Swellable packer evaluation has become a critical component of Greater Prudhoe Bay (GPB) well design, surveillance and diagnostic strategy. Currently in the field there are several wells constructed with cementless completions with over 500 water or oil swellable packers across three different reservoirs. Several early gas or water breakouts have been documented since these types of completions have been deployed and the need for an accurate diagnostic technique to distinguish between a reservoir phenomenon or a completion failure motivated this work.
The borax evaluation technique historically has been successfully used in oil fields on the North Slope of Alaska to detect fluid channeling mainly in horizontal cemented and perforated wells. This technique however, was never used to evaluate swellable packers in horizontal cementless completions. Even when the same multi-detector pulsed neutron (MDPN) instrument could be used in real time or memory conveyance to evaluate either one, there are fundamental differences in how these cementless completions are designed and evaluated compared to the cemented and perforated ones. Ignoring those differences could lead to the wrong nuclear attribute selection and incorrect interpretations, diagnostics and remediation strategies.
The objective of this paper is to describe the nuclear modelling performed, the wellsite procedures used, the interpretation workflow, and the results of evaluations of these completions.