14-15 May 2012 Register

Microseismic Monitoring in Oil or Gas Reservoir

by Leo Eisner

Duration: 1-2 days

Summary:
This course will discuss principles of microseismic monitoring. A brief historical overview of earthquake and micro-earthquake monitoring techniques in related fields will allow basic insight and provide list of most important publications. Downhole monitoring techniques will be described with detailed examples of complete process from velocity model building, through geophone orientation to microseismic event locations. Principles of surface monitoring will be also discussed with examples of velocity model calibration, location of microseismic events and source mechanism analysis. The course will also explain principles of source mechanisms inversion and an estimation of strength of anisotropy from shear wave splitting. The course will briefly discuss application of microseismic monitoring to reservoir stimulation, particularly to estimate Stimulated Reservoir Volume. Finally, case studies and broader discussion of felt seismicity in the vicinity of oil and gas fields will be discussed.

Course Outline:

  • Definition of microseismicity, induced/triggered seismicity, a brief review of microseismicity outside of oil industry: water reservoirs, mining, geothermal. Historical review of microseismicity in oil industry with focus on hydraulic fracturing (M-site, Cotton Valley, Barnett, etc). Review of the main results obtained to date. Brief overview of the hydraulic fracturing.
  • Location techniques for earthquakes: number of unknowns, differences from active seismic. Large earthquake locations: Grid search techniques. Relative locations. Order of magnitude estimates of locations. Earth velocity model and crustal waves. Introduction to anisotropy.
  • Downhole location technique: single well monitoring technique - S-P wave time + P-wave polarization technique location, P-wave and S-wave polarization. Single phase location and uncertainty. Class exercise on moveout-distance. Picking strategies for microseismic data, class exercise. Orientation of downhole geophones/deviation surveys/velocity model calibration. Anisotropy and geometry. Inclined/dual and multi well monitoring techniques. Designing of downhole monitoring array.
  • Surface monitoring technique: vertical component only, uncertainty associated from P-wave locations: depth vs. origin time, class exercise. Frequency content, attenuation and detection. Calibration shots/velocity model building: isotropic vs. anisotropic velocity. Relative locations through cross-correlations of the vertical component. Downhole and surface location case study. Near surface amplification. Designing of surface monitoring array.
  • Source mechanisms: concept of source mechanism, definition of dip, strike and rake for shear source. Description of shear, tensile, volumetric, CLVD source through moment tensor. Inversion for source mechanisms from single monitoring borehole/ multiple monitoring boreholes/ surface P-only data, class exercise. Picking of data for determination of source mechanisms. Radiation pattern of various source mechanisms. B-value, moment, magnitude, Stress drop, source dimensions.
  • Anisotropy: Effect of anisotropic media on S-waves: shear wave splitting. Source radiation pattern and shear wave splitting. Shear wave splitting observed in microseismic data. Inversion of anisotropic media from P and S-waves using microseismic events. P-wave anisotropy on surface monitoring data. Time-lapse changes in anisotropy. Effects of VTI vs. scaled isotropic velocity model.
  • Reservoir simulations: Diffusion model for pressure triggering of microseismic events. Current use of microseismicity in oil industry and implementation of microseismicity into modeling.
    Discrete Fracture Networks constrained by microseismicity. Reservoir simulations and history matching.
  • Review of recent important case histories. Seismicity felt in the vicinity of oil or gas reservoirs with focus on hydraulic fracturing. Summary of the class. Most important things to remember about microseismicity.

Learner Outcomes:

  • Design an optimal array for passive seismic (surface or downhole) monitoring and estimate uncertainties of locations for microseismic events.
  • Orient downhole geophones from a perforation or calibration shot, estimate approximate distance and depth of a recorded microseismic event.
  • Locate from the surface monitoring array and estimate source mechanisms of visible microseismic events, pick first arrivals on surface array.
  • Measure S-wave splitting.
  • Calculate Stimulated Reservoir Volume from microseismic event locations.

Instructor Biography
Leo Eisner