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Sainte-Tulle, France

Gesret A.,MINES ParisTech | Desassis N.,MINES ParisTech | Noble M.,MINES ParisTech | Romary T.,MINES ParisTech | Maisons C.,Magnitude SAS
Geophysical Journal International | Year: 2015

Earthquake hypocentre locations are crucial in many domains of application (academic and industrial) as seismic event location maps are commonly used to delineate faults or fractures. The interpretation of these maps depends on location accuracy and on the reliability of the associated uncertainties. The largest contribution to location and uncertainty errors is due to the fact that the velocity model errors are usually not correctly taken into account. We propose a new Bayesian formulation that integrates properly the knowledge on the velocity model into the formulation of the probabilistic earthquake location. In this work, the velocity model uncertainties are first estimated with a Bayesian tomography of active shot data. We implement a sampling Monte Carlo type algorithm to generate velocity models distributed according to the posterior distribution. In a second step, we propagate the velocity model uncertainties to the seismic event location in a probabilistic framework. This enables to obtain more reliable hypocentre locations as well as their associated uncertainties accounting for picking and velocity model uncertainties. We illustrate the tomography results and the gain in accuracy of earthquake location for two synthetic examples and one real data case study in the context of induced microseismicity. © The Authors 2014. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Godano M.,University of Nice Sophia Antipolis | Godano M.,Magnitude SAS | Gaucher E.,Magnitude SAS | Bardainne T.,Magnitude SAS | And 3 more authors.
Geophysical Prospecting | Year: 2010

We have developed a method that enables computing double-couple focal mechanisms with only a few sensors. This method is based on a non-linear inversion of the P, Sv and Sh amplitudes of microseismic events recorded on a set of sensors. The information brought by the focal mechanism enables determining the geometry of the rupture on the associated geological structure. It also provides a better estimate of the conventional source parameters. Full analysis has been performed on a data set of 15 microseismic events recorded in the brine production field of Vauvert. The microseismic monitoring network consisted of two permanent tools and one temporary borehole string. The majority of the focal mechanisms computed from both permanent tools are similar to those computed from the whole network. This result indicates that the double-couple focal mechanism determination is reliable for both permanent 3C receivers in this field. © 2010 European Association of Geoscientists & Engineers.

Rosca A.,Magnitude SAS | Maisons C.,Magnitude SAS
Society of Petroleum Engineers - SPE/EAGE European Unconventional Resources Conference and Exhibition 2012 | Year: 2012

Monitoring reservoir Stimulation operations provides data for predicting production performance and for reservoir characterization but also, potentially, for compliance with local regulations. With improved drilling and completion technology the depth of the unconventional reservoirs produced increases and the options for deploying cost-effective microseismic monitoring equipment become limited. The monitoring technology has to adapt by optimizing acquisition geometry and data processing as well as the procedures that demonstrate the validity of me results. A practical solution for microseismic monitoring of stimulation operations in an unconventional reservoir under development is a surface or shallow distributed array. We are analyzing three such datasets together with complementary deep borehole sensor datasets to understand how to predict and validate the expected performance of distributed surface and shallow arrays. The surface recorded data is processed by stacking and event detection and location are accepted based on statistical criteria. This catalog of events is compared to the one obtained from borehole array where waveforms can be analyzed individually in order to validate the quality of event analysis. Copyright 2012, Society of Petroleum Engineers.

Belayouni N.,Magnitude SAS | Gesret A.,MINES ParisTech | Daniel G.,Magnitude SAS | Noble M.,MINES ParisTech
Geophysics | Year: 2015

Locating microseismic events accurately is essential to characterizing hydrofracked reservoirs. Several location approaches have been developed to solve this problem. We have developed a global grid search method based on the Bayesian probabilistic approach. In addition to retrieving the global minimum of the cost function, it enabled the computation of the uncertainty that was essential to quantify the quality of the results. The location uncertainty was tightly related to the amount and the quality of observed data used to perform the location. Using multiple arrivals increased the quantity of information collected in a cost-effective manner (no additional receivers were required). In this location algorithm, we have used the first and reflected arrivals to constrain the locations. To locate the events, it was essential to model the first and reflected arrivals given a velocity model and acquisition geometry. We have developed a ray-tracing algorithm capable of computing traveltimes and polarization of direct, refracted, reflected waves in layered velocity models. We have applied this methodology for several examples. The synthetic data set was generated using full-waveform finite-difference modeling and recorded in a single vertical well. The first and reflected traveltimes were picked using the 3C seismograms. In the last example, we used the Cotton Valley real data set in which reflections could be seen for strong events due to the high velocity contrasts. The applications revealed that the location uncertainty was significantly reduced when using both arrivals compared with the case when only first arrivals were used. Combining the first and reflected arrivals even allowed us to improve the location accuracy when the velocity model was inaccurate. © 2015 Society of Exploration Geophysicists.

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