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

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

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

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Reflection (CMP Spread) 5 km line ‘Tanos Fault Profile’ 20 m Geophone intervals Source: Vibroseis, 20 m VP spacing, Sweep 10-70 Hz, 12 s, 1.0 taper Receivers: L-28, 3-component (vertical only used), 4.5 Hz geophones

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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

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More Processing Butterworth filter (15-70 Hz) Muting CMP Sort CMPLoc 404.5 Mute Example

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

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

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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

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

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Constant Velocity Stacks Create velocity function and apply NMO

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

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Velocity Analysis Integration of CVS and Hyperbolic picks 360420480 500 ms 1000 ms 1500 ms

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Comparison CVS Final Stack CVS + Hyper- bolic Final Stack

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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

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Fault Interpretation

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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

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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)

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

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