Work

A fluid identification method for deep low-porosity buried-hill reservoirs based on coupled energy spectrum-time spectrum pulsed neutron logging

Year: 2026

Type: article

Abstract: This work addresses the challenge of fluid identification in complex low-porosity buried-hill reservoirs in the Bohai Sea by developing a fluid identification method based on the coupled responses of energy spectra and time spectra. First, a regularized spectral decomposition algorithm is employed to analyze pulsed neutron gamma-ray spectra and obtain the carbon-to-oxygen (C/O) yield ratio, enhancing the capability of quantitatively characterizing differences in oil and water signal responses under low-porosity conditions. Second, an oil-water identification method is established by integrating energy-spectrum and time-spectrum parameters, improving the accuracy of oil-water discrimination in complex lithological environments. Finally, a gas layer identification parameter is introduced to distinguish gas-bearing zones and fluid-bearing zones, which is then combined with the oil and water identification results to form a three-phase fluid identification workflow. Field applications in drilled wells penetrating granite gneiss buried hills and carbonate buried-hill reservoirs in the Bohai Sea demonstrate that the proposed method significantly enhances the response contrast between oil and water under low-porosity conditions, substantially reduces the uncertainty of single-parameter interpretation, and enables accurate discrimination among oil, gas, and water. The method provides an effective solution for fluid identification in complex low-porosity buried-hill reservoirs in the Bohai Sea.

Source: Petroleum Exploration and Development

DOI: 10.1016/s1876-3804(26)60740-9