Validation of Reservoir Simulation Study in Mahanagdong Geothermal Field, Leyte, Philippines

Abstract

The Mahanagdong field experienced field wide pressure drawdown four years after the start of the MG-A and B power plants operation in 1997. This resulted to faster rate of returns of injected brine and condensate from its two injection areas as well as the migration of cooler peripheral waters from the western part of the field. As a consequence, most of the affected wells have indicated cooling and decline in nearby Tongonan field in order to augment the steam supply to the two power plants.

Reservoir simulation study was conducted using the TETRAD software to evaluate several scenarios involving injection strategies to address the problem in Mahanagdong. Results of the simulation study indicated that improvement in Mahanagdong steam supply outlook could be achieved through implementation of optimized injection strategy. This include: a) transfer of condensate injection away from the MG-9D (located near MG-B production sector) to MGRD (farther south of MG-A production sector, b) cessation of condensate injection into MG4DA (located infield of MG-A production sector, and: c) utilization of MG-21D (located northwest if MG-B production field) to provide pressure support in the western part of the production field and minimize migration of cooler fluids.

Results of the present reservoir assessment in Mahanagdong showed significant improvement in the output of the wells previously affected by migration of cooler waters and injected fluids. Steam supply decline rate has likewise improved resulting to the better performance of the Mahanagdong field in terms of field generation. This also validated the results of the reservoir simulation study.