| Abstract |
The Bulalo geothermal field has been operational since 1979, and currently has 426 M We of installed capacity. High to moderatetemperature recharge is a key factor in sustaining power generation. Four types of recharge fluid provide support to the Bulalo reservoir: upflo w, marginal recharge (MR), injectate, and meteoric recharge. This study quantifies the amounts of production of each of these fluids in approximately 50 production wells using simple assumptions about end-member fluid composition. Since the dominant trend in time is dilution, a binary mixing model using endmember compositions of upflow and MR were used to calculate proportions of each fluid. Injectate production was calculated by using a similar mixing model when only mixed with upflow. In the case of three fluid components, historical reservoir chloride (CI) well data determined a background reservoir value. This background reservoir CI was then mixed with me awed inje ctate values. Mass balance calculations required historical CI analyses of injected brine. Meteoric recharge production is calculated using the tritium mass balance. The highest recharge rates (MR and injectate) at Bulalo appear to delimit an E-W corridor from the central western edge into the central pottion of the reservok In map view, injectate and MR appear to use the same pathways for recharge. It is likely that injectate travels along deeper and hotter permeability pathways, whereas MR utilizes shallower, more permeable pathways. Injectate is calculated to be -3-8 times smaller in terms of historical importance compared to the mass of marginal recharge produced. These results helped to constrain the Bulalo reservoir numerical model. Location of recharge flowpaths, both in terms of depth and direction were determined. In addition, connections between injectors and producers were identified. Relative proportions of production of injectate, MR and upflow helped determine zones of high permeability. Barriers to flow were identified based on differences in produced injectate and marginal recharge coupled with changes in excess steam. |