A New Method to Identify Proppant Location in Induced Fractures
A new technique is discussed and tested in this work for proppant placement determination. A high thermal neutron capture compound (HTNCC) is inseparably incorporated into a ceramic proppant during manufacturing in sufficiently low concentration that it does not affect proppant properties. Proppant is detected using standard compensated neutron tools or pulsed neutron tools, with detection based on the high thermal neutron absorptive properties of the compound relative to downhole constituents. Compared to the traditional radioactive tracer (RA) techniques, the new detectable proppant is not radioactive so there are no HSE or regulatory issues. Additionally, since the high thermal neutron absorbing compound is placed in the proppant during the process of manufacturing, there is no requirement for special handling or mixing processes at the well site.
Specifically, proppant is detected using after-frac compensated neutron logs combined with corresponding before-frac logs. Increased thermal neutron absorption by the compound reduces count rates in the near and far detectors, with approximately the same percentage reduction observed in each detector, leaving the near-to-far detector count ratio (N/F) unchanged. One detection method utilizes a comparison of before-frac log count rates and after-frac count rates, with reduced after-frac count rates observed in zones containing proppant. A second detection method, especially useful when formation gas saturations change, involves only the after-frac log. Since the near to far detector count ratio is unaffected by proppant, after-frac count rates predicted from the ratio will also be unaffected. These computed/synthetic count rates will be greater than the observed after-frac count rates in intervals containing proppant.
Nuclear Monte Carlo modeling was performed to demonstrate the validation of this technique employing both compensated neutron logging tool (CNT) and pulsed neutron capture (PNC) logging tools. Two field examples from China are illustrated in this paper. The final interpreted locations of proppant are shown in the field examples.
Authors: Robert John Duenckel (CARBO Ceramics, Inc.) | Harry D. Smith (CARBO Ceramics, Inc.) | Simon Hao (CARBO Ceramics, Inc.) | DaKang Gao (CARBO Ceramics, Inc.) | Terry T. Palisch (CARBO Ceramics, Inc.) | Xiaogang Han