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.

What is claimed is: 
     
         1 . A method for displaying microseismic events, comprising:
 obtaining location estimates of a plurality of microseismic events;   obtaining statistics of the event location estimates; and   based on the statistics, displaying the events such that poorly localized events occupy a large area of the display, and accurately localized events appear only in a relatively small area around the estimate.   
     
     
         2 . A method according to  claim 1 , wherein all location estimates are plotted as points, with a shade or color indicating localization accuracy and/or energy. 
     
     
         3 . A method according to  claim 2 , wherein on a white background, more accurately localized events are plotted using darker colors. 
     
     
         4 . A method according to  claim 1 , further comprising:
 dividing a display volume into voxels, each of the voxels being no larger than the greatest possible localization accuracy; and   for each event location estimate, adjusting each voxel according to the probability that it contained the event.   
     
     
         5 . A method according to  claim 4 , wherein adjusting includes assuming that the estimate errors are Gaussian and unbiased, and using the information inequality or other means to infer the covariance of the estimate. 
     
     
         6 . A method according to  claim 5 , wherein an estimate with high variance darkens a region in the space, whereas an accurately localized event will darken only one or more voxels. 
     
     
         7 . A method according to  claim 6 , wherein the fine structure of the fracture is not obscured. 
     
     
         8 . A method according to  claim 6 , wherein adjusting includes, for each event, drawing a semi-transparent ellipsoid, centered on the estimated location and sized according to the estimate standard deviation. 
     
     
         9 . A method according to  claim 8 , wherein a transparency of the ellipsoid is inversely related to its volume, such that the smaller the ellipse the less transparent it would be. 
     
     
         10 . A method according to  claim 9 , wherein the transparencies are nonlinearly combined such that a number of nearby inaccurately localized events produce a relatively small opaque region. 
     
     
         11 . A method according to  claim 9 , further comprising performing erosion and dilation operations to bridge small gaps in an estimated fracture structure resulting from undetected events.