MicroSeismic Downhole Monitoring

With EventPick® Technology

Downhole-animation-title-slide-lgDownhole Monitoring with EventPick technology provides an independent evalution of well stimulation results in areas less suitable for surface-based microseismic acquisition. Final results determined using the proprietary EventPick processing technology can be delivered within a month of the acquisition. The solution provides operators with the fracture geometry and azimuth, discrete fracture network characterization, estimations of stimulated reservoir volume, and recommendations for completions optimization.

The results help operators determine well spacing, improve fluid and proppant selection, alter pressure pumping schedules, avoid geohazards, and delineate reservoir boundaries. The Downhole Monitoring product can be combined with MicroSeismic surface acquisition products like FracStar™ and BuriedArray®, and patented PSET™ processing to provide the leading technology for combined downhole + surface acquisition.

MicroSeismic has been in operation since 2003 and has performed downhole microseismic processing work since 2008, spanning three countries and across fifteen different formations. Our downhole processors have over 50 years of geophysical experience, located in both our Houston and Calgary offices. MicroSeismic uses the earthquake seismology derived technology of p-wave and s-wave first arrival picking for processing microseismic events acquired via downhole geophone arrays.

In order to accurately process and interpret the data, MicroSeismic performs the following activities:

  • Instrument calibration - Geophone rotation performed using a string shot or perforation shot.
  • Velocity calibration - Velocity models are derived using existing sonic logs or pre-existing velocity models. Vertical Transverse Isotropy (VTI) single-well-downhold-acquistionFigure 1: single-well downhole acquisitioncorrections made using Thomsen's parameters. Stage-by-stage velocity calibration is performed.
  • Raw data converted from SEGD to SEGY format - A debias filter is applied (where applicable). Then a band pass filter is used to eliminate high and low frequency noise.
  • Data processed - In addition to the proprietary and automated software, EventPick, experienced processors manually validate triggers to eliminate false positives.
  • Event hypocenters located - Origin times are defined for microseismic events. Additional attributes generated include amplitudes for picked events, back azimuth of events in relation to the monitoring well, and event magnitude. Detection thresholds can go down to -4.0 magnitudes depending on SNR and distance to observed microseismicity.

 

Array Design

Most commonly, the Downhole Monitoring hydraulic fracture monitoring service is deployed within a single nearby downhole monitoring well, optimally placed within 500m of the fracture zone. Where the monitoring well location is sub-optimally located, detectability can be improved through the use of multi-well downhole acquisition. Through the use of 3 downhole arrays, where such additional monitoring wells are available, locations can be more confidently determined.

single-well-downhold-acquistionFigure 2: Multi-well steam injection
downhole monitoring

An advantage of the more azimuthally varied acquisition in the multi-well scenario is the ability to calculate focal mechanisms. The focal mechanisms describe the dip, strike and rake of the mechanical failure occurring due to stimulation. This information identifies local stress orientation and nearby wellbore geology, and reveals how the horizontal maximum stress is changing over the field. In addition, more refined discrete fracture network models can be created.

A further refinement can be made through the combination of surface and downhole acquisition to provide a more comprehensive view of the fracture network. The wide aperture of the surface array minimizes positional error in the x and y direction and provides for more reliable source mechanism detection. The z direction resolution is improved by stage to stage velocity calibration. The downhole array provides for a lower threshold of event magnitude detectability and when the array is deployed at a target depth, the z direction positional error can be better constrained. The positional error in the x and y direction will depend on the proximity of the monitoring instruments to the fracturing activity.

Differentiators

  • Raw results and microseismic viewer provided on every job for QC
  • Multi-well acquisition can be imaged using full waveform migration or first arrival picking
  • Interpretation that goes beyond the dots, inclusive of Discrete Fracture Networks creation and EUR analysis
  • Unmatched knowledge of shale plays with 20,000 stages monitored overall
  • Final analysis and results, inclusive of all interpretation, delivered in under one month
  • Combined surface and downhole acquisition

For more information on our Downhole Monitoring with EventPick® Technology, please contact MicroSeismic.