Fundamentals of Horizontal Wellbore Cleanout: Theory and Applications of Rotary Jetting Technology

By Xianzhi Song, Gensheng Li, Zhengming Xu and Subhash Shah

Fundamentals of Horizontal Wellbore Cleanout delivers the latest methods regarding effective sand cleanout tools in horizontal wellbores. Providing the most relevant information, including sand bed formation, sand settling velocity, friction and hydraulics, this book covers the most effective tools and emerging technologies. Sections discuss the settling characteristics of sand and the effects of particle shape and size on drag coefficients, along with models for drag coefficients using experimental data. Numerical studies on sand transport efficiency as well as prediction models of sand concentration and an evaluation of friction between pipe and sand bed are also included.

Illustrative case studies include cleanout with varying nozzle assemblies leading to optimum design on operation procedures, bottomhole assembly, and other lessons learned from known field experience. Rounding out with future research on cost-saving strategies including CO2 used as a washing fluid in water-sensitive formations, Fundamentals of Horizontal Wellbore Cleanout gives today’s petroleum and drilling engineers alternative methods to hole cleaning in today’s horizontal wells.

• Presents flowcharts, methods and field studies to help readers develop cost-saving strategies and optimal performance
• Helps users build their own models using the experimental data provided
• Guides readers on how to build research and operation capabilities by providing extensive literature reviews and references

• Language: English
• Publisher: Elsevier Science
• Release date: May 20, 2022
• ISBN: 9780323858779

Xianzhi Song

Dr. Xianzhi Song is the Professor of College of Petroleum Engineering and the Vice Dean of College of Artificial Intelligence, China University of Petroleum at Beijing (CUPB). He is also the Vice Director of CUPB Geothermal Research Center, and the Director of CNPC Key Laboratory of Drilling Engineering, etc. He has obtained the National Natural Science Funds for Excellent Young Scholars of China, the Awards of Science and Technology for the Excellent Youth by Sun Yue-Qi Foundation, and National Excellent Doctoral Dissertation. His research areas involve drilling and completion, geothermal exploitation, and artificial intelligence. He has authored more than 50 papers and earned 20 patents. He received his B.S degree in petroleum engineering from China University of Petroleum at East China and PHD degree in oil and gas well drilling engineering of CUPB in 2010.

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Preface

Sand transport in wellbores occurs during various phases of a well's life. During horizontal well drilling, fracturing, and production processes, cuttings, proppant, and formation sand are often encountered, and a solids bed is easily formed at the bottom of the horizontal wellbore. Poor hole cleaning may result in lost circulation, hinder running the casing into the selected position, excessive bit wear, and pipe sticking. The conventional horizontal well cleanout technique is to increase the surface pump flow rate; however, the maximum flow rate is restricted to the surface pump capability and wellbore stability.

Horizontal solids cleanout by the rotary jet is a high-efficiency, low-cost technology. In this book, we attempt to address the theory and applications of rotary jetting for sand cleanout in horizontal wells. The annular helical flow of the rotary jetting greatly improves the transport efficiency of sand in horizontal wells. The book includes nine chapters: Chapter 1 introduces the fundamentals of rotary jetting; Chapter 2 experimentally investigates the drag coefficient and settling velocity of sand in cleanout fluids; Chapter 3 analyzes the cuttings transport efficiency during horizontal well drilling; Chapter 4 presents the sliding friction between coiled tubing and solids bed in cleanout operations; Chapter 5 investigates the characteristics of helical flow field in horizontal annulus; Chapter 6 presents the behavior of solids transport in annular helical flow field; Chapter 7 describes the cleanout model development and hydraulic parameters calculation; Chapter 8 provides some field cases of sand cleanout by the rotary jetting; Chapter 9 presents the sand cleanout by the supercritical CO2.

As a novel technology in recent years, sand cleanout by rotary jetting has not yet been investigated thoroughly or completely. The purpose of this book is not intended to solve all the sand cleanout problems in horizontal wells. It describes the main ideas of the subject with the purpose of providing the reader with tools to tackle other problems; some of these contents have been published previously in papers written by the authors; and this book aims to serve graduate students, advanced seniors, and field engineers.

The authors gratefully acknowledge the financial support from the Major Program of National Natural Science Foundation of China (No. 52192621), the Joint Funds of the National Natural Science Foundation of China (No. U19B6003-05), National Key Scientific Research Instrument Research Project of National Natural Science Foundation of China (No. 51827804), National Natural Science Funds for Distinguished Young Scholar (No. 52125401), State Key Program of National Natural Science Foundation of China (No. U1562212), National Science and Technology Major Project of China (No. 2016ZX05023-006).

Chapter 1

Introduction

Xianzhi Songa, Gensheng Lia, Zhengming Xub, Subhash Shahc

aChina University of Petroleum, (CUPB), Beijing, China

bDepartment of Petroleum Engineering, China University of Geosciences, Beijing, China

cMewbourne School of Petroleum and Geological Engineering, University of Oklahoma, OK, United States

1.1 Background

During horizontal well drilling, fracturing, and production processes, cuttings, proppant, and formation sand are often encountered, and a solids bed is easily formed at the bottom of the horizontal wellbore (Heinrichs and Dedora, 1995; Walton, 1995). In this book, particle represents cuttings during the drilling process, proppant during fracturing operations, and formation sand during production operations. Poor hole cleaning may result in lost circulation, hinder running the casing into the selected position, excessive bit wear, and pipe sticking. These hazards not only increase the difficulty of the oil field development, but also increase the production cost of oil and gas, which has a great impact on subsequent production operations (Walton, 1997; Power et al., 2000; Kuchel et al., 2002). To restore the production capacity of the oil and gas well, solids cleanout operations are required to carry downhole particles from the bottom to the surface.

The conventional horizontal well cleanout technique is to increase the surface pump flow rate, the fluid flow velocity, and turbulence in the annulus, achieving the goal of maintaining suspension of the particles so that they move up and out of the well (Loveland and Pedota, 2005; Zhou et al., 2005). However, increasing the flow rate of the surface pump, or using efficient well cleaning fluids, could greatly increase the cost of well cleaning operations. Besides, the conventional horizontal well cleanout operations take a long time to achieve. Moreover, in most cases, the formed solids bed has a certain cohesive strength, and an increased drilling fluid flow rate is not able to completely destroy the solids bed. Therefore, it is advantageous to develop a more efficient solids cleanout technology for horizontal wells.

Horizontal solids cleanout by the rotary jet is a high-efficiency, low-cost technology, which has developed rapidly in recent years (Li and Walker, 2001; Li et al., 2002). By using a high-pressure water jet and rotation control technology, an annulus vortex effect is produced in the wellbore that increases the efficiency of solids cleanout in horizontal wells. Thus, it is of great significance to understand the mechanism of solids cleanout by rotary jets and particle transport characteristics in horizontal wellbores.

1.2 Research status

1.2.1 Hole cleaning in horizontal wells

Particle transport in horizontal wells is affected by many parameters, which could generally be categorized into three groups: fluid properties, particle properties, and operational parameters (Bilgesu et al., 2007). The first group, fluid properties, includes fluid density and fluid rheology. The second group, particle properties, includes particle density, particle size, and particle shape. The third group, operational parameters, includes wellbore angle, wellbore size, drill pipe eccentricity, pipe rotation speed, flow rate, and rate of penetration (ROP). Practical use of these parameters to control particle transport also depends on their controllability in the field (Mohammadsalehi and Malekzadeh, 2011). Adari et al. (2000) summarized the major factors influencing cuttings transport in relation to their ease of control in the conventional well drilling, as shown in Fig. 1.1.

Figure 1.1 Key variables controlling cuttings transport in conventional rotary drilling.

The drill pipe eccentricity is defined as (Sayindla et al., 2019),

(1.1)

where, e is eccentricity, E is the offset distance between the centers of the drill pipe and the wellbore, do is the wellbore diameter, and di is the outer diameter of the drill pipe. As shown in Fig. 1.2, when e = 0, it represents the concentric annulus. When 0 < e < 1, it represents a partially eccentric annulus. When e = 1, it represents a fully eccentric annulus, and the drill pipe contacts with the hole wall.

Figure 1.2 Schematic of the concentric and eccentric annulus.

For small-diameter horizontal wellbores, the degrees of influence for these variables on hole cleaning efficiency is different. Song et al. (2017) summarized the major factors influencing cuttings transport in relation to their ease of control in the microhole horizontal well drilling, and analyzed the difference between the conventional rotary drilling and the microhole horizontal well drilling, as shown in Fig. 1.3. Yellow symbols represent variables controlling cuttings transport in microhole drilling in their study, light blue symbols represent variables controlling cuttings transport in conventional rotary drilling for comparison with microhole drilling, and white symbols represent variables controlling cuttings transport in conventional rotary drilling which were not investigated in their study. Variables represented by light blue and white symbols in conventional rotary drilling are cited from the study of Adari et al. (2000).

Figure 1.3 Comparison of key variables controlling cuttings transport in microhole drilling and conventional rotary drilling.

As shown in Figs. 1.1 and 1.3, wellbore size and wellbore angle have a strong influence on cuttings transport. However, wellbore size and wellbore angle are rarely changed to improve hole cleaning efficiency.

Flow rate is the primary parameter that significantly influences cuttings transport, and its control in the field is relatively easy. Thus, researchers have conducted numerous studies to determine the minimum transport velocity (MTV) and maintain the annular velocity above the estimated value (Shah and Lord, 1991; Ford et al., 1996; Bizanti and Alkafeef, 2003; Malekzadeh and Mohammadsalehi 2011; Bizhani et al., 2016). MTV is defined as the annular fluid velocity which keeps the cuttings moving upwards without the formation of solids bed in the wellbore.

However, the flow rate can only be increased to a point, limited by the available rig hydraulic power, permissible equivalent circulating density, and the susceptibility of open hole sections to hydraulic erosion (Mohammadsalehi and Malekzadeh, 2011). When the annulus flow rate is less than MTV, some particles will settle to the bottom of wellbore and form a solids bed.

Researchers use two-layer or three-layer models to simulate the particle transport process in the horizontal wellbore. As for the two-layer model, there are a solids bed layer and a suspension layer in the wellbore (Gavignet and Sobey, 1989; Li and Liu, 1994; Liu and Wang, 1995; Wang and Liu, 1996; Luo et al., 1997; Wang and Zhang, 2003, 2004; Long et al., 2005; Naganawa and Nomura, 2006; Li et al., 2007; Naganawa et al., 2017). As for the three-layer model, there are a suspension layer, a moving bed layer, and a stationary bed layer in the wellbore (Doron and Barnea, 1993, Nguyen and Rahman, 1996, Cho et al., 2000, Ozbayoglu et al., 2005, Aitken and Li, 2013). The two-layer or three-layer models usually are difficult to solve, thus, some researchers developed empirical models to predict the particle concentration or solids bed height in the wellbore based on the dimensional analysis (Yu et al., 2007; Ozbayoglu et al., 2010; Song et al., 2017).

When regular fluid circulation is not sufficient for the effective hole cleaning, wiper trips, and/or drilling fluid sweeps can be used to clean the wellbore or reduce the solids bed height. A wiper trip is defined as the movement of the end of the drill string in and out of the wellbore, a certain distance (Walker and Li, 2001). The drilling fluid sweep could be classified into: (1) high-viscosity sweep, (2) high-density sweep, (3) low-viscosity sweep, (4) combination sweep, and (5) tandem sweep. The solids cleanout fluid is circulated down through the drill string and returned to the surface throughout the annulus. The flow direction changes at the end of the coiled tubing (CT) and the jet generated at the end of the CT fluidize the solids bed and transport particles backward to the surface (Li and Walker, 2001; Walker and Li, 2001; Li and Wilde, 2005; Li et al., 2010).

It should be noted that the worst hole-cleaning performance occurs at angles of 40○–60○ (Zhang et al., 2018; Pandya et al., 2020). However, in this book, we only focus on the solids cleanout in horizontal wells.

1.2.2 Solids cleanout in horizontal wells

Different from conventional solids cleanout operations, solids cleanout operations in horizontal wells have the following unique characteristics: (1) the tubing string axis does not coincide with the wellbore axis, and the flow geometry is an eccentric annulus; and, (2) the direction of annulus fluid flow is perpendicular to the direction of particle settling velocity. Therefore, the short vertical distance allows particles to accumulate and form a solids bed. The above unique characteristics have an important effect on the particle accumulation in horizontal wells, making it difficult to effectively remove the solids bed from the horizontal well using conventional cleanout operations.

Solids cleanout technology has been widely used since the introduction of CT (Engel and Rae, 2002; Rolovic et al., 2004; Ali et al., 2005). At the same time, with the development of water jet technology (Li and Shen, 1991; Shen et al., 1991; Shen, 1998), the water jet technology has also been adopted in solids cleanout operations. By using the high-speed water jet, particles in the bed could be stirred up and suspended in the fluid. At present, solids cleanouts using CT remain a major part of total activity in the CT industry. Through several decades of development, the solids cleanout technology using CT is maturing gradually (Sach and Li, 2007).

Many companies performed a series of studies on the CT solids cleanout technology, such as Schlumberger, Baker Hughes, BJ, Halliburton, Weatherford. Schlumberger developed an integrated well cleaning system trade named—PowerClean, which integrates the software, well cleaning fluid, jet tool, nozzle design, and monitoring system (Rolovic et al., 2004, Ali et al., 2005).

The CT solids cleanout technology in China has achieved numerous application results in recent years (Yang et al., 1998; Huang et al., 2002; Liu et al., 2002; Zhou et al., 2002; Song, 2004; Cai, 2005; He, 2006; Zhang et al., 2007). For example, by using three sets of CT machines from BOWEN company in the United States, the First Petroleum Exploration Bureau of LiaoHe Oilfield successfully solved the problem of condensate plugging in 948 wells after the solids cleanout operations. The CT-220 unit produced by Hydro-Rig was used in TuHa oilfield to carry out solids cleanout operations, which also achieved good economic benefits. Besides, the CT solids cleanout technology has also been widely used in DaGang, SiChuan, and DaQing oilfields.

At present, there are two kinds of jet flushing technology, namely directional jet flushing technology and rotary jet flushing.

1.2.2.1 Directional jet flushing technology

Directional jet flushing technology involves installing several nozzles with a fixed angle in the jetter. The tool does not rotate during operations. The CT drags the tool up and down to clean particles from the bottom of wellbore.

At present, Schlumberger provides a mature jetting solids cleanout technology. As shown in Fig. 1.4, the PowerClean integrated well cleaning system was launched in 2002. There are no moving parts in this tool. During the solids cleanout process, directional jet flow induces a swirling effect to improve transport efficiency of particles in horizontal wellbores.

Figure 1.4 Horizontal wellbore cleanout by the PowerClean tool from