Airgun Cluster Frequency Locking for Low Frequency Output

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Solution Overview

Problem

The low frequency output of marine airgun seismic source arrays is limited by the resonance frequency of the largest airgun volume, which is inversely proportional to the cube-root of the bubble volume, making it challenging to achieve substantial increases in low frequency source output without significantly increasing the bubble volume.

Innovation Solution

The design involves creating airgun clusters with significantly larger total volumes, where high pressure gas is released in close proximity to achieve a bubble oscillation frequency associated with the total cluster volume, effectively increasing the effective bubble volume to exceed 2000 cubic inches, allowing for optimized low frequency output by fully frequency locking multiple airgun bubbles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the bubble volume is increased to decrease the bubble frequency and enhance low frequency output, then the low frequency source output is improved, but the device complexity and manufacturing difficulty increase significantly

Engineering Contradiction:

Improvelow frequency source outputVSAvoidbubble volume requirements

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The invention divides the total source volume into multiple separate airgun bubbles instead of using a single large bubble. Each airgun operates as an independent unit, and the combined effect of multiple smaller bubbles achieves the desired low frequency output without requiring a single oversized bubble that would be complex to manufacture and deploy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention merges the output of multiple airgun bubbles through constructive interference to achieve the low frequency enhancement. By carefully spacing the airguns and timing their firing, the individual bubble oscillations combine to produce a unified low frequency signal, effectively achieving the performance of a large single bubble using multiple smaller bubbles.

Inventive Principle:

Principle #5Merging (Combining)

2Power

If multiple airguns are placed in close proximity to form a cluster, then the total cluster volume increases and low frequency output improves, but the spatial arrangement complexity increases

Engineering Contradiction:

Improvelow frequency outputVSAvoidairgun cluster arrangement

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The invention applies different spacing requirements to different regions of the airgun array. Airguns are placed in close proximity (less than one meter) within local clusters to maximize bubble interaction and low frequency output, while maintaining overall array geometry that facilitates deployment and handling. This localized optimization allows low frequency enhancement without requiring the entire array to be densely packed.

Inventive Principle:

Principle #3Local quality

3Power

If the airgun bubbles coalesce into one non-spherical bubble, then the bubble frequency decreases and low frequency output improves, but the control over individual bubble oscillations is lost

Engineering Contradiction:

Improvelow frequency outputVSAvoidbubble oscillation control

Core Design Contradiction:

PowerVSEase of operation

Solution Approach 1:

The invention maintains dynamic control over bubble oscillations by keeping the airguns spaced apart rather than allowing complete coalescence. This spacing allows each airgun to independently control its bubble oscillation timing and phase, enabling active control of the overall signal characteristics while still achieving low frequency enhancement through constructive interference of the individual bubble oscillations.

Inventive Principle:

Principle #15Dynamics

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 approach significantly enhances the low frequency output of seismic source arrays, increasing the effective bubble volume to up to 100% of the total source volume, thereby extending the source bandwidth towards zero Hertz and improving the imaging of subsurface formations for hydrocarbon detection.

Implementation Method 1

the resulting bubble oscillates with the frequency associated with the total cluster volume

Methodology Applied

Scientific EffectBubble oscillation: Bubble

Implementation Method 2

The low frequency output of marine airgun seismic source arrays is limited by the resonance frequency of the largest airgun volume

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 3

wherein the airgun bubbles coalesce into one non-spherical bubble

Methodology Applied

Scientific EffectCoalescence: Coagulation

Implementation Method 4

generate acoustic output, which when reflected off of subsurface formations may be detected by associated seismic receivers

Methodology Applied

Scientific EffectAcoustic wave reflection: Reflection

Data Source

PatentUS9025417B2Systems and methods for optimizing low frequency output from airgun source arrays

Publication Date: 2015.05.05 REFLECTION MARINE NORGE AS

AI summary

Systems and methods for optimizing low frequency output of marine sources are described. The marine source arrangements and associated methods disclosed herein seek to fully frequency lock bubbles emitted by airguns in close proximity to one another. In this manner, larger effective bubble volumes can be achieved, thus increasing low frequency output.