| Title | An Evaluation of the Impact of MatRidge Injection to Matalibong Production, Tiwi Geothermal Field, Philippines |
|---|---|
| Authors | Aimee CALIBUGAN, Larry VILLASEÑOR, Anthony MENZIES, Mitchel STARK |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | breakthrough, tracer, microgravity, geochemistry, downhole monitoring, capillary tubing, liquid level, economics |
| Abstract | The Matalibong production sector of the Tiwi Geothermal Field is currently contributing ~35% of the total steam flow to the Tiwi power plants. The MatRidge Hot Brine Injection System (MatRidge) wells are located north of the Matalibong area near the northeastern edge of the geothermal reservoir. Initially, the injection rate at MatRidge was ~60 kg/s but starting in 2004, the injection rate increased significantly due to operational changes and decreasing enthalpy of produced fluids. By 2006, the total injection at MatRidge had quadrupled compared with the initial injection rate. Geochemistry, geophysics, downhole pressure, tracer and production data all indicate that MatRidge injection has had a negative impact on Matalibong production. From 2004-2010, it was estimated that approximately 60 kg/s of steam production was lost due to the rising liquid level within the reservoir that could be directly attributed to high brine injection rates in the MatRidge injectors. Continued high injection at MatRidge is expected to result in additional liquid level rise and further loss of steam production in the Matalibong area. To test this prediction, injection into the MatRidge injectors was significantly reduced from March to July 2010 by temporarily diverting some of the brine eastward to injection wells in the North Naglagbong area. Continuous downhole pressure monitoring showed that the diversion of brine quickly resulted in the stabilization and possible slight reduction of deep reservoir liquid pressures in the vicinity. These changes, which quickly reversed after the diversion was terminated, provided evidence that reduction of injection in MatRidge can have a favorable result on production in the area. To permanently mitigate the detrimental impact of MatRidge injection, a pipeline was constructed in 2012 to allow diversion of brine away from MatRidge to the South East Hot Brine Injection System (SEHBIS), an injection area in southeast Tiwi. With this diversion in place, it is expected that deep reservoir pressures and liquid levels in the Matalibong area will stabilize or even recede toward the 2006 values. Partial brine diversion from MatRidge to SEHBIS has been implemented on a continuous basis starting in July 2013 but the amount diverted has not yet been sufficient to cause any appreciable reduction in the deep pressures and more diversion is necessary. The impact on Matalibong production is also not yet clear. Modeling of the downhole pressure response indicates that injection would need to be reduced by more than 50% to cause deep pressures to decline appreciably. |