Dissolved gas as a problem in oil well cements

Dissolution of high-pressure gas in drilling fluids and oil well cement slurries may cause problems when the gas is liberated. A literature survey on solubility data confirms that gas may he dissolved and liberated at typical well conditions. Formation gas dissolved in the drilling mud is liberated when the mud returns to the surface, but this is normally not a problem. It is not known whether dissolved gas in the cement slurries may create any problems. A new hypothesis is introduced, claiming that gas from the formation may enter into the cement slurry and eventually lead to a weaker cement and/or to fractures, enabling a continuous migration of gas to the surface. Laboratory experiments have been carried out on cement slurries. Thin sectioned samples of the hardened cement showed that more gas bubbles and fractures had indeed developed in the cements that had been exposed to pressurized gas before and during the hardening process.