MINERALOGY BASED GEOMECHANICAL BEHAVIOR OF DRAUPNE CAPROCK SHALES IN THE NORTHERN NORTH SEA, OFFSHORE NORWAY

The geomechanical behavior of shale caprock demonstrates the seal effectiveness, which is an essential part of any reservoir-seal system and equally important in both CO₂ injection and hydrocarbon explorations. Mineralogical compositions have a direct impact on the mechanical behavior of caprock though the whole process is very complex and depends on many other factors. In this study, we evaluate the caprock geomechanical properties of organic-rich Draupne Formation shale using core and cutting samples from six exploration wells (32/2-1, 32/4-1, 35/11-4, 15/3-8, 15/12-21 & 34/4-3) in the northern North Sea, offshore Norway. Bulk mineral fractions are estimated using XRD, SEM and thin section analyses to calculate mineralogy based brittleness indices (MBI) using empirical equations. For comparison, an elastic property-based BI also estimated. Results show that the strong and soft mineral fractions varied significantly within the Draupne Formation which leading to different brittleness values within the studied wells. Moreover, significantly different brittleness values observed when compared to MBI and EBI. The well (15/3-8) penetrated the Draupne Formation at higher depth has comparatively low brittleness values due to maturation and generated hydrocarbon from the formation. Brittleness indices can be very useful but have to use carefully because of many other factors contribute combinedly.