Precision Gravity Data of the Miravalles Geothermal Field an Ongoing Assessment.

Abstract

For Miravalles geothermal field the geophysical data are abundant. For adding value to the decisions, precision gravity has been obtained since 1985. But it was not but until 1999 that measuring protocol with regular samplings systematically achieve an SD of 12 microgal. The strategy implied the simultaneous use of 4 gravimeters a digital one and 3 analogical, and the stations redistribution guided by the conceptual and reservoir model as main criteria. In the last campaign (2006) a correlation with the enthalpy measured in deep wells under exploitation at the north and injection trends towards the south was shown. The latter, and trends from individual stations, will be verified with a digital gravimeter in the next April of 2010. The purpose of the paper is to confirm a correlation between the steady production decline observed for the northern wells, the expansion of the steam cap, and the microgravity data. A modeling base on well temperature logs, and production head monitoring were also attempted. We are aiming to consider precision gravity as a tool that helps to evaluate the sustainability of the resource.