The most prolific reservoir package in the SW Barents Sea is currently the Upper Triassic–Middle Jurassic Realgrunnen Subgroup, comprising the main hydrocarbon accumulations in the Goliat, Snøhvit and Johan Castberg fields and the Wisting discovery. The interval continues to be the main target as hydrocarbon exploration ventures further into this region. However, the package varies considerably in thickness and reservoir quality throughout the basin, and it is therefore very important to understand how this package developed and what has affected it in the time since it was deposited. Here we review controls on the tectonostratigraphic evolution and facies distribution within the Realgrunnen Subgroup, and exemplify the variability in reservoir characteristics within the subgroup by comparing some key wells in relation to their depositional environment and provenance. New provenance data that record a turnover from reworked Triassic- to Caledonian-sourced mature sediment support facies observations which suggest temporal changes in the depositional environment from marine to fluvial. Much of the variability within the subgroup is attributed the tectonostratigraphic development of the basin that controlled accommodation, facies transitions and sediment distribution. This variability is reflected in subtle differences in reservoir quality important both for exploration and production in the remaining underexplored basin.

The process of geosteering, using real-time logging-while-drilling data to actively steer horizontal or highly deviated wellbores, has been in use for more than 20 years. Over this period, the demand for more sophisticated measurements has developed along with the need to access increasingly difficult reservoirs as the simpler drilling scenarios are being exhausted.Such a case is evident in the Yme Gamma development, located offshore south-western Norway, consisting of four horizontal producing wells and two vertical injectors. Abandoned by the original operator because of high water cut, to redevelop the field the current operator needed to drill subsequent wells in a narrow corridor up-dip between the existing producer wells and the bounding fault, in the thin YS 7 (4 to 8 m) inner-estuary sands or the YS 5/4 (2 to 6 m) inner/central-estuary sands.The Yme 9/2-C-2A well was successfully drilled as a replacement for the C-2 well, which had been redrilled because of the reservoir being swept in that area. Since the neighbouring well, C-3T3, showed encouraging results in the YS 5/4 reservoir, which was not targeted in that well, a horizontal well was planned to exploit this reservoir.There were several challenges that needed to be addressed in the geosteering of this well: the need to keep the wellbore within a narrow reservoir (between 2 and 6m in thickness); a very narrow lateral corridor between the main bounding fault and existing wells; observed sub-seismic faulting in neighbouring wells; and the possibility of a coal layer, which would necessitate a sidetrack if intersected.As with any geosteering operation, success is often the result of a combination of inter-department team work and communication as well as the use of appropriate technology. Integrated use of a bed boundary mapping device and real-time density images allowed the 9/2-C-2A well to be geosteered within these tight tolerances, skirting the bounding fault by less than 1 m lateral displacement, and allowing for the drilling of other tight tolerance wells.

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We analysed the fault rocks of a compartmentalized field in the Barents Sea, in an area with several tectonic elements, which formed at different tectonic events. Standard Fault Seal Analysis (FSA) was conducted to predict the shale content of the fault rock (SGR). A static cellular model based on well data, seismic data and geological concepts served as input. The fault rock calibration workflow required various data acquired by different methods. We analysed the Mid-Triassic to Upper Jurassic clastic deposits to reconstruct the tectonic history. Apatite fission track and (U-Th)/He thermochronology were used to determine the maximum burial depths and exhumation history. The results of high-resolution shale ductility analysis (BIB-SEM), a compaction trend study, kinematic analysis and structural modelling (section balancing) served as additional input constraints for fault rock calibration. The evaluation of the results helped to reconstruct the following tectonic evolution: The orthogonal faults of the analysed area developed at an early stage, during Late Triassic to Early Jurassic times at relatively shallow depth, below 1000 m. Ongoing subsidence created accommodation space for Upper Jurassic to Cenozoic deposits with a maximum burial depth of 2000 m for the analysed Mid-Jurassic rocks. Exhumation of the area started around 10 Ma and continued through to Quaternary times. The calculated values for fault rock permeability show a wide range when using poorly constrained input for fault rock calibration: 10 to 1000 mD for SGR values around 0.08 at reservoir/reservoir juxtaposition. Fault rock calibration using above described results concluded in reliable values for fault rock permeability and ultimately, for transmissibility multipliers. The reason for the sensitivity of the fault rock calibration is a combination of multiple factors: highly permeable reservoir sandstone, shallow depth of initial faulting, maximum burial depth and low shale content at the primary reservoir level. The study shows that an accurate reconstruction of the geohistory provides essential parameters for fault rock calibration and fault rock permeability calculation. The range of values can widely scatter if preconditions are not acknowledged. Well-constrained fault rock calibration reduces the uncertainty on possible flow scenarios, increases the reliability on production forecasts and helps to determine the most efficient drainage strategy.

Summary We analyzed the fault rocks of a compartmentalized field in the Barents Sea, in an area with several tectonic elements, which formed at different tectonic events. Standard fault seal analysis (FSA) was conducted to predict the shale content of the fault rock (shale gouge ratio, SGR). A static cellular model based on well data, seismic data, and geological concepts served as input. The fault rock calibration workflow required various data acquired by different methods. We analyzed the Middle Triassic to Upper Jurassic clastic deposits to reconstruct the tectonic history. Apatite fission track (AFT) and (U-Th)/He thermochronology were used to determine the maximum burial depths and exhumation history. The results of high-resolution shale ductility analysis, a compaction trend study, kinematic analysis, and structural modeling (section balancing) served as additional input constraints for fault rock calibration. The interpretation of the results helped to reconstruct the following tectonic evolution. The orthogonal faults developed shortly after deposition, during Late Triassic to Early Jurassic times at relatively shallow depth, below 1000 m. Ongoing subsidence created accommodation space for Upper Jurassic to Cenozoic deposits with a maximum burial depth of 2000 m for the Middle Jurassic rocks. Exhumation of the area started around 10 Ma and continued through to Quaternary times. The predicted across-fault-flow values for fault rock permeability show a wide range when using poorly constrained input for fault rock calibration: 9.9E−15 to 9.9E−13 m² for SGR values around 0.08 at reservoir/reservoir juxtaposition. Fault rock calibration using elaborated results reduced the uncertainty of fault rock permeability estimates, and ultimately, for transmissibility multipliers (TMs). The reason for the sensitivity of the fault rock calibration is a combination of following factors: highly permeable reservoir sandstone, shallow depth of initial faulting, maximum burial depth and low shale content at the upper, main reservoir level. The study shows that an accurate reconstruction of the geohistory provides essential parameters for fault rock calibration and fault rock permeability prediction. The range of values can widely scatter if boundary conditions are not acknowledged. Well-constrained fault rock calibration reduces the uncertainty on possible flow scenarios, increases the reliability on production forecasts and helps determine the most efficient drainage strategy.

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<p>The Barents Sea consists of several tectonic elements which were formed at different plate tectonic collisional and rifting stages. This work focuses on the Early Mesozoic to recent events of the central Barents Sea, the eastern edge of the Bjarmaland platform.</p><p>We have analysed the clastic deposits of Mid-Triassic to Upper Jurassic to reconstruct the tectonic history of the Hoop Fault Complex, Barents Sea/Norway. Apatite fission track and (U-Th)/He thermochronology were used to determine the maximum burial depths and exhumation history. According to the combined evaluation of results from shale ductility analysis (BIB-SEM), fault kinematic analysis and structural modelling (section balancing based on a 125 km long 2D seismic section line) the following tectonic evolution can be drawn: deflation of late Palaeozoic salt deposits was initiated by the tectonic activity on the early structures of the Hoop Fault zone. The orthogonal faults of the Hoop Fault Complex developed at the early stage, during Late Triassic to Early Jurassic times at relatively shallow depth, below 1000m. Ongoing subsidence related to the extension caused by the opening of the Atlantic Ocean created accommodation space for Upper Jurassic to Cenozoic deposits with maximum burial depth of 2000 m for the analysed Mid-Jurassic rocks. The exhumation of the Hoop Fault complex started around 10 Ma and remained constant until Quaternary times (140 m/Myr).</p>