ABSTRACT The purpose of this thesis project work is to build reservoir models (structural, facies and Petrophysical property models) of the different reservoir surfaces using integrated data sets (seismic, wells, fault sticks, eclipse models, horizon surfaces) of the Norne field which is located in blocks 6608/10 and 6508/1 in the southern part of the Nordland II area. Different visualizations techniques, volume rendering and seismic attributes were applied to aid the seismic interpretation and to provide detailed evaluation/integration of the data. 3D seismic interpretation for the whole seismic volume within the reservoir section was done manually with controlled input surfaces/reflectors of the Top horizons of the Not and Åre Formations. Fault and surfaces interpretation of the reservoir were generated as key inputs in the modeling process The structural 3D grid skeleton and models were generated with critical inputs of the manually interpreted faults/horizons, using different qualitative/quantitative templates in Petrel. This was followed by well interpretation and upscaling to provide discrete facies which are needed in populating the structural models of each of the reservoir surfaces. A probabilistic facies model was done to capture the proportion of the spatial dimensions of each discrete facies in the model frame. The initiation of this study involves quantitative data quality controls and management of inputs files into the Petrel window, qualitative control involves transferring geologic licenses/understanding to the various interpretations in the visualization schemes, seismic interpretation and reservoir modeling templates. The combination of different data type and idea (volumes, wells, top surfaces, and fault sticks) types means that the user must have a multivariate understanding (Geologic, Geophysical, Petrophysical, Geostastistic, Geo-Modeling and Reservoir Engineering) in other to integrate the data sets and deliver the models. Eleven wells were used in reference to the Top surface of the Not, Åre Top surfaces and Statoil Reference report of the field, to deliver and control the seismic interpretation. A wedge shape structure was observed in the reservoir section. Typically, minor and major faults were interpreted as forming compartments in the reservoir, which were interpreted across the different lines. The structural framework in the field was largely defined by the Norne Horst and associated faults, with the erosional surface of the BCU with internal sub unconformities observed. The property facies model of the reservoir surfaces (Garn, Ile, Tofte, and TIlje) suggest that the Norne Horst and sub relief structures are mainly sand rich, which provides additional prospect indicators in exploring the field

Seismic interpretation of 13 lines has been conducted in the Hammerfest and Tromsø basin areas in the southwestern Barents Sea. Based on interpretations, a 3D Geomodel comprising 10 layers has been constructed. Depth conversion of the Geomodel was accomplished after building of the herein required velocity model. Paleobathymetric reconstruction was performed for 9 time intervals from Top Oxfordian/Late Jurassic until Intra Sotbakken/Base Pliocene utilizing SINTEF´s basin modeling tool SEMI Paleowater. The restoration method is based on the information about depositional geometries from seismic sequences combined with zero or near zero water depth indicators. The time intervals have been restored using the deep marine infill scenario. The reconstruction showed that the Early Cretaceous paleo-water depth was greatly influenced by the Late Jurassic-Early Cretaceous rifting episode that resulted in the formation of deep marine basins and structural highs. Differential subsidence during the Cretaceous led to more stable areas in the east and rapidly subsiding basins in the west of the study area. Compressional tectonics in the Early Paleogene resulted in the development of the Senja Ridge as a positive structure. From the Oligocene until the Miocene, a period of shallow marine conditions was restored in the Hammerfest and Tromsø basins. The transition to a passive continental margin and resulting thermal subsidence led to a new deepening in the Neogene.

The Statfjord Formation (Rhaetian-Sinemurian) produces from six fields across the North Sea, but no discoveries have yet been made in the 12 exploration wells across the Oseberg South Field. The field has undergone two major periods of rifting in the Permian-Triassic and from the mid-Jurassic to Early Cretaceous. The Statfjord Formation was deposited during the Permian-Triassic post-rift period, but its tectonic influence on the paleogeography of the formation is not well understood. An isopach map produced from seismic interpretation and RMS modelling of the Statfjord Formation showed a westward thickening trend towards the present-day Viking Graben. This study presents results obtained using new, high-quality OBC seismic data that has allowed for faults throughout the field to be mapped in great detail. Supported by stratigraphic correlations and biostratigraphy, the mapping has showed that most faults can be assigned to either of the main rifting phases or their associated post-rift subsidence histories. Large, east-dipping faults are believed to have originated during the Permo-Triassic rifting, with evidence of movement into the Cretaceous. Large thickness increases of the formation over the westward dipping Oseberg and Brage Faults, as well as syn-rift sediments within some grabens in the J structure indicate movements of these faults during deposition. Biostratigraphic data show that the lowermost part of the Statfjord Formation was approximately the same thickness across the field until the Late Triassic, constraining the initiation of the Oseberg and Brage Faults to the Early Jurassic. Interpretations from timelines correlated within the Statfjord Formation suggest that the rate of subsidence along different faults was not consistent through time. Thickness changes along strike of the fault indicate that the movement along the fault was diachronous. This study aims to show that major fault activity influenced the deposition, and possibly preservation potential of sediment in the Statfjord Formation. The second phase of rifting is believed to have initiated many of the faults within the field, as well as reactivated the Oseberg and Brage Faults. Additional NW-SE faults in the Omega structure show no evidence of syn-rift sediments at the Statfjord Formation level, suggesting a mid-Jurassic post-rift origin. Similarly oriented faults were seen in the C structure, however, the presence of syn-rift sediments was difficult to ascertain, and no conclusions about the timing of initiation were made.

In this study 19 tunnel valleys within block 2/4 in the central North Sea basin have been mapped. Furthermore, the possibility for these valleys to act as migration paths for leaked gas has been evaluated. In January 1989 a kick occurred while drilling well 2/4-14 in the area of study, hence the pertinence of evaluating this hypothesis at this locality is evident. The work has been performed using multichannel 2D lines and a conventional 3D seismic survey. The quality of the 2D and 3D data is clearly dissimilar at shallow burial depths, as the 2D data is considered to be high-resolution while the 3D data is low-resolution. However, both data sets have proved to give valuable information on the valley morphology. Great details about the extent and basal morphology have been retrieved from the conventional 3D volume; whereas seismic characteristics of the valley infill have been interpreted from the 2D lines. Tunnel valleys are major, elongated incisions carved into sediments or permeable bedrock during glaciations. They tend to be sinuous in planform, but might also appear as straight valleys. Tunnel valleys often consist of several cut- and fill-structures, both laterally and vertically, and thus form a network of interconnected valleys. This has also been observed in the area of study. No sedimentological logs have been available in the study. Hence, the interpretations of valley fill lithologies are based on the seismic characteristics, and thereby they are quite cautious. The typical fill sequence observed correlates fairly good with similar valleys mapped in the area previously. A lower part of chaotic reflectors, believed to be glaciofluvial sands and gravels, is overlain by sub-horizontal layers of glaciomarine mud. Moreover, velocity pull-up effects are seen in the underburden of some of the valleys. These indicate relatively high velocities of the infill sediments, and hence, it is likely to be clayey tills. Even so, the possibility of gas migration within the tunnel valley system is believed to be conspicuous.

We use rock physics models for poorly consolidated rocks to diagnose reservoir sandstones in the Alvheim Field, North Sea. Geological factors that will control the rock physics and seismic properties include clay content, sorting, diagenesis, mineralogy, and bedding configuration. The various geologic factors will affect the fluid and stress sensitivity in these rocks. We investigate the interrelationships between various geological factors and seismic fluid and stress sensitivity, by combining well log data and rock physics models. Finally, we determine inter-well characteristics in terms of varying geological factors at different locations and discuss the results in terms of expected seismic signatures in the area.

Time-lapse seismic inversion approach to reservoir management has proven to be a vital tool in the industry today because of its effectiveness in tracking the movement of fluid front within the reservoir as well as identifying isolated bypassed accumulations. A base (2001) and three monitor (2003, 2004 and 2006) seismic surveys from the Norne field were inverted during this research. Water and gas have been injected into the reservoir to maintain the initial pressure within the field. These seismic surveys were analyzed for time-lapse impedance changes due to the differences in the produced hydrocarbons and the injected fluids. Check-shot corrected well data as well as interpreted horizons were integrated in the inversion process. Two independent wavelets were extracted from base and monitor surveys and combined to form an all-encompassing frequency and amplitude wavelet. The base and monitors were jointly inverted. This is because of the reduction in inconsistencies that are associated with independent inversions of surveys and the production related changes expected in time-lapse inverted seismic data.The results of the inversion show the impedance difference across the field for the various monitor surveys. Areas surrounding producer wells show slight changes in impedance while great impedance difference are observed around injector wells. A statistical analysis of the inversion results also shows steady increase in impedance across the field for the subsequent monitors. Structural and stratigraphic interpretation of the time-lapse inverted data also confirmed the sealing properties of some formations. This sealing property supported the impedance changes within the field. Fault interpretations as well as its sealing and non-sealing properties were inferred from the impedance differences across various discontinuities. Time-lapse acoustic impedance inversion of the Norne post-stack seismic data has revealed the impacts of production, dynamic fluid changes across main identified geologic structures, fluid front migration, fluid communication across structures and segments and other identified stratigraphic elements.

The North Sea basin is one of the best-studied areas in the world with respect to thestructural and sedimentary architecture of rift zones. The Base Cretaceous Unconformity,which defines a mappable horizon at the transition from synrift to postrift sequencesassociated with the Jurassic–Cretaceous rift, is well known as a reference marker for bothseismic and well log interpretations and covers most of the basin. This unconformity isinterpreted at the locations of the Øygarden Fault Zone, the Troll Fault Block, the NorthViking Graben, the Tampen Spur, the Snorre Fault Block, the Sogn Graben and the HordaPlatform. The complexities of the unconformity have been established and vary with thestructural and geographical position within the basin. However, as the Base CretaceousUnconformity covers most of the northern North Sea, its structural time map, is used to derivethe picture of post-structural framework of a rift basin and to locate essential structures in thedeeper sections.Three main reflectors (Pre-Jurassic 1, Pre-Jurassic 2 and Top seismic basement)located beneath the Base Cretaceous Unconformity on the Horda Platform, and have beeninterpreted using 2D seismic reflection data. These three reflectors have been studied in orderto investigate in detail the displacement gradients and possible linkage of the early faultsystem under the Horda Platform, and to evaluate their effect on the large-scale sedimentarchitecture. A main reason to work on the structures under the Horda Platform is due to thefact that these structures are believed to have existed already in the early stages of thenorthern North Sea basin development.The extensional normal fault systems of both the Permo-Triassic and the Late Jurassicrifts are considered a key control on the geological structures and sedimentary architecture ofthe region as presently seen. The basin evolution related Permo-Triassic rifting is mostpronounced on the eastern part of the Horda platform where its synrift geometry is obviouslyseen with the huge segment length and largest uplift explainable by a flexural stretchingmodel. The rift axis is transferred to position at base of the Viking graben during the Late-Jurassic rifting with the smaller magnitude of extension than the Permo-Triassic as clearlyseen by the less thickness of the synrift geometry. However, the structural evolution of normalfaults and the basin architecture under the Horda Platform is particularly affected by thecomplex interaction of fault linkage, fault propagation, fault growth, and death of faultthrough times from the early stage to the final stage of the basin development. Apart from theeffects of major tectonic controls, additionally, non-tectonic parameters, such as climate, seaor lake level changes, and differences in amount and type of sediment supply, should be takeninto account to influence the stratigraphic and sedimentation patterns in the basin.