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.