Dissolved gas as a problem in oil well cements

Abstract

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 be 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.

Threats to the environment in the areas of abandoned extraction of hydrocarbon deposits

“…According to Sechman et al [35] well leakages may be divided into two categories: primary and secondary. The primary leakages are results of improper drilling and/or cementing of the casing [24,26]. The secondary leakages may come out during the operation of producing well and are usually the effect of cement and casing [6,10].…”

Computed X-ray Tomography Study of Carbonate Precipitation in Large Portland Cement Pores

“…In wells, such a gas entrapment may be a result of gas intrusions when cementing wells that penetrate into high-pressure reservoirs. Thus, it is likely that cement hardened at downhole conditions will contain natural gas bubbles. , Lile et al have shown that wellbore cement when cured in contact with gas (CH 4 ) may possess bubbles (spherical pores) of comparable pore size as the air bubbles in the cement slurry cured at low pressure. According to these authors, the reason why the bubbles form is dissolution of gas in the slurry and subsequent gas liberation due to pressure reduction during cement hydration.…”