Seismic Processing - What is Required?
Author: Tony Martin, Øystein Korsmo, Nizar Chemingui
EAGE Workshop on Optimizing Project Turnaround Performance - 24 February 2021
In a turnaround and cost-conscious environment, do we really need to apply all the algorithmic processes in a seismic processing sequence? Full wavefield migration may be one way to eliminate certain processes. If we treat the full wavefield migrated image as part of an inverse problem in a least-squares migration, we may exclude more steps. Least-squares full wavefield migration (Lu et al., 2018) uses the raw seismic data, and many processing steps in both the data and image domain can be excluded, potentially reducing turnaround whilst maintaining, or improving, image quality for the entire data record.
What’s New in OBN Imaging at EAGE 2020?
Author: Andrew Long
Industry Insights - 6 December 2020
The source and wavefield spatial sampling of towed streamer acquisition exceeds that of Ocean Bottom Node (OBN) and Ocean Bottom Cable (OBC) acquisition, and the survey costs are considerably less. Nevertheless, the decoupled source and receiver locations, the flexibility of OBN deployment in certain environments, and the growing industry focus upon very low frequency signals and very long offsets for FWI applications are motivating a growing market for OBN. After reviewing some recent developments in the application of Full Wavefield Migration (FWM) and Least-Squares Migration (LSM) of OBN and OBC data, I share a rather contrary perspective on receiver-side spatial sampling, and note how FWM can exploit the decoupled nature of OBN receivers, and may enable sparser (and lower cost) acquisition than is typical. This consideration of sparse and/or irregular OBN acquisition geometry leads to a brief overview of several presentations that address the acoustic imaging of OBN data at the upcoming virtual EAGE conference in December.
Full Waveform Inversion Using Wave Equation Reflectivity Modeling
Author: Yang Yang, Jaime Ramos-Martinez, Norman Dan Whitmore, Alejandro Valenciano, Nizar Chemingui
EAGE - 1 December 2020
Full Waveform Inversion (FWI) is routinely used to improve the accuracy and resolution of velocity models. However, utilizing reflections to produce low-wavenumber updates creates more operational challenges than using transmitted events. In order to simulate backscattered sensitivity kernels, FWI needs hard boundaries in the velocity/density models. Alternatively, one can apply the wave equation and first-order Born approximation to decompose the seismic wavefields into background and perturbation. Here, we derive an acoustic wave equation in terms of vector reflectivity to be used as the wave’s propagation engine of FWI. The new derivation results from the change of variables from impedance to reflectivity in the variable density wave equation. The main advantages of its insertion in our FWI algorithm are the following: it does not require the construction of density/hard boundaries in the velocity model to generate reflections; it allows the use of reflected events without the need of solving two different wave equations in the forward and backward propagation; it is more accurate than the method based on the first-order Born approximation to perturbation theory. We show synthetic and field data examples illustrating the advantages of the new algorithm.
Broadband 4D Seismic Provides New Level of Detail
Author: Yulia Biryaltseva, Tor Vegar Mårdalen, Per-Harald Saure-Thomassen, Marta Wierzchowska, Anastasiya Tantsereva, Julien Oukili
GeoExpro - 1 December 2020
Understanding new details in the 4D seismic signal uncovered by a broadband timelapse dataset at Gullfaks Main Field in the North Sea.
Quantifying 4D Repeatability Improvements with Evolutionary Acquisition on the Gullfaks Field, North Sea
Author: Marta Wierzchowska, D. Anderson, Julien Oukili, Y. Biryaltseva, D. Fischer, E. Sadikhov, B. King
EAGE - 1 December 2020
This article presents quantitative measures of geometrical repeatability versus time-lapse data quality, showing the advantages of the deep-tow multisensor streamer acquisition for 4D projects. Authors demonstrate that the multisensor streamer enabled the optimization of the acquisition turnaround together with the improvement of the 4D data quality. They propose to look at both the NRMS and the fNRMS attributes (NRMS value calculated per
single frequency) to evaluate 4D repeatability and therefore data quality improvements with evolving acquisition technology over the last 34 years of the reservoir monitoring program over the Gullfaks field, North Sea.
Can we reduce significantly the number of OBN by using Full Wavefield Migration?
Author: Didier Lecerf, Amir Asnaashari, Abderrahim Lafram, Rasaki Salami
EAGE - 1 December 2020
This paper analyses the ability of Full Wavefield Migration (FWM) algorithms for providing an extended illumination for imaging without the OBN positioning constrain. Using deep-water OBN datasets, we investigate the effect of minimal sensor distributions on the resolution of the seismic image. Unusual OBN acquisition parametrization such as very limited aperture, extensive separation distance and innovative “donut” layout designs are investigated and discussed. The results demonstrate that the Full Wavefield Migration algorithm allows the reduction of OBN density, enabling a large distance between receivers and providing more geometry flexibility without compromising the image quality. An innovative OBN acquisition with a “donut” design is proposed for combining velocity modeling using refracted and diving waves (FWI) and imaging with Full Wavefield Migration. Reducing the number of nodes deployed for the same final image quality can
positively influence the economics of an OBN acquisition survey.
Deep Learning at SEG 2020
Author: Andrew Long
Industry Insights - 3 November 2020
Machine learning dominated the technical program at the Society of Exploration Geophysicists (SEG) conference this year; with Deep Learning applications being most popular. A consideration of the mechanics of convolutional neural networks (CNNs) and generative adversarial networks (GANs) leads to a comparison of several complementary efforts to resolve the most obvious challenge to such pursuits in the geosciences (the lack of real training data), and several complementary efforts to resolve one of the key weaknesses in Full Waveform Inversion (the lack of very low frequency signal in the recorded data). Despite the hype that can accompany this broad topic, encouraging progress is being made towards geoscientists being able to make better informed decisions, using more (all) data, and in less time.
First 4D broadband using multicomponent streamers acquisitions for deep water reservoir monitoring: benefits and lessons learned
Author: Didier Lecerf, Didier Rappin, Mikhail Baturin, Raphael Lencrerot
SEG - 1 October 2020
During the last decades, broadband seismic surveys became more prevalent and for several years this has also been used for time-lapse seismic monitoring of hydrocarbon producing fields or CO2 storage targets. With optimized survey design and dedicated processing sequences, both the monitor acquisition repeatability and the frequency bandwidth of the useful seismic signal at target level are improved. Since the low frequency part of the seismic signal has a direct impact on the reliability of seismic
amplitude inversion, this has led to improving relevant 4D resolution which is crucial during 4D interpretation and integration. In our context of oil field monitoring, we
compare base and monitor seismic from standard good quality bandwidth to broadband data. We decoupled the Signal-Noise component of the data from the seismic frequency bandwidth. This permits a more robust estimation of our different 4D attributes. In addition, geostatistical tools have been used to better quantitatively compare
conventional and broadband monitor pairs. The final 4D interpretation and integration step takes benefit of the useful bandwidth from the broadband data thereby allowing for easier 4D attribute handling, the possibility to consider lower values of relevant 4D attributes and the computation of a more representative 4D geobody volumes in the allocation matching process. Also, the geobody interpretation on different monitor pairs can help to better precise the effective fluid and pressure pathways due to field production mechanisms.
Full Waveform Inversion (FWI)
Author: Andrew Long
Industry Insights - 3 September 2020
Andrew Long attempts to explain FWI in accessible terms by presenting the critical steps for the methodology to yield useful results, and refers to some common ambitions of the many industry and academic implementations: 1. Setting up a scheme that adjusts the differences between modeled and measured shot gathers so that the subsequent steps in the iterative workflow are stable, 2. Isolating only the seismic information that is relevant to the subsurface parameters being isolated, and 3. Guiding the iterative recovery of an accurate subsurface model in a manner that reduces spurious artifacts.
If you’re a strong mathematical geophysicist this is probably below your competency, but if you can tolerate some basic algebra and have an interest in what FWI is about, then hopefully this might help you complete the initial journey. This article is written to accompany the three-part TechByte webinar series on FWI.
GeoStreamer X in the Viking Graben Illuminates Complex Targets
Author: Kai Fløistad, Julien Oukili
GeoExpro - 8 June 2020
To meet the industry demand for improved subsurface insight at a reduced cost and with faster turnaround time than ocean bottom surveys, PGS deployed a pioneering acquisition configuration in the Viking Graben in the autumn of 2019. Three months after the last shot on the GeoStreamer X survey in the Viking Graben, the early-out multi-azimuth (MAZ) PSDM seismic stack was delivered to pre-funders. From an interpreter’s point of view the results are stunning, and what started as a novel concept now provides new insight to geoscience teams in near-field exploration, appraisal and development.
There are many targets in the area, ranging from Eocene sand injectites to fractured basement, and an approach integrating survey design, imaging solutions and quantitative interpretation has enabled a significant improvement in the resolution of these reservoirs. The main imaging challenges are the large shallow channels and massive sand mounds in the Miocene as these introduce shadow zones beneath them. Eocene cemented sand injectites, called V-brights, have anomalously high velocities which historically have been very difficult to estimate. Deeper, a thin, rugose Cretaceous chalk layer causes multiples and dispersion of the seismic energy.