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: (1) decreases in after-pack PNC detector count rates relative to corresponding before-pack count rates, (2) increases in PNC formation and borehole component capture cross-sections (Ʃfm and Ʃbh), and/or (3) increases 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 Ʃfm and Ʃbh 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, Monte Carlo modeling of downhole gravel and frac pack applications, and field log examples illustrating the detection of gravel packs, frac packs, and proppant placement in fractures, demonstrate the viability/applicability of this effective, safe, and environmentally friendly logging technique to locate the placement of downhole pack material.
Author(s): Xiaogang Han: CARBO Ceramics Inc., Harry Smith: Harry D. Smith Consulting, Robert Duenckel: CARBO Ceramics Inc.
Paper Number: OTC-25166-MS