Although isolation of lines and wellheads using ice plugs is not new in itself, the liquid nitrogen approach developed for use on Aera Energy LLC’s ("Aera’s") Diatomite Steam Drive steam injection wells offered several creative and novel aspects. The procedure was first thoroughly shop-tested and then field-tested on two wells. Bentonite gel was used as a plugging agent due to its rheological characteristics and low thermal expansion compared to water. The gel was mixed to ensure sufficient viscosity to remain in place once spotted across the freeze interval. Cooling was applied by circulating cold nitrogen gas through copper tubing wrapped on the outside of a 13⅜" surface casing string. Contact temperatures on the surface of the external casing were closely monitored to ensure they were never lower than approximately –100°F throughout the process to minimize risk of casing embrittlement.

At 12 hours or less on each well, the time to form ice plugs to the core through a multiple string completion and two cement layers was very manageable. All seven injection strings above the wellhead on the two test wells were safely cut off, and each string fully converted to the desired new injection configuration above the casing bowl.

Thorough safety and technical planning prior to the field trials, creation of several new tools to assist with various program steps, and identification / consideration of contingencies helped in avoiding mistakes, encountering difficulties during the job and, ultimately, making the trials a thorough success.

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