| Abstract |
Changes in the chemistry of fluids from the production wells in Bacon-Manito geothermal field indicate that pressure drawdown has induced various physical processes. These processes are: 1) local boiling and subsequent reservoir cooling, 2) inflow of cooler fluids from upper feed zones of some wells, 3) mixing of fluids between adjacent wells and 4) migration of gas-depleted, cooler fluids from the Masakrot-Cawayan area towards the Palayang Bayan production sector. The lateral migration of fluids served as a natural recharge that has resulted in a minimal power output decline of 2.7 MWe between 1994 and mid-1996. However, the output and chemistry of most wells have been relatively stable since 1997. Apparently, they have recovered through continuous recharge except for three wells that have been exhibiting gradual decline of mass flows, suggesting formation of blockages. There has been no indication of reinjection fluid return in any of the wells. In the Cawayan production sector, pressure drawdown was accompanied by inflow of SO4-rich acid fluids from shallow depths, which caused deposition of anhydrite blockages in two production wells. In Botong sector, pressure drawdown has resulted in local expansion of the two-phase zone. This process is manifested by increases in discharge enthalpies and non-condensable gas (NCG) levels with declining mass flows in the affected wells. |