PDC Drill Research Articles

Fracture Mechanism of the Formation with a Natural Flaw Under a Single-Tooth Cutting

The process of a single-tooth cutting formation is taken as the representative to analyze the fracture mechanism of the formation with natural flaws under the PDC drill bit. The modeling of the stress field distribution of the formation under a single tooth is proposed first. Subsequently, the modeling of the stress intensity factor K, T-stress and the initiation angle $$\theta $$ of the flaw under two far-field compressive loads in two cases are presented based on the mode-II fracture. Finally, the results of theoretical calculations and simulations are given and discussed. Based on the analysis undertaken, it can be concluded that the confinement ratio $$\lambda $$ applying on the flaw changes nonlinearly with the variation in $$\alpha +\varphi $$ . The relationship between the dimensionless ratio $$\beta _{{x}}/\beta _{{y}}$$ of T-stress and the rotational polar angle $$\varphi $$ is a parabola with an upward opening. When the direction of the cutting force is consistent with the flaw, the stress intensity factor K and the initiation angle $$\theta $$ at the tip of the flaw reach the maximum. In addition, the angle between the cutting force and the flaw weakens the T-stress and inhibits the crack initiation and propagation of the flaw. The results of numerical simulations show good agreement with theoretical calculations.

Анализ работы алмазных долот при строительстве скважин в сложных условиях

The purpose of the study has been to analyze the operation of diamond drill bits of a PDC type (polycrystalline diamond cutters) in the regions with a complex geological section, and to develop recommendations on optimizing the drill bits. The PDC drill bits are originally designed for soft to medium-hard rocks, thus being ineffective for complex geological sections. As part of the research, the mechanics of the build-up formation on the drill bit cutter and its impact on the rock destruction have been studied. The influence of the pumped drilling mud volume and the pressure differential in the downhole motor on the mechanical drilling speed of the PDC bit has been analyzed. Proposals on improving the geometry and orientation of the tool cutters and optimizing the design of the cutting structure calibratation site and the bit blades have been given; measures on reducing the bottomhole vibrations of the bit during its operation have been suggested. As a result of the study, the mechanism of the build-up formation on the cutter’s working edge and its advance influence on the fracturing in the rock volumetric stratum has been determined. It has been found that the maximum feed of the drilling mud results in the complete absence of the build-up formation and a sharp increase in the mechanical speed of drilling. The study has shown the high performance of high-torque downhole screw motors and defined the optimum range of the pressure differential for the PDC drill bits as a function of the drilling mud flow rate. The authors have suggested the ways to reduce the vibration and stabilize the PDC drill bits by optimizing the structure and geometry of the tool’s cutters and blades, and by using hybrid cutters as auxiliary ones. The conclusion is that the optimization of the PDC drill bits enhances their operation performance under complicated geological-engineering conditions in Eastern Siberia and Yakutia.

Долота PDC со сменными промывочными узлами новой конструкции

Долота PDC со сменными промывочными узлами новой конструкции

Finite-element simulation of PDC drill bit’s operational stress-strain state

Наведено результати скінчено-елементного моделювання напружено-деформованого стану доліт ріжучо-стираючої дії (PDC) під час їхньої експлуатації з метою визначення ділянок долота, де є найбільші напруження і деформації з метою вироблення подальших рекомендацій для удосконалення технології виготовлення долота. Визначення деформацій, які виникають під час експлуатації, має важливе значення, оскільки втрата долотом зовнішнього діаметру є однією із причин виходу з ладу долота. Виконане моделювання роботи долота із суцільним корпусом та із привареними лопатями. Під час скінчено-елементного дослідження засобами AnsysWorkBench (академічна ліцензія) встановлено, що як для суцільних, так і для доліт із привареними лопатями найбільші напруження спостерігаються в момент врізання долота у породу. Для всіх типів доліт ділянками із найбільшими напруженнями є нарізеві ділянки. Для доліт із привареними лопатями такими ділянками є і ділянки зварних швів. При цьому, деформації, що виникають в області зварних швів, є причиною втратою долотом діаметра, що є основним експлуатаційним показником роботи долота. Розглянуто залежність деформацій та напружень у цих ділянках від товщини зварного шва. Таким чином, зроблено висновок про те, що долота із привареними лопатями є більш схильними до втрати діаметра, тобто мають гірші показники експлуатації, що висуває певні вимоги до удосконалення технології виготовлення доліт такого типу. Запропоновано зменшення товщини зварного шва. Виконано скінчено-елементне дослідження експлуатації доліт із зварними швами у 5, 7 і 10 мм. Встановлено, що рівень напружень і деформацій, що виникають під час експлуатації, залежить від товщини шва: зменшення товщини зварного шва викликає зменшення напружень і деформацій.

Study of PDC drill bit crown shape for design optimization: angle of blade inclination aspect

The article studies PDC-type bit operation, in particular, the redistribution of loads on drill bit blades is simulated, depending on “cutter-rock” contact areas, which is determined by a drill bit design. This work aims at PDC bit design optimization, namely to study the effect of the blade angle to the horizontal axis on the torque generated by the bit. The study is based on the Voitanovich and Kuru’s model of Voitanovich and Kuru’s and has its core at determining the balance of forces acting on a single cutter. The scientific novelty of the work is that two areas of contact are considered for each cutter – the on the front and side surfaces. Also, it is hypothesized that the force of the reaction of the pore is directed towards the placement of heterogeneities of the rock. This approach makes it possible to consider the fluctuations of the bits due to the instability of the cutting forces, which in turn are caused by the instability of the properties of the fractured rocks (first of all, their structural heterogeneity).The spatial shape of the PDC cutter crown was studied, characterized primarily by the shape of its upper part, which in turn is characterized by the angle of inclination of the cutting part of the cutter. Contact areas for each cutter, the volume of the destroyed rock depending on the location of the cutter, as well as the loading for a single cutter, the torque for the whole blade and the bit were simulated in the work. The angles of inclination of the blade to the horizontal axis at which the minimum / maximum torques are observed are determined.Changing the inclination of the cutting part causes the redistribution of the destroyed rock volumes. This section dealt with worn-out chisels, and the load was distributed in proportion to the volume of the destroyed rock. It was found that increasing the angle of the blade causes an increase in the total torque for the bit. A method is proposed that allows optimization of the PDC bit design. An increase in the total twisting angle and the total deflection is observed for the cutters, which are most separated from the borehole face.

Development of the New Type Conical Teeth of PDC Drill Bit

The work elements of PDC drill bits are cylindrical polycrystalline diamond composite sheet and the cutting teeth of such shape can only cut the rock with the caster angle rake. In the process of drilling hard rocks, due to the large shear resistance and discontinuous cutting and rock breaking process, the rotation torque and torque ripple of drill bits are relatively large, resulting in low rock breaking efficiency and serious impact damage of composite sheet (Wilmot, 1998). In order to improve the ability of PDC drill bits to drill hard rock, a kind of cone PDC tooth is designed, which can plough and cut rocks with top rake, with low rock breaking resistance. It can reduce the rotation torque and torque ripple of drill bits, and improve the rock breaking efficiency and impact resistance of PDC drill bits.

Моделирование резания горной породы резцами долот типа pdc методом конечных элементов

Моделирование резания горной породы резцами долот типа pdc методом конечных элементов

Stress distribution analysis of PDC drill bits by computer modeling

Stress distribution analysis of PDC drill bits by computer modeling

Morphology of powders of tungsten carbide used in wear-resistant coatings and deposition on the PDC drill bits

Modern drill bits have high abrasive wear in the area of contact with the rock and removed sludge. Currently, these bits have a protective layer on the bit body, which consists of a metal matrix with inclusions of carbide particles. The research matrix of this coating and the wear-resistant particles is a prerequisite in the design and production of drill bits. In this work, complex investigation was made for various carbide powders of the grades Relit (tungsten carbide produced by Ltd “ROSNAMIS”) which are used as wear-resistant particles in the coating of the drill bit body. The morphology and phase composition of the chosen powders as well as the influence of a particle shape on prospects of their application in wear-resistance coating presented in this work.

Development and Application of a Cutting - Abrasive Impregnated Diamond Bit

Igneous rocks of Junggar Basin are hard, strong abrasive and poor drillability. ROP is low in drilling these rocks, and drilling cycle is long, which seriously affect the process of exploration and development in the Carboniferous reservoir. Considering the igneous rock formation characteristics and the drilling problems, using PDC impregnated diamond high strength, super abrasion as the main rock breaking device, a new type of cutting and grinding of diamond impregnated bit was developed. This bit has the following characteristics: Compound cutting structure with blades and cylindrical Impregnated cutters; big nozzle in the center + deep radiation water slot hydraulic structures; Natural diamond and TSP lengthened gauge design; Selection of 40/50 mesh diamond grit, mix two kinds of inserts with diamond concentration 70%.The bit has the combination of impregnated bit and PDC drill bit technical advantages, which improve the bit adaptability to the formations. Hassan3 Carboniferous igneous formations field test shows that: average ROP is 0.71m / h, single bit footage is 86.5m, which increased by about 20% and 302% respectively compared with high efficient three-roller bits. The success usage of this bit in Hassan 3 provide an effective means for high quality fast drilling in Junggar Basin igneous rock formation.

Microwave PDC Drill Bit

On the rotary drilling system, the technologies for fracturing and cutting hard rock are mainly mechanical rock breaking methods by use of improving bottomhole water horse power and bit energy, and the working life and rock breaking efficiency have much room for improvement. Microwave crag broken is a thermal assisted rock breaking method which could melt rocks. Microwave assisted rock breaking method will not bring new impact, wear and tear, instead, the microwave pretreatment on the rock reduces the difficulty of breaking rock and prolongs the service life of the drill bit. Under the combined action of microwave heat and mechanical energy of PDC bit, the rock breaking efficiency is improved greatly, and the drilling cost is reduced significantly.

A swirling jet from a nozzle with tangential inlets and its characteristics in breaking-up rocks

In order to apply a swirling jet to a PDC drill bit, the nozzle performance influenced by nozzle inlet geometric parameters and rock breaking tests under submerged conditions were studied. Numerical simulation was used to study the influence of the nozzle structure on the swirling intensity and nozzle discharge coefficient. Simulation results indicate that spreading angle of the swirling jet is greater than that of the non-swirling jet, and the swirling intensity of the jet is strongly influenced by the length of the nozzle body but weakly by the number of tangential inlets. Rock breaking tests were conducted to evaluate the performance of the swirling jet. It is found that the swirling jet shows a lower threshold pressure to break the rock samples and could break rock more efficiently compared with the non-swirling jet.

Collision-Free Trajectory Generation for Waterway Surfaces of a PDC Drill Bit

After describing geometric characteristics of a PDC drill bit’s waterway surfaces, an approach for collision-free trajectory generation are proposed. The trajectory is planned by an iso-parametric method firstly, while the tool orientations are determined by visibility cones, which are the bounded regions between the opposite surfaces of neighboring blade wing pairs. Tool orientations are produced by calculations of critical points and interpolations between them. Furthermore, the criterion of whether tool orientations pass through the constraint surface and the linear interpolation formula of tool orientations are given. The research has created conditions for the success machining of PDC drill bits, and related machining enterprises of impellers and propellers will also be benefited.

Development of PDC Drill Bits for MWD Directional Drilling in Underground Coal Mine

Design of high quality PDC drill bits is necessary to perform MWD directional drilling for underground coal mine. Relatively deepened analysis was carried out here from the structural parameters to the type selection of cutting teeth of PDC drill bits. φ96mm matrix-body PDC drill bit for directional drilling was developed followed by field tests, for which four branch holes were dilled. The average drilling speed was 4.12m/h and the total drilling footage was 1001.6m. The experimental results indicate that the deflecting effect as well as the service life of the developed drill bit can completely meet the application requirements.

Experimental Research on Erosion and Corrosion of WC-Base Matrix Materials for Drill Bits under Impingement of Drilling Muds

In oil drilling the failures of PDC drill bits are exhibited as erosive wear, dropping and breaking of cutters, so the erosion and corrosion resistance of the matrix is one of the key factors affecting the quality of PDC bits. In order to understand the degradation mechanism of matrix materials for drill bits, a kind of loop recirculation rig is adopted to measure total mass loss TML, mass loss E by pure mechanical erosion, and then through calculation the mass loss C+S by corrosion and synergy is obtained. The tested and calculated results show that TML of matrix materials is not only caused by pure mechanical erosion, but also by corrosion and their synergy of mechanical erosion and corrosion. In the discussed scope of this paper the volume loss produced by corrosion and synergy is 24.16% of the total volume loss (TVL) at most, which tells us that the corrosion resistance of matrix materials should be considered carefully besides their erosive resistance in the design and selection of PDC drill bits used in the corrosive drilling muds.

High Penetration Rates and Extended Bit Life Through Revolutionary Hydraulic and Mechanical Design in PDC Drill Bit Development

Summary PDC drill bit developments have been made to achieve higher penetration rates and longer life, involving a compromise between open, light set, bits for speed, and heavy set ones for durability. Developments are described which provided the benefits of both in a revolutionary hydraulic and mechanical design. The hydraulic design causes mud to flow first towards the bit center and then outwards. It was extensively flow tested using high-speed photography to ensure that bit balling was prevented. It includes features to address bit whirl which were demonstrated in full scale laboratory testing to reduce the bit's vibration level. The mechanical design maximizes open-face volume, known to benefit penetration rate, by using very high blades. However, the heights attainable can be limited by the bit body's mechanical strength. Steel was chosen to maximize blade strength and was coated with a newly developed hardfacing to improve erosion resistance. A program of fatigue testing assured adequate strength.

An experimental study of sliding friction between PDC drill cutters and rocks : E. Kuru & A. K. Wojtanowicz, International Journal of Rock Mechanics & Mining Sciences, 32(3), 1995, pp 277–283

An experimental study of sliding friction between PDC drill cutters and rocks : E. Kuru & A. K. Wojtanowicz, International Journal of Rock Mechanics & Mining Sciences, 32(3), 1995, pp 277–283

An experimental study of sliding friction between PDC drill cutters and rocks

A medium-scale laboratory instrument was constructed and successfully used to measure friction between the sliding surface of a rock and polycrystalline diamond compact cutter