An injection backflow method for measuring fracture surface area adjacent to a wellbore measures an initial temperature profile along the length of a wellbore. A tracer composition is injected into the wellbore at an initial concentration. The tracer composition includes a reactive tracer and a secondary tracer that is less reactive than the reactive tracer. The tracer composition diffuses within subterranean reservoir for a time. A secondary tracer concentration and a reactive tracer concentration are measured as a function of time. A reservoir fracture surface area is calculated using a reservoir fluid flow model.