Co-polymer Beads Reduce Friction In Horizontal Wells

Many problems in a drilling operation can be caused by excessive contact forces between the drill pipe and the casing or hole wall. The contact force pipe and the casing or hole wall. The contact force is mainly controlled by the hole curvature, drill pipe stiffness, and the axial load on the drill pipe. pipe stiffness, and the axial load on the drill pipe. This paper discusses the relationship between the magnitude of the contact forces and the above three variables, as well as several other less significant variables. Introduction The lateral force with which the drill string interacts with the casing or open hole wall should be of vital concern in a drilling operation. Large lateral forces can result in excessive casing wear, excessive drill pipe and tool joint wear, and key seats in the hole wall. An understanding of the factors that control the lateral contact forces may allow preventative action to be taken before a problem develops. The problem of excessive contact force between the drill pipe and the hole wall has been recognized for many years. It was addressed in 1960 by Lubinski, but it has only been during the last few years that detailed computer modeling of the problem has been feasible. This paper presents the results of a finite element computer study of the variables that affect the magnitude of the contact forces under a variety of conditions. The parameters were chosen to represent conditions that may occur in realistic drilling operations. Finite Element Model During 1975 a consulting firm was contracted and directed by Amoco to write a dynamic triaxial finite element computer program for the analysis of bottom hole assemblies. This program can be used to analyze any multi-component drill string in a wellbore. The drill string can be divided into a maximum of 51 elements of uniform cross sectional geometry and uniform material. An iterative process of solving for deflections and forces is then performed until the drill string deflections converge within the boundary conditions of the borehole. The required input data is a description of the drill string, wellbore diameter, wellbore survey, drilling fluid density, and axial load (weight on bit). The computed data includes the forces and deflections for each node point. Further discussion of the program is included in the appendix. Two drill pipe models were investigated before one was chosen for the study. The first model represented a joint of drill pipe with five equal length finite elements and the tool joint as a single element with its length equal to the tool joint length. This model was unstable under certain combinations of axial load and hole curvatures. The second model represented a joint of drill pipe with two finite elements and the tool joint as a zero length element. The zero length element resulted in a single point of contact with the hole wall rather than a point of contact on each end of a short element. Both models gave the same results for the cases in which the first model would converge, thus the second model was used for the study. Figure 1 shows a diagram of the drill pipe configuration that was used for decreasing curvature and Figure 2 shows the increasing curvature configuration. Table 1 gives the drill pipe and tool joint dimensions that were used in the study. Cases were run for 3-1/2", 4-1/2", 5", 5-1/2", and 6-5/8" drill pipe, with 20", 13-3/8", 9-5/8", and 7" casing sizes. pipe, with 20", 13-3/8", 9-5/8", and 7" casing sizes. The 13-3/8", 9-5/8", and 7" casing sizes will give approximately the same results as 12-1/4", 8-3/4", and 6-1/4" open hole sizes. The effects of hole size, drill pipe size, axial load, hole curvature, length and orientation of the curve, and hole inclination were investigated. Unless otherwise noted, the drill pipe was positioned in the hole so that a tool joint would be at the center of the hole curvature. All the results presented in this paper were generated from a static (non-rotating) model. The results accurately represent the forces which develop while going in or out of the hole with the drill pipe. pipe.

Study on modified maximum extension length prediction model for horizontal wells considering differential sticking

Horizontal drilling is one of development strategies to optimize the oil recovery, especially in a mature field. Horizontal well can reduce water and gas coning and prevent the pressure drop around the well bore, therefore the oil recovery can be increased. Radioactive source in Logging While Drilling (LWD) tools is used for X-42 horizontal drilling well but stuck problem that occurs during the drilling operation can be caused by differential sticking or failure hole cleaning. High angle inclination in horizontal well certainly increases the difficulty of retrieval job. As a company regulation, the radioactive source should be retrieved before continuing the efforts to free the drill string. The wireline has agreed to help the radioactive retrieval but this operation should be done in 81° of inclination. Then, it will need a thrusting force to facilitate the bottomward movement of the assembly. Two attempts of retrieval with wireline are made before they bring up the idea of using sucker rod as the replacement a wireline cable. This paper explains how the unconventional radioactive retrieval method with sucker rod as the alternative of wireline is more reliable to retrieve the radioactive fish especially in horizontal wellbore which technically has a very high inclination and 3D profile which the tool need a thrusting force to push the fishing tool assembly to the bottom.

Drill string torque and drag is one of the major limitations of horizontal wells. Torque and drag modeling is regarded as an invaluable process to assist in well planning and to predict and prevent drilling problems. Soft string model are widely used in the industry, which has good matching result with field data when bit off bottom, but has low matching accuracy in horizontal wells when bit on bottom. In horizontal section the string is in compression when drilling. The compression force is not always in the same direction with well bore axis. The compression force has a component perpendicular to well bore and this force should be considered when modeling the drilling torque in horizontal wells. Off bottom torque and on bottom torque should use different models as the string in horizontal section has different status. Horizontal section drill string is separately discussed in the paper. By study the off bottom torque, on bottom torque and bit torque, the WOB effect on torque was captured. String status when bit on bottom was analyzed. New model was presented considering the WOB affect along drill string for horizontal section of wells. Model validity was checked by field case at Changbei project.

Rigless radial drilling, or radial jet drilling involves drilling lateral holes from a vertical wellbore to enhance reservoir contact. Radial jet drilling system components (diverter, hose, and bit) are conveyed via coiled tubing. A high-pressure hose and jetting bit drill lateral holes. Without a drill string, axial force cannot transfer to the bit. As a result, the bit is hydraulically propelled. Radial jet drilling bits utilize back-jetting nozzles in addition to front-jetting nozzles. Maximizing penetration rate and hole length requires hydraulic optimization. Existing hydraulic models rely on field-measured parameters (discharge coefficient and flow rate ratio) that vary by bit design to predict propulsion force, bit hydraulic power, and maximum lateral hole length. This study aims to develop a generalized hydraulic model without requiring field-measured parameters for predictions. This model can optimize radial jet drilling by selecting suitable bit designs and lateral hole geometries. Based on fluid dynamics theory, the calculation model of circulation pressure loss in a horizontal well with a radial lateral is established; according to the on-site situations and characteristics of horizontal well with radial lateral, with the purpose of optimizing the maximum pressure drop of the drill bit, considering the constraint conditions such as breaking capability, rated pump pressure, strength of the equipment and rated pump power, the optimization model of hydraulic parameters of water jet radial horizontal drilling is built, which provides a new idea for the design of hydraulic parameters. The optimum displacement and maximum pressure drop of the drill bit increase with the increase of continuous tubing, diameter of high-pressure flexible hose and allowable value of maximum pump pressure, and decrease with the increase of drilling fluid viscosity. The technology of "high pump pressure and low displacement" is recommended in the operation of horizontal drilling with radial laterals. This paper discusses the deployment of the rigless radial drilling technology on two wells, one is in China, and the other is in Kuwait. Based on movement characteristics of the universal joint, its 3-dimension model and static simulation were respectively analyzed via CATIA Mechanical Design Model and ANSYS Software. The conventional diverter was compared with the novel one for CT radial drilling technologies, so that the effective curvature of the later was determined according to accurate calculation, mathematical modeling, and simulation experiment. BHA was optimized based on the circle equation, while the cutter's blade, material and PDM were all studied in accordance with mechanical theories. After many years of production, this technology has demonstrated its reliability and durability. Radial drilling processes have been optimized to maximize the value of radial drilling and mitigate any potential formation damage during lateral drilling. This has been confirmed by extensive testing, which has demonstrated and validated a significant improvement in well productivity and other ESP operating parameters. The results are encouraging and support technical decisions for production optimization leading to significant oil recovery for CNPC and Kuwait Oil Company in mature oil fields. Additional advancements are currently being considered to optimize and maximize the impact of this technology, including extending laterals beyond 300 ft in length, developing an advanced directional nozzle to target lateral holes in specific reservoir areas, and evaluating the use of larger nozzles to drill lateral holes.

Improvements in horizontal drilling technology made it possible to drill almost in all types and shapes of reservoirs. No change, however, was made in the design of drill pipes to overcome the high stresses especially for drill pipe rotating in medium or short radius horizontal wells. During drilling of some horizontal wells in the Middle East area, an abnormal amount of tubular failure was noticed in the drill string being used. This paper presents a field case study of drill string failure during drilling of medium radius horizontal wells. Investigations as well as a metallurgical evaluation were conducted in an attempt to establish the possible causes of the drill string failures. Other possible reasons for drill string failures and suggestions to minimize the bending stress of drill pipes are also discussed.

A study dealing with formation damage and damage control for horizontal wells drilled in the Shengli and Dagang (both in East China) sandstone formations is reported in this paper. The factors influencing the productivity of horizontal wells were quantitatively analyzed. The results show that formation damage is an important factor affecting productivity, compared with other factors, such as reservoir thickness, horizontal well length and anisotropy ratio of permeability, for the low permeable formations with permeabilities less than 80 md. It was also found that the effect of formation damage on production rate is constantly much higher for a horizontal well than that for a vertical well drilled in the same formation under the similar drilling conditions. To minimize the formation damage during horizontal drilling, three less-damaging drilling and completion fluids (a newly developed polymer mud, SN-1 oil emulsion mud and MMH mud) were used in these horizontal wells. The design criteria, formulation, properties and applications of these fluids were discussed. For each mud system CaCO3 was used as a bridging agent. The particle sizes of CaCO3 were selected based on the average pore sizes of the target formations. It was observed that the three mud system had provided excellent formation protection with much less skin factors and much larger percentages of regained permeability as compared with other commonly used drilling and completion fluids. The oil production rates of most horizontal wells are three to five times higher than that of their adjacent vertical wells, which is highly related to the effective prevention of formation damage. Introduction It is well known that the major purpose of horizontal well drilling is to increase the contact area with reservoir exposed in the well and thereby enhance well productivity. In recent years, the horizontal well technology has been developed quickly in China, and more than fifty horizontal wells with various radii, most of which were located in Shengli field, were drilled in the 90's. It should be noted that the difficulty and cost of drilling and producing increase with the augmentation of well productivity. One of the major concerns is that the drilling-induced formation damage may be more pronounced for a horizontal well than that for a vertical well in the same formation from the point of view of the production loss (i.e economic loss) although it is generally considered that the horizontal well will likely be more tolerant of formation damage than the vertical well since the horizontal completion interval length is much longer. Thus, in order to give a full play to the economic benefit of horizontal well technology, it is necessary to know the characters of damage accounted during horizontal drilling and to develop techniques to minimize the extent of damage caused by drilling muds. The formulations, performance and effectiveness of these drilling muds were discussed. All this work was in connection with the horizontal wells drilled in Shengli and Dagang low-permeable sandstone formations. The test procedures to evaluate drilling-induced damage are similar to those provided in Ref. 2. Both the values of skin factor and regained permeability are mainly used as the measures of damage in this work. Flow tests through field cores were conducted at ambient temperatures. All the core samples were taken from vertical wells in the same formation and saturated with synthetic formation brines. These tests involved comparing the final (regained) permeability, after treated with drilling fluids, to the initial undamaged permeability. P. 739

Kuwait has been drilling and producing from the deep, sour Jurassic reservoirs during the past 20 years. These vertical wells penetrate heavily fractured, highly pressured reservoirs and produce high quality light oil. There are an increasing number of wells in which depletion, low reservoir pressures and poor reservoir rock quality have meant that they can no longer flow at commercial rates. Horizontal well technology can provide a means to increase reservoir section length and intersect possible oil bearing fractures, thereby enhancing well productivity. This paper will discuss the challenges of designing and drilling the first deep, medium radius, high pressure well bore sidetrack, from an existing production well, into the Jurassic HPHT reservoirs. These challenges include the necessity to mill up the existing liner hanger and 80 ft. of casing to allow for any future re-completion, the restricted drill string size of 3 ½″ due to the well being completed with 7 5/8″ casing to surface, the directional target constraints, the hole cleaning difficulties due to the restricted pump rates, hard formations with low drilling rates, drill pipe buckling, the ability to slide in the lateral, and to drill the well without gains, losses or differential sticking. All these difficulties were tackled using optimized drill string designs, advanced milling and directional technologies including; medium radius build profile, lateral drilling with PDC/insert bits on motors equipped with ABI (at bit inclination) for enhanced steering capabilities and LWD tools. Using these technologies plus recommended practices developed by the operator and service companies enabled the establishment of record performances in Kuwait for this type of well. The results of the drilling will be presented along with conclusions drawn on the overall operation which will then provide the basis for future optimization in the design and drilling of these types of wells.

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.

A new water-soluble polyglycol/asphalt product (PGA) is described which provides the permeability plugging advantages of traditional deformable resins over a broader temperature range as well as the lubricity of refined petroleum oils and traditional lubricants without the agglomeration and environmental problems. Laboratory results presented include particle size distribution, lubricity, "Cloud Point", toxicity, permeability plugging and HPHT dynamic filtration. Case histories documenting the use of PGA offshore in the Gulf of Mexico are included.

Both Saudi Aramco and Total Indonesia found benefits in selecting 4 in. drill pipe with streamlined double shoulder connections for the drilling of wells, for which the 3 1/2 in. drill pipe was unsuitable. Although dealing with different environments and applications, these benefits can be summarized in "successfully drilling longer slim holes with a drill string having enhanced torsional, tensile and hydraulic characteristics at a lower overall cost". For the Saudi Aramco QTF field, Extended Reach Drilling (ERD) was required with the objective to deliver pay zones located at measured depths of 18,000 ft (for the 1,500 HP rigs) and 25,000 ft (for the 2,000 HP rigs). These depths correspond to step outs ranging from 13,000 ft to 20,000 ft respectively from the drill site. For its Kalimantan field, Total was in a need of higher torsional capacity and also an improvement of the hydraulic characteristics of the drill string. Selecting a larger size of pipe was the retained option against an upgrade of the rig pump installation. The casing and drilling program remained unchanged with the drilling of a 6 in. hole after setting the 7 in. casing, adding a constraint for fishability of the string. In both cases, fishability and torque objectives made the selection of the appropriate connection essential. The selected double shouldered connection maintained a tool joint outside diameter similar to standard 3 1/2 in. drill pipe tool joints, that maintains fishing ability of the 4 in. pipe, in casing and open hole, despite the pipe size increase. The streamline connection design provides 22,000 ft-lb working torque, an outside diameter of 4–7/8 in. and an oversized internal bore that promotes hydraulic efficiency. Other important improvements include considerable gain in pipe resistance under buckling loads, increased available pressure at the bit, better telemetry for the MWD and LWD tools and improved hole cleaning and rate of penetration. Introduction Drilling deeper, slim hole wells has revealed limitations of 3 1/2 in. drill pipe traditionally used to drill the 6 to 6–1/4 in. hole sections. The level of torque that API rotary shoulder, as well as first generation double shoulder connections, can deliver does not match the new requirements for these deeper drilling programs. This increase in drill string length also puts an additional constraint on hydraulic performance. This encouraged drilling engineers to re-evaluate the drill string design requirements and select a new configuration of pipe that would respond to these new requirements. This paper addresses these pipe and connection design considerations and provides two case histories showing the benefits that were realized from using this new drill pipe design configuration. Over 1,400,000 ft of this pipe has been built to date and is in service all over the world. It is also important to mention that this new drill pipe arrangement can also be used for drilling upper hole sections eliminating the need for a string 5 in. drill pipe in many applications. Streamlined Double Shoulder Connections for 4 in. Drill Pipe There has been increasing requirements for drill pipe with improved hydraulic performance and mechanical properties to replace 3–1/2 in. drill pipe traditionally used in slim-hole drilling.

Bit feed principles and operations of slide drilling

Canada has played a prominent role in the development of horizontal drilling technology. To date, over 1,400 "grassroots" and "re-entry" wells have been drilled. Although other countries have experienced greater numbers of wells, the number of different types, varieties, and formations tested with this technology in Canada is unparalleled. Due in part to the exponential growth of horizontal well applications since the mid-1980's, coiled tubing CCT) technology in Canada has been adapted and evolved for more traditional uses such as horizontal well stimulation, evaluation, workovers, and clean-outs. The principal nontraditional aspect of CT is its use in drilling operations. This paper will deal with the current state and recent advances in CT horizontal drilling in Canada, A brief historical perspective will be presented that highlights Canada's presence as a pioneer in CT drilling and documents its evolution from vertical re-entries dating back to 1974, grassroots vertical wells in 1976, to the industry's current efforts at vertical and horizontal CTD. The principal Canadian service companies are reviewed in terms of present capabilities in CTO applications and the perceived driving forces that are stimulating the development of this emerging technology. The key factors such as diameter and fatigue life of the coil, length limitations, bottom hole assemblies, surveying methods and the economic and market factors affecting CTO relative to more conventional drilling techniques are reviewed. Finally, the future technological, market and economic developments necessary for the successful implementation of CTO for grassroots vertical and horizontal well re-entry projects are suggested. Introduction The exponential growth in the number of horizontal well applications in Canada and internationally over the past eight years has led to a relatively rapid development of both personnel and equipment to enhance the horizontal drilling method of exploiting existing oil and gas pools. In Canada, there are an estimated 70,000 producing wells: 40,000 gas wells and 30,000 oil wells. Recently, the National Energy Board (NEB) presented a study on horizontal oil wells and their impact on future crude oil supply in Canada. They estimated that there is a potential market of over 12,000 horizontal wells that can be economically drilled within 1,800 oil pools at a market price of $20 US/Bbl. Of these 12,000 wells, 5,000 were believed to be grassroots in nature (1 I 100 have been drilled to date) while 7,000 were horizontal re-entries through existing cased wells (300 have been drilled to date). Of the 6,700 remaining re-entries, the competition for services will be between slim hole (less than or equal to 6–1/4 in. hole size) conventional drilling systems using drilling rigs or modified service rigs and coiled tubing drilling (CTD) technology. Add to this potential market vertical deepenings, horizontal lengthenings and grassroots wells coupled with increasing interest in horizontal exploitation of gas pools, and the development of CTD appears to be poised for exponential growth in Canada over the next five years. Some of the questions that will be addressed during the course of this paper are:

With the unconventional energy sector (e.g., shale gas) increasingly focused on precision drilling and cost-effective extraction, slim-hole horizontal well technology is gaining prominence. However, drill string dynamics in narrow, complex fluid environments are not fully understood. This study presents a novel bidirectional fluid–structure interaction (FSI) model, uniquely integrating recursive algorithms with the Moving Particle Semi-implicit (MPS) method to couple drill string–wellbore contact with drilling fluid interactions. Key findings show that drilling fluid significantly impacts drill string behavior; for instance, it can reduce natural frequencies by 20–25%, while stiff formations amplify lateral resonance risks. Optimizing fluid properties can substantially cut energy losses, though TREE is marginally elevated when viscosity exceeds the threshold (2.5 × 10−5 m2/s). The drill string typically displaces rightward, but higher viscosity can shift it left; a moderate friction coefficient aids centering. Excessive lateral displacement impairs cuttings removal, affecting fracturing. These insights enable actionable strategies: adjusting fluid viscosity and drag reducers can optimize drill string position and enhance cleaning. This research provides a framework for energy-efficient drilling in complex reservoirs, balancing efficiency with wellbore integrity and improving outcomes in the unconventional energy sector.

A laboratory and field study directed at improved well performance of horizontal wells is discussed. During the study, several wells were matrix acidized using bullhead and coiled tubing placement techniques. The study performed in carbonate reservoirs indicates acid placed with coiled tubing diverted with foam provides excellent zone coverage and damage removal. Conventional bullhead techniques do not result in effective damage removal. The study emphasizes the evaluation of the treatment results and the development of improved acidizing techniques. Laboratory simulations of matrix acidizing indicate proper placement techniques are essential. This observation is supported by field data in oil wells completed in carbonate reservoirs. The key to successful damage removal is 1) the placement of acid via coiled tubing and 2) proper diversion. Production logging and well performance data support this claim. The proposed treatment is applicable in both horizontal and vertical wells completed in carbonate reservoirs.