Getting high quality and reliable data in shallow water areas is by far one of the most difficult challenges. Sercel strives to develop better and more efficient solutions to meet the high-resolution requirements expected in these complex environments. This article focuses on the importance of the signal quality emitted by the seismic source and on the innovative solution offered by Sercel to obtain a clean acoustic signature. It comes with a video presented by Julien Large, Sercel’s marine seismic sources Product Champion, in which he introduces the GI-Source, a seismic impulsive air-driven source based on a revolutionary architecture, specifically designed for shallow water operations, 4D and high-resolution surveys.
Role of the air-driven source
The most common and reliable marine seismic source is the air-driven source. It uses high compressed air discharged suddenly into the water to create acoustic waves that penetrate the subsurface sediments. The resulting seismic reflections are recorded to image the structure beneath the seabed. The seismic signal generated by the air source is characterized by its signature which has to be as clean as possible especially for high resolution surveys. But disturbances mainly due to the bubble noise generated by the air source itself make the task very difficult to achieve.
Bubble noise and its impact on the source signature
Ideally, a perfect signal would be obtained if the bubble generated by the air source remained in its first phase of expansion. However, the signal quality is impacted by the bubble collapse and its resulting oscillations. As the bubble expands, the imbalance between its internal pressure and the hydrostatic pressure grows causing the collapse of the bubble and the emission of undesired interfering pressure pulses. This phenomenon is all the more impactful in shallow water areas as this interference is amplified by reflection from the sea surface.
GI-Source, the air-driven impulsive source that mitigates its own bubble effect
For years now, research has been carried out to design marine seismic sources that provide a controlled oscillation and a clean acoustic signature by avoiding the violent collapse of the bubble. The solution developed by Sercel enables the injection of an adjustable volume of air just as the bubble reaches its maximum size in order to increase its internal pressure and thus prevent its collapse. In the video below, Julien Large, marine seismic sources Product Champion, introduces GI-Source, Sercel’s Generator/Injector air impulsive source, specifically designed for the shallow water environment, 4D and high-resolution surveys. He explains how the GI-Source’s innovative design, consisting of two independent impulsive air chambers embedded within the same body, enables the suppression of the source bubble effect and provides a clean acoustic signature. With the added flexibility of monitoring the volume of air to be injected, the exact time of the injection and its duration, the GI-Source is the most versatile and accurate solution on the market. It offers greatly improved performance when compared with conventional solutions and with high enough efficiency to fulfill the needs of shallow water surveys. Thanks to its ‘all-in-one’ design, it can be used as a single source which greatly simplifies the bubble control process. Light and compact, the GI-Source facilitates the operational logistics onboard the vessel (deployment and retrieval) which is all the more challenging in complex environments.
For further details on the GI-Source and a compelling demonstration of its benefits, please watch the video ‘GI-Source – A clean acoustic signature’ by Julien Large.