Rock Drilling Research Articles

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.

Assessment of rock drillability by the method of analytic hierarchy process combined with fuzzy comprehensive evaluation

Assessment of rock drillability by the method of analytic hierarchy process combined with fuzzy comprehensive evaluation

Determination of Abrasiveness in Copper-Gold Sulfide Ores: A Contribution to the Geometallurgical Model of the Sossego Deposit

The geological context of this study is established in the iron oxide-copper-gold (IOCG) deposit of Sossego (Canaã dos Carajás, Brazil), where hydrothermal alterations in shear zones concentrated the metals of interest and added new characteristics to the metavolcanic-sedimentary and granite rocks. The mineral transformation of rocks by hypersaline fluids enriched in metals and silica also modifies some metallurgical properties, such as abrasiveness. Special bench tests on rock drill cores are used in mapping the abrasiveness of rocks, with the Bond abrasion test being more commonly used in the mining industry, but it has a restrictive sampling protocol and mass requirement for geometallurgical studies. As a counterpoint, the test of the Laboratoire Central des Ponts et Chaussées/Central Laboratory of Bridges and Roads (LCPC) requires a smaller amount of fine material and a finer granulometric range. The study on the use of LCPC was implemented in 40 samples, using Bond Ai as a reference. The results showed a strong correlation between both methodologies (R2 = 95%), validating the use of LCPC to quantify abrasiveness in the Sossego mine. It was also possible to classify the most abrasive lithologies.

Investigation of the rock drilling performance of rotary core drilling

Investigation of the rock drilling performance of rotary core drilling

Measurement and Analysis of Downhole Drill String Vibration Signal

Downhole drill string vibration data can provide an effective reference for research drill string vibration during drilling. In this paper, the research group used a storage-type downhole vibration measurement equipment equipped with an orthogonal, three-axis accelerometer to measure and collect drill string vibration signals during drilling in an oil well. Based on the installation characteristics of the sensor, the relationship between the acceleration measurement value of the sensor and the center acceleration value of the drill string is obtained. Then the time-domain signals representative of the vibration in igneous rock drilling is analyzed. It can be found that the occurrence of stick-slip vibration can be judged by the regular wave packets in the time-domain signal, while the time-domain signal of whirl is disorderly. The main frequency of stick-slip vibration in the low-frequency band is 0.1221 Hz and the period of stick-slip vibration is very close to 10 s through Fast Fourier (FFT) and Short-time Fourier transform (DTFT) methods. In the process of whirling, two frequencies, respectively, 0.05341 Hz and 155.5 Hz, play a major role. The frequency 0.05341 Hz is very close to the reciprocal of the period of 20 s when the peak energy spectrum density appears, indicating that the occurrence of whirl is very likely to be related to the natural frequency of the drilling tool. Through further time-frequency analysis, it also can be found that the occurrence of whirl and stick-slip is greatly related to the use of torsional impactors and jars.

A Study of The Design Method and Similitude for A Small-Scale Test Drilling Rig (Part 1): An Application of The Geometrically Distorted Scaled Modeling Method

Drillstrings often vibrate severely and tend to twist off during hard rock drilling. Therefore, dynamic testing is crucial in the design of drilling systems. Designers tend to employ the most powerful analytical tools, using the most elaborate electronic computers, however, actual testing is required to the designed system function optimally. In cases of enormous drilling systems, complex dynamic tests are often performed on a smaller-scale replica of the system, referred to as the model, which is more convenient, cost-effective, and time-effective. This study, therefore, describes the establishment of similar conditions among structural systems, with the main objective of studying the similitude theory’s applicability in establishing the necessary similar conditions for designing scaled-down models to predict the drillstring’s vibration behavior. The scaling laws for all the relevant parameters regarding the scaled drillstring model, as well as the full-size drillstring system, were derived from the respective equations of motion. The scaling factors for all relevant parameters are determined using the theory of dimensional analysis. In addition, the geometry distorted similitude theory is revisited and employed to overcome the physical limitation and develop the necessary similar conditions for dynamic testing of the scaled drillstring. Meanwhile, the similitude relationship between the prototype and the model was validated with a case study using lumped segments bond graph modeling and simulation software.

Design of a New Type of Torsional Impactor and Analysis of Its Impact Performance

In view of the stick-slip phenomenon in deep and hard rock drilling, a new type of torsional impactor that can provide torsional impact vibration was designed. According to the working principle and structural characteristics of the designed torsional impactor, this paper theoretically analyzes the influences of different structural parameters and motion parameters on the impact frequency, impact force, and impact torque of the torsional impactor. The results show that the impact frequency f is directly proportional to the rotational speed VZ of the transmission shaft and the installed number n of torsional impact generating devices. Additionally, the impact force F is directly proportional to sine value of the impact angle α (i.e., sinα), impact hammer mass m, impact hammer rotation speed VZ (i.e., transmission shaft rotation speed), and impact hammer rotation radius r and is inversely proportional to action time Δt of the impact hammer and impact anvil. Furthermore, the impact torque M is directly proportional to the impact force F and rotary radius r of the impact hammer. This article lays a foundation for further theoretical and experimental research of torsional impactors and provides a reference for the design and testing of torsional impactors.

One-Dimensional Convolutional Neural Network for Drill Bit Failure Detection in Rotary Percussion Drilling

Drill bit failure is a prominent concern in the drilling process of any mine, as it can lead to increased mining costs. Over the years, the detection of drill bit failure has been based on the operator’s skills and experience, which are subjective and susceptible to errors. To enhance the efficiency of mining operations, it is necessary to implement applications of artificial intelligence to produce a superior method for drill bit monitoring. This research proposes a new and reliable method to detect drill bit failure in rotary percussion drills using deep learning: a one-dimensional convolutional neural network (1D CNN) with time-acceleration as input data. 18 m3 of granite rock were drilled horizontally using a rock drill and intact tungsten carbide drill bits. The time acceleration of drill vibrations was measured using acceleration sensors mounted on the guide cell of the rock drill. The drill bit failure detection model was evaluated on five drilling conditions: normal, defective, abrasion, high pressure, and misdirection. The model achieved a classification accuracy of 88.7%. The proposed model was compared to three state-of-the-art (SOTA) deep learning neural networks. The model outperformed SOTA methods in terms of classification accuracy. Our method provides an automatic and reliable way to detect drill bit failure in rotary percussion drills.

Predictive modeling of drilling rate index using machine learning approaches: LSTM, simple RNN, and RFA

Drilling rate index (DRI) is a fundamental parameter in the investigation of rock drillability, as drillability is considered one of the main problems in rock engineering. Several researchers have continuously tried to analyze and correlate rock DRI, but the problem remains unchanged. This study elucidates the machine learning approaches, namely long short term memory (LSTM), simple recurrent neural network (RNN) and random forest algorithm (RFA) to predict DRI of rocks using multivariate inputs, that is, uniaxial compressive strength in MPa; Brazilian tensile strength (BTS) in MPa; brittleness value (S20); Sievers’ J value (S j); modulus ratio (MR); shore hardness (SH), porosity (n) in %; shimazeks F abrasitivity in N/mm; and equivalent quartz content in %. For all proposed methods, the original dataset was divided into 70% for training and the remaining 30% for testing. Next, the performance indices, such as correlation coefficient (R 2), root mean square error (RMSE), variance accounts for (VAF) and a-20 index of each proposed method were determined to examine the accuracy of the predicted data. In this study, according to the results of LSTM, simple RNN and RFA methods, the LSTM revealed the best prediction output for DRI with the strongest R 2, the lowest RMSE, the largest VAF and an appropriate a-20 index values as 0.999, 0.13416, 0.997, and 0.999 in the training stage and 0.998, 0.19479, 0.996, and 0.997 in the testing stage, respectively. Therefore, LSTM is an applicable machine learning approach that can be applied to accurately predict the DRI.

Fabrication of diamond enhanced WC-Ni composites by spark plasma sintering

Wear resistance of the rock drill bit is one of the important factors affecting drilling efficiency and exploration cost. Hence, the development of tool materials with high wear resistance has been widely concerned by researchers. The composites of cemented carbides and Ti-coated diamond (Ti/Dia) were successfully prepared by spark plasma sintering with excellent wear resistance. The characterization of microstructure and phase composition revealed that diamond particles distributed homogeneously without obviously graphitization. With 2–6 wt% Ti/Dia, the relative density, hardness and flexural strength of the composites were all improved. However, with the further increase in Ti/Dia content, the relative density and flexural strength sharply decreased. The composites with 2 wt% Ti/Dia shown the best wear resistance and the wear rate was reduced by 50 times compared with that of the sample without diamond addition. The diamond plays an important role in the rock cutting and grinding for the sample with 2 wt% Ti/Dia. However, for the samples with 18 wt% Ti/Dia, the cutting edge is easy to fracture and the diamond is more likely to pull-out whole because of the weak retention ability of the matrix to diamond.

Drillability characteristics of sandstone with different pores under simulated bottom hole conditions

Rock drillability has an important application value in oil and gas well engineering. Accurate evaluation of rock drillability characteristics is the theoretical basis of improving the rate of penetration (ROP) in the drilling process of the deep well. Up to date, few scholars have studied the degree of rock break difficulty according to the rock’s pore structure characteristics. In order to study the influence of pore structure characteristics on sandstone drillability under the condition of the bottom hole and realize the accurate prediction of sandstone drillability. Sandstones with different pore structures were collected as the research object. The pore structure characteristics of the collected sandstone were studied by casting thin section identification. The porosity, permeability, acoustic wave, and Richter hardness of sandstone with different pore structures were tested, and the sandstone drillability experiment was carried out under simulated bottom hole conditions. The relationship between the characteristics of pore structure and drillability was analyzed by statistical method. The experiment results show that sandstone’s pore structure characteristics have an important effect on the drillability of sandstone. The porosity, permeability, and acoustic wave of sandstone have a very high correlation with the Richter hardness. The drillability of sandstone decreases exponentially with the increase of porosity and permeability. With the increase of borehole pressure, sandstone’s drillability with different pore structures generally increases exponentially. When the porosity is less than 0.19, the drillability of rock decreases gradually with the increase of porosity. When the porosity is more than 0.19, the drillability of rock decreases significantly under different borehole pressures. The characteristics of pore structure are an important factor affecting the drillability of rock, which should be paid more attention to by related scholars. The study is of great significance for revealing the mechanism of rock breaking, objectively evaluating the characteristics of drillability, and establishing the prediction model of drillability.

Improving drilling speed and borehole quality in ultra-deep complex formations through rock mechanics research

Halahatang oilfield in Tarim Basin is a typical ultra deep fractured vuggy carbonate reservoir, which is the main production area of crude oil in Tarim Basin. The wellbore instability is serious in Triassic and lower strata (the borehole enlargement rate is 22% - 31%). Due to the complex rock characteristics, the drilling cycle for single well is long (124 days on average), and it is difficult to speed up. Based on the log interpretation curves, the calculation methods of pore pressure, collapse pressure and fracture pressure profiles established, and the spatial distribution characteristics of three pressures in this area were analysed; The rock drillability, rock hardness, compressive strength and abrasiveness of the roller bit and PDC bit single well measured by laboratory tests. Based on the statistical regression method, the relationship between the above drilling rock mechanical parameters and logging acoustic time difference and the formation drillability profile single were studied. The research results guide the drilling design optimization and operation of 15 wells in Ha 8 and Ha 12 blocks, The average drilling cycle is reduced by 21% (from 124 days to 98 days), and the hole enlargement rate is reduced from 24% to less than 10%.

Modeling and simulation of the effect of rock grain sizes on vibration characteristics when rock drilling

A numerical simulation method and an experimental method were employed to investigate the relationships between the mineral particle sizes and spectral characteristics of the sound or vibration signals generated during rock drilling processes. Several rock models with different aggregates were generated by means of determining the locations of aggregates randomly. The modal analysis of the rock models was conducted to reveal their vibration characteristics. Simulation results indicated that the smaller the aggregate size, the larger the high-frequency composition of sound and vibration. Several drilling experiments were performed on the rock specimens of different aggregate sizes. By using an indoor signal acquisition and analysis system, data from the sound waves and vibrations were collected, and characteristic signals were extracted. Moreover, the spectral characteristics of the sounds and vibrations of different aggregate sizes were identified. The experiment results are consistent with the conclusion of the simulation. The study provides a possibility for developing a method to evaluate the rock structure information collected from drilling vibration or sound signals for a fine exploration of geological surveys.

Petrophysical Property Modifications by Alteration in a Volcanic Sequence at IODP Site U1513, Naturaliste Plateau

AbstractPetrophysical properties of volcanic rocks are controlled by lithology and subsequent modification by alteration processes. Investigating the linkages, using a range of different techniques, are important to establish how petrophysical properties can inform about the alteration state of volcanic rocks. Here, we compile petrophysical data and correlate these with geochemical and mineralogical analyses acquired from a volcanic sequence on the Naturaliste Plateau, offshore southwest Australia (International Ocean Discovery Program Site U1513). The sequence consists of alternating basalt lava flows and volcaniclastic deposits, intruded by multiple dolerite dikes. Variable alteration intensities from fresh‐slight to strong are quantified using Chemical Index of Alteration. Intervals of slightly altered dikes exhibit low porosity and high values of bulk density, P‐wave velocity, and thermal conductivity. The increase of alteration intensity corresponds to decreases in bulk density to ∼2 g/cm3, P‐wave velocity to ∼2,000 m/s, thermal conductivity to ∼1.2 W/(m·K) and an increase in porosity up to 50%. Natural Gamma Ray and magnetic susceptibility vary downhole with rock composition and at lithologic boundaries. The distinct variations exhibit a good correlation with primary lithologic characteristics and secondary mineralogical and textural changes attributed to alteration processes. We provide synthesis models of petrophysical variation with alteration intensity. Although differences in primary lithology and alteration type introduce limitations and uncertainties, there is a reasonable applicability of our results to rapidly characterize the alteration intensity and volcanic stratigraphy in volcanic sequences and to calibrate wireline log‐based determinations. This will help others to develop strategies for exploration, drilling, and geophysical research of volcanic rocks.

Study on the law of drillability of stratum in ShunBei #1 block

ShunBei 1 block is located in the northwest of Shuntuoguole low uplift in the north of Tarim Basin, with a block area of 4453km2. The reservoirs are mainly distributed in the Middle Ordovician carbonate rocks, and the burial depth is generally more than 7500m. A large number of strike-slip fault zones are developed in ShunBei #1 block, which results in low drilling rate, difficult drilling and poor formation drillability. In this paper, through rock drillability experiment and acoustic test experiment, the experimental analysis of the core of the study block is carried out, and the fitting relation formula of drillability level value is determined by comparing a variety of fitting methods. Based on the calculation model of drillability class value, this paper calculates the drillability class value of Well X in No. V fault zone of ShunBei #1 block, and establishes the drillability profile of Well X. Through the analysis of the drillability profile and drilling conditions, it is believed that with the increase of formation depth, the drillability class value of formation increases, and the drillability of formation becomes worse. Because the fluctuation of the strata drillability class value in the fault zone is small, but the strata drillability class value is large. The drillability class value of induced fracture zone strata changes dramatically, showing obvious sawtooth shape, but in general, the value of drillability class value is consistent with that of conventional strata. The strata drillability level of sliding crushing zone increases obviously, but its fluctuation is small. In addition, the drillability of the strata under different fault types is compared. It is concluded that the drillability class value of the strata controlled by the compression fault zone and the strata controlled by the translation and pull-apart fault zone fluctuates very little, but the drillability class value of the strata controlled by the compression fault zone is larger, and the formation drilling difficulty is greater, and the drillability is worse.

Experimental study on the preparation method of coal-like materials based on similarity of material properties and drilling parameters

Natural coal used in experiments often contains unknown substances which endow it with strong anisotropy and affect the accuracy of experimental results. This paper is aimed at analyzing the single-factor and two-factor-coupling influences on the properties of coal-like materials with different proportions. A coal rock drillability evaluation system was developed based on the principle of Fréchet distance algorithm to evaluate the similarity between drilling simulation experiment data of coal-like materials and natural coal. The results disclose that the cement is of the most notable regulating effect on the material properties. Under the coarse-to-fine ratio of 1:4, the cement content of 20%, the molding pressure of 25 MPa and the pressure holding time of 0.5 h, the coal-like materials are of the optimal mechanical and gas adsorption properties. The fluctuation characteristics of drilling experimental data curve are the most similar to those of natural coal, with the similarity ratio being 0.54.

The process of crack propagation during rotary percussion drilling of hard rocks

Rotary percussion drilling determines the possibility of reducing waste and intrusion of foreign objects into the solution. It reduces drilling costs and increases the processing speed of the resulting product, and also contributes to the high-quality result at the beginning of the drilling string project design. Reducing the number of cracks decreases the amount of rock used and improves the quality of the resulting product. The novelty of the study lies in development and practical application of fibreglass drilling strings that provide reduced energy consumption for drilling and increased elasticity. The authors show that the use of such strings makes possible to shorten the time of field development and increase the yield in difficult geological conditions. Establishment of strings made of polymeric materials and composite structures can significantly reduce the number of cracks in hard rocks. This determines the conditions for the environmental friendliness of the entire production process, the gradual reduction of waste rock usage and increase in the secondary use of oil production materials.

Evaluation of the Diametrical Core Deformation and Discing Analyses for In-Situ Stress Estimation and Application to the 4.9\xa0km Deep Rock Core from the Basel Geothermal Borehole, Switzerland

The in situ state of rock mass stresses is a key design parameter, e.g., for deep engineered geothermal systems. However, knowledge of the stress state at great depths is sparse mostly because of the lack of possible in situ tests in deep boreholes. Among different options, core-based in situ stress estimation may provide valuable stress information though core-based techniques have not yet become a standard. In this study we focus on the Diametrical Core Deformation Analysis (DCDA) technique using monzogranitic to monzonitic rock drill cores from 4.9 km depth of the Basel-1 borehole in Switzerland. With DCDA the maximum and minimum horizontal stress (SHmax and Shmin) directions, and the horizontal differential stress magnitudes (∆S) can be estimated from rock cores extracted from vertical boreholes. Our study has three goals: first, to assess photogrammetric core scanning to conduct DCDA; second, to compare DCDA results with borehole breakout and stress-induced core discing fracture (CDF) data sets; and third, to investigate the impact of rock elastic anisotropy on ∆S. Our study reveals that photogrammetric scanning can be used to extract reliable core diametrical data and CDF traces. Locally aligned core pieces showed similar SHmax orientations, conform to borehole breakout results. However, the variability of core diametrical differences was large for the Basel-1 core pieces, which leads to a large spread of ∆S. Finally, we demonstrate that core elastic anisotropy must be considered, requiring robust estimates of rock elastic moduli, to receive valuable stress information from DCDA analyses.

Study of Effect of Cooling/Lubricating Fluids, Machining Parameters, and Rock Mechanical Properties on Penetration Rate in Rock Drilling Process

In most rock drilling operations, the low rate of penetration (ROP) can be primarily attributed to the presence of the cuttings produced during drilling and the thermal stresses caused by friction at the bit-rock interface, which can be exacerbated with the increasing strength, hardness, and abrasivity of the drilled rock. In order to improve ROP, drill bit lifetime, and cutting power, it is necessary to minimize the process forces due to the mechanical bit-rock interaction and the thermal stresses generated in the drill hole. Any improvement in these areas is extremely important from both the technical and the economic perspectives. This improvement can be achieved by the use of appropriate cooling/lubricating fluids in the drilling process in order to increase ROP, reduce the temperature of the drilling environment, and create a clean drill hole free of cuttings. In this work, a series of laboratory drilling tests are performed to investigate and compare ROP in the drilling of seven samples of hard and soft rock in the presence of six different cooling-lubricating fluids. The drilling tests are performed on the cubic specimens with a laboratory-scale drilling rig at several different rotation speeds and thrust forces. The statistical analyses are performed in order to investigate the relationship between ROP and the mechanical properties of the rock, properties of the fluid, and machining parameters of the drilling rig. These analyses show that under similar conditions in terms of mechanical properties of the rock using Syncool with a concentration of 1:100 and soap water with a concentration of 1:120 instead of pure water leads to the average 31% and 37% increased ROP in granite, 36% and 43% increased ROP in marble, and 47% and 61% increased ROP in travertine, respectively. These results demonstrate the good performance of these cooling/lubricating fluids in increasing ROP.

Modeling drill bit wear mechanisms during rock drilling

Modeling drill bit wear mechanisms during rock drilling