| Authors |
Iglesias, Eduardo R.; Armenta, Magaly Flores; Leon, Jose Luis Quijano; Rodriguez, Marco A. Torres; Torres, Rodolfo J.; Picasso, Neftali Reyes; Montes, Miguel Ramirez; Medina, Fernando Sandoval |
| Abstract |
Comisión Federal de Electricidad (CFE), the owner and operator of the Los Azufres geothermal field, injects separated water in several areas of the reservoir to recharge it, maintain its pressure and preserve the local natural environment. In mid 2006 it was decided to explore the possibility to inject separated water in a new zone, the Maritaro – Laguna Verde area of the field. In order to assess the likely consequences of this injection, and to prevent thermal interference with neighboring producing wells, we designed and implemented a tracer study in this area. The existing well Az-64, a former producer, was targeted as the injector for this study. Six production wells, namely Az-5, Az-13, Az-32, Az-43, Az-48 and Az-51, were selected for monitoring tracer returns. Three of these wells produce only steam, the rest produce steam and small amounts of water. For this and for economic reasons, we decided to use only a steam-phase tracer. Based on our successful previous experience in this field, we selected sulfur hexafluoride (SF6), a non-toxic, non-flammable, non-corrosive gas with solubility in water similar to that of nitrogen. On 24 October 2006 we injected 96.4 kg of this tracer in well Az-64. Sampling of the designated producers was initiated about four hours after completing the tracer injection. The tracer was detected in the six producers, with widely variable recovery percentages. The highest tracer recoveries occurred in wells Az-05 and Az-43. We concluded that the six monitored producers are recharged, in widely differing proportions, by brines injected in Az-64. The fast and very high recovery at well Az-5 indicates that sustained injection in Az-64 would likely result in significant thermal interference. With the possible exception of Az-43, our results indicate that the rest of the monitored wells are not at risk of thermal interference by injection in Az-64. Our results revealed that the hydraulic connections between Az-64 and the monitored producer wells are probably associated with specific faults in the area. The details of these connections are discussed below. |