Low frequency seismic acquisition using a counter rotating eccentric mass vibrator

摘要

Method for seismic prospecting using counter-rotating (207-208) eccentric-mass (201, 202) vibrator (CREMV) technology adapted as vibrator sources for seismic prospecting to produce controlled sweeps, as in the manner used in modern seismic prospecting, but with large forces at low frequencies, e.g. forces >275 kN at frequencies between 1 and 5 Hz. This is achieved by adapting the CREMV to enable rotational frequency and the eccentricity (205, 206) of the masses relative to their rotation axes (203-204) to be varied independently and simultaneously, and by designing the CREMV such that the radius of rotation of the center of mass of each rotating mass is on the order of 50 cm or more. The low frequency data obtained from such a seismic source enables improved detection and resolution of subsurface structures and better determination of subsurface properties.

主权项

1. A seismic vibrator comprising:
an actuator comprising two oppositely rotating, adjustably eccentric masses; a motor that powers the actuator, and controls a rotation frequency of the eccentric masses; an eccentricity adjustment system that changes eccentricity while the actuator is operating, whether or not the rotation frequency is simultaneously being changed, and independent of any change in rotational frequency; and a sweep controller that controls the motor and the eccentricity adjustment system to provide a combination of eccentricity and frequency required to produce an output proportional in magnitude to, and in phase with, a pre-selected sweep input signal.