A Recent Advancement: Casing while Drilling – A Viable Alternative to Conventional Drilling

Drill string models are of two major types- Conventional and Periodic. Conventional drill string models are widely used due to their simplicity in manufacturing and dynamics analysis. Drill strings are affected mainly by torsional, lateral and axial vibrations. The dispersive or propagative nature of these vibrations can only be analyzed by using periodic drill string models. Drill pipe makes up the majority of the drill string. In reality, at each end of the drill pipe, tubular, larger-diameter portions called the tool joints are located. Since the dimensions of the tool joint are negligible when compared to the drill pipe, conventional drill string models assume drill strings to be uniform structures. The tool joints in drill strings introduce a geometrical periodicity in the structure.A periodic structural component is comprised of a repeating array of cells, which are themselves an assembly of elements. The elements may have differing material properties as well as geometric variations. The periodic structures act as mechanical filters for the wave propagation. A material or geometrical change in the structure causes a disruption to the continuous propagation of vibration waves.There are three types of waves propagating in rotating structures: torsional, flexural (bending) and longitudinal. Of these waves, torsional and longitudinal waves are dispersive while flexural waves are non- dispersive. The proportions of the waves which are dispersed vary according to the Wavenumber. The wavenumber is a property of the wave and depends on the structural, material and geometrical properties of the wave guide. Waveguide is the medium through which a wave travels. The wave number, and hence the dispersion and propagation characteristics of waves can be tuned by varying the material and geometrical periodicity in the drill strings.This paper presents the vibration propagation and attenuation characteristics in conventional and periodic drill string models. The periodic drill string model is developed such that it can be easily scaled to a real drilling rig model. The research also features a laboratory setting which comprises a mini drilling rig and actual drilling samples. These features ensure robustness of the dynamics analyzed for the periodic drill string model.The research findings are analyzed under zero and non- zero borehole drill string interactions. Vibration information is collected from upper and lower parts of the drill string models to compare the propagation and attenuation characteristics. Proximity sensors are used for the data acquisition which is then analyzed using frequency and power spectrum graphs. The time and frequency domain vibration propagation characteristics are investigated for both the conventional and periodic drill string models. Laboratory testing analyzes (1) introduction of stop and pass band regions in frequency spectra by periodic drill string models, and (2) vibration attenuation in torsional and lateral vibration modes. The tests confirm the introduction of stop bands in frequency spectra for the periodic drill strings, while they were absent and had an all pass-band for conventional drill string models.The research opens up a new method of passive control of drilling vibrations- by introducing tool joint designs which could be tuned to efficiently dampen out the harmful vibrations affecting the drilling rigs.

The vibration characteristics of drillstring with positive displacement motor in compound drilling Part1: Dynamical modelling and monitoring validation

An inexpensive computer program, utilizing the graphical capability of the IBM-PC, has been developed that demonstrates and teaches the control procedures to be used as the result of a gas kick taken during drilling. In order to properly diagnose and control a kick, one must have a complete understanding of what is happening downhole and why. The color simulation that is presented in this paper – which can be run in real-time or accelerated time – aids in this understanding process. The status of the drilling process, as well as the critical surface measurements available, are displayed graphically on the screen before, after, and during the control of the kick. The display shows the gas bubble, its growth as it is circulated out of the hole, locations of all of the different fluids that are involved in the system (drilling mud, kill mud, and gas bubble), and the surface effects that occur during the control procedure. The program can be run in either a demonstration mode or a control mode. In the demonstration mode, a kick is circulated out by the computer by both the driller's and the wait and weight methods, using the ideal control procedure. An instructor can utilize the demonstration to point out particular points of interest during the process. In the control mode, the operator of the program uses the keyboard to control the process. That is, he or she has direct control of the mud weight to be pumped, choke opening, and pump speed. At the conclusion of a run in either mode, graphs are produced of various pressures as functions of the number of strokes pumped. In the control mode, the program monitors the correctness of the control scheme and highlights incorrect procedures that would result in either a low bottom hole pressure, causing a secondary kick, or a high pressure at the bottom of the casing, causing a loss of circulation.

A new mathematical model was developed in this study to simulate the unsteady flow in controlled mud-cap drilling systems. The model can predict the time-dependent flow inside the drill string and annulus after a circulation break. This model consists of the continuity and momentum equations solved using the explicit Euler method. The model considers both Newtonian and non-Newtonian fluids flowing inside the drill string and annular space. The model predicts the transient flow velocity of mud, the equilibrium time, and the change in the bottom hole pressure (BHP) during the unsteady flow. The model was verified using data from U-tube flow experiments reported in the literature. The result shows that the model is accurate, with a maximum average error of 3.56% for the velocity prediction. Together with the measured data, the computed transient flow behavior can be used to better detect well kick and a loss of circulation after the mud pump is shut down. The model sensitivity analysis show that the water depth, mud density and drill string size are the three major factors affecting the fluctuation of the BHP after a circulation break. These factors should be carefully examined in well design and drilling operations to minimize BHP fluctuation and well kick. This study provides the fundamentals for designing a safe system in controlled mud-cap drilling operati.

Field redevelopment reflects the unique foci of the integrated project team built between Ecopetrol and Oxy to redevelop the LCI oilfield. La Cira Infantas (LCI) is the oldest Colombian field, production started almost at the beginning of the twentieth century and since late 2005 is under a redevelopment phase, increasing production by more than 5 times in less than 5 years. Redevelopment involves over 1500 wells being drilled or worked over in order to increase recovery factor by about 8% from the C sands. Hundreds of wells are scattered throughout this brownfield which is divided in two principal areas, Cira and Infantas. This field is crossed by faults characterized by depleted and shallow gas bearing formations, challenging drilling with loss of circulation and well control issues, somehow unpredicted given the faulty nature of the area and the impact on the producing sands of previous EOR and drilling campaigns (early to mid twentieth century) (Fig. 1). This paper will describe the benefits of using the casing while drilling technology to drill wells where loss of circulation is anticipated, successfully eliminating flat times that otherwise would be used to cure losses when drilling conventionally due to the smearing effect which is enhanced by the addition of bridging agents and loss circulation material; and setting casing at the planned TD. Drilling with casing has shown that 10% cost reduction and 30% time savings were achieved against conventional drilling, with additional potential to reduce costs and time by improving the operational times employed for drill-out, BHA recovery, and cementing operations.

With the rapid development of drilling technology, air drilling technology and large displacement well, and horizontal well drilling technology are also known as the main directions of the future drilling development. Compared with conventional drilling mode, air drilling is particular, such as drilling fluid with low density, poor lubrication, large friction coefficient between the drill string and borehole, irregular borehole, well trajectory control difficulty, and so on. Along with the change of drilling condition, the stress of drill string is also changed. However, irregular borehole has a direct impact on the fatigue failure and the stress of drill string. Therefore, it is necessary to analyze drill string stress and influence factors in irregular hole. Based on the previous studies, application of drill string mechanics and statistical regression methods is used to study drill string drag and torque, and it can predict the drilling string stress state with the hole enlargement rate, meanwhile, it also provides a theoretical basis for gas drilling and complex drilling technology.

Introduction Divinyl benzene co-polymer beads, better known as plastic beads, have been used for reducing torque and drag in conventional drilling operations for 17 years. Over the last four years, they have also been utilized to reduce friction in horizontal wells when drill pipe is not sliding at a fast enough rate, or is not moving at all. Co-polymer beads have also gained recognition as a means of reducing friction in coiled tubing workovers. Friction is reduced by introducing co-polymer beads between the drill string and bore hole. Laboratory testing and field experience have developed methods for reducing friction through specific application techniques. Application of the beads can vary, from spotting small "pills" in specific sections of the bore hole to carrying a concentration of beads throughout the system using a bead recovery unit. Drill string drag is the incremental force required to move pipe up or down in the hole, and torque is the force required to rotate pipe. The magnitudes of torque and drag are related in any particular well, and high drag forces and excessive torque loads normally occur together. There are a number of causes for excessive torque and drag. They include:tight hole conditions;sloughing hole;key seats;differential sticking;cuttings buildup because of poor hole cleaning; andsliding well bore friction. With the exception of sliding friction, these causes are associated with problem conditions in the well bore. Although all of these conditions can occur in horizontal wells, the primary source of torque and drag in a horizontal well with good hole conditions is sliding friction. The ability to alleviate sliding friction using co-polymer beads has proven to be extremely beneficial in horizontal drilling and workover operations, including standard pipe and coiled tubing. Sliding Friction Normal contact force and the coefficient of friction between contact surfaces are the two factors that affect sliding well bore friction. Another factor, capillary attraction, must be considered in open hole situations. Capillarity is described as the relative attraction of the molecules of a liquid where it is in contact with a solid. The relative attraction of molecules leads to a force of adhesion between a solid and a liquid. The wallcake of a well bore will exert very strong capillary attraction forces on a drill string when it comes in close contact with the drill string. This is explained by the fact that the wallcake or mudcake is composed of very small particles of clay, barite, sand, or other matter, and these minute particles will have considerably more surface area exposed for wetting by liquid than would larger particles in the same section of mudcake. The smaller the particles, the more surface area exposed for liquid wetting, thus the greater the attractive capillary force exerted. The capillary attractive force could lead to the drill string adhering to the wallcake, creating torque and drag. The beads, having a larger particle size than the solids in the wallcake, reduce this adhesive force.

In extended open-hole sections, the industry's typical operational sequence to preserve wellbore cleaning is performing frequent wiper trips to remove ledges/tight sections (example of the frequency is every 2,000 ft drilled) or performing single wiper trip across the entire open-hole. To reduce the operational time and operational risks of tripping in/out of the extended drilled section, level-1 casing-while-drilling (CwD) is utilized to hard ream the casing string across the entire open-hole to section total depth. It also serves to optimize the casing design of different areas to interest by combining multiple trouble zones in one section. To ease running casing through the extended already drilled open-hole, single or several wiper trips are performed clear ledge/obstructions/tight holes if any. After reaching the previous casing, the drill string is run back through the drilled section, reaming through obstructions/tight holes. The drill string is pulled out again to surface. This operational sequence consumes about 2.5-3 days, in addition to the increasing risk of getting the string stuck. All these operational sequences are replaced by the utilization of the Level-1 CwD technology to hard ream the casing string. The operational days and associated extra cost are controlled and reduced. Main challenge in drilling through unconsolidated sand zones in shallow sections, and time-dependent unstable shale zones in deeper sections is inability to secure them without significant rig time delay. Loss circulation zones exist around these problematic zones. When severe to complete loss of circulation is experienced, the complexity of securing the problematic zones increases. The level-I casing-while-drilling (CwD) technology was utilized successfully to hard ream and permanently isolate the problematic zones without nonproductive time. CwD were successfully utilized to hard ream the casing strings to target depth to case-off the severely unstable zones experienced in the offsets. The additional NPT trips were eliminated completely. In addition, the 9-5/8-in casing string hard reaming was performed while incorporating a multistage differential valve (DV) and cemented in two stages. During the job execution, the reaming parameters are constantly monitored to not exceed casing strings limitations, especially the accumulated fatigue on the string as they are rotated. As a result, the troubles experienced in offset wells were successfully managed. Complexity in drilling wells is increasing. Therefore, introducing innovative solutions that enable reducing the number of extra trips, is essential to reducing NPT. The offset wells drilling troubles related to securing unstable formations were studies thoroughly. Level-I CwD technology was successfully utilized to eliminate those identified troubles without adding additional time-delaying trips. The unstable zones were secured in a record time compared to the offsets. The results were reaming the casing through extended open-hole sections until reaching the longest open-hole interval worldwide to be reamed with the 9-5/8-in casing allowing combining and isolating multiple trouble zones together.

The introduction of large size materials in the drilling mud circuit has become a common practice over the past few decades for the mitigation of Lost Circulation while drilling in permeable intervals. Solids with an average diameter larger than 100 pm are carried with the drilling mud and, when fractures occur, they deposit at the opening of the fractures, successfully blocking the discharge of fluid out of the wellbore. The effectiveness of such material has been observed, however, to decline over time as the drilling mud circulates through the mud pumps, the drill string, the bit nozzles, the wellbore annulus, and the mud recycling system. The decline over time in the effectiveness of Lost Circulation Materials (LCM) and Loss Prevention Materials (LPM) during drilling is widely linked to the degradation of the LCM/LPM components whose average size drops with circulation time. A large amount of literature in the petroleum industry is dedicated to the investigation of the issue and numerous experimental studies have attempted to quantify the LCM degradation by reproducing the root phenomena in laboratory. The concept of "shear degradation" has thus become a synonym for such studies and it is widely used for the selection of materials to be used in drilling operations. In the present paper, a harder look is taken on the very concept of "shear degradation" and on its effectiveness in capturing the progressive size reduction of LCM/LPM during circulation. Using dimensional analysis, the tendency of a material to degrade can be determined in advance, whereby the density of the particles and suspending fluid, the size of particles, and the fluid viscosity are examined as the governing parameters. Understanding the underlying physics enables the selection of a more shear-resistant engineered-particle drilling fluid, regardless of its application.

The development of a sour gas reservoir (7000 ppm H2S and 20–25% CO2) in the Kujung fractured-limestone formation in the Gundih Field, Java, Indonesia faced challenges related to drilling operations that are prone to kick - loss cycles. Well control incidents were experienced on previous wells drilled in the area and large amounts of cement and lost circulation materials were used to mitigate severe and total circulation losses, which consequently reduced the productivity of the wells. To further add to the complexity of the situation that the sour gas development project faced, the field's location is adjacent to a populated area, thereby increasing the requirement and need to prevent the release of sour gases during drilling operations. This condition ruled out the use of underbalanced drilling (UBD) to address circulation losses as bringing sour reservoir fluids to surface, even at a controlled condition, carried too much of a risk. In the process of finding a solution to these issues, the operator has identified that safety is the primary issue for the development of Gundih field, closely followed by the ability to drill these wells and maintaining reservoir performance. The solution developed involved the use of pressurized mud cap drilling (PMCD) techniques (along with a guaranteed and sufficient supply of sacrificial fluid, mostly water) and the installation of a downhole isolation valve (DIV), to isolate and prevent sour gas from the formation from reaching the surface, should severe losses and subsequent kicks be encountered. The PMCD+DIV system has allowed recent drilling operations to properly address the situation where severe, total and immediate circulation losses are encountered, thereby concurrently minimizing reservoir damage and the amount of sour reservoir fluid released at surface while penetrating deeper into the fracture limestone reservoir. In one instance, the DIV was able to keep sour reservoir fluids from reaching surface during PMCD operations, undergoing as much as 47 open/close cycles during drilling, tripping, fishing and well test operations, all of which were performed while experiencing total loss of circulation. The details of the PMCD+DIV system utilized will be presented in this paper, together with an assessment of how the system enhanced and improved the handling of health, safety and environment (HSE) issues during the drilling process, thereby assisting greatly in the accelerated development of the sour fractured-limestone gas reservoir in Gundih Field.

In Part 1, the Engineering Simulator for Drilling (ESD) is described, explaining the overall design, the engineering algorithms, the use of the interactive graphics, and the software and hardware used to create and operate any drilling system. Part 2 presents how the ESD is designed as a tool for the drilling person, giving the person the flexibility to use the ESD as a drilling time and cost analysis tool, or for well planning, or a full engineering simulator. A stand alone capability to use parts of the ESD for real time drilling analysis is also possible. An example of how a drilling person would use the ESD to build a drilling system is given. This includes logging onto the ESD, selecting the drilling location and geology, selecting the drilling rig, the initiation of the wellbore and the design of the mud system and the drill string. A description is given of how the user can operate the newly created drilling system, describing some of the options available to him. All Figures are actual photographs or plots of the various ESD graphic's pictures and menus.

В работе было расмотрено внедрение бурения водозаборных скважин большого диаметра, как способа радикального решения проблемы водоснабжения территории, где важной проблемой является необходимость в специальных бурильных колоннах, резко повышающих себестоимость работ. В данной работе предлагается технология, позволяющая обойтись обычными серийно выпускаемыми бурильными трубами, которая защищена патентом Республики Казахстан. Создана компьютерная модель и проведены исследования работы предлагаемой технологии в условиях Самского месторождения подземных вод. Исследованы и представлены зависимости выходных параметров (подача аэрированной смеси, ее плотность и скорость) от заданных условий – глубины бурения, глубины смесителя и скорости углубки. The paper considered the introduction of drilling large-diameter water wells as a way to radically solve the problem of water supply to the specified territory, where an important problem is the need for special drill strings that dramatically increase the cost of work. This paper proposes a technology that makes it possible to get by with conventional mass-produced drill pipes, which is protected by a patent of the Republic of Kazakhstan. A computer model has been created and studies of the operation of the proposed technology under the conditions of the Samskoye groundwater deposit have been carried out. The problem is solved by installing special devices in the drill string that allow aerating the liquid in it in parts, in order from top to bottom, which further complicates the design.

With the increasing intensity of oil and gas field exploration and development, oil and gas wells are also drilling into deeper and more complex formations. Conventional steel drilling tools can no longer meet the requirements of ultra-deep, high-temperature and high-pressure wells. The paper first analyzes the advantages of titanium alloy drill pipe based on basic performance of titanium alloy drill pipe. The experimental results show that the basic properties of titanium alloy drill pipes meet the operating standards of the petroleum industry. Then the buckling performance of titanium alloy drill pipe and steel drill pipe is compared, the calculation results show that the buckling performance of titanium alloy drill tools is slightly lower than that of steel drill tools. Secondly, the maximum allowable buildup rate of titanium alloy drill pipe and steel drill tool is studied. The research shows that under the same condition of the drill pipe outer diameter, titanium alloy drill pipe can be used for a smaller curvature radius and greater buildup rate. This advantage of titanium alloy drill pipe makes it more suitable for short radius and ultra-short radius wells. Finally, taking a shale gas horizontal well as an example, with the goal of reducing drill string friction and ensuring drill string stability, a comparative study on the application of titanium alloy drill pipe and steel drill pipe is carried out. The results show that titanium alloy drill pipe has a wider application in the field, and is suitable for operations under various complex working conditions.

Conventional drilling techniques used in harsh drilling environments are sometimes impractical or uneconomical. This was experienced while drilling through the reservoir section being investigated. This section is characterized by high pressure and formation fluids estimated to contain 18-20% of H2S and 4-6% of CO2. The presence of extensive karst/fractures along with severe circulation losses prevents successful drilling using the conventional circulation technique. For this scenario, the Pressurized Mud Cap Closed Hole Circulation Drilling (CHCD) technique was applied, and proved to be the most effective method to drill through the Lower Carboniferous Carbonate. In conventional drilling through such loss circulation zones, the typical method is to isolate the thief formation (LCM's pills, gunks and cement plugs) in order to maintain an overbalanced condition. These methods have their disadvantages: uncertain results, time and cost increase, damages on well productivity. Furthermore, it may be a long, ineffective process due to multiple leak-off zones or massively fractured zones. Where unsustainable losses occur and conventional circulation is no longer possible, the "CHCD" technique may be used to allow the continuation of drilling. This technique is not under balanced drilling. The annulus is closed and no returns are circulated to the surface. The CHCD is not a simple or an inexpensive system. It is used only when other systems for controlling losses have proven to be ineffective. Large quantities of water and mud are required as well as additional equipment and specialized personnel. An accurate evaluation of several factors has to be performed. Drilling hazard is the major issue as the primary barrier to well influx is jeopardised, but also rig time, material availability and consumption have to be considered. The aforementioned uncertainties can be addressed through risk evaluations by comparing two drilling scenarios of a typical development well where one uses CHCD technology and the other uses conventional drilling techniques. This paper will discuss the operational details of conducting CHCD as well as the risk management approach which involves the identification, evaluation and mapping of all risks involved in each scenario (qualitative risk assessment). A probabilistic model is therefore developed in order to combine all the risks identified and to address their consequences within operational time (quantitative assessment).

ARG-1 exploration sour and high CO2 gas well was drilled vertically in South Sumatra, Indonesia, with a total depth (TD) of around 5000 ft-MD. The operation has been facing many challenges in drilling and completion phase; one of them is the occurrence of massive fluid losses in fractured limestone formation. Pressurized mud cap drilling (PMCD) technique is the possible solution to complete this well without sacrifice drilling fluids in enormous volume and minimize non-productive time (NPT). PMCD is one of managed pressure drilling (MPD) techniques applied in situations when drilling without return to the surface and with a full annular fluid column which is maintained above the formation. The key of successful PMCD technique is the rotating circulating device (RCD) which is used to close the annulus. Furthermore, sacrificial fluid is injected through drill string and light annular fluid is pumped down from the annulus to maintain borehole fill and prevent annular gas migration. Limestone formation was drilled with 6 in slim hole which is a contingency plan. In addition, the premature set of 7 in casing was to cover the gas zone which is located above the limestone formation. Total loss circulation occurred when drilling through upper limestone formation. Conventional combat loss techniques i.e. spot loss circulation material, gunk plug, and cement plug were used to cure the loss but none of them give significant result. It took approximately 2 months for combat loss with such common technique. In consequence, PMCD technique was decided to apply in this situation and it only required 4 days to drill until TD and ready to run 4-1/2 in casing. By successfully utilizing the PMCD technique, the company was able drastically to reduce the NPT and reach the TD successfully. This paper presents a case study of the drilling operation in ARG-1 exploration well that had massive loss circulation while using common combat loss techniques were unable to reach TD. Furthermore, it explains how drilling in PMCD mode allowed operation in ARG-1 to reach the TD after total loss of circulation was experienced and how the completion assembly was run and cemented in PMCD mode.