Paper: Precipitation Caused By Liquid CO2 In Carbonate Formation Treatments, A Potential Problem Resolved

Injection of liquid carbon dioxide with treating fluids has been used for many years to improve results and to eliminate some of the problems associated with the stimulation of oil and gas wells. One purpose is to promote faster cleanup without the need of swabbing. When the pressure is released at the wellhead after the treatment, the carbon dioxide vaporizes and forces the treating fluids from the formation. Presence of this gaseous carbon dioxide in these fluids reduces the weight of the fluid column so that normal reservoir drive can then help unload the fluids from the well. Rapid recovery of the stimulation fluids is normal. Under certain conditions, dissolved carbon dioxide and calcium salts can react to form a calcium carbonate precipitate. This paper discusses the conditions of temperature, pressure, and pH under which calcium carbonate does not precipitate.