Bottom Hole Assembly Research Articles

Study on factors affecting vertical drilling bottom hole assembly performance and a new bottom hole assembly design method considering formation uncertainties

Drilling a deep vertical well at a low cost is very important for accelerating the exploration and development of oil and gas resources. Vertical drilling BHA design is the key to drill a vertical well, however the BHA design is still an art not science in some formation. In this paper, a new mechanical model of bent-housing motor BHA is established, a build rate prediction method considering formation properties is presented and a BHA design method considering formation uncertainties is proposed. The evaluation results of vertical drilling BHA show that formation dip, formation anisotropy and hole diameter expansion are the main factors affecting pendulum BHA performance, and formation dip, formation anisotropy, hole diameter expansion and the distance from the upper stabilizer to the bit are the main factors affecting bent-housing motor BHA performance. The case study of the proposed BHA design method demonstrates that hole diameter expansion is very important for vertical drilling BHA performance, and should be taken in to account during the design process. The models and method proposed in this paper is helpful in maintaining verticality and reduce drilling cost.

Research on the dynamics of drillstring considering bit–rock nonlinear interaction

This study focuses on the nonlinear dynamic characteristics of the bottom hole assembly (BHA). One of the most important features of this work is that the nonlinear interaction model of polycrystalline diamond compact (PDC) bit and rock is proposed. The PDC bit dynamic characteristics are used as the boundary conditions of the drillstring dynamic model. To more realistically simulate the drillstring dynamics, the drillstring dynamic model is established with the beam finite element method and solved by the generalized-α method. The model is verified by the field data. The PDC bit dynamic characteristics are analyzed, and the effects of weight on bit, rotation speed and rock drillability on the drillstring dynamic behavior are discussed. We hope that our research will aid in the development of the drillstring dynamics in the future.

The ability of triangular prism drill collar BHA to prevent and correct deviation in drilling

A new bottom hole assembly (BHA) with a triangular prism drill collar and a flexible joint was developed to enhance the BHA’s ability of deviation prevention and correction in drilling. The deformation of the conventional BHA and the triangular prism drill collar BHA under working loads were simulated by finite element method. The result showed that the ability of the triangular prism drill collar BHA to prevent deviation in vertical well was superior to that of the conventional BHA and the triangular prism drill collar BHA had some certain ability to correct deviation in deviated well. The flexible joint length had an effect on the performance of the triangular prism drill collar BHA: when the length of the flexible joint was less than 6 m, the shorter the flexible joint length, the better the deviation prevention ability in vertical well, when the length of the flexible joint was within the range of 9–12 m, the longer the flexible joint length, the better the deviation correction ability in deviated well. Different kinds of BHAs were used in single well and adjacent well for field contrast test. The result showed that in anti-deflection fast drilling, the triangular prism drill collar BHA had excellent deviation prevention ability and it was helpful to get straight and smooth well track.

Ultradeep Resistivity Tool Maps Waterfloods Effectively

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 207385, “Ultradeep LWD Electromagnetic Directional Resistivity for Waterflood Mapping: A Game Changer,” by Parmanand Thakur, SPE, Maniesh Singh, SPE, and Saif Al Arfi, ADNOC, et al. The paper has not been peer reviewed. _ Abu Dhabi’s thick Lower Cretaceous carbonate reservoirs experience injection water overriding oil. The water is held above the oil by negative capillary pressure until a horizontal borehole placed at the reservoir base creates a small pressure drawdown. This causes the water above to slump unpredictably toward the horizontal producer, increasing water cut and eventually killing the well under natural lift after a moderate amount of oil production. Water slumping is difficult to forecast using the reservoir model. This paper showcases the successful deployment of an ultradeep electromagnetic (EM) directional resistivity instrument to map injection-water movement. Ultradeep Electromagnetic Technology Two of the most-significant drivers of the depth to which an EM field will penetrate the formation are the spacing between transmitter and receiver antennas and the transmission frequencies. These can be modified at the tool-design stage and with ultradeep EM tools by placing the transmitter and receiver antenna on different drill collars. Modifying the bottomhole assembly (BHA) allows the spacing between the antennas to be optimized for reservoirs of differing thickness (Fig. 1). Increasing the transmitter-receiver spacing, coupled with decreasing the transmission frequency, generates an EM field that penetrates further into the formation and allows a greater depth of investigation. The transmitter is placed closest to the bit, with two receivers placed farther back in the BHA. To map reservoir units close to the wellbore in greater detail, the first receiver can be connected directly to the transmitter. To increase depth of investigation in thicker reservoirs, the spacing can be increased. The farther the receivers are placed from the transmitter, the greater the depth of detection. Lower frequencies are used by these tools in the range of 2–64 kHz. In low- to mid-range resistivities, the lower frequencies provide a greater depth of investigation but with lower spatial resolution. At higher resistivities, greater depths of detection can be achieved with the higher-frequency options. In one field example, using the lowest frequencies and a transmitter-to-receiver spacing of 133 ft, it was possible to identify resistivity boundaries up to 225 ft away from the well. Measurements from ultradeep azimuthal EM tools are pulsed to the surface as components of the EM field from multiple spacings for multiple frequencies. Inversion algorithms are used to convert this to a model representing the subsurface, depicting resistivity boundaries. The position of these boundaries can be tracked many feet from the wellbore and used to place the well in the optimal position during drilling. This technology can be used to map units that the well may never penetrate, such as the water zone in this case, which was anticipated to be approximately 80 ft above the well.

Development of Monitoring and Forecasting Technology Energy Efficiency of Well Drilling Using Mechanical Specific Energy

This article is devoted to the development of technology for improving the efficiency of directional well drilling by predicting and adjusting the system of static and dynamic components of the actual weight on the bit, based on the real-time data interpretation from telemetry sensors of the bottom hole assembly (BHA). Studies of the petrophysical and geomechanical properties of rock samples were carried out. Based on fourth strength theory and the Palmgren–Miner fatigue stress theory, the mathematical model for prediction of effective distribution of mechanical specific energy, using machine learning methods while drilling, was developed. An algorithm was set for evaluation and estimation of effective destruction of rock by comparing petrophysical data in the well section and predicting the shock impulse of the bit. Based on the theory provided, it is assumed that the given shock impulse is an actual representation of an excessive energy, conveyed to BHA. This excessive energy was quantitively determined and expressed as an adjusting coefficient for optimal weight on bit. The developed mathematical and predictive model helps to identify the presence of ineffective rock destruction and adjust drilling regime accordingly. Several well drilling datasets from the North Sea were analyzed. The effectiveness of the developed mathematical model and algorithms was confirmed by testing well drilling data.

Fully Automated Directional Drilling Used on the Norwegian Continental Shelf

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 204016, “Fully Automated Directional Drilling Is Now a Reality: An Example From the Norwegian Continental Shelf,” by Jorge Heredia, SPE, Julien Marck, SPE, and Sara Heller, Halliburton, et al. The paper has not been peer reviewed. _ This paper presents an automated directional-drilling process executed on a commercial well in the Norwegian sector of the North Sea, where an intelligent rotary-steerable system (RSS) completed a well section in a single run with all drilling commands automatically computed, optimized, and downlinked by a drilling-automation platform. The section was complex, consisting of two intervals requiring steering in three dimensions separated by a tangent section. Directional-drilling engineers onshore supervised the operation remotely. No override was required, and the automated system was able to drill the entire section while sending steering decisions automatically. Advances in Drilling Automation Two primary automation controllers that were used in recent steering-automation successes on the Norwegian Continental Shelf are discussed in the complete paper. Recent advancements in RSS technologies use downhole sensors, high-speed processors, and survey packages to provide the backbone for an autonomous downhole navigation system. This type of development enables an automated closed-loop attitude-hold feature. Once configured, the only required downlinks correct trajectory, therefore reducing the total number of downlinks required to steer per section and creating a consistent wellbore quality between wells. This system was applied during the tangent portion of the well discussed in the complete paper. A second development is that of steering automation and advisory systems for deviated steering applications. These systems respond to real-time information from surface systems, including continuous inclination and azimuth measurements from downhole sensors and surface-drilling parameters. The real-time information then is fused with a physics-based digital twin model of the bottomhole assembly (BHA) to produce a calibrated steering model. Based on this hybrid model, the system combines control and optimization algorithms to reconstruct the borehole geometry between the last-available survey and the borehole depth and then provide recommendations for steering magnitudes and direction to meet drilling objectives while accounting for safety margins and drilling constraints. Benefits of the advisory system include reducing human error by removing unnecessary intervention, and automating calculations based off continuous real-time sensor information as opposed to the conventional method of requiring manual interpretation of data. The presented results illustrate the effect of these integrated systems on the improvement of borehole quality and placement and how the controller overcomes typical field situations successfully, such as challenging formations and wellbore conditions and changes in targets and steering objectives. The drilling-automation platform allows the directional-drilling operator to remain onshore in a remote drilling center as opposed to being on the offshore platform. Previous challenges and risks associated with holding operations remotely are being left behind as Internet bandwidth increases and no requirement exists to rely simply on phone and email correspondence; instead, onshore operators can view computers and cameras located at the rigsite in real time.

Non-smooth dynamics of Anti Stick–Slip Tool

This paper investigates non-smooth dynamics of an Anti Stick–Slip Tool (ASST) and its effects on a simulated downhole drilling. An ASST is a mechanical tool mounted on a Bottom Hole Assembly and designed to suppress stick–slip phenomena arising in drill-strings. In this paper the ASST is considered as a non-smooth dynamic system, where the presented modelling accounts for switching between Activated and Non-Activated states and proposes quantitative conditions for observing each state. In this tool, a helical spline couples axial and rotational movements acting together with an internal preloaded spring. The helical spline governs a relative motion of coupled parts and the preloaded spring determines a threshold value for activation of the ASST. The internal friction between coupled components contributes to conversion of excessive loads to a relative motion of two coupled parts. The proposed model describes the effect of internal friction forces on the operation of the tool whilst the tool is subject to nonlinear cutting forces from bit–rock interactions. Prescribed kinematics imposed on the tool allows to simplify the model of entire system and to provide an insight into the complex behaviour of the tool. Nonlinear responses of the developed model for a range of system parameters were numerically simulated to explore the dynamic behaviour of the ASST.

Overcoming Fundamental Restrictions: Novel Multistation Measurement While Drilling Survey Correction

Summary The traditional multistation analysis (MSA) method for drilling string magnetization compensation considers significantly limited information, only consisting of a single measurement while drilling (MWD) six-axis survey run. The limitations of this approach are an excessive scatter in the corrected azimuth values, poor accuracy in attitudes near the horizontal east/west directions, and low robustness of the algorithm, which make it nearly impossible to automate the survey processing. A novel MSA correction, involving further elaboration of the conventional MSA method, is proposed in this study. The proposed algorithm utilizes all available drilling information, including data from geomagnetic reference, error models, multiple six-axis runs, bottomhole assembly (BHA) designs, and slide sheets. This improvement moves the optimization task to find the survey correction vector from multiple independent spaces of total gravity field, total magnetic field, and dip angle (GBD) for each MWD run into a single GBD + north/east/vertical space of the entire well. Unlike the conventional MSA, which processes only a small portion of the available information, each MWD runs independently, the proposed algorithm finds the survey correction vector for all MWD runs simultaneously with additional constraints of trajectory steering and drillstring interference (DSI) modeling. Consequently, the proposed MSA method provides the best borehole positional accuracy for MWD surveys. Depending on the input conditions, the accuracy of the proposed MSA can be improved by an order of magnitude relative to the accuracy performance of the conventional MSA correction. In addition, this approach demonstrates better stability and robustness than the conventional MSA. The proposed method provides high startup performance, especially during the drilling of the tangent section. This is critically important for building automatic drilling systems and avoiding nonproductive time. Under normal conditions, the proposed MSA algorithm does not have a no-go zone and allows the correction of MWD surveys at the horizontal east/west tangent sections.

Stuck Pipe Detection in Geothermal Operation with Support Vector Machine

One of the biggest problems during drilling operation is a stuck pipe in which the drill string would stick or freeze in the well. This challenge leads to a significant amount of remedial costs and time. Many researchers have investigated different factors regarding the stuck pipe. These factors include poor hole cleaning, improper mud design, key seating, balling up of bit, accumulation of cutting and caving, poor bottom hole assembly configuration, differential pressure, etc. (Chamkalani, Pordel Shahri, and Poordad 2013). Since geothermal drilling targets lost circulation zones at reservoir depth, the chance of getting stuck pipe events becomes higher. Many publications reported that lost circulation events that lead to stuck pipe events have become the top non-productive time (NPT) contributor to costs in many geothermal drilling projects. The consequences of a stuck pipe are very costly, that include lost time when releasing the pipe, time and cost of fishing out the parted Bottom Hole Assembly (BHA), and efforts to abandon the tool(s) in the hole. Despite many observations that have been done to develop a system in avoiding stuck pipe incidents in oil and gas drilling operations using artificial intelligence (AI), few works have been developed for geothermal drilling operations. In this research, we propose a method to build an early warning system model for stuck pipe conditions based on a Support Vector Machine. Based on the experiment result Support Vector Machine Algorithm showed good performance with 89% accuracy and 81% recall for limited training dataset.

Case Study: Automated Stringer Detection Boosts Drilling Efficiency With Less Downtime

_ Horizontal drilling has evolved over decades to become a trusted well construction technique in mature oil-producing regions. However, many challenges remain in geologically complex drilling environments. One challenging drilling scenario arises when the drill bit encounters hard stringers interbedded within softer formations like sandstone. The sudden change in rock mechanics in moving from the formation to the stringer often results in deflection of the drill bit and a deviation in the well path known as a dogleg. The rapid directional changes caused by doglegs lower drilling efficiency by moving the drilling assembly off its planned path, and sometimes, out of the desired reservoir zone. The static loads generated in a dogleg can damage the bottomhole assembly (BHA) and lead to premature bit wear, shortened run life, higher maintenance costs, and more trips downhole. The curved path also increases the risk of stuck casing or completions strings, which can prevent the well from being completed to planned target depth (TD). An operator of a mature field in the North Sea faced such challenges while drilling multilateral wells through reservoir sections containing hard calcite stringers interspersed in sand formations with low unconfined compressive strength. The operator aimed to keep its lifting costs low by increasing the gross rate of penetration (ROP) through these sections. But the doglegs created at each stringer often required pulling back to perform a costly, time-consuming reaming operation to smooth out the well path and allow drilling to continue to TD. On average, the operator amassed 2.7 hours of invisible lost time (ILT) on reaming for every 3,300 ft (1000 m) drilled and achieved significantly lower gross ROP—both of which increased the operator’s per-well lifting costs above plan. Working with the operator, Baker Hughes developed an automated stringer detection service that would identify stringers earlier than previously possible to minimize local doglegs, reduce reaming time, and efficiently deliver wells to plan. Developing an Early-Warning Stringer Detection Service With operator input, the service provider developed an automated service that provided reliable, consistent, and early stringer detection to guide fast corrective action. The service includes an automated stringer-detection module embedded in an advanced measurement-while-drilling (MWD) sensor sub. The sub contains several dynamic sensors that collect a range of vibration and load measurements. The detection module uses a physics-based algorithm that combines two MWD measurements—tangential acceleration and dynamic torque at the bit—to calculate a value for high-frequency torsional oscillation (HFTO) in the BHA. HFTOs are torsional vibrations with frequencies between 50 Hz and 450 Hz that only occur during bit-rock interactions in hard formations. The distinct change in HFTO response during the transition from soft formations to hard formations makes it a leading indicator for detecting stringers in real time during drilling.

Tube-Based Adaptive Model Predictive Control for Deviation Correction in Vertical Drilling Process

The build-up rate of bottom hole assembly (BHA) fluctuates violently during deviation correction in vertical drilling process due to the mutation of stratum, low operation accuracy of BHA, etc. As a result, the uncertainty of the build-up rate of BHA has great influence on the performance of correction control and the quality of drilling trajectory. To deal with this control problem, a tube-based adaptive model predictive control (MPC) method is developed in this paper. By dividing the trajectory extension model into two lower-order models, the calculability of the disturbance invariant set of the tube-based MPC controller is ensured. Meanwhile, the bootstrap sampling method with a sliding window is used to estimate the range of the uncertainty online to reduce the conservativeness of the controller based on practical drilling data. Moreover, rules and a small interim deviation are introduced to adjust the parameters adaptively to decrease the curvature of the drilling trajectory and the calculation time. Simulations and hardware-in-the-loop experiment tests are carried out to illustrate the effectiveness of the control method. The results show that the proposed method completes the drilling task with higher quality of trajectory and needs less time for calculation.

Characteristic analysis and experimental study of rotary impact screw drilling tool

With the development of petroleum exploration and drilling, the current drilling tools are facing more difficulty situations, which lead to these problems such as low drilling speed, weak rock breaking ability or short service time. Based on this background, we propose a new drilling tool is proposed in this paper. By analyzing the force of the cam roller system, the dynamic differential equations of the horizontal drill string are established. The key parameters’ influences on the axial impact force of the new tool are studied first. Based on the new outputs, the vibration characteristics of drill string system are studied. For discovering the internal mechanism, the impact part dynamic analysis of this new tool is carried out, so as the contact force between roller and cam, the impact force between upper shaft body and pad. Furthermore, for verifying the rationality and accuracy of theoretical calculation, these parameters’ results are compared and analyzed under different drilling weights. Through laboratory and field tests, the impact frequency and impact force of this new drilling tool are analyzed, the effectiveness of theoretical models are also demonstrated. This research can provide an effective technical references to solve the current drilling difficulty in new situations. HIGHLIGHTS The rotary impact screw drilling tool has the function of impact while rotating, realizing the combination of shear and impact rock breaking, so as to improve the mechanical drilling speed. The impact load on the drill bit is produced by the combined action of hydraulic and mechanical forces. The impact force is generated in the form of mechanical structure movement, and it is a continuous and stable periodic impact force, which makes the bottomhole assembly produce benign vibration. Through experiments, the effectiveness of theoretical calculation and dynamic model is proved successfully, and the drilling tool can effectively improve the drilling rate.

Mechanical Modeling and Oblique Evaluation of a Full Rotation Steering Tool

Directional rotary steerable is one of the key components of modern intelligent drilling, and the analysis of force and deformation in bottom hole assembly is the key to control a well trajectory. Although the introduction of edge calculation will significantly improve the case requirements in engineering application, due to the complexity of directional rotary steerable BHA, such as variable stiffness and discontinuity, few theoretical mechanical models can simultaneously solve the above problems and obtain accurate solutions. In this paper, the inclination angle and diameter of borehole are considered comprehensively. From weight on bit in drilling parameters, assembly structure parameters of multiple variable cross section, discontinuity, stabilizer diameter and position of all sorts of influencing factors, such as the vertical and horizontal bending method combined with the finite element method, a point-type rotary steering BHA is established as a new type of mechanical model, with actual project as an example, through iteration, and the calculated results with the software of numerical verify the correctness of the model. Finally, the model is used to study the bit side force of discontinuous directional rotatory stepping-type BHA, and the effects of offset, weight on bit, and distance between two stabilizers on bit side force are analyzed. The research results provide support for structure optimization and BHA parameter evaluation of directional rotary steerable tools.

Solution and Analysis of Wellbore Temperature and Pressure Field Coupling Model under Lost Circulation.

The fluid in the annulus is in a variable mass flow state under the lost circulation condition, significantly affecting wellbore pressure distribution and the heat transfer efficiency between wellbore and formation. Therefore, based on the hydrodynamics and energy conservation law, a coupling model of transient wellbore temperature and pressure field under lost circulation conditions is established, which fully considers the casing program, bottom hole assembly, and heat source generated in drilling, as well as the influence of the temperature and pressure coupling in wellbore on the physical parameters of drilling fluid. The calculation results of the model in this paper are in good agreement with the field measured data and the previous research results, which verifies the rationality and accuracy of the model in this paper. The effects of the loss rate and the lost circulation zone location on the wellbore temperature and pressure distribution are analyzed, and the variation rule of the physical parameters of drilling fluid under the lost circulation condition is studied. The numerical simulation results show that the density and viscosity of drilling fluid in the annulus and bottom hole pressure increase with the increase in the circulation time; the annulus temperature decreases gradually with the increase in cycle time and tends to become stable after 8 h of the cycle. The annulus temperature and bottom hole pressure decrease with the increase in loss rate and closeness of the loss zone to the well bottom. When the loss zone is in the upper open-hole section, an inflection point consistent with the location of the loss zone appears on the annular temperature difference curve between the loss circulation and the nonloss circulation, and the position of the loss zone can be judged according to the inflection point.

Dynamics characteristics of axial–torsional–lateral drill string system under wellbore constraints

The combination of air and liquid drilling technologies is usually used for increasing rate of penetration (ROP) and protecting reservoir in drilling engineering. Meanwhile, dynamics characteristics of drill string system are closely relevant to drilling safety and well trajectory quality in the practical drilling engineering. Hence, in this paper, dynamics characteristics of axial–torsional–lateral coupled drill string system under wellbore constraints are emphatically concerned in the air and liquid drilling process. Firstly, a rotor dynamics model for revealing the dynamics characteristics of bottom hole assembly (BHA) with single stabilizer is established by the lumped parameter method. Moreover, two novel contact models for describing real-time interactions of BHA-sidewall and bit-formation are established through Hertzian contact theory and discontinuous support model, respectively. Then normal, stick–slip and bit-bounce modes of BHA are discussed on basis of coupling vibrations of drilling string in lateral, axial, torsional and whirling motion. Meanwhile, the dynamics responses of the BHA in the processes of air and liquid drilling are conducted by contrast analysis. Subsequently, dynamics behaviors of the BHA at different hardness formations are further revealed through numerical computations. The results indicate that the lateral, axial and torsional vibrations of BHA in the air drilling process are obviously stronger than the liquid drilling process in the same operation conditions. When drill bit suddenly encounters hard formation, especially in air drilling process, the dynamics characteristics of drill string system are easily disturbed, and the coexistence motion of stick–slip and bit-bounce is appeared in BHA, thereby leading to severe whirling and lateral impact of drilling string. Besides, when the BHA is out of contact with the sidewall, only the forward whirling of BHA is implemented; when the sidewall is frequently impacted by the BHA, forward and backward whirling of drilling string are easily happened; when the BHA is contact with the sidewall, the backward whirling of drilling string is easily appeared. Therefore, the proposed model in this paper may offer a comprehensive understanding for dynamics of BHA, and is expected to further develop dynamics studies of the BHA with double or multiple stabilizers.

Full waveform vibration and shock measurement tool for measurement-while-drilling

The bottom hole assembly during the drilling process is prone to fatigue and damage under the influence of alternating stress, particularly the drill bit and bottom part of the bottom hole assembly. The vibration and shock data are normally used to estimate the working status of the drill collars and for data post-processing of a particular logging method. The recent developments in drilling technology have increased investigations into continuous vibration and shock information measurement. However, existing tools store only the results of signal processing and cannot determine the raw full waveform; thus, they cannot be used to extract comprehensive information. Therefore, we proposed a novel tool for measurement-while-drilling, equipped with triaxial vibration and shock sensors. The tool can record the full waveform of six channels and use a large-capacity NAND flash to store the recorded raw full waveform. We performed laboratory and field tests to verify the stability and reliability of the tool at temperatures up to 150 °C to support operations in deep downhole environments. Furthermore, the tool can aid in effectively analyzing actual vibration and shock data to simulate a downhole test environment.

Concurrent 5. Presentation for: Seamless in seam – new geosteering technology delivered challenging coal seam gas project with success

Presented on Tuesday 17 May: Session 5 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. To access the presentation click the link on the right. To read the full paper click here

Analysis of Whirl Characteristics of Drill String Under Multidirectional Coupling Conditions

Summary The nonlinear contact between the bottomhole assembly (BHA) and the borehole can cause backward whirl. During an actual drilling process, the backward whirl will increase wear of the downhole drilling tool and lead to bending or even bulking failure. Therefore, analyzing the drillstring whirl characteristics considering multidirectional coupling effects, combined with field conditions, is a key issue and research hotspot. In this paper, considering the relationships between axial, torsional, and lateral vibrations of the drillstring system, the whirl model is established with finite element method. Research results indicate that with higher driving speed and larger friction coefficient between drillstring and borehole wall, the drillstring lateral vibration changes from forward to backward whirl. On the contrary, the increasing of drilling fluid density can effectively suppress the occurrence of backward whirl. As drilling fluid density increases, forward and backward whirl coexist, and only the forward whirl occurs at last. The research results can provide a basis for formulating whirl control strategy, and promoting the efficient and safe operations of drilling engineering.

Abrasive Jet Perforating Restores Productivity of an Inactive Oil Producer

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208988, “Novel Application of Abrasive Jet Perforating To Restore Productivity of a High-Potential Inactive Horizontal Oil Producer,” by Sadaf S. Chishti, SPE, Steven H. Craig, SPE, Baker Hughes, and Edward J. Wheatley, SPE, ADNOC, et al. The paper has not been peer reviewed. The complete paper illustrates a novel methodology that enabled the safe application of coiled tubing (CT) abrasive perforation to increase production in a sour horizontal extended-reach (ER) oil producer. The well was underperforming at 10% of the anticipated production rate because of a damaged lower completion. To avert a costly workover, abrasive perforation with CT was selected as a safe alternative to conventional explosives-based perforating conveyed on electric line. Introduction An offshore horizontal ER producer well was drilled with a total depth (TD) in excess of 24,000-ft measured depth (MD). During the completion phase, a 4.5-in. liner with 16 inflow control devices (ICDs) and eight swellable packers was run with the ICDs in the closed position. Swellable packers were placed after every two ICDs. To open these ICDs, an internal pressure of 2,500 psi was required, achieved by dropping a ball that would seat in the float collar. Multiple attempts were made to pressure up and open the ICDs without success. The decision was made to run the upper completion with a plan to activate the ICDs using rigless CT intervention. After a drift CT run, multiple attempts were made to run a through-tubing inflatable packer bottomhole assembly (BHA) on CT to isolate and pressure up the well. All attempts failed to reach target depth, with repeated holdup at approximately 20,273-ft MD. Production-logging passes performed in injection mode determined that the well interval between 20,262 and 20,300 ft was taking more than 80% of the injected fluid. In a subsequent CT logging run, a caliper log identified that the liner section in this interval was parted and identified an openhole section with washouts in excess of 7-in. inner diameter. The results from the log are shown in Fig. 1, with the enlarged section representing the parted liner/openhole interval. Because the ICDs remained closed along with a damaged liner section, the options of recovery leaned heavily toward a rig-based workover for sidetrack and recompletion. Considering time and cost constraints, studies commenced to identify an efficient alternative to establish flow contribution from the inactive compartments by adding perforations. CT was chosen as the conveyance method based on previous success in reaching TD, and three options were evaluated. Based on the lowest risk level and availability of resources, the safest and most-viable option was abrasive perforation with CT. This technique uses a sand jet perforator, a downhole tool that uses high-pressure abrasive-laden fluids to penetrate the casing, liner, and cement and extend a cavity into the reservoir.

Influence of shock-vibration loads of drilling equipment on the drilling indicators of oil and gas wells

When drilling oil and gas wells, downhole and drilling wellhead equipment is subject to the influence of significant vibration processes of different directions with different amplitude-frequency characteristics. The paper describes the main sources of vibration of drilling equipment, which have a downhole origin. In this paper an amplitude-frequency characteristic of oscillatory processes of a drill string and their influence on drilling performance are given. In addition to the sources of fluctuations of the bottomhole nature of origin, sources of the wellhead nature can also be distinguished. Thus drilling mud pump is a generator of pulsations and beats of the pressure of drilling fluid, which in turn leads to the increase in the dynamics of the drilling tool, the appearance of torsional vibrations of downhole motors and bits. We established the negative influence of vibrations of the bottomhole assembly and drilling mud on the stability of the operation of hydraulic downhole motors, penetration on the bit, durability of the elements of the string and energy indicators of drilling. The proposed device allows reducing the amplitude of pressure fluctuations of the drilling fluid and drilling tool.