Analysis of unusual scale build‐up in a CO 2 injection well for a pilot‐scale CO 2 storage demonstration project

An unusual scale build‐up was identified with a series of analytical methods in a CO 2 injection well that was part of a pilot‐scale carbon capture and storage system at an active coal‐fired power plant in West Virginia, USA. After over a year of operation, a decrease in injection performance was seen in wellhead pressure and flow‐rate monitoring. A blockage in the injection tubing was considered the most likely problem, and samples of the scale material were collected during well maintenance activities. The scale material was analyzed with inductively coupled plasma mass spectrometry (ICP‐MS), X‐ray diffraction, and scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) for identification of principal elemental species. The primary phase identified in sample was antarcticite (CaCl 2 ·6H 2 O) with lesser amounts of calcium chloride hydrate and halite. Review of the injection system components indicated that the calcium chloride based annular fluid in the well most likely contributed to the antarcticite precipitation. The evaporite minerals identified in the well suggest that a highly saline water mixture had been exposed to very dry, desiccating conditions related to CO 2 injection, which may be present during well workovers and interruptions in injection. The scale build‐up was addressed by running a gauge ring to physically remove the material and flushing the well with a light brine solution, which is not unusual for injection well operations. Scale build‐up should be considered for operations and monitoring of CO 2 injection systems, because the process can reduce injection rates.