| Title | Screening of thermal fractures in geothermal doublets |
|---|---|
| Authors | Loeve, D; Peters, E; Pizzocolo, F; Veldkamp, H; van Wees, J-D; Fokker, P A |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | thermal fractures, (enhanced) geothermal doublets |
| Abstract | In the production well of a low-enthalpy geothermal doublet, hot water is pumped from reservoirs at about 60-90°C. After passing through a heat exchanger, the cold water is re-injected into the hot reservoir at about 30-35 °C Under favourable circumstances, this may lead to the initiation of thermal fractures around the injection well. This effect is known from water injection in oil fields. The fractures increase the injectivity index (II), thereby also increasing the efficiency and profitability of the doublet. In the Netherlands, this effect has not been observed or studied previously in geothermal wells. The objective of this study is to screen whether these fractures will develop, using physical models and observations. First, we developed a simple analytical approach to determine whether thermal fractures are theoretically expected under average Dutch reservoir and injection conditions. The analytical approach is developed into a tool that can be applied to predict thermal fractures under any set of conditions and is easy to handle. The model has been validated with literature. Second, we analysed doublet data at high temporal resolution of multiple geothermal doublets. Both short term and long term injectivity effects were studied to identify the possible development of thermal fractures. The analytical tool predicts that cold fractures are unlikely to develop in the Dutch subsurface given the conditions of most existing geothermal doublets. The studied geothermal doublets production/injection data do not show conclusive evidence for the initiation of thermal fractures and propagation into the reservoir. |