Fault Rock Property Prediction On Jurassic Clastics Of The Barents Sea/Norway

Abstract

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.