Methods, systems and devices for near-well fracture monitoring using tomographic fracture imaging techniques
View Patent ↗Described herein are various embodiments of methods and corresponding hardware and software configured to permit the vicinity around and/or near a well to be imaged, where the well is being subjected to, or has been subjected to, fracking operations. The methods and corresponding hardware and software permit the generation of images of near-well fractures or faults resulting from the fracking.
1. A method of imaging a volume of the earth's subsurface near a well bore, comprising:
selecting a first sub-set of a microseismic data set acquired over a data acquisition time period with a plurality of sensors located at a plurality of sensor positions disposed in proximity to the well bore, said microseismic data set representing microseismic emissions originating from faults or fractures generated in the subsurface of the earth near said well bore during a hydraulic fracturing stage at a hydraulic fracturing stage location during a hydraulic fracturing stage time period, the first sub-set of said microseismic data set representing seismic energy emissions from a first set of nodes or voxels in the earth's subsurface near said well bore at the fracturing stage location;
dividing said first sub-set of a microseismic data set into a plurality of time intervals and stacking the microseismic data within each time interval;
voxel-value filtering the stacked microseismic data within each of said plurality of time intervals;
selecting only voxels within each time interval having voxel value magnitudes greater than a selected magnitude, thereby generating a second voxel-value filtered sub-set of said microseismic data set;
within each time interval selecting from said second voxel-value filtered sub-set of said microseismic data set only groups of one or more voxels having voxel-value magnitudes greater than said selected magnitude, the selected voxels in each group being contiguous with each other, with at least one selected voxel in each group encompassing or contiguous with said well bore, thereby generating a third voxel-value-filtered sub-set of said microseismic data set determined to be near the hydraulic fracturing stage location of said well bore;
stacking data across time intervals in the third voxel-value-filtered sub-set of said microseismic data set to form stacked filtered voxel values in the third set of nodes or voxels to generate a fourth sub-set of said microseismic data set, and
skeletonizing the stacked filtered voxel values of the fourth sub-set of said microseismic data set to generate a fifth sub-set of said microseismic data set corresponding to a spatial representation of the fracture or fault near the wellbore at the hydraulic fracturing location.
2. The method of claim 1 , wherein voxel value filtering further comprises computing at least one local maximum in the voxels of the corresponding data subset.
3. The method of claim 1 , wherein voxel value filtering further comprises passing voxel values that exceed a predetermined minimum value.
4. The method of claim 1 , wherein voxel value filtering further comprises filtering each data subset to pass a predetermined percentage of the highest voxel values associated therewith.
5. The method of claim 1 , wherein voxel value filtering further comprises filtering each data subset to pass voxel values that exceed a calculated value computed on the basis of a range of values in the data subset.
6. The method of claim 1 , wherein stacking further comprises computing the cumulative sum of the filtered voxel values.
7. The method of claim 1 , wherein stacking further comprises computing the maximum value of the filtered voxel values.
8. The method of claim 1 , wherein stacking further comprises computing the average of the filtered voxel values.
9. The method of claim 1 , wherein the voxel values in the sub-sets of said microseismic data set are semblance values.
10. The method of claim 1 , further comprising acquiring a microseismic data set for use in the method.
11. The method of claim 10 , further comprising disposing at least some of the plurality of sensors along the surface of the earth.
12. The method of claim 10 , further comprising disposing at least some of the plurality of sensors beneath the surface of the earth in a borehole.
13. The method of claim 10 , wherein the data acquisition time period ranges between about 1 minute and about one week.
14. The method of claim 1 , wherein the selected time period corresponds approximately to a time period over which hydraulic fracturing operations occur.
15. The method of claim 1 , wherein voxel value filtering further comprises one of median filtering, threshold filtering, 2-D filtering, 3-D filtering, coherence filtering, and statistical filtering.