Shape memory cement annulus gas migration prevention apparatus

A gas migration control assembly for an annular space surrounding a tubular in a subterranean location defined by a borehole wall and further contains a sealing material, comprising:

• a tubular having an outer surface;
• a sealing material in an annular space between said tubular and the borehole wall;
• a gas migration control device having at least one member mounted on the outer surface of said tubular and held in alignment with said outer surface on a long dimension thereof;
• said gas migration control device mounted to said outer surface that has a smaller dimension for facilitating insertion to the subterranean location and a larger dimension spanning said annular space with the transition to the larger dimension selectively triggered thermally from well fluid when said annular space in the vicinity of said control device is substantially full with said sealing material so that said thermally triggered shape change of said gas migration control device alone displaces said sealing material in making contact with the borehole wall to at least impede gas migration through said sealing material in said annular space;
• said gas migration control device comprises an annular cylindrical shape in said smaller dimension with subsequently extending said at least one member and, when thermally triggered, said at least one member moving away from said alignment with outer surface and generally radially toward the borehole wall to engage the borehole wall such that a compressive stress is generated within said at least one member.