A method of tracing flow from a subterranean well comprising a well bore penetrating a fluid-bearing rock formation, comprising the steps of: a. inserting a well-liner into said well, said well-liner comprising a plurality of liner portions, each joined at at least one end to an adjacent liner portion, wherein at least one of said liner portions comprises a tracer-liner portion comprising an inner tube and an outer tube, each comprising at least one wall having an internal surface and an external surface, the walls of the inner tube and the outer tube being impermeable to fluid flow, said outer tube having an internal diameter which is larger than the outer diameter of said inner tube, said inner tube being arranged coaxially within said outer tube such that at least a portion of the external surface of said inner tube is covered by said outer tube; wherein the internal diameter of the outer tube exceeds the outer diameter of the inner tube by an amount sufficient to form a space between the external surface of the inner tube and the internal surface of the outer tube, and a tracer material containing a tracer compound is present in said space, the outer wall of said well liner and the inner surface of said well-bore defining a gap, b. filling said gap with a settable fluid material and thereafter allowing said fluid material to set to form a solid material; c. forming perforations in the inner and outer tubes and the solid material so that fluid flowing within or over the liner may contact the tracer material located between the inner and outer tubes; d. collecting a sample of fluid at a location downstream of said perforations; e. analysing said sample to determine whether said tracer compound is present; and f. inferring from the presence or absence of said tracer compound in the sample whether fluid has contacted the tracer in the region of said perforations; wherein said tracer material is a solid tracer material and does not fill said space and the fluid flows within the space. a. inserting a well-liner into said well, said well-liner comprising a plurality of liner portions, each joined at at least one end to an adjacent liner portion, wherein at least one of said liner portions comprises a tracer-liner portion comprising an inner tube and an outer tube, each comprising at least one wall having an internal surface and an external surface, the walls of the inner tube and the outer tube being impermeable to fluid flow, said outer tube having an internal diameter which is larger than the outer diameter of said inner tube, said inner tube being arranged coaxially within said outer tube such that at least a portion of the external surface of said inner tube is covered by said outer tube; wherein the internal diameter of the outer tube exceeds the outer diameter of the inner tube by an amount sufficient to form a space between the external surface of the inner tube and the internal surface of the outer tube, and a tracer material containing a tracer compound is present in said space, the outer wall of said well liner and the inner surface of said well-bore defining a gap, b. filling said gap with a settable fluid material and thereafter allowing said fluid material to set to form a solid material; c. forming perforations in the inner and outer tubes and the solid material so that fluid flowing within or over the liner may contact the tracer material located between the inner and outer tubes; d. collecting a sample of fluid at a location downstream of said perforations; e. analysing said sample to determine whether said tracer compound is present; and f. inferring from the presence or absence of said tracer compound in the sample whether fluid has contacted the tracer in the region of said perforations;