Microseismic emissions

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Microseismic emissions Heartbeats of a
reservoirProgramseminar for Norges
forskningsråds Olje og gass program3. 4. April
2003, Stavanger Michael Roth, NORSAR

• Introduction
• Processing
• Applications
• Outlook
• Related projects

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Introduction

• Projects
• Internal strategic institute program
• Research project (NFR, Read Well Sevices,
  Statoil, TFE)
• PhD - project (NFR)
• Objectives
• Development of an automatic microseismic
  monitoring system
• Real-time processing and localization
• Visualization of seismic events with subsurface
  structural model
• Analysis and interpretation of microseismic data
• Prototype monitoring software for microseismic
  data as
• recorded with 3C-geophones installed in an
  observation well

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Introduction

• Analyses of microseismic data has the potential
  to
• image the internal structure of the
  subsurface (faults, fractures)
• monitor fluid pressure front movements
• identify sealed-off reservoir volumes
• identify regions of reservoir compaction
• provide input for reservoir management
• provide feedback during hydrofracturing
• map thermal fronts
• provide input for hazard mitigation

Production of hydrocarbon reservoirs Hydrofracturi
ng Geothermal energy production Subsurface gas
storage Mining activity
Changes in stress field, pore pressure and load
Microseismic events
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Introduction
Typical features of microseismic data Signal
frequency 100 - 1000 Hz Fault plane
radius 10 1 m Seismogram duration lt 1 s
Magnitude 3 0 Mb Sourcereceiver
distance up to 1000 m Frequency of
occurrence 10 1000 per hour
Observation with 3C-geophones receiver downhole
installation
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Processing
Calibration
Detection
S-onset
Polarization
P-onset
Hypocenter
Localization
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Processing
Calibration
arbitrary orientation

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Processing
Calibration
shot position, geophone position,velocity model
polarization analysis of P-wave signal
measured azimuths (am)i
theoretical azimuths (ath)i
differences Dai (am - ath)i
rotation by Dai
consistent orientation
arbitrary orientation

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Processing
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Processing
Calibration
Detection
S-onset
Polarization
P-onset
Hypocenter
Localization
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Processing
Detection
based on the evaluation of signal-to-noise ratio
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Processing
P-onset determination

• compute AR model
• error prediction filtering
• compute AIC function
• find AIC minimum

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Processing
Detection
S-onset
Polarization
P-onset
Hypocenter
Localization
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Localization (3D velocity model)
Processing
3D raytracing for specific receiver geometry and
3D velocity model
Tabulated travel times and angles
Directed grid search
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Hydrofracturing Data Set
Applications

• 12 3C geophones deployed in a vertical
  observation well
• gimbal mounted, i.e. vertical components are
  oriented
• non-rigid connection, i.e. horizontal
  orientation is inconsistent
• 10 m receiver spacing
• 100 m distance to injection well
• 1h contineous recording, sampling interval
  0.5 msec
• 1000 microseismic events
• homogeneous velocity model

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Data Example
Applications
Left 4 s time window 4 microseismic events
0.2 s signal duration
Right Close up of the first event (channel 4
36)
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Applications
Data Example
Left 4 s time window 4 microseismic events
0.2 s signal duration
Right Close up of the first event (channel 4 6)
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Data Example
Applications
Left 4 s time window 4 microseismic events
0.2 s signal duration
Right Close up of the last event (channel 31
36)
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Applications
P-wave polarization
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Applications
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Hypocenters of microseismic events
Applications
View from SW
View from SE
Color-coded origin time (early blue, late red)
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Ekofisk Data Set
Applications

• 6 3C geophones deployed in a vertical
  observation well
• passive listening in 3 km depth close to
  the hydrocarbon reservoir
• 20 m receiver spacing
• event-triggered recording for 18 days, 1 ms
  sampling intervall
• 4000 events

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3D raytracing for EKOFISK velocity model
Applications
Velocity model has a strong vertical gradient at
the receiver depth Model volume (2 km)3 413
potential sources on a regular grid with 50 m
spacing 6 receivers Application of
reciprocity 6 sources and 413 receivers
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Applications
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Applications
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Applications
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Applications
Radius magnitude Color location error
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Outlook

• Future plans for monitoring software
• Restructuring for heterogenous network (3C-,
  1C-geophones, hydrophones)
• Restructuring for arbitrary receiver deployment
  (wells, surface, sea floor)
• Facilitate interactive processing for selected
  events
• Waveform analyses
• Source mechanisms

Related Projects
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Related Projects
San Andreas Fault Observatory at Depth (SAFOD)
Cooperation with Duke University, North
Carolina US Geological Survey, Menlo Park,
California

• penetrate fault zone
• directly sample fault zone materials
• directly measure physical and
• chemical fault zone properties
• monitor an active fault at depth
• pilot hole to identify and localize earthquake
  targets
• 1.8 km distance to San Andreas Fault
• 32 3C geophones
• depth 850 2090 m
• 40 m spacing
• 1 ms sampling

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Pyhaesalmi Ore mine, Finland
Related Projects
Research cooperation with Lawrence Livermore
National Laboratory

• Monitoring of explosions and rockbursts
• 4 3C and 12 1C geophones deployed in drifts in
  the lower part of the mine
• 3D velocity model
• 3D receiver distribution
• Determination of hypocenters and radiation
  patterns

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Related Projects
Rock-slope failures Models and risk assessment

• Monitoring of potential
• rockslide sites in Norway
• Extensometers
• Photogrametry
• GPS
• Synthetic Aperture Radar
• Laser measurements
• Microseismic monitoring

Preliminary regional rock-avalanche hazard zones
in Møre Romsdal