The Germencik Omerbeyli geothermal field is considered to be one of the most important geothermal fields in Turkey. A numerical modeling study was carried out to simulate the response of the field to different production/injection scenarios. The reservoir performance evaluation was based on the numerical simulation of the reservoir behavior using the simulation code TOUGH2. The numerical simulation model includes a total area of 85.8 km2 and extends from the surface at +330 m msl (mean sea level) to a depth of -4581 m msl. Through a trial and error process, the natural state model was satisfactorily matched with the initial temperature and pressure data measured at the wells. The natural state model was further calibrated using the long term flow test (LTFT) data conducted in 2006, including OB-6 and OB-9 as flowing wells and OB-8 as an injection well. The model was then used to predict reservoir performance under different production/injection scenarios over the next 30 years. Forecast runs showed that the pressure declines almost equally in all areas, consistent with the high permeability and connectivity of the reservoir, which had been established from the LTFT.

The aim of this study is to construct a numerical reservoir model for Bal&ccedil / ova geothermal field, which is located in the izmir bay area of the Aegean coast. A commercial numerical simulation program, TOUGH2 was utilized with a graphical interface, PETRASIM to model the Bal&ccedil / ova geothermal field. Natural state modeling of the field was carried out based on the conceptual model of the field, then history matching of production &ndash / injection practices of the field was established for the period of 1996 &ndash / 2008. The final stage of modeling was the future performance prediction of the field by using three different Scenarios. In Scenario-1, production and injection rates in year 2008 were repeated for 20 years. In Scenario-2, production and injection rates in year 2008 were repeated for the first 3 years, then they were increased at every 3 years. In Scenario-3, a new well (BT-1) that is assumed to be drilled to 1000 m depth is added for injecting some portion of water that was injected through BD-8 well. In that scenario, similar to Scenario-2, production and injection rates in year 2008 were repeated during the first 3 years, and then the rates of these wells (except the new well) were increased every three years. Analysis of the results indicated that in Scenario-2, compared to Scenario-1, both the temperatures of deep wells located at the eastern portion of the field (BD-6, BD-2, BD-14, BD-9, BD-11, BD-12) and the temperatures of deep wells located at the western portion (BD-4, BD-15, BD-7, BD-5) decreased more. In Scenario-3, compared to Scenario-1, the deep wells located at the eastern side experienced less temperature drops while the deep wells located at the western side experienced higher temperature drops. Such temperature differences were not encountered in shallow wells. No significant changes in bottom hole pressures of deep wells occurred in all three scenarios. On the other hand, shallow wells, especially B-10 and B-5, responded to Scenario-2 and Scenario-3 as decrease in bottom hole pressures.

Hydrothermal systems change in response to volcanic activity, and in turn may be sensitive indicators of volcanic activity. Fumaroles are a surface manifestation of this interaction. We use time series of soil temperature data and numerical models of the hydrothermal system to investigate volcanic, hydrologic and geologic controls on this diffuse degassing. Soil temperatures were measured in a low-temperature fumarole field located 3.5 km from the summit of Masaya volcano, Nicaragua. They respond rapidly, on a time scale of minutes, to changes in volcanic activity also manifested at the summit vent. The soil temperature response is repetitive and complex, and is characterized by a broad frequency signal allowing it to be distinguished from meteorologic trends. Geophysical data reveal subsurface faults that affect the transport of fumarole gases. Numerical modeling shows that these relatively impermeable faults enhance flow through the footwall. On a larger scale, modeling suggests that uniform injection of fluid at depth causes groundwater convection in a permeable 3-4 km radial fracture zone transecting the entire flank of the volcano. This focuses heat and fluid flux and can explain the three distinct fumarole zones located along the fracture. We hypothesize that the rapid response of fumarole temperature to volcanic activity is due to increased flow of gas through the vadose zone, possibly caused by changes in the subsurface pressure distribution. Numerical models show that an abrupt injection of hot gas, at approximately 100 times background rates, can cause the rapid increase in temperature observed at the fumaroles during volcanic activity. A decrease in hot fluid injection rate can explain the gradual decrease in temperature afterwards. Mixing with surrounding vadose-zone fluids can result in the consistent and abrupt decreases in temperature to background level following hot gas injection. Fumaroles result from complex interaction of the volcanic-hydrologic-geologic systems, and can therefore provide insight into these systems. Increases in fumarole temperature correspond to increased gas flux related to changes in volcanic activity, suggesting that monitoring of distal fumaroles has potential as a volcano monitoring tool, and that fumarole temperatures can provide insight into the response of shallow gas systems to volcanic activity.