Recent advances in marine seismic acquisition allow for the recording of vector-acoustic ([VA] pressure and particle velocity) seismic data from dual-source configurations, i.e., using monopole as well as dipole sources. VA reverse time migration (RTM) can be custom designed to accurately handle amplitude and directivity information from 4C seismic data. We present a method for multicomponent RTM that is based on an adjoint-state formulation using the full VA wave equations for pressure and corresponding displacement fields. This method takes advantage of the directional finite-frequency information contained in the 4C acoustic fields by using source and receiver weighting operators in the adjoint-state imaging scheme. With this adjoint-state method, the source and receiver radiation properties are tailored by choosing specific weighting operators. Weighting operators were chosen so that source- and receiver-side ghost arrivals are jointly migrated with primary energy. Because the dipole field components (e.g., components of particle displacement or acceleration) are proportional to the spatial gradient components of the pressure field, our method is in fact a formulation for reverse-time map migration that images pressure fields while jointly using the directional information contained in its full 3C gradients. As a result, our reverse time 4C map migration method yields less aperture- and sampling-related artifacts when compared to imaging of the pressure-only or 2C seismic data. In addition, our method sets a framework for full-waveform inversion using dual-source 4C seismic data. We demonstrated our findings with synthetic data, including a subsalt imaging example.
ABSTRACT. One of the major limitations of imaging methods is, usually, the incomplete recorded seismic data that cause difficulties for the subsurface imaging techniques...Keywords: seismic imaging, resolution, modeling, iterative method, computational coast. RESUMO. Uma das limitações das técnicas de imageamento é que, via de regra, os dados sísmicos registrados são incompletos. Isso impossibilita uma correta reconstituição dos refletores em subsuperfície...Palavras-chave: imageamento sísmico, resolução, modelagem, método iterativo, custo computacional.
Methods for wavefield injection are used in, for instance, reverse time extrapolation of shot gathers in reverse time migration. For correct injection of recorded data without any ambiguity of the propagation direction, the wavefield-injection methodology requires pressure and particle velocity data such as multicomponent towed marine or seabed seismic recordings. We discovered that by carefully considering the models (medium parameters and boundary conditions) for injection, wavefield injection of multicomponent data can also be used to solve several long-standing challenges in marine seismic data processing by means of conventional time-space-domain finite-difference propagators. We outlined and demonstrated several of these important applications including up-down separation of wavefields (deghosting), direct-wave removal, source-signature estimation, multiple removal, and imaging using primaries and multiples. Only acoustic models are considered, but the concepts are straightforward to generalize to elastodynamic and electromagnetic models.
Abstract
This work presents a full waveform sonic (FWS) dataset processing to generate high-resolution images of the near-borehole area. The dataset was acquired in a nearly horizontal well over a distance of 5400 feet. Multiple formation boundaries can be identified on the final image and tracked at up to 200 feet deep, along the wellbore's trajectory.
We first present a new preprocessing sequence to prepare the sonic data for imaging. This sequence leverages denoising algorithms used in conventional surface seismic data processing to remove unwanted components of the recorded data that could harm the imaging results. We then apply a reverse time migration algorithm to the data at different processing stages to assess the impact of the main processing steps on the final image.
Abstract
Processing of the seismic data acquired in areas of complex geology of the Dnieper-Donets basin, characterized by the salt tectonics, requires special attention to the salt dome interpretation. For this purpose, Kirchhoff Depth Imaging and Reverse Time Migration (RTM) were applied and compared. This is the first such experience in the Dnieper-Donets basin. According to international experience, RTM is the most accurate seismic imaging method for steep and vertical geological (acoustic contrast) boundaries. Application of the RTM on 3D WAZ land data is a great challenge in Dnieper-Donets Basin because of the poor quality of the data with a low signal-to-noise ratio and irregular spatial sampling due to seismic acquisition gaps and missing traces. The RTM algorithm requires data, organized to native positions of seismic shots. For KPSDM we used regularized data after 5D interpolation. This affects the result for near salt reflection. The analysis of KPSDM and RTM results for the two areas revealed the same features. RTM seismic data looked more smoothed, but for steeply dipping reflections, lateral continuity of reflections was much improved. The upper part (1000 m) of the RTM has shadow zones caused by low fold. Other differences between Kirchhoff data and RTM are in the spectral content, as the former is characterized by the full range of seismic frequency spectrum. Conversely, beneath the salt, the RTM has reflections with steep dips which are not observed on the KPSDM. It is possible to identify new prospects using the RTM seismic image. Reverse Time Migration of 3D seismic data has shown geologically consistent results and has the potential to identify undiscovered hydrocarbon traps and to improve salt flank delineation in the complex geology of the Dnieper-Donets Basin's salt domes.
LEAST-SQUARE REVERSE TIME MIGRATION (LSRTM) IN THE SHOT DOMAIN