Comprehensive reservoir quality assessment of Buntsandstein sandstone reservoirs in the West Netherlands Basin for geothermal applications in Zuid Holland province area

Abstract

This report presents the results of a study on the reservoir quality of Main Buntsandstein formations in regard with possible geothermal energy development and exploration in the Zuid Holland area of the West Netherlands Basin. The assessment of the possibility of using the Triassic Buntsandstein sandstone reservoirs for geothermal application is carried out in a similar way of basin exploration for hydrocarbons with major focus on reservoir quality. Geothermal energy is becoming increasingly important as an alternative source of energy and heat for the Dutch agriculture and urban areas. In order to determine the possibilities for geothermal exploration in the target area the reservoir properties have to carefully studied and assessed. This is done with respect of the original depositional environment of the sediments, the burial history of the basin and the related diagenetic history. The results are summarized in reservoir geologic models and evaluated. The study on the depositional environment of the Main Buntsandstein formations is the most extensive for the project and covers basin wide well correlations, petrophysical and sedimentological evaluation and interpretation of the encountered facies, and introduction of sequence stratigraphic model for interpretation of the formations. The results of the study include new insights on the formation boundaries and lateral continuity. Each formation member is described separately and examples are provided to support the suggested interpretations. The burial history study is carried out on three two dimensional seismic surveys in-lines in the offshore and onshore part of the target area. The work is performed using specialized software and the result indicate that specific parts of the basin have experienced significantly stronger effect from the different stages of the tectonic development of the West Netherlands Basin. The major conclusion of the study is that although the Triassic sediments have not been exposed to burial depths of more than 700 meters of their current depth, individual fault blocks have experienced very varied burial histories and have therefore different diagenetic footprint. The results of the previous studies are used to evaluate and explain the available information for the diagenetic history of the sediments in the target area. The results indicate that significant differences are to be expected between adjacent fault blocks in regard with the late diagenetic processes such as quartz dissolution and precipitation. The acquired knowledge for the reservoir properties in the target areas in the basin is summarized in extensive reservoir models and grids. The resulting grids represent the observed spatial variations in reservoir quality and also the changes in reservoir thickness across major faults. The resulting grids have also suggested well planning and evaluated for the expected temperatures using available well temperature data. The time of thermal breakthrough is calculated using a theoretical approach and suggestions are made for further dynamic simulations of the already created reservoir simulation models. The project is then evaluated in terms of financial planning and expected costs. A suggestion is made and explained for the improved project feasibility and rate of return for co-production of gas and condensates with the hot water. The report is summarized with an overall evaluation of the project feasibility in terms of reservoir quality and known uncertainties. The final conclusion of the report can be described as conservatively positive as additional studies are required and recommended in order to reduce the still remaining uncertainty.