Dynamic Rock Properties Research Articles

Determination of Frequency-Dependent Dynamic Properties of Rocks Using the Nonresonance Method

Determination of Frequency-Dependent Dynamic Properties of Rocks Using the Nonresonance Method

Drilling wells taking into account the dynamic properties of rocks

The application of high-frequency vibrations to a drill bit is a promising means of increasing rate of penetration in deep hard formations. The implementation of such drill bit high-frequency vibrations is possible by installing the cavitation hydraulic vibrator in the drill string in front of the rock-cutting tool. Purpose. Evaluation of resonant modes (frequencies of oscillations) for the dynamic interaction of the mud pressure in the drill string and the drill bit longitudinal vibrations in case of contact with the rock being destroyed while drilling using the cavitation hydraulic vibrator; comparative analysis of the effectiveness of using a high-frequency mechanical vibrator and a cavitation hydraulic vibrator in case of drilling in hard rocks. Methodology. The research is based on a comparative analysis of the amplitudes and power spectral density of mud pressure oscillations of the mud and vibration accelerations in the drill bit cross section of drill string. Findings. The results are presented in the form of amplitude spectra and power spectral densities of mud pressure and vibration acceleration, as well as the dependence of the increase in the rate of penetration on the frequency of forced oscillations of the drill bit. Originality. Taking into account the influence of the cavitation hydraulic vibrator on the drill rig ROP made it possible: - to determine the resonant frequencies of pressure oscillations of the mud of the drilling tool, for the effective removal of drilled rock at the point of its contact with the drilling tool, and the longitudinal vibration accelerations of the drilling tool, to speed up rate of penetration during the construction of a well; - to evaluate the effectiveness of using a cavitation hydraulic vibrator in comparison with a high-frequency mechanical vibrator. For the studied modes of operation of the hydraulic vibrator at values of the cavitation parameter  = 0.19, the well rate of penetration increases by 40 % compared to the traditional rotary method and by 26 % compared to the vibratory hammer. For the cavitation operating mode of the hydraulic vibrator  = 0.41, the increase in the rate of penetration is 62 and 37 %, respectively. At the same time, the operating efficiency of the hydraulic vibrator was ensured at the resonant frequencies of the mud pressure with a frequency of 1,580 Hz at  = 0.19 and 1,980 Hz at  = 0.41. Practical value. For a specific design of the cavitation hydraulic vibrator as part of a drill string, by changing the frequency of the drill bit vibration impact on the rock, resonant frequencies are established that ensure the high ROP of the well.

Quantitative investigation of rock dynamic failure using Voronoi-based discontinuous deformation analysis

Dynamic failure widely exists in rock engineering, such as excavation, blasting, and rockburst. However, the quantitative measurement of the dynamic damage process using experimental methods remains a challenge. In this study, a SHPB modeling technique is established based on Voronoi-based DDA to study the damage evolution of Fangshan granite under dynamic loading. The assessment of cracking along the artificial joints among Voronoi sub-blocks is conducted using the modified contact constitutive law. A calibration procedure has been implemented to investigate the rock dynamic properties quantitatively. The dispersion and damping effect can be effectively eliminated by regular discretization in SHPB bars, based on which the dynamic stress equilibrium can be satisfied. To reproduce the loading rate effect of the dynamic compressive strength, which has been observed in the experiment, a modification strategy considering the influence of the rate effect on the strength meso-parameters is proposed. Using this strategy, the peak stresses of the transmitted waves predicted by DDA match well with those obtained from experiments conducted at different loading rates. The simulation results show that more microcracks are generated and the proportion of tensile cracks decreases as the loading rate increases. Furthermore, the dynamic mechanical behavior and fracturing process have also been discussed and compared with the experiments. The results show that the established SHPB system is a powerful tool for quantitative analysis of rock dynamics problems and can handle more complex problems in the future.

Coupled hydro-mechanical simulation in the carbonate reservoir of a giant oil field in southwest Iran

The Asmari reservoir in southwest Iran has been producing oil continuously for over 50 years. However, due to an essential pressure decline, the reservoir is now a potential candidate for injection projects. The geomechanical analysis is essential for a successful injection operation to enhance reservoir production and address possible challenges. An accurate estimation of the injection pressure is necessary to maintain optimal conditions during the injection process and reduce possible risks. In this work, a coupled reservoir-geomechanical model, as well as rock mechanical tests, is performed to evaluate not only pressure variation and the associated in situ stress changes but also their potential influences on fault reactivation, reservoir–caprock stability, and surface displacement. For geomechanical evaluation, empirical correlations are derived between static and dynamic rock properties based on core data and existing petrophysical logs for the studied reservoir–caprock system. Based on the hydro-mechanical results, the maximum displacement is limited to the vicinity of the injection wells, where the highest pressure changes occur. The geomechanical analysis of the reservoir–caprock system shows that this system is stable until the injection pressure reaches 4.3× the initial reservoir pressure. Also, the injection pressure is not high enough to compromise the integrity of faults, indicating that the loading on the fault planes is too low to reactivate the pre-existing faults. The approach followed in this study can be applied to future field development strategies and feasibility considerations for CO2 sequestration and underground gas storage projects.

Dynamic Tensile Failure Characteristics and Energy Dissipation of Red Sandstone under Dry–Wet Cycles

Studying the dynamic properties of rocks in complex environments is of great significance to the sustainable development of deep-sea metal mineral resource extraction. To investigate the influence of dry–wet cycles on the dynamic tensile properties and energy dissipation of red sandstone, a series of dynamic Brazilian disc tests was carried out through the split Hopkinson pressure bar (SHPB) apparatus. The dynamic tensile behaviors and energy dissipation distribution of the red sandstone specimens after different dry–wet cycles (0, 10, 20, 30 and 40 cycles) were analyzed in this study. The degree of dynamic tensile fragmentation and energy dissipation of red sandstone is significantly affected by the loading rate. Specifically, when the number of dry–wet cycles remains constant, an increase in loading rate results in a significant reduction in the average fragment size, while the energy consumption density exhibits an approximately linear increase. At a fixed loading rate, the energy consumption density decreases approximately linearly with the increase in dry–wet cycles, and the higher the loading rate, the more sensitive the energy consumption density is to the dry–wet cycle. Under a fixed number of dry–wet cycles, the dynamic tensile strength has an exponential relation with the increase in energy consumption density.

Impacts of different cooling methods on the dynamic tensile properties of thermal-treated granite

Hot dry rock (HDR) is a kind of clean, renewable energy and has received widespread attention worldwide in recent years. It is significant to explore the dynamic tensile properties of thermal-treated granite using different cooling methods for mining HDR. In the current work, a series of tests were performed containing ultrasonic testing and Split Hopkinson Pressure Bar (SHPB) tests on granite at different temperatures (25, 200, 400, 500, 600, and 800 °C) after different cooling methods (including natural, water, and liquid nitrogen cooling). Then the dynamic tensile properties, thermal shock damage, and energy evolution process of granite using different cooling methods were compared and analyzed. The high-speed camera and Digital Image Correlation (DIC) technology were used to analyze the tensile failure mode and the failure mechanism under different thermal treatment and cooling conditions. According to the experimental results, with the increasing thermal treatment temperature by adopting the three cooling methods, the P-wave velocity, dynamic tensile strength, and final absorbed energy of granite decreased, and thermal shock damage increased. In addition, the effect of liquid nitrogen cooling on thermal-treated granite was the most obvious among the three methods, followed by water cooling and natural cooling. Moreover, with the increasing treatment temperature, the time for the occurrence of central cracks in the specimen after impact was prolonged, and the areas of the shear failure zone and tensile failure zone increased; the influence of different cooling methods was also evident (natural cooling < water cooling < liquid nitrogen cooling). The experimental findings were expected to offer a reference for understanding the dynamic tensile properties and failure mechanism of thermal-treated granite after rapid cooling. By studying the degree of deterioration of rock dynamic properties by different cooling methods, the exploitation efficiency of geothermal wells can be improved.

Dynamic behaviors of water-saturated and frozen sandstone subjected to freeze-thaw cycles

In high-altitude cold areas, freeze-thaw (F-T) cycles induced by day-night and seasonal temperature changes cause numerous rock mass slope engineering disasters. To investigate the dynamic properties of rock in the natural environment of a high-altitude cold area, standard specimens were drilled from the slope of the Jiama copper mine in Tibet, and dynamic compression tests were performed on water-saturated and frozen sandstone with different numbers of F-T cycles (0, 10, 20, 30, and 40) by the split Hopkinson pressure bar (SHPB) system with a cryogenic control system. The influence of water-saturated and frozen conditions on the dynamic performance of sandstone was investigated. The following conclusions are drawn: (1) With increasing strain rate, the attenuation factor (λa) of water-saturated sandstone and the intensifying factor (λi) of frozen sandstone linearly increase. As the number of F-T cycles increases, the dependence factor (λd) of water-saturated sandstone linearly decreases, whereas the λd of frozen sandstone linearly increases. (2) The prediction equation of the dynamic compressive strength of water-saturated and frozen sandstone is obtained, which can be used to predict the dynamic compressive strength of sandstone after various F-T cycles based on the strain rate. (3) The mesoscopic mechanism of water-saturated and frozen sandstone's dynamic compressive strength evolution is investigated. The water softening effect causes the dynamic compressive strength of water-saturated sandstone to decrease, whereas the strengthening effect of pore ice causes it to increase. (4) The decrease in the relative dynamic compressive strength of water-saturated sandstone and the increase in the relative dynamic compressive strength of frozen sandstone can be attributed to the increased porosity.

Dynamic response characteristics and damage rule of graphite ore rock under different strain rates

In the process of mining graphite mine, rock mass is often subjected to dynamic loads such as blasting or mechanical crushing, which involves dynamic responses of different strain rates, and blasting and crushing effect are affected by the rock dynamic properties and damage specials. The dynamic response characteristics and damage rule of graphite ore rock under different strain rates are very important but rarely studied in the past. To study these issues and provide support for graphite ore rock mining, the dynamic compression tests of graphite ore rock under five kinds of impact pressures were designed and carried out by using the Split Hopkinson Pressure Bar (SHPB) test system, combining with the high-speed photography system and crushing screening tests. The dynamic characteristics, crushing process, crushing mode, crushing form and fragmentation distribution of the graphite ore rock under different strain rates were analyzed. The results show that the dynamic characteristics of the graphite ore rock have obvious strain rate effect. The hardening coefficient (DIF) is positively correlated with the cubic root of strain rate, and the softening factor (K) is negatively correlated with the cubic root of strain rate. Shear failure mainly occurs in the graphite ore rock under impact load, and the crushing process can be divided into five stages, they are compaction, crack initiation, crack expansion and penetration, fragmentation collision and fragmentation fall. In addition, the crushed blocks are mainly triangular pyramid (or cone-like) fine granular and powder. The broken fragments of the graphite ore rock are in accord with the fractal geometry characteristics. That is, the average broken particle size (dS) decreases linearly with the increase of strain rate, and the fractal dimension (Da) increases weakly with the increase of strain rate. Based on D-P fracture criterion and Weibull distribution model, the dynamic damage constitutive model of the graphite ore rock was established, and the correlation between strain rate and Weibull distribution parameters (m and F0) was used to reasonably modify the damage constitutive model. The modified damage constitutive model curve is in good agreement with the experimental curve, which can basically reflect the strain rate effect of the dynamic characteristics of the graphite ore rock and the evolution characteristics of the dynamic stress–strain curve at different stage.

An investigation on relations between dissipated energy and dynamic compressive strength of Kemi-peridotite at high strain rates

Dynamic properties of rocks are essential for planning sustainable engineering structures in regions prone to dynamic loading as well as effective fragment size distributions during quarrying activities. Due to the vast application of dynamic rock properties, several studies have been conducted on the context. However, studies on relations between dissipated energy and dynamic compressive strength are scanty. The aim of the study is to investigate relations between dynamic compressive strength and dissipated energy during fragmentation of Kemi-peridotites at high strain rates. To achieve this, cored specimen was prepared according to recommendations of the International Society for Rock Mechanics and fractured using the split Hopkinson’s pressure bar. Results indicate that the dissipated energy during rock fracture generally increases at high dynamic compressive stress. However, the regression square of dissipated energy and dynamic compressive strength plots suggest poor relations between both variables. Further evaluation of measured strain at maximum dynamic compressive stress indicates that strain in specimen continued significantly after maximum dynamic compressive stress was attained. However, evaluations on relations between dissipated energy and strain indicates that energy dissipation continued along a significant portion of the measured strain during rock fracture at high strain rates. Visual evaluation of broken fragments also indicates good relations between dissipated energy and fragmentation results of Kemi-peridotites at high strain rates. Based on study findings, dissipated energy provides improved indices for evaluating strain and fragment size distribution while dynamic compressive stress provides indices on maximum stress required for rock failure.

Research on dynamic compression failure characteristics and damage constitutive model of sandstone after freeze–thaw cycles

Tongchuan sandstone in northwest China was taken as the research object to study the micro-damage, macro-fracture characteristics and dynamic properties of rocks after freeze–thaw (FT). It is found that almost all of the pores that increased after FT of the sandstone specimens are minipores through the nuclear magnetic resonance test, while the initial pores do not expand further. The Φ50mm split Hopkinson pressure bars (SHPB) equipment was used to test the dynamic compressive properties of sandstone specimens with different FT cycles under different impact speeds, the fractal characteristics, energy evolution and dynamic compressive strength variation laws were discussed. The effect of impact loading on rock is greater than that of FT, and it weakens as the rock softens. A damage constitutive model considering various forms of dissipated energy is proposed, which is closer to the experimental results than the previous damage constitutive model based on energy.

Influence of Static and Dynamic Rock Properties on Drillability Prognosis for Mining and Tunnelling Projects

Influence of Static and Dynamic Rock Properties on Drillability Prognosis for Mining and Tunnelling Projects

INTEGRATION OF GEOLOGY AND PETROLEUM ENGINEERING ASPECTS FOR CARBONATES ROCK TYPING

Carbonate rocks are highly heterogeneous. That which leads to rock typing of carbonate rocks is noteasy to do even by integrating static and dynamic properties of rocks. In accordance with the defi nition ofrock types that are commonly used, rocks or parts of rocks that have been deposited in the same environmentand experienced similar diagenetic process have similar physical characteristics, such as grain orrock fabric texture, pore geometry and structure pores, then the characters that will be used as the basisfor determining rock types. The use of rock fabric has been performed by many previous researchers. Whilethe use of attributes in the rock pores typing is still limited and more emphasis on engineering purposes.The objective of this study is to integrate all three of these characteristics in the determination ofrock typing. Theories that have been established and related to fl uid fl ow in capillaries and porousmedia that will be used to characterize the pore geometry and pore structure. Furthermore, thecharacteristics of the geological evidence will be conducted using core description, petrographyand other data to obtain the relationship between aspects engineering and aspects geology inaccordance with concept or defi nition of rock type in question. In rock typing, permeability and porosity characterize the pore geometry and pore structure. This study proves that there is a strongrelationship between the characteristics of the detail geological and architecture pores. Thus,the resulting methodologies rock typing can be universal with respect to aspects of geology andpetroleum engineering.

Experimental assessment on the dynamic mechanical response of rocks under cyclic coupled compression-shear loading

Rock engineering structures are quite susceptible to cyclic coupled compression-shear loading. Accurately characterizing the dynamic compression-shear behaviors of rocks is thus crucial for the construction safety and disaster prevention of rock engineering. In this study, a convenient and reliable testing method is proposed to characterize the fatigue mechanical response of rocks under cyclic coupled compression-shear loading: an inclined specimen under cyclic uniaxial loading. With the specimen axis inclining the loading direction, a cyclic shear component is introduced into rocks when subjected to cyclic uniaxial compression. Our method has certain distinct merits in the specimen preparation and experimental operation since no undesired loading devices are required. To demonstrate this method, 21 cyclic loading tests are conducted on inclined sandstone specimens with different tilting angles (i.e., 0°, 3°, 6° and 10°) and under different loading frequencies (i.e., 0.5, 1, 2, and 3 Hz). Based on experimental results, the influence of the tilting angle and loading frequency on the dynamic properties of rocks is revealed and a fatigue life prediction function is proposed. With increasing tilting angle of rock specimens or decreasing loading frequency, rock specimens are featured by an increase of nominal hysteresis energy density, leading to higher damage variable and lower fatigue life. Quite different from the axial splitting failure of right cuboid specimens along the loading direction, all inclined rock specimens (i.e., 3°, 6° and 10°) exhibit a prominent shear-dominated failure accompanied by localized tensile damage, and the shear component becomes more remarkable as the tilting angle increases. In addition, with a higher tilting angle or under lower loading frequency, the cyclically failed specimen is characterized by a higher degree of fragmentation.

Numerical simulation of rock cutting process induced by a pick cutter considering dynamic properties of rock at intermediate strain rate

Numerical simulation of rock cutting process induced by a pick cutter considering dynamic properties of rock at intermediate strain rate

Dynamic mechanical properties and constitutive model for jointed mudstone samples subjected to cyclic loading

The dynamic properties of rocks are of great significance to the stability and safety of rock slopes and geological engineering under dynamic loads (e.g. seismic load). In this paper, triaxial cyclic tests were carried out on jointed mudstone samples with the prefabricated half-through joint, and their corresponding dynamic properties and deformation features are explored and analyzed in accordance with the hysteresis characteristics and the residual deformation forms. Moreover, based on the obtained fatigue properties under test conditions of diverse dip angles, confining pressures and dynamic stress, a dynamic stress ratio is proposed, which gives a logarithmic correlation with the fatigue life of mudstone samples. Finally, on the basis of the breakage mechanics and homogenization theory, a dynamic binary-medium constitutive model is proposed, and the validations accompanied with the comparisons to test results are also given. It shows that this model can not only preferably duplicate the typical features of hysteresis loops and the gradually accumulation of the residual strain, but also gives a good consistence with the deformation features and fatigue life obtained from cyclic tests.

A waveform modification method for testing dynamic properties of rock under high temperature

In this study, a waveform modification method was proposed using a self-designed heating device combined with the split Hopkinson pressure bar (SHPB) technique for determination of dynamic behaviors of rock at high temperature. Firstly, the temperature gradient distribution on the incident bar was measured according to the variation of elastic modulus of the bar with temperature, and the relationship between the longitudinal wave velocity and temperature of the bar was obtained based on one-dimensional stress wave theory. The incident bar with a temperature gradient was divided into a series of microelements, and then the transmission coefficient of the whole incident bar was obtained. Finally, the stress wave was modified by the transmission coefficient from 25 °C to 600 °C. This method was used to study the dynamic properties of rock at high temperature, which not only preserves a classical SHPB device, but also effectively ensures the accuracy of the experimental results. A dynamic Brazilian disc experiment was carried out to explore the influences of loading rate and temperature on dynamic tensile strength of sandstone at high temperature using the proposed waveform modification method.

Integrated geoinvestigation for evaluation of an engineering site—a case study from the western Riyadh city, central Saudi Arabia

Microtremors were measured at 18 stations to the west of Riyadh, and the H/V spectral ratio method was used to estimate the resonance frequency and amplification factor. These parameters indicate the presence of foundation bedrocks at various levels with variable thickness of soil where resonance frequency varies from 0.26 to 2.63 Hz, while the amplification factor ranges from 1.1 to 8.9. Moreover, four seismic refraction profiles have been carried out and illustrated two layers: the first of which has a P-wave velocity of 2000 m/s and a thickness of 1.5 m, whereas the second layer is characterized by P-wave velocity from 4010 to 4274 m/s. Besides, four multichannel analyses of surface wave (MASW) profiles have been conducted along the same refraction profiles to estimate the shear wave velocities along these profiles. The constructed 1D and 2D models indicate shear wave velocity ranges from 400 m/s to more than 4000 m/s with horizontal and vertical variation through the investigated area. Furthermore, the dynamic properties of rock and soil materials including Poisson’s ratio, Young’s modulus, shear modulus, material index, concentration index and ultimate bearing capacity have been calculated based on P- and S-wave velocities. These properties reveal less competent to competent material scales. Subsurface karst cavities have been detected in the study area at different depths and various dimensions. It is highly recommended that preventive measures including probing drilling to anticipate karst cavities below the designed foundations must be applied before construction of new engineering facilities in the study area. Otherwise, it will be geotechnical problems in the future.

Dimensional Effects on Dynamic Properties and the Relationships between Ultrasonic Pulse Velocity and Physical Properties of Rock Under Various Environmental Conditions

The ultrasonic pulse velocity (UPV) test is an extensively used, nondestructive, and simple test to delineate the dynamic properties of rocks for geotechnical and rock engineering applications under various environmental conditions. Rock materials that host engineering applications must be studied in detail under laboratory or in situ conditions. However, generally, in situ practices are more expensive and time consuming than those undertaken in the laboratory. The present work aimed to investigate (i) how existing core samples with different sample diameter (D) and sample length (L)/D values affect the dynamic properties of rock materials and (ii) the relationships between UPV and physical properties under various environmental conditions. In total, 190 limestone core samples with five different diameters and various lengths were prepared. UPV, density (ρ), unit weight (γ), specific gravity (Gs), water absorption (wc), and porosity (n) tests were conducted on the core samples according to suggested standards. Results reveal that (i) the dynamic properties of limestone under different environmental circumstances change with sample D and L/D, and (ii) relationships exist between the UPV and the physical properties of limestone. Consequently, it is possible to use the correlation equations presented in this study to assess dynamic features and predict UPV values based on the physical properties of limestone, particularly during the preliminary stage of engineering works. However, this should be done with caution and only for the selected rock type.

Characterization of carbonate rocks using seismic wave for tunnel design stability

The design and construction of a tunnel depends on the mechanical properties of the rock mass around the tunnel. Seismic method can be used to characterize the dynamic properties of rocks. The technique is mostly conducted in geophysical surveys and geotechnical investigations. The method utilizes reflected sound waves that can be used to describe the dynamic properties of rocks. Physical properties of carbonate rocks such as water content, density, hardness, permeability, porosity, wave velocity and abrasivity can be assessed and estimated using P-wave velocity. One of the important characteristics in rock is its ability to remain stable. In this research, seismic refraction survey was applied to measure the strength of carbonate rocks for tunnel stability design. The findings revealed that the regression between the primary velocity and the uniaxial compressive strength R2 was 0.8592, indicating that the rock was firm and solid. Observation by physical visual test showed that the rock samples with yellowish-grey and light grey colours were categorized in the weathering grade II and III, respectively. The results have concluded that the rocks in the proposed area met the full requirements for tunnelling construction.

Estimation of Fines Generation in Blasting Using Dynamic Rock Properties and a Near-Field PPV Damage Model

In the hard-rock mining industry, the generation of fines during blasting is an important issue because it has a significant effect on production processes. Although various approaches have been used to estimate fines generation in recent decades, as a practical matter, measuring the amount of fines is nearly impossible given the technical limitations and the scale of mine blasts. In this study, a dynamic PPV damage model was developed and applied to predict fines generation as a result of blasting. This modified version of the crushed zone model (CZM) considers dynamic rock properties and peak particle velocity (PPV), which represents the induced stress in blasting. Dynamic rock-fracturing tests were conducted using a split Hopkinson pressure bar (SHPB) to determine the parameters that represent the relationships between rock strength and strain rate as well as the relationships between fines amount and strain rate in the model. A case study was conducted that entailed determining the radius of the crushed zone for given blast designs and rock properties and then measuring the fines amount within this crushed zone. This case study indicated that the dynamic PPV model can provide a rough estimate of fines generation for given dynamic rock properties and blast design parameters and that this method has the potential to be a useful indicator, or index, of fines generation.