Rolf Baardman

Estimation of primaries by sparse inversion using dual-sensor data

Summary Most wave-equation based multiple removal methods, such as the surface-related multiple elimination (SRME) method, are based on prediction and subtraction of the multiples. Although this approach has proven successfully for many cases, it still shows some drawbacks such as handling missing near-offsets and distortion of primaries during the subtraction process. The recently introduced estimation of primaries by sparse inversion (EPSI) method estimates the primaries as unknowns in a multi-dimensional inversion process, where primaries are parameterized by spikes and a corresponding wavelet. Furthermore, it can reconstruct missing near offset data simultaneously. In this paper the EPSI method is extended to handle time-variant wavelet variations in the parameterization, which is necessary to obtain good results on field data. Because of the strong physical constraint between primaries and multiples, EPSI requires the upgoing wavefield at the surface. Therefore, it is very well suited for field data from a dual-sensor measurement, which provides a reliable upgoing wavefield.

An Inversion Approach to Separating Sources in Marine Simultaneous Shooting Acquisition

In seismic exploration, there is continuous drive towards more dense data sampling to better image complex geological structures. Recent advances in acquisition such as Wide-Azimuth, Multi-Azimuth or Rich-Azimuth acquisition can deliver a more diverse range of source, azimuth and offset sampling. To collect such data, multiple source and receiver vessels are deployed, thereby increasing the costs of the survey significantly. In conventional acquisition, there is zero time overlap between shot records, and data are recorded discontinuously. The source domain is often poorly sampled, leading to aliasing. In simultaneous acquisition, data can be recorded continuously, and temporal overlap between shots is allowed. Consequently, more sources are fired during the same period of acquisition, which greatly enhances the flexibility in survey geometries. As a result, a more densely sampled data set in terms of source spacing, but also azimuth and offset distributions can be obtained. In terms of efficiency, simultaneous acquisition can contribute by reducing survey times, which is of particular value in critical situations where small acquisition timewindows dominate due to severe safety, environmental or economic restrictions. As such, from an acquisition point of view, simultaneous acquisition holds the promise of both efficiency and quality improvements. However, unless source separation can be achieved to a sufficiently high degree, the enormous potential benefits of simultaneous sources remain unrealized. Two approaches are currently utilized by the industry to achieve source separation: methods based on random noise attenuation and inversion-based methods. By regarding the energy from secondary sources as incoherent noise, after sorting the acquired data into an appropriate domain, the interference noise appears as random spikes which could be attenuated using well-known random noise removal procedures. Alternatively, inversion-driven methods aim to construct the separated sources through the minimization of a cost function that describes the “data misfit”. In such methods, incoherent energy is no longer regarded as noise that is to be removed. Instead, this energy is recognized as a representation of coherent events belonging to (one of) the interfering shots. An inversion approach aims to distribute all energy in the blended shot records by reconstructing the individual unblended shot records at their respective locations. In this abstract, an inversion-driven method is utilized that uses coherency measures to reconstruct the individual shot gathers from the blended data. The method is demonstrated to be capable of separating sources, even in the presence of strong diffraction energy. The method can be used in conjunction with other methods, resulting in so-called hybrid solutions. A simultaneous source wide-azimuth 3D data set from the Gulf of Mexico is presented.

Flam - A Simultaneous Shooting Test in West Africa Deep Offshore

In recent years the search for better marine seismic acquisition efficiency has being pushing the Simultaneous Shooting methodology assessment further. Significant efforts have been spent to understand the implications of simultaneous source acquisition, and different techniques have been developed to optimize required processing methods to separate the sources. Moved by that impetus, in 2010, during its first WATS survey in West Africa (in Angola deep offshore), Total EP Angola/Total and partners took the opportunity to undertake a simultaneous shooting test using real data. Taking advantage of the WATS survey design (two shooting vessels, front and rear, and one recording vessel) a complete 3 tiles seismic line was shot in simultaneous shooting mode. The line was acquired in an area with negligible feather and complex geological settings, which would allow a straightforward comparison between the two datasets. Different approaches to separate the blended sources have been tested, having most of them revealed to be effective. In this paper we will present and describe two of the tested approaches and respective results, and show that we can effectively separate/process simultaneous source data and obtain, as expected, images with a better S/N ratio than the ones obtained from conventional acquisition.