TRACER TEST ANALYSIS FOR CHARACTERIZATION OF LAUGALAND GEOTHERMAL FIELD
This paper presents the tracer data analysis obtained from the single-phase, conservative tracer experiments conducted during a two-year reinjection project at Laugaland geothermal field in N. Iceland. Three tracer tests were conducted during the two-year period (1997-1999). The tracers injected were sodium fluorescein in Test 1 and Test 3 and potassium iodide in Test 2. We concentrated on Test 1 only, the reasons for which are explained in the paper. Axelsson et al. (2000; 2001) have conducted a comprehensive analysis of the Laugaland reinjection project tracer test data, including both qualitative and quantitative aspects using multi-flow-channel models. In this study, we focus only on the quantitative analysis of tracer test data using analytical interpretation methods . It has been proved extensively that the first temporal moment analysis leads to an estimation of the tracer swept pore volume in a closed boundary with a balanced injection/production rate scenario. But in this paper, we prove that the first temporal moment does give the swept pore volume, even for open boundaries with an unbalanced rate scenario such as existed at the Laugaland geothermal field. The produced tracer concentration history was used to estimate the interwell reservoir relative flow capacity versus storage capacity (F-C plot). The F-C plot is a simple and powerful semi-quantitative tool to evaluate the conceptual model’s relative flow and storage geometries. The relative flow and storage capacities calculated from the flow channel geometry obtained from multi-flow-channel modeling (Axelsson et al. 2001) for one production well LN-12 agreed well with the continuous F-C plot obtained from the tracer return data. The second temporal moment of tracer production history was used to derive an equivalent dispersion coefficient. The reservoir interwell heterogeneity was characterized using the Lorenz coefficient derived from the F-C plot. The Lorenz coefficient for well pair LJ-08/LN-12 was 0.509, indicating that it is moderately heterogenous. Reservoir information was obtained for interwell LJ-08/LN-12 and, to some extent, LJ-08/TN-04. The tracer data for other wells could not be analyzed, since the streamlines were not constant, and deconvolution techniques need to be developed to do meaningful interpretation. Recommendations for possible future Laugaland reservoir modeling are offered in order to obtain a better description of the reservoir.
Predicting thermal drawdown in geothermal systems using interwell tracer tests
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.%%%%Ferilprofanir gefa goða moguleika til að meta rennsli vokva innan jarðhitakerfa. Aðferðir til að tulka niðurstoður ferilprofa framkvaemdar innan vatnskerfa voru endurskoðuð og raedd. Reiknilikan sem lýsir flutningi ferilefnis innan tvileks (double-porosity) kerfis var þroað. Forritið getur meðhondlað almenn jaðarskilyrði asamt þvi að meta hringrasun ferilefnis og linuleg efnahvorf. Sa moguleiki er fyrir hendi að þroa reiknilikanið frekar svo það geti einnig lýst olinulegum efnaferlum.

Tolulegar aðferðir voru notaðar til að aðlaga reiknilikon að maelingum ferilprofana fra Soda Lake jarðhitasvaeðinu i Nevada i Bandarikjunum, og laghitakerfinu að Laugalandi i Eyjafirði.. Tvilekt reiknilikan sem gerði rað fyrir hringrasun ferilefnis bar best saman við maelingar ferilprofsins i Soda Lake. Einfaldari einviðar lausnir voru naeganlegar til að meta niðurstoður ferilprofana að Laugalandi. Þessar niðurstoður benda til þess að sveimferli eru mikilvaegari i Soda Lake en að Laugalandi. Reiknilikanið var einnig notað til að spa fyrir um kaelingu vegna niðurdaelingar i jarðhitakerfinu að Laugalandi. Hitaspar voru bornar saman við maeldar hitastigsbreytingar að Laugalandi. Spalikon sem gera rað fyrir dreifni (dispersion) innan rennslisrasa stoðust best samanburð við maeld hitastig. Hugsanlegar urbaetur voru raeddar fyrir þaer aðferðir sem stuðst var við i verkefninu.%%%%Landsvirkjun - Orkurannsoknarsjoður
GEOTHERMAL TRAINING IN ICELAND
An international training programme in geothermal energy research and technology has been operated in Iceland under the auspices of the government of Iceland and the U.N. University since 1979. Twenty­ two participants from leading energy agen­ cies in Africa. Asia. and Central America have received six to eight months special­ ized training. and eight scientists and engineers have come for shorter study tours. Specialized training is offered in geological exploration. borehole geology, geophysical exploration. borehole geo­ physics. chemistry of thermal fluids, res­ ervoir engineering, geothermal utiliza­ tion. and drilling technology. A summary is given of the conclusions of an inter­ national committee which reviewed training needs in geothermal energy in developing countries in 1980.