Microseismic Interferometry: Transforming dots in a box into a 3D seismic image
Traditionally, operators plan and execute a hydraulic fracturing project based in part on available seismic data, which lacks the resolution needed to see fine-scale geophysical features and reservoir extent. Without a detailed understanding of a reservoir’s geophysical characteristics, the chosen fracturing parameters may not be optimal, resulting in diminished performance and wasted money.
OptaSense has released an advanced method of imaging called microseismic interferometry that uses the microseismic events themselves as seismic sources to generate high-resolution three-dimensional images. Using data recorded on either DAS fiber optic tools or conventional three-component receivers, microseismic interferometry improves upon traditional microseismic processing which produces event locations (dots in a box) along with some event attributes but no image.
OptaSense’s new technique employs thousands of microseismic events to build up a 3D image of the stimulated reservoir volume and supply a high resolution image of the subsurface geology around event locations.
Microseismic interferometry works by gathering data from a long borehole seismic array, ideally with 3C sensors straddling the stimulation zone. The data is then processed in a conventional manner to produce event locations and magnitudes. Following this initial analysis, the full waveform data is processed using interferometry – imaging the P and S wave fields to produce a local image for each microseismic event. These local images are combined into one large 3D volume covering the entire extent of the frac zone. This analysis can be performed on newly-acquired microseismic data or on existing surveys.
The 3D interferometric image volume can be analyzed using standard seismic analysis tools and can be integrated with existing surface seismic interpretations, well logs, formation tops, horizons or geomechanical analyses to build a better understanding of the reservoir and its geology. This improved understanding may be particularly useful for planning additional wells in nearby areas or re-fracturing wells in the imaged area.
OptaSense’s microseismic interferometry method extracts high-resolution information from existing data. Customers benefit from optimizing the costs of completion and drilling as they can use the information to plan subsequent fracs in nearby areas, re-fracs in the same formation or for time-lapse reservoir characterization.
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