Multiple suppression for marine seismic data with strong shielding layer

The study of multiple wave suppression methods has always been a difficulty of marine seismic data processing. At present, multiple wave suppression methods can be roughly divided into two categories: the first type is filtering methods, the second type is the wave dynamics and kinematic theory method. When the water depth in the study area is shallow, and strong seabed oscillations are formed between the seabed and the sea surface. The surface multiple suppression method (SRME) is not ideal for suppressing such short period seabed multiples. The deterministic seabed multiple prediction method (DWMP) can more accurately predict shallow water seabed periodic multiples. Long period multiples other than seabed multiples require surface multiple prediction (SRME) to suppress multiples.

When the research area is not only shallow in water depth, but also has a strong wave impedance interface in the formation, the difficulty of suppressing long-period multiples further increases. This is because various types of strong energy multiples, such as surface multiples, seabed multiples, and interlayer multiples, are formed between the sea surface and the strong wave impedance interface. The energy of multiples is one order of magnitude higher than that of weak effective reflections below the strong wave impedance interface. The strong energy of wide-angle multiples in the mid to far triangular region affects the effective utilization of reflected waves at mid to far offset distances. Diffraction multiples are developed in areas with severe fluctuations in the impedance interface of strong waves. Diffraction multiples are difficult to suppress using conventional multiples, and strong energy diffraction multiples can produce migration phenomena, affecting imaging in mid to deep layers. The effective suppression of various multiples is the key and difficult point in seismic data processing under strong shielding layer conditions.

Based on the characteristics of multiples under strong shielding layer conditions in shallow water, targeted suppression strategies were studied: using three methods to predict multiple wave models: deterministic seabed multiple prediction, deterministic seabed multiple prediction and surface multiple prediction, and surface multiple prediction. Firstly, frequency division combined with adaptive subtraction was used to achieve simultaneous suppression of short period seabed multiples and long period surface multiples. Then, application of CMP domain for high precision radon removal of multiples with dynamic calibration time difference. Finally, residual multiple suppression method is applied in the common offset domain to remove strong energy diffraction multiples. Through the suppression strategy proposed in this article, various types of multiples under the conditions of shallow water strong shielding layers can be effectively suppressed, thereby obtaining weak reflection signals in the middle and deep under the strong shielding layer. Through the calculation examples in the study area, it can be seen that the suppression strategy proposed in this article can suppress multiples interference while protecting effective reflection information. It is of great significance for imaging inside buried hill, imaging under volcanic shielding layers, and imaging under gypsum-salt layer.