Thermal methods consist of measuring thermal gradient and satellite data, which can be used to determine the Earth's surface temperature and thermal inertia of surficial materials, of thermal infrared radiation emitted at the Earth's surface.
Thermal gradient measuring, with a knowledge of the thermal conductivity provides a measure of heat flow. Conditions that may increase or decrease and heat flow are influenced by hydrologic, topographic factors and anomalous thermal conductivity.
Also, oxidation of sulphide bodies in-place or on waste deposits, if sufficiently rapid, can generate thermal anomalies, which can provide a measure of the amount of metal being released to the environment.
The geothermal gradient on the territory of Romania, the increase of the temperature with the depth, has an average value of 2.5°-3°C/100m, which corresponds to a temperature of 100° C at 3000 m deep. There are many areas where the value of the geothermal gradient differs considerably from this average.
For example, in areas where the rock plate suffered rapid dips and the basin was filled with sediment "very young "from a geological point of view, the geothermal gradient may be less than 1° C/100m. On the other hand, in other geothermal areas the gradient exceeds much this average.
These areas are true underground thermal reservoirs of potentially high geothermal energy which under certain favourable conditions can be exploited to serve heating installations and domestic hot water systems.
The geothermal prospecting for the entire territory of Romania, carried out by temperature measurements allowed the development of geothermal maps, highlighting the temperature distribution at different depths.
Geophysical data obtained through various methods and geophysical modelling provide generalized and non-unique solutions to the geometry of underground geological relations as well as to the physical characteristics of different formations.
The non-uniqueness of these models (solutions to the direct problem) arises from the impossibility of knowing the boundary conditions between different strata, which together with the propagation equations of the different fields (depending on the geophysical method used for the investigation of the basement) form the systems that offer the solutions of the model.
122
The Oradea geothermal reservoir is located in the Triassic limestones and dolomites at depths of 2,200-3,200 m, on an area of about 75 km2 , and it is exploited by 14 wells with a total maximum flow rate of 140 l/s geothermal water with well head temperatures of 70-105°C. There are no dissolved gases, the mineralisation is 0.9-1.2 g/l, the water being of calcium-sulphate-bicarbonate type.
The Oradea Triassic aquifer is hydrodynamically connected to the Felix Spa Cretaceous aquifer, and together are part of the active natural flow of water. The water is about 20,000 years old and the recharge area is in the northern edge of the Padurea Craiului Mountains and the Borod Basin.