|Title||Wavefield characterization of perforation shot signals in a shale gas reservoir|
|Publication Type||Journal Article|
|Year of Publication||2017|
|Authors||Li, Y, Wang, H, Fehler, M, Fu, Y|
|Journal||Physics of the Earth and Planetary Interiors|
|Pagination||31 - 40|
Signals of perforation or string shots, which are usually used for calibrating velocity models and estimating the orientation of 3 component down-hole receivers during microseismic monitoring, are occasionally hard to identify due to poor signal-to-noise ratios (SNR) or confusion with the events induced during fracturing in adjacent wells. A significant feature for distinguishing perforation signals from hydraulic fracturing events is the tube wave, which is generated in the treatment well and received in the monitoring well. We analyze seismic wavefields from perforations during a hydraulic fracturing operation on a pad well (a group of horizontal wells with the wellheads at a same small surface area) in a shale gas reservoir to understand the wave propagation phenomena including attenuation and the identification of tube waves (guided wave in borehole) and their conversions. Since they are dominated by high frequencies and lack energy at low frequencies, the P- and S-wave arrivals of perforation shots decrease much more rapidly with propagation distance than that of induced events. We identify six modes within the wavefields of the perforation or string shots recorded in a nearby well that are related to the tube waves. The six modes include P- & S-waves converted from tube waves in the shot (treatment) well at plugs or the well bottom, an up-going tube wave in the monitoring well generated by the tube wave in the nearby treatment well, a down-going tube wave from the treatment wellhead and the multiple, a scatting body wave activated by tube waves in the treatment well. These wave modes all originate from the waves radiated at the perforation point in the treatment well as tube waves and are then radiated into the formation and received by geophones in the nearby borehole as P, S, or tube waves. If energy from the perforation shot is strong enough, the tube wave will turn back from the surface and be reflected at the well bottom or plugs, which would excite the further waves. Based on the features of the wavefield, we identify the perforation events and facilitate better use of calibration from the perforation seismic recording for microseismic data processing. We also evaluate attenuation of the signals with propagation distance and propose a procedure for developing a plan for monitoring of perforation and string shot signals.
|Short Title||Physics of the Earth and Planetary Interiors|