, followed by a preview of advanced well control topics. **Key topics:** Constant BHP principle · Kill mud weight · Initial and final circulating pressure · Driller's Method pressure profiles · Wait-and-Weight pressure profiles · Choke pressure schedule construction · Kill sheet worked example · Shoe integrity check · Negative MAASP · Kick fluid identification · Common errors and deviation recognition --- ### Part IV: Directional Drilling --- #### Chapter 11 — Introduction to Directional Drilling Almost no well drilled today is purely vertical. This chapter introduces the geometry of three-dimensional wellbore trajectories, the field applications of directional drilling (sidetracks, extended-reach, multilateral, relief wells, salt dome avoidance, urban and offshore development), the key geometric quantities (inclination, azimuth, DLS, radius of curvature), the three standard 2D profile shapes (build-and-hold, S-type, continuous build), wellbore surveying, and the three classes of directional drilling systems: passive (whipstocks, stabilizer assemblies), semi-active (mud motors, rotate vs. slide), and active (rotary steerable, push-the-bit vs. point-the-bit). **Key topics:** Applications of directional drilling · Measured depth and true vertical depth · Inclination, azimuth, declination · Horizontal departure, northing, easting · Dogleg severity and radius of curvature · Build-and-hold, S-type, and continuous-build profiles · Wellbore survey · Whipstocks · Slick, pendulum, and fulcrum BHAs · Mud motors · Rotary steerable systems --- #### Chapter 12 — Directional Drilling Calculations This chapter develops the quantitative methods for translating wellbore survey measurements (MD, inclination, azimuth) into three-dimensional wellbore position (TVD, northing, easting). The radius of curvature method is derived and applied to vertical, build, drop, and tangent sections. Students learn to construct complete wellbore position tables for planned wells and to reconstruct well paths from existing survey data. The minimum curvature method is then introduced and applied to a survey interval, and the chapter closes with an introduction to torque and drag: where contact forces originate, their practical implications for extended-reach wells and trip monitoring, and the soft-string modeling concept developed fully in Chapter 13. **Key topics:** Radius of curvature method · ΔTVD and ΔHD for build, drop, and tangent sections · Northing and easting from azimuth · Wellbore position table construction · Reading and drawing well plots · Minimum curvature method · Introduction to torque and drag --- #### Chapter 13 — Advanced Directional Drilling Topics This chapter completes the directional drilling toolkit with the two quantitative models every directional engineer uses daily. The survey calculation methods used in industry (average angle, radius of curvature, constant build and turn, minimum curvature) are compared, and the minimum curvature method is developed in full: the 3D dogleg angle, the ratio factor, position increments, and dogleg severity from survey data, with a worked 3D interval combining simultaneous build and turn. The second half develops torque and drag from the physical picture — gravity contact on inclined hole and tension acting through curvature — through the complete Johancsik soft-string model (JPT, 1984): the element force balance, sign conventions for pick-up, slack-off, and rotation, and the bit-to-surface marching procedure, applied in a worked element-by-element example. Friction factor calibration from measured hookloads, and the use of torque and drag analysis for well feasibility, casing running, rig selection, and hole-condition monitoring are covered. The chapter closes beyond the soft string: stiff-string models (Tikhonov et al., 2013), where local contact forces demand them, and the three modes of drillstring vibration, including stick-slip. **Key topics:** Survey calculation methods (AAM, RCM, CBTM, CCBM, MCM) · Dogleg angle and ratio factor · MCM position increments · DLS from surveys · Origins of torque and drag · Pick-up, slack-off, and rotating hookloads · Johancsik soft-string model · Normal force from curvature and gravity · Friction factor calibration · Buckling and lock-up · Design applications · Stiff-string models · Contact force localization · Drillstring vibration (stick-slip, whirl, axial) --- ### Part V: Stresses and Wellbore Stability --- #### Chapter 14 — Introduction to Geomechanics The stability of a wellbore depends on whether the stresses acting on the borehole wall exceed the strength of the surrounding rock. This chapter provides the physical and mathematical framework for answering that question. It begins with definitions of stress and strain, the formation stress tensor, and the three principal in-situ stresses: vertical overburden stress (Sv), maximum horizontal stress (SHmax), and minimum horizontal stress (Shmin). Anderson's (1951) fault classification connects the relative magnitudes of these stresses to the tectonic regime: normal, strike-slip, or reverse faulting. The effective stress principle — that rock failure is governed by total stress minus pore pressure — is developed and applied, with the Mohr circle as the graphical tool for visualizing stress states and the destabilizing effect of rising pore pressure. Rock mechanical properties (Young's modulus, Poisson's ratio, UCS, cohesion, friction angle) and the laboratory tests that measure them (unconfined and triaxial compression) lead to the Mohr-Coulomb failure criterion. The chapter closes with worked procedures for determining the failure envelope from one or two laboratory tests. **Key topics:** Normal stress and shear stress · Effective stress · Formation stress tensor · Principal stresses Sv, SHmax, Shmin · Anderson's fault classification (normal, strike-slip, reverse) · Salt as an isotropic exception · Mean stress and maximum shear stress · Rock elastic properties (E, ν) · Rock strength properties (UCS, cohesion, friction angle) · Mohr circle construction · Effect of pore pressure on the Mohr circle · 3D Mohr circles · Brittle, semi-brittle, and ductile failure · Mohr-Coulomb failure criterion · Determining C and θ from one or two tests --- #### Chapter 15 — Wellbore Geomechanics This chapter applies the geomechanical framework of Chapter 14 directly to the borehole wall. When a cylindrical hole is drilled through rock, the stresses redistribute around the void — and whether that redistribution exceeds the rock's strength determines whether the wellbore survives. The chapter introduces cylindrical coordinates at the wellbore wall (axial, radial, and tangential stresses), the Kirsch equations for stress around a circular hole, and their simplified forms at the wall: Sr = Pm and Sθ = (SH + Sh − Pm) − 2(SH − Sh)cos 2θ. Maximum and minimum hoop stress expressions are derived and interpreted: maximum hoop stress drives breakout in the direction of minimum horizontal stress; minimum hoop stress drives fracturing in the direction of maximum horizontal stress. Breakout is analyzed quantitatively with the Mohr-Coulomb approach, fracturing with the tensile criterion, and breakout geometry (the 90° arch-support rule) determines whether a damaged hole stabilizes or collapses. The effect of well orientation on hoop stress is developed for vertical and horizontal wells in each fault regime, including lower hemisphere stability plots for arbitrary trajectories. A complete worked example in a reverse faulting environment demonstrates breakout and fracture analysis at a given mud weight. **Key topics:** Types of hole problems (breakout, washout, induced fractures, creep) · Cylindrical coordinates at the wellbore wall · Axial, radial, and tangential stresses · Kirsch equations · Simplified wellbore wall equations · Maximum hoop stress: 3SH − Sh − Pm · Minimum hoop stress: 3Sh − SH − Pm · Breakout (compressive failure) and Mohr-Coulomb criterion · Fracture (tensile failure) criterion · Fracture reopening vs. initiation · Breakout arch stability (90° rule) · Caliper and image log detection · Effect of well orientation on hoop stress · Horizontal wells in normal faulting · Lower hemisphere plots --- #### Chapter 16 — Wellbore Stability This chapter turns the physics of Chapters 14 and 15 into engineering practice. The drilling window is assembled from all of its bounds — pore pressure and the breakout-stability mud weight below, fracture reopening and the fracture gradient above — and the dynamic pressure effects that move the effective downhole pressure within it (ECD, breaking circulation, swab, surge, and solids loading) are quantified as operating margins. The minimum stability mud weight design problem is solved in full: setting the Mohr circle tangent to the failure envelope and solving for mud pressure, with the key geometric insight that mud weight shrinks the circle's radius without moving its center. Stability requirements are compared across fault regimes and well orientations. Shale stability receives dedicated treatment as a chemo-mechanical, time-dependent problem: the clay swelling mechanism, reactive clay mineralogy, inhibitive mud systems (OBM, KCl-WBM, high-salinity), and the role of filtrate invasion in degrading support over open-hole time. The chapter closes with the pore pressure / fracture gradient plot — equivalent mud weight coordinates, kick and trip margins, and the narrowing windows that mark casing setting points, leading into Part VI. **Key topics:** The drilling window and all four bounds · Dynamic pressure effects (ECD, breaking circulation, swab, surge, solids loading) · Minimum stability mud weight design · Mohr circle center/radius insight · Stability vs. fault regime and well orientation · Managed pressure drilling for narrow windows · Clay swelling mechanism · Smectite, illite, chlorite, kaolinite reactivity · OBM, KCl-WBM, and salinity inhibition · Invasion and time-dependent instability · Open-hole time management · PP/FG plot in EMW coordinates · Kick and trip margins · Casing setting point logic --- ### Part VI: Tubulars --- #### Chapter 17 — Introduction to Casing and Cementing Casing is the permanent steel lining that gives the wellbore its structural integrity, isolates pressure zones from one another, and protects freshwater aquifers. This chapter introduces the functions that casing and cementing must perform and the engineering context in which they are designed. It covers all casing string types — from conductor through production liner and tie-back — and introduces the role of tubing. The chapter also establishes casing nomenclature: OD, nominal weight, API grade, and connection type, including the distinction between nominal and drift ID. API casing grades from H40 through Q125 are presented, with special attention to sour-service grades and the limitations of high-strength steels in H₂S environments. Connection types from API threaded and coupled (STC, LTC, BTC) to premium metal-to-metal seal designs are compared. **Key topics:** Casing functions · Tubing and packer systems · Conductor · Surface casing · Intermediate casing · Production casing · Drilling liner · Production liner · Tie-back · Casing OD and nominal weight · Wall thickness and ID · Drift diameter · API grades (H40 through Q125) · Sour service (L80, C90, T95) · STC, LTC, BTC connections · Premium connections (Tenaris Blue, Hydril 511) · Cementing objectives and overview --- #### Chapter 18 — Casing Design: Selecting Setting Depths With the casing string types established, this chapter covers how to select the setting depth for each string in the program. The foundation is the bottoms-up design methodology: start with the completion requirements at the bottom of the well, select the production string, and work upward through each string to the surface. The pore pressure and fracture gradient profile developed in Chapter 16 is the primary design input; the drilling window analysis with kick and trip margins identifies where casing must be set to allow safe drilling of the next interval below. The bit/casing compatibility chart establishes the hole-size and casing-OD relationships for each string. Real-world design factors — regulatory requirements, formation mechanical stability, contingency strings, and problem zones — are discussed. **Key topics:** Bottoms-up design methodology · Pore pressure and fracture gradient profiles · Drilling window and setting depth selection · Starting from completion requirements · Bit/casing compatibility chart · Casing OD selection · Multi-string programs (land and offshore) · Regulatory freshwater protection requirements · Overpressured zones · Depleted reservoirs · Lost circulation zones · Salt formation challenges --- #### Chapter 19 — Tubular Design: Casing This chapter develops the quantitative methods for determining whether a selected casing specification can withstand the loads it will experience. The three primary failure modes — burst (internal pressure), collapse (external pressure), and tension (axial load) — are analyzed using the uniaxial design approach with industry-standard design factors (1.1, 1.125, and 1.3 respectively). Burst is calculated from the formation pore pressure; collapse from the mud column acting on an evacuated casing; tension from the string weight. The buoyancy factor distinguishes air weight from weight in mud, and a complete worked example walks through casing selection using API tables. The von Mises (triaxial) criterion is developed for combined loading cases including bending and torsion, with discussion of when triaxial design is required, how annular pressure buildup affects collapse design, and special considerations for sour service, HP/HT, and slim-hole wells. **Key topics:** Burst, collapse, and tension design · Design factors (1.1 / 1.125 / 1.3) · Barlow formula · D/t collapse regimes · Buoyancy factor · API casing tables · Casing selection worked example (5½ in, 15,000 ft) · H₂S and sour service grades · Von Mises triaxial criterion · When triaxial design is required · Annular pressure buildup (APB) · HP/HT and slim-hole considerations --- #### Chapter 20 — Drillstring Design This chapter covers the design of the rotating machine element that connects the rig to the bit. The drillstring components and their specifications are established first: drill pipe (OD, nominal weight, grades E-75 through S-135, connections), tool joints and upsets, drill collars including non-magnetic collars, heavy weight drill pipe, BHA tools (stabilizers, jars, pony collars, subs), and the inspection program that manages fatigue. The design calculations build from the weight-in-air formula and buoyancy factor to the central concept of the neutral point: drill collars are sized so the transition from compression to tension stays inside the BHA, protecting the drill pipe from buckling — with Lubinski and Dawson-Paslay buckling providing the physics, and explaining why compression is tolerable in laterals but not vertical hole. Tensile load analysis leads to the margin of overpull check at the top drill pipe joint and to tapered string design for deep wells. The chapter closes with bending stress from dogleg severity and the von Mises combined-load check at the top of the build section. **Key topics:** Drillstring functions · Drill pipe nomenclature (OD, weight, grade, connection) · Tool joints, upsets, and ranges · Drill collars and non-mag collars · Heavy weight drill pipe · BHA components (stabilizers, jars, pony collars) · Drillstring inspection (MPI, UT) · Weight in air: $w = 2.67(OD^2 - ID^2)$ · Buoyancy factor · Neutral point and WOB vs. hookload · Buckling modes (Euler, sinusoidal, helical) · Drill collar length for WOB · Tensile load analysis · Margin of overpull vs. safety factor · Tapered string design · Bending stress: $\sigma_b = 218 \times \text{DLS} \times OD$ · Von Mises combined-load check --- #### Chapter 21 — Cementing Cement fills the annulus between the casing and the formation, converting the steel string into a true pressure barrier and creating the zonal isolation that the wellbore requires. This chapter covers everything from the chemistry of Portland cement to the interpretation of cement evaluation logs. The API cement classes are introduced with emphasis on the industry-standard Class G and Class H. Cement hydration — the exothermic reaction sequence from mixing to final set — is explained, along with the effects of temperature, pressure, and contamination on setting behavior. Every major piece of cementing equipment (float shoe, float collar, plugs, stage collars, centralizers, scratchers) is described. The chapter then walks through the step-by-step primary cementing procedure, liner cementing, and the essential principles of a good cement job. Basic cementing calculations — annular volume, sacks of cement, mixing water, and displacement volume — are developed and demonstrated with a worked example. The chapter closes with the three methods of cement evaluation: lift pressure (qualitative), temperature log (cement top), and cement bond log / CBL (bond quality). **Key topics:** Primary cementing objectives · Portland cement composition · API cement classes (A through H; Class G and H) · Cement hydration stages · Thickening time · Effect of temperature, pressure, and contamination · Free water · Float shoe and float collar · Bottom and top cementing plugs · Stage collars · Centralizer types (bow spring and solid body) · Standoff · Spacer and preflush · Lead and tail cement stages · Step-by-step primary cement procedure · Liner cementing and dart system · Keys to a good cement job · Cementing calculations (annular volume, sacks, water, displacement) · Lift pressure · Temperature log · Cement bond log (CBL) interpretation --- ### Part VII: Professional Practice --- #### Chapter 22 — The Drilling Engineer and the Drill Well on Paper (DWOP) This chapter synthesizes the technical content of the book by asking: how does all of this knowledge get organized into a plan for actually drilling a well? The answer is the DWOP — a structured pre-drill planning process in which the operator, drilling contractor, service companies, and consultants align on objectives, share geological and engineering information, review the well design, and agree on schedule and risk management before the rig ever sets up. The chapter begins with the drilling engineer's role as technical hub, then covers the distinct functions of the operator, drilling contractor, service companies, and consultants, and explains the liability framework and the daily drilling report. The six standard DWOP components are developed in sequence. The days vs. depth plot — the central scheduling tool — is explained in detail. The chapter closes with a case study of the publicly available Utah FORGE geothermal DWOP, which illustrates how geology, well design, directional planning, special operations, and schedule all appear in a real planning document. **Key topics:** Drilling engineer's role · Operator, drilling contractor, service companies, consultants · Tool liability and daily drilling reports · DWOP definition and purpose · Program objectives · Site and geological information · Well design summary · Operational program · Days vs. depth plot · Flat time · Special operations and risk identification · Anti-collision analysis · Utah FORGE case study · Well naming conventions --- #### Chapter 23 — Social Responsibility and the Social License to Operate This chapter addresses the relationship between the drilling industry and the communities, regulators, and public that shape its ability to operate. It introduces the concept of social license to operate (SLO) — the informal but essential community acceptance that complements formal regulatory permits — and traces its implications through a series of case studies. The Crane County geyser (2022) anchors an extended discussion of legacy well liability, the shifting uses of the subsurface over time, and the questions of moral and legal responsibility that arise when "properly abandoned" infrastructure fails decades later under changed subsurface conditions. The Colorado noise abatement case illustrates the paradox of mitigation: how technically sound engineering responses to community concerns can, without communication, deepen rather than repair trust deficits. Placeholder sections cover the Deepwater Horizon disaster (well control failure at scale and its regulatory and social consequences), induced seismicity from saltwater disposal (distributed liability for aggregate harm), and hydraulic fracturing and water (the gap between scientific risk and public perception). The chapter closes with the engineer's professional responsibilities under applicable codes of ethics, the duty to speak when safety is at risk, and a framework for thinking about stakeholder engagement and design for social license. **Key topics:** Social license to operate — definition and levels · Legal compliance vs. community acceptance · Federal, state, and local regulatory frameworks · Regulatory gaps and orphan wells · Legacy well liability · Subsurface as a shared resource · Zombie wells and "whack-a-mole" subsurface pressure management · The paradox of mitigation · Noise, light, odor, and traffic as community impact vectors · Deepwater Horizon (placeholder) · Induced seismicity and distributed liability (placeholder) · Hydraulic fracturing and public perception (placeholder) · NSPE and SPE codes of ethics · Duty to speak · Designing for social license · Stakeholder engagement principles --- ### Part VIII: Advanced Topics --- #### Chapter 24 — Managed Pressure Drilling Managed pressure drilling (MPD) solves the bottomhole pressure oscillation inherent in conventional drilling by actively controlling a surface back pressure to compensate for annular friction as the pump cycles on and off. This chapter begins by quantifying the BHP oscillation problem and explaining why narrow drilling windows make it intolerable. The constant BHP principle is restated in the MPD context: the surface back pressure when the pump is off must exceed the surface pressure when the pump is on by exactly the annular friction loss at operating rate. The pivot point — the depth at which pressure is held constant — is chosen by the engineer and determines the reference for back pressure calculations. The pump schedule (a table of flow rate vs. back pressure at each ramp step) is derived from the Newtonian frictional pressure loss equations and applied in a worked example. Equipment — the rotating control device (RCD), choke, Coriolis flow meter, and MPD skid — is described and the critical requirement for separation of the MPD flow line from the choke/kill manifold is explained. The chapter surveys the MPD system types and closes with mud cap drilling and underbalanced drilling applications, kick detection advantages, and the pipe-light hazard. **Key topics:** BHP oscillation · Constant BHP principle in MPD · Pivot point · Pump schedule calculation · Newtonian annular friction equations · Rotating control device (RCD) · MPD choke and Coriolis flow meter · MPD skid · Back pressure pump · Density control · Dual gradient drilling · Mud cap drilling (floating and pressurized) · Underbalanced drilling · Kick detection with MPD · Pipe light hazard --- #### Chapter 25 — Drilling Performance and Drilling Problems This chapter addresses two complementary topics: how to optimize drilling performance through physics-based analysis, and how to recognize and respond to the most common drilling problems encountered in the field. The drilling performance section develops the concept of mechanical specific energy (MSE) — the energy required to destroy a unit volume of rock — as the primary diagnostic tool for bit efficiency. The fundamental point is that a bit does only two things (press and turn), and ROP is linear in both WOB and RPM when the bit is working correctly; any nonlinearity signals dysfunction. The limiter redesign loop — identify one constraint, remove it, find the next — provides a systematic framework, illustrated with the Utah FORGE drill-rate progression, and step tests are developed as the field implementation tool. Bit dysfunctions (stick-slip, bit whirl, bit balling) are described with their causes and remedies. The drilling problems section covers the three most costly operational problems: lost circulation (seepage, moderate, and total losses; causes; LCM treatments; the principle that ROP is the best LCM), stuck pipe (pack-off, differential sticking, and key seat — each with distinct symptoms, causes, and remedies), and fishing (fishing tools, pre-planning, and the economics of when to stop). **Key topics:** What a bit does (press and turn) · Rate of penetration · Mechanical specific energy (MSE) · MSE vs. rock UCS · Limiter redesign loop · FORGE drill-rate progression · Step tests · Bit dysfunctions: stick-slip, bit whirl, bit balling · PDC bit damage modes · EDR and MWD data · Lost circulation categories and causes · LCM types and selection · ROP as the best LCM · ECD in long laterals · Stuck pipe: pack-off, differential sticking, key seat · Differential sticking force · Fishing tools and economics · Nuclear source protocol --- #### Chapter 26 — Geothermal Drilling This chapter opens with a short introduction to geothermal energy and closes the loop between the drilling engineering of this book and its fastest-growing application. The Earth's heat sources and geothermal gradient, the five requirements of a working geothermal system, and the governing energy-flow relationships (Darcy flow, conduction, convection, and working-fluid heat capacity) establish the fundamentals, with the shale-gas analogy motivating enhanced geothermal systems: hot rock has the energy but not the permeability, and horizontal drilling plus multistage stimulation supplies what nature did not. Geothermal system types (hydrothermal, EGS, closed-loop; heat-only, power, and CHP), flash and binary conversion cycles, and the levelized cost of electricity — dominated by drilling at 40–60% of capital — frame the economics. The drilling half covers what changes in hard, hot, fractured rock: bit and cutter design for granite, extreme-temperature tool limits, severe lost circulation in the productive fractures themselves, and thermal stress from quenching, which can fracture rock at the bit face (helping) and at the wellbore wall (threatening). The Utah FORGE limiter-removal campaigns and Fervo's shale-style doublets demonstrate the transfer of drilling performance methodology, and an integrated worked example — drilling trouble near a fault that becomes the production target of a buoyancy-driven doublet — ties together the geomechanics, stability, and drilling problems threads of the book. **Key topics:** Earth's heat sources and geothermal gradient · Requirements of a geothermal system · Darcy, conduction, convection, and heat-capacity relationships · MWth vs. MWe · Hydrothermal, EGS, and closed-loop systems · Flash steam and binary cycles · Levelized cost of electricity and drilling's share · Hard crystalline rock drilling · High-temperature tool limits · Lost circulation in fractured reservoirs · Thermal stress and spalling · Mud cooling · Utah FORGE limiter campaigns · Fervo and Eavor case studies · Fault-zone worked example --- #### Chapter 27 — Novel Drilling Methods for the Future The closing chapter surveys the technologies that may someday replace — or augment — the rotary drilling system this book is built around. It begins with the functional requirements any drilling method must satisfy (rock destruction, cuttings transport, borehole stability, well control, completion, steering), then examines the directed-energy candidates: laser drilling (thermal spallation and melting), plasma or electro-pulse drilling (explosive internal fracturing via high-voltage discharge), and millimeter wave drilling (gyrotron-driven melting and vaporization for ultra-deep geothermal). Mechanical alternatives — hydraulic and abrasive jetting, percussion hammers — lead to the pragmatic near-term path of hybrid bits combining PDC mechanics with jet or plasma rock weakening. The modeling frontier is surveyed through its key dichotomies (soft vs. stiff string, lumped vs. distributed, steady-state vs. transient) as the foundation of drilling automation, alongside 3D-printed bit prototyping. The chapter — and the book — close with the open research questions that tie every novel method back to drilling fundamentals: whatever destroys the rock, something must still hold the hole open, keep formation fluids out, and deliver a well. **Key topics:** Functional requirements of any drilling method · Laser drilling and thermal spallation · Plasma/electro-pulse drilling · Millimeter wave drilling and gyrotrons · Hydraulic and abrasive jetting · Percussion drilling · Hybrid bits (PDC + jet or plasma assist) · Specific energy comparisons · Soft/stiff string, lumped/distributed, steady/transient models · Drilling automation · 3D-printed bit prototyping · Open questions (thermally induced breakout, cuttings transport without circulation, well control without a mud column) ## A Note on Units Drilling engineering in practice uses a mixture of US customary and SI units that reflects the industry's history as an American-led enterprise that has become global. This textbook uses oilfield units (lb/gal, psi, feet, barrels) throughout, which is the standard for field operations in North America and much of the world, and includes SI conversions where they aid understanding. ## A Note on Sources and Attribution This textbook was developed from lecture materials created for PETE 225 and PETE 355 at Texas A&M University. Key reference texts consulted during development include: - Mitchell, R.F. and Miska, S.Z. (eds.), *Fundamentals of Drilling Engineering*, Society of Petroleum Engineers, 2011. - Bourgoyne, A.T., Millheim, K.K., Chenevert, M.E., and Young, F.S., *Applied Drilling Engineering*, Society of Petroleum Engineers, 1986. - API RP 13D, *Rheology and Hydraulics of Oil-well Drilling Fluids*, American Petroleum Institute. This book is released under the [Creative Commons Attribution 4.0 International License (CC BY 4.0)](https://creativecommons.org/licenses/by/4.0/). You are free to share and adapt the material for any purpose, provided appropriate attribution is given. Contributions, corrections, and suggestions are welcome via the [GitHub repository](https://github.com/romanshor/Introduction-to-Drilling-Engineering). ## A Note on AI-Assisted Authoring The chapter drafts in this textbook were created with the assistance of Claude, a large language model developed by Anthropic. The drafting process used slide decks and closed-captioned transcripts of lectures taught by the author at Texas A&M University as primary source material. Claude was used to transform that lecture content — including explanations, worked examples, and problem sets developed by the author over years of teaching — into structured textbook prose. All technical content, learning objectives, worked examples, and problem solutions were reviewed by the author. The ideas, pedagogical choices, and engineering judgments in this text originate from the author's teaching and research; the AI served as a drafting assistant, not a subject-matter expert. This acknowledgment is made in the interest of transparency. The use of AI tools in academic writing and open educational resource development is evolving rapidly, and the author believes that honest disclosure of how such tools are used is important for the integrity of educational materials.