Method and system for microseismic event location error analysis and display

Abstract

According certain aspects, embodiments of the invention consider the problem of microseismic event localization from a parameter estimation perspective, and include a method and system for computing and displaying characteristics of event localization errors. According to certain other aspects, embodiments of the invention include techniques for deriving aggregate statistics from a set of event location estimates, including methods for computing and displaying the probability that an event occurred in any given volume, and methods for describing and displaying the smallest volume that contains a specified percentage of the event probability or expected to contain the specified percentage of the events.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application claims priority to PCT / US2013 / 022950, filed Jan. 24, 2013, which application claims priority to U.S. Prov. Appln. No. 61 / 590,189 filed Jan. 24, 2012. The present application is also a continuation-in-part of U.S. application Ser. No. 13 / 598,580, filed Aug. 29, 2012, which application claims priority to U.S. Prov. Appln. No. 61 / 528,730, filed Aug. 29, 2011. The contents of all of the above applications are incorporated herein by reference in their entireties.FIELD OF THE INVENTION[0002]The present invention relates generally to seismic monitoring and more particularly to a system and method for location error analysis and the display of information regarding microseismic events associated with a monitored volume.BACKGROUND OF THE INVENTION[0003]Passive localization of microseismic events is commonly used to monitor resource extraction processes such as hydraulic fracture stimulation, or “fracking,” and has also been...

AI Technical Summary

Benefits of technology

The patent describes a method for displaying an estimated location of an event in a space using voxels. The method assigns a probability to each voxel in the space, based on the likelihood of the event occurring there. The probability is computed by averaging the likelihoods of each voxel in the space. By default, the method displays the estimated location using a fixed set of characteristics (e.g. color, intensity, and transparency) that reflect the computed probability. However, the method also allows the intermediate step of computing the probability volume to be skipped, and each event can be used to modify the properties of a set of voxels in the surrounding area. This results in a nonlinear decrease in the transparency of the modified voxels, based on the estimated event location. Overall, the method allows for more accurate and efficient display of estimated locations in a space, which can be useful in various applications such as augmented reality and virtual reality.

Problems solved by technology

Inaccuracies in location estimates result from seismic background energy and uncertainties in seismic wave propagation, and are related to the array and fracture geometry.

While some rules of thumb have been developed using this approach, they are not easily applied to real-world scenarios, and their limits of applicability are not known.

Without having a known mathematical relationship between the scenario geometry and signal characteristics and the localization error, it may not be possible to determine whether a characteristic of the collection of event locations results from measurement error or is important to the interpretation of the treatment.

A difficulty with this approach has to do with the handling of estimated locations that appear to be outliers and the choice of the subset of localized events that is to define this convex hull: the stimulated volume estimate should be extended to include positions of accurately localized outlying events, but should not be extended in the case of poorly localized outlying events.

One problem with this approach is that the greater the event energy, the more accurately the event may be localized—it has greater amplitude, and its features more visible above the seismic background.

As a result, it is misleading to plot energetic events with markers that span larger volumes.

In addition, the event spheres are opaque, and it is not possible to understand the density of events within a given volume if there are more than a few events present.

One issue that arises is how to correlate the discrete locations of the events with the continuous data, especially if the event positions are known with varying accuracy.

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