| Abstract |
Calcite deposition in geothermal well is commonly expressed as: Ca++ + 2HCO3- = CaCO3(s) + H2CO3 (or dissolved CO2) For calcite supersaturated reservoir fluids, at constant reservoir and boiling temperatures, deposition was triggered by boiling through release of dissolved CO2. This paper evaluated this equilibrium based from the gas and water samples collected in one of the calciting well, PT2D, in Northern Negros Geothermal Project. This type of study is possible because water and gas data are available as the wellÆs massflow and wellhead pressure declined caused by calcite deposition. Through the series of time-plots of chemical speciesÆ activities related to calcite, and comparison of GibbÆs Free energy from each postulated equilibria, calcite deposition was likely through dissociation of CaHCO3+: Figure CaHCO3+ = CaCO3(s) + H+ commonly deposition, wells. gas Negros is reservoirÆs are other calcite In this reaction, deposition of supersaturated reservoir fluids in the wellbore was possible because there was an increase in reservoir temperature during discharge, as manifested by increase in quartz geothermometer (Tqtz) with time. It is not clear if mixing of the supersaturated fluids and the hotter up-flowing fluids or heating of the reservoir fluids in the wellbore caused calcite deposits found in the bore. |