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

摘要

Recently a new non-radioactive tracer (NRT) technology has become available to locate proppant ininduced 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/Amaterials. This new non-radioactive tracer technique also has application in evaluating gravel packs andfrac packs. The new technology employs a non-radioactive ceramic proppant containing a high thermalneutron capture compound (HTNCC). This compound is inseparably incorporated into each ceramicproppant grain during manufacturing in sufficiently low concentration that it does not affect any proppantproperties. This tagged proppant can also be used as, or mixed with, conventional gravel or frac packingmaterials prior to downhole placement. The NRT taggant is detected using standard pulsed neutroncapture (PNC) logging tools, with detection based on the high thermal neutron absorptive propertiesand/or capture gamma ray spectral properties of the tagged pack material relative to other downholeconstituents. The tagged pack material is indicated from: (1) decreases in after-pack PNC detector countrates relative to corresponding before-pack count rates, (2) increases in PNC formation and boreholecomponent capture cross-sections (Σ_(fm) and Σ_(bh)), and/or (3) increases in the computed elemental yield ofthe neutron-absorbing tag material, derived from the observed PNC capture gamma ray energy spectra. Inmany frac-packing situations, combining Σ_(fm) and Σ_(bh) data permits identification of fracture height behindcasing. In some applications, enhancements to these methods have also been developed to eliminate therequirement for the before-pack log. In this paper, log examples illustrate the effective detection ofHTNCC tagged proppant placement in fractures and cement, and Monte Carlo modeling illustrates theviability 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 friendlylogging technique to locate the placement of non-radioactively tagged downhole pack material in bothgravel pack and frac pack evaluation.