Scale Management in Mature Gas Field: Case Study of Peciko

Peciko is one of the giant gas fields located in the Mahakam area, Indonesia, operated by Total E&P Indonesie. Since start up in December 1999, until May 2012, the average wellhead pressure and temperature of its wells have decreased from 150 barg to 20 barg and from 95 °C to 60 °C, respectively, while the average water/gas ratio (WGR) has increased from approximately 2.5 to 20.5 bbl/MMscf. These dramatic shifts of production parameter and borehole environment are believed to be the main factor of the increasing rate of scale deposition in significant number of its wells in the last few years. The nature of the scale encountered is mainly calcium carbonate and iron carbonate. Reviews have been carried to better understand the phenomena of scale formation in the field and to formulate the optimum solutions in overcoming it. Guidelines have been established to facilitate early detection or prediction of scaling, which includes routine water analysis, periodic check of tubing clearance, and running multifinger caliper in the well. Numerous attempts of removing the scale have been tried, with mechanical and/or chemical techniques, from light intervention using slick line unit, until semi-heavy intervention with coiled tubing unit (CTU). Several successful results have been observed, to some extent. Calcium carbonate scale showed to be relatively easy to remove, but the presence of iron carbonate imposes more challenge and complication. The milling operation, in particular, has been improved to minimize the negative effect of liquid circulation in sensitive wells, i.e. evolving from CTU milling using brine, to CTU milling using nitrified base oil, to electric line milling without liquid circulation. The guidelines, lessons learned, and the foreseen solutions are considered as the key elements of scale management in the field, and will be described further in the paper.