A novel quantitative measurement method for formation element via iterative support vector regression

Abstract

Pulsed neutron sources provide notable advantages in well logging tools. They emit high-energy neutrons and can be controlled effectively. These emitted neutrons induce gamma rays, which can be detected and utilized to estimate diverse formation properties. One such application is the determination of elemental concentrations using gamma spectroscopy, enabling accurate characterization of mineralogy and total organic carbon in complex reservoirs. However, in field tests, the extraction of net inelastic energy spectra becomes challenging due to the diverse environment. Additionally, the measurement of actual gamma spectra is susceptible to the effects of formation conditions and detector performance, resulting in statistical errors and unavoidable noise within the measured gamma spectra. Consequently, the accuracy of elemental concentration estimation is reduced. To address these challenges, this paper proposes a novel method for accurately estimating formation elemental concentrations. Initially, the capture deduction coefficient is calculated by fitting the gamma time spectra iteratively, enabling the extraction of net inelastic gamma spectra in various formation environments. Subsequently, an iterative support vector regression (ISVR) method is proposed to obtain the stable and accurate non-negative elemental yields, even in the presence of gamma spectrum noise. Finally, the obtained elemental yields are converted to accurate elemental concentrations using the oxide closure model and pseudo-capture spectroscopy. The accuracy and robustness of proposed method are validated on simulated mixed spectra with high noise. Field test results are compared with core analysis results to assess the accuracy of the determined elemental concentrations.