Modeling scaling of silica from reinjection waters at well head conditions in the berlin geothermal field, el salvador, central America

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Conference Proceedings: Modeling scaling of silica from reinjection waters at well head conditions in the berlin geothermal field, el salvador, central America

Abstract

Generation of electricity at the Berlin Geothermal Field (Eastern El Salvador) started in February 1992. All the residual waters (~ 350 kg/s) produced during the conversion of thermal to electrical energy have been reinjected to the same field. Reinjection was the only feasible option for this field. However, silica scaling problems in the reinjection wells decrease the capacity of these wells to absorb water. The temperature of the reinjected waters is 175 oC and the reservoir temperature at the reinjection wells ranges from 280 ºC to 200 ºC. The mineral that presents a higher saturation index and it is more likely to precipitate at the pressure and temperature conditions of the water transport pipes and wellhead is amorphous silica. However, high precipitation of amorphous silica is not happening in the water transport system and the waters are reinjected supersaturated. Modeling of cooling of the hot reservoir waters in equilibrium with quartz and mixing with reinjection waters was done using the programs SOLVEQ and CHILLER. The modeling results show that the mass of quartz precipitated within the reservoir per unit mass of reinjected water strongly depends on the initial silica concentration of the reinjected water. The temperature and mixing fraction of the reservoir does not seem to have a deep effect if the reservoir is at a higher temperature. Most of the silica precipitated is coming from the reinjected water with only a minor fraction coming from the temperature reequilibration of the reservoir. However, a slightly higher mass fraction of silica is precipitated when the temperature difference between reinjected and reservoir water is greater. Considering the flow rate of reinjected water at well TR-1A, the volume of quartz precipitated per kg of reinjected water, a 10% porosity, and a thickness of the reservoir of 200 m, the volume of pores clogged per year was found as well as the percentage of clogged reservoir volume assuming different radius for the deposition of quartz around the well. A radius between 5 and 15 m for the precipitation of quartz could explain the decline in absorption capacity. Higher radius would give only a few percent change in porosity that cannot explain the change in absorption capacity. As the clogging of the pores seems to happen close to the wells, hydraulic effects are proposed to explain the abrupt response of nearby wells when reinjection starts in a

new well.

Authors 
Marlon R. Castro, Dina L. Lopez, Jaime A. Reyes-Lopez, Francisco E. Montalvo, Raul Romero, Jorge Ramirez-Hernandez and Octavio Lazaro-Mancilla






Conference 
, 31st Workshop On Geothermal Reservoir Engineering; Stanford University; 2006/01/30


Published 
Stanford University, 2006





DOI 
Not Provided
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Citation

Marlon R. Castro, Dina L. Lopez, Jaime A. Reyes-Lopez, Francisco E. Montalvo, Raul Romero, Jorge Ramirez-Hernandez, Octavio Lazaro-Mancilla. 2006. Modeling scaling of silica from reinjection waters at well head conditions in the berlin geothermal field, el salvador, central America. Proceedings of , 31st Workshop On Geothermal Reservoir Engineering; Stanford, California: Stanford University.