A wellbore system having a borehole extending into an earth formation, a tubular element extending into the borehole whereby a cylindrical wall surrounds the tubular element in a manner that an annular space is formed between the tubular element and the cylindrical wall, at least one seal member arranged in the annular space, each seal member being movable between a retracted mode in which the seal member has a first volume and an expanded mode in which the seal member has a second volume larger than the first volume, wherein the seal member in the expanded mode thereof seals the annular space, and wherein the seal member includes a material which swells upon contact with a selected fluid so as to move the seal member from the retracted mode to the expanded mode thereof.