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Abstract The paper describes the principal geomechanical approaches to ensuring stability and integrity in mining salt deposits. The various dimensioning methods usually applied are subjected to a comparative analysis. Geomechanical discontinuum models are identified as essential physical models for examining how the collapse of working fields in potash mining areas can occur. A visco-elasto-plastic material model with strain softening, dilatancy and creep is used to describe the time-dependent softening behaviour of the salt pillars. The pillar stability critically depends on the shear conditions of the bedding planes to the overlying and underlying beds. Therefore, a shear model is introduced, describing interface properties, i.e. velocity-dependent adhesive friction with shear displacement-dependent softening for the bedding planes and discontinuities in the contact zone of the pillars with the surrounding salt rocks. As an outcome, the fundamental mechanical and hydraulic conditions that lead to an integrity loss of saliferous barriers are derived. Several examples of worldwide events of flooded salt mines are back-analysed with coupled hydro-mechanical calculations, demonstrating the prominent role of fluid-pressure-driven generation of hydraulic flow paths as a failure mechanism of saliferous barriers. 1. INTRODUCTION For a long time, the dimensioning of underground openings in salt rocks was primarily based on mining experience. Only in the last century, analytical and numerical calculation methods of geomechanics have been increasingly used. This was not least due to some catastrophic collapses of mining fields (rock bursts) with a strong mining-induced energy release [1], and the loss of potash and rock salt mines by flooding. Both practical experience and geomechanical calculations are essential for an economical and sustainable salt extraction at high recovery rates and complement each other. The fundamental requirements of safe dimensioning for potash or rock salt mining are the guarantee of stability of the mining system integrity and protection of the hydraulic protection layers or geological barriers. For the collapse of mining fields insufficient pillar dimensioning and the brittle fracture behaviour of the mined rock salt played a particularly crucial role [2]. The tendency of brittle fracture decreases from carnallitite, hard salt, trona, sylvinite to rock salt. Therefore, rock bursts occurred primarily in potash mines where carnallitite was mined. In sylvinite and rock salt mines few rock bursts are known worldwide, only if extremely high recovery rate and, accordingly, very slender pillars were realised. The analysis of in situ collapses provides a basis to check dimensioning approaches and to derive empirical relationships for the necessary ratio of pillar width to pillar height (slenderness ratio), which is required ensure the viability and stability of pillars in salt rocks.
- Europe (1.00)
- North America > United States > Kansas > Butler County (0.24)
- Geology > Mineral > Halide > Halite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.93)
- North America > United States > North Dakota > Williston Basin > Dawson Bay Formation (0.99)
- North America > Canada > Alberta > French Field > Arl French 16-26-64-1 Well (0.98)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.95)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.67)
Abstract The attenuation characteristics of compressional (P) and shear (S) waves in dry water, and varyingly saturated brine (10, 20 and 30% NaCl by weight) saturated Hawkesbury sandstone samples were measured in the laboratory within the ultrasonic frequency range of 0.1-1.5MHz. The results were analyzed using the pulse transmission technique and spectral ratios were used to calculate the attenuation coefficient and quality factor (Q). The values were calculated relative to a reference sample of aluminium with negligible attenuation, and the effect of salinity on the attenuation characteristics of sandstone was evaluated. Velocity dispersion was observed for both P and S waves for all the tested conditions. It is observed that the attenuation coefficient is frequency-dependent, and the attenuation coefficient of the tested sandstone is linearly proportional to frequency for both P and S waves. Interestingly, with respect to dry value, the attenuation coefficient increases with the fluid saturation (both water and brine). Moreover, the calculated Q values reveal that the values are highly dependent on saturation condition, and reduce with saturation. Varyingly saturated brine (10, 20 and 30% of NaCl) was then used to simulate the brine saturation effect. According to the results, although the sample saturated with 10% NaCl had similar attenuation characteristics to the water-saturated sample, 20 and 30% NaCl saturated samples displayed considerable variations in attenuation coefficient and quality factor, where the attenuation coefficient decreases with increasing salinity level of the pore fluid and consequently, the quality factor of the rock formation is also increased. 1. INTRODUCTION Carbon capture and storage (CCS) in geological reservoirs is one of the best ways to reduce anthropogenic CO2 emission into the atmosphere. It is now well accepted that CO2 geo-sequestration in deep saline aquifers can accommodate large amounts of captured anthropogenic CO2 compared to other geological reservoirs [1, 2] such as depleted oil/gas and coal formations. Generally, the most preferable saline aquifers are of sandstone and most are highly saline [3]. During long-term injection in CO2 sequestration, the reservoir undergoes different mineralogical reactions, including the dissolution and precipitation of rock minerals, which in turn alter the hydro-mechanical properties of the formation. Therefore, it is essential to evaluate the possible changes in the hydro-mechanical properties of undisturbed formations before initiating the injection process.
- North America > United States (1.00)
- Europe > Norway > Norwegian Sea (0.24)
- Research Report > New Finding (0.64)
- Research Report > Experimental Study (0.41)
- Reservoir Description and Dynamics > Storage Reservoir Engineering > CO2 capture and sequestration (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Health, Safety, Environment & Sustainability > Environment > Climate change (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.94)
Abstract Fracture intersections play a crucial role in the hydraulic connectivity of flow paths in rock, yet no technique has been developed to characterize the condition of an intersection. An approach, to elastic wave characterization of intersections, is to assume each block that composes the intersection supports a wedge wave and that these wedge waves are coupled through the points of contact along an intersection. In this paper, we demonstrate the use of group theory to predict the number of vibrational modes supported by a fracture intersection. Five predicted vibrational modes are supported by the intersection for the case of a fracture intersection formed from fractures with the same specific stiffness. Laboratory measurements on an intersection between two orthogonal fractures showed the existence of several vibrational modes that are strongly affected by the polarization of the shear wave source and the uniaxial loading conditions 1. INTRODUCTION Throughout the subsurface of the Earth, fracture networks often control the three dimensional connectivity of the hydraulic flow paths. Fracture networks are composed of multiple fractures and fracture intersections. Although much work has been performed on elastic wave propagation across/along single fractures and sets of parallel fractures [1-4], the effect of intersections on elastic waves has been largely ignored or assumed to have little influence [5]. Typically, single and parallel sets of fractures are characterized by their mechanical properties, e.g. specific stiffness, which in turn provides information about the fracture topology, especially under stress [6-7]. These mechanical properties are linked to the hydraulic response of a fracture, i.e., linked to the spatial distributions of apertures and contacts within the fracture [8-11]. Here, we present results from a group theory analysis on an orthogonal fracture intersection under uniform loading conditions and fracture properties, i.e., a highly symmetric intersection. Several vibrational modes are predicted and described. The existence of these waves is demonstrated by using ultrasonic waves propagating along a fracture intersection on the laboratory scale.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.94)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (0.68)
Coupled Interactions between Coal Fracture Containing Gas and the Induced Shock Monitored by Microseismic and Acoustic Emissions
Lu, C. P. (China University of Mining and Technology) | Zhang, L. (China University of Mining and Technology) | Liu, G. J. (China University of Mining and Technology) | Liu, Y. (China University of Mining and Technology)
Abstract Clear understanding of coupled interactions between coal-rock and gas subjected to static and dynamic loading will be crucial to convince that coal-gas dynamic events can be effectively monitored. Here, we attempt to fill this gap by gathering microseism (MS) and acoustic emission (AE) information on the interactions of gas with coals and the effects of coal-rock fracture on abnormal gas emission. Field investigations disclose two phenomena observed for interactions of coal-rock fracture and gas emission: (1) overpressuring gas in coal can induce fast crack initiation and growth ultimately producing a gas outburst with relatively low energy; and (2) under the influence of a shock wave generated by dynamic loading such as a rockburst, the coal-gas medium may be destroyed. For smaller pressure and lower desorption energy, only abnormal gas emission is generated. The abovementioned phenomena occurred in a gas-containing coal seam, MS&AE activities prior to, during, and after two unusual gas emissions and the spectrum evolutions were analyzed, and the corresponding mechanisms were revealed. 1. INTRODUCTION Since the first reported coal and gas outburst in the Issac Colliery, Loire coal field, in 1843[1], more than 14,000 outbursts have occurred in China [2]. Many researchers have studied relationships between coal outbursts and geological factors for different coal fields, and have come to different conclusions because of the complexity of the mechanisms. Coal and gas outbursts in mines are engineering geological hazards. The dynamic stress on coal and rock material closest to the outburst source results from additional impact load produced by roof fracture or blasting, will result in sudden rupture of coal material in the critical stress condition, produce fissures forming outburst channels, and accelerate the escape velocity of gas resulting in coal and gas outbursts [3]. For coal seams containing gas, an abnormal emission due to higher pressure of gas and higher stress may be an effective precursor for a rockburst. Simultaneously, recorded MS signals from roof strata may also be a precursor of coal and gas outbursts. Many abnormal gas emission phenomena following rockbursts have been reported and recorded in Chinese coal mines in the Fuxin and Beipiao coal fields in Liaoning province and Hegang coal mines in Heilongjiang province [4-6]. In addition, in the Rhine-Westphal coal field, Hawusike coal field, and Ruhr coal field in Germany, many rockbursts events have been accompanied by abnormal gas emissions [7, 8]. The correlation between rockburst and gas outburst was confirmed by MS observation, gas monitoring, and accident investigations by some scholars [9, 10-12].
- Asia > China > Liaoning Province (0.24)
- Asia > China > Heilongjiang Province (0.24)
- Materials > Metals & Mining > Coal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Coal seam gas (0.92)
Abstract A geomechanics study was conducted to examine the seismic risks associated with late stage mining at a case study mine in Canada. Recent large scale pillar extractions and increasing seismicity at the site identified the need to consider seismic risk as the mine extends deeper and sill pillars are thinned and removed. Due to a lack of available quantitative data, a 3D FDM model was developed and the rock mass strength and behaviour was qualitatively calibrated to various geotechnical data sources. With the installation of a mine-wide seismic array, as well as measures of "depth of damage" during drilling and observed damage recorded throughout the mine during several field visits, sufficient data was accumulated to qualitatively calibrate a plastic model of the mine. The challenges in implementing a mine-wide inelastic model calibration with data acquired late in mine life are discussed. 1. INTRODUCTION Numerical methods are utilized in geomechanical engineering to improve understanding of physical processes, to determine stress or strain at specific instances in space or time and to predict rock mass response to excavation, construction or support. Some of the key advantages of numerical methods in mine design include the timely prediction of rock mechanics processes for the duration of a mining project, experimentation with design and construction options (e.g. stand-off distances and sequencing strategies), and performance of sensitivity analyses. Numerical analyses also allow engineers to gain a qualitative understanding of the complex geomechanical system through quantitative evaluation. The largest challenges faced in numerical modelling of geomechanical problems originate from lack of complete knowledge of the true rock mass properties, fracture networks, stress conditions and groundwater influences for the entire region of interest (i.e. project site). Rock masses are discontinuous, anisotropic, inhomogeneous, and for inelastic mine-scale simulations; the determination of material properties or in situ stress conditions is typically difficult over the full extent of a region being modelled.
- North America > United States (0.94)
- North America > Canada > Ontario (0.46)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
Abstract Underground mines commonly use drill core rigs to anticipate future ground conditions. These drill core rigs can be highly expensive and can easily miss changes in rock characterization, depending on the amount of drilling taking place. In an attempt to provide a more efficient means of determining changes in rock characterization, a study was conducted using the Refraction Microtremor (ReMi) process in an underground mine. ReMi involves acquiring noise data along a linear array of geophones. Data is processed to obtain shear-wave velocities underneath the array. The data for our study was collected at an underground gold mine in Nevada, and was analyzed using the SeisOpt® ReMi™ (© Optim, 2015). The data was collected using horizontal and vertical geophones, placed into the ribs of the drift in a horizontal plane, rather than the industry standard placement of vertical geophones into the ground in a vertical plane. In order to determine whether the changes seen actually exist, shear wave velocities were measured in location of known rock characterization. These shear wave velocities were then compared with the Rock Mass Rating (RMR) and previously published correlations between RMR and shear wave velocity. This comparison yielded results that did not match the published correlation between RMR and shear wave velocity. It is likely that the stresses surrounding the excavation affected the shear wave velocity values recorded; however, it is difficult to quantify these affects due to minimal research regarding in-situ stresses in the area. In addition, the use of ReMi as a tool to determine the extent of voids underground was investigated. This can then be used to determine the extent of voids underground and help to distinguish locations where voids may be near above or below excavations. The recordings showed that a void existed, however, did not show the entire extents of the void. This is because the geophone array was not long enough to cover the full length of the void. In order to determine if the ReMi process can effectively be employed to detect voids into the rib, further research is suggested.
- Geology > Mineral > Native Element Mineral > Gold (0.84)
- Geology > Geological Subdiscipline > Geomechanics (0.67)
Application of HPC and Non-Linear Hydrocodes to Uncertainty Quantification in Subsurface Explosion Source Physics
Ezzedine, S. M. (Lawrence Livermore National Laboratory) | Vorobiev, O. (Lawrence Livermore National Laboratory) | Glenn, L. A. (Lawrence Livermore National Laboratory) | Antoun, T. H. (Lawrence Livermore National Laboratory)
Abstract To understand shear wave generation observed during underground explosions several source-physics experiments (SPE) in fractured granitic rock mass were conducted at the Nevada National Security Site (NNSS). Fractured rock present challenges: fractures are poorly characterized and sparsely sampled; the geomechanical and geophysical properties of fractures are unknown and measured at the laboratory scale; and the spatiotemporal scale-disparity between the near source explosion physics and the far-field wave propagation physics requires considerable computing resources to simulate geophysical signatures from source-to-receiver. To build a credible model of the subsurface we integrated the geological, geomechanical and geophysical characterizations conducted at NNSS. Because detailed site characterization is limited we numerically investigated the effects of the characterization gaps on the overall response of the system. Using HPC, we performed several computational studies to identify the key geologic features that affect the most the ground motion in the near-field and in the far-field using stochastic representation of the subsurface. Using brute force Monte Carlo simulations and sampling judiciously the large hyperspace of parameters, we have probabilistically conducted several sensitivities studies on the geological, geomechanical and geophysical parameters. Such studies would help guiding site characterization efforts to provide the essential data to the modeling community. 1. INTRODUCTION Improved understanding of explosion generated wave motions through numerical modeling helps advancing the interpretation of seismic data for nuclear explosion monitoring (NEM) and nuclear explosion forensics. Currently, there are several significant challenges for the monitoring community, such as understanding the effects of emplacement material properties, depth of burial, damage, pre-stress and near-source heterogeneities on wave motion amplitudes, and the generation and partitioning of energy into different modes (e.g., compressional and shear waves, body and surface waves). Understanding these phenomena will improve yield estimation and event identification by accounting for predictable effects on wave motions due to source emplacement, near source heterogeneity, and path specific propagation effects. Knowledge gained on these effects can then be applied to regions where no empirical data exist, either in regions without historical explosion sources or seismic recordings or for explosions conducted under un-calibrated emplacement conditions. Numerical simulations provide a versatile tool to gain insight into the generation and propagation of wave motions, including both nonlinear and linear effects. Explosions are well known to involve the near instantaneous release of high temperature and pressure gas in a small volume of space. These high energy densities cause irreversible nonlinear behavior in the surrounding host material (rock) due to the generation and propagation of the outgoing hydrodynamic shock wave. It has been long appreciated that nonlinear response effects at the explosion emplacement have a strong impact on the observed far field seismic motions (e.g., Werth and Herbst, 1963; Perret and Bass, 1975; Murphy, 1981; Rodean, 1981; Denny and Johnson, 1991). However, a full understanding of these effects has been hampered by limitations in the knowledge of and computational requirements to represent all relevant nonlinear material response effects and to propagate waves from the source region to receivers. Advances in numerical methods and more powerful computational resources now make it possible to routinely compute the hydrodynamic response of earth materials to buried explosions with continuing improving fidelity. These studies justify optimism that explosion generated waves for other emplacement geologies and conditions can be predicted by hydrodynamic modeling and that the proposed approach can reduce uncertainties in NEM source estimates. Furthermore, to understand shear wave generation observed during underground nuclear explosions several surrogate chemical source-physics experiments (SPE) in fractured granitic rock mass were conducted at the Nevada National Security Site (NNSS). SPE data will be used to explain the genesis of the observed shear motions.
- North America > United States > Nevada (0.45)
- North America > United States > California (0.28)
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.46)
Abstract Block caving is an underground mining method that enables profitable extraction of massive, low-grade orebodies, provided orebody geometry, size and competence (quality) favors caving. The use of the block cave mining method is increasing in popularity as it is the lowest cost underground mining method and it enables large production rates. Despite the trend towards block cave mining, the method still faces several challenges. Improved understanding of how a rockmass responds to caving will lead to safer, more predictable and more productive cave mining operations. Combining large datasets from multiple sources with virtual reality scientific visualization (VRSV) is a viable alternative to understanding complex cave behavior without access to the cave. The block caving mining system is complex due to multiple interrelating factors and it is vital that the block cave mining system is analyzed holistically, rather than optimizing individual factors in isolation. The block cave mining system visualizer (BCMSV) software module was developed within the School of Mining Engineering at the University of New South Wales to harness VRSV for this purpose. The back analysis of Newcrest Mining Limited’s Ridgeway Deeps operation using the BCMSV enabled the phenomenon of pulses in the rate of seismic activity to be identified in the active region of cave propagation. Capturing these regions with seismic space-time sequences (SSTS) led to further analysis into the source mechanisms. Orientation analysis of SSTS damage volumes has enabled active joint sets in critical areas of cave propagation to be correlated to the SSTS, suggesting that the seismicity is related to joint activity. This observation is supported by numerical modelling results and seismic property analysis. The potential exists for the location of SSTS events to be used within the management cycle of a block caving operation to provide an indication of the critically stressed region of the caving column, where cave propagation is likely migrating. Engineering/geology teams can also utilize the contained SSTS orientation information for quickly imaging the rockmass fabric response to stress change to identify the caving mechanisms dominant within that damage volume.
- Oceania > Australia > New South Wales (0.34)
- North America > United States > California (0.28)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.93)
Abstract In unconventional hydrocarbon resources, the estimation of the expected ultimate recovery for individual wells and the appropriate spacing for infill drilling near existing wells both have strong economic implications. A field test called microseismic depletion delineation has previously been proposed as a method to probe the reservoir directly to determine the extent of the depleted region near horizontal wells that have been produced for a significant period of time. In this work, we performed a numerical simulation of a microseismic depletion delineation field test in order to further understand the physical mechanisms that underpin the method. The modeling framework developed herein can be used to help design field tests and interpret field observations. We observed that application of a model that coupled fluid flow, fracture mechanics, poroelasticity, and geologic structure was able to produce the physical behavior necessary to interpret observations from microseismic depletion delineation field tests. 1. INTRODUCTION The successful exploitation of unconventional resources depends on the ability to develop strategic engineering designs using economic considerations as the primary drivers. In shale oil plays, like the Bakken for instance, suitable wellpad geometries and well trajectories are first determined and then repeated many times in an efficient pattern in order to reduce drilling costs. Similarly, hydraulic fracture treatments are commonly performed in repeatable patterns across many wells. This methodology is attractive from an economic standpoint, but given that heterogeneity exists in all reservoirs and that operational difficulties can arise, the approach may not always result in the optimal recovery for a given well. Evidence from field data has indicated that productivity of individual wells, and even individual completion stages, can be highly variable [1, 2]. It is useful to develop tests that can be applied in the field in order to assess the recovery efficiency of wells and individual completion stages within each well. This information can be helpful from a reservoir management perspective, for example, in order to estimate ultimate recovery or to determine appropriate spacing for infill drilling in a given asset.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
Abstract Compressional and shear waves propagated across single fractures are sensitive to the size and distributions of voids and contact area in a fracture. Fracture geometry is often altered by geochemical reactions among pore fluids and rock. In this study, acoustic monitoring was performed while two chemical solutions were flowed into a fracture to induce chemical precipitation. Mineral precipitation along the fracture plane was not uniform and significant gas bubble evolution occurred during the chemical invasion. Compressional wave amplitudes were significantly affected by the size and distribution of gas bubbles. Once the chemical invasion was halted, bubble formation was minimized but the redistribution of bubbles still occurred. Transmitted wave amplitudes increased in regions with significant amounts of mineral precipitation. The detection of mineral precipitation within a fracture is possible but requires an understanding of the effect of each component that arises from reactive flow on acoustic signals. 1. INTRODUCTION Fractures in the Earth’s subsurface are subjected to natural and induced physical processes that alter a fracture. For example, a change in stress on a fracture deforms the void geometry and affects the amount of contact area between the two fracture surfaces. Geochemical reactions between pore fluids and the host rock also alter fracture void geometry through dissolution and mineral precipitation. The ability to detect and monitor alterations to fractures using geophysical methods requires a link between a measured geophysical response and a property (or properties) of the fracture. Compressional and shear waves propagated across single fractures are sensitive to the size and distributions of voids and contact area in a fracture [1, 2]. The complexity of this fracture topology is captured by fracture specific stiffness which is an effective parameter that captures the deformed state of a fracture topology under stress [1, 3]. Fracture specific stiffness increases with an increase in contact area and a decrease in fracture aperture [4-7]. Normal and shear fracture specific stiffness are used in many theoretical and numerical approaches to wave propagation in fractured media to represent the complexity of fracture topology (for example see: [8-14]). From the theory for single fractures, an increase in fracture stiffness results in an increase in transmitted wave amplitude and a decrease in group time delay. Few studies have examined the effect of chemical alteration of fractures on fracture stiffness and/or elastic wave transmission [15]. In this study, we examined the effect of mineral precipitation in a fracture on compressional wave transmission to determine the effect of geochemically altering fracture void geometry.
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)