Abstract: A method of monitoring a fluid is described comprising: introducing a tracer into the fluid and analysing the fluid to determine if the tracer is present in the fluid; characterised in that the tracer comprises luminescent carbon-based nanoparticles exhibiting a peak luminescence intensity at an emission wavelength of at least 500 nm. The method is in particular a method of monitoring a parameter of a hydrocarbon well, pipeline or formation. A use of a tracer and a tracer composition comprising carbon-based nanoparticles exhibiting a peak luminescence intensity at an emission wavelength of at least 500 nm are also described.

Abstract: Compositions having a core and a coating that covers at least part of the core, where the core comprises a mixture of at least one oil field chemical and at least one core matrix polymer are described. The composition provides a slower release of an oil field chemical into an eluent compared to the release provide by the core. The compositions provide for the controlled release of tracer over long periods of time than is provided by the release from the core. Methods of making the compositions and systems containing the compositions are described. Methods of tracing the movement of fluid in a hydrocarbon reservoir using the compositions and methods of releasing biocides and other well treatment agents into reservoir fluids over time are also described.

Abstract: A method of monitoring a fluid is described comprising introducing a luminescent nanoparticle into the fluid; removing a fluid sample from the fluid; adding a reagent to the fluid sample to vary the luminescence behaviour of the luminescent nanoparticles and/or of other luminescent species present in the fluid; analysing the luminescence of the modified fluid sample to determine an amount of the nanoparticle present therein. A use of a tracer based on these principles is also described.

Abstract: Compositions having a core and a coating that covers at least part of the core, where the core comprises a mixture of at least one oil field chemical and at least one core matrix polymer are described. The composition provides a slower release of an oil field chemical into an eluent compared to the release provide by the core. The compositions provide for the controlled release of tracer over long periods of time than is provided by the release from the core. Methods of making the compositions and systems containing the compositions are described. Methods of tracing the movement of fluid in a hydrocarbon reservoir using the compositions and methods of releasing biocides and other well treatment agents into reservoir fluids over time are also described.