Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
This phenomenon is caused in a number of ways, including removal of part of a rock mass (mining, tunneling), perturbation of the natural hydraulic regime (fluid injection or extraction, dam construction) and perturbation of rock temperature (thermal cracking). In the first case, excavation of large volumes of rock at depth and the resulting stress redistribution can give rise to crack propagation and movement along preexisting fracture planes. Two scales can be considered for mine-induced seismic events: small events due to stress concentration and sudden failure of rock close to mining faces and large seismic events due to the interaction of tectonic and mine-induced stresses on pre-existing fault planes. The primary concern from the point of view of the mining industry is to deal with large events which could cause fatalities and severe damage to mine openings and equipment. Although most daily recorded events are small and the level of activity is, in general, an indication of rockburst potential, the relationship between large and small events is complex. For example a major rockburst with a magnitude of 3.4 occurred in Creighton mine, studied in this paper, in 1989. The level of microseismic activity began to increase three days before the occurrence of the main event, but subsided the day before the rockburst. Most of these events were close to the hanging wall, some 150 m away from the rockburst located near a drift in the footwall (Ge and Kaiser, 1991). In this paper, we study source parameters and scaling relations for mine-induced events in the magnitude range 0-3 in order to examine any fundamental differences between the physical properties and characteristics of events of different magnitudes.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.73)
Abstract A new technique has been developed to estimate how seismicity evolves through the mine, making the technique an interesting addition to defining areas with high, medium, and low damage potential due to their embedded seismic history. The use of solid triangulations in representing the areas of interest makes the developed methodology a simple and powerful addition to the study of seismicity in mines. The research illustrates a new technique to model seismic events and combine them into block models, providing the user with the ability to analyze these data as a function of time (4-D) model, with the possibility of combining different analysis criteria to display the data, create sections of the information in any direction needed, cut the data at any elevation to see what has happened through the life and development of the mine. The seismic history of the mine can be displayed and analyzed using the developed technique, defining areas of progressive deterioration associated to the energy levels released by the seismic events.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.95)
ABSTRACT Fluid injection operations and the connected increase in pore pressure can have undesirable side effects such as induced seismic activity, fault slip and wellbore damage. Here, we present two statistical methods that allow for an identification of fault activation and induced seismic activity. First, we differentiate induced from tectonic seismicity based on a significant increase in background seismicity rates. We determine temporal variations in background rates by fitting earthquake interevent-times with a two-parametric gamma distribution. The corresponding parameters provide insight into short-period aftershock clustering and longer period background seismicity rate changes. We show that temporal changes in background rates can be used to identify regions with induced seismicity in the central United. Second, we identify fault activation processes by analyzing temporal variations in Gutenberg-Richter -value A significant drop in -value can potentially be indicative of fault activation during continuous injection operations. Adjusting injection operations in response to jumps in background rates and decreasing -values may help control fault activation and induced earthquake activity. Presentation Date: Wednesday, October 19, 2016 Start Time: 8:00:00 AM Location: Lobby D/C Presentation Type: POSTER
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- North America > Canada > Alberta > Youngstown Field > 591536 Yngstn 5-32-31-9 Well (0.97)
- North America > United States > California > Ventura Basin (0.94)
- (3 more...)
ABSTRACT: Seismic events near the stope face of six longwalls at Western Deep Levels Limited are discussed in terms of their relation to blasting time. First, the time period is established during which seismic events can be regarded as directly blasting-induced. Later, the different seismicity levels of the six longwalls are discussed. Finally, the ratio of the number of seismic events, which occurred during the blast and after the blast is evaluated for several magnitude categories. Longwall geometry, geological discontinuities of large and small scales did however result in anomalies such as abnormal concentrations of rockbursts during and outside blasting time. It is also shown that seismicity levels of longwalls, which advanced at an oblique angle to geological features, were strongly reduced when compared with other longwalls. The potential of production blasts to trigger impending seismic events under certain conditions becomes apparent. INTRODUCTION The gold mine Western Deep Levels Limited (WDL) is situated in the Witwatersrand Basin approximately 75 km south-west of Johannesburg. The lease area totals nearly 45 km, extending 11km on strike and about 4km on dip. Mining operations began in 1957 with shaft sinking operations. The first gold pour took place in 1962. Two economic gold-bearing reefs, the Ventersdorp Contact Reef (VCR) and the Carbon Leader Reef (CLR), are extracted (Fig. 1). The VCR is worked between 1500m and 2300m below surface, dipping on average 21 degrees South-east and sub-outcrops in the north-west. About 900 m below the VCR lies the CLR horizon which is continuous over the whole lease area. The VCR consists of a conglomerate with a great variation in pebble sizes and channel width Which exceeds 2,5 m in places ("reef roll"). The CLR is formed by a narrow, carbon-rich conglomerate with a channel width of a few centimetres. For the exploitation of the VCR both, No.2 and No.3, shafts were sunk in the northern part of the lease area to 1930 m below surface. To gain access to the CLR sub-vertical shafts were sunk down to 2975 m below surface. Further development in the form of tertiary vertical shafts was necessary to enable mining in the lower sections of the CLR-horizon. (Figure in full paper) The mine adopted a longwall mining system in which approximately 75 % of alliongwalls are protected by systematic stabilizing pillars. Mini-longwalls consisting of six panels, with a total length of about 200m on dip, are separated by 40 m wide strike stabilizing pillars. Stabilizing pillars were introduced in 1980 to address the eminent rockburst problem of the late 70's. Since 1987 backfill in the form of classified tailings is added in some areas to improve the regional support. The reef is extracted conventionally by drilling and blasting. The broken rock is scraped to boxholes which lead to haulages in the footwall. These haulages ("follow-behinds") are developed some distance behind the actual face-position to avoid high field stresses. Both horizons are intersected by a number of dykes which are mainly north east - south west orientated.
- Europe > Austria (0.28)
- Africa > South Africa > Gauteng > Johannesburg (0.25)
Modelling Induced Seismicity with a Hydraulic-Mechanical-Stochastic Simulator: Review of Case Studies.
Ritz, V. A. (Swiss Seismological Service) | Rinaldi, A. P. (Swiss Seismological Service) | Zbinden, D. (Swiss Seismological Service) | Nespoli, M. (University of Bologna) | Karvounis, D. (Swiss Seismological Service) | Wiemer, S. (Swiss Seismological Service)
ABSTRACT The risk of inducing seismic events is nowadays compromising the full development of new forms of exploitation of the georesources. Understanding the physical mechanisms is pivotal to the development of numerical tools to forecast induced seismicity and to elaborate mitigation strategies. Modelling tools constitute the base of the so-called Adaptive Traffic Light System (ATLS), which could provide in the future a real-time evaluation of the geoenergy system performance. While several coupled simulators (continuum or DFN) are able to describe most of the physical processes, their application in real-time could be quite computationally expensive. For this reason, a hybrid approach combining physical/mathematical models with a stochastic description of some of the processes might be required for future applications. In this work, we present the current development of modelling tools for an ATLS and review case studies applications of the TOUGH2-Seed simulator: a coupled hydro-mechanicalstochastic approach providing a good representation of various physical mechanisms. The modelling approach has been applied to simulate injection operations at Enhanced Geothermal Systems (Basel) and hydrothermal (St. Gallen) projects in Switzerland that have seen a significant number of induced sequences of earthquakes, as well as to the hydrothermal area of Hengill in Iceland, where reinjection has been seen to trigger induced seismicity crises. 1. INTRODUCTION Induced seismicity has become the topic of discussion in multiple areas, especially pertaining to the exploitation of geo-resources. Large magnitude induced seismic events are a risk for populations and structures, as well as an obstacle for the development of viable industrial activities. Mining, hydrocarbon and geothermal exploitation as well as underground storage can alter the stress field of the shallow Earth's crust by pore pressure changes, or volume and/or mass changes inducing or triggering seismicity (Ellsworth, 2013). In particular, the injection or withdrawal of fluids from the subsurface that occurs in geothermal plants carry significant risk of inducing seismic events (Evans et al., 2012).
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.72)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.90)
- Europe > Switzerland > Alpine Foreland Basin (0.99)
- Europe > Italy > Alpine Foreland Basin (0.99)
- Europe > France > Alpine Foreland Basin (0.99)
- (2 more...)