Johan Robertsson

Source Wavelet Amplitude Spectrum Estimation Using Marchenko Focusing Functions

Summary Marchenko focusing enables the redatuming of seismic surface data to an arbitrary new datum level in the subsurface. One requirement for an accurate redatuming is the correct deconvolution of the source signature from the acquired surface reflection response. Using an erroneous source wavelet for deconvolution leads to inaccurate redatuming and, thus, to artefacts in the redatumed data. However, the true amplitude spectrum of the source wavelet is often unknown. We propose a novel approach to invert for the amplitude spectrum of the source wavelet using focusing functions obtained by the Marchenko redatuming process. Deconvolving the data with an incorrect source wavelet generates undesired coda events in the focusing function. We identify such coda events by the analysis of an ensemble of focusing functions, where differently scaled source wavelets are used for deconvolution prior to redatuming. The amplitude spectrum of the identified coda is strongly related to an error in the source wavelet. Thus, we can iteratively invert for the correct scaling of the source wavelet by analyzing the amplitude spectrum of coda events in the focusing function. This approach yields the correct scaling of the amplitude spectrum of the source wavelet and enables accurate Marchenko redatuming.

Joint 3D reconstruction and deghosting of multisensor streamer data by generalized matching pursuit

Summary Multichannel reconstruction and 3D deghosting techniques based on multisensor streamer measurements of the pressure wavefield and its associated gradients were recently introduced in literature. In particular, the Generalized Matching Pursuit (GMP) technique was applied to 3D-4C synthetic data bringing significant improvements to address the aliasing arising from sparse crossline sampling. In this abstract, we present an example of real data acquired by an experimental 3D-4C towed cable array and show the performance of GMP applied to the multisensor measurements. The real data examples illustrate that GMP reconstructs and deghosts the pressure wavefield onto a 2D receiver grid uniformly sampled at 6.25 m in both, the inline and the crossline directions, starting from a very limited number of crossline samples at realistic spacings (i.e., 75 m). We describe the main technical challenges due to the nature of the signal and the limitations of the experiment. Despite these challenges, we show that GMP has produced a very effective reconstruction of the threedimensional wavefield back-scattered by the subsurface for each recorded seismic shot.