Beach Energy Ltd Lake Tanganyika 2D Marine Seismic Survey Data Processing, 2014 Revised Displays...

Beach Energy LtdLake Tanganyika 2D Marine Seismic SurveyData Processing, 2014

Revised DisplaysTau-P Domain Linear Noise Attenuation Tests

Lines BST14B24 and BST14B67 Revised Feb. 25, 2015

Notes on Revisions:

• Tau-P transform was originally performed using a bandwidth of 2 to 125 Hz.• The data contains water-borne dispersive and direct arrival noise up to 200 Hz (data beneath water-bottom may contain useable frequencies up to 90Hz in the shallow)• Therefore stacks and difference plots required a 3-10-80-120 Hz to equalize to the transformed data in order not to show differences along the water bottom and shallow areas. The image at the water bottom will also improve greatly with improved stacking mute design.

• A Bandpass filter was applied to the data before shot record, stack and difference plot displays were generated, to remove the data differences not inherent in the Tau-P linear noise attenuation process.

• Linear Noise can be removed in the Tau-P domain using a mute defined by slowness or velocity.

• For testing, shot records and stacks were viewed before and after the application of Tau-P Domain Linear Noise Attenuation. Line BST14B24 was used as an example of data from a shallow water area and Line BST14B67 was used as an example of data from a deep water area.

• The design of the Tau-P mute is fairly "mild" to ensure preservation of dipping reflection data on the shot records and this process should not be applied in the areas where the water bottom dip is very steep. Each line will have to be QC'd for site specific application.

• The application of Tau-P Linear Noise Attenuation is recommended.

Tau-P Linear Transform Parameters Type: Hi res Radon

Min Frequency: 2 Hz Max Frequency: 125 Hz Max. Offset : 3100 m

Min Slowness: -0.7 msec/m Max Slowness: 1.2 msec/m

Lake Tanganyika 2D Marine Seismic SurveyLocation of Test Lines

Shot Record Displays

Sequence

Input field data/ReformatAdd Geometry: (theoretical straight line)Spherical Divergence Correction: (V**2)(T**1.6)Ensemble Balance: entire record scaledLow-cut: 4 HzSquelch: noise reduction band, 1-3-6-16 HzFXSwell: noise freq. Range: 3-30 HzTau-P Domain Linear Noise Attenuation: Hi-res, 2-125 Hz, mutedBandPass Filter: 3-10-80-120 Hz (before differencing)

Display: -ve = blue, +ve = red

Note: impulsive source reflection data positive reflection co-eff. = -ve number or blue color

Shot Gather 1208, Line B24 (shallow water)Before Tau-P Linear Noise Attenuation Applied

Shot Gather 1208, Line B24(shallow water)After Tau-P Linear Noise Attenuation Applied

Shot Gather 1208, Line B24 (shallow water)Difference After Tau-P Linear Noise Attenuation Applied

Shot Gather 1208, Deep Zone, Line B24 (shallow water)Before Tau-P Linear Noise Attenuation Applied

Shot Gather 1208, Deep Zone, Line B24(shallow water)After Tau-P Linear Noise Attenuation Applied

Shot Gather 1208, Deep Zone, Line B24 (shallow water)Difference After Tau-P Linear Noise Attenuation Applied

Tau-p Domain Display , Line B24 (shallow water)

Tau-p Domain Display , Line B24 (shallow water)with Mute applied

Tau-P Transform OnlyForward/Reverse/Difference

Shot Record Displays

Input Shot Gather 1208, Line B24 (shallow water)

After Forward/Reverse Tau-p Transform

Difference After Forward/Reverse Tau-p Transform

Stack Displays

Sequence

Input field data/ReformatAdd Geometry: (theoretical straight line)Spherical Divergence Correction: (V**2)(T**1.6)Ensemble Balance: entire record scaledLow-cut: 4 HzSquelch: noise reduction band, 1-3-6-16 HzFXSwell: noise freq. Range: 3-30 HzTau-P Domain Linear Noise Attenuation: Hi-res, 2-125 Hz, mutedBandpass Filter: 3-10-80-120Hz

NMO correction: preliminary velocitiesStackHigh-cut: 83 HzTrace Balance: .7 sec. windowsDisplay: -ve = blue, +ve = red

Note: impulsive source reflection data positive reflection co-eff. = -ve number or blue color

Stack, Line B24 (shallow water)No Tau-P Linear Noise Attenuation Applied

Stack, Line B24 (shallow water)Tau-P Linear Noise Attenuation Applied

Stack, Deep Zone, Line B24 (shallow water)No Tau-P Linear Noise Attenuation Applied

Stack, Deep Zone, Line B24 (shallow water)Tau-P Linear Noise Attenuation Applied