Manito Lowlands: a Low-Enthalpy Field Under Exploitation in the Philippines

Abstract

The Manito Lowlands is a low-enthalpy field situated at the outflow of the main geothermal reservoir of the Bacon-Manito Geothermal Production Field. Exploitation officially started with the inauguration of the Manito Geothermal Livelihood Project (MGLP) in October 1998, comprising of a 1.5 MWe pilot power plant and a multi-crop drying facility. PNOC-EDC spearheaded the project in response to the governmentÆs program of helping economically marginalized communities, in this case, by providing cheap electricity and crop drying facilities.

Three medium-depth wells were drilled in the early 80Æs which produced low-enthalpy fluids. Highest temperature recorded was 227?C compared to 326?C in the main geothermal upflow area in Palayang-Bayan. Only one well, MO-2 yielded neutral discharge fluids suitable for exploitation. However, the well had to be shut down because of calcite deposition. It was reconsidered recently as a production well and was worked-over to remove the blockage. A new shallow well, MO-4R was drilled as an injection well for the separated brine.

Calcite deposition in MO-2 is the main field management problem and this has been addressed through mechanical work-overs. Well parameters, resistivity data, and temperatures were used to determine the capacity of the low temperature reservoir. Prospects for additional developments of the field are under evaluation.