| Abstract |
As one main component of geothermal production operation, well integrity is an important issue to be taken care of. Parts of it are casing integrity and casing head integrity. Both are supposed to be closely monitored through routine inspection since there is no method to calculate lifetime of a wellbore. What we can do is make prediction based on monitoring data. Casing integrity is under constant threat from its completion process, completion fluid, formation fluid, formation pressure and temperature, and surface soil movement (i.e. land slide). All of those affect condition of the casing. Examples of methods applied to monitor casing condition are ring gauge and caliper log. These surveys give us qualitative and quantitative data on changing casing condition. In the upper part of casing, casing head is not only under constant threats from same hazards that are harmful to casing integrity, but also taking external hit from corrosion due to its contact with air and humidity. DRJ-3 case was a great example of how casing head integrity was weakened and finally damaged by erosion from inside and corrosion from outside. Even when casing head thickness was measured regularly, DRJ-3 casing head failure occurred several months earlier than prediction – where prediction was made based only on DRJ-3 casing head thickness data. DRJ-3 was one of Darajat injection wells, which active as injector since November 16, 1994. Injection wells have important role in injection management, where every geothermal producer has to comply with Government of Indonesia regulation concerning Environment Management and Protection (UU Nomor 32 tahun 2009 tentang Perlindungan dan Pengelolaan Lingkungan Hidup), where anything produced from earth should be injected back into earth instead of dumped to surface. As to comply with that need, DRJ-3 should be plugged and abandoned because casing head leak was observed on this well since November 2011. Initially, DRJ-3 casing head failure was predicted to occur on June 2012. Immediate action to prevent condensate spill from DRJ-3 had been done by performing casing head repair by installing casing collar - which was installed surrounding the leaking casing head section. The well was successfully and safely plugged and abandoned on May 9, 2012. Based on experience of DRJ-3 casing head failure where it occurred 8 months earlier, it indicates that there was something missing/inaccurate concerning failure prediction based on casing head thickness data. Applying more appropriate/thorough calculation method, it is expected that casing head failure prediction could be more precise to avoid environment damage and unplanned well plug and abandonment. |