Effects of Brine Concentration and Pressure Drop on Gypsum Scaling in Oil Wells

Abstract

Gypsum scale is a problem in oil wells that produce from reservoirs containing calcium sulfate. It becomes particularly troublesome in waterflood operations where large volumes of water are being produced. The solubility of gypsum or anhydrite in water increases with pressure due to a slight decrease in total volume as the salt dissolves. Upon release of pressure a supersaturated solution is obtained that deposits gypsum for a period of time. This is believed the most reasonable explanation for gypsum deposits at the bottom of producing wells. The study reveals that the amounts of scale formed at a given pressure drop and temperature depend on the amount of sodium chloride and other salts dissolved in the brine. The quantity of gypsum deposited increases with salt concentration to a maximum, then decreases until, with strong brines, no scale is formed.