ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉High-resolution 3D (HR3D) seismic data are important for hydrocarbon exploration of shallow reservoirs, site characterization, and geohazard assessments. The goal of this contribution is to identify and quantify the parameters to increase the resolution of HR3D seismic data to meter scale. The main acquisition parameters controlling the resolution of the collected data are the spectrum of the seismic source, source-receiver offset range, and trace density. An evolution to one-meter-scale resolution of 3D seismic will rely on combining a reproducible seismic source with high frequencies up to at least 600 Hz, a high uniform trace density of more than 4 million traces per square kilometer, and an offset range shorter than approximately 200 m. The resulting 3D seismic data volume will reach meter-scale resolution for water and target depths of less than 600 m. The proposed HR3D system will be suitable for 3D and 4D characterization of seabed properties and shallow stratigraphy, the identification of geohazards and hydrocarbon leakage, and monitoring the environmental impact of offshore activities. The P-Cable 3D system is an excellent starting point for achieving one-meter-scale resolution due to its flexible and tight meter-scale shot and receiver spacing.〈/span〉

Description: 〈p〉High-resolution seismic data are powerful tools that can help the offshore industries to better understand the nature of the shallow subsurface and plan the development of vulnerable infrastructure. Submarine mass movements and shallow gas are among the most significant geohazards in petroleum prospecting areas. A variety of high-resolution geophysical datasets collected in the Barents Sea have significantly improved our knowledge of the shallow subsurface in recent decades. Here we use a 〈i〉c.〈/i〉 200 km〈sup〉2〈/sup〉 high-resolution P-Cable 3D seismic cube from the Hoop area, SW Barents Sea, to study a 20–65 m thick glacial package between the seabed and the Upper Regional Unconformity (URU) horizons. Intra-glacial reflections, not visible in conventional seismic reflection data, are well imaged. These reflections have been mapped in detail to better understand the glacial deposits and to assess their impact on seabed installations. A shear margin moraine, mass transport deposits and thin soft beds are examples of distinct units only resolvable in the P-Cable 3D seismic data. The top of the shear margin moraine is characterized by a positive amplitude reflection incised by glacial ploughmarks. Sedimentary slide wedges and shear bands are characteristic sedimentary features of the moraine. A soft reflection locally draping the URU is interpreted as a coarser grained turbidite bed related to slope failure along the moraine. The bed is possibly filled with gas. Alternatively, this negative amplitude reflection represents a thin, soft bed above the URU. This study shows that P-Cable 3D data can be used successfully to identify and map the external and internal structures of ice stream shear margin moraines and that this knowledge is useful for site-survey investigations.〈/p〉

Description: High-resolution seismic data are powerful tools that can help the offshore industries to better understand the nature of the shallow subsurface and plan the development of vulnerable infrastructure. Submarine mass movements and shallow gas are among the most significant geohazards in petroleum prospecting areas. A variety of high-resolution geophysical datasets collected in the Barents Sea have significantly improved our knowledge of the shallow subsurface in recent decades. Here we use a c. 200 km 2 high-resolution P-Cable 3D seismic cube from the Hoop area, SW Barents Sea, to study a 20–65 m thick glacial package between the seabed and the Upper Regional Unconformity (URU) horizons. Intra-glacial reflections, not visible in conventional seismic reflection data, are well imaged. These reflections have been mapped in detail to better understand the glacial deposits and to assess their impact on seabed installations. A shear margin moraine, mass transport deposits and thin soft beds are examples of distinct units only resolvable in the P-Cable 3D seismic data. The top of the shear margin moraine is characterized by a positive amplitude reflection incised by glacial ploughmarks. Sedimentary slide wedges and shear bands are characteristic sedimentary features of the moraine. A soft reflection locally draping the URU is interpreted as a coarser grained turbidite bed related to slope failure along the moraine. The bed is possibly filled with gas. Alternatively, this negative amplitude reflection represents a thin, soft bed above the URU. This study shows that P-Cable 3D data can be used successfully to identify and map the external and internal structures of ice stream shear margin moraines and that this knowledge is useful for site-survey investigations.

Description: Injection of CO2 in subsurface reservoirs may cause overburden deformation and CO2 leakage. The aim of this study is to apply technologies for detection and monitoring of CO2 leakage and deformation above the injection reservoirs. The examples of this study include data from the Vestnesa Ridge natural seep site, the Snøhvit gas field and CO2 storage site region, and the Gemini North gas reservoir. Reprocessing of existing 3D high-resolution seismic data allows resolving features with a vertical and lateral resolution down to c. 1 m and c. 5 m respectively. The current acquisition systems could be modified to image structures down to one meter in both the vertical and horizontal directions. We suggest a monitoring workflow that includes baseline and time-lapse acquisition of high-resolution 3D seismic data, integrated with geochemical, geophysical, and geotechnical seabed core and water-column measurements. The outcome of such a workflow can deliver reliable quantitative property volumes of the subsurface and will be able to image meter-sized anomalies of fluid leakage and deformation in the overburden.

Description: A dramatic reduction in global greenhouse gas emissions is necessary to achieve climate change targets. Wide ranging measures are required to reduce emissions with carbon capture and storage forming a vital component. Current carbon sequestration occurs in volumes of Mt/a into dominantly sedimentary reservoir rocks. Pilot tests have demonstrated that basalt reservoirs provide an alternative and permanent carbon capture scenario (e.g. Carbfix project). Here, we use 2D and 3D seismic data combined with well data to identify and map potential permanent and safe carbon storage reservoirs in offshore basalt sequences in the NE Atlantic. Well data support the presence of reservoir properties within extrusive basaltic sequences with porous lava flow tops and volcaniclastic lithologies comprising the most prolific sequestration targets. The basalt sequences are overlaid by several hundred meters of Cenozoic sediments with sealing properties, consisting mainly of marine shales and glaciogenic sediments. We hypothesize that offshore CO2 sequestration into porous basaltic lava flows may allow permanent CO2 sequestration of several gigatons per year, however more research and testing is needed to verify this potential.

Description: Highlights • Increased glacial sedimentation rates do not generate sufficient overpressure to trigger a landslide. • Simulated overpressures for different sedimentation scenarios do not significantly differ. • A glacimarine layer underneath rapidly-deposited sediments is important for overpressure build-up. • An earthquake of M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the Tampen Slide. Abstract Trough mouth fans are environments characterized by high sediment supply during glacial stages and the occurrence of large-scale instabilities. The geological record indicates that several of these environments have failed repeatedly resulting in large submarine landslides. The roles of sedimentation rate, weak layers, glacial loading and unloading as well as seismic activity on triggering megaslides in trough-mouth-fan systems is still unclear. A better understanding of the preconditioning factors, triggers and consequences of these landslides is crucial due to the hazard they pose to coastal communities and offshore industries. In this paper, we focus on the North Sea Trough Mouth Fan, which is the result of massive glacial sediment input delivered to the shelf edge through the Norwegian Channel, southeast Nordic Seas margin. The Tampen Slide, one of several large paleo-landslides that have happened within the North Sea Trough Mouth Fan, took place at c. 130 ka (end of MIS 6), and removed an estimated 1800 km3 of sediment. Here, we use boundary conditions from the Tampen Slide and 2D Finite Element Modeling (Abaqus software from Simulia) to evaluate the effects of variations in sedimentation rates as well as sediment properties on the generation of excess pore pressure, fluid flow, and slope stability along the axis of the trough-mouth-fan system. The model domain, 40 km in length and 2 km in height, is dominated by glacigenic debris flows and glacimarine sediment deposits. We use geotechnical data measured on samples of glacigenic and glacimarine sediment deposits from the nearby Ormen Lange gas field area to constrain the model. We evaluate the stability of the slope under various scenarios, including constant sediment loading, episodic changes in sedimentation rates and abrupt pulses in sediment delivery for a 61 kyr period (MIS 6). The models show that increased sedimentation rates during glacial stages do not generate sufficient excess pore pressure to set off a landslide. Furthermore, the simulated overpressures for the different sedimentation scenarios do not significantly differ at the end of the model runs. The results also highlight the importance of a basal glacimarine sediment layer underneath the rapidly-deposited sediments for the build-up of overpressure. Consequently, this glacimarine sediment layer has the inherited potential to act as a weak layer facilitating instability. However, as overpressure due to sediment deposition alone does not result in slope failure, we couple the preconditioned slope with earthquake ground shaking. Based on attenuation models, an earthquake of approximately M6.9 or larger at a short distance from the Tampen Slide headwall could have triggered the landslide. Therefore, we suggest glacial sedimentation and a glacimarine sediment layer to represent preconditioning factors, and seismic shaking as the final trigger mechanism for the Tampen Slide, i.e. similar to the situation that lead to the development of the Storegga Slide in the same area.