Influence of Fluvial Sandstone Architecture on Geothermal Energy Production

Abstract

Fluvial sandstone reservoirs composed of stacked meander belts are considered as potential geothermal resources in the Netherlands. Net-to-gross, orientation and stacking pattern of the channel belts is of major importance for the connectivity between the injection and production well in such reservoirs. Understanding the influence of the fluvial sandstone architecture on the heat recovery is necessary for designing geothermal doublet projects in fluvial reservoirs. A detailed outcrop study of the Huesca fluvial fan is used as an analogue for fluvial reservoir architecture. The study shows meandering fluvial sandstone bodies, laterally amalgamated and vertically stacked within the meander belts. Meander belts in the outcrop have a width of 1 to 1.5 km and are up to 4 km long. Sandstone bodies are surrounded by impermeable floodplain deposits and poorly permeable crevasse splay sandstones (Donselaar & Overeem, 2008). The floodplain deposits decrease the net-to-gross and connectivity in the meander belt. In order to identify the most influential geological features controlling the flow and heat transfer in geothermal aquifers, several reservoir models of fluvial sandstones are constructed with increasing geological detail. These models are based on the results of geological fieldwork on the Huesca fluvial fan in Miocene, Ebro Basin, Spain. Several models with different geometry of the fluvial sandstone bodies, orientation of the channel belts and stacking patterns of the channel bodies are considered. A finite-element approach is utilized to study the geothermal energy production. The effects of different levels of architectural complexity on the geothermal energy production, by conducting several accurate numerical simulations, are discussed. The results show that utilizing simplified reservoir models can lead to a significant error in predictability of the heat recovery from deep fluvial sandstone formations.