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Second EAGE Passive Seismic Workshop - Exploration and Monitoring Applications 2009
- Conference date: 22 Mar 2009 - 25 Mar 2009
- Location: Limassol, Cyprus
- ISBN: 978-90-73781-59-7
- Published: 22 March 2009
21 - 35 of 35 results
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Locate Microseismicity by Seismic Interferometry
Authors X. Xiao, Y. Luo, Q. Fu, M. Jervis, S. Dasgupta and P. KelamisWe present a new seismic interferometry method to locate microseismicity by crosscorrelating the direct P- and S-waves from repeating sources, e.g., hydro-fracture. Typically microseismic data by surface array are below signal-to-noise ratio for a migration-type approach, and barely pickable for a traveltime-base approach. The repeating sources inside a resolution zone give high signal-to-noise ratio arrivals after stacking in a virtual source gather. This gives us superiority over traditional microseismic processing to remove noises, reflections and surface waves in the virtual source gather. Knowledge of the source excitation time is not needed and more reliability is provided. Numerical tests on an elastic model and noisy field microseismic surface array data partly demonstrate its superiority over the traditional microseismic processing.
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Microseismic Monitoring at the Basel, Deep Heat Mining Project
Authors B.C. Dyer, U. Schanz, T. Spillmann, F. Ladner and M.O. HäringThe Deep Heat Mining project in Basel, Switzerland aimed to create a cogeneration pilot plant, producing both electricity and thermal energy for district heating, from an Enhanced Geothermal System (EGS). The project is located in the Upper Rhine Graben within the city of Basel, Switzerland. During 2006 the exploration well BS1 was drilled to a total depth of 5000 m. The granitic basement was found at ~2257 m below ordnance datum (bOD). The estimated temperature at 5000 m depth was 190°C. In December 2006 an hydraulic stimulation of the openhole section of BS1, from 4379 to 4750 m bOD, was performed. The microseismic monitoring techniques and results of the stimulation are discussed here.
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Seismic Attenuation Assessment in Passive Seismic Investigations Using Pulse Width Analysis and Considering Source Effects
Authors G.A. Tselentis, P. Paraskevopoulos, N. Martakis, A. Serpetsidaki and E. SokosKnowledge of attenuation can be very useful in many stages of conventional seismic data processing as its removal increases resolution. Recent advances in passive seismic investigations involving microearthquakes indicate that attenuation assessment has a great potential as a direct hydrocarbon indicator and reservoir structural delineation. The purpose of this investigation is to assess the use of pulse width analysis to invert for attenuation structure.
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The Detectability of Microseismic Events Using Surface Arrays
Authors K. Chambers, J.M. Kendall, S. Brandsberg-Dahl and J. RuedaRecently there has been much interest in using data from surface arrays for passive seismic monitoring, where migration-based processing methods can be used to locate events in both space and time. Here we test the sensitivity of such methods to signal to noise ratio using signals embedded in different amounts of realistic noise. The data for this study consist of signals recorded across a temporary array of surface instruments in Wyoming, whilst a perforation shot was detonated in the subsurface. Applying a stacking procedure to the data with different signal to noise ratios demonstrates that surface arrays in conjunction with migration style processing methods can successfully image sources that are too weak to be observable in the raw data. The results show that the imaged shot position is relatively insensitive to the level of added noise. The primary effect of adding noise is that it defocuses the image of the shot location. We find that given our migration approach, the experiment geometry and recording conditions for the Wyoming dataset, signals embedded in noise with signal to noise ratios >0.1 can be successfully used to image and locate events.
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Correlation between the Reservoir Dynamics Performance and Production/Injection Induced Microseismicity – A Field Case
Authors J.G. Osorio Ltd and G. Peñuela Ltd LtdMapping passive seismics in Cusiana and Cupiagua fields has revealed a strong correlation between reservoir dynamic performance and production induced microseismicity. Fluid production/injection causes changes in reservoir pore pressure and, therefore, in local effective stresses. The changes in effective stresses cause natural fracture deformations which, in turn, change local transmissibilities and triggers microseismic events. The interplay of these two latter effects determines the relationship between microseismicity and reservoir dynamics (pressures and fluid saturations among other factors).
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Kinematic Features and Magnitudes of Fluid Induced Seismicity – Case Studies and Their Interpretation
Authors S.A. Shapiro, C. Dinske and J. KummerowSometimes fluid injections are characterized by a risk to induce a seismic event of a significant magnitude. Here we address magnitude distribution of seismicity induced by borehole fluid injections. However, firstly we give a short introductory review of microseismicity interpretation in geothermic reservoirs and by hydraulic fracturing. Then, we introduce a simple theoretical model, which predicts the earthquake magnitude distributions for fluid injection experiments. The temporal distribution of microearthquake magnitudes depends on the injection pressure, the size of the borehole injection section, the hydraulic diffusivity of rocks, and is also inherited from the statistics of pre-existing crack/fracture systems controlling the local seismicity. We consider different case studies and show how our model can be used to optimise the design of fluid injection experiments and reduce their seismic risk.
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Location Accuracy of an Integrated Microseismic Monitoring Network: A Saudi Arabian Case Study
Authors J. Vernier, E. Gaucher, S.N. Dasgupta and M. JervisA Saudi Arabian oil field was monitored during 28 days using three different networks of receivers: a digital wireline array set close to the reservoir depth, a permanent analogue array set at mid-depth and a dense surface array. A total of 267 receivers monitored the area when three 4-day injection tests occurred. About 9,500 microseisms were recorded. Recorded and picked microseisms ranging from magnitude -2.2 to 1.1 and were separately located using the different networks. The locations were consistent despite their uncertainties, especially in shape. The location using all networks strongly improved the location thanks to the monitoring coverage. However, this was only possible for 1% of the detected events because it required phase-picking on surface and a signal-to-noise ratio higher than one.
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Imaging Conditions for Time-reverse Acoustics
Authors B.W. Artman and I. PodladtchikovThe time reverse modeling (TRM) algorithm is almost identical to making shot illumination maps in shot-profile migration by extracting the zero lag of an autocorrelated wave field after successive extrapolation steps. Time reverse modeling is designed to locate sources within a model domain by producing energy intensity images after propagating reversed data traces into the interior of the domain with wave-equation extrapolators. This is closely related to illumination maps because both procedures require extrapolation of a seismic wave field into the model domain, but differ by utilizing slightly variant imaging conditions. The imaging condition for TRM is conventionally the maximum amplitude value extracted from the time axis after propagation. This assumes that the energy recorded at each receiver will constructively interfere in the model domain at the (x-z) location of the source to produce a maximum. The autocorrelation imaging condition for an illumination map solves the same kinematic imaging problem but differs from TRM by a square-root.
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Acoustic Emission Experiments and Microcrack Modelling on Porous Rock
Authors E. Aker, H.D.V. Khoa, F. Cuisiat and M. SoldalTo exploit the full potential of passive seismic data we study the acoustic emissions (AEs) that are generated as a result of microcracking or movement on microcracks in stressed rock. Microcracking is directly related to the release of stored strain energy inside stressed rock and coalesce of microcracks might result in macroscopic fractures. Therefore, studying AEs and microcracking in rock samples may aid the interpretation of microseismic events recorded around e.g. oil fields. Our work focuses on experimental measurements of AEs with corresponding numerical modelling in order to characterize the AE intensity and capability of typical intact or fractured reservoir rock like sandstone and chalk.
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Passive Seismic Monitoring of Gas Storage – Challenges for Improving Interpretation and Reducing Uncertainties
Authors J.-P. Deflandre, N. Dubos-Sallée and F. HuguetDuring several years passive seismic monitoring was performed at Céré-la-Ronde, an underground gas storage facility located in a saline aquifer. The permanent survey delivers interesting information on the initial reservoir fill-up, especially when considering the geomechanical behavior of the site. Location of microseisms by using two techniques is discussed. A comparison between the 1D and 3D results points out the limit of using simple structural models and gives some idea on associated uncertainties. The discussion deals also with the necessity of improving the workflow to take into account the induced seismic hazard in coupled reservoir and geomechanical modeling and constraining models with passive seismic data too. This experience is very useful in the context of CO2 storage and it constitutes an excellent analogue for short term considerations.
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Microseismic Monitoring of a Carbon Sequestration Field Test
Authors T.I. Urbancic, J. Daugherty, S. Bowman and M. PrinceEvent location and failure mechanism analysis of microseismicity to identify processes associated with a CO2 injection program
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The Challenge for Surface Passive Seismic Measurements in Kuwait
By G.R. RachedSurface passive seismic is a direct hydrocarbon saturation indicator technology. It detects the presence of subsurface hydrocarbons by recording and spectroscopically analyzing the low-frequency acoustic/seismic background noise (between 0.5 - 10 Hz) which is actively emitted by the earth. The measurements after filtering and analysis can be calibrated with well data and integrated with other geophysical data to provide information which can lower the uncertainty level for hydrocarbon exploration, appraisal and field development decisions. Surface passive seismic measurements were carried out in Kuwait to evaluate the suitability of the technology to detect and the map the extent of hydrocarbon occurrences. The main concern was the suitability of the technology to differentiate between various reservoirs in carbonate stacked-reservoir environment. The level of certainty in the result of the measurements could not be accurately assessed as there is a possibility that some deep reservoirs have not been penetrated by the wells in the area of the experiment. It was concluded that the technology (at that point) could not indicate the distribution of the hydrocarbon occurrences among the stacked reservoirs since the measured indicators are the summation of the responses of all the underlying reservoir layers. Nevertheless, the areas with highest hydrocarbon potential indication are considered the most interesting ones. A number of advancements in surface passive seismic have been recently reported and research results are indicating that the distribution of the hydrocarbon occurrences among stacked reservoirs is becoming achievable. However, It remains a challenge for the surface passive industry to demonstrate convincing successful case histories.
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Passive Seismic Study at an Oil and Gas Field in Voitsdorf, Austria
Authors M.-A. Lambert, S.M. Schmalholz, E.H. Saenger and B. SteinerWe present the results of a passive seismic survey over two separate reservoirs of an explored oil and gas field near Voitsdorf, Austria. Four different spectral attributes of the ambient seismic wave field are used to identify spatial correlations between anomalies in the surface wave field and the presence of hydrocarbons in the subsurface. The attributes quantify characteristic features of the wave field’s Fourier spectra in the low-frequency range (< 10Hz). The data indicate the position of the southern reservoir. The northern reservoir is less clearly identified. Nevertheless, using several attributes significantly increases the reliability of hydrocarbon reservoir detection compared to using only one attribute. Time-reverse modeling applied to the same data-set shows that the observed attribute anomalies at the surface may be caused by low-frequency seismic energy that is emitted from the reservoir areas. Preliminary results of a time-lapse experiment (comparison of data acquired in April 2007 and in April 2008, respectively) reveals a good reproducibility for two of the four attributes. A first comparison between time reverse modeling applied to the 2007 and the 2008 data-set consistently indicates the presence of seismic sources in the area of the two reservoirs.
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Pilots to Determine if Passive Seismic Technologies Can Aid in Solving Field and Exploration Challenges in Carbonates
Authors W.L. Soroka and M.S. Al-JenaibiIn the Middle East where giant billion barrel oil fields exist and there is the potential to find additional reserves, efforts to pilot advanced geophysical technologies to overcome carbonate challenges are often under consideration. Passive seismic technologies are a new source of information that has the potential to add value in helping overcome field and exploration challenges. Some passive seismic methods are now considered proven technologies in clastic rocks, such as hydro-frac monitoring and microseismic. There are other passive seismic methods which are still considered to be in a research stage. Whether a method will perform the same in a carbonate environment as in the clastic environment is also an important consideration when considering a new technology project in carbonates. When a challenge presents itself and a potential new technology is identified to overcome the challenge it is common practice to first conduct a small pilot. Field and Exploration challenges or problems that the passive seismic technologies have the potential to overcome include among other things, monitoring the impact of faults and fractures on flood front advance, identification of thin thief zones, sweep efficiency and by-passed reserves, water fingering and in exploration the direct detection of hydrocarbons to identify new reserves. Progress in advancing the microseismic technologies suggests that these technologies are not without limitations and should not be treated as a “silver-bullet”. The results of pilots suggest that passive seismic results should be treated like an additional seismic attribute to be integrated with other reservoir characterization and exploration information. The proper matching of passive seismic with other appropriate technologies, such as seismic or VSP images can help overcome limitations and improve interpretation reliability. How to properly pilot a new technology is not always as straight forward and easy as one might think. Difficulties in surface conditions, well integrity, equipment availability and the proper situation to demonstrate value from the passive seismic information often lead to inconclusive results and can make it difficult to get approvals to proceed with yet another redesigned pilot. The following paper documents some of the positive and negative lessons learned from passive seismic pilots.
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Recent Passive Experiments in Abu Dhabi
Authors M.Y. Ali, K.A. Berteussen, J.R. Small, B.T. Anjana and B. BarkatPassive seismic experiments using a small array of 3-component instruments were conducted over an onshore carbonate oilfield in Abu Dhabi. The aim is to confirm and understand the origins of a low frequency signals (2.5-2.8 Hz) that has been observed above several hydrocarbon reservoirs in the area and considered as a hydrocarbon indicator. The results of the experiments indicate that a narrow-band of low frequency signal is present above the hydrocarbon reservoir as previously claimed, but that this signal is also observed over nearby assumed non-reservoir locations. Variations in the character of the signals recorded 12 hours apart during midday and midnight periods were observed. The possible causes of this low frequency energy are not well understood. However, using the array of 3-components instruments, we are able to determine the apparent velocities and the azimuth of the wave fronts as well as the particle motion of the recorded low frequency waves. The results indicate that the observed signals are most likely due to some type of surface waves with the azimuth to the source pointing towards the nearest coastline in the area (the Arabian Gulf).
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