Drilling and completing Enhanced Geothermal Systems (EGS) / geothermal wells poses unique well construction problems and challenges. These operations have proven to be especially challenging for the wells drilled in the Cooper Basin, South Australia. High temperatures encountered, in combination with the high pressures are a key consideration in the design of the well, for both drilling and stimulation operations.

A well failure in 2009 led to an in-depth investigation into the cause of the failure. Results of the investigation revealed the most probable cause of the failure was caustic stress cracking corrosion as a result of unset cement plus cyclic temperature and pressure loading of the casing string. This discovery had a major affect on the subsequent well design and operational plan for well construction. The learnings that came about from the failure and subsequent investigation were incorporated into the well design and operations of the following well, Habanero 4. A key area of focus in the investigation lay with the cementing of the primary production casing. It was identified that risk of unset cement in the annulus needed to be reduced. To accomplish this, a reverse circulation cement job was planned and executed.

Details of planning the reverse cementing operation, including cement design and placement modelling will be provided. In addition, a comprehensive account of the execution and equipment used to carry out the operation will be given. Job results will be provided along with a detailed analysis of the final outcome. A discussion of the accomplishments will also be included. Recommendations and conclusions for other operators facing similar challenges and/or who are considering a reverse circulation cement job will also be provided. This will include conclusions on what was critical to the success of the job, limitations and potential improvements for fluid modeling programs, and rheological properties and other related drilling fluid properties.

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