Bottom Hole Assembly Research Articles

Three dimensional wellbore feature of air drilling hole and its influence on bit side force

In existing drill string mechanics analysis, smooth and regular wellbore is assumed and makes the calculated results sometimes differ greatly from the actual situation. In this study, based on measured data, the well characteristics of air drilling are shown from static and dynamic aspects, which proves the irrationality of this assumption. A six-arm calliper logging tool was applied to measure the wellbore data, and a cubic spline function was firstly adopted to reconstruct the wellbore. Then a 3D dynamic visualization description of the wellbore was realized based on the visualization toolkit. The results indicate that the 3D dynamic wellbore view can intuitively describe the characteristics of a high ovality and notable axial irregularity of the cross section of the wellbore drilled with BHA with an air hammer (AH-BHA), while the wellbore drilled with a pre-bent pendulum bottom hole assembly(PBP-BHA) exhibits low ovality and a smooth and regular shape along the axial direction. This can explain why it is difficult to run casing in a hole section drilled with AH-BHA. The FEM calculation example shows that the regularity of wellbore has a great influence on the bit side force. The BHA, which generates a bit side force that would reduce wellbore deviation in regular wellbore, may even produce a bit side force that increases wellbore inclination in severely irregular wellbore, and can be used to reveal the deviation mechanism in the air/gas drilling process. Importantly, this result indicates that the assumption of irregular wellbore should sometimes be taken seriously in drill string mechanical analysis.

Simulation Analysis of Combined Mechanics of the Thrust Rotary Guide Drill

The force and deformation analysis of the bottom hole assembly (BHA) is the foundation and essential component of good trajectory control technology. Still, the BHA structure has complexity (multiangle), making it challenging to analyze the force and deformation of the BHA accurately. In this paper, we consider the factors such as well drilling parameters (drill pressure), drill combination structure parameters (multivariable cross section, stabilizer, and flexible short section diameter and position, etc.), a mechanical analysis model of the push-the-bit rotary steering tool is established based on the infinitesimal method and continuous beam-column theory. Taking the push-the-bit rotary steerable drilling assembly as an example, the influence of force and deformation of the rotary guided drilling assembly, such as drill pressure, stabilizer, and flexible short section parameters, was analyzed. The research results of this paper can solve the mechanical modeling problem of the variable cross section in the bottom drill combination, can deal with the combination of infinite multiple stiffnesses according to the actual situation, bring the analysis results closer to the real problem, and provide theoretical support for the design optimization of the bottom drill combination. In addition, edge computing can provide sufficient computing power for the calculation of this paper to ensure operational efficiency. It can realize the online real-time transmission of mechanical analysis results through powerful calculation examples and effectively guide the field operation.

Study on the Main Controlling Factors and Formation Mechanism of Motion States of Bottom Hole Assembly in Slightly Deviated Wells

Abstract With the further development of deep oil and gas resources, the deep and ultra-deep wells are used widely, which make lateral vibration of bottom hole assembly (BHA) more violent. Lateral vibration greatly restricts the service efficiency and life of downhole devices. To study the main controlling factors and formation mechanism of lateral motion states in slightly deviated wells, the numerical simulation and indoor experiment were conducted. A drillstring dynamics model with three-dimensional beam elements was built, which combined the advantage of the finite element method and the beam-column theory. The simulation and experiment were carried out to analyze the motion states and motion laws under different drilling coefficients. Four kinds of conventional motion states were classified, and the physical characteristics, forming conditions, and identification methods were given. Four main controlling factors of motion states were summarized, and the formation mechanism was discussed through the principle of least energy consumption and least work consumption. The researches show that the numerical and experimental results are in good agreement. Meanwhile, well inclination, rotational speed, and friction coefficient have significant effects on motion states. The states contain forward whirl, random motion, and backward whirl in vertical wells, and circular arc swing in slightly deviated wells. Moreover, radial component of gravity promotes the formation of circular arc swing, centrifugal force promotes forward whirl before drillstring contacts wellbore and promotes backward whirl after that, tangential friction promotes backward whirl, and internal friction promotes forward whirl. Finally, the paper holds that BHA in vertical wells should operate in the motion state with least output power of the system and also operate in the motion state with least input power of external force during steady motion. The study can lay a theoretical foundation for predicting, identifying, and controlling motion states in drilling field to reduce vibration and improve drilling efficiency.

Seamless in seam – new geosteering technology delivered challenging coal seam gas project with success

A recent coal seam gas (CSG) appraisal project posed several challenges. The target reserve area had limited seismic data available and yet had complex structure with several faults of variable orientations and throws between 2 and 25 m. Dual-lateral extended-reach drilling (ERD) wells needed to be drilled in order to access this reserve, with a 1000 m in-seam section for each lateral planned to maximise production. Conventional technologies for CSG projects included motor bottom hole assembly with a boundary mapping tool for geosteering in the coal seams. However, for drilling ERD wells in this unknown area, these methods were insufficient to deliver success, due to the limited mapping capabilities and drilling efficiencies. Recently there has been significant development on the directional resistivity-based mapping tool, on both the measurements and processing. The operator adopted a new mapping-while-drilling technology which has the first-in-industry tool with axial, tilted and transverse antennas integrated in one module. This new technology can provide high-resolution multilayer mapping with doubled depth of investigation, even when drilling out of the coal seam. The results from utilising this new tool, together with a rotary steerable system for directional control, were very encouraging. The new multilayer mapping-while-drilling tool mapped both the top and base of the coal seam throughout horizontal sections in-seam. In addition, it detected the coal seams during landing and after fault-crossing from up to 4 m true vertical depth away, enabling the team to navigate through complex fault zones confidently, and to deliver the project with success.

Machine Learning Aids Early Detection of Stuck Pipe in Extended-Reach Wells

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 206516, “Stuck-Pipe Early Detection in Extended-Reach Wells Using Ensemble Method of Machine Learning,” by Rushad Ravilievich Rakhimov, SPE, Schlumberger, and Oleg Valerievich Zhdaneev, SPE, and Konstantin Nikolaevich Frolov, SPE, Ministry of Energy of the Russian Federation, et al. The paper has not been peer reviewed. The objective of this paper is to describe the experience of using a machine-learning model prepared by the ensemble method to prevent stuck-pipe events during construction of extended-reach wells. The tasks performed include collecting, analyzing, and cleaning historical data; selecting and preparing a machine-learning model; and testing it on real-time data by means of a desktop application. The idea is to display the solution at the rig floor, allowing the driller to take actions quickly for prevention of stuck-pipe events. Problem Analysis Packoff is the blockage of the annular space with drilled cuttings or parts of rocks fallen from wellbore walls. In a packoff situation, circulation is severely limited or impossible. With an inadequate response to packoff, fracturing of rocks below the bottomhole assembly (BHA) can occur, which leads to losses of drilling fluid and possible kick. In addition to time spent and technological risks, high expense is possible. In a worst-case scenario, the BHA can be left in hole and the bore must be redrilled, leading to a multimillion-dollar financial loss caused by nonproductive time. Packoff events fall mainly into two categories: - Caused by a cuttings bed that occurs when drilled cuttings are caught up while backreaming out of hole too promptly - Caused by wellbore collapse because of insufficient mud properties During the past 10 years, 28 wells have been drilled in the field of interest. Two hundred and twenty-seven incidents associated with stuck-pipe events have been registered. The light cases required an additional rereaming of the problematic interval, with a loss of time of up to 20 minutes. The most severe cases resulted in multimillion-dollar financial losses because of the BHA being lost in hole and the time spent on redrilling the wellbore. Classification of the incidents showed that 24 cases (11%) belong to the differential type of sticking, while 17 cases (8%) belong to the wellbore-geometry type and 186 cases (81%) to packoff events. The data collected at the field show that packoffs were encountered only during backreaming operations. Packoffs evolve rapidly. Thus, in most cases on the studied field, the time interval between trouble-free operation and sticking events is between 20 and 90 seconds (Fig. 1). Unlike physical modeling methods, machine-learning methods serve as a base for development of tools that work solely from historical data, allowing a more-precise simulation of real parameter behavior. Another advantage of machine-learning methods is the ability to select only the best historical cases for use. However, the use of historical data for prediction of downhole accidents in the well-construction process is not a novel approach. It has been used in the industry for more than 30 years. The complete paper includes an extensive discussion of examples in the literature.

Case Study: Space-Age Directional Drilling Improves Efficiency, Economics

Directional drilling has been used in oil and gas operations since the 1930s when onshore drillers employed the technology to reach offshore reservoirs. Over the years, technologies have been introduced to improve precision and control and at the same time have allowed multiple reservoirs to be produced through a single well, which reduces drilling costs and minimizes the environmental impact of the drilling process. In designing drilling plans, operators have considered economics when deciding whether to employ the traditional process of rotating the drillstring to control well trajectory or use more precise directional drilling techniques, but an either/or approach is not always the best one. The introduction of software that analyzes drilling conditions and determines the most appropriate drilling solution is changing the status quo, streamlining the drilling process and changing the playing field for drillers. The Evolution of Directional Drilling The widespread adoption of horizontal drilling from narrowly spaced slots on a centralized pad location has led to the introduction of complex wellbore geometry intended to maximize field development while minimizing geographical footprint. The growing need for precise execution of complicated well trajectories increased the demand for directional drilling expertise. Using a steerable bottomhole assembly (BHA) comprising a mud motor with a bent housing, an experienced directional driller can orient the bend of the motor in the direction prescribed on the well plan to steer the well on the intended trajectory in a process known as sliding. When the well trajectory is intended to remain relatively straight, the entire drillstring is rotated from surface in a process referred to as rotating. Experience and research have shown, however, that the well trajectory is rarely straight during periods of rotation due to rotational tendencies, a combination of systematic and random influences from BHA design, drilling parameters, and geological formation characteristics that can cause a significant divergence from plan. Rotational tendencies, along with designed well plan deviations, often require sliding to ensure the well follows the planned trajectory. All else being equal, it might seem that sliding should be applied across the board, but there are two reasons that sliding is not the default solution.

Methodology to Remediate and Evaluate Surface Flowline Capacity with Coiled Tubing Cleanouts

Summary Customers in Ecuador inject the byproduct formation water from production wells into injector wells. A limited injection rate bottlenecks production, which is economically undesirable. Two major contributors limit injection capacity: reservoir injectivity and flowline pressure losses. In the latter case, paraffins, asphaltenes, and scale, collectively referred to as “schmoo,” progressively build in the flowline and reduce the internal diameter (ID), limiting flow rate capacity. One cost-effective method to remediate flowlines with significant deposits is coiled tubing (CT) cleanouts. This unconventional method, which calls for optimized planning, execution, and performance evaluation, has been implemented in five flowlines. An economic analysis shows that remediating flowlines using CT cleanout yields significant savings as compared with replacement. After a candidate is identified, job planning takes into consideration flowline length and deviation (to identify maximum reach of CT), schmoo analysis (to design an optimal bottomhole assembly and fluid treatment), and execution logistics (to ensure a viable, reliable, and safe operation). After the cleanout, the flowline is put back into service, and the effectiveness of the treatment is estimated based on system flow rates and pressure losses. The equivalent ID for the flowlines was improved by more than 49% in each of the remediated flowlines, achieving an effectiveness of more than 89% of nominal ID and increasing flow rates without a detrimental effect on system pressure. The cleanouts reestablished nominal capacity in more than 50,000 ft of flowline that no longer needed replacement. Lessons learned include the ability to complete the cleanout with water alone. The chemical analysis in planning stages showed the absence of carbonates, which enabled a mechanical cleanout with a high-pressure nozzle. Nonetheless, a chemical treatment was designed as a contingency. Another learning was that though tubing force models helped predict the reach of the CT, other factors created limitations. For example, the weld bead on the flowline limited the reach of the CT and required reevaluating where to create cuts along the flowline. Finally, deploying the CT in a flowline required configuring the injector head horizontally, which required a customized base for safe rig-up and operation of the injector head and pressure-control equipment (PCE). CT successfully cleaned out five flowlines with IDs ranging from 6 to 8 in. and reestablished 89 to 98% of their nominal ID. As a result, the operator saved upward of USD 14 million in flowline replacement costs, increased asset usage, and decreased deferred injection. Historically, there is limited documented experience with flowline cleanouts using CT. The paper documents a repeatable methodology for candidate selection, planning, execution, and performance evaluation. It also provides basic building blocks to meet treatment design, rig-up, and execution requirements that are unique to this application.

Retracted: “A New Mathematical Model for Evaluating the Safe Margin of Deep-water Landing Operation”

Abstract For an accurate prediction of heave induced dynamic tensile load on landing strings and determining the safe margin of deepwater landing operation, a comprehensive mathematical model is proposed in this study. The novelty of this mathematical model lies in that it incorporates the effect of Bottom Hole Assembly (BHA) as well as Guide Base Plate (GBP) which were neglected by other researchers. The proposed mathematical model is solved with Galerkin’s method and verified by comparing the corresponding results calculated by the numerical method established in a previous research work. The results of this model are used to compare with those from existing models to emphasize the important role that BHA and GBP act on heave-induced dynamic response of the landing string assembly. Meanwhile, criterion for evaluating the safe margin of deepwater landing operation is presented. Sensitivity analysis is carried out to investigate the effect of GBP area and hydrodynamic damping coefficients. This study shows that the maximum allowable heave amplitude of drillship is relatively small if its heave frequency is in the vicinity of the resonant frequencies of landing string assembly’s longitudinal oscillation. By incorporating the effect of BHA, the resonant frequency and stress state of landing string assembly both have changed; while, the GBP only affects the stress state. Besides, the dynamic tensile load decreases with the increase of GBP area and hydrodynamic damping coefficients in near resonant conditions. This work provides a theoretical guidance to the design of deep-water landing string, which is essential for deep-water drilling operation.

Seismic Drill-Bit Tracking for Improved Well Positioning

Summary The lateral well position uncertainty of magnetic/gyro measurement-while-drilling (MWD) measurements can often exceed the requirements regarding anticollision, for optimal placement of infill wells between existing producers, or for hitting targets with limited geological extent. The positional uncertainty can be significantly reduced by implementing high-precision drill-bit localization using passive seismic data. Consequently, not only drilling risks can be reduced, but optimal reservoir drainage is ensured as well. By using passive seismic recordings from the seafloor, we can “listen” to the noise generated by the bottomhole assembly (BHA) while drilling. Despite various noise sources in the vicinity (e.g., vessels and rigs), advanced data processing and the combination of hundreds of seafloor receivers spread above the ongoing drilling enable us to detect the drilling signal and locate the drill bit. Whereas the magnetic and gyro MWD tools have errors that accumulate with measured depth (MD), each bit position derived from seismic (usually every 90 seconds) is completely independent. For horizontal sections, the error does not increase with MD and hence can provide improved lateral accuracy. No additional BHA tool is required, and the measurements are neither dependent on the magnetic nor gravitational field. Moreover, the passive seismic measurements can be used to obtain an improved lateral well position estimate. This is done by optimizing the azimuth information of the well trajectory in the minimum curvature method. A lateral uncertainty measure can be derived from the residuals between the passive measurements and the updated well path. Since 2018, we have used the continuous stream of passive data from permanent seafloor sensors at the Grane Field, with its reservoir depth of around 1800 m true vertical depth subsea (TVDSS) to follow all wells with this drill-bit tracking scheme. Lateral deviations from the official well path based on magnetic/gyro measurements are mostly within ±30 m. The lateral position uncertainty can be as low as a couple of meters under optimal conditions.

Investigation on axial-lateral-torsion nonlinear coupling vibration model and stick-slip characteristics of drilling string in ultra-HPHT curved wells

In view of the vibration failure of drilling string system in ultra-high temperature and high pressure (ultra-HPHT) curved wells, an axial-lateral-torsion coupling (ALTC) nonlinear vibration model of drilling string system was established using energy method and Hamiltonian principle, in which, the influence of wellbore trajectory change, wellbore constraint, interaction between bit and rock and ultra-HPHT of wellbore on elastic modulus and viscosity of drilling fluid were taken into account. The finite element method (FEM) is used to realize the numerical solution of the nonlinear vibration model. The correctness and validity of the ALTC nonlinear vibration model was verified by comparing the measured data of four ultra-HPHT wells with the theoretical calculation results of the proposed model.Based on this, according to the parameters of M directional well in Ledong ultra-HPHT block, South China Sea, the influences of ground rotation speed, drilling string length, weight on bit (WOB), torsional impact tools and drill collar length on stick slip vibration characteristics were investigated, and the method of increasing drilling speed in ultra-HPHT curved wells was put forward. The results obtained demonstrate that, firstly, when other requirements were met, the rotary speed should be increased as much as possible, which can effectively improve the drilling efficiency. Secondly, with the increase of drilling depth on-site, the drilling efficiency will be reduced, the whirl phenomenon of drill string system will be intensified, and the service life of bottom hole assembly (BHA) will be reduced. Thirdly, the optimized parameters of WOB and the torsional impact tool depended on the well structure, downhole tool size, etc. and can be determined using the proposed analysis method. The research results provide a theoretically sound guidance for designing and practically sound approach for effectively improving rate of penetration (ROP) and the service life of drilling string in ultra-HPHT curved wells.

Stick-slip vibration behaviors of BHA and its control method in highly-deviated wells

Stick-slip vibration is a common phenomenon met in oil gas drilling, especially in the complex trajectory wells such as highly-deviated wells, it will cause the earlier failure of BHA (bottom hole assembly) and lower drilling efficiency. In this present paper, a finite element model of highly-deviated well, which consists of a drill string system, a borehole, a PDC bit (Polycrystalline Diamond Compact bit) and a rock model, is carried out to investigate the stick–slip vibration behaviors of drill bit and BHA. Besides, the torsional impact drilling method is proposed in the context to control the stick–slip vibration of BHA. The research results show that, the phenomenon of stick–slip vibration of BHA gradually weaken and disappear with the distance from the drill bit increases, and the stick–slip vibration mainly occurs at the BHA which near drill bit. The high frequency torsional impact drilling method can reduce the resistance torque of the bit by 34.71%, and increase the drilling depth by about 58.28%. It can effectively improve the drilling efficiency of the bit, making the rotation of drill bit becomes relatively more stable, and reducing or even eliminating the stick–slip vibration. These results lead to an enhanced understanding of stick–slip vibration behaviors of drill bit and BHA in highly-deviated wells, and provide the basis for improving the drilling efficiency.

A study of the heave-induced surge and swap pressures when a drillstring is in the slips of a floating vessel

This study presents a theory describing surge and swab pressure when a drillstring is hanging in the slips of a heaving vessel. Downhole pressure measurement shows high pressure pulses in these instances, higher than can be explained with simple steady-state calculation. Several factors and parameters affect this pressure, such as annulus geometry, drillstring elasticity, wellbore friction, fluid compressibility, advanced fluid rheology, and fluid inertia. The advanced fluid rheology includes a flow-development phase and a simple fluid thixotropy model. The theoretical model is tested and compared with actual field data recorded at the surface and downhole, both pressure and string acceleration are measured. Key findings from this study are: (1) The annular flow is induced by the axial stick–slip motion of the bottomhole assembly; (2) The surge swab pressure consists of a pressure-loss term and an inertia term, where the latter is the dominating one in this case; (3) The short periods of the axial string motion call for a transient analysis to get an accurate estimate of the pressure amplitude. • Transient surge and swab model. • Stick slip induced pressure pulses. • Fast model for thixotropy and flow pattern development. • High resolution downhole measurements. Both string acceleration and downhole pressure.

Nonlinear dynamic characteristics of the drill-string for deep-water and ultra-deep water drilling

Riser will bend and deform in deep-water and ultra-deep water drilling, which may affect the dynamic characteristics of the drill-string. The analysis of drill-string dynamic characteristics is very difficult due to its super slenderness ratio. As the drill-string rotates in a curved narrow wellbore, the geometric nonlinearity and contact nonlinearity must be considered. In this study, a new method is proposed to analyze the drill-string dynamics considering the influence of riser deformation. The configuration of riser, based on different sea current velocities, is calculated to form a quasi-dynamic well trajectory combining with the fixed wellbore under mudline. In order to solve the dynamic problem of an extra-long drill-string model, the node iteration method is used to judge whether contact occurs at each node, and the Newmark method is used to calculate the spatial configuration of the drill-string at each time step. A program is successfully developed to analyze the dynamic characteristics of the drill-string in a deformed riser. The simulation results show that the deformation of the riser caused by ocean current has a great influence on the lateral vibration of the upper drill-string, and relatively little effect on the bottom-hole assembly. The contact and collision force near subsea wellhead is so large that may result in eccentric wear and leakage of the nearby riser.

Development of a supra-bit jet pump for opening a productive formation

The article proposes a jet pump for the bottom hole assembly. The developed supra-bit jet pump provides an additional circulation loop of the drilling fluid above the bottom of the well, which creates a local depression of the formation. In addition, the jet pump grinds the sludge injected from the annular space in the mixing chamber and feeds it to the bridging machine, which is included in the assembly, for temporary isolation of the productive formation. Isolation of the productive formation is necessary to prevent the flow of formation fluids into the wellbore when underbalanced. Grinding of the sludge in the jet pump is ensured by the cross flows of the working and injected liquid, which occur during the angular and eccentric displacement of the working nozzle of the jet pump relative to the mixing chamber. The angular and eccentric displacements of the working nozzle, the roughness of the flowing part of the mixing chamber and the diffuser, at which the pressure losses in the jet pump are insignificant, have been determined. Recommendations are proposed for increasing the efficiency of the jet pump in case of non-stationary operation at the bottom of the well, which occurs as a result of ground vibrations of a roller cone bit and uneven supply of working fluid by mud pumps.

When Slick Is Not Smooth: Bottomhole Assembly Selection and Its Impact on Wellbore Quality

Summary Appropriate selection of a bottomhole assembly (BHA) is critical to the success of a drilling operation. In US land drilling, these assemblies are often selected using local heuristics rather than rigorous analysis. These heuristics are frequently derived from the incentives of the directional contractor as opposed to incentives for the operator. Large motor bends enable more rotation through the curve and reduce the possibility of tripping for build rates. Unstabilized motors are believed to aid sliding and tool face control. Both of these practices lead to drilling a more tortuous wellbore and may cause problems later in the well’s life. This study quantifies the impact of these practices and proposes alternatives that can balance the needs of directional companies with the desire of operators for high-quality wellbores. More than 60 conventional motor assemblies used to drill curves in the Eagle Ford and Permian basins were analyzed for directional performance using commercial drillstring analysis software. The sliding and rotary tendencies were modeled through the curve across a range of potential drilling conditions. Expected build-rate models were validated by comparison to the maximum achieved doglegs in the directional surveys. When available, additional validation was performed using motor yields calculated from slide sheets. The validated models were compared to the dogleg severity (DLS) requirements for each assembly’s respective well plan. Comparisons of slide ratios and slide/rotate tendencies of the BHAs were used to estimate the impact on wellbore quality using the tortuosity metric proposed by Jamieson (2019). Typical well plans for both basins had curves of 10° per 100 ft with no well plan greater than 12° per 100 ft. Typical BHAs were capable of >15° per 100 ft under normal sliding conditions, with some assemblies capable of >20° per 100 ft of build. Predicted build rates were validated by slide sheets and observed DLSs. Common characteristics among assemblies with excess capacity were high-bend angles (≥2°) and minimal stabilization. These understabilized assemblies exhibited unstable rotary tendencies across a range of drilling parameters. The combination of high-build rates with rotary drop masks the true level of tortuosity in a wellbore, leading to an underestimation of unwanted curvature. A minority of the assemblies used a lower motor bend angle (<2°) combined with multiple stabilizers. These assemblies had a more consistent directional capability throughout the curve and exhibited stable behavior in rotation. The success of these assemblies confirms that there is potential for tailoring BHA designs to improve wellbore quality without compromising the technical objectives of the well. As increasing attention is afforded to the topic of wellbore quality, it is important to have methods available to technically achieve high-quality wellbores. In addition to the management of drilling practices, it is also important to have an appropriate BHA design that can enable those practices

Investigation of Mud Related Wellbore Problems in Drilling Well-A in the Niger Delta Region

Wellbore instabilities due to mud related issues during well construction in the wetland Niger Delta region were analyzed, reviewing well A as a case study. Time distribution plots and activity break down summary were evaluated for the candidate well. From the analyses, drill bit and bottom hole assembly balling, largely due to soft sticky and reactive gumbo shale with high swelling and dispersive tendencies in the mud system, severe down hole losses, hole pack off, pipe stuck potentials and kicks are some likely mud related challenges often encountered drilling in the Niger Delta region. Consequent upon which there would be reduced rate of penetration, tight spot, increased torque and drag, as seen in well-A. The drilling fluids play pivotal roles in oil extraction processes as their type; design and formulation determine the ultimate success of the entire drilling operation and overall production performance of the well. A poorly designed mud system may trigger wellbore instability that could lead to non-productive time, loss of drilling equipment, even loss of the entire well, kick and blowout scenarios due to loss of primary and secondary barriers. Formation damage may occur, which ultimately leads to reduction in permeability and poor well performance,

Lateral Vibration Simulation and Laboratory Experiment of Bottom Hole Assembly Based on Cosserat Theory

Lateral Vibration Simulation and Laboratory Experiment of Bottom Hole Assembly Based on Cosserat Theory

ШЛЯХИ ІНТЕНСИФІКАЦІЇ ВИБІЙНИХ ПОРОДОРУЙНІВНИХ ПРОЦЕСІВ ПРИ СПОРУДЖЕННІ СВЕРДЛОВИН

Purpose. Development of structural foundations for downhole devices (hydraulic hammers) to create dynamic loads on the drilling technological tool and study of the basic physical and chemical processes occurring in their hydraulic circuit and the bottomhole zone of the well. Methodology. The study of the patterns of constructive and technological interaction of the main parts and assemblies of the hydraulic percussion mechanism was carried out when testing its physical model included in the functional diagram of a special drilling stand equipped with appropriate power and hydraulic units, as well as a control and measuring unit. Studies of the physicochemical properties of flushing fluids and their influence on the course of rock mass destruction processes, intensified by the application of generated dynamic loads, were carried out using standardized devices for monitoring the parameters of special process fluids, as well as by bench destruction of experimental rock blocks with the appropriate complex technical measurements. Findings. A basic structural diagram of a hydraulic percussion device has been developed, with its physical embodiment, in which a significantly different execution and functioning of the interacting nodes creates the prerequisites for effective control of the machine in question. The presence of mutual consistency of the circulation processes implemented in the hydraulic hammer model allows its use in various modifications of the regime and technological support of progressive methods of wellbore formation. The proposed hydraulic hammer contains in its design a fairly large number of unified parts and is practically devoid of the presence of wear elements, which ensures its significant motor resource and high maintainability. Simultaneous combination of a hydraulic hammer with the use of activated flushing fluids in the technological scheme of bottomhole assemblies allows to obtain a significant increase in the mechanical fracture rate due to reduced surface tension and acceptable rheological characteristics of the dispersion medium for rock destruction. Originality. The use of alternately different pressure chambers in the design of the hydraulic hammer makes it possible to form a single closed circulation-technical system, with the possibility of effective regulation of its energy performance and operational transition between different drilling modes. Practical value. The proposed layout of the hydraulic percussion machine makes it possible to expand the areas of its possible application in the technical and technological schemes of downhole drilling tools, as well as the implementation of measures to eliminate downhole accidents and complications. Key words: well, hydraulic hammer, drilling, surfactant, rock destruction, flushing fluid, mechanical speed, bottom hole.

Analysis of the deep drilling technology in unstable formations at the Semyrenky gas condensate field

The paper presents a general overview of deep drilling in unstable formations at the Semyrenky gas condensate field of the Dnipro-Donetsk Trough, including well design, bottom hole assemblies (BHA), drilling conditions, and drilling muds. Problems encountered during drilling for production casing of Wells 72- and 75-Semyrenky using high-speed drilling methods are analyzed. The relationships between the rate of penetration and disturbed rock stability, volume excess and depth, as well as consistent empirical patterns in changes in mud properties and depth are established. With these technical and economic performance indicators for well drilling are given, elements of a borehole stability management strategy were defined, the principles of mud selection for drilling through problem zones are validated. The paper discusses the requirements to a mud hydraulics program to reduce the erosion of borehole walls, specific borehole preparation techniques, such as reaming and gauging, for drilling in problem zones, and alternative options to ensure borehole stability. Keywords: borehole stability; statistical models; hole gauging; hole geometry; drilling mud; BHA.

Analysis of the work of steps using the eccentricity limiter for drilling wells with a diameter of 393,7 mm

Based on the results of the analysis of theoretical and practical studies of drilling large diameter boreholes, a method is proposed for designing the bottom hole assembly with two rock cutting tools, taking into account geological and technical factors that influence the formation of the well trajectory. Prospects for controlling the direction of the wellbore are substantiated using the limiter of the eccentricity value. The calculation of double-hole assemblies of the bottom of the drill string with different diameters of eccentricity limiters, allowing to achieve eccentricities of 10 mm, 20 mm, 30 mm and 40 mm has been performed. The analysis of the operation of the mentioned bottom hole assemblies when drilling a well to a depth of 900 m is carried out. The analysis is carried out in the field of construction of deep boreholes of large diameter and the efficiency of drilling a pilot hole of a smaller diameter with simultaneous formation of the final diameter using a reamer is substantiated. A brief analysis of modern foreign and domestic studies and publications related to the expansion of the pilot wellbore is presented, as well as the influence of the expansion eccentricity on the elastic-deformation state of the BHA and, as a result, on the deviation of the well is considered. A conclusion is made about the possibility of using the phenomenon of eccentric expansion to control the trajectory of the wellbore. The graphical dependences of the change in the intensity of the borehole deviation during deepening using the eccentricity of the limiter for a specific BHA, including a bit with a diameter of 295.3 mm and a reamer with a size of 393.7 mm, are shown. It is shown that with this type of arrangement at different values ​​of eccentricities, it is possible to achieve the intensity of borehole curvature in the range from 0 deg/10 m to 0.44 deg/100 m, 0075, indicating a change in the direction and magnitude of eccentricity during drilling. The graphical dependences of the change in the zenith angle of the well when deepening it for the assembly of the bottom of the drill string with different diameters of the eccentricity limiter are given. The graphical dependencies indicate that when using stops of different sizes, which make it possible to control the eccentric displacement of the reamer at the final drilling depth of a section of 500 m, it is possible to reduce the increase in the zenith angle of the well from 17.5 degrees to 10 degrees. It is concluded that by using the limiters of the eccentric displacement of the expander relative to the pilot borehole, it is possible to control the deviation of the well during the construction of conditionally vertical and inclined sections.