Paper No. 6
Presentation Time: 2:15 PM
INTEGRATING MULTI-SCALE BOREHOLE-BASED GEOPHYSICAL MEASUREMENTS TO IMPROVE FORMATION UNDERSTANDING
We present the results of a microseismic monitoring campaign performed on multi-stage hydraulic fracturing treatments using two nearby pseudo-vertical monitoring arrays composed of eight 3C geophones each. To derive confident mapped hypocentral locations and associated source parameters we benefit from several borehole-based geophysical measurements such as sonic logs, cross well tomographic and attenuation profiles as well as multiple calibration points. Though, all these measurements take place in different frequency domains they allow to document very efficiently the variations in space and time of the velocities, anisotropies, attenuations, and rock physics in the zones of interest and surrounding formations. Initial results show that the hydraulic treatments performed in the sandstone formation are not fully contained by the surrounding coal layers. Microseismic activity monitoring seems to correlate with rock fabric despite slight seismic signal attenuation likely associated to coal. Apparent asymmetry of the mapped hydraulically fracture network seems to relate to the monitoring geometry. Velocity of the formation seems to change in relation to pressure and effective porosity and/or shear-wave attenuation. In addition, early interpretations relied on filtering events with low signal-to-noise ratio and high location uncertainty in association to various source parameters. This approach may significantly reduce the number of events available for interpretation since most microseismic events are by definition weak rather than strong. Using a series of quality control attributes based on various characteristics to increase confidence in interpretation using examples to ascertain usefulness. Quality control attributes quantify for both P- and S-waves signal-to-noise ratio, time and azimuthal residuals, orthogonality and confidence factor. These quality control attributes can be used to systematically compare data quality between various events within one stage, between various stages within a single well, between various treatments among many wells in one or more fields or basins. Initial moment tensor inversion results tend to indicate a large population of strike-slip events and few mode I events; thus, maybe explaining the small velocity and attenuation variations observed.