Geomechanics of Sand Production and Sand Control

By Nobuo Morita

Geomechanics of Sand Production and Control delivers a convenient resource for both academia and professionals to gain understanding and results surrounding sand production. Packed with rock mechanic fundamentals and field case studies, this reference offers theoretical knowledge, field and laboratory data, and operational methodologies. Gaining knowledge on better sand control production improves environmental impact, preventing corrosion of pipes, damage to surface production facilities, and disposal of produced sands, among other considerations. Sections are supported by field case studies, lab tests and modeling studies to explain the most environmentally supportive wellbore stability step-by-step methods.

Authored by a very experienced professor, this reference helps engineers learn how to solve sand problems in various types of energy wells. Production engineers in oil and gas utilize sand production and sand control equipment in many completion methods, with a growing interest to expand these methods in wells for CO2 sequestration and geothermal areas, but knowledge on these methods is fragmented and lacks a bridge to support energy transition. This book provides the coverage needed to address this advancing field.

• Includes visual graphs derived from real-world fields and numerical models
• Covers transition methods into other energy assets, including CO2 sequestration and geothermal wells
• Provides solutions and examples with the inclusion of real field case studies

• Language: English
• Publisher: Elsevier Science
• Release date: Jun 29, 2022
• ISBN: 9780323955065

Nobuo Morita

Nobuo Morita is a professor at the Harold Vance Department of Petroleum Engineering, Texas A&M University, College Station, Texas. He teaches courses on boundary element methods for application to petroleum engineering problems, non-linear mechanics and finite element methods for geomechanics. He is a supervising professor of the Texas A&M Geomechanics Joint Industry Project. He holds sand control, borehole stability and hydraulic fracturing workshops twice per year around the world and has provided consulting services in major oil companies around the world. He was previously employed by ConocoPhillips for 14 years.

Book preview

Front Cover for Geomechanics of Sand Production and Sand Control - 1st edition - by Nobuo Morita

Geomechanics of Sand Production and Sand Control

Nobuo Morita

Texas A&M University, College Station, TX, United States

Table of Contents

Cover image

Title page

Copyright

Acknowledgments

Introduction

Chapter One. Fundamental rock mechanics theory of sand production from oil and gas reservoirs

Abstract

1.1 Linear elasticity theory

1.2 Finding analytical solutions useful for petroleum engineers

1.3 Application of the linear elasticity theory to thick wall cylinder test for predicting the onset of sand production

1.4 Application of plasticity theory to medium-strength rock

1.5 In situ stress

1.6 General rock properties

Chapter Two. Natural completion

Abstract

2.1 Field and laboratory observations of sand production from naturally completed wells

2.2 Evaluation tool of onset of sand production

2.3 Prediction of long-term sand production rate using an analytical model

2.4 Prediction of perforation cavity evolution during early sand production using Geo3D finite element code: sand release rate coefficients obtained from SINTEF triaxial sand rate experiments

2.5 Discussion and conclusions

2.6 Pressure profile around perforations

Chapter Three. Completion methods for weak formation

Abstract

3.1 Gravel pack

3.2 Frac packs

3.3 Selective perforation

3.4 Cased hole completion with a compartmentalized screen

3.5 Openhole completion

3.6 No sand control

3.7 Oriented perforation

3.8 Casing patch

3.9 Resin treatment

3.10 Skin damage and risk of completion methods

Chapter Four. Sand control for heavy oil reservoirs

Abstract

4.1 Heavy oil resources

4.2 Cold heavy oil production with sand

4.3 Field operation to identify the magnitude of matrix bypass event and the plugging capability

4.4 Laboratory experiments observing long stable finger growth

4.5 Simulation of laboratory flow tests

4.6 Field simulation

4.7 Conclusion of simulation and laboratory test analyses

Chapter Five. Guidelines to solving sand problems for water or gas injection wells

Abstract

5.1 Completion methods for water or gas injection wells

5.2 A phenomenon observed for perforated injection wells—rock strength distribution

5.3 A phenomenon observed for perforated injection wells—injectivity

5.4 Sand settlement in the rat hole

5.5 Cross flow

5.6 Screenless frac pack

5.7 Guidelines for completing water and gas injection wells

Chapter Six. Erosion and sand production monitoring

Abstract

6.1 Typical high flow gas/condensate production facilities

6.2 Hot spots

6.3 Types of erosion

6.4 Equations of erosion

6.5 Erosion analysis of wellhead and Xmas tree

6.6 Sand rate monitoring

Bibliography

Appendix 1. Proof of continuity and uniqueness of displacement with compatibility condition

A1.1 Gauss theory

A1.2 Stokes theory

Appendix 2. Strain nuclei method

Appendix 3. Erosion equations induced by sand particles

A3.1 Solid particle erosion rate

A3.2 Erosion equation for flowline and Xmas tree. (Empirical relation, University of Tulsa consortium)

A3.3 WCU separator system erosion

A3.4 Upper completion erosion

A3.5 Wellhead and Christmas tree erosion

Index

Copyright

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Acknowledgments

This book uses laboratory and field data that the author and his coworkers took efforts at measuring while at ConocoPhillips, where the author had been employed as a research fellow and consultant for 40 years. He appreciates the support from ConocoPhillips and his coworkers, especially Donald L. Whitfill, Giin-Fa Fuh, and Kenji Furui. The book also uses the sand rate measurements performed by SINTEF under the aegis of Dr. Euripides Papamichos as the project leader. All their efforts are deeply appreciated.

Introduction

A significant portion of the world’s oil and gas reservoirs is in various degrees of unconsolidation with extensive sanding problems. The problems are observed in both production and injection wells in the oil industries. Similar problems are observed in CO2 injectors and wastewater injectors in CCS (Carbon Capture Storage) and wastewater management industries. These problems include plugging the perforations and formations of production and injection wells, plugging the downhole screens and the gravel pack, surface facility erosion, and collapse of borehole and cased hole. On the other hand, the controlled volume of sand production significantly increases the well productivity and injectivity for both light and heavy oil reservoirs.

The selection of sand control methods depends on oil viscosity and oil and gas production rate. If the viscosity of oil is large, the production of solid does not damage surface facilities. The problem is in the sand-up where, if the density of the mixture of sand and heavy oil is large, oil production stops due to gravity. The sand rate is controlled using slotted liners for heavy oil to prevent the sand-up problem. The oil rate is high if the oil is produced with sand, but an excessive sand rate causes the problem of sand-up to linger. The amount of sand production is also a problem which means sand must be hauled away from the production site rather than leave it to compound the well’s problems further.

If the viscosity is low, the velocity of sand particles is high, which erodes the metal surface and narrow choke. Especially, the sand rate must be reduced for gas since a small amount of sand cuts the choke and erodes the inner surface of production lines with elbows.

Figure 1 Selection of sand control methods judging from production rate, sand production rate, and fluid viscosity.

The allowable sand production depends on field conditions. Normally, the standard allowable sand production is 10 lbs/1000 bbl for oil and 2 lbs/day per well for gas wells. The erosion due to sand production does not induce a sudden explosion. Normally, some leakage starts around wellheads so that the problem can be fixed without inducing accidents. However, if the leak occurs frequently, the best method is to reduce the sand production rate causing erosion.

Figure 2 Allowable sand production depends on field condition.

The selection of sand control methods varies between companies. Some companies have confidence in the benefits of gravel packing, so field engineers tend to gravel pack for most sand-producing wells. The merit of the gravel pack is that the field engineers do not need to worry about damages caused to surface facilities from sand production after completion. The oil production rate may be significantly reduced after several years due to fine-particle plugging. But the well can be re-completed by removing the screens or by side-tracking. Normally, if the permeability is less than 100 md, the gravel pack damage due to fine-plugging does not cause significant flow reduction. Having said that, the fact remains that the skin may increase to 4–6 but without significantly reducing the oil rate. On the other hand, some companies have confidence in the benefits of rock mechanics. Most reservoirs are significantly heterogeneous. If one section is strong, then another section may be weak. The field engineers can measure the distribution of rock strength using cores such that if the weak intervals are short, the production rate is not reduced without perforating the weak intervals. Again, if the rock has medium strength, then sand production may occur after two-thirds of the reservoir life. The oil production rate is reduced, and it no longer damages the surface facilities. The skin will become negative due to some sand production which enhances the oil production. Because the skin becomes negative after some sand production, some companies choose to use heavy-duty production facilities to tolerate a high sand rate. If the erosion rate of facilities is monitored, then the benefits ensuing from enhanced oil and gas production often overweigh the trouble of sand production problems.

Figure 3 Applications of sand control methods vary between companies for gas and light oil reservoirs.

In oil and gas industries, injection wells are essential to maintain the reservoir pressure and to sweep oil and gas with water and CO2. CO2 is injected and stored underground in CCS industries. Wastewater and contaminated water are injected and stored in highly porous layers in wastewater management companies. Injection wells are normally completed with perforations or a slotted liner for a strong formation and with metal woven screens or gravel packs. The injectivity of these wells is initially good, as expected. However, as injection continues, the wells are sometimes shut in for various reasons. Each time the well is shut in, the injectivity declines when the well injection restarts. The main reason for the reduction of injectivity is fine plugging during the well shut-in. The problem starts with the fact that the formations are heterogeneous. The permeability and the storage capability are different between layers. Thus, when the well is shut in, the fluid flows from the layers with a higher storage capacity to those with a lower storage capacity. Given formation and screen plugging occur during the fluid movement, it follows that a certain section of the perforations and open holes may also become unstable during injection due to the reduced tangential effective stress around them. However, these sections also produce fines resulting in a fine-plugging problem in the formation during injection without well shutting-in.

Figure 4 Cross flow during well shut-in.

This book describes the basic theory of sand production mechanism and rock formation and screen plugging problems. It explains the methods of forecasting the onset of sand production and sand rate based on laboratory experiments and numerical models. Various completion methods are described to mitigate sand production problems which the author of this book has practical experience of implementing while working in oil industries as a research fellow and consultant.

Most of the pages in this book have one figure without detailed explanations so that readers can interpret the graphs and figures for their own field applications.

Chapter One

Fundamental rock mechanics theory of sand production from oil and gas reservoirs

Abstract

Fundamental rock mechanics theories are the subject matter of this chapter. These theories are used for deriving analytical solutions and numerical solutions for predicting the onset of sand production. A simple analytical solution is developed using a set of poro-plasticity-elasticity equations to illustrate the controlling parameters inducing sand production. Oil companies normally use the thick wall cylinder tests (TWC tests) to identify the rock strength of perforation collapse. The equations used for TWC tests are different between companies, as is noted here with explanations on how to use these equations. Since the in situ stress is the primary factor affecting the onset of sand production, the calculation method of the change in the in situ stress during reservoir compaction is described.

Keywords

Stress; strain; displacement; stress-strain relation; equation of equilibrium; displacement-strain relation; effective stress for deformation; effective stress for failure; plane stress and strain problems; analytical solution of incline well displacement and stress; thick wall cylinder test; triaxial perforation stability test; nonlinear stress strain; analytical solution of perforation stability; stress state during compaction

This chapter describes the fundamental rock mechanics theories controlling the sand production and the in situ stress change during oil and gas production. Knowledge of the basic theories deepens the understanding of sand production mechanism.

1.1 Linear elasticity theory

1.1.1 Stress

Force is a vector. It can be split between normal and shear forces across and along a plane as shown in Fig. 1.1. For the structures with a finite surface, the concept of stress is introduced where the force divided by the area is the stress. The normal stress is the normal force divided by the area and the shear stress is the shear force divide by the area. For beam objects, forces and moments are used since they have no area.

(1.1)

(1.2)

(1.3)

Figure 1.1 Force vector.

For 3D object (finite surface area)

For beam object (infinitely small surface area, infinitely thin)

1.1.2 Stress components

Consider a cube (Fig. 1.2). The faces perpendicular to x-coordinate are called x-faces. Similarly, y-face and z-face are the faces in perpendicular direction to the y and z coordinates. On the x-face, the stress has three components in x,y, and z directions. The normal component is and the shear components are and . The first subscript shows the x-face and the second subscript shows the directions y and z. The normal stress is written as for simplicity. Similarly, on y-face, the stress components are , and and, for z-face, they are , , and .

Figure 1.2 Stress components in a three-dimensional object.

1.1.3 Strain components

If stress is applied on a structure, it deforms. The intensity of deformation is expressed by the strain. Two types of deformations are induced: normal and angular strains. Normal strain is the deformation in x, y and z directions divided by the length for each direction and the angular strain is the angular deformation between xy, yz, and zx faces (Fig. 1.3). The angular deformation is expressed by . However, for the convenience of computation, the definition by is also used if the equations are expressed by tensor notations. For beam analysis, the displacements and angular deformations are directly used instead of the strains.

(1.4)

(1.5)

(1.6)

Figure 1.3 Strains.

For 3D object (finite surface area)

For beam object (infinitely small surface area, thin)

1.1.4 Displacements

Suppose a structure is moving while deforming. Every point in the structure moves in different directions. If the points move in parallel with the same velocity, the movement is called rigid body movement. The movement of a point from the original coordinate is called displacements expressed by u, v, and w. Consider a square structure in Fig. 1.4.

Figure 1.4 Displacements.

Normal strain in x direction is calculated as follows:

(1.7)

The angular deformation between x and y planes is calculated as follows:

(1.8)

(1.9)

(1.10)

1.1.5 Symmetry of stress components

Consider the moment around a square structure with and width w as shown in Fig. 1.5. The moment around the center must be canceled if the structure does not rotate. Then, we have:

(1.11)

Figure 1.5 Moment around the center of a square structure.

Therefore, .

It shows that the stress components are symmetric.

1.1.6 Number of unknowns

For elasticity problems, we have nine components of stress. But because of the symmetry, the number of unknowns are reduced to six. The number of strain components are six and the number of displacements are three. Therefore, the total number of variables are 15 for elasticity problems. Since we have 15 unknown variables, 15 equations are required for relating all these variables.

Nine stress components:

– x-plane toward x,y,z coordinate directions.

Six independent components:

By symmetry: .

Six independent strain components:

Three independent displacements:

1.1.7 Displacement strain relation

If the movements of points in a domain are not parallel nor do the velocities move the same, the material expands and shrinks along x,y, and z coordinates and in angular directions. The magnitudes are called strains. Six equations are derived between displacements and strains.

(1.12)

(1.13)

(1.14)

(1.15)

(1.16)

(1.17)

1.1.8 Equation of equilibrium (Fig. 1.6)

The forces in the x direction for a cubic body are given by:

Figure 1.6 Forces in x direction acting on each surface.

Body force:

The sum of the forces is zero if they are in equilibrium. Then, the following equilibrium equation holds in the x direction.

(1.18)

Similarly for y and z directions, the equations of equilibrium can be derived.

(1.19)

1.1.9 Stress-strain relation for isotropic linear elasticity

If a normal stress is applied in the z direction, a structure shrinks in the z direction and expands in the lateral direction. The strain in the vertical direction is proportional to and the proportional constant is called Young’s modulus.

The ratio of the deformations in lateral and vertical directions is the Poisson’s ratio denoted by ν.

If a shear stress is applied, the angular deformation becomes proportionally larger (Fig. 1.7). The proportional coefficient is called the shear modulus.

Figure 1.7 Linear stress-strain relation.

In three dimension, we have the following stress-strain relations.

(1.20)

1.1.10 Surface traction versus stress

The stress applied on a boundary surface is in equilibrium with the internal stress. Suppose a tetrahedral body is considered as shown