Traceable Proppant Eliminates Need For Radioactive Detection Material

Abstract

Technology Update A new ceramic proppant has made detection possible without placing radioactive material downhole. The new detection method makes use of a high thermal neutron capture compound (HTNCC) incorporated into the ceramic proppant. Traditional fracture-height or proppant-placement evaluation after hydraulic fracturing relies on the detection of radioactive tracers pumped downhole with the proppant. Although this technique is useful, it raises environmental, safety, and regulatory issues. The HTNCC is added to the proppant during its manufacture and is included in concentrations low enough not to affect the proppant’s strength or conductivity. The proppant is detected using standard compensated or pulsed neutron tools, with detection based on the high thermal neutron capture of the compound relative to the surrounding downhole constituents. This new detectable proppant was used in the T sand of the Villeta and Caballos formations of the Juanambu field in the Putumayo Basin of Colombia. Two detection methods use a comparison of before-fracture log count rates and after-fracture count rates, with reduced after-fracture count rates observed in zones containing proppant. Another detection method, especially useful when formation gas saturations change, uses only the after-fracture log. The HTNCC method has advantages over the common radioactive particle method. First, the HTNCC tagging material is incorporated in very small quantities into each proppant grain during the manufacturing process. Because it is present in every particle of the fracture treatment, the detection of all propped fractures is insured. With traditional radioactive tracers, which are blended into the slurry at extremely small ratios compared with total proppant volume, segregation can occur, which can lead to misinterpretation of fractures in which no radioactive particles are contained near the wellbore in the propped fracture section. A related but opposite problem also can occur in situations in which a stray radioactive particle is located in an area that is not a propped fracture (e.g., a casing collar or perforation). These false positives are eliminated by the new method because the small quantities of HTNCC in a few stray pellets will not create a log response. A second advantage, and more important in many cases, is that the new method contains only inert materials, thereby eliminating the need for the special requirements or permitting necessary for handling, transporting, pumping, or flowing back of hazardous materials associated with traditional radioactive tracers. This new method provides intrinsic value to operators by providing an environmentally friendly and virtually hazard-free alternative to radioactive tracers. A third advantage is that the HTNCC is inherently stable and permanently incorporated within the proppant. The HTNCC can be logged at any time in the future to evaluate remedial operations or determine whether proppant has flowed back from any interval. Typical radioactive tracers experience radioactive decay, and the detectability declines as a function of the isotope half-life, which prevents the accurate identification of proppant location after a few months.