Application of a Laboratory-Scale Apparatus to Simulate Gas Migration during Cement Slurry Hydration

ABSTRACT Numerous research investigations have been devoted to simulating gas migration through cemented wellbore annuli as a result of the presence of non-targeted pressurized gas along the wellbore adjacent to the outer annulus. Despite these research efforts, developing a laboratory-scale apparatus that allows for the measurement of the time period that a cemented annulus is vulnerable to gas migration has remained a challenge. In this research, an experimental procedure to simulate the gas migration during cement slurry hydration in wellbores is presented. A previously developed wellbore simulation chamber (WSC) is used to further investigate the factors that affect the gas migration period. Limitations with the original WSC design are identified and several modifications are implemented to more adequately define the onset and termination of the gas migration period. The modified WSC (MWSC) apparatus is then used to perform a series of gas migration tests to identify the effect of overburden pressure and formation gas pressure on the vulnerability period. It is shown that for an identical cement slurry, both the onset and the termination of the gas migration period are, in part, functions of the difference between the overburden pressure and the formation gas pressure. In addition, the vulnerability period for a slurry mixture under a select representative borehole condition is measured. Finally, the results of the MWSC apparatus are compared with one of the widely used approaches in predicting the vulnerability period.