The Enigma of Silical Scaling in Dry Production Wells of Tongonana

Abstract

Silica scaling is believed to be affecting the output of the production wells in Tongonan geothermal field. Ihis theory came into being after a number of "dry" or steam-dominated production wells showed progressive decline in output. Mineral scaling, e.g. calcite and anhydrite, in Tongonan and in the neighboring Mahanagdong geothermal field had always been obserued in 'wet" production wells or in injection wells.

Reservoir processes like cold water inflow, injection returns and pressure drawdown as well as mechanical failure in well casrngs, which impact the performance of production wells, had been ruled out as the causes based on historical trends of gas chemistry, gas geothermomefers and flow measurement data. Furthermore, it appears that there are two possib/e means by which silica is deposrfed: (a) s/rba-sa turated injection returns become increasingly concentrated due to continuous flashing as rT migrates fo the dry steam zone of the reseruoir and (b) globules of rese ruoir brine are carried by the sfeam and then flashed at the wellbore.