Advanced Cement Systems Used to Improve Geothermal Well Reliability in Java

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Abstract An operator developing a geothermal field to generate and provide electricity in Indonesia focused on minimizing the potential for failure of planned wells throughout the expected field life. One of the main areas where this effort was directed was in the design and execution of primary cementing jobs during well construction. Wells drilled and completed earlier, in Phase I, were found to suffer from various wellbore integrity issues. Inspection log data and cement job records from existing wells suggest the zonal isolation problems experienced on earlier wells may have been related to (1) structural failure of the conventional cement sheaths used and/or (2) ineffective cement slurry placement caused by poor hole cleaning of the drilling fluid and/or (3) ineffective removal of drill cuttings from the well during the hole cleaning. Structural damage to the cement sheath can sometimes be in the form of debonding at the casing, formation interfaces, cement sheath cracking, and/or compressive shear. The damage can be caused by stresses on the cement sheath brought on by well events such as cement hydration, well completion, and steam production. These events change the temperature and pressure under which the cement slurry is placed and cured. If these changes are severe, the cement sheath may be damaged, leading to zonal isolation failure. After detailed analysis, and by using an integrated design approach to effectively address the challenges identified, it was decided to use innovative elastic cement systems incorporating various mechanical property enhancement additives expected to withstand the predicted well operations with less possibility of failure than conventional cements. These advanced cement systems were placed in the planned development using conventional cementing equipment. Industry-recognized best practices were also used to maximize mud displacement and enhance hole cleaning. These wells were steamed, and no wellbore integrity issues have been reported. Additional benefits observed while using the advanced cement systems in these applications include a reduction in lost circulation and significantly reduced wellhead growth.