Positive Displacement Motor Research Articles

Numerical validation of a novel cuttings bed impeller for extended reach horizontal wells

To reduce the risk of downhole accidents resulting from poor wellbore cleaning during the drilling of extended reach horizontal wells, a new cuttings bed impeller is developed. The performance of existing cuttings bed impellers on wellbore cleaning efficiency is analyzed by multiphase numerical simulation. Based on this analysis, a new type of cuttings bed impeller is proposed, and its key structure parameters are optimized. Its cuttings removal performance under different working conditions is verified. The results show that the spiral impellers have the highest annular velocity, promoting the movement of the cuttings bed. Increasing the rotation speed of the impeller causes the cuttings bed to move further from the low side of the wellbore, facilitating the cuttings removal. Two major improvements are introduced to the new cuttings bed impeller: a positive displacement motor that enables the self-rotation of the impeller, and the elastic contacts on the spiral blades that stir cuttings bed and reduce friction with the wellbore. The optimized parameters of the new impeller are: helix angle of 60°, 4 blades, elastic contacts arranged in crossed pattern, and self-rotation speed of 60 r/min. It is also demonstrated that the new impeller achieves satisfactory cleaning results in both rotary drilling (84.71%) and sliding drilling (71.07%) conditions. This work provides a new solution for the efficient removal of cuttings in extended reach horizontal wells.

Steering ability rapid evaluation of the slide drilling system based on multi-body dynamics model

Efficiently and accurately predicting the steering ability of the bottom hole assembly (BHA) in slide drilling is a crucial yet challenging task. While the industry standard three-point geometry method is computationally efficient, it cannot capture the intricate mechanics involved in the drilling process. Conversely, utilizing the whole drill string dynamics model for simulating slide drilling provides a more comprehensive representation but involves time-consuming evaluations, making it difficult to balance precision and efficiency. This study addresses this challenge by proposing a rapid evaluation method that ensures both speed and accuracy by developing a multi-body dynamics rapid model of the slide drilling system. Based on the whole drill string model, this method incorporates two key techniques to achieve its primary objective. Firstly, it utilizes the equivalent torque model of the bit, which includes the fixed joint and the virtual rotational velocity, to replace the original revolute joint between the positive displacement motor (PDM) and the bit. Secondly, a segmentation model is established to decouple the simulation of the BHA drilling process from the drill string equilibrium process, thereby significantly reducing the slide drilling system’s degree of freedom (DOF). The proposed method offers a new approach to improving the efficiency of evaluating the steering ability of the slide drilling system while ensuring a high level of accuracy.

A New Design of Vibration Damping Structure for Positive Displacement Motor

Positive displacement motor (PDM) is a downhole power drilling tool, and the bottom of the drilling tool is directly connected to the drill bit. During the drilling process, the drilling tool will be directly affected by the impact load caused by the drill bit breaking the rock. Severe vibration can easily cause drill tool bearings to break and fail, threads to trip and other problems. The new PDM vibration damping structure uses wear-resistant and heat-resistant metal rubber instead of disc springs as energy-absorbing materials, and designs a "keyway type" vibration damping structure; a two-degree-of-freedom "spring - mass" model is established based on actual working conditions. , determine the basic size of the metal rubber pad based on the metal rubber stress-strain curve, and bring it into the drilling tool dynamics equation to verify that the stiffness and damping parameters of the metal rubber pad will not resonate; finally, compare the drilling conditions under different excitations in the dynamics simulation software The amount of impact the tool receives. Finally, the dynamics simulation of the new vibration-damping drilling tool under different frequency excitations was carried out in Adams simulation software, and it was concluded that in the common working environment of 6-15 Hz, the new vibration-damping drilling tool can effectively reduce the stress on the drilling tool. Impact force, the new vibration-damping drilling tool can reduce the impact force by about 40% when excited at 12 , 15 Hz . The conclusions drawn from the study have reference value for the development of long-life drilling tools and the design of drilling tool vibration damping structures.

Enhancing the benefit of slide steering drilling systems in horizontal wells of unconventional reservoirs

The slide steering drilling system consisting of a bent positive displacement motor (PDM) and measurement while drilling (MWD) system is widely used to continuously implement all wellpath control operations by alternately applying the slide and compound drilling modes. Due to the large friction force on the drilling string during slide drilling in the horizontal section, there is a significant adverse impact on both the drilling speed and horizontal extension ability. To efficiently and economically drill long horizontal sections, it is essential to increase the compound drilling proportion and decrease the alternative times of the two drilling modes. According to the features of wavy or tortuous horizontal sections and wellpath calculation models, a prediction and control method for the compound drilling proportion of horizontal sections is first established, and subsequently, its influencing factors and laws are analyzed and verified using an example. Theoretical research and drilling practice have shown that the compound drilling proportion of the horizontal section depends on the build-up rate of slide drilling and the inclination and azimuth change rates of compound drilling and is independent of the target area parameters and wellpath fluctuation ratio. In order to increase the compound drilling proportion and reduce the slide drilling frequency in the horizontal section, it is necessary to increase the build-up rate of slide drilling properly and reduce the inclination and azimuth change rates of compound drilling to the greatest extent. This paper is helpful to enhance the benefit of slide steering drilling systems in horizontal wells of unconventional reservoirs.

Study on the Influence of Fluid Pulsation on Hydraulic Impactor Performance in Drilling Engineering

The combination of the hydraulic impactor and positive displacement motor (PDM) is becoming more and more popular in drilling engineering. However, the negatives of the PDM on the impactor cannot be ignored. To improve the performance of the technique, the influence of fluid pulsation from the PDM on the hydraulic impactor was studied first; then, the structure of the impactor was optimized to improve its impact force; finally, field tests were carried out in 2 wells in the shallow formation. The results indicate that the fluid fluctuation generated in the PDM can restrain the performance of the impactor, and that the impact force can be increased by 24.4% to 28.6% through the optimization of design. Field tests show that this technique can further improve the drilling efficiency and rotating stability of the polycrystalline diamond compact bit, and that the rate of penetration and bit footage increase by 32.5% and 34.6%, respectively. In the study, the effect of inlet fluid fluctuation on the performance of the hydraulic impactor was studied using the computational fluid dynamics method. This is unlike other studies that have mostly considered the inlet fluid as a steady flow. Furthermore, the performance of the combine used of the impactor and PDM can be improved through structural optimization.

Experimental investigation of suspension-type abrasive water jet machining of nitrile rubber for positive displacement motor applications

The lightweight elastomers (such as nitrile rubber) frequently used in the Positive Displacement Motor (PDM) stator assembly are subjected to harsh environmental conditions. These elastomeric components are manufactured by primary casting/shaping methods, followed by secondary manufacturing/machining processes. The production of intricate shapes/sizes in single or batch-size elastomeric components using primary casting methods requires a customized mould to fulfil the requirement of sudden breakdown conditions, which is uneconomical. It necessitates an alternate production method that can satisfy the need for the elastomeric component at the stage of failure. The current research focuses on the possibility of producing nitrile rubber components using a non-conventional machining method, Suspension-type Abrasive Water Jet Machining (AWJM), suitable for batch production with better dimensional stability and versatility in shape/size. This work presents the experimental investigation of Suspension-type AWJM of nitrile rubber specimens (15 mm thick) using a custom-designed Tungsten Carbide (WC) nozzle under room-temperature condition. The top surface of the machined slot is analyzed to determine the mineral composition and abrasive particle embedding through Energy Dispersive Spectroscopy (EDX) and Backscatter Electron (BSE) detector. The Taguchi Orthogonal Array (OA) is employed to study the effect of the process parameters (Water Jet Pressure (WJP), Traverse rate (Vf), and Stand-Off Distance (SOD)) on the performance parameters (Kerf Taper Ratio (KTR), and Material Removal Rate (MRR)). The Analysis of Variance (ANOVA) is applied to check the statistical significance and percentage contribution of each process parameter on the performance of Suspension-type AWJM. The uniformity in the geometry of the machined slot is analyzed by the waviness patterns observed in the profile images of the cut specimen. The analysis of the EDX results reveals the presence of Manganese (Mn) and an increased percentage of Silicon (Si) particles near the top surface of the machined slot. The SOD influences KTR the most, whereas Vf highly influences MRR. It is observed that the waviness pattern is minimal at high WJP experimental runs. The outcome of this research work provides a quick and economical method of producing the PDM bushings instead of the casting/moulding method.

A Fuzzy Inference System for Detection of Positive Displacement Motor (PDM) Stalls during Coiled Tubing Operations

Positive Displacement Motors (PDM) are extensively used in the oilfield, either in drilling or in coiled tubing (CT) operations. They provide a higher rate of penetration and the possibility of drilling horizontal wells. For coiled tubing operations, PDMs can mill through obstructions and enable shut-in wells to work again. One of the major challenges while using these tools is the motor stalling, which can lead to serious damage to the PDM and lost time events in drilling and workover rigs. These events result in total losses of hundreds of thousands of dollars, and their avoidance mostly depends on trained and fully aware equipment operators. If a PDM starts to stall, the pumping needs to be halted immediately or the tool may fail. This paper describes the use of a Fuzzy Inference System (FIS) to detect the stalling events as they start to happen using the acquisition data from the coiled tubing unit, the output of the FIS could then trigger an alarm for the operator to take the proper action or remotely stop the pump. The FIS was implemented in Python and tested with real CT milling acquisition data. When tested using real data, the system analyzed 68,458 acquisition points and detected 94% of the stalling events across this data during its first seconds, whereas, during the real job, a CT operator could take longer to notice this event and take the proper action, or even take no action. If the FIS was applied on a real coiled tubing acquisition system, it could reduce PDMs over-pressurization due to stalling, leading to an increase on its useful life and decrease on premature failure. As of now there is no similar system in the market or published and this kind of operation is fully performed using human supervision only.

A method for predicting the build-up rate of single-bending positive displacement motor assembly in compound drilling

Accurately predicting the build-up rate of single-bending positive displacement motor (PDM) assembly in compound drilling is helpful to rational design the well trajectory, realize compound drilling in long well sections and improve the rate of penetration. Based on the calculation model of corrected build-up rate of single-bending PDM assembly in sliding drilling, the build-up rate calculation method of single-bending PDM assembly in compound drilling was established by combining the trajectory measurement data of the drilled sections, and the influence law of parameters such as bending angle, weight on bit, bit anisotropy index and formation inclination on the build-up rate of compound drilling was analyzed. And the following results are obtained. First, the build-up effect of the single-bending PDM assembly during compound drilling is mainly the result of the leverage effect and pendulum effect of the drill tool assembly, as well as the natural deviation of formation. Second, the composite drilling build-up rate is related to the drilling tool structure, bit performance, drilling parameters, formation inclination and other factors. In conclusion, the factors affecting the build-up rate of conventional drilling tool assembly also have impacts on the composite drilling build-up rate of single-bending PDM assembly. The method is important for the control of well trajectory during compound drilling.

Suspension-type abrasive water jet machining of slot on nitrile butadiene rubber: A preliminary study

Nitrile butadiene rubber (NBR) bushings, having thickness of 10–20 mm, are widely used in mining equipment such as positive displacement motor or mud motor stators. The most common methods used for batch production of these components are compression and injection molding followed by milling. It is very difficult to transfer the used molds to other working units, which necessitates an alternate method for manufacturing such components. Out of available non-conventional machining methods, the abrasive water jet (AWJ) machining methods are a better option due to less burr formation and absence of heat-affected zone. The present study focuses on the machining of NBR at room temperature, using a non-conventional machining method, namely, suspension-type abrasive water jet (AWJ) machining. The objective is to verify if slots could be produced using AWJ machining on 10 mm thick NBR samples. The preliminary results confirmed that the suspension-type AWJ machining is able to produce the slots in 10 mm thick NBR samples with the absence of cracks near the machined kerf profile. Wavy edges were observed in the machined kerf profile; however, further investigation would be required to find out the optimum values of the process parameters to get the waviness-free kerf profile.

Modeling and experiment of pressure drop on valve section of hydraulic oscillator

The article at hand focuses on the pressure drop at the hydraulic oscillator valve section. The flow path of the valve section is simplified through the hydraulic oscillator working principle and the valve structure. Further, based on the kinematic model of the positive displacement motor (PDM) and the moving valve, the flow area calculation model between valve sections was deduced. Next, using the simplified valve section flow path, said path is divided into four stages, and the analytical model of pressure drop was established by applying the fluid mechanic theory. Aiming to verify the analytical model, the transient finite element model, and the test bench were set up. Finally, three methods were used to calculate the pressure drop within the 1.3-inch and 1.4-inch stationary valves corresponding to the same input parameters. The results have shown that pressure drops obtained by all the methods are in good agreement; the maximum error between the analytical and experimental results was 7.6 %. Additional comparisons were made between the analytical and finite element model (FEM) results at various flow rates. In that case, the maximum error between the two methods was 7.05 %. Thus, the model can be used to further study the hydraulic oscillator mechanisms and provide a useful reference for both the design and optimization.

Evaluation on Efficient Crushing Test in Deep Poor Drillability Formation

The ancient formation is very thick, strong abrasion and poor drillability. Formation pressure of some area is abnormal high-pressure, induced high mud density, and borehole instability problems in some formation restrict the positive displacement motor (PDM) application, and impact drilling tools are instable. All above factors restraint the rate of penetration. Based on the result of litho-mechanical experiments, the impacting experiments are performed on samples of the Jurassic formation, impact fractured efficiency are evaluated, the results show high impact resistance in the formation, the best impact speed is over 12m/s, and the result was important design basis for impact tools improvement to increase the rate of penetrate (ROP) in the deep poor drillability formation.

Self-Powered Multifunctional Sensor of Positive Displacement Motor Based on Triboelectric Nanogenerator

In response to the testing requirements of downhole positive displacement motor (PDM), this research proposes a self-powered multifunctional sensor based on the triboelectric nanogenerator that can simultaneously measure the rotating speed, rotating angle and abrasion. Tests, including speed measurement tests, angle measurement tests, abrasion tests and reliability tests, were respectively tested after the sensor is manufactured. Speed tests results show that the measurement range is 0 to 900 r/min, the measurement error is less than 3%, and the maximum output voltage amplitude can reach 5.5 V. Angle tests results show that the minimum resolution is 60 degrees, and the measurement error is less than 5%. Abrasion tests results show that three abrasion thresholds of 0 mm, 0 to 20 mm and greater than 20 mm can be detected. Reliability tests results show that the sensor can work normally in an environment where the temperature is less than 250 degrees Celsius and the humidity is less than 90%. In addition, the power generation performance had also been tested, and the results show that the friction model and the sensing model of the sensor can output a maximum power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$28.3 \times 10.9\text{W}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.7 \times 10.9\text{W}$ </tex-math></inline-formula> respectively when connected in series with a 1000M <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> load. Compared with the traditional downhole sensors, this research can working normally in self-powered model at higher temperatures, and has more measurement parameters.

Research on the hydroformed metal stator bushing based on full restraint at both ends

The rubber bushing of the positive displacement motor is easy to age, and the metal bushing stator is proposed. We designed and carried out an experiment of hydroforming of metal stator bushing with equal wall thickness. After the experiment, we found that the metal stator bushing was wrinkled. We applied the finite element method to study the cause of wrinkles in the metal stator bushing. The research results show that the main reason why the metal stator bushing is wrinkled is that the inner diameter of the tube blank is larger. Therefore, We use the finite element method to study the influence of the inner diameter of the tube blank on the quality of the metal stator bushing. From the research results, we found that the suitable inner diameter of the tube blank is 86.5 mm. The surface of the metal stator bushing is smooth, the inner surface of the metal stator bushing is close to the mold, and the maximum gap is 0.15 mm. The metal stator bushing formed by tube blank III has a larger minimum wall thickness, a smaller maximum wall thickness, and the smallest wall thickness variance, which is 2.6 mm, 3.22 mm, and 0.028, respectively. The smallest plastic strain, the largest plastic strain, and the largest displacement of the metal stator bushing formed from the tube blank III are 0.2, 0.7, and 14 mm, respectively. When L2/L1 = 0.9577, the quality of the metal stator bushing is better.

Hybrid Approach for Health Monitoring of Mud Motor Fleet

A mud motor is a kind of positive displacement motor (PDM) that is used to transform the hydraulic energy of drilling fluids (mud) into mechanical energy. This mechanical energy enables the drill bit to cut the rock and drill a well. It is one of the key parts of downhole assembly that is placed in the drillstring to provide additional power to the bit while drilling as its power downhole output is still unmatched. Mud motor failure is a common and costly issue in drilling operations. A proper prediction of the failure as well as an estimation of the remaining useful life (RUL) are essential for timely downhole mud motor maintenance and drilling optimization.&#x0D; Until now, the oil and gas industry has lacked reliable procedures to monitor and maintain the health of mud motors, resulting in unnecessary maintenance costs as well as unpredictable and costly drilling failures. Recently, Schlumberger has addressed this problem with an industry-first prognostics and health management (PHM) solution, which not only estimates the health of the mud motor and tracks RUL, but also creates a new service for clients and provides a competitive advantage. Timely mud motor retirement and maintenance will ultimately reduce failures and NPT.&#x0D; The proposed PHM solution is suitable for real-time implementation and combines two different sterling algorithms for reliable prediction of possible problems with the mud motors. It enables the estimation of the mud motor health both on the system level with the entire mud motor (system level PHM model) and on the subcomponent level (power section PHM model) – the most critical component of the mud motor.&#x0D; The system-level algorithm model leverages both surface and downhole drilling data as well as mud motor characteristic curves to compute the severity of mud motor degradation. A special mud motor degradation indicator is defined. The indicator is calculated to evaluate the degree of power section decay at each time recorded from thousands of field jobs. The trends of the degradation with respect to drilling time and drilling distance are extracted for each motor job. Based on the study of large datasets, good correlation was observed between the mud motor degradation indicator and mud motor failures.&#x0D; The power section PHM model uses downhole measurements to estimate the RUL of the elastomer – the life-limiting component inside the power section. It is based on a high-fidelity model and uses a hybrid approach by combining a high-fidelity physics-based model of a power section and data-driven approaches with machine learning techniques. Machine learning methods were applied to derive a reduced order surrogate model (ROM) of power sections from the original physics-based models for real-time applications. This ROM outputs the estimation of performance and fatigue characteristics of the considered power section depending on the considered drilling conditions such as differential pressure, downhole temperature, flow rate, and mud compatibility. As the result, the model analyzes accumulative risk of fatigue failure and produces real-time health information for the power section as a percentage of the remaining lifespan.&#x0D; The new solution for mud motor PHM was successfully verified and tested in the field. Comparison of the predicted mud motor fatigue life with the actual observed postjob conditions and job failures demonstrated good results of the developed models. The PHM enables optimization of mud motor selection, drilling configuration, and maintenance operations by minimizing RUL uncertainties while facilitating rerun decisions and avoiding overmaintenance and premature retirements. The whole solution is currently being integrated into a drilling platform including the maintenance system, the well construction planning, and the execution. It maximizes the equipment usage with increased drilling performance without sacrificing reliability and enables optimal fleet management of a drilling process for revenue maximization.

Optimization of the Configuration of the Power Sections of Special Small-Sized Positive Displacement Motors for Deep-Penetrating Perforation Using the Technical System “Perfobore”

Innovative technologies for the secondary drilling of productive reservoirs, based on the multihole drilling deeply remoted from the wellbore and with controlled trajectories, to overcome the contamination of the pay zone, and with the ability to carry out various geological and technological wellworks many times over, can significantly increase the efficiency of the development of old and marginal wells. To implement such tasks, it is necessary to use special technological drilling equipment, one such technical system (TS) is the Perfobore system, which uses a modular construction. The methodology allows to choose an optimal variant for the power sections with a high-torque, small-sized positive displacement motor PDM, previously developed by specialists at the Perfobore company. This made it possible to design universal sectional motors with diameters of 43 to 54 mm with improved characteristics compared to serial PDMs. The production of prototypes of multi-section PDMs and their successful bench and then field tests (FT), from 2018 to 2020, in the Uralopovolzhskaya and West Siberian oil and gas provinces, as part of the TS Perfobore, proved the correctness of the chosen technical strategy.

A study on mechanical properties of equal wall thickness rubber bushing of positive displacement motor based on hydrogenated nitrile butadiene rubber aging test

Shale gas production has become the main driver of global gas production growth. Deep shale gas is difficult to extract, which puts forward higher requirements for drilling speed increase. The downhole power drilling tools are mainly screw drilling tools. Conventional screw drill tool stator bushing has poor heat dissipation, which is prone to thermal hysteresis failure, shortening drilling tool life, and is not suitable for high temperature and high pressure environment of deep shale gas wells. Equal wall thickness screw drilling tools and hydrogenated nitrile rubber have better high temperature resistance. Therefore, based on the thermal aging experiment and constitutive model of the rubber changes the displacement of the inner cavity of the stator bushing and the difference between the front and the back is up to 21.6%. The increase of the interference and eccentricity between rotor and motor leads to the increase of the maximum von Mises stress of the stator bushing and the thermal hysteresis temperature. The influence of the interference is greater than the influence of the eccentricity so that the interference should be given priority in the design. This paper provides a theoretical reference for the design and optimization of equal wall thickness bushing of positive displacement motor.

Bridge Plug Drillouts Cleaning Practices—An Overview

Horizontal fracture-simulated completions remain the most reliable method of producing hydrocarbons from shale formations. The vast majority of unconventional wells are completed using the “Plug and Perf” method. This method involves using either a coiled tubing (CT) with a positive displacement motor or a jointed pipe to mill out composite plugs after fracturing operations are completed. An estimated average of 120,000 composite plugs is installed in the US alone each year. Bridge plug drillouts from milling operations tend to accumulate in horizontal wells and can cause stuck pipe incidents and loss of well control. Efficient removal of composite plugs’ debris is crucial in achieving operational efficacies and full production potential. This paper provides an overview of the various bridge plug drillouts cleaning practices adopted in horizontal wells. It discusses several case histories, showcasing how operators solved cleanout challenges. Developed mechanistic models to better understand hole cleaning are also reviewed. As more unconventional wells are being set at more extensive depths, an economical and optimized coiled tubing process becomes increasingly important. This paper focuses on delivering a more conclusive set of recommendations to increase efficiency and improve current composite plug coiled tubing cleaning-milling practices, increase operational efficiency and reduce cost.

External high-pressure forming of metal spiral tube of equal wall thickness

Positive displacement motors are widely used underground power tools in oil and gas extraction. In order to solve the problems of the short life of the conventional positive displacement motor and the difficulty of machining the constant wall positive displacement motor, this paper proposes a metal bush stator. Based on theoretical analysis and tensile experiment of 304 stainless steel, a finite element model of an external high-pressure forming equal-wall-thickness metal spiral tube was established. The finite element method is used to study the external high pressure forming spiral tube with equal wall thickness. According to the results of the numerical simulation, we choose the tube blank with the inner diameter of 88 mm×the wall thickness of 3 mm for the experiment of external high pressure forming spiral tube. The result of the experiment is that the inner and outer surfaces of the metal spiral tube are smooth, and the spiral tube has no wrinkles or cracks. The maximum gap between the spiral tube and the mold is 0.12 mm, and the inner surface of the spiral tube is close to the mold. The maximum gap are at the transition of convex arc and concave arc. The minimum wall thickness and the maximum wall thickness of the spiral tube are 2.6 mm and 3.205 mm, respectively. The quality of the spiral tube is better when the inner circumference length of the tube (D2)/the contour line circumference (D1) of the mold is 0.974. The experimental results are in good agreement with the numerical simulation results. We have designed an assembled mold, which can be removed smoothly after the experiment. The research results of this paper have important engineering significance for improving the working performance of positive displacement motors.

Optimization and application study on targeted formation ROP enhancement with impact drilling modes based on clustering characteristics of logging

Rate of penetration (ROP) is affected by many factors (i.e. rock properties, drilling parameters), and the increase of ROP is required to meet the needs of modern drilling operations. This paper presents a methodology to increase ROP by developing targeted impact drilling plans according to classify rock mechanic parameters of the different formations. In this paper, rock mechanic parameters are calculated based on well logging data, and the results are clustered according to unsupervised clustering algorithm. Then, the clustering data are used as the material parameters for numerical simulation, and the rock-breaking performance of polycrystalline diamond compact (PDC) cutter in different formations under determined impact load and, cutting velocity is discussed as well as the coupling of these two factors. It is shown that the crushing volume of the rock clustering from upper softer formations can be significantly increased by coupling impact load and higher cutting velocity while maintaining the lower specific energy consumption. In the cluster rock of harder formations which needs maximum mechanical energy to break, impact load can greatly reduce its specific energy consumption. However, after increasing the cutting velocity, the specific energy increases greatly while the rock crushing volume increases insignificantly, which is not expected in the drilling. According to simulation results, the paper developed two ROP enhancement modes, using impact drilling mode (Drilling Pipe+ Axial Impact Hammer+ Bit) in well interval of harder volcanic rock formations drilling while high-speed rotary impact mode (Drilling Pipe+ Positive Displacement Motor+ Axial Impact Hammer+ Bit) drills the well interval of upper softer formations. The feasibility of these modes has been verified by field experiments. The figures show that compared with offset well which drilled by positive displacement motor (PDM), high-speed rotary impact drilling increases ROP by 48.44% on average in three trips in the well interval of upper softer formations. Meanwhile, conventional impact drilling mode has the strongest ROP improving ability in the well interval of harder volcanic rock formations, reaching 113.45% in the fourth trip, and also has the advantage of saving PDM rental costs.

Elastic-plastic fracture analysis of external thread of drive shaft shell of a positive displacement motor

For a positive displacement motor (PDM), the threaded joint connecting drive shaft shell (DSS) and universal shaft shell that is close to the bit is inclined to fracture. In this paper, elastic-plastic fracture performance of the threaded connection is simulated under both make-up torque and bending moment. Firstly, an FE model, which includes a cracked external thread of the DSS and an engaging internal thread of the universal shaft shell, is established and validated. Secondly, influences of both plastic deformation and the helix angle on fracture properties of the cracked thread are evaluated quantitatively. Meanwhile interactions between two cracks are also discussed. Finally, under the two kinds of loading conditions, i.e. loaded by pre-load only and loaded by both pre-load and bending moment, explicit relationships between characteristic J-integrals and the crack depth are obtained for the DSS.