Counter-Rotating Eccentric Mass Vibrator for Low Frequency Seismic Acquisition
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Solution Overview
Problem
Current seismic prospecting technologies face limitations in generating sufficient force at low frequencies (1-5 Hz), which restricts the range of frequencies that can be used for subsurface exploration, leading to incomplete data and increased survey times and costs.
Innovation Solution
The use of counter-rotating eccentric-mass vibrator technology, which allows for large displacements and maintains force output by quadrupling displacement to offset frequency-squared dependence, enabling seismic sources to produce forces comparable to hydraulic actuators at higher frequencies down to 1 Hz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If hydraulic actuators with inertial mass are used to generate seismic forces, then force output can be maintained at higher frequencies (5-250 Hz), but force output decreases significantly at low frequencies (1-5 Hz) due to the frequency-squared dependence of inertial force
Solution Approach 1:
The patent replaces the hydraulic actuator system with an electromagnetic linear motor system. The linear motor directly converts electrical energy to mechanical motion without hydraulic fluid dynamics, eliminating the frequency-squared force limitation. The motor drives the inertial mass to produce seismic forces across the extended frequency range (1-250 Hz) with consistent force output, as the electromagnetic force generation is not dependent on frequency in the same way hydraulic systems are.
Solution Approach 2:
The patent changes the fundamental operating parameters of the seismic vibrator by using a linear motor with variable frequency drive. This allows independent control of motor speed and torque, enabling the system to maintain optimal force output across different frequencies. The control system adjusts electrical parameters (frequency, voltage, current) to the linear motor to compensate for the frequency-squared effect that limits traditional hydraulic systems at low frequencies.
2Loss of information
If the frequency range is extended to include low frequencies (1-5 Hz), then more subsurface information can be obtained for improved seismic inversion, but existing seismic sources cannot generate sufficient force at these frequencies
Solution Approach 1:
The patent replaces the hydraulic actuator system with an electromagnetic linear motor system. The linear motor directly converts electrical energy to mechanical motion without hydraulic fluid dynamics, eliminating the frequency-squared force limitation. The motor drives the inertial mass to produce seismic forces across the extended frequency range (1-250 Hz) with consistent force output, as the electromagnetic force generation is not dependent on frequency in the same way hydraulic systems are.
Solution Approach 2:
The patent changes the fundamental operating parameters of the seismic vibrator by using a linear motor with variable frequency drive. This allows independent control of motor speed and torque, enabling the system to maintain optimal force output across different frequencies. The control system adjusts electrical parameters (frequency, voltage, current) to the linear motor to compensate for the frequency-squared effect that limits traditional hydraulic systems at low frequencies.
3Speed
If hydraulic actuators are used with limited stroke capability, then the system can operate at higher frequencies, but the maximum displacement is limited which restricts force output at low frequencies
Solution Approach 1:
The patent replaces the hydraulic actuator system with an electromagnetic linear motor system. The linear motor directly converts electrical energy to mechanical motion without hydraulic fluid dynamics, eliminating the frequency-squared force limitation. The motor drives the inertial mass to produce seismic forces across the extended frequency range (1-250 Hz) with consistent force output, as the electromagnetic force generation is not dependent on frequency in the same way hydraulic systems are.
Solution Approach 2:
The patent implements a dynamic control system with variable frequency drive that continuously adjusts the operational parameters of the linear motor. This allows the system to adapt its motion characteristics in real-time, optimizing both displacement and force output across the full frequency range. The dynamic control enables the vibrator to achieve large displacements at low frequencies while maintaining high-frequency operation capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables seismic prospecting at low frequencies with forces comparable to those at higher frequencies, improving data quality and reducing survey time and costs by maintaining large force output across the 1-5 Hz range.
Implementation Method 1
A low frequency range for which the present invention is particularly needed and therefore may be considered to be particularly advantageous is 1-5 Hz. From Eqn. [2], it may be seen that a figure of merit for producing a given level of ground force at a given frequency, is the product of mass times displacement times frequency squared (mdf2).
Implementation Method 2
Considering the case where the baseplate is relatively immobile (i.e., the 'clamped force' case) the force to accelerate the inertial mass in an oscillatory motion described by where x is the motion of the mass, d is the maximum displacement of the mass from a center position, f is the frequency of motion, and t is the independent variable of time; is given by the product of mass and acceleration (that is, second derivative of motion), where F is the force and m is the mass of the inertial mass.
Data Source
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AI summary
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