Repeat Microgravity and Precise: Leveling Response to Production in EDC Geothermal Fields, Philippines

Abstract

Energy Development Corporation (EDC) conducted repeat microgravity and precise leveling surveys from 2016 to 2018 in two of its geothermal fields namely Tongonan and Mahanagdong in Leyte Geothermal Project (LGP) and Palinpinon in Southern Negros Geothermal Projects (SNGP). This is to determine the changes in microgravity and elevation values brought about by more than 10 years of production since the last gravity and elevation surveys. Negative gravity and elevation changes were observed within the production area of each field (i.e. PAL-1 and PAL-2 in SNGP and Mahiao, Tongonan sectors in LGP) while positive gravity and elevation changes were noted in the reinjection areas. However, negative anomalies were also observed to extend even in reinjection areas. This could be attributed to contraction of mass due to inflow of cooler fluids and the sum of regional tectonics in the area. Other observed correlation between the gravity and elevation data with reservoir data included the delineation of the extent of the two phase zone within and beyond the drilled areas of the fields.