An Environmentally Friendly Method to Evaluate Gravel and Frac Packed Intervals Using a New Non-Radioactive Tracer Technology

Abstract

Abstract Recently a new non-radioactive tracer (NRT) technology has become available to locate proppant in induced fractures that offers a viable alternative to the prior technology which utilizes radioactive (R/A) tracers, thereby eliminating the environmental, safety, and regulatory concerns associated with the R/A materials. This new non-radioactive tracer technique also has application in evaluating gravel packs and frac packs. The new technology employs a non-radioactive ceramic proppant containing a high thermal neutron capture compound (HTNCC). This compound is inseparably incorporated into each ceramic proppant grain during manufacturing in sufficiently low concentration that it does not affect any proppant properties. This tagged proppant can also be used as, or mixed with, conventional gravel or frac packing materials prior to downhole placement. The NRT taggant is detected using standard pulsed neutron capture (PNC) logging tools, with detection based on the high thermal neutron absorptive properties and/or capture gamma ray spectral properties of the tagged pack material relative to other downhole constituents. The tagged pack material is indicated from:decreases in after-pack PNC detector count rates relative to corresponding before-pack count rates,increases in PNC formation and borehole component capture cross-sections (Sfm and Sbh), and/orincreases in the computed elemental yield of the neutron-absorbing tag material, derived from the observed PNC capture gamma ray energy spectra. In many frac-packing situations, combining Sfm and Sbh data permits identification of fracture height behind casing. In some applications, enhancements to these methods have also been developed to eliminate the requirement for the before-pack log. In this paper, log examples illustrate the effective detection of HTNCC tagged proppant placement in fractures and cement, and Monte Carlo modeling illustrates the viability of the detection/evaluation of gravel packs and frac packs using HTNCC tagged pack material. The modeling data and logs indicate the applicability of this effective, safe, and environmentally friendly logging technique to locate the placement of non-radioactively tagged downhole pack material in both gravel pack and frac pack evaluation.