Method of creating an annular zonal isolation seal in a downhole annulus

A method of creating an annular zonal isolation seal in a downhole annulus between a string of downhole tubular joints inserted within a bore in a borehole in the Earth, and an inner wall of the bore, comprising:

• providing an isolation joint in the string, the isolation joint having a first separator, a second separator, and a circumferential band of increased wall thickness, wherein the circumferential band of increased wall thickness is sandwiched in an axial direction between the first separator and the second separator, and the wall thickness of the circumferential band of increased wall thickness is greater than the wall thicknesses of the first separator and the second separator, providing a mating support at a predetermined axial location relative to the circumferential band of increased wall thickness, the mating support adapted for mating with a local expander device within said downhole tubular;
• lowering the local expander device through the downhole tubular string and at least partially into the isolation joint, the local expander device comprising:
• a force imparting section configured to impart a transversely directed expansion force to the circumferential band of increased wall thickness, and
• a carrier section, carrying the force imparting section, and comprising a complementary mating support at a predetermined axial separation distance relative to the force imparting section for engaging the mating support transversely aligning the force imparting section of the local expander device with the circumferential band of increased wall thickness;
• and
• activating the force imparting section of the local expander device to impart a radial strain on the isolation joint exclusively on the circumferential band of increased wall thickness, thereby locally expanding the downhole tubular in the downhole annulus;
• wherein the circumferential band of increased wall thickness is formed as a unitary single-piece.