Small Microseismic Surface Acquisition System for oilfield monitoring is presented. Algorithms for data processing are based on the mathematical theory of inverse problems and the using of the supercomputer calculations. A distinctive feature of the suggested system is high mobility, compactness and universality. The technology based on the this acquisition system is intended not only for hydraulic fracturing monitoring but also for long-duration passive monitoring of fluid injection, for hydrocarbon drainage area estimation and for oilfield block structure mapping. Case Study has more than 50 examples.

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We introduce an adaptive FK filter to improve the signal to noise ratio of passive seismic data. This method integrates the unique geometry of surface seismic arrays and the distribution of microseismic events induced by hydraulic fracturing. Results from both synthetic and field data show that this technique significantly improves the visibility of microseismic events in the surface recorded data. Applied together with envelope stacking, this method can efficiently locate events with various focal mechanisms.

A matched filter technique that uses cross-correlation and migration of the recorded waveforms has been successfully used to relatively locate microseismic events. In addition to producing consistent relative locations, the matched filter corrects for radiation pattern effects and near-surface structure. The relative locations produced using this methodology were compared with a proprietary, direct location method. The new results produce a solution set that reveals two parallel trends of microseismic events which are interpreted as 1500' long fracture zones approximately 100' wide. We observed asymmetric fracture growth and re-fracturing of the previously stimulated zones. Time correspondence of the observed evolution of seismic events with engineering pump curve data reveals approximate linear growth rates of several feet per minute and possible proppant placement along the induced fractures.

The mapping of microseismic events induced by hydraulic fracturing plays an important role in well completion and design. This is especially true in a newly developing area of gas producing shales. In this case study, we will show how the microseismic monitoring of a hydraulic fracture treatment in the Marcellus Shale identified a pre-existing natural fault which intersected the wellbore. The data from nearby wells indicated several possibilities of structural evolution affecting the producing formation. These range from regional reverse or strike-slip faulting to small displacement local reverse faulting. The hydraulic fracture stimulation was monitored using a 10 line, radial surface array composed of 1000 vertical component geophone stations. The treatment consisted of seven perforated stages stimulated with slickwater and proppant. Microseismic activity mapped during the early stages of the treatment is consistent with the regional stress direction and indicates that stages 1-4 activated natural fractures oriented along the maximum horizontal stress direction. During stages 5 and 6, the hydraulic fracture encountered a pre-existing natural fault. A source mechanism was determined for events occurring along the fault, identifying oblique failure with strike-slip and reverse faulting along the steeply dipping fault with SSE strike. This indicates that the regional strike-slip fault, with a strike similar to the break we observed at other offset wells, is most likely responsible for the geological evolution of this formation.