Hole Assembly Research Articles

Uncertainty analysis method for the output force vector control on the rib of the orienter in coiled tubing drilling

This work addresses the uncertainty associated with downhole parameters in coiled tubing drilling and proposes a new method for controlling the output force vector on the ribs of the orienter, enabling more precise control of the actual wellbore trajectory. Based on the principles of longitudinal and transverse bending beams, we construct a 3D mechanical model of the Bottom Hole Assembly (BHA) used in coiled tubing drilling. We then analyze the spatial geometry relating the force direction on the orienter's rib and the tool face angle, establishing a comprehensive steering resultant force vector model. Applying the principle of minimum energy, we explore traditional control schemes for the output force on each rib and reveal its intricate variation patterns. We conduct a statistical analysis to investigate the randomness distribution state and sensitivity of the experimental parameters, allowing us to derive the probability density and cumulative probability functions for the two-dimensional random variables linked to the output force on the ribs. Confidence interval models are constructed to predict the output forces with a predetermined level of certainty. Finally, we experimentally verify the proposed uncertainty control method in real-world coiled tubing drilling. Our results show that the randomness of weight on bit (WOB) and the tool face angle of rib 1# are the main factors influencing the uncertainty of the output force control. When the output forces vector on the ribs exceeds the uncertainty confidence interval, the actual wellbore trajectory significantly deviates from the designed one. Conversely, when the output forces vector falls within the confidence interval, the error between the actual and designed wellbore trajectories is significantly smaller. This validates the rationality and effectiveness of the proposed uncertainty analysis method, providing valuable guidance for implementing wellbore trajectory control in coiled tubing drilling.

Best Practices to Achieve Optimal Geothermal Drilling Performance in A Cost-Effective Manner: Case Study of the Fastest Geothermal Well Drilling in Java and Sumatra

Indonesia, recognized for possessing substantial geothermal energy potential, is working towards harnessing the resource to achieve numerous objectives. Among the primary challenges encountered is the considerable expense of geothermal drilling. One of the most significant obstacles to achieving this objective is the high drilling cost, which constitutes 35-40% of the total cost of geothermal energy development. The drilling cost is mainly affected by the time needed to drill one well because the faster the time, the lower the cost. Therefore, this research analyzed drilling activities, identified the fastest and most effective methods for optimal geothermal drilling performance, and reduced costs. The research also determined the factors that contributed to the sustained status of Well X as the fastest well drilled in the past decade. The methodology comprised literature review, data collection through adequate background on well and geothermal field, and data analysis. The result showed that the fastest drilling operation of a geothermal well in Indonesia in 2012 occured in West Java (Well X) for only 9.9 days with 1736.5 meters (mMD). Meanwhile, in 2021, Well Y in Sumatra spent 21.74 days to reach a depth of 2200 mMD. The use of a single-run and clean-out Bottom Hole Assembly (BHA) throughout the entire section affected the drilling duration and significantly reduced the inner side cleaning time, respectively. The cost of Well Y drilling, achieved using the best performance of two wells, reduced drilling costs by 19.2%.

Coupled drillstring dynamics modeling using 3D field-consistent corotational beam elements

Drilling is essential to extract subsurface hydrocarbons and geothermal energy, or store waste fluids/gases underground. Drilling efficiency directly affects the economics of well construction, and is to a large extent determined by the non-productive time (NPT) associated with downhole tool failure, bit wear/damage, unexpected drillstring vibrations, and insufficient surface-to-bottom energy transfer. Various models have been developed since the 1960s to understand and mitigate undesired drilling system oscillations to ensure efficient drilling operations and help optimize the well design. Significant recent advancements in drilling engineering technology, sensor development, and data science make it possible to develop and apply a faster and more comprehensive drilling system dynamic model that can be used for real-time drilling optimization and automation.In this study, a novel control-oriented physic-based drillstring dynamic modeling framework is developed using 3D field-consistent corotational beam elements with an updated Lagrangian formulation. The structure and element kinematics are firstly derived in global and local coordinate systems respectively, based on which the system dynamics are formulated by integrating the element stiffness, damping, and mass matrices. Different drilling boundary conditions and forms of external loads, including bit-rock interaction, wellbore-drillstring contact, stabilizers, bottom hole assembly (BHA) eccentricities, and gravity/buoyancy are defined within the modeling framework. The numerical accuracy of the model with linear/quintic beam elements is discussed and verified in four different static/dynamic loading cases, which are typically used for beam analysis. Simulations of different drilling scenarios, including dynamics during the pipe connection process, bit on/off bottom process, and pipe rocking during slide drilling, are conducted for an actual L-shape well configuration with comparison to field data. The simulated drillstring tri-axial vibrations exhibit diverse characteristics and patterns in terms of oscillation amplitudes, frequencies, and modes at varying depths, generating valuable understanding of potential drilling dysfunctions and insights for real-time drilling optimization and automation.

Distributed model for the drill-string system with multiple regenerative effects in the bit-rock interaction

In this paper, an integrated model is presented to study the axial–torsional dynamics of a distributed drill string. The coupled axial and torsional drill string dynamics typically lead to severe phenomena such as bit-bounce and stick–slip, which are the main causes of failure and efficiency reduction. The top-drive dynamics and the Bottom Hole Assembly (BHA) dynamics are interconnected through the drill pipes. In order to preserve the infinite-dimensional feature of the drill pipes in the mathematical modeling, a distributed model in terms of Delay Differential Algebraic Equations (DDAE) is proposed to represent the dynamics of the drill string. The bit-rock interaction, which consists of the cutting and the frictional components, is responsible for the coupling between the axial and torsional dynamics. A rate-independent bit-rock interaction law is employed for both cutting and frictional components. In order to capture the global bit motion, including multiple regenerative effects, the well-bottom depth function is used to determine the depth of cut. The well-bottom pattern evolution is formulated through algebraic equations rather than Partial Differential Equations (PDEs). A new formulation for the linearized drill string system in terms of Neutral-type Delay Differential Integral Equations (NDDIEs) is proposed to investigate the initiation of the oscillations around the nominal operation. By this formulation, the local stability of the distributed system is studied by determining the right-most eigenvalue of the linearized dynamics. A simulation-based case study reflecting real-life scenarios is presented to investigate the dynamical behavior of the system under different operating conditions.

An approach for optimization of controllable drilling parameters for motorized bottom hole assembly in a specific formation

This study focuses on optimizing drilling parameters when using Positive Displacement Motors (PDMs). In drilling operations involving mud motors, weight-on-bit (WOB) alterations lead to variations in the system's parasitic pressure drop. Consequently, this affects the optimum flow rate and the hydraulic power of the bit. Also, if the flow rate changes, the bit's rotations per minute (RPM) also change. In other words, using PDMs creates a link between the hydraulic system and the drilling speed, such that changing drilling parameters such as the WOB causes changes in the hydraulic system's performance. Therefore, one possible way to optimize the drilling parameters is to consider the drilling rate and hydraulic system simultaneously using a multi-objective approach. This study used an integrated approach encompassing data mining and mathematical modeling, employing a multi-objective framework to identify optimal parameters. The approach was applied to Dariyan Formation drilling data. The data mining approach revealed a well-distributed data set covering optimal and suboptimal zones suitable for optimization. In data mining, the identification of optimal conditions included a WOB of 11500 lb, a rotation speed of 105.8 rev/min, and a flow rate of 843 gpm, leading to an ROP of 44.23 ft/h. In multi-objective optimization, the optimal parameters consisted of a WOB of 14480 lb, a rotation speed of 115 rev/min, and a flow rate of 920.8 gpm, resulting in an ROP of 40.49 ft/h. Comparing optimal results with the drilling data shows a substantial MSE reduction of over 35 %. The results show the good performance of this approach in detecting the optimal and non-optimal drilling variables.

Massive black hole assembly in nuclear star clusters

Massive black hole assembly in nuclear star clusters

Using Analytical and Artificial Intelligence Models to Estimate Drilling Rate of Penetration (ROP)

Drilling a new oil or gas well to reach at reservoir involves a set of processes. Optimized drilling plan is critical to reach the target in the shortest possible time and at the lowest possible cost .Drilling plan and efficiently drilling a new well requires analysis of well data to properly determine bottom hole assembly, drilling bit, drilling fluids, and operational parameters such as weight on bit (WOB) and drill-string rotary speed. The purpose of drilling planning is to optimize the Rate of Penetration (ROP) by reducing non-productive time (NPT). In this article two different estimating drilling rate of penetration (ROP), analytical model and artificial intelligence model were described.

Real-time rate of penetration prediction for motorized bottom hole assembly using machine learning methods

Drilling rate of penetration (ROP) is one of the most important factors that have their significant effect on the drilling operation economically and efficiently. Motorized bottom hole assembly (BHA) has different applications that are not limited to achieve the required directional work but also it could be used for drilling optimization to enhance the ROP and mitigate the downhole vibration. Previous work has been done to predict ROP for rotary BHA and for rotary steerable system BHA; however, limited studies considered to predict the ROP for motorized BHA. In the present study, two artificial intelligence techniques were applied including artificial neural network and adaptive neurofuzzy inference system for ROP prediction for motorized assembly in the rotary mode based on surface drilling parameters, motor downhole output parameters besides mud parameters. This new robust model was trained and tested to accurately predict the ROP with more than 5800 data set with a 70/30 data ratio for training and testing respectively. The accuracy of developed models was evaluated in terms of average absolute percentage error, root mean square error, and correlation coefficient (R). The obtained results confirmed that both models were capable of predicting the motorized BHA ROP on Real-time. Based on the proposed model, the drilling parameters could be optimized to achieve maximum motorized BHA ROP. Achieving maximum ROP will help to reduce the overall drilling cost and as well minimize the open hole exposure time. The proposed model could be considered as a robust tool for evaluating the motorized BHA performance against the different BHA driving mechanisms which have their well-established models.

Chaotic Effect-Based Array Duffing Systems with Improved Nonlinear Restoring Force for Weak Signal Detection in Dynamic MWD.

In the process of dynamic Measurement While Drilling (MWD), the strong vibration and rapid rotation of the Bottom Hole Assembly (BHA) lead to multi-frequency and high-amplitude noise interference in the attitude measurement signal. The weak original signal and extremely low signal-to-noise ratio (SNR) are always the technical difficulties of dynamic MWD. To solve this problem, this paper uses the chaotic effect of the Duffing system, which takes the expression (-x3 + x5) as a nonlinear restoring force to detect the weak characteristic signal of downhole dynamic MWD. First of all, in order to meet the limit condition of the chaotic phase transition of the system output, the frequency value of the characteristic signal is reconstructed and transformed based on the variable scale theory. Then, in order to solve the influence of the initial phase of the characteristic signal on the detection accuracy, a detection model based on the array Duffing system is presented, and a frequency-detection scheme with all-phase coverage is given. Finally, another array Duffing system is designed for the parameter estimation of the characteristic signal. The critical value of chaotic phase transition is determined by adjusting the amplitude of the driving signal of the array Duffing system, and then the amplitude and phase parameters of the characteristic signal are synchronously estimated. The experimental results show that the proposed method can effectively extract the weak characteristic signal within the strong noise, and the SNR of the characteristic signal can be as low as -21 dB. Through the attitude calculation for the extracted characteristic signal, it can be seen that the proposed method can improve the accuracy of the inclination of the drilling tool significantly, which proves the feasibility and effectiveness of the method proposed in this paper.

Evaluation of distributed damping subs with active control for stick–slip reduction in drilling

Drill string vibrations can cause damage to the equipment and reduce drilling performance. There are two primary methods to address this issue: top drive control or the use of specialized tools near the bottom hole assembly (BHA). Another previously published idea is to have several torsional damping sleeves along the drill string, adding viscous damping to the system. The sleeves are designed to be non-rotating, held in place by static friction, but if the combination of braking coefficient and relative pipe velocity gets too high, the sleeve will slip. This paper examines the effectiveness of active control of the braking coefficient, using an On–Off-based control scheme with proportional control. Stability maps are employed to assess the effects of this control scheme on the system for various combinations of top drive feed rates and revolutions per minute (RPM) set points. Such maps allow for a performance comparison of passive sleeves and active sleeves. The results show that active control can improve the drill string behavior both when drilling and when rotating off-bottom, by reducing the slippage of the sleeves. The settling time is reduced to up to a third of the settling time of the passive sleeves.

Development of a vision-based automated hole assembly system with quality inspection

This study proposes a novel mechatronics system capable of automating a peg-in-hole assembly process and inspecting the quality of the assembly with vision. The proposed mechatronics system integrates a customized peg insertion tool, a new assembly mechanism, and a control algorithm to efficiently insert pegs into holes with a tolerance of 200 µm. The system improves assembly performance by utilizing dual cameras and several computer vision techniques, including Contrasted Limited Adaptive Histogram Equalization, Canny Edge Detector, Hough Circle Transform, and YOLOv5. In addition, a real-time statistical quality inspection method is proposed and compared with machine learning-based inspection approaches. Various surface textures and materials of the cylindrical workpiece are used to assess the robustness of the proposed inspection methods. Experimental results demonstrate that the proposed system and quality inspection methods exhibit high performance and adaptability.

Motion Simulation Analysis and Experimental Verification of Drill String Rotation Controller

Abstract Conventional directional drilling mainly relies on the sliding of screw motor and drill string to realize the change of wellbore trajectory, so the friction force is large. The use of friction reduction tools that generate axial force to change the friction state can only achieve partial friction reduction, and drill string is still in a sliding state during directional drilling. These problems are solved by using rotary steerable drilling system, which can achieve directional drilling when drill string rotates. But its use cost is high. Considering the principle of high efficiency and economy, a new friction reduction tool called drill string rotation controller is proposed, which is also used to reduce friction during directional drilling through drill string rotation. By adjusting the pump pressure, the meshing state of spline module of drill string rotation controller is changed to realize the conversion of drilling mode. In rotary drilling mode, upper drill string, drill string rotation controller, and bottom hole assembly rotate together. In directional drilling mode, upper drill string rotates and drill string rotation controller slides with bottom hole assembly. The function of the tool is verified by field experiment, and motion simulation of the tool is carried out. The results show that when the driving torque is set to 25,000 N · m, more reverse torque can be overcome in the directional drilling mode, and the drilling fluid pressure is set to 25 MPa, which can be converted to the rotary drilling mode faster.

Calculation method of the build-up rate of the internal push point-the-bit rotary steering tool

The internal push point-the-bit rotary steering tool is a new type of dynamic point-the-bit rotary steerable system. This paper comprehensively uses the mechanical and trajectory method to calculate the build-up rate of the tool to evaluate its build-up ability and realize accurate control of the wellbore trajectory during the directional drilling process. The influence of tool structure, wellbore geometric parameters, drilling process parameters, bit-cutting anisotropy, and formation characteristics on the build-up ability are considered. The tool deflection force, the structural lateral force on the bit, and the formation deflection force were calculated respectively, and the calculation model for the build-up rate of the internal push point-the-bit rotary steering tool is established according to the relationship between force and cutting displacement. In order to study the variation of the build-up rate of the tool in different well slope sections under the conditions of fixed bottom hole assembly and formation parameters, the build-up rate simulation calculation was carried out. The calculation results show that the maximum build-up rate of the tool under stable and controlled conditions increases with the increase of the well inclination, which means the internal push point-the-bit rotary steering tool is suitable for extended reach wells and horizontal wells. The research results provide a theoretical basis for the design of bottom hole assembly and the optimization of drilling process parameters when using the internal push point-the-bit rotary steering tool for directional drilling.

Cuttings transport: Back reaming analysis based on a coupled layering-sliding mesh method via CFD

Inadequate hole cleaning is one of the main reasons for inefficient operations in extended-reach drilling. The mechanism of cuttings transport under the back reaming operation, which is frequently adopted to remove the cuttings, has been investigated in this study. To this end, a coupled layering-sliding mesh method with the Eulerian-Granular approach has been established innovatively. The dynamic layering method has been employed to simulate the axial motion of the pipe, whereas the sliding mesh method has been used to simulate the pipe rotation. The back reaming operation of a connector-furnished pipe has been simulated, and the sensitive parameter analysis has been conducted. The results thus obtained demonstrate that the increase in the initial bed height, inclination, and the diameter and length of the connector causes a significant increase in the cuttings concentration. In addition, the cuttings concentration is observed to decrease significantly with the pipe rotation speed. Furthermore, two main factors contribute towards the cuttings accumulation around the connector, namely, the difference in the cross-sectional area and the pushing effect of the connector—like a “bulldozer”. The “bulldozer” effect of the connector dominates when the tripping velocity is significant compared to the velocity of the cuttings. Conversely, the effect of the difference in the cross-sectional area becomes the leading factor for cuttings accumulation. The “bulldozer” effect of the connector causes a more severe impact on hole cleaning. In both cases, increasing the tripping velocity only mildly affects the cuttings concentration. It is therefore suggested that the tripping velocity should be slower than that of the sand during the back reaming operation. Furthermore, increased fluid velocity might lead to a higher accumulated cuttings concentration around the connector when the cuttings bed has not entirely passed through the connector. A significant flow rate can be safely applied after the cuttings have passed through the connector furnished with a large diameter, such as the bottom hole assembly. This exploration serves as an essential guide to predicting and controlling tight spots while back reaming.

Drilling Optimization by Using Advanced Drilling Techniques in Buzurgan Oil Field

Efficient and cost-effective drilling of directional wells necessitates the implementation of best drilling practices and advanced techniques to optimize drilling operations. Failure to adequately consider drilling risks can result in inefficient drilling operations and non-productive time (NPT). Although advanced drilling techniques may be expensive, they offer promising technical solutions for mitigating drilling risks. This paper aims to demonstrate the effectiveness of advanced drilling techniques in mitigating risks and improving drilling operations when compared to conventional drilling techniques. Specifically, the advanced drilling techniques employed in Buzurgan Oil Field, including vertical drilling with mud motor, managed pressure drilling (MPD), rotary steerable system (RSS), and expandable liner hanger (ELH), are investigated and evaluated through case study analyses, comparing their performance to that of conventional drilling techniques. The findings indicate that vertical drilling with mud motor exhibits superior drilling performance and wellbore verticality compared to conventional rotary drilling bottom hole assemblies (BHA) for drilling the 17 ½" hole section. MPD systems employed in the 12 ¼" hole section demonstrate safe drilling operations and higher rates of penetration (ROP) than conventional drilling methods. Rotary steerable systems exhibit reduced tortuosity and achieve higher ROP when compared to mud motor usage in the 8.5" and 6" hole sections. Lastly, investigations of expandable liner hanger cases reveal subpar cement quality in the first case and liner remedial work in the second case, highlighting the successful implementation of ELH techniques in the offset field. Overall, this paper highlights the advantages of utilizing advanced drilling techniques in Buzurgan Oil Field, showcasing their ability to mitigate drilling risks and enhance drilling operations when compared to conventional drilling approaches.

Symplectic space wave propagation method for forced vibration of acoustic black hole assemblies

Recently, acoustic black holes (ABHs) have been widely used for vibration and noise reduction. Compared with a single ABH, multiple ABHs embedded in a structure can achieve better vibration suppression. However, most of the current research focuses on embedding a single ABH. In this study, a symplectic space wave propagation method was proposed for the forced vibration of ABH assemblies. The governing differential equations based on the Euler-Bernoulli beam model of the ABH beam for vibration were first converted into Hamiltonian canonical equations. A symplectic eigenvalue problem was then formed, and the wave propagation parameters and wave shapes were obtained analytically. A Gaussian-discretization scheme was used to discretize the ABH beam, whereas the proposed method was used to evaluate the wave amplitude at each point. Second, a combination of the ABH beams of various forms was considered, in which the ABH beams are coupled directly or through a joint. A semi-analytical solution for the forced vibration of ABH assemblies was established by satisfying the dynamic coupling between the ABH beams and the joint. Because the proposed method utilizes symplectic analytical solutions of wave modes, its computational efficiency and precision are high.

Drilling operation optimization using machine learning framework

Optimizing the surface parameters to maximize the rate of penetration (ROP) could be achieved through a machine learning (ML) framework. Hence, predicting ROP is a crucial factor in any optimization problem. A defined range of surface parameters will provide the maximum ROP for a given bottom hole assembly (BHA) while drilling a particular formation lithology. This maximization of ROP value is valid for a specific range of certain combinations of surface parameters and subsurface equipment. However, tuning these surface parameters is an art rather than a science. Despite the abundance of offset wells data, local experience and trial-and-error methods are the current keys for this tuning. This work used a large drilling dataset (460,076 records) to develop two artificial neural network (ANN) models. The first ANN model is used to predict standpipe pressure (SPP) and the apparent surface torque for the drilling system. In addition to other inputs, these two parameters are used in the second ANN model to predict the ROP. The first ANN achieved 92.39% and 93.71% accuracy in predicting the apparent torque and standpipe pressure values respectively; while the second ANN achieved 87.63% accuracy when tested against 39,294 records that were not used in training. To apply the system in real applications, the ROP is predicted, and a genetic algorithm (GA) is used to optimize both the surface parameters and the downhole equipment while drilling a section of the hole. This system or framework (ANN models coupled with the GA algorithm) was used in a field trial in one of the Egyptian Western Desert routine wells. The framework was used in two sections within the 8 ½” hole and enhanced these sections' ROP by 15.05% and 14.41% compared to similar sections in different offset wells. It resulted in an overall best-in-class (BIC) well performance compared to similar wells in the field.

Influence of torsional stick-slip vibration on whirl behavior in drill string system

Torsional and lateral vibrations, which are important causes of drill string failure, are harmful vibration modes that can occur during drilling. As its form of expression, stick-slip and whirl significantly limit the drilling efficiency and the bottom hole assembly (BHA) performance. Prediction of the correlation between these vibration modes has an important significance in adjusting basic parameters to avoid the effects of stick-slip and whirl vibration in the drilling process. In this work, in order to provide a general understanding of the vibration mechanism, a coupled torsional stick-slip and whirl model with 6 degrees of freedom (6-DOF) was proposed, and numerical simulations were conducted. The Lagrange method was used to derive the model, and the stabilizer-borehole wall interaction, drill collar-borehole wall interaction, and bit-rock interaction were additionally considered. Torsional vibrations were modeled with respect to the entire drill string system, while the lateral vibration was restricted to the BHA part. The results showed a correlation between torsional and lateral vibration modes when stick-slip vibration occurs and disappears. These correlations were performed by analyzing the time domain, frequency domain, and correlation coefficients. The relationship between torsional and lateral vibration modes was verified by performing a qualitative comparison with field experiments.

Evolution and explosions of metal-enriched supermassive stars: proton rich general relativistic instability supernovae

ABSTRACT The assembly of supermassive black holes poses a challenge primarily because of observed quasars at high redshift, but additionally because of the current lack of observations of intermediate mass black holes. One plausible scenario for creating supermassive black holes is direct collapse triggered by the merger of two gas-rich galaxies. This scenario allows the creation of supermassive stars with solar metallicity. We investigate the behaviour of metal enriched supermassive stars which collapse due to the general relativistic radial instability during hydrogen burning. These stars contain both hydrogen and metals and thus may explode due to the CNO cycle (carbon–nitrogen–oxygen) and the rp process (rapid proton capture). We perform a suite of stellar evolution simulations for a range of masses and metallicities, with and without mass-loss. We evaluate the stability of these supermassive stars by solving the pulsation equation in general relativity. When the stars becomes unstable, we perform 1D general relativistic hydrodynamical simulations coupled to a 153 isotope nuclear network with cooling from neutrino reactions, in order to determine if the stars explode. If the stars do explode, we post process the nucleosynthesis using a 514 isotope network which includes additional proton rich isotopes. These explosions are characterized by enhanced nitrogen and intermediate mass elements ($16\ge \rm {A}\ge 25$), and suppressed light elements ($8\ge \rm {A}\ge 14$), and we comment on recent observations of super-solar nitrogen in GN-z11.

Feasibility of periodic stabilizers for extending coiled tubing reach

Coiled tubing (CT) operations are widely used to maintain and service wellbores for optimal production. Compressive forces, arising from friction, can cause buckling induced lock-up of the CT, bringing the operation to a halt. This paper investigates the feasibility of using strategically placed periodic supports in the wellbore to increase the buckling stability of the CT. Tubing force analysis (TFA) and finite element analysis (FEA) models from literature are modified and used in conjunction to determine exact locations of the individual supports. For the investigated CT operation this resulted in a total of 2153 periodic supports spanning 7 regions of stabilization covering 1890 m. With a strength and strain wise feasible individual support length of 2 mm, the accumulated collapsed length of supports is 4.3 m. This length scale makes it realistic to bring the periodic supports into the wellbore with the bottom hole assembly during CT operations. Conducted experiments demonstrate how inadequate support causes potential detrimental effects for the operation, however, sufficient periodic support maintains its stabilizing integrity beyond the point of helical buckling.