Effect of gas pressure on the sealing efficiency of compacted bentonite-sand plugs

We show that gas pressure Pg does not affect significantly Pswell until a threshold Pg > 2 MPa. When swelling occurs inside a tube with a smooth (turned) inner surface, continuous GB occurs when Pg is equivalent to the effective Pswell (obtained without gas pressure, at 7.32 MPa ± 0.11). When the plug swells inside a grooved tube, continuous GB does not occur up to Pg ≥ 10.5 MPa: smooth interfaces are a preferential gas migration pathway rather than grooved interfaces, and rather than water-saturated bentonite-sand plugs. With smooth tubes, in presence of Pg ≥ 2 MPa, although Pswell is not affected, gas passes through the sample at significantly lower values than Pswell, due to partial sample saturation. It is concluded that GB pressure is a more accurate indicator of partial sample saturation than swelling pressure Pswell alone.