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Analysis of coda waves of the West-Bohemian earthquakes
Bachura, Martin ; Fischer, Tomáš (advisor) ; Vavryčuk, Václav (referee)
Coda of high frequency earthquakes contains information about attenuation propetries of the environment between earthquake hypocentre and seismic station. By application of different methods of coda anlysis one can derive these properties. I applied three methods to seismograms from autumn 2011 from WEBNET network monitoring seismic activity in West Bohemia/Vogtland area: basic method to derive Qc parameter of the environment, and two methods that allow for separation of intrinsic attenuation (Qi) and attenuation due the scattering (Qsc): method MLTWA (Multiple Lapse Time Window Analysis) and method based on energy flux model. Values of Qc are relatively small (from 22 to 600, which depends on the length of the window in which the analysis is carried out and on the frequency and station used), which is in good agrement with the high seismic activity in the area. Qc shows frequency, depth and lateral dependances. It increases with frequency and depth and in the southwest direction. The applicability of methods for separation of Qi and Qsc are limited. With short hypocentral distancies as we have coda is not affected by scattering. Because of this, I was unable to use MLTWA method and the method of energy flux model was usable to derive only the values of Qi. These values are from 120 (1,5 Hz at...
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Relocation of the 1962 earthquake swarm in West Bohemia
Konrádová, Diana ; Fischer, Tomáš (advisor) ; Doubravová, Jana (referee)
Since the swarm at the turn of 1985/86 the current activity of seismic swarms in western Bohemia takes place mainly in the area of Nový Kostel at the eastern edge of the Cheb basin. However, the location of previous activities, where only more remote seismic stations were in operation, is not exactly known. This also applies to the swarm of 1962, which this bachelor thesis is focused on. Seismic bulletin data are available from eight seismic stations at a suitable distance for sufficient localization quality for this swarm. The theoretical part of the thesis presents research results of fundamental existing localization methods and their properties. In the practical part, the location of the earthquake epicenter of swarm 1962 is presented.
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Seismic monitoring of fluid contacts from horizontal wells
Janská, Eva ; Vilhelm, Jan (advisor) ; Fischer, Tomáš (referee)
When producing oil from a thin layer with a gas cap, gas is generally unwanted since the reservoir looses pressure. The pressure loss might cause the fluid vertical migration and therefore a misplacement of the horizontal production well. This is the main reason why the oil production is held back when a gas breakthrough occurs. The well is chocked, or run on lower production rates, until the oil column is recovered, but it is not known how long this will take. If the gas-oil contact could be monitored over time, then the gas breakthrough could be better prevented by reducing production from a particular well branch or even by blinding a specific part of the branch. The aim of this research is to test if monitoring of the gas-oil contact by a seismic acquisition inside the horizontal well is feasible. This could be done much cheaper, more often and with better repeatability than classical 4D seismic. The feasibility was investigated on 2D Troll subsurface models, using finitedifference acoustic modelling. Receivers are planned in the horizontal part of the production well and suggesting the best source position was one of objectives. The influence of variations in geological settings was also investigated. The most accurate information about the gas-oil contact shape and its distance from the well is...
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Injection-induced seismicity: statistic and energetic analysis
Vlček, Josef ; Fischer, Tomáš (advisor) ; Horálek, Josef (referee)
Fluid injection into the rock formations represents a valuable analog to study the role of high-pressurized fluids in the seismogenic process. It is carried out in depths up to first thousands of meters in order to increase the permeability of rock formation for better exploitation of hydrocarbons and geothermal energy. The increased fluid pressure results in decrease of the strength of fractures and faults which causes their brittle failure that is observed in the form of microearthquakes and enables imaging of the stimulated rock volume. Besides this positive role, seismicity sometimes increases to the level that can be felt by the population, which can cause concerns about the seismic risk of these industrial operations. Thus, one of the main interests focused by recent studies deals with the maximum earthquake that can be triggered by hydraulic stimulations. I introduce the ratio between the hydraulic energy and released seismic energy, the seismic efficiency of injection, to assess the effect of fluid injection to the seismicity. This parameter is applied to data from two geothermal reservoirs (Gross Schönebeck and Soultz-sous-Forets) and one gas reservoirs (East Texas). We find that for different data sets, the seismic efficiency encompasses a broad range of magnitudes; from about 10-6 to...
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Magnitude calibration of seismic network WEBNET
Kolář, Dominik ; Fischer, Tomáš (advisor) ; Jakoubková, Hana (referee)
This thesis deals with determination of seismic magnitudes of West-Bohemian earthquakes. The first part summarizes basic information from the field of seismology and also about the earthquake swarms in the area of interest. The second part deals with calibration of magnitudes, i.e. determination of coefficient that corrects for attenuation and station corrections. Seismic data from the WEBNET network from 2012 were used to this purpose. In order to suppress tradeoff among the studied parameters the data were filtered and also usage of a fixed hypocenter depth was tested. The results show that the optimum attenuation correction is smaller than that used so far magnitude determination. It turns out that a deeper analysis is needed in order to find an optimum formula for magnitude determination at the West-Bohemia WEBNET network.
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Natural CO2 outburst and their relation to tectonic processes
Balák, František ; Fischer, Tomáš (advisor) ; Kolínský, Petr (referee)
This thesis is deals with the running geodynamic activity of NW Bohemia, where frequent earthquake swarms and natural CO2 emanations occur as a possible fade-out of the Tertiary rift activity. The first part summarizes the nature of these geological phenomena with a focus on CO2 escapes and its characteristics. These escapes are viewed from the viewpoint of geology and chemical and isotopic composition along with the effect of earth tides, barometric pressure and seismic activity. In the second part I analyse the records of two CO2 monitoring stations in terms of atmospheric pressure and ambient temperature.
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Joint interpretations of geophysical measurements as the key to understand landscape evolution
Tábořík, Petr ; Fischer, Tomáš (advisor) ; Kněz, Jaroslav (referee) ; Putiška, René (referee)
Užitá geofyzika představuje rychlý, efektivní a nedestruktivní způsob získávání informací o složení a stavu horninového prostředí, jakož i o studovaných geologických či geomorfologických procesech. Kombinování různých metod geofyzikálního průzkumu přináší ve srovnání s použitím pouze jedné geofyzikální metody výrazně širší rozsah měřených fyzikálních parametrů, což umožňuje získání mnohem podrobnějších informací o zkoumaném geologickém prostředí. K interpretacím geofyzikálních dat je vždy potřeba přistupovat obezřetně, protože jde mnohdy jen o jedno z pravděpodobných, nikoli však jediných možných řešení. Předkládaná disertační práce na několika vybraných případech ilustruje, jak snadno může dojít k nepřesné, nebo dokonce mylné interpretaci. V řadě případů přitom nemusí jít o problém kvality dat nebo chybného nastavení parametrů výpočetního modelu. Problém nastává při interpretaci výsledků, kdy dochází k přiřazení určité geologické kvality ke konkrétní měřené nebo modelované hodnotě nebo pozorované anomálii. Sdružené interpretace geofyzikálních metod (ideálně doplněné informacemi "negeofyzikálního" charakteru) mohou nejen přinést zásadní informace o studovaných geologických či geomorfologických fenoménech, ale také přispět metodickými poznatky, a to jak k metodám jednotlivým, tak zejména k jejich...
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Hydraulic fracturing
Mazáček, Michal ; Mls, Jiří (advisor) ; Fischer, Tomáš (referee)
This bachelor thesis deals with the process of hydraulic fracturing. Hydraulic fracturing (also called fracking or fracjob) is a method used for the stimulation of the oil or gas reservoirs. The point of the method is to inject the liquid under high pressure into the formation. The injection cause widening of existing fractures or making new ones. The goal of this thesis was to describe basic knowledge that are necessary to successful treatment. There were basics of rock mechanics described such as linear elasticity, plasticity etc. The main chapter describes the parameters of the fracture such as fracture wide, fracture height, fluid flow and fluid loss. Furthermore, the kinds of liquids were discussed in one chapter. In the end, the fracturation which had been done in Texas(USA) were shown and the spreading of the fractures were discussed.
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