Marine Seismic Source De-ghosting Using Monopole and Dipole Polarity
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Solution Overview
Problem
Marine seismic exploration faces interference from sea surface reflections, known as 'ghosting,' which reduces the information available in seismic data by modulating the amplitude spectrum and creating notch frequencies, making it difficult to accurately estimate subsurface properties.
Innovation Solution
The use of two source types, monopole and dipole sources, either simultaneously or in separate surveys, to generate seismic waves with specific polarity relationships that allow for the constructive or destructive summation of waves, effectively reducing or eliminating the source ghosting effect in seismic data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single marine source is used to acquire seismic data, then the acquisition process is simple and cost-effective, but source ghosting occurs due to sea surface reflections which reduces data quality and information availability
Solution Approach 1:
The seismic source is segmented into two distinct source types (monopole and dipole) that are activated at different times. Each source type generates seismic waves with different polarity characteristics, allowing the ghosting effects to be separated and subsequently removed through processing. This segmentation resolves the contradiction by maintaining acquisition simplicity while preserving data information through multi-source differentiation.
Solution Approach 2:
The invention converts the harmful ghosting effect into a beneficial signal by using the predictable polarity reversal characteristic of dipole sources. The ghosting from dipole sources has opposite polarity to the primary signal, which allows it to be identified and removed through polarity-based processing. This transforms the previously harmful ghosting interference into a useful feature for source identification and ghost removal.
2Measurement precision
If two source types are used to reduce source ghosting, then seismic data quality improves, but the acquisition process becomes more complex and time-consuming
Solution Approach 1:
The acquisition process uses periodic activation of different source types in a systematic sequence. Monopole and dipole sources are activated in alternating shots or in predefined patterns, allowing for structured data collection that simplifies subsequent processing. This periodic approach reduces complexity by providing a predictable acquisition pattern that is easier to manage and process compared to simultaneous multi-source activation.
Solution Approach 2:
The invention uses dipole sources as a form of copy with inverted polarity characteristics to represent and cancel the ghosting effects. By acquiring data from dipole sources that replicate the ghosting pattern with opposite polarity, the system creates a reference signal that can be subtracted from the monopole data. This copying approach simplifies the problem by using a replicated signal rather than requiring complex real-time ghost removal.
3Object-affected harmful factors
If dipole sources are used to cancel ghosting through polarity reversal, then source ghosting is reduced, but the signal strength may be affected due to the nature of dipole radiation
Solution Approach 1:
The invention merges the data from both monopole and dipole sources through polarity-based combination. The dipole data, which contains the ghosting signal with opposite polarity, is combined with the monopole data to cancel the ghosting effects. This merging process preserves signal energy by utilizing the complementary nature of the two source types rather than relying solely on one source with reduced energy.
Solution Approach 2:
The invention changes the polarity parameter of the seismic signal by using dipole sources instead of monopole sources. This parameter change allows the ghosting effect to manifest with opposite polarity, making it distinguishable and removable. The parameter change approach maintains signal energy while transforming the ghosting characteristic into a removable feature through simple polarity inversion.
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 enables the acquisition of seismic data with reduced source ghosting, allowing for more accurate subsurface analysis by enhancing the signal and reducing interference, similar to existing two-component sensor seismic acquisition methods.
Implementation Method 1
The sea surface is a boundary between water and air and is highly reflective to seismic waves. Reflections from the sea surface cause interference, a phenomenon often referred to as 'ghosting'.
Implementation Method 2
The use of two source types, monopole and dipole sources, either simultaneously or in separate surveys, to generate seismic waves with specific polarity relationships that allow for the constructive or destructive summation of waves, effectively reducing or eliminating the source ghosting effect in seismic data.
Data Source
AI summary
Method for marine seismic acquisition using both monopole (91) and dipole (92) source types. Through a combination of source design and operation and/or combination or summing of the data in a processing step, the source ghost is either attenuated or, if desired, enhanced (93). The properties of the two different source types allow them to be adjusted so that the first down going wave from each has either opposite polarity or the same polarity, whereas the source-ghost wave will have, respectively same polarity or opposite polarity. This allows cancellation or enhancement of the source ghost. If the survey also employs two-component sensor acquisition, then the combined data sets may be both sensor de-ghosted and source de-ghosted.