Practical Wellbore Hydraulics and Hole Cleaning

Unlock Faster, more Efficient, and Trouble-Free Drilling Operations

Mark S. Ramsey

• Publisher: Gulf Professional Publishing
• Year: 2019
• ISBN:
  9780128170892
• Topic: Physical Sciences
• Subtopic: Energy

Practical Wellbore Hydraulics and Hole Cleaning presents a single resource with explanations, equations and descriptions that are important for wellbore hydraulics, including hole cleaning. Involving many moving factors and complex issues, this book provides a systematic and practical summary of solutions, thus helping engineers understand calculations, case studies and guidelines not found anywhere else. Topics such as the impact of temperature and pressure of fluid properties are covered, as are vertical and deviated-from-vertical hole cleaning differences. The importance of bit hydraulics optimization, drilling fluid challenges, pressure drop calculations, downhole properties, and pumps round out the information presented.

Packed with example calculations and handy appendices, this book gives drilling engineers the tools they need for effective bit hydraulics and hole cleaning operation design.

• Provides practical techniques to ensure hole cleaning in both vertical and deviated wells
• Addresses errors in predictive wellbore hydraulic modeling equations and provides remedies
• Teaches how to improve the economic efficiencies of drilling oil and gas wells using calculations, guidelines and case studies

Chapter One

Introduction

Abstract

The current chapter introduces the book and sets the stage for why optimizing both wellbore hydraulics (including bit nozzle selection) and hole cleaning are important for efficiently drilling wells either on land or offshore. The book is structured for both rapid problem-solving and diving into the technical details as desired, and specific parts can be successfully used to improve efficiencies (i.e., bit nozzles, flow rate optimizations, hole cleaning, etc.) without required reading of the entire book.

Keywords

Introduction; book organization; wellbore hydraulics; hole cleaning; rate of penetration; pressure losses; rheology; downhole properties; pumps; target audiences

Contents

• 1.1 Wellbore Hydraulics 1
• 1.2 Hole Cleaning 2
• 1.3 Organization of the Book 2
• 1.4 Rate of Penetration 3
• 1.5 Pressure Losses 3
• 1.6 Rheology 4
• 1.7 Downhole Properties 4
• 1.8 Pumps 4
• 1.9 Operators, Drilling Contractors, and Service Company Partners 5

In today’s competitive oil and gas-drilling environment, all available skills should be utilized by rigsite and office personnel to maximize efficiencies in constructing the wellbore. A thorough understanding of wellbore hydraulics and its close associate, hole cleaning, are two of those critical skills. An engineer’s job is, in part, to predict the future. Operations personnel make that future happen. Wellbore hydraulics and hole cleaning enable both to control that future with respect to drilling a well.

1.1 Wellbore Hydraulics

As the title of this book suggests, there are two broad overarching and connected technologies covered. The first, and perhaps the most misunderstood, is that of wellbore and bit hydraulics. Understanding and properly utilizing the various levers of adjustment around wellbore hydraulics can literally make the difference in drilling ahead or not, but more commonly it is a matter of how efficiently the drilling is progressing. Significantly, the ability to drill longer laterals can also be a function of proper wellbore hydraulics. Last, but always of great importance to drillers, tool pushers, and drilling engineers alike, rate of penetration can be greatly enhanced through the proper use of wellbore hydraulics.

While not the only critical component of a well-designed and executed drilling project, the optimum selection of flow rates, pipe sizes (where this is an option), and nozzle sizes can truly make-or-break the economics of a well.

1.2 Hole Cleaning

An older operations superintendent in this author’s early engineering days advised that “it is not how much hole you make, it is how much hole you keep!” He wisely recognized that there were ways to improve rate of penetration short term that could lead to longer term problems or even complete loss of a well. A key component of “keeping” the hole is to have a consistent and reliable approach to removing cuttings from both under the bit and from the wellbore itself—transporting them out of the hole at the surface.

There is an enormous variety, some might say endless variety of well designs today. Directionally, these designs range from more-or-less vertical to fully horizontal (or higher angle). Plan views (or birds-eye top-down views) of wells range from a straight line to a curved line to a full 180 degree or more “hook.”

Due in part to this variety, there are numerous difficulties in both transporting cuttings from the wellbore to the surface where they can be removed from the mud system.

1.3 Organization of the Book

Wellbore hydraulics and hole cleaning are the title topics of this book, and the following two chapters address them.

Within those chapters, the solution to the problem is presented in several ways. Typically, a quick and usable solution is given for those situations when extensive analysis is neither warranted nor practical due to limited time constraints. When you come upon an accident victim needing assistance, stop the bleeding first.

After the quick-but-usable solution is presented, more detailed discussions and more elegant technical approaches are examined. Where time is available or well criticality requires it—for example, when drilling through an extremely narrow pore-pressure/frac-pressure window—the more detailed approach may be preferred.

In this manner, the book may be effectively used as a quick reference tool to solve immediate and pressing problems and yet also serves the inquisitive to bore deeper into the issues.

1.4 Rate of Penetration

The chapter after those two ties the wellbore hydraulics, bit hydraulics, and hole cleaning together in the interest of drilling faster, near and dear to all drillers’ hearts.

After these cardinal chapters, the remaining chapters in the book address tightly related subjects in sufficient details with suitable equations to permit modeling of pressure losses.

The overall approach is that some pressure losses are required by the drilling operation and cannot nor should not be minimized. Mud motor losses come to mind as these (and the associated torque and rpm they impart to the bit) can be extremely important to drilling rate. However, if the rig pumping capability is sufficient, any extra pressure that is available should be spent across the bit nozzles, rather than being wasted as friction loss in pumping drilling fluid through the drill string and up the annulus.

1.5 Pressure Losses

To the uninitiated, pressure losses seem simple to calculate, especially if the reader has a background or coursework in calculating pressure losses in Newtonian liquids flowing through pipes. However, for the case of a drill well, the liquid is not Newtonian, the flow regime is never fully laminar nor fully turbulent (the two cases simplest to model), and the flow is in a nonuniform series of conduits, some of which change sizes along their length and others are moving!

The result is that it is extraordinarily difficult to accurately model pressure losses accurately downhole. Hence, an entire chapter is devoted to these pressure loss issues in a manner not found in any extant text.

1.6 Rheology

“Panta rhei”—everything flows. The study of rheology is next. In order to deal with pressure losses and modeling, an understanding of rheology is important, so a chapter on this subject is next. Everything that flows exhibits some resistance to flow. That resistance, in the case of drilling fluids or muds, takes the form typically as a “shear-thinning” liquid. In such liquids, the viscosity is fairly high when the fluid is shearing (particle or streamline to particle or streamline) slowly. Conversely, the viscosity actually decreases as the shearing (or shear rate) is increased, much in the same way that ketchup from a plastic bottle is higher viscosity while in the bottle than while going through the cone-shaped nozzle as the bottle is squeezed.

1.7 Downhole Properties

Next to last in this first edition is a chapter discussion on the variability of fluid properties as the fluid is transported down the drill pipe, through the nozzles, and back up the annulus in a wellbore. Increased pressure increases density and viscosity. Increased temperature decreases density and viscosity. Pressure and temperature can affect the effect of chemicals in the mud on their properties. Low shear rate values may be affected in a different manner than high shear rate ones. Chemical additives to accomplish other functions, such as protect the formation from damage, may interact with the rheology differently downhole than on the surface.

1.8 Pumps

Last, a brief discussion on rig pumping equipment is provided. These include both kinetic (or centrifugal) pumps and positive displacement types generally used to store energy (as pressure as the mud compresses) for use downhole.

1.9 Operators, Drilling Contractors, and Service Company Partners

In an industry where many of the players may have differing economic interests in various parts of drilling a well, wellbore hydraulics and hole cleaning can benefit all of the companies. A good understanding of how energy is used in a wellbore—usually measured as pressure losses—can greatly improve the drilling performance for the operator who is paying for the operation. For the drilling contractor and service companies involved, that efficiency plays out as significantly improved life of capital-intensive equipment.

It is the author’s desire that this book’s readers reap economic benefits far in excess of the monetary cost and time to read and understand it on the very first well it is used on. Though equipment and measuring techniques improve with time, its concepts are timeless and can be used on all wells thereafter.

Enjoy your read.

Chapter Two

Bit Hydraulics

Abstract

The key to improving penetration rates, extending bit life, ...