Control algorithms for marine vibrator source and Handling concepts for marine vibrator source
Publication Date: 2016-Mar-22
The IP.com Prior Art Database
The marine-vibrator application offers opportunities to apply non-linear control principles that are optimized for the new specialized equipment operating in the controlled, repeatable marine environment. We propose a number of concepts for addressing the two primary handling activities: transferring equipment between the vessel's stern and the water (Deployment/Recovery), and moving equipment on deck (Storage).
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Title: Control algorithms for marine vibrator source
Geophysical considerations require seismic vibrators (both land and marine) to emit the highest possible amplitude with the lowest possible distortion. These two objectives represent a fundamental tradeoff, which is excacerbated by the inherent non-linearities of vibrator hardware. Some, such as hydraulic valves' quadratic relationship between flow and pressure, hydraulic valve zero-crossing discontinuities, and fluid compressibility, are related to the hydraulic actuators that are used in nearly all vibrator hardware. Others, such as unpredictable soil non-linearities (in land seismic) or the contained air-spring (in marine seismic) apply regardless of the actuator. Vibrator controllers are designed to counteract these effects and output a high-amplitude, low distortion waveform.
The marine-vibrator application offers opportunities to apply non-linear control principles that are optimized for the new specialized equipment operating in the controlled, repeatable marine environment.
Commercial land-vibrator controllers are the result of decades of experience in optimizing output in the presence of non-linear effects. The market is dominated by two suppliers: Sercel and INOVA.
The Sercel controller is based on Linear Quadratic Gaussian (LQG) control. A Kalman filter first estimates the system state, and a linear-quadratic regulator (LQR) then attempts to minimize a quadratic objective function over a time window into the future. This controller is common on land vibrators, but has not, to our knowledge, been used in the marine application. This system is described in the following references, among others:
D. Boucard and G. Ollivrin, "Developments in vibrator control", Geophysical
Prospecting, 2010, 58
Castanet A. and Lavergne M. 1965. "Vibrator controlling system". US patent 3,208,550
INOVA supplies the Pelton VibPro control system, which is based on a PID control loop. The PID gain is adjusted based on the desired sweep frequency, a form of gain scheduling. The VibPro is common on land vibrators. WesternGeco used one of its predecesors, the Pelton Advance II, on experimental marine-vibrator surveys in the 1990s. References include the following:
Zhouhong Wei, "Design of a P-wave seismic vibrator with advanced p erformance",
GeoArabia, Vol. 13, No. 2, 2008
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The third supplier, Seismic Source, uses similar principles as the VibPro.
DESCRIPTION OF THE INVENTION
A number of control strategies have been evaluated jointly with LMS Imagine SA, under the scope of a Consulting Services Agreement. Excerpts from the LMS report (GeMS record 101498466) are included below. The invention consists of two levels: high-level control strategies, and specific implementation features for the WesternGeco marine vibrator.
High-Level Control Strategies
H control design is a method in which a controller K(s) is...