Seismic Reflection Processing/Velocity Analysis of SAGE 2007 Data Andrew Steen Team Members; Stan, Tim, Josh, Andrew

Overview  Location  Reflection (CMP) Spread  Processing Steps  Velocity Analysis  Interpretation  Conclusions

Location State map – New Mexico Area of Study + Seismic Line

Reflection (CMP Spread) 5 km line ‘Tanos Fault Profile’ 20 m Geophone intervals Source: Vibroseis, 20 m VP spacing, Sweep Hz, 12 s, 1.0 taper Receivers: L-28, 3-component (vertical only used), 4.5 Hz geophones

Processing Geometry  Account for lateral position change  Corrects for profile meanders  Use GPS Deconvolution  Inverse filter for earth  Reduces multiples  Adds high frequency Trace Kills

More Processing Butterworth filter (15-70 Hz) Muting CMP Sort CMPLoc Mute Example

Velocity Analysis Purpose  Assign average velocities  Determine best stack  Important for interpretation Techniques  Semblance Plots  Constant Velocity Stacks  Hyperbolic Picks

Velocity Analysis Semblance Plots  Semi-Automatic  Plot shows density/strength  Need good S/N ratio  Not Used

Velocity Analysis Constant Velocity Stacks (CVS)  Assume homogeneous velocity  Range of velocities (+/-) 30% of expected  Smaller step-size is better  Vary NMO to maximize coherency  Useful for stacking and complex structures  Examples

Constant Velocity Stacks Blue = Good StackRed = Poor Stack 300 ms CMPLoc CmpLoc V= 3000 m/s V= 2400 m/s

Constant Velocity Stacks Create velocity function and apply NMO

Hyperbolic Picking Use CMP Gathers Identify prominent reflectors Fit hyperbolas Example:  CMP Gather File  CMPLoc 380  Before and After

Velocity Analysis Integration of CVS and Hyperbolic picks ms 1000 ms 1500 ms

Comparison CVS Final Stack CVS + Hyper- bolic Final Stack

Maybe the West Tanos Fault? Pros  Noticeable offset with CVS/Hyperbola stack  Correlates with proposed fault Cons Need more velocity analysis Some opposition / lack of supporting evidence

Fault Interpretation

Potential Fault displacement Calculated time offset Multiplied by approximate velocity Determined displacement.073 s * 2504 m/s = 183 m = 558 ft.069 s * 2504 m/s = 173 m = 528 ft

General Conclusions Processing seismic reflection data  Understand the science  Trial and error  Identifying reflectors and velocity analysis! Interpreting seismic reflection data  Hopefully it was processed effectively  Need a ‘trained eye’ West Tanos fault….might exist (optimistic tone)

Thank You All SAGE 2007 Staff  Especially  Dr. Braile  Dr. Ferguson  Dr. Biehler Seismic Reflection Crew And everyone who kept it real