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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Geophysical Benefits of from Improved Seismic Vibrator

Michael Hall1; John Wei2; Tom Phillips2

(1) ION Geophsyical, Calgary, AB, Canada.

(2) ION Geophysical, Stafford, TX.

Vibroseis, a key source in land seismic exploration, has recently experienced many initiatives to increase productivity and seismic data quality. Most of these innovations deal with the signals used to generate the Vibroseis sweep and techniques for simultaneous acquisition.

This paper deals with physical modifications to the Vibrator itself designed to enhance performance at both low and high ends of the frequency spectrum and also attempt to provide a more accurate measure of the ground force from the weighted sum.

Most of the recently introduced simultaneous Vibroseis techniques rely on the measured weighted sum as a good indicator of the actual ground force or the source signature for the Vibrator. In reality it is common for there to be substantial differences between the weighted sum and the ground force, especially as a function of varying near surface conditions. Modelling was undertaken to investigate how the physical properties of a Hydraulic Vibrator could be modified to improve this relationship while also extending the useful bandwidth. As a result of this modelling modifications were made to a production hydraulic Vibrator, which was then tested against the production Vibrator both on load cells and at a site in Texas with an instrumented well plus a 2D surface line.

Analysis of these tests will be presented to confirm that the expected improvements were achieved. The implications of this are several fold. The bandwidth at the low frequency end of the spectrum can be usefully extended below 5Hz with considerably less harmonic distortion; this will aid in the exploration for deeper targets and also improve the accuracy of inverting seismic data to match well log data. The bandwidth at the high end can be similarly improved by about 6dB at 150Hz enabling improved resolution for quantitative analysis of shallower reservoirs. The overall reduced harmonic distortion means that more of the energy generated by the Vibrator goes into the fundamental Vibroseis signal yielding a higher energy level of useful signal. The weighted sum is also closer to the ground force put into the earth by the Vibrator. This, along with the reduced harmonic distortion will enable improved separation of overlapped source signals in simultaneous Vibroseis acquisition schemes.

This improved seismic Vibrator is complimentary to recent developments in improving Vibroseis productivity and will further improve the quality of the acquired Vibroseis data.

680713_A.jpg

Enhanced low frequency energy from the improved Vibrator (lower image).

680713_B.jpgEnhanced high frequency energy from the improved Vibrator (lower image).

680713_C.jpgThe improved Vibrator (lower) shows a better match between weighted sum and far field signal than does the original Vibrators (upper) that contains more harmonic energy.