EDC Experience in Vapor Tracing

Abstract

Proper management of oil or geothermal reservoirs requires tracing of fluid paths. In geothermal systems, the results of tracing dictate the measures that are put in place to counteract the drastic effect of injection returns, optimize injection well capacities and adopt appropriate production and reinjection well utilization strategies. Energy Development Corporation (EDC) has integrated in its resource management strategy the tracing of fluid flowpaths, especially between reinjection and production sectors. Most EDC production fields are still liquid-dominated, thus water-based tracers have been tested and utilized through the years. Tracers that have been tested in EDC operating steamfields, so far, include naphthalene disulfonate (NDS), sodium fluorescein, sodium benzoate, Iodine-125, and Iodine-131.
Continuous production has transformed some liquid-dominated reservoirs or production sectors into highly two-phase reservoirs, such that liquid-based tracers no longer become relevant. There is then the need to test vapor-phase tracers in producing fields where steam expansion has become very apparent, and where challenges/problems due to injection or cold water incursion occur.
Tritiated water and HCFC have been injected in two EDC production fields, on an experimental basis, and results were evaluated. Tritium breakthroughs have been observed in Leyte production wells from the injector, with tracer recovery and swept-volume calculated. HCFC, on the other hand, injected in Mt. Apo, only manifested a weak signal in the nearby thermal area (gas seepage). Tracer return quantification was not doable given the monitoring data available.