Profiling the vibrator envelope at low frequencies

Abstract

At low frequencies the energy produced from a seismic vibrator is constrained by several mechanical and hydraulic limitations: the reaction mass stroke, the hydraulic pump flow, the pump response time, the servo valve stroke, the accumulator size, the engine horsepower, the peak‐decoupling force, the harmonic distortion, and the vehicle chassis isolation. Among these factors the reaction‐mass stroke and the peak‐decoupling force are key parameters for setting the target fundamental force that can be achieved at low frequencies. The peak‐decoupling force defined as the smaller value of either the maximum peak force or the hold‐down weight. Formulas for estimating fundamental force, peak force and reaction‐mass stroke are derived as a guideline for sweep designers who plan to design low frequency sweeps with considerable dwell time there. Test data show that formulas can be used to profile the vibrator envelope at low frequencies.