Tracer Tests Using Naphthalene Di-Sulfonates in Mindanao Geothermal Production Field, Philippines

Abstract

Complete injection of hot brine from separators has been practiced in Mindanao Geothermal Production Field (MGPF) since 1997. About 200 kg/s of brine is injected into Matingao (MT) re-injection wells and more than 150 kg/s of brine is injected into Kullay (KL) re-injection wells both located at the outflow area of the geothermal system. As early as middle of 1998, significant increase in chloride and other chemical components have been noted in discharge fluids of production wells close to the injection sectors. To establish fluid breakthrough in the production area from the re-injection wells, tracer tests using naphthalene di-sulphonates (NDS) were conducted. Four hundred kilograms of 1,6-NDS and 400 kilograms of 2,6-NDS were injected into wells MT2RD and KL1RD respectively. Well SK2D, the steam producer nearest to MT2RD in terms of bottom hole distance showed significant RI fluid breakthrough. Tracer returns in SK2D are about 20% based on simple one-dimensional flow-channel tracer transport model calculations. Production temperature predicted from cooling model of the well is matched with historical data and showed good conformity.