APPLICATION OF COILED TUBING FOR LIVE WELL WORKOVERS

Abstract

Production wells in many Geothermal fields are susceptible to calcite scaling. Depending on the reservoir chemistry this scale can completely block the wellbore over periods ranging from a few weeks to years. Scale buildup can typically be controlled by the downhole injection of inhibitors that prevent formation of scale in the wellbore. In some cases the use of inhibitor systems is not practicable and scale deposits must be mechanically removed by using a workover rig to mill out blockages.
Traditional rig workover operations require a well to be shut for several weeks with a consequent loss of steam production and power generation where there is insufficient contingency production capacity. A workover will normally require the well to be quenched, which over time will subject the well casing to additional stresses and potential damage due to repeated cooling and heating cycles.
Contact has recently carried out several Live Well Workovers, (LWW), using Coiled Tubing (CT) supplied by Western Energy Services, (WES) as part of a programme to assess alterative workover technologies with the aim of minimising production downtime, reducing cost and reducing the potential for casing damage. Initial results indicate that although coiled tubing well cleanouts may not be quite as effective as those performed with a workover rig, the overall economics strongly favour the live workover option using coiled tubing. Many lessons have been learned in the initial operations and continuous improvements of the downhole tools and optimisation of the live well workover process will continue with every project.