Comparative analysis of roller drill bit performance

Currently, roller bits are widely used in rock drilling, which are devices with rotating rollers armed with teeth. There are various approaches in assessing the effectiveness of rock destruction by a roller drilling tool, which can be conditionally divided into structural and technological ones. In addition, all the efficiency factors of the roller bit are related to the correspondence of its characteristics and the drilling process to the properties of the rock it destroys. The article analyzes the operating conditions of the roller bit during drilling of rocks of various hardness. On the example of operation of a two-screw drill bit, the process of power interaction of the toothed weapon with rock is considered depending on various factors, such as the shape and pitch of the teeth, angle of inclination, sharpness of the tooth and others. It is shown that kinematic characteristics of interaction of toothed armament with drilled rock have a significant influence on efficiency of process of face destruction. Keywords: drill bit; drilling tool; destruction; drilling; roller cutter; rock.

Study on Failure Characteristics and Rock Burst Mechanism of Roadway Roof under Cyclic Dynamic Load

Rock burst is a catastrophic phenomenon that often occurs in underground rock mass engineering. In order to reveal the essence of rock burst of a hard roof in the process of roadway excavation, the particle discrete element method is used to establish a roadway model and simulate the disturbance of harmonic dynamic load based on the analysis of a rock burst accident in a deep mine. The crack field, stress field, displacement field, and kinetic energy of roadway surrounding rock disturbed by cyclic dynamic load were analyzed, and the disaster mechanism of roadway impacting roof instability was discussed. The results show that, compared with the roadway support structure under static load that can give full play to its control function of surrounding rock, the roadway surrounding rock will collapse and lose stability in a large area under the roof cyclic dynamic load, and the ordinary supporting structure cannot give full play to its control function of surrounding rock, resulting in the surrounding rock destruction and supporting structure failure. In addition, the essence of rock burst in a hard thick roof is due to the instantaneous superposition of static stress and dynamic load, leading to the instantaneous instability and collapse of roadway roof in a large area. The research is of great significance to further understand the deformation and failure mechanism of roadway surrounding rock under strong impact load, to guide the safe production and prevent the occurrence of rock burst hazard in underground rock mass engineering.

Drilling Efficiently, Durably and Consistently Through Cherts and Conglomerates with PDC Bits is Possible

Drilling into harsh environment with heterogeneous formations including chert or conglomerate is usually a boundary that can't be crossed with standard PDC bit technology. This paper will show how an innovative PDC cutter shape combined with a novel 3D approach of cutting structure design have withstood this challenge and successfully replaced 16-in. traditional roller cone application in United Arab Emirates by the latest PDC technology delivering an average 35% improvement on Rate Of Penetration (ROP) while continuously drilling to Total Depth (TD) on each section. When drilling chert or conglomerate type of formation with a PDC drill bit, uneven load per cutters is detrimental to their integrity and results in short runs or brutal stop in the drilling operation triggering a trip for drill bit change. The new technology shown in this paper includes a unique hybrid combination of cutter shapes with a design arrangement of the cutting structure to allow for the pre-fracturing of any hard formation heterogeneity by 3D shaped cutters while standard cutters ensure a high level of cutting efficiency through their shearing action. This innovative concept has been intensively tested in the lab through single cutter and full bit scale drilling testing. In addition, in-house 3D bit simulation software has been used to optimize the cutting structure and assure performance within a wide range of drilling scenarios. Based on these simulations, an optimized design was manufactured for 16-in. directional applications usually tackled by roller cone drill bits and known for having heterogeneous cherty formations to drill throughout the end of the 5,000 ft section. Simulation results helped to validate the unique shaped cutters placement on the cutting structure to maximize the pre-fracturing effect. This design was run on Rotary Steerable System (RSS) and Positive Displacement Motor (PDM) assemblies and successfully drilled 5 wells in a challenging field of the United Arab Emirates offshore operations. 100% successful rate to reach TD in one run was achieved while increasing drastically the average ROP of the section by at least 35%. Moreover, the unique design configuration allowed to better control the directional behavior of the drill string, which resulted in a significant reduction in the overall cost per foot. A new boundary has been breached in several wells of a complex 16-in. chert and conglomerate application in the United Arab Emirates thanks to a years-long effort combining an innovative cutter technology, an optimized bit design process including a state-of-the-art 3D simulation software with lab and field experimental testing campaigns. By looking at the micro level structure of the rock destruction mechanism, a huge improvement has been obtained at the macro level of drilling operation economics.

The influence of flushing fluids rheological properties on rock breaking efficiency when drilling wells by pellet impact drilling method

Introduction. Pellet impact drilling method which is basically the destruction of rocks by blows of pellets, has been studied by many researchers. Despite this, the rheological properties of the drilling fluid used in pellet impact drilling have not been investigated yet. All bench and field tests were carried out using service water. The use of a drilling fluid with a higher viscosity than water has the potential to expand the field of application of pellet impact drilling. Therefore, it becomes urgent to study the effectiveness of destruction of rocks when using flushing fluids with different rheological parameters. Objective of this research is to investigate the efficiency of rock destruction in the process of drilling wells using the pellet impact drilling method at various rheological parameters of the drilling fluid. Methods of research. A scaled laboratory bench was used in the research. The bench was a closed system of circulation of the drilling fluid (drilling mud). The solution was prepared separately on a high-speed mixer. The main part of the bench was a scaled pellet drill bit located in a simulated well. After the experiment, the destructed rock volume and the rheological parameters of the flushing fluid were measured. A series of experiments was carried out with a gradual increase in the viscosity of the flushing fluid. A biopolymer (xanthan gum) in various concentrations was used to thicken the flushing fluid. Drilling fluid rheological parameters were measured using an eight-speed rotary viscometer and a Marsh funnel. Results. For the first time, a relationship has been established between the efficiency of rock destruction during pellet impact drilling and the rheological parameters of the drilling fluid used. It was found that with an increase in the concentration of biopolymer and an increase in viscosity, at first, there was a significant increase in the volume of drilled rock per unit time, and with a further increase in concentration, a gradual decrease occurs. Conclusions. The results obtained expand the field of application of pellet impact drilling. The reliability of predicting the drilling speed is improved depending on changes in the properties of the drilling fluid. Based on the results, recommendations were made for the selection of the optimal parameters of the drilling fluid, depending on the drilling conditions.

Physical and mathematical model of rock destruction by a milling machine cutter

As a result of the analysis of the work on rock destruction by cutters of milling of machines, it was found that the existing developments do not allow us to proceed to the derivation of calculation d dependencies for determining fracture resistance, or can be used only in preliminary calculations of the known by design parameters of milling machines. To eliminate these disadvantages, a combined physical and mathematical model of the process of interaction of a single milling cutter with a spherical tip with the rock has been developed. Consideration of the physical picture of the action of forces and stresses acting from the cutter with spherical tips on the separating rock element in the limiting condition allowed to describe analytically the components of total resistance, which are the mathematical part of the physical and mathematical model of rock destruction by cutters. Analytical dependences for determining the tangential and normal components of fracture resistance of rocks of medium hardness have been obtained. The adequacy of the physical and mathematical model to the physical process of destruction of rocks of different hardness by cutters on a universal stand was tested both in the field and in the laboratory conditions. Technical evaluation of the results of experimental studies confirms the reliability of the developed physical and mathematical model.

Analyzing methods of determining pre-destruction of blast hole vicinity

The level of deformation of the rock massif of a blasted slab must be planned in advance, depending on the required results of blasting. Thus the energy costs of barren rock overfilling as part of preparing for overburden excavation are inefficient. On the contrary, an increase in the blast energy spent on degrading and breaking the ore mass is an efficient measure of preparing for the excavation of mineral wealth. There are currently two methods used to determine the pre-destruction of a blasted rock massif. The first one is based on determining the number of strain waves passing through locations of borehole charges. However, this method fails to determine the preliminary rock destruction level. The second method is based on determining coefficients of the pre-destruction of a rock massif by these strain waves. The merit of this method is that it allows evaluating the quality pattern of the pre-destruction of a rock massif. The procedure of considering the fraction of energy of the strain waves, reflected by the shielding rock mass to the destructive amount of blasting charges and refracted to this destroyed rock, is proposed.

Prospects of Electric Drilling for the Development of Well Construction Technologies

The purpose of this work is to analyze the prospects for efficiency increasing of high-tech wells construction using a drilling complex based on downhole permanent magnet motor. For the first time, the article provides information about new drilling complex. Considered technology could provide a breakthrough in drilling high-tech wells. This technology combines advantages of drill string with electric wire and an ideal downhole motor with a wide rotational speed range, regardless of the type and flow rate of circulating agent. The article provides a brief comparative analysis of electrodrilling implementation results "generation 70s", the composition of new electric drilling complex and its difference from the previous one are considered in details. Complex meets the requirements of high-tech wells construction and allows automating drilling process using ultra-high-speed bi-directional data transmission channel and quickly assessing the parameters of drilling regime and direction of drilling, characteristics of rocks, pressure and temperature distribution along the wellbore. Permanent magnet motor ensures optimum drilling parameters for rock destruction at the bottomhole, regardless of the well profile and the type of circulating agent, including managed pressured drilling. Effectiveness of accidents prevention and mitigation is increased. Authors propose to discuss the prospects of electrodrilling technology using downhole permanent magnet motor, which is currently at TRL-3 level, to assess and specify adopted concept of electrical drilling complex development.

Determination of the Extent of the Rock Destruction Zones around a Gasification Channel on the Basis of Strength Tests of Sandstone and Claystone Samples Heated at High Temperatures up to 1200 °C and Exposed to Water

This article presents the results of laboratory tests regarding the influence of high temperatures on changes in the strength and structural parameters of rocks that are present in the immediate vicinity of a gasification channel. Sandstone and claystone samples were heated at 300 °C, 600 °C, 900 °C and 1200 °C. Additionally, the heated samples were placed in water for 24 h. The results of the laboratory tests were used in the numerical simulation using RS2 software. The main goal of modeling was to determine the extent of the rock destruction zone around the gasification channel for dry and wet rock masses. In the numerical simulations, three widths of the gasification channel and three ranges of high-temperature impact were modeled. On the basis of the obtained results, it was found that the extent of rock destruction, both in the roof and in the floor, is greater by several percent for a wet rock mass. For the first time, this research presents the effect of water on heated rock samples in terms of the underground coal gasification process. The results of laboratory tests and numerical simulations clearly indicate a reduction in strength, deformation and structural parameters for the temperature of 1200 °C.

Influence of bit size on stability bottom drill column balance when drilling a horizontal well

The article raises the question that if you change the bit type, the "critical length" of the lower part of the drill string change too. For the first time, the issue of the stability of the lower part of the drill string when drilling a horizontal section of the wellbore was formulated and solved, taking into account the features of the bit designs (roller bit, wing bit, PDC bit) and the mechanism of rock destruction in well drilling. The research uses the generally accepted provisions of the linear theory of elasticity of materials, the theory of stability of rods and shells. It is assumed that the lower part of the drill string is a heavy elastic rod, experiencing the combined action of the forces of the pipe's own weight and the axial load on the bit, and the twisting moment from the rotor table acting on the pipe string is not taken into account. To find the "critical length" of the lower part of the drill string, simple approximate formulas are obtained that take into account the bit size, drill collar and axial load.

Study on the wear mechanisms and rock destruction of core surface set bit in drilling for solid mineral exploration

In this paper, the authors present some research results of wearing process and rock destruction by diamond grit of core bit depending on drilling regime, rock hardness, diamond grit strength, etc. through the simulation of the interaction effect between diamond grit attached to the core bit and the rock. The relationship of the wear rate and rate of penetration of diamond core bit to the rotation per minute has been tested. On the basis of the research results, the authors have proposed solutions to select the appropriate technology for diamond drilling to improve the efficiency of solid mineral exploration in Vietnam.