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Fifth EAGE Passive Seismic Workshop
- Conference date: September 28-October 1, 2014
- Location: Lisbon, Portugal
- Published: 28 September 2014
1 - 20 of 31 results
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Keynote Presentation - The Role of Rate and State Seismcity Models for the Discrimination and Characterization of Induced Seismicity
By T. DahmSummaryThe public perception for human-induced and triggered seismicity is often very high and public safety is a major issue for approving authorities. Even weak non-damaging events felt by population have led to major debates and in some cases fostered the closing down of geotechnical projects. Often, we cannot convincingly answer the question of the likelihood that damaging earthquakes may occur or not before the start or during the course of the engineering operations. Passive seismic techniques and advances in theoretical seismicity models are needed to improve the current situation.
Seismological methods towards the characterisation of seismic sources are well advanced in mining applications (e.g. Grigoli et al., 2013 , Sen et al., 2014 , Maghsoudi et al., 2014 ). Micro-seismicity is also recognized as a valuable tool for completion, optimization, characterization and modelling of reservoirs or storage facilities (e.g. Cesca et al., 2014a ). However, although the probabilistic description of seismicity is established in seismology since decades, a probabilistic approach is still not common practice for induced seismicity and reservoir studies in industry. A possible reason may be that seismicity models in seismology are often based on steady state or quasi static loading rate conditions, a situation rarely valid for engineering activities. Therefore, seismicity models considering the stress and pressure loading conditions of engineering activities need to be further developed andvalidated.
The discrimination between natural and human related earthquakes is important for both issues. For instance, the nature of induced seismicity implies nearby geotechnical operations and engineering activity. However, the occurrence of a close-by earthquake does not always mean that the earthquake is human related, especially in regions with high tectonic activity. We need to establish community accepted methods for the discrimination of events. These should consider (geo-)physical and structural parameter from the natural background processes and the human related activities (e.g. Dahm et al., 2010b ). Beside the discrimination by means of source parameter estimations (e.g. Cesca et al., 2013b , 2014b ), probabilistic methods based on seismicity parameters are important (e.g. Dahm et al., 2012 ). A database of case studies, including both seismicity and production parameters, is important to validate such models and to establish common accepted procedures. Unfortunately, such databases are still not available or not accessible to a wider scientific community.
The presentation reviews and summarizes the basics of seismicity models and their current role in natural earthquake and triggered / induced earthquake studies. Specific problems and questions for the different cases of induced / triggered seismicity and applications will be clarified. The behaviour and different aspects of a rate and state seismicity model are demonstrated. We discuss implementations of the rate and state model ( Dietrich, 1994 ) for the characterization of triggered and induced seismicity, comprising the characterization of seismicity clouds related to hydro-fracture formation and the evaluation and discrimination of isolated significant earthquakes. Knowledge gaps and unsolved questions will be discussed.
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Keynote Presentation -Hazard Mitigation of Induced Seismicity Effects through Implementation of Protocols and Practical Strategies That Gain Public Acceptance
By C. BromleySummaryBest practice procedures are being developed and implemented to deal with hazard mitigation of the effects of induced seismicity. Improved protocols and practical strategies are required to gain public acceptance. Developing such protocols is an important research objective ( Bromley & Majer, 2012 ). The strategies build on better understanding of the triggering mechanisms, and the underlying causes of induced seismicity. Some of the key questions that remain to be fully addressed are as follows:
- What methods can be used to differentiate between triggered, induced and natural seismicity?
- How can we improve estimations of the damaging potential of triggered earthquakes?
- How can we mitigate the seismic hazard due to resource exploitation?
- How should a monitoring network be optimally designed to deliver the required information for seismic hazard mitigation?
- How can an exploitation strategy be optimally designed to avoid causing large earthquakes?
- What decisions are influenced by the micro-seismic monitoring and interpretation results? [For example: stimulation optimization, reservoir production/injection management, or make-up drilling targets.]
- What are the best ways to build public acceptance for resource utilisation?
Based on experience gained from many decades of geothermal exploration and development, often within earthquake-prone geological settings, these major questions regarding induced seismicity are discussed from the end-user point-of-view. Those issues which require more research are identified. Suggestions are offered to facilitate better cooperation between academic institutions and industry partners to foster information exchange and better serve public and company interests.
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Keynote Presentation - Microseismic Data Integration: How Connecting the Dots can Help Solve the Unconventionals Puzzle
Authors B.E. Cox, R. Lehner, P. Webster, M. Molenaar and A. AzadSummaryUnconventional reservoirs are generally developed using hydraulic fracturing. Having a good understanding of the hydraulic fracture characteristics helps in optimally and efficiently developing the reservoir. Microseismic monitoring has proven to be a valuable technique to monitor hydraulic fracturing operations. During the hydraulic fracture treatment fluid is injected in the reservoir and cracks form, which results in the occurrence of microseismic events. The monitoring and interpretation of this microseismic events can lead to a better understanding of the hydraulic fracture characteristics. Microseismic monitoring of hydraulic fracturing is generally used to assess the fracture parameters like hydraulic fracture height, length, orientation, and complexity. However, it is a challenge to retrieve information like effective (producing) fracture parameters and hydraulic fracturing efficiency. Besides, the value of information from microseismic would become larger when it can be used to go beyond retrospective analysis, and can help to facilitate the prediction of the hydraulic fracture behavior. In order to solve this unconventional puzzle and to maximize the learnings from microseismic data, it is required to evaluate this microseismic data along with other sources of data.
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Temporal and Spatial Variability of Microseismic Events due to Water Flooding: A Case Study from the Tazlau Field (RO)
Authors M. Behm, A. Egreteau, M. Afifi, F. Ogliani and A. VoskampSummaryEnhanced oil recovery is routinely performed by water flooding in the Tazlau field in Eastern Romania. By the end of 2013, a borehole microseismic feasibility study was launched to gain better understanding of the producing reservoir behavior. Two wells were equipped with 8 geophones in approximately 1000 meters depths in two consecutive periods coinciding with the initiation of the injection phase. In the first well, a significant amount of microseismic events (2566) was recorded during 14 monitoring days, in contrast to a very small number of events (54) observed in the second well in the following 14-day period. This significant difference is related to the varying fracture density in the area and, to a lesser degree, to the amount of injected water.
In general, event hypocenters can be located within distances of 600 meters from the monitoring well with sufficient accuracy, and their moment magnitudes range from -1.5 to -3.5. Fracture network characterization based on the microseismic pattern is supported by the analysis of fullbore formation imaging. The study provides new insight on potential water paths. We conclude that borehole microseismic monitoring appears as a promising and useful technique for steering water injection.
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Filling in the Gap: Capturing the Full Scaling Relationships of Hydraulic Fracturing
Authors A.M. Baig, T.I. Urbancic and K. BosmanSummarySeismicity associated with hydraulic fracturing can range in magnitude up to and beyond +M3, large enough in many cases to be felt on surface. These higher magnitude events are in contrast to the smaller magnitude events that are normally used to characterize the efficacy of fracture treatments, as they can represent the activation of structures on the scale lengths of hundreds of meters, whereas the microseismicity (below M0) in the reservoir is associated with the activation of structures up to the scale of 10s of m. To accurately characterize events activating structures of intermediary lengths, i.e. between 10 m and 100 m, deploying instruments at or near the reservoir level, and low-frequency instruments at shallower depths and on the surface will help determine accurate source parameters for events not only one the surface, but also for events not necessarily strong enough to propagate clearly to the surface but high enough magnitude to saturate typical 15 Hz downhole geophones.
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Mine Induced Seismicity: From a Passive Microseismic Monitoring in Complex Near-Field Underground Conditions to an Open & Accessible Database
Authors M Marot, J. Kinscher, S. Coccia, I. Contrucci, E. Klein and P. BigarréSummaryIn the scope of cavity surveillance and instability forecasting, the underground salt mine cavity of Cerville-Buissoncourt, NE France, was monitored during 5 years and represents a large collection of microseismic data, encompassing the cavity’s stability phase until its provoked collapse. The growing instability of the cavity is witnessed by several microseismic crises recorded at 1D and 3D geophone stations deployed at the surface and in boreholes. Event localizations indicate that they lie near the cavity roof and are interpreted as block falls and growing of the cavity.
Our objectives are (1) to follow the cavity’s growth over time until its collapse, in order to improve prognostics of underground cavity collapses in a general sense, and (2) to make accessible our catalog data and methods via open source web platforms, e.g. e.cenaris (INERIS) and EPOS.
In order to achieve this, a comparison is made between event localizations and characteristics along the different evolution stages of the cavity: stable, unstable and collapse. Once data processing is automated and a calibration magnitude law is found for each time period, we apply them to a much larger dataset within each time period and obtain a complete catalog describing the evolution of the salt mine cavity.
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Ambient Seismic Noise Analysis from Array and Borehole Networks in Svalbard, Norway
Authors J. Albaric, G. Hillers, D. Kuehn, D. Harris, F. Brenguier, M. Ohrnberger and V. OyeSummaryIn the present study, we analyse the ambient seismic wave field recorded at two different sites in Svalbard (Norway), namely the CO2Lab and the SPITS array. The CO2Lab consists of 18 geophones deployed in shallow and deep boreholes (down to 540 m depth). The SPITS array is composed of 9 broadband stations. At each site, we compute the cross-correlation of the ambient seismic noise recorded at different pair of receivers in order to estimate the Green’function between these receivers. The objective is to characterize the frequency dependent properties of the ambient wave field and to estimate the resolution power of passive methods for future monitoring of subsurface velocity variations induced by anthropogenic and natural processes.
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Scaled Energy for Natural and Induced Seismicity
By G. KocharyanSummaryThe relations between seismic moment M0 and seismic energy Es for various scale events were considered.
Averaging over the entire scale range gives relations close to the self-similar assumption. A more detailed examination reveals several hierarchical levels, in which changing the event parameters with the scale occurs by different laws, often strongly deviating from the self-similar scaling.
The first class of events is presented by small events with Mw <1 ÷ 2, located at shallow depths of about 1–2km. In this interval, the value of scaled energy Es/M0 regularly increases with the scale, which is related mainly to the dependence of rock shear modulus on scale. The second interval should include small earthquakes located at seismogenic depths. If hypocenters are confined to small cracks located aside from the central part of major faults, their parameters correspond to the self-similar laws and Es is proportional to M0. Earthquakes with moment magnitude Mw ~ 3.5–4 make the transition band, which is the boundary between the two ranges in which the scaling relations differ significantly.
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Stress Tensor Changes Related to Fluid Injection at The Geysers Geothermal Field, California
Authors P. Martinez-Garzon, G. Kwiatek, M. Bohnhoff and G. DresenSummaryStudying variations of the stress field caused by fluid injection is relevant towards an improved understanding of geomechanical reservoirs processes. We present a software package performing stress tensor inversion based on SATSI algorithm (Hardebeck and Michael, 2006, J. Geophys. Res.) with overall performance and stability improvements, versatile graphical output allowing visualization of 0 to 3D stress inversion results, and user friendly interface. The MSATSI package is composed of two elements: one for performing the stress inversion and uncertainty assessment, and second providing the graphical visualization of the results. The package is GPL-licensed and freely available.
In this study, we estimated potential spatiotemporal variations of the local stress field orientation at The Geysers geothermal site by using fault plane solutions of local events provided by the Northern California Earthquake Data Center. First, we investigated the stress field orientation at different depths using high quality focal mechanisms of induced seismicity over the whole reservoir. The results point out a clear variation of the stress field orientation at reservoir depth (normal regime) with respect to above and below (strike-slip regime). These observations were interpreted as an effect of the reduction of horizontal stresses due to the depletion of reservoirs. Second, we look at the temporal changes of the stress tensor at a particular seismicity cluster in the northwestern part of the field. Results show a clear correlation between detected stress field orientation changes and injection rates. We interpreted these observations either as the reactivation of pre-existing cracks oriented in the direction NE-SW, or as the opening of new fractures.
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Induced Repeating Earthquakes: An Indicator for Pore Pressure Changes?
Authors J. Kummerow, C. Dinske, M. Haring and H. AsanumaSummaryWe propose a method to identify repeating events and apply it to microseismic data recorded during and after the stimulation of the geothermal reservoir at Basel-1, Switzerland. Our method is based on a combination of the measured waveform similarity between event pairs and an estimate of the source radii. In our case study, at least 15% of the microseismic events can be grouped into repeating earthquake sequences. We then analyse the spatial and temporal characteristics of the repeating events and find that they differ significantly from the behaviour of the entire microseismic dataset. Repeating events are a common feature during the stimulation phase and at small distances from the injection source (<250–300m), but they are clearly under-represented after the shut-in and at larger distances. The distance interval, where the behaviour of seismicity changes abruptly, correlates with the occurrence of the largest induced events (here Mw > 2.0). The observations suggest that the repeating earthquakes define a subset of seismicity which is particularly sensitive to pore pressure changes and is less affected by earthquake interaction. Therefore, the analysis of injection-induced events may provide a tool to identify the dominant triggering mechanism of seismicity and to detect possible changes of the triggering mechanism (e.g. pore pressure versus stress transfer).
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Seismic Efficiency, Overshoot and Enhanced Dynamic Weakening of Fractures
Authors T.I. Urbancic, L. Meighan, G. Visgas and A. BaigSummarysee attached extended abstract
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Assessing Active Perforation Clusters through High-Resolution Fracture Mapping from Surface Array
Authors T Bardainne, M. Chmiel, R. Macault and M. Van ParysSummaryEither geomechanical modeling or reservoir engineering require a consistent microseismic cloud obtained through accurate location of very low magnitude events. In this abstract, we compare the different processing methodologies we have recently developed to improve sensitivity and accuracy of microseismic events located with a surface array.
First we developed the so-called multi-local-template approach, which strongly improves location accuracy. Relative locations using such a template remain very efficient even with an inaccurate velocity model.
We introduced two high sensitivity methods: the first is based on a joint mechanism and location inversion and the second is based on the use of a signed template, somewhat similar to a multiplet relative location scheme. There’s a twofold increase in number of detected events when using a joint inversion, as it takes into account the focal mechanism amplitude effects prior to forming the beam. The so-called signed template approach is even more sensitive.
Lastly we adapted these algorithms to 3C sensors-dedicated P+S, in order to reduce the vertical uncertainty.
The combination of these methods allows for new interpretation of the microseismic cloud. We can now observe the separated fractures growing from the perforation clusters of a stage, assessing which one is active.
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Infering Dynamic Rock Properties During Hydraulic Fracturing from Microseismicity
Authors L. Smith-Boughner, A.M. Baig and T.I. UrbancicSummaryBeing able to estimate the dynamic properties of rock failure in shale from microseismic data allows for the characterization of reservoir rock at resolutions that are unattainable from conventional 3D seismic imaging and allows for additional insight into the fracturing process that will help constrain different models for the fracture generation. Using events generated by hydraulic fracturing, we demonstrate a technique for estimating the Vp/Vs ratios throughout a hydraulic fracture from seismic moment tensors. Downhole recording microseismic events allow us to estimate the seismic moment tensor of shear-tensile events. Using a set of well-located, high quality events with similarly oriented fracture planes, we can invert for Vp/Vs, the ratio of the compressional to shear wave velocities, of the volume around the fracture. While traditionally this parameter is used as a proxy for reservoir rock properties, decreases in this ratio likely indicates a reduction in the rock strength due to fracturing. From sets of events on nearly vertical fractures, we observe decreasing Vp/Vs ratios throughout the stage. Lowering Vp/Vs is also observed in previously fractured areas. We also estimate the variations in apparent Vp/Vs as a function of the dip of the fracture plane to constrain anisotropic responses.
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Towards Numerical Modelling of Triggered and Induced Seismicity
Authors D. Kuehn, T. Dahm, M. Wangen and S. HeimannSummaryHuman-induced earthquakes are more and more brought into the focus of public attention. E. g. Ellsworth (2013) attracts notice to the dramatic increase of the number of earthquakes in the central and eastern United States over the past few years. Environments prone to induce or trigger seismicity are numerous, e. g. oil and gas exploration sites, large-scale surface quarries and mines, Enhanced Geothermal Systems (EGS), dam sites and injections of e.g. CO2 or waste water. Since the nature of induced and triggered earthquakes implies their occurrence near engineering activity, even earthquakes of small magnitude are a cause for concern. We present several numerical methods to enhance the understanding of the spatial and temporal occurrence of seismicity, which has been triggered or induced by human operations: a) poroelastic modelling employing elementary Green’s functions, b) analytical fracture model combined with a rate- and state- dependent constitutive model and c) a 3D FEM able to handle both heterogeneous rocks and branched fractures.
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Utilizing Moment Tensors to Identify Fracturing Behavior for Hydraulic Fracture Stimulations in Complex Geologic Domains
Authors Sheri Bowman, Andy Cochrane and Ted UrbancicSummaryMicroseismic monitoring has become an accepted method for monitoring fracture growth and stimulation effectiveness during hydraulic fracturing. In addition to delineating fracture dimensions and orientation, microseismic methods can also provide insight into local stress states adjacent to geological structures and their influence on fracture propagation. Understanding the role geology plays on fracture growth is integral to the planning and completion program of a hydraulic fracture treatment. In general, fractures will propagate in the direction of maximum horizontal stress which is controlled by the regional stress in the area. In contrast, we will show how local complex geologies can have a greater effect on fracture growth and fracture orientation as compared to a fracture network directly influenced by the regional stresses.
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Vector Fidelity of Downhole Receivers for Microseismic Monitoring Revisited
More LessSummary3-C seismic receivers in a single vertical well are used to monitor micro-seismic activity in unconventional reservoirs. In such cases, locations of micro-seismic events depend on a velocity model and a particle polarization of a body-wave arrival. In this abstract, we show evidence for the lack of vector fidelity on downhole receivers. We are presenting a workflow to identify receivers with the lack of vector fidelity and a methodology for correcting the sensitivity of the components of the receiver to preserve the vector fidelity. This methodology enabled us to correct a 13° error in event backazimuth in the presented case study.
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