In a previous ENGINE workshop we discussed the seismic hazard/risk aspects of the 
Berlín, El Salvador HDR project. In this presentation the seismological and 
hydraulic aspects will be summarised. The project, a joint venture with the 
Salvadorean geothermal operator, GeSal, set out to extend the Berlín hydrothermal 
field by means of a Hot Dry Rock stimulation of a low injectivity well, TR8A, 
located outside the currently productive zone. The HDR approach was based on the 
expectation that experiences in the Soultz granites could be carried over and 
applied in the layered lavas and tuffs of the Berlín field on the flanks of the 
Cerro Tecapa volcano. A seismic monitoring array, comprising 12 stations deployed in 
6 boreholes ranging in depths from 50m to 550m below surface, was set up to monitor 
the injection operations which took place in three periods between mid 2003 and 
early 2004. Sustained injection of waste water from the Berlín power plant at rates 
of 35-140 litres/s into two distinct intervals in the well resulted in surprisingly 
low levels of microseismic activity. Analysis of the hydraulic data and a 
quantitative comparison with the summer of 2000 data set from Soultz suggest that 
the injection resulted in cleaning of the near-wellbore region and/or the 
propagation of hydrofractures rather than large-scale shearing along pre-existing 
planes of weakness. The injection operations resulted nevertheless in a greatly 
increased well injectivity but, with the limited subsurface image provided by the 
sparse microseismic catalogue, it was difficult to confidently build a case for a 
circulation trial between TR8A and one of the other nearby wells in the field. 
Practical details of the monitoring array deployment and the learnings based on 
these experiences conclude the presentation.

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