Drill String Research Articles

Improving Drill-String Extended Reach Efficiency in High-Temperature and High-Pressure Conditions: An Experimental Investigation

Abstract Drill string buckling behavior is of interest to the oil and gas industries. Buckling severity increases as drilling continues and causes a lock-up condition beyond which drilling cannot commence. The friction force between the drill string and the wellbore is key in influencing drill string buckling initiation and progression. Herein, the effects of adding nano-sepiolite (NSP) as an additive to water-based drilling fluids on the friction between the drill string and wellbore wall were investigated. Various samples with different sizes and compositions of NSP were tested for their ability to reduce the coefficient of friction (COF) that delays the onset of buckling to facilitate deep drilling by providing improved lubrication characteristics. The drill string sinusoidal and helical buckling and lock-up condition and the axial force transfer (AFT) were experimentally investigated. The water-based drilling fluids’ lubricity, COF between the drill string and the wellbore wall, and the stability of the rheological properties of the NSP-modified water-based drilling fluids containing 1–6 wt% NSP were tested in a high-temperature and high-pressure (HTHP) environment utilizing an in-house experimental setup. Sepiolite in nano-form at 4 wt% and with a size distribution of 30–60 nm improved the stability of the water-based drilling fluids rheology, significantly decreased the COF of the water-based drilling fluids, and improved the drill string axial force transfer. NSP additives significantly improved the COF and the drill string AFT in the HTHP environment compared with that of other commercial drilling fluids.

Experiment Study of Deformable Honeycomb Triboelectric Nanogenerator for Energy Collection and Vibration Measurement in Downhole

Downhole drilling tool vibration measurement is crucial for drilling exploration safety, so real-time monitoring of vibration data is required. In this research, a honeycomb triboelectric nanogenerator (H-TENG) capable of adapting to various downhole environments is proposed. It can measure the frequency of downhole drilling equipment’s vibrations and transfer mechanical energy to electrical energy for use in powering other low power downhole meters. In order to preliminarily verify the possibility of sensors used for vibration measurement of downhole drilling tools, we built a simulated vibration platform to test the sensing performance and vibration energy collection performance of H-TENG. According to the testing results, the measurement range of vibration frequency and amplitude are 0 to 11 Hz and 5 to 25 mm, respectively, and the corresponding measurement errors are less than 5% and 6%, respectively. For vibrational energy harvesting, when four sensors are wired in series with a 107 resistance, the maximum power is approximately 1.57 μW. Compared to typical methods for measuring downhole vibration, the honeycomb triboelectric nanogenerator does not need an external power source, it has greater reliability and output power, and it can vary its shape to adapt to the complicated downhole environment. In addition, the H-TENG can be combined freely according to the diameter of the drill string, and even if one sensor unit is damaged, the other units can still be used normally.

Analysis and Multi-Objective Optimization of the Rate of Penetration and Mechanical Specific Energy: A Case Study Applied to a Carbonate Hard Rock Reservoir Based on a Drill Rate Test Using Play-Back Methodology

Until early 2006, in Brazil, the focus used to be on oil and gas exploration/exploitation of post-salt carbonates. This changed when the industry announced the existence of large fields in pre-salt layers across the South Atlantic Ocean from nearshore zones up to almost 350 [km] from the shore. With the discovery of pre-salt hydrocarbons reservoirs, new challenges appeared. One of the main challenges is the necessity to optimize the drilling processes due to their high operational costs. Drilling costs are considerably high, which leads the oil and gas industry to search for innovative and entrepreneurial methods. The coupling of the mechanical specific energy (MSE) and the rate of penetration (ROP) is a method that allows for the identification of ideal conditions to efficiently enhance the drilling process. In addition, the performance of the drilling process can be estimated through pre-operational tests, which consist in continuously testing the applied drilling mechanic parameters, such as the weight-on-bit (WOB) and drill string rotary speed (RPM), looking for optimum sets that would ultimately provide the most desirable ROP. Thus, the goal of this research was to analyze field data from pre-salt layer operations, using a multi-objective optimization based on the play-back methodology for pre-operational drilling tests, through the ideal combination of the highest ROP and the lowest MSE. The results showed that the new concept of pre-operational tests based on the MSE proved to be effective in the drilling process optimization. The combination of the highest ROP and the lowest MSE allows for a high-performance drilling process. For WOB intervals of 5 and 7 [klb], a good fit of the parameters was obtained. Through the parameters obtained from pre-operational tests, the eventual cost-saving and time-saving values could be estimated, respectively, ranging from USD 1,056,180 to 1,151,898 and 19.50 to 21.27 [h], respectively. In addition, the results of this research can be applied to the exploration of other natural resources, such as natural hydrogen and geothermal sources.

Load Calculation and Strength Analysis of the Deepwater Landing Drill Pipe-Lowering Operation

A landing string is directly exposed to seawater and subjected to significant stresses and complex deformations due to environmental loads such as wind, waves, and ocean currents during the phase in which the drill string carries the casing to the wellhead. Meanwhile, as the water depth increases, the weight of the drill string increases, leading to an increase in the tensile loads borne by the drill string, which can easily cause a risk of failure. Therefore, a quasi-static load calculation model for the deepwater insertion of the pipe column was established. Using the Ansys platform, simulations were conducted for average wind, wave, and ocean current conditions during different months throughout the year. The ultimate loads and stress distributions of the string were derived from theoretical analyses and numerical simulations for different operational sea states, and the suggested safe operating window and desired BOP trolley restraining reaction force for landing strings’ lowering are given according to the existing industry standards. The research findings can help in identifying the potential risks and failure modes of the deepwater landing string under different working conditions.

INVESTIGATION OF THE IMPACT OF DRILLING WITH SIMULTANEOUS EXPANSION TO THE RATE OF CHANGE IN THE ZENITH ANGLE OF THE WELL

The article discusses the use of various methods and techniques for isolating complication zones during drilling in the oil and gas industry. The main focus is on the process of isolating complication zones using profile closures, which allow maintaining the nominal di-ameter of the wellbore. To achieve this, it is necessary to increase the diameter of the complication interval using expanders. The article notes that the highest efficiency is achieved when drilling and expanding the wellbore simultaneously using expandable expanders. Such expanders have high wear resistance and can withstand significant loads. The article also ex-amines the challenges that arise when drillinginclined and directional wells with simultaneous wellbore expansion. One of the main problems is the spontaneous increase in zenith angle when incorporating the expander into the bottom assembly of the drill string. Wells drilled with simultaneous wellbore expansion were an-alyzed. After the analysis, it is evident that when the zenith angle exceeds 300 before the start of expansion, a more intense increase in zenith angle is observed during wellbore expansion. To solve this problem, the use of a managed drill string is proposed, which can adjust the zenith angle with a specified intensity or stabilize it throughout the interval.

Modeling and friction response analysis of rocking-sliding friction of drill string in directional wells

The main goal of this research is to conduct a quantitative assessment of how rocking influences friction during sliding. The kinetic equations were developed, accounting for the friction coefficient's velocity weakening effect. The model's precision and dependability were confirmed by comparing simulation results against experimental data. Furthermore, the study discovered that the Stribeck model presents benefits when compared to alternative models. Investigations were carried out to examine how rocking parameters affect axial friction during rocking motions. The findings indicate that variations in axial friction forces are predominantly observed during the phase of tangential acceleration. Crucially, the research demonstrates that modulating the rocking velocity's waveform can markedly decrease the average axial friction, even when the maximum rocking speeds remain the same.

Research on the influence factors of hydraulic oscillator on drag reduction efficiency in horizontal well drilling

The application of hydraulic oscillator can solve the problems of large friction and serious pressure support in the drilling process of extended reach well and long horizontal well, but the conventional hydraulic oscillator parameter setting is not reasonable, high pressure consumption, easy to make the ground machine pump overload operation and failure. Therefore, based on the LuGre dynamic friction model theory, a calculation model for the friction between drill string and rock wall under the condition of longitudinal oscillation is established, and the influence law of hydraulic oscillator oscillation parameters on drag reduction efficiency is studied. The results show that the change of oscillation intensity, oscillation frequency and oscillation amplitude can improve the drag reduction efficiency, and the increase trend of drag reduction efficiency is first increased and then decreased. The selection of each parameter has the optimal value. According to the analysis of orthogonal test results, it is found that the reduction degree of friction between drill string and borehole wall rock by each parameter is in the order of oscillation intensity, oscillation frequency and oscillation amplitude from the largest to the smallest.

A comprehensive prediction model of drilling wellbore temperature variation mechanism under deepwater high temperature and high pressure

Comprehensively considering the impact of properties of drilling fluid at high temperature and high pressure (HTHP), drill string eccentricity, rotation, and rock breaking of drill bit on the annular temperature profile, transient temperature variations were predicted by using a wellbore heat transfer model. The model was numerically solved using the finite difference method. Compared to DRILLBENCH simulations, the predicted model was more consistent with the field-measured data. The calculations revealed that comprehensively considering various heat source factors made the annular temperature closer to the actual wellbore value, with a temperature difference of up to 10.66 °C. When considering variations of properties of drilling fluid at HTHP, the lower section of the annulus showed a significant decrease in temperature with depth, with a bottom-hole temperature difference of 5.4 °C. The bottom-hole temperature decreased by about 2.6 °C from concentric to eccentric drill string, and the pressure difference was about 1 MPa. Compared to drill string eccentricity, rotation and rock breaking of drill bit had a greater impact on annular temperature, with bottom-hole temperature differences of 13 °C and 22 °C, respectively. Accurate temperature modeling can better understand and predict the variation patterns of wellbore temperature, providing important guidance for the development of deepwater drilling.

Research on the Influence of Deep-Water Drilling Risers on Drillstring Motion Trajectory and Vibration Characteristics

The swing of the riser in deep-water drilling can significantly impact the drill string. In this study, we establish a riser model that considers the combined disturbance of periodic dynamic wind and wave loads. By coupling it with the drill string model, we develop a dynamic model for deep-water drilling systems. Through analyzing multiple sets of different drilling parameters, we examine displacements and impact forces at various positions along the drill string system. Specifically, our focus lies on velocity, acceleration, and rotational speed information of BHA. We investigate how WOB and rotational speed influence motion trajectory and vibration characteristics of the drill string within the dynamic model of deep-water drilling systems. Simulation results reveal slight differences in whirling trajectories between inside the riser and below mud line for the drill string. Rotational speed has a greater impact on the drill string compared to WOB; higher rotational speeds lead to increased collision forces between the drill string system and both riser and wellbore. Our findings identify specific combinations of WOB and rotational speed parameters that can stabilize drilling operations within dynamic models for deep-water drilling systems. These research results provide valuable insights for adjusting WOB and rotational speed parameters in deep-water drilling.

Buoyancy effect dualism on drill string axial forces calculation

This paper discusses the use of two buoyancy schools in determining the axial forces in the drill string, which leads to the duality of the solution. The difference in the results in determining the true and effective force and their relationship with each other using the strength of stability were revealed. It is shown that only the true force can be used to calculate the stresses and deformations of the drill string elements, since their actual values correspond to this force. At the same time, taking into account the effective forces, it is possible to more fully use the actual stability of the drill string, increasing the permissible loads on the bit and increasing the penetration rate. Thus, the presence of two buoyancy schools and, accordingly, two types of axial forces, makes it possible to more accurately and comprehensively assess the operability of the drill string.

Buckling and dynamic analysis of drill string system in horizontal wells

Buckling and dynamic analysis of drill string system in horizontal wells

A new detection method of co-existence of well kick and loss circulation based on thermal behavior of wellbore-formation coupled system

Accurately obtaining wellbore-formation temperature distribution during drilling in fractured carbonate formations is the basis for effectively solving the problem of the well kick and loss circulation coexisting (WK-LC). Therefore, based on the energy conservation law and considering the convective heat transfer and variable mass flow caused by well kick and loss circulation, this paper developed a full transient heat transfer model of wellbore-formation coupled system under the WK-LC. The reliability of model was verified by field measured temperature data. Based on field well, the thermal behavior of wellbore-formation coupled system under normal condition, well kick, loss circulation and WK-LC were compared and studied.The results showed that the bottom-hole temperature of well kick and Case1-2 is higher than that of normal condition, while the bottom-hole temperature of loss circulation and Case3-4 is lower than that of normal condition. The temperature difference between annulus and drill string (TD-AD) shows a “wavy line” trend of increasing-decreasing-increasing-decreasing along the well depth. The TD-AD of wellhead is about 6 °C in normal and WK-LC conditions. The traditional wellhead temperature monitoring method can only distinguish well kick and leakage, and it is difficult to judge whether WK-LC occur.In addition, the influence of the distance and well kick/leakage rate difference between the well kick region and the leakage region on thermal behavior of wellbore-formation coupled system was discussed. Finally, a new auxiliary method is proposed to identify the well kick, the loss circulation and the WK-LC. Which will have a significant implication for well killing and leaking stoppage operations.

Investigation of drill string dynamics using probabilistic methods

The object of research is a drill string. The work is directed to the study of the drill string dynamics and its influence on the rock, which is drilled using probabilistic methods. It is shown that the nature of the vibrations of the top of the drill string and the downhole signals are different and have a stationary random character. It is proved that the process at the output of the drill string, taking into account random disturbances, is narrow-band (quasi-harmonic) or close to it. It is found that the energy composition of the spectrum sections and the appearance of resonance peaks and their displacement is directly determined by the physical and mechanical properties of the rocks being drilled, as one of the factors that determines the vibration state of the drill string. Graphs of the spectral density of the power of pitting vibrations are given, showing their amplification at frequencies of 30–40 Hz as the hardness of the rocks being drilled increases. The maximum of the power density bending curve shifts towards low frequencies. There is a «mutual convergence» of the maxima of the power spectral density of the oscillations of the top and bottom of the drill string. It is shown that an important feature of drill string vibrations in the process of drilling with ball bits is that the intensity of vibrations of the top of the drill string passes with frequencies close to low frequencies, and the vibrations of the bottom of the string – to high frequencies. It is determined that the process at the output of the drill string, taking into account random disturbances, is narrow-band (quasi-harmonic) or close to it. As a result, the assumption of a narrow band at the output of the system, which is the basis of theoretical research, is justified. It is proven that the drill string, as a system with liquid filling under pressure, is more stable compared to a hollow structure. The washing liquid, in this case, plays the role of a dynamic absorber.

Laboratory measurements on the suppression of vortex-induced vibrations and rotation in long-span riserless drill strings

Riserless drilling is a leading offshore technology, but the absence of a riser causes significant vibration during outflow and rotation. However, effective methods for addressing vortex-induced vibration coupling rotation are inadequate. Experiments were conducted on riserless drill strings, and the dynamic responses were analyzed by modal decomposition theory. Results indicate that structures with higher helix numbers and screw heights exit or delay entry to the lock-in region. Triple-helix designs with screw heights of 0.2 Diameter (D) and 0.25D achieve up to 93% suppression efficiency. Increasing helix number and screw height reduces rotating drill string frequencies and delays the occurrence of the dominant frequency jump phenomenon, resulting in enhanced suppression effects. Amplitude suppression primarily occurs in medium and weak regions, while helical strakes significantly reduce amplitudes in lock-in regions. For controlling vibration and minimizing fatigue damage in rotating drill strings, it is recommended to use triple-helix structures with lower screw heights.

Drill string vibrational analysis and parametric optimization for a portable water well rig development

The vibration of a drill string is a key topic of study in drilling and mining engineering. Excessive Drill String (DS) vibrations can lead to early failure of bits due to fatigue, Drill Pipe (DP) fractures, bearing damage, and a decrease in the Rate of Penetration (ROP). This occurs when the drill string rotates at its natural frequency, which is known as resonance. A modal and harmonic vibrational analysis of a drill string up to 60-65 meters long was conducted in a vertical water well through parametric studies. This project investigates the vibration of a drill string under various parameters, including drill string lengths, Weight on Bit (WOB), and drill string rotational speeds. The Rotational Speed (RS) in the drill string induces lateral vibrations and stick-slip in torsional vibrations. Finite element modeling of the drill string was performed using ANSYS Workbench (Mechanical). Modal and harmonic frequencies were determined to obtain the optimal drill string length and rotational speeds, using Campbell diagrams and varying weights on bits. Different weights on the bit were assumed to simulate the drilling environment. One of the modern methods used to simulate dynamic behavior in drilling operations is random vibrational analysis. A random vibrational analysis of the drill string was performed in a vertical water well using ANSYS Workbench 2020. This analysis aimed to identify the frequency response of the drill string, with the probability of deformation for each sigma under random vibration being evaluated. The analysis indicated a higher probability approximately 99.7% of failure along the axis of the supplied PSD acceleration. The response power spectral density (RPSD) was analyzed in the x, y, and z directions, focusing on any point in the bottom hole assembly, primarily the bit. The response PSD results indicated that as the Drill Pipe (DP) increased, resonance spikes rose across all axes, leading to lateral and longitudinal vibrations in the drill string. These findings highlight lateral movement as a primary cause of vibration, offering insights for optimizing drilling parameters.

Extraction of biodiesel from pomelo peel and investigation of its efficiency as a lubricant in water-based drilling fluid

Abstract Reducing friction between drill string and wellbore wall is one of the key functions of drilling fluid which may result from tight holes, key seats, differential sticking, or cutting build up along the drill string. However due to growing environmental concerns, biodegradable lubricants which are also cost-efficient are appreciated and mandated in many countries. This study discusses the performance analysis of biodegradable biodiesel produced from pomelo peels and Petroleum-based lube oil as drilling fluid lubricants. The test samples comprise 700 mL of water + 10 % bentonite + 3 % barite + 0.25 % CaCO3 + 0.25 % KOH + 1 % CMC + lubricant. Two sets of lubricants were utilized to prepare 10 samples of drilling fluid, one set with petroleum-based lubricant and other with biodiesel. Essential oil was extracted from pomelo peel with the help of the Clevenger apparatus. The oil was then converted to biodiesel through the process of transesterification. Biodiesel properties were tested for the ASTM standards. Both sets of drilling fluid samples were tested for their rheological, filtration and lubricating properties and from the results obtained it can be concluded that both type of lubricating agents have almost negligible impact on rheological and filtration loss properties. However, the lubricity coefficient values drastically decreased as we increased the lubricant content, which is an indication that biodiesel extracted from pomelo peel acts as a better lubricant. The values of the lubricity coefficient for biodiesel based drilling fluid also fell well within the advised range (<0.30). We can therefore draw the conclusion that biodiesel made from pomelo peel can replace petroleum-based lubricants while also lowering the environmental concerns related to lubricants.

A drill string as a chain of elastically connected cylindrical elements in torsion-longitudinal self-oscillations

A drill string as a chain of elastically connected cylindrical elements in torsion-longitudinal self-oscillations

Laboratory Study of KCl-Polymer and Soltex Utilization in Preventing Swelling Shale in High Temperature

Mismanaging mud characteristics can create drilling issues and financial losses. Field drilling operations can avoid lost circulation (mud loss), stuck drill strings, uncontrolled blowouts, and caving shale by carefully selecting drilling mud that matches the formation characteristics of a well. The aim of this study is to develop a mud formulation that effectively mitigates shale-related issues while preserving the integrity of the physical properties of the formation. The use of appropriate polymer mud and shale stabilizers at 250 degrees Celcius, with KCl at 9 percent and Soltex at 2, 4, and 6 ppb, will help this study achieve its aim. In this study, clay swelling is measured with a linear swell meter. Test results will be shown as charts or graphs. We can see from the linear swell meter graph that using KCl polymer mud with Soltex at a concentration of 4 ppb is an effective way to reduce shale formation swelling by about 21.20 percent. This study proposes employing KCl polymer and Soltex to decrease shale swelling at high temperatures, which could have a positive effect on petroleum engineering. Precision in drilling mud composition and selection can improve drilling operations, which could reduce drilling expenses and financial losses.

Fatigue failure analysis based on coupling vibration of drill string in ultra-deep wells

Fatigue failure analysis based on coupling vibration of drill string in ultra-deep wells

MODELLING OF A DRILL STRING MOTION UNDER SEISMIC IMPACT

The article studies nonlinear dynamics of drill strings in a seismically active environment. The influence of seismic waves on the vibrations of drill strings for shallow drilling is considered. Deformations of drill strings are assumed to be finite. Based on the Ostrogradsky-Hamilton variational principle and the laws of soil motion, a nonlinear mathematical model of spatial deformation of drill strings is constructed. A numerical analysis of the model is performed using the Wolfram Mathematica symbolic computing package. Qualitative and quantitative changes in the dynamics of drill strings are observed, manifested in the form of beats due to the influence of seismic waves.