Subsalt Marchenko imaging: A Gulf of Mexico example

Abstract

Marchenko redatuming allows one to use surface seismic reflection data to generate the seismic response at any point in the subsurface due to sources at the surface. Without requiring much information about the earth's properties, the seismic response generated by Marchenko redatuming contains accurate estimates of not only the primaries, but also internal multiples. A target-oriented imaging method, referred to as Marchenko imaging, was implemented for imaging complex structures of the earth using the seismic response obtained through Marchenko redatuming. Taking account of the contribution of both primaries and internal multiples, Marchenko imaging provides more accurate information about the earth's structures than standard imaging methods (e.g. Reverse Time Migration). In order to apply Marchenko redatuming and imaging to field seismic data, we investigate two important aspects of the Marchenko framework: 1) the missing near offsets in marine shot records, and 2) the calibration of the reflection data. With numerical experiments using a Gulf of Mexico salt model (inspired by a Gulf of Mexico field dataset), we present a criterion to determine whether the missing near offsets of the towed-streamer dataset need to be reconstructed. We also demonstrate the importance of proper calibration for the amplitudes of the reflection data in removing the artifacts caused by the mismatch between the amplitudes of the two inputs, the reflection response and the first arrival, for Marchenko redatuming. Finally, we suggest a work flow for processing the marine towed-streamer field dataset acquired at the Gulf of Mexico, and present a complete theoretical and practical framework to produce a target-oriented subsalt image using the Marchenko methods. The images obtained from Marchenko imaging are consistent and comparable, for the most part, with conventional migration methods. However, Marchenko imaging achieves improvements in the continuity of the geological structures and in suppressing the artifacts, which we think are caused by internal multiples.

Single- and Double-Sided Marchenko Imaging Conditions in Acoustic Media

“…Imaging by deconvolution has been demonstrated in e.g. [15], [22], [23]. To reduce the computational burden of this problem, it has recently been proposed to deconvolve the upgoing Green's function with the downgoing Green's function at a single focal point and stack over sources [31].…”

“…In step (3), we obtain an image of the internal reflectivity from the retrieved wavefields. This can be done by solving an inverse problem [22], [23] (this approach is commonly referred to as multidimensional deconvolution). Unfortunately, this process is intensive from a computational point of view.…”

Imaging strategies using focusing functions with applications to a North Sea field

“…Varying only densities allows straight raypaths to be assumed, so that events observed in the data and focusing functions can be interpreted more easily. However, this is not a limitation of the new methods as Marchenko focusing functions can also be found for media with varying velocities, including highly complex media (Behura et al 2014;Vasconcelos et al 2015;Jia et al 2017). …”

Marchenko methods in a 3-D world

“…Further developments have extended Marchenko methods to elastic media (da Costa Filho et al 2014Wapenaar 2014 and to seismic data containing free surface multiples (Singh et al 2015(Singh et al , 2016. More recently Marchenko methods have been applied to real, reservoir scale, seismic data sets (Ravasi et al 2016;Jia et al 2017;Staring et al 2018) and to real ultrasonic data (Cui et al 2018a;da Costa Filho et al 2018;Wapenaar et al 2018). However, given the novelty of these methods there are still aspects that are poorly understood.…”