Microseismic Monitoring in Oil or Gas Reservoir

by Leo Eisner, Ph.D., MSc.

Duration: Two days

Intended Audience: Entry and Intermediate levels

Prerequisites (Knowledge/Experience/Education Required): The course is designed to be followed by anyone with a broad geoscience background: no specific detailed foreknowledge is required, although a familiarity with geophysical terminology will be useful.

Summary:
This course will discuss principles of microseismic monitoring. The goal of this class is to explain principles of microseismic monitoring ranging from single monitoring borehole to surface and near surface networks. This class focuses on understanding the measurements made in passive seismic and their uncertainties. The case studies are used occasionally however they are not the main focus of this class. Attendee should be able to design, possibly use the right kind of processing and mainly understand the uncertainties in the obtained microseismicity hopefully avoiding interpretation of noise and gaining insight in true information provided by microseismicity. No requirement on prior class is needed, although knowledge of hydraulic fracturing and seismology helps. The course will also discuss the latest development in microseismic applications from source mechanisms, though anisotropy to reservoir simulations. Last but not least the course discusses also social and scientific aspects of seismicity related to oil and gas reservoir.

Course Outline:

  1. Introduction
    • Definition of microseismicity, induced/triggered seismicity, a brief review of microseismicity outside of oil industry: water reservoirs, mining, geothermal
    • Oil reservoir production induced seismicity
    • Historical review of microseismicity in oil industry with focus on hydraulic fracturing (M-site, Cotton Valley, Barnett, etc.)
    • Principles of the hydraulic fracturing
  2. Earthquakes
    • Number of unknowns, differences from active seismic
    • Classical earthquake location techniques
    • Relative locations
    • Location techniques and exercise
    • Earth velocity model and crustal waves
  3. 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
    • Picking strategies for microseismic data
    • Optimal design of downhole monitoring array
    • Orientation of downhole geophones/deviation surveys/velocity model calibration
    • Inclined/dual and multi-well monitoring techniques
  4. Surface monitoring technique
    • Vertical component only, uncertainty associated from P-wave locations: depth vs. origin time
    • Detection uncertainty and signal-to-noise ratio
    • Frequency content, attenuation and detection
    • Design of surface monitoring array
    • 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
  5. 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
    • Radiation pattern of various source mechanisms
    • B-value, moment, magnitude, stress drop, source dimensions
  6. Anisotropy
    • Introduction to 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
  7. Reservoir simulations
    • Current use of microseismicity in oil industry and implementation of microseismicity into modeling
    • Diffusion model for pressure triggering of microseismic events
    • Discrete fracture networks constrained by microseismicity
    • Reservoir simulations and history matching
  8. Seismicity in the vicinity of oil or gas reservoirs
    • Theory and history of induced felt seismicity
    • Seismic moment and total injected volume
    • Blackpool case study as an example of induced seismicity
    • DFW seismicity case study
  9. Review of recent important case histories
    • Recent important case studies
    • Relationship between microseismicity and hydraulic fracturing
    • Most important things to remember about microseismicity

Learner Outcomes:

  1. Design an array for passive seismic (surface or downhole) monitoring and estimate uncertainties of locations for microseismic events
  2. Orient downhole geophones from a perforation or calibration shot, estimate approximate distance and depth of a recorded microseismic event
  3. Build a velocity model (P and S-wave) from a sonic log or check shot measurement suitable for microseismic monitoring
  4. Estimate source mechanism from surface microseismic monitoring
  5. Design a monitoring array that would allow avoiding of significant (felt) seismic events induced by hydraulic fracturing (traffic light system)

Instructor Biography:
Leo Eisner