| Title | Implications of Temporal Changes in Solute Concentrations for the Mass Balance of the Berlin Geothermal Reservoir |
|---|---|
| Authors | Lopez, Dina L.; Matus, Antonio; Castro, Marlon; Magana, Maria Ines; Sullivan, Michael |
| Year | 2008 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Hydrothermal System; Water Balance; Water Chemistry; Exploitation |
| Abstract | Berlin Geothermal Field is located in eastern El Salvador, Central America. The exploitation of this field started in February 1992 with a 5 MW unit, the addition of a similar unit in 1995, and large scale exploitation in December 1999 with the operation of two turbogenerating condensation units of 28 MW each. In December 2006, a third unit was installed that provides additional 40 MW. Since the beginning of exploitation, all the residual waters generated during the generation of electricity have been reinjected back to the reservoir. Records of the mass extracted and mass reinjected to the different wells, as well as the results of frequent chemical analysis of the extracted and reinjected waters and gases have been kept. The exploited area measures around 4.4 E6 m2. The thickness of the reservoir is around 200 m and the porosity around 0.1 (Castro et al., 2006). The concentrations of the different solutes throughout time were used to generate best fitting equations that describe the average variation of concentration with time. These equations were used to calculate the expected concentration of the solutes at each production or reinjection well each day. Multiplication of the volume of water produced or reinjected times the expected concentration produces the expected mass of solute extracted or reinjected each day. The volume of water within the reservoir seems to have decreased with time, as it is evident from the increase in concentrations of ions in the extracted waters. Only SiO2 and alkalinity show a decreasing trend. Comparison of the net extracted water mass and the decrease in reservoir water predicted by the change in chloride concentration have allowed the calculation of the water mass supplied to the reservoir by the net natural recharge (natural inputs-natural outputs). For the last year of the study period (July 2004 to June 2005) the total net mass extracted from the reservoir is 3.8E9 kg, with 2.4E9 (around 64%) coming from the reservoir storage and 1.4E9 kg coming from natural water recharge to the reservoir. |