Efficient Through-Casing Surveillance of Steam Chamber and Reservoir Oil Using a New Pulsed Neutron Technology and an Advanced Interpretation Algorithm

Abstract

Steam flooding is an essential recovery process in developing heavy oil reservoirs. Operators typically drill and case observation wells to monitor the movement of the injected steam and changes in heavy oil and water saturations. This in-well surveillance is performed using pulsed neutron well logging techniques. Pulsed neutron well logging technology has been used for more than 60 years to determine formation fluid saturation behind casing. We introduce a next-generation slim multi-detector pulsed neutron well logging tool. The new pulsed neutron tool integrates an upgraded pulsed neutron generator, lanthanum bromide scintillation detectors, and an improved electronics system. A robust data analysis technique is another vital component of through-casing multiphase formation fluid quantification. A conventional method for analyzing three-phase saturation uses two pulsed neutron logs in sequence. We have adopted a simultaneous analysis approach that combines two pulsed neutron measurements simultaneously to evaluate the volumes of multiphase fluid components. We present a case study of oil sands produced by the steam-assisted gravity drainage (SAGD) method. We also show comparisons of data acquisition with the previous-generation and new pulsed neutron tools, operating time, and data quality. We acquired time- and energy-based gamma-ray spectra from multiple detectors to extract key pulsed neutron measurements such as ratios of inelastic and capture gamma rays and carbon/oxygen ratios. Time- and energy-spectra-based salinity-independent nuclear measurements were combined to compute three-phase formation fluid saturation. The new tool acquired data of the same quality at least three times faster than the legacy tool. The new tool that offers three improved features (higher pulsed neutron outputs, denser scintillation detectors, and high-speed digital electronics) combined with a new acquisition technology that records time- and energy-spectra-based pulsed neutron data sets simultaneously enables faster reservoir surveillance. Operators using thermal methods for heavy oil recovery must understand the current underground steam distribution. This affects steam injection optimization and determines subsequent reservoir management activities. A technique for delineating steam, heavy oil, and water through cased monitoring wells was improved by incorporating a new well logging tool, an innovative acquisition mode, and an advanced nuclear data analysis workflow.