This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 174979, “Refracturing—Diagnostics Provide a Second Chance To Get It Right,” by R.S. Leonard, SPE, C.P. Moore, SPE, R.A. Woodroof, SPE, and C.W. Senters, SPE, Core Laboratories, prepared for the 2015 SPE Annual Technical Conference and Exhibition, Houston, 28–30 September. The paper has not been peer reviewed. The surge in unconventional completions has created a substantial accumulation of previously hydraulically fractured wells that are candidates for hydraulic refracturing. Completion diagnostics are a valuable tool in determining the most cost-effective stimulation and completion parameters, part of the refracturing optimization process. Refracturing allows the operator to capitalize on this continuous improvement in stimulation design. It also provides an excellent opportunity to add incremental production. Introduction The primary purpose of refracturing is to increase production from an existing wellbore through stimulation of new rock and the re-establishing of conductive pathways between the reservoir and wellbore. This paper analyzes diagnostic results for a variety of wells in restimulated formations around the country (data for all 69 wells restimulated in 11 formations are provided in the complete paper). This analysis process illustrates that all formations are unique and need to be evaluated independently. What works well in one area often does not apply in other areas because of reservoir differences along with pressure and temperature variances. Diagnostics Proppant Tracers. The primary diagnostic technique discussed in this paper is proppant tracing, using three distinct low-level gamma-emitting tracers: iridium-192, scandium-46, and antimony-124. The tracers are pumped primarily throughout the proppant-laden portion of the stimulation. A spectral gamma ray logging tool is run to identify near- wellbore proppant placement of each individual tracer. The proppant tracers are ceramic beads, typically 40/70 mesh. The specific isotopes fall in a sweet-spot of half-lives that make them ideal for this application. Through the years, production-log data have shown an excellent correlation with near-wellbore proppant placement, and this same strong correlation exists with traced refracturing.