New Integral Neutron-Neutron Logging for Cement Integrity Analysis of any Backfilling

Background: The article presents a new technology of integral neutron-neutron logging technology for cement integrity analysis (hereinafter – NNL-C) of wells in hydrocarbon fields, developed by GeoSpectr Oil and Gas Technology Institute (Russia). NNL-C is designed to ensure the quality of well cementing focusing on the condition, integrity and leak tightness of any type and density of cement casing (including light cement). It can be used in any kind of well filling whether liquid, gas, or a mixture. NNL-C is applicable at all stages of the oil and gas well lifecycle – from construction to operation – without well-kill operation and tubing removal. This technology is free from the major limitations of standard (conventional) gamma-gamma and acoustic logging techniques for cement integrity evaluation. Aim: The purpose of the NNL-C is to offer a prompt and cost-effective evaluation of the integrity or failure of cementing in any active wells. In contrast to NNL-C, the standard methods for analyzing cement integrity are inadequate for this purpose, as they cannot be applied to lightweight cement, tubing wells, or gas-filled wells. Materials and methods: The science behind, methodology, and interpretation software for NNL-C were developed employing mathematical modeling. This technology hs been tested against measurement data from real wells. Results: The NNL-C method was tested in 12 and tried in more than 20 wells, demonstrating a good correlation with standard methods and achieving high accuracy of cement-bond logging. The possibility of quantifying cement under field conditions was confirmed in scenarios where standard cement-bond logging techniques are typically not applicable, such as in tubing wells, gas-filled wells, and during the use of lightweight cement. The NNL-C technology has been successfully implemented in Kazakhstan at the Kozhasai and Alibekmola oil and gas condensate fields, as well as the Bozoi underground gas storage facility. Conclusion: The technology provides reliable, accurate, and cost-effective information on the quality of cementing of wells under construction such as condition, integrity and tightness of cementing (cement sheath) of production wells.