Reservoir Tracer Testing at San Jacinto-Tizate Geothermal Production Field, Nicaragua
Julio Alberto GUIDOS, Lester Lenin PRADO, Idalia MATUS, Gregory N. USSHER and Ramonchito Cedric M. MALATE
[KDA Consulting Limited, New Zealand]
The San Jacinto-Tizate Geothermal Production Field in Nicaragua has been developed by Polaris Energy Nicaragua S.A. (PENSA) for power production since 2005. A 10 MWe back pressure power plant was initially installed in the field and was decommissioned in 2012 after the full planned development of 72 MWe condensing plant (2 x 36 MWe units) began operation. PENSA implemented reservoir management strategies for the sustainability of the resource through intensive monitoring, one of which is reservoir tracer testing. A series of reservoir tracer tests using naphthalene disulfonate salts (NDS) was conducted by PENSA with the following objectives: 1) quantify the rate and extent of brine injection returns from the northern, infield and southern injection wells to the central production wells, 2) identify fluid flow paths/channels of the returning brine and 3) to predict possible cooling rates of production wells due to injection returns. The tracer tests were conducted after commissioning of the condensing plants in 2011 and completing the production drilling and well remedial operations in January 2014 to improve and sustain the steam availability at San Jacinto. The reservoir tracer test in 2015 was conducted to validate/confirm the positive tracer returns from the southern injection well SJ10-1 based on earlier tests conducted in July 2012 and also to determine the effects of prolonged infield injection at SJ12-1 ST1 which was not evaluated in the earlier tracer test. Positive tracer returns were observed in production wells SJ4-1, SJ6-2 and SJ9-1 from the injection fluids coming from SJ10-1. The tracer return curves were processed and interpreted using simple radial flow tracer model. Modelling of NDS tracer recoveries in the affected wells gave a fraction of returning fluid ranging from 10% to 16%. The return of injection fluids into SJ4-1 has resulted in gradual decline in measured temperature in the well. This thermal decline is modelled by coupling the chloride mass balance model to a fracture flow model. The simple heat advection model satisfactorily represented the thermal decline observed in the well. The reservoir tracer tests implemented in San Jacinto geothermal production field helped understand the hydrological connection of northern and southern injection wells to the main production area together with the impact of limited infield injection. The results of reservoir tracer testing have also provided PENSA the flexibility to optimize injection and balance pressure support against the risk of reservoir cooling.
|        Topic: Injection Technology||Paper Number: 23008|