An updated conceptual model of the Los Humeros geothermal reservoir (Mexico)

An analysis of production and reservoir engineering data of 42 wells from the Los Humeros geothermal field (Mexico) allowed obtaining the pressure and temperature profiles for the unperturbed reservoir fluids and developing 1-D and 2-D models for the reservoir. Results showed the existence of at least two reservoirs in the system: a relatively shallow liquid-dominant reservoir located between 1025 and 1600 m above sea level (a.s.l.) the pressure profile of which corresponds to a 300–330°C boiling water column and a deeper low-liquid-saturation reservoir located between 850 and 100 m a.s.l. with temperatures between 300 and 400°C. Both reservoirs seem to be separated by a vitreous tuff lithological unit, but hydraulic connectivity occurs through faults and fractures of the system, allowing deep steam to ascend while condensate flows down (porous heat pipe). The geochemical and isotopic (δ18O, δD) composition of the produced fluids can be explained as the result of a boiling process with reservoir steam separation and partial condensation, a fact that agrees with the proposed reservoir engineering model.