Beach Energy Ltd Lake Tanganyika 2D Marine Seismic Survey Data Processing, 2014 Squelch Tests for Streamer Noise Attenuation Lines BST14B24 and BST14B67 Jan. 21, 2014

➢ Low frequency additive noise, generated along the streamer at Digibird locations was recorded on the marine 2D shot records in the field. A proprietary noise reduction method named Squelch can be employed to remove this noise. Other spurious noise segments are removed using an algorithm that compares RMS amplitude levels in a moving window against neighboring seismic traces. ➢ Using Squelch, the noises are separated from the signal by frequency bands and their amplitudes are reduced. Then the frequency bands are combined back together to create the noise-attenuated dataset. ➢ For testing, shot records and stacks were viewed before and after the application of Squelch and Spurious 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 effects of Squelch noise attenuation are much more pronounced on the pre-stack data than on the stack data, because the stack is also a very good noise filter. ➢ Squelch will enhance the reliability of pre-stack data analysis such as AVO Analysis and the improvements can also be clearly seen on the stack data. ➢ The application of Squelch and Spurious Noise Attenuation is recommended

Noise Attenuation Parameters Squelch Bandwidth: Hz Noise Reduction: approx. 50% Spurious Noise Attenuation Running ave. window length: 200 msec Mute taper: 30 msec Amplitude threshold : 2

Lake Tanganyika 2D Marine Seismic Survey Location of Test Lines

Shot Records

Shot Gathers, Line B24 (shallow water), spherical divergence correction applied Before Squelch Applied

Shot Gathers, Line B24 (shallow water), spherical divergence correction applied After Squelch Applied

Shot Gathers, Line B24 (shallow water), spherical divergence correction applied Difference After Squelch Applied

Shot Gathers, Deep Zone, Line B24(shallow water), spherical divergence correction applied Before Squelch Applied

Shot Gathers, Deep Zone, Line B24(shallow water), spherical divergence correction applied After Squelch Applied

Shot Gathers, Deep Zone, Line B24(shallow water), spherical divergence correction applied Difference After Squelch Applied

Shot Gathers, Line B67 (deep water), spherical divergence correction applied Before Squelch Applied

Shot Gathers, Line B67 (deep water), spherical divergence correction applied After Squelch Applied

Shot Gathers, Line B67 (deep water), spherical divergence correction applied Difference After Squelch Applied

Shot Gathers, Deep Zone, Line B67(deep water), spherical divergence correction applied Before Squelch Applied

Shot Gathers, Deep Zone, Line B67(deep water), spherical divergence correction applied After Squelch Applied

Shot Gathers, Deep Zone, Line B67(deep water), spherical divergence correction applied Difference After Squelch Applied

Stacks

Brute Stack, Line B24 (shallow water), prelim. NMO velocities applied No Squelch Applied

Brute Stack, Line B24 (shallow water), prelim. NMO velocities applied Squelch Applied

Brute Stack, Deep Zone, Line B24 (shallow water), prelim. NMO velocities applied No Squelch Applied

Brute Stack, Deep Zone, Line B24 (shallow water), prelim. NMO velocities applied Squelch Applied

Brute Stack, Line B24 (shallow water), prelim. NMO velocities applied No Squelch Applied

Brute Stack, Line B67 (shallow water), prelim. NMO velocities applied Squelch Applied

Brute Stack, Deep Zone, Line B67 (shallow water), prelim. NMO velocities applied No Squelch Applied

Brute Stack, Deep Zone, Line B67 (shallow water), prelim. NMO velocities applied Squelch Applied