Dissolved methane in sedimentary brines; potential effects on the PVT properties of fluid inclusions. Economic Geology,

There is a strong correlation between d18O of blocky
kaolin and depth for kaolin samples from two wells
from the Cormorant Field, with a 2‰ offset corresponding
to the Mid-Ness Shale. The correlation is
interpreted as due to kaolin recrystallisation during
hydrocarbon filling from 45 to 70 8C, at which time
modelling of a kitchen area in an adjacent depo-centre
shows potential source rocks to be at peak maturity.
The Mid-Ness Shale sub-divided the reservoir. Filling
ended approximately 60 Ma ago, which is coincident
with the single K–Ar age of an illite sample from the
water-leg of the field. The (lowermost) oil–water
contact at this time is proposed to have been
significantly lower in the stratigraphy than the
present-day equivalent, as shown by minute oil-bearing
inclusions and oil-stained clay within the present-day
water-leg. The reservoir was within the zone of active
meteoric water recharge, and bitumen was formed by
water washing or biodegradation