Predicting thermal drawdown in geothermal systems using interwell tracer tests

• Main Author: Elvar Karl Bjarkason 1988-
• Other Authors: Háskóli Íslands
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: Jarðeðlisfræði; Reiknilíkön; Ferilprófun; Jarðhitakerfi; Rennsli; Laugaland; Iceland
• Online Access: http://hdl.handle.net/1946/17337

Tracer experiments offer a unique way to characterize flow within geothermal systems. Methods for interpreting tracer tests conducted within hydrological systems were reviewed and discussed. A numerical algorithm, describing tracer transport within a double-porosity system, was developed using a fully implicit, upstream weighted finite volume scheme. The numerical code is capable of handling general boundary conditions, which can include effects of recirculation, and linear tracer reactions. It would be possible to develop the numerical code further to account for non-linear reaction kinetics. Analytical and numerical methods were used to match observed tracer returns at the Soda Lake geothermal field, Nevada, USA, and the Laugaland low-temperature geothermal field, N-Iceland. The double-porosity model including tracer recirculation provided the best fits to the Soda Lake tracer data. Simpler one-dimensional analytical solutions were sufficient to estimate the interwell tracer transport within the Laugaland system. These results indicate that tracer diffusion is an important process at Soda Lake but not within the Laugaland reservoir. The finite volume algorithm was used to predict cooling, resulting from reinjection of spent fluid, at the Laugaland site. The thermal predictions were compared with measured temperature changes at the Laugaland field. Temperature predictions which included flow-channel dispersion appeared to characterize the thermal drawdown best. Potential improvements to the methods used were suggested. Ferilprófanir gefa góða möguleika til að meta rennsli vökva innan jarðhitakerfa. Aðferðir til að túlka niðurstöður ferilprófa framkvæmdar innan vatnskerfa voru endurskoðuð og rædd. Reiknilíkan sem lýsir flutningi ferilefnis innan tvíleks (double-porosity) kerfis var þróað. Forritið getur meðhöndlað almenn jaðarskilyrði ásamt því að meta hringrásun ferilefnis og línuleg efnahvörf. Sá möguleiki er fyrir hendi að þróa reiknilíkanið frekar svo það geti einnig lýst ólínulegum efnaferlum. Tölulegar ...