Reservoir Engineering in Geothermal Fields

A geological formation (or formations) which contains water or geothermal fluid and will allow fluid movement.

Data set acquired before exploitation begins, against which any future measurements are compared.

Region of single-phase liquid conditions below a two-phase (liquid and vapor) zone.

Boundary between the two-phase and deep liquid zones.

Term that refers to the thermodynamic cycle used to convert the heat energy from geothermal fluids into electricity, there are several of these technologies. Binary in which the heat of the geothermal fluids is transferred to a low-vaporization-temperature fluid (usually isopentane, ammonia, or a combination of water-ammonia) that is the working fluid driving the turbine generator. The heat source for the binary technology could be the separated geothermal brine or the steam or both exchanging energy in separated exchangers. When the steam is used directly, it can be used in single-flash or double-flash cycles, depending on the number of times the geothermal brine is flashed into steam or a combination of binary and steam technologies in the conversion cycle.

A body of hot water and rock within the Earth.

The formation into which injected fluid is put. Generally, this has high porosity and permeability.

A geothermal system, or part thereof, containing fluid having a temperature greater than 150 °C.

In which the temperature is less than 150 °C. Note, however, that this temperature value is arbitrary and that different authorities adopt different values or divide the range into low, intermediate, and high temperature.

Well drilled to replace production lost from an existing production well due to decreases in fluid temperature or pressure or permeability of the production zone, or drilled to replace reinjection lost from an existing reinjection well because of a decrease of permeability in the injection zone(s) or excessive rise of water level within the well.

In the reservoir engineering terminology, there are two kinds of models: one is called the conceptual model that is an integration of all the physical features of a reservoir such as size, geological structure, geochemical features, temperature and pressure, underground fluid flow patterns, etc., that is estimated through the integration of all available surface and underground geoscientific information. The other kind of model is called the numerical model, and it is the conceptual model itself presented in terms of elements that can be manipulated using numerical tools in order to extrapolate, from known information and following strict physical-mathematical rules, features of the underground that cannot be directly measured, such as volume, recharge and discharge zones, pressure and temperature distribution, energy content, etc., with the objective to mathematically forecast the response of the reservoir when subjected to different exploitation scenarios. Numerical models are constructed in three dimensions (x, y, and z); this is the common denomination of 3D numerical model. These numerical exercises of reservoir modeling will lead to crucial decisions such as to develop or not to develop the geothermal field and if decision to develop is made, then what would be the size of facilities that, in terms of economy, will produce an acceptable return to the country and investors.

A measure of the capacity of a geological rock formation to transmit a fluid.

That region (depth) of the geothermal reservoir from which most of the production of fluid occurs.

Pressure and temperature wellbore surveys could be static (not flowing conditions) or dynamic (flowing conditions). When a spinner tool is added in the dynamic surveys, the activity is called PTS wellbore survey.

The region of a geothermal system from which geothermal fluid is withdrawn or is capable of being withdrawn.

The amount of liquid that remains in the pores (as % of pore volume) and which decreases in pressure will not vaporize. The liquid saturation level below which vaporization of liquid will not occur.

A region where the liquid and vapor (steam) phases of water coexist in pores or fractures.