System and method for narrow beam scanning microseismic monitoring

摘要

Disclosed herein are various embodiments of methods and systems for optimizing signals generated by microseismic sources, comprising recording microseismic data using patches of geophones, filtering the data to impart a directionality to the data, and performing a source scan to determine the times and locations of microseismic events. The subsurface is divided into a voxel grid that is further subdivided into subgrids. Using a filter designed for each patch-subgrid pair, only data arriving within a predetermined angle of incidence are input to the source scan, thus reducing noise, and enhancing the quality and accuracy of the identified microseismic events. The method is also applicable to data previously recorded with sensor grids or other arrays such as star arrays.

主权项

1. A method for determining the location of at least one microseismic event in a subsurface volume comprising:
obtaining a microseismic data set for a selected subsurface volume, the microseismic data being recorded at a sampling interval of between 0.25 and 16 milliseconds, over a predetermined time window in the range of one minute to several days, at a plurality of surface sensor patches; conceptually dividing the subsurface volume into a primary grid comprised of a plurality of voxels; determining a transformed spectrum of observed noise within the microseismic data using a transform algorithm; specifying subgrids of voxels within the primary grid of voxels, the size of the subgrids being based on the transformed spectrum of observed noise; for each subgrid; narrow beam filtering the microseismic data for each patch wherein narrow beam filtering comprises;
(i) transforming the data into a transform domain using a transform algorithm;(ii) zeroing all data except that within a transform domain filter cone, with tapering at the edges of the cone;(iii) transforming the data back to the time-space domain using a reverse transform algorithm;combining the narrow beam filtered data from all the patches;performing a microseismic source scan on the combined narrow beam filtered data, at each voxel within the subgrid; combining the microseismic source scanning results from all subgrids and identifying the location of at least one microseismic event.