Tool and method for verification of pressure integrity behind downhole casing

A method for verifying the pressure integrity of a barrier in an annulus located outside of a casing string in a wellbore, the method comprising the steps of:

• establishing a first fluid connection through the casing string between an inside of the casing string and the annulus outside the casing string at a first position in the wellbore;
• establishing a second fluid connection through the casing string between the inside of the casing string and the annulus outside the casing string at a second position in the wellbore, the second position being offset from the first position along the axial direction of the wellbore, and the barrier in the annulus being located radially outside the casing string and axially between the first and second fluid connections at the first and second positions;
• establishing a retrievable barrier in the casing string axially between the first and second fluid connections in the wellbore;
• establishing a pressure differential across the retrievable barrier;
• releasing a tracer below the retrievable barrier in the wellbore;
• and
• sniffing for tracer above the retrievable barrier to verify a leakage through the retrievable barrier and/or the barrier in the annulus, wherein the step of sniffing for tracer above the retrievable barrier comprises:
• sniffing for tracer from a position A proximate the fluid connection through the casing string at the first position in the wellbore;
• and
• sniffing for tracer from a position B, position B being closer to the retrievable barrier than position A, in the well.