Since the start of large-scale exploitation of the Mindanao Geothermal Production Field in 1997, changes in temperature and chloride concentration in some production wells are observed. Well SK-2D is one of the wells that have exhibited a remarkable increase in chloride and a noticeable decline in temperature. The cause was assumed to be the invasion of injectate fluids from the injection wells.

Reservoir chloride changes in SK-2D were modeled by using a time-dependent production-injection lumped-parameter model. By matching the calculated chloride values with the observed values the fraction of injectate returning in well SK-2D is obtained. The total mass in place in SK-2D production sector is approximately 15.8x109 kg. The rapid increase of injectate fraction returning to SK-2D in the early months of exploitation clearly indicates good connection between SK-2D and injection wells MT-1RD and MT-2RD.

The fraction of injectate returning to the production sector varies depending on the injection load of Pad RA wells. The returning injectate peak to 70-75% from April 1998 to March 2000 when injection load was increased from 200 kg/s to 350 kg/s. In the succeeding months the injectate fraction declined to around 45-50% equivalent to around 145 kg/s of injectate returning to the production sector. Around 35% of the fluids produced by well SK-2D are injection returns.

The decline in reservoir temperature based on quartz geothermometer is then modeled by coupling the lumped parameter model to a one-dimensional fracture flow model. The final model that reasonably matches the thermal decline suggests a fractured zone and production zone porosity of 8-10%.

Press the Back button in your browser, or search again.

Copyright 2001, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.