Seismic processing faces a significant challenge known as internal multiple attenuation (IMA). This process revolves around removing internal and interbed seismic multiples using a data-driven methodology applicable to various seismic surveys, whether on land or ocean bottoms. Failure to address IMA can introduce unwanted artifacts and noise, disrupting the accuracy of primary seismic imaging and complicating geological interpretation. These multiples, occurring in regions with complex overburden and highly reflective shallow geological features, can lead to misinterpretations like mistaking them for components of the basement or deep sediment layers. Specifically, internal multiples in seismic data are reflections originating within subsurface layers, distinct from primary reflections directly above or below them.
Free surface multiples: are a significant concern in seismic data processing and interpretation. These multiples are generated when seismic waves encounter the Earth's surface and interact with it in complex ways. The process begins when a primary wave, such as a P-wave or S-wave, strikes the surface. Upon hitting the surface, the primary wave reflects back and travels through the subsurface layers. However, instead of reaching the receiver directly, it undergoes additional reflections from these subsurface interfaces. These subsequent reflections create a series of secondary waves that can interfere with the primary reflections.
The interference caused by free surface multiples can lead to various challenges in seismic data analysis. For instance, these multiple reflections can overlap with the primary reflections, causing amplitude distortions and making it difficult to distinguish between different seismic events. Moreover, the timing and phase of the multiples may align in a way that masks important geological features or creates false interpretations of subsurface structures.
To mitigate the effects of free surface multiples, seismic processing techniques often involve sophisticated algorithms and filtering methods. These techniques aim to separate the primary reflections from the multiples and enhance the quality of the seismic data. Additionally, careful interpretation and modeling of subsurface conditions are crucial for accurately identifying and correcting for free surface multiples during seismic data processing
Water-bottom multiples: are a persistent challenge that marine seismic survey's grapple with due to their complex nature and significant impact on data interpretation. These multiples occur when seismic waves traveling through the water column encounter the ocean floor, where they reflect back upward. However, instead of reaching the receiver directly, these reflected waves can bounce off subsurface layers multiple times before being detected. This bouncing off the water bottom and subsequent interactions with subsurface formations create a series of overlapping reflections that can obscure the primary seismic signal, leading to distortion and inaccuracies in the data.
Understanding water-bottom multiples is crucial for several reasons. Firstly, they can create false images of subsurface structures, leading to misinterpretation of geological features and potentially misguided drilling decisions. Secondly, these multiples can mask weak signals from deeper formations, reducing the overall resolution and clarity of the seismic data. As well, ignoring or improperly handling water-bottom multiples can result in costly errors during exploration and production phases, impacting project timelines and budgets.
To mitigate the effects of water-bottom multiples, seismic processing techniques have evolved to include advanced algorithms and filtering methods. These techniques aim to separate the primary seismic signal from the multiples, often using data from multiple source-receiver offsets and sophisticated deconvolution processes. Additionally, the use of specialized acquisition equipment, such as multi-component sensors and wide-azimuth surveys, can help in better characterizing and mitigating water-bottom multiples.