Method and Case History of a New Full-waveform, Migration-based Deconvolution Approach* to Locating Microseismic Events

 

Nick Brooks (READ US)

 

 

Oil and gas held in tight shale formations does not flow in to a well unless the formation is stimulated. The stimulation process involves injection of fluid and proppant at high pressure to overcome the rocks natural breaking strength. The process fractures the rock and the proppant rushes in to the fractures. The proppant remains in the rock and holds the fractures open to semi-permanently increase the permeability for the required flow of hydrocarbons to surface. Very small earthquakes are produced during this process that can be monitored with sensitive geophone equipment. Mapping these micro-earthquakes is critical to understanding well efficiency, optimizing field production and minimizing environmental risk.

 

We present a new approach to generating 3D location maps for microseismic events from 3-component data. The method combines full-waveform vector migration with an imaging condition based on semblance-weighted deconvolution. The semblance-weighted deconvolution keys in on the signal-to-noise conditions of the data to give a high-resolution, low-noise estimate of the locations for the microseismic sources. As the method requires no explicit time picking or event association, it is well suited to be run as an either fully-automated or a semi-automated process. Almost as a byproduct, the method provides a natural measure of the uncertainty associated with the locations of the individual micro-earthquakes.

 

We present the results of the new processing method with real data acquired in Canada. We compare this to the traditional time-pick based approach and validate the method. The case history demonstrates improved microseismic event accuracy and a more consistent approach for solving microseismic event locations.

 

*Patent Pending