| Abstract |
Monitoring of mass flow and enthalpy of well discharges is an integral element of reservoir and production management. Several methods can be employed to determine these parameters. The chemical tracer dilution method is a recent development in the determination of mass flow and enthalpy of geothermal wells. It has been investigated as an alternative to currently employed conventional devices such as orijce plate and critical lip pressure methods. This study aims to look into mass flow and enthalpy determination of two-phase lines at Br-8, Br-20 and Br-25 wells at the Broadlands-Ohaaki geothermaljeld. Benzoate and bromide ions were utilized as the water phase tracer, and isopropanol as the gas tracer. Results indicated that Br-8 has a water flow of about 17 kg/s and a steam flow of about 4.8 kg/s, resulting in a total massflow of about 21.8 kg+, and an enthalpy of about 1000 kJ/kg. Br-20, on the other hand, has a total massfrow of approximately 41.5 kgh, wherein the water flow is about 32 kg/s and steam flow is 9.5 kg/s. It has a calculated discharge enthalpy of about 990 Wkg. For Br- 25, the steam flow is about 16 kgh, the water flow is 29 kg/s, and the total mass flow is 45 kg/s, with a computed enthalpy of about 1400 kJ/kg. Compared to the output tests, large variations in the mass flows were obtained, ranging from 9-240%. However, acceptable variations of 2.8-6.1% in the enthalpy values were obtained for Br-8 and 20, while a large deviation of 31% was obtained for Br-25. The mass flow deviations may be due to the sensitivity of the method to errors in sampling and analysis (e.g. dosing rate measurement, loss of constituents during sampling/ analyses). The effect on the enthalpy is not very signijcant, except for well Br-25. Also, the output tests and tracer tests were not conducted at the same time frame, hence, accurate comparison of the tracer data with other measured data was not possible. The application of chemical tracers in steam transmission lines was also investigated at Lines B (20ö pipe) and G (48ö pipe) in the Wairakei geothermal jeld. Isopropanol was used for the determination of steam flows, while bromide was used to monitor the scrubbing efficiency at these two lines. The steam flows obtained are 13.3 kg/s and 30.2 kgh, for Line B and G, respectively, Compared to measured flow data, a difserence of <O.I% in the steam flow was obtained for Line B, while a large difference of 58% was obtained for Line G. æThe difference may be due to opening of the vents during testing at Line G, which caused signijcant pressure drop at the pipeline. Hence, the steam flow obtained may indeed have been signijkantly lower at that time. The scrubbing eflciency of 0.794Ydm for Line B and 0.079Ydm for line G, which were previously determined by Bacon and Tracey (1984), were used in simulating the theoretical bromide concentrations obtained from the drain pot discharges. The results showed consistent trends for Line B, however, Line G is difficult to simulate due to the change in the steam line condition. |