Field Development Strategy in the Exploitation of Mahanagdong Geothermal Resource, Philippines

Abstract

Results of drilling the first six deep exploratory wells in the Mahanagdong area, south of the existing Tongonan-1 geothermal field, revealed the presence of a commercially exploitable geothermal resource with temperatures of 260?-2770C at a depth of 2000-2100 m. Resistivity surveys delineated this separate geothermal system characterized by low resistivity values of 10-30 ohm-m and covering an area of 7.5-14 kmÆ. Volumetric stored heat estimates and numerical simulation of the area indicated a potential resource equivalent to 170 W e.

Full-scale delineation drilling of production and reinjection wells ensued based on an updated conceptual hydrological field model. Innovations on the casing and well design parameters were efSected to achieve drilling targets and maximize steam production. Reinjection pads were sited at the peripheries of the postulated Mahanagdong production sector to provide additional pressure support and prevent rapid reinjection returns to the reservoir. Acidizing jobs were conducted on wells that were mud-damaged during drilling to improved their power outputs.

To date, nineteen production wells and ten reinjection wells have been drilled in the area with a total generating capacity of 209 Mwe. This is suBcient for the start of the commercial operations of the installed 180 Mwe capaciy geothermal power plant by the year 1998.