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Seventh EAGE Workshop on Passive Seismic 2018
- Conference date: March 26-29, 2018
- Location: Krakow, Poland
- Published: 26 March 2018
21 - 25 of 25 results
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Origins Of Rayleigh Wave Overtones In Ambient Noise
Authors A. Kazantsev, M. Peruzzetto, H. Chauris, P. Dublanchet and F. HuguetSummary2D spectral element simulations in the frequency range 0.1–3 Hz were performed on a large-scale model (1200×50 km). Ocean water, sediments, granitic crust and mantle were included. Two seismic arrays were modeled on the continent in order to analyze the wavefield composition on the granitic crust and above a sedimentary basin. Four source locations were tested: ocean surface in deep and shallow water, ocean bottom and continental surface near the array. Finally, the effect of removing the mantle from the simulation was investigated. The deep-water surface source was able to excite a clear Lg phase, which disappeared when the mantle was removed. The Lg phase, in turn, excited the overtones above the sedimentary basin. The Rayleigh fundamental mode was dominant for the other investigated source locations. This might explain the presence of the Lg phase and Rayleigh overtones in the short-period seismic noise, which is probably a signature of shortperiod sources near the surface in deep ocean.
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How The Choice Of Location Algorithm Affect Results: A Synthetic Comparison
Authors A. Wuestefeld, S.P. Näsholm and S.M. GreveSummaryA priori assessment of the expected location accuracy of a sensor network is typically done through inversion of the travel-time spatial gradients. This approach assumes that the applied location algorithm successfully recovers the global minimum of the objective function. However even for phase-picks without errors, complexity in the velocity model and limitations in network layout may inhibit the finding of a global minimum. The location algorithms may end up in a local minimum instead. This study focuses solely on the algorithmic aspects of the event location procedure. For a series of synthetic microseismic event locations, we calculate arrival times, add picking errors, and then feed these synthetic picks into a set of different location routines which look for minima in selected misfit objective functions. While most of the analyzed location approaches mainly lead to good location results, none of the analyzed approaches recovered the correct location for all event locations.
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Remote Real-Time Processing Of Hydraulic Fracture Treatment Microseismic Data Using Large Arrays
More LessSummaryReal-time processing of microseismic downhole data has been performed for many years, see for example Maxwell et al. (2000) . Downhole data lends itself to real-time processing, because the data volume is relatively small, typically less than 200 channels, and the relative high signal/noise ratios of downhole data makes it possible to perform “event triggering” to identify isolated segments of data that contain events, which can be remote transmitted to remote processing centers. Real-time microseismic processing of surface data is also not new, see for example Furong et al. (2017) . But real-time microseismic processing of surface data is generally done by placing large and expensive compute resources in the field, such as specialized trucks that are outfitted to house clusters of computers. Here we describe a workflow whereby data from large surface arrays with over 2,000 channels are processed in real time remotely, and we describe the benefits of this workflow for hydraulic fracture treatments.
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The Enigma Of Dip-Slip And Aligned Strike-Slip Events Within The Same Event Cloud
Authors W.M. Heigl, D.E. Diller, B. Fish, T. Shuck and S. WilsonSummaryOver the past decade, various authors have observed a dominance of dip-slip or strike-slip P-wave first motion patterns and the juxtaposition of both within the same microseismic event cloud (e.g. Eisner & Stanek, 2017 ; Tan & Engelder, 2016 ; Wilson & Diller, 2016 ; Diller et al., 2015 ; and references therein). The steeper, and sometimes near vertical, nodal plane of these dip-slip first motion patterns is often found to strike approximately parallel to the direction of maximum horizontal stress ( Fig. 1 ). Aligned strike-slip first motion patterns show a similar behavior: steeply dipping nodal planes and one of them striking parallel to the direction of maximum horizontal stress ( Fig. 2 ). Moreover, Rutledge et al. (2015) showed that both dip-slip and strike-slip events can concentrate in discrete depth intervals. One type of mechanism tends to dominate in a given reservoir, presumably reflecting different regional stress states. Tan and Engelder (2016) demonstrate that events in neighboring clusters can have opposing P and S wave polarities …
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Microseismicity To Production - What Do We Need To Measure First?
More LessSummaryCurrently there are four widely discussed theories how microseismicity interacts with hydraulic fracturing. Each theory has different implication for interpretation of microseismicity in the reservoir modeling. Therefore, better understanding of relationship between microseismicity and hydraulic fracture stimulation is needed before further reservoir models are developed and applied. That would lead to more precise estimation of hydrocarbon production and give greater value to microseismic. We may use either seismic or non-seismic methods. While non-seismic methods provide independent view on hydraulic fracture they seem to be limited in the amount of information on the relationship between hydraulic fracture and microseismicity. We propose microseismic monitoring of directivity as the most promising way to find out the orientation of fault planes and determine a slip vector on them. It seems to be the most suitable method but requires sensors in multiple azimuths and well coupled due to high frequency signals. We suggest using DAS sensors which are capable of sampling high frequency and may provide continuous data along long offset at reasonable costs.
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