Chalk facies and its Petrophysical Expression from Core and Wireline Data, North Sea Basin, The Netherlands (2016)

This MSc thesis has been written by former intern Erwin van Wingerden.

With new hydrocarbon discoveries in the Chalk Group in the North Sea Basin, questions rise regarding the predictability and geological controls of possible reservoir units. This thesis captures all the core and wireline data from the cored Chalk intervals in the Netherlands to date, in order to find the influence of facies on the petrophysical signature. Existing facies model from GEUS has been generalized and combined with other facies core reports and literature, where after the facies of the cores have been reinterpreted. It was found that marly, glauconitic and siliciclastic content have lowering impact on the porosity in comparison to homogeneous chalk. Bioclast content was found to increase porosity. Secondary alteration in the chalk is has a negative impact on the reservoir properties due to diagenetic processes as cementation and recrystallization. Pelagic chalk is most prospective in middle to late Maastrichtian and Danian without intercalations of hemipelagic clay. Detrital clay is found to have relative higher permeabilities than clean chalk. It is furthermore suggested that inversion and salt movement may have enhanced the porosity and permeability of the system. Danian chalk is found to have different  characteristics than Maastrichtian or older chalk, depicted from its deviations from the wireline logs. Sonic depth trends for pelagic chalk, except for chalk with high bioclast content is found to behave in a linear relation with depth.