Diagenetic controls on dryland clastic reservoirs from the Buntsandstein Subgroup in the Netherlands

Abstract

The Buntsandstein subgroup in the southeastern part of the Netherlands represents one of the most promising, but risky, geothermal plays. To understand the main controls on Buntsandstein reservoir quality, we combine petrophysical (porosity and permeability) and petrographic (point counting) data derived from different wells and different depth levels. Results show that porosity ranges from 2 to 18.5 and permeability from 0.001 to 285 mD. Dolomite represents the most abundant cement and show an inverse correlation with porosity. Illite occurs in higher concentrations in samples with values of permeability below 20 mD, while kaolinite becomes the most dominant phyllosilicate cement in samples with higher permeability. By looking at the main cement distribution over the sedimentary facies, it appears that dolomite is strongly related to depositional facies and has a positive correlation with grain size, while illite and kaolinite yield a negative correlation with grain size. Pedogenic dolomite nodules are often reworked as detrital grain into the channel scour deposits and are the main source for dolomite cementation. The current study has shown how diagenesis makes Buntsandstein reservoir complex and heterogeneous, and how reservoir quality is strongly related to the depositional environment.