Calcite Inhibition System (CIS): The MGPF Experience

Abstract

There are four production wells in Mindanao Geothermal Production Field (MGPF) that are affected by calcite deposition, namely, APO-1D, APO-3D, SP-4D, and MD-1D. Calcite Inhibition Systems (CIS) were set up in APO-1D in May 2000 and in MD-1D in December 2002 to address recurring output decline due to calcite scaling. To evaluate the performance of the Calcite Inhibition Systems, comparison of the dosage program during changes of feed inhibitor concentration and monitoring of feed parameters, bore output and well chemistry were undertaken.

Well APO-1D was found to be underdosed by í?1.3 ppm starting July 2003. Water flow showed a decline of 8.4 kg/s in ~4 years, and steam flow by 5.51 kg/s or an equivalent of ~2.7 MWe loss. The CIS of well MD-1D is satisfactory in terms of its feeding parameters and dosing program, but a decline in output by 2.9 kg/s of steam or 1.4 MWe during April to July 2004 still occurred. Well parameters such as Ca, HCO3, CO2TD, pH and Tquartz showed changes reflective of calcite deposition beginning in year 2004.

Well outputs were sustained in both wells after the installation of CIS. APO1D has sustained discharge for nearly five years until injection failure occurred in December 2004. Interrelated factors contributed to the injection failure, ranging from chemical inhibitor limitation, injection equipment limitation and power outages. On the other hand, MD1D has sustained discharge for more than two years since the CIS was installed.