The Use of Ahuachapan Fluid Chemistry to Indicate Natural State Conditions and Reservoir Processes during Exploitation

Abstract

Chemical analyses of production fluids from Ahuachapan, El Salvador, have been used to ndicate natural state reservoir fluid temper- atures and chloride concentrations and reservoir processes resulting from exploitation. Geothermometer temperatures (Na-K-Ca and Si021 and calculated aquifer C t for early flows show a gradient from about 265OC and 9000 ppm C1 in the western part of the wellfield to 235'C and 6000 ppm C1 in the eastern part. The geochemical temperatures are 1O-2O0C higher than early downhole measurements. Since exploit a - i o n started, pressures have declined over most of the drilled area with boiling and excess-enthaby discharges in the eastern and western parts. In the center of the field, a number of wells show mixing with cooler, less- saline water. These wells are nearly coincident with a major NE-SW oriented fault that may be the conduit for downward recharge of cooler fluids from an overlying aquifer.