Geological modelling for investigating CO2 emissions in Florina Basin, Greece

Published version also available at http://dx.doi.org/10.1515/geo-2015-0039This paper presents an investigation of naturally occurring CO2 emissions from the Florina natural analogue site in Greece. The main objective was to interpret previously collected depth sounding data, convert them into surfaces, and use them as input to develop, for the rst time, 3D geological models of the Florina basin. By also locating the extent of the aquifer, the location of the CO2 source, the location of other natural CO2 accumulations, and the points where CO2 reaches the surface, we were able to assess the potential for CO2 leakage. Geological models provided an estimate of the lithological composition of the Florina Basin and allowed us to determine possible directions of groundwater ow and pathways of CO2 ow throughout the basin. Important modelling parameters included the spatial positions of boundaries, faults, and major stratigraphic units (which were subdivided into layers of cells). We used various functions in Petrel software to rst construct a structural model describing the main rock boundaries. We then de ned a 3D mesh honouring the structural model, and nally we populated each cell in the mesh with geologic properties, such as rock type and relative permeability. According to the models, the thickest deposits are located around Mesochorion village where we estimate that around 1000 m of sediments were deposited above the basement. Initiation of CO2 ow at Florina Basin could have taken place between 6.5 Ma and 1.8 Ma ago. The NESW oriented faults, which acted as uid ow pathways, are still functioning today, allowing for localised leakage at the surface. CO2 leakage may be spatially variable and episodic in rate. The episodicity can be linked to the timing of Almopia volcanic activity in the area

Monitoring Of CO2 Leakage Using High-Resolution 3D Seismic Data – Examples From Snøhvit, Vestnesa Ridge And The Western Barents Sea

Source at https://doi.org/10.3997/2214-4609.201802965.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 highresolution 3D seismic data, integrated with geochemical, geophysical, and geotechnical seabed core and watercolumn 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

Fluid flow at the Snøhvit field, SW Barents Sea: processes, driving mechanisms and multi-phase modelling

The research undertaken in this PhD project was part of a large EU interdisciplinary project named ECO2: Sub-seabed CO2 Storage: Impact on Marine Ecosystems. The overall goal of the ECO2 project was to understand the short-term and long-term impacts of CO2 storage on marine ecosystems. I concentrated my work on the Snøhvit site, which is located in the SW Barents Sea, on the Norwegian continental shelf, and more specifically in the ENE-WSW oriented Hammerfest Basin (HFB), which is about 130km off the coast of Finnmark, in northern Norway. Snøhvit, receives ~0.7 Million tons of CO2 per year and has been in operation since late 2008. By injecting CO2 back into the earth and not leaving it to accumulate in the atmosphere, through the process of Carbon Capture and Storage (CCS), we can put forward a potential and innovative way of reducing CO2 emissions and thus mitigate climate change. My work mainly focused on the Snøhvit hydrocarbon field and CO2 storage site in the Hammerfest Basin in the SW Barents Sea. The main basis of my work consisted of an interpretation of conventional 3D and high-resolution P-Cable 3D seismic data that were used to obtain a better understanding of deep-to-shallow fluid flow. I was mainly involved in work, which concentrated on the architecture and integrity of the sedimentary cover at storage sites and in activities aiming at coordinating the development of monitoring techniques and strategies. I also contributed to the development of a framework of best environmental practices in the management of offshore CO2 injection and storage. Methodology used throughout the project included the use of new state-of-the-art technology, employed for an enhanced imaging of the seafloor and its sub-surface at unprecedented resolution. New P-Cable high-resolution 3D seismic imaging techniques provided us with more detailed images of subsurface architecture and enhanced detection of fluid leakage, which led to a better understanding of the mechanisms of fluid flow through the sedimentary overburden of CO2 storage sites. The primary method employed in this thesis is thus seismic interpretation of both conventional and P-Cable 3D seismic data using Schlumberger’s Petrel software. The seismic interpretation consisted of mapping key reflectors located in the Snøhvit subsurface and deriving volume-based attribute information, like RMS amplitude or variance. Interpreted horizons were then used to construct surfaces and layers, which were subsequently populated with geological properties. Abundant and widespread fluid flow can be observed in the SW BS. The observed fluid flow features can be of various types, interpreted as gas chimneys, leakage along faults and fractures and other related features. Although fluid migration has taken place in the past in the study area, we clarify that at present, there is no active seepage of gas in the Snøhvit area

Geological modelling for investigating CO2 emissions in FlorinaBasin, Greece

This paper presents an investigation of naturallyoccurring CO2 emissions from the Florina natural analoguesite in Greece. The main objective was to interpretpreviously collected depth sounding data, convert theminto surfaces, and use them as input to develop, for thefirst time, 3D geological models of the Florina basin. Byalso locating the extent of the aquifer, the location of theCO2 source, the location of other natural CO2 accumulations,and the points where CO2 reaches the surface, wewere able to assess the potential for CO2 leakage. Geologicalmodels provided an estimate of the lithological compositionof the Florina Basin and allowed us to determinepossible directions of groundwater flow and pathways ofCO2 flow throughout the basin.Important modelling parameters included the spatial positionsof boundaries, faults, and major stratigraphic units(which were subdivided into layers of cells). We used variousfunctions in Petrel software to first construct a structuralmodel describing the main rock boundaries.We thendefined a 3D mesh honouring the structural model, andfinally we populated each cell in the mesh with geologicproperties, such as rock type and relative permeability.According to the models, the thickest deposits are locatedaround Mesochorion village where we estimate thataround 1000 m of sediments were deposited above thebasement. Initiation of CO2 flow at Florina Basin couldhave taken place between 6.5 Ma and 1.8 Ma ago. The NESWoriented faults, which acted as fluid flow pathways,are still functioning today, allowing for localised leakageat the surface. CO2 leakage may be spatially variable andepisodic in rate. The episodicity can be linked to the timingof Almopia volcanic activity in the area

Simulating seismic chimney structures as potential vertical migration pathways for CO2 in the Snøhvit area, SW Barents Sea: model challenges and outcomes

Carbon capture and storage (CCS) activities at the Snøhvit field, Barents Sea, will involve carrying out an analysis to determine which parameters affect the migration process of CO2 from the gas reservoir, to what degree they do so and how sensitive these parameters are to any changes. This analysis will aim to evaluate the effects of applying a broad but realistic range of reservoir, fault and gas chimney properties on potential CO2 leakage at various depths throughout the subsurface. Fluid flow might take place through parts of or the entire extent of the overburden. One of the aims of the analysis is assessing the potential of CO2 reaching the seabed. Using the Snøhvit gas reservoir and overburden in the Barents Sea, a series of geological models were built using seismic and well-log data. We then performed numerical simulations of CO2 migration in focused fluid flow structures. Identification of potential migration pathways and their extent, such as gas chimneys and faults, and their incorporation into these models and simulations will provide a realistic insight into the migration potential of CO2. In the simulations the CO2 is injected over a 20 year period at a rate of 0.7 Mt/year and migration is allowed to take place over a 2000 year time frame for domains of approximately 21 km2 for the caprock fault models, 24 km2 for the realistic gas chimney models and 35 km2 for the generic gas chimney models, in a layered sedimentary succession. The total mass of CO2 injected in the reservoir during the 20-year injection period is 14 Mt. There is a strong interaction between the various parameters but the parameter that had the most influence on the CO2 migration process was probably the permeability of the reservoirs, especially the average permeability (k). Also, for the faulted caprock scenarios, it should be noted that at near surface depths the permeability of 765 mD is already adequate for a good CO2 flow. At the chimney top level (600 m) however, a further increase in permeability has an additional effect on improving CO2 flow. Overall, considering the slow upward migration velocity of the plume, this geological setup can be regarded as a suitable storage site

High-resolution 3D seismic study of pockmarks and shallow fluid flow systems at the Snøhvit hydrocarbon field in the SW Barents Sea

The Barents Sea is an epicontinental shelf sea with a fragmented structure consisting of long fault complexes, basins and basement highs. Fluid leakage from deep-seated hydrocarbon accumulations is a widespread phenomenon and mostly related to its denudation history during the glacial/interglacial cycles. In this study, we aimed to better understand shallow fluid flow processes that have led to the formation of numerous pockmarks observed at the seabed, in this area. To achieve this goal, we acquired and interpreted high-resolution 3D seismic and multibeam swath bathymetry data from the Snøhvit area in the Hammerfest Basin, SW Barents Sea. The high-resolution 3D seismic data were obtained using the P-Cable system, which consists of 14 streamers and allows for a vertical resolution of ~1.5 m and a bin size of 6.25 × 6.25 m to be obtained. The frequency bandwidth of this type of acquisition configuration is approximately 50–300 Hz. Seismic surfaces and volume attributes, such as variance and amplitude, have been used to identify potential fluid accumulations and fluid flow pathways. Several small fluid accumulations occur at the Upper Regional Unconformity separating the glacial and pre-glacial sedimentary formations. Together, these subsurface structures and fluid accumulations control the presence of pockmarks in the Snøhvit study area. Two different types of pockmarks occur at the seabed: a few pockmarks with elliptical shape, up to a few hundred meters wide and with depths up to 12 m, and numerous circular, small, “unit pockmarks” that are only up to 20 m wide and up to 1 m deep. Both types of pockmarks are found within glacial ploughmarks, suggesting that they likely formed during deglaciation or afterwards. Some of the larger normal pockmarks show columnar leakage zones beneath them. Pressure and temperature conditions were favourable for the formation of gas hydrates. During deglaciation, gases may have been released from dissociating gas hydrates prolonging the period over which active seepage occurred. At present, there is no evidence from the 3D seismic data of active gas seepage in the Snøhvit area. Low sedimentation rates or the influence of strong deep ocean currents may explain why these pockmarks can still be identified on the contemporary seabed