A new directional gamma ray tool has been developed and is being incorporated into an innovative togging service. The service determines the azimuthal pattern of gamma ray emission from a completion material that has been tagged with a radioactive isotope. This paper discusses the interpretation of directional gamma ray logging data following hydraulic fracturing operations. By measuring the intensity of gamma rays emitted from tagged material placed in the induced fracture, the directional gamma ray measurement can be combined with auxiliary wellbore survey information to assist in the determination of propagation azimuth. Such results have a variety of applications – for example, designing a systematic well placement scheme to optimize reservoir drainage efficiency.
Log examples derived from prototype tool measurements following hydraulic fracturing operations are presented and the analysis of the data is discussed. The interpretation of directional gamma ray data is adversely affected by damage to the near-wellbore region during fracturing operations. Data interpretation was found to be more consistent and reliable following micro-frac or mini-frac stress determination operations. In addition, where perforations were oriented in the direction of the anticipated fracture propagation, directional gamma ray data demonstrated an improvement in fracture efficiency.