TGS

Carbon Capture and Storage (CCS) technology is recognised as an important contribution to mitigate climate changes and monitoring of the injected carbon dioxide (CO2) is an important element of this technology to ensure that the CCS system operates within the required legal and regulatory standards. To be able to offer more flexible monitoring solutions the potential of mini streamers for overburden and shallow CCS monitoring has been investigated. The results from a series of 2D and 3D mini-streamer operations across the Sleipner CO2 storage site are assessed and compared with conventional streamer seismic. The results show a clear enhancement in overburden imaging and higher detail at the CO2 plume level compared to conventional streamer seismic data. However the mini streamers also come with limitations related to the acquisition configuration (for example limited fold offset etc.).

The text discusses the acquisition and imaging of 3D seismic data in the ultra-shallow waters of the Black Sea’s northwestern shelf focusing on the Dolfin Inner shelf license areas. Despite depths ranging from 14m to 40m an efficient acquisition setup has been chosen to navigate seafloor obstacles. The data underwent advanced processing including 3D wavefield separation deghosting demultiple and machine learning-guided denoising. Results demonstrate the final migration velocity model’s ability to capture high and low velocity contrasts critical for depth imaging. Separated wavefield imaging (SWIM) enhances imaging of the seafloor providing a very good match with bathymetry data. Comparing 2D and 3D seismic data emphasizes the latter’s superior quality crucial for evaluating the Dolfin Inner shelf area’s hydrocarbon potential. Next study will focus on the exploration in the Outer Shelf and adjacent deepwater domains highlighting the Black Sea’s Ukrainian waters as a promising frontier for oil and gas exploration. The acquired 3D seismic data plays a pivotal role in advancing this exploration contributing valuable insights in a cost-effective manner.

A growing Geophysical argument for the use of single-element pneumatic points sources has been developing over the last several years. They have been shown to significantly improve the low-frequency signal-to-noise ratio (SNR) on both towed-streamer and ocean bottom node (OBN) surveys thereby extending the available bandwidth in the recorded data. Udengaard et al (2023) and Shang et al (2023) made separate demonstrations for using the Gemini extended frequency source and the Tuned Pule Source (TPS) respectively as exclusive sources in support of Imaging and FWI model building on sparse OBN surveys in the Gulf of Mexico. Ou et al (2023) documented the use of Gemini as the only source in a full survey application of a dual-vessel quad-source Wide Azimuth (WAZ) towed-streamer design in the Eastern Mediterranean.

Field implementations of large point sources thus far however have been limited to two sources per vessel mainly due to the perception that this represents the limits of capacity of modern survey vessels. We embarked on field trials over the last six months to understand the feasibility of operating more than two Gemini units concurrently on the same vessel.

Streamer-tails an extended subset of the main streamer spread are a pragmatic and cost-effective method to achieve longer offsets for refraction full waveform inversion (FWI) based velocity model building (VMB). To our knowledge there is currently no established best practice to design streamer-tail solutions. We present a new survey design workflow that finds the optimal streamer-tail geometry for towed streamer and source configurations that is fit-for-purpose and limited primarily by a finite streamer inventory. We also show a case study from the Norwegian Sea to demonstrate the uplift from streamer-tails during VMB.

Offshore Benin and the wider Keta Basin remains an underex-plored area of the West Africa Transform Margin. The evolution of the different sediment fairways and their depocentres can be identified on structure maps from the mapping of a regional 2D seismic dataset. The 3D seismic offshore Benin supports the 2D interpretation but in addition allows for a more complete evaluation through detailed seismic attribute analysis. The use of 3D spectral decomposition highlights the changes in fairway directions with clear imaging of the channel systems and their orientations correlating with the thicknesses observed from regional 2D seismic mapping.

The transform faults strongly control the overall structur-ation of offshore Benin and the depositional style during the Cretaceous period. The onshore Togo and Benin river systems supply sediment directly to the basin in a north to south direction which is limited and directed by the transform movement and ridges outboard. Towards the end of the syn-transform deposition the main fairway input changes from a directly northern source to a north eastern source in the Dahomey Embayment. Finally in the Cenozoic the Niger River system drainage increased leading to the Benin Ultra Deep area to form part of the Niger prodelta with a predominant easterly sourced sediment input. The transform faults are no longer active and no longer control sediment distribution leading to an unconfined channelised system.

We propose an elastic dynamic matching full waveform inversion (EDMFWI). Similar to the acoustic case EDMFWI tries to invert a velocity model that maximizes the local windowed cross-correlation of the dynamically matched synthetic and field datasets with an optimized matching scheme. Though it can be applied to jointly invert multi-parameters like [(v_pv)] _s and density(ρ) this paper focuses on inverting P wave velocity. With the successful applications to different datasets it demonstrates that EDMFWI can significantly improve P-wave images by properly handling the elastic impacts in different scenarios: it derives a higher resolution velocity model for a target reservoir with a known class 2p amplitude variation with offset response; in the area where salt bodies present EDMFWI can produce velocity model with sharp salt interface and reduced salt halo resulting the improved subsalt images; on the other hand it can significantly improve illumination and fold coverage in the subsalt area by taking advantage of the contribution of mode converted waves at the salt boundaries.

Seismic velocity models derived via ray-based tomography and full waveform inversion (FWI) are typically non-unique as the observed data may be explained by many possible models. Constraints may limit these possibilities but even then many viable models can appear equally correct. Here we present a methodology for quantifying model uncertainty and use the NOAKA ocean bottom node dataset from the Norwegian North Sea to demonstrate our approach.

Recognizing and quantifying uncertainties is pivotal for evaluating risks in interpreting seismic volumes which can then be used in the well planning process. We propose a model building workflow that collates statistics of the derived models and focuses on the key reflections of interest. The model statistics are used for quantifying how model uncertainty impacts the image used by interpreters in the decision making process. Our approach empowers decision-makers with a low-cost metric set to comprehend and mitigate uncertainties offering a clearer perspective on the potential risks associated with final seismic interpretations.

Acoustic FWI has been widely applied in seismic work programs. The normal derivative of the FWI velocity model which is known as the FWI Image has been shown to provide a highly interpretable product within a fraction of the time of conventional processing. FWI images are widely used to image reservoirs in a variety of settings from simple stratigraphic traps to sub-salt exploration targets. However failing to take into account the elastic effects in acoustic FWI can result in a smeared FWI image caused by amplitude and phase distortions. Elastic FWI can intrinsically solve for this but it requires not only much more computational cost but also accurate elastic models. Alternatively a multi-angle acoustic FWI can be applied to handle the elastic AVO effects. The input data is first decomposed to different angle ranges then acoustic FWI is applied to each of them separately and FWI Image angle gathers are generated. With this approach high resolution features are maintained in each angle gather. The elastic AVO parameters can then be accurately extracted from the FWI Image angle gathers term applied. This paper discusses the successful application of this approach to an OBC data set from the North Sea.

This study provides a detailed analysis of seismic interpretation techniques by moving from 2D to 3D Convolutional Neural Networks (CNNs). The study focuses on the effectiveness of these networks in interpreting salt bodies. The paper highlights the limitations of traditional 2D CNNs and showcases the improved spatial and contextual capabilities of 3D models enabled by the latest computing technologies. Our research compares model performances using a large dataset of 20 seismic surveys from the Gulf of Mexico and demonstrates significant improvements in accuracy and efficiency when using 3D CNNs.

Europe need more energy supplies in the current geopolitical situation. Natural gas is a key energy source and Norway is stepping up to meet the demand. The Norwegian Sea sit relatively close to this gas market and big parts of this basin is still poorly explored or not at all. The Norwegian Atlantic marginal highs covering 25000sqkm or about 5 quadrants at this latitude have no exploration wells. This is despite large structural closures great two-sided migration catchment areas and Pre-Cretaceous to Paleogene age reservoir potential. Latest seismic imaging shows that the sub-basalt highs typically sit within a present-day-oil-window and the volcanic succession may only be a few hundred meters thick. We have used our latest PSDM technology including Dynamic Matching FWI (DW FWI) on our recent datasets yielding a new indicative tool where distinct slowness anomalies may provide insights on presence and quality of subvolcanic reservoirs. We are currently higher frequency re-modelling using FWI for the next generation of exploration in sub-basalt terrains. Overlaying the FWI velocities helps an interpreter understand the geology but the latest trend of inverting the FWI velocity into a reflection model (FWI image) enables us to simplify the geological image even more.