The Permian Rotliegend Reservoir Architecture of the Dutch Koekoekspolder Geothermal Doublet

Abstract

The Dutch Koekoekspolder geothermal doublet was drilled in 2011. It targets the Permian Rotliegend reservoir. The reservoir properties encountered were less favorable than expected pre-drill. Post-drill integrated evaluation of vintage data and the new data from the geothermal wells resulted in a refined depositional model of the area. The Rotliegend sediments comprise predominantly horizontally, bimodally laminated fine to coarse grained red sandstones. These sediments were deposited on an aeolian sandflat. Gypscretes were formed on this sandflat in the relative low-lying areas, which coincide with palaeo-lows of the pre-Permian palaeotopgraphy. These gypscretes were periodically exhumed and (partly) eroded providing gypsum grains. These were subsequently incorporated in the predominant quartz rich sand sediments on the sandflat forming typical bimodally laminated Aeolian deposits. The gypscretes are now present as pervasively anhydrite cemented horizons haphazardly vertically distributed. The improved understanding of the formation and occurrence of the gypscretes, in combination with advanced seismic attribute analysis can help in the identification of low-permeability zones that may impede the performance of future doublets.