A geometric factor theory-based method for formation and cement density inversion in cased hole.

Area of Science:

• Petroleum Engineering
• Geophysics
• Nuclear Logging

Background:

• Uncertainties in cement sheath properties complicate formation density and porosity evaluation in cased holes.
• Nuclear logging tool responses are attenuated by casing and cement, with poor cementing conditions adding complexity.
• Accurate annular cement density determination is crucial for reliable cased hole formation evaluation.

Purpose of the Study:

• To establish a unified inversion framework for determining annular cement density.
• To apply this framework to azimuthal cement density evaluation and simultaneous formation-and-cement density determination.
• To validate the methodology using high-fidelity simulations and field data.

Main Methods:

• Development of a unified geometric factor theory-based inversion framework.
• High-fidelity Monte Carlo modeling using the Geant4 toolkit to simulate logging tool responses.
• Application of the framework to two distinct logging scenarios: azimuthal and multi-detector density logging.

Main Results:

• The proposed methodology achieved a maximum cement density measurement error of 0.031 g/cm³.
• A mean absolute formation density inversion error below 0.025 g/cm³ was demonstrated.
• The framework successfully adapted to different tool configurations for distinct logging scenarios.

Conclusions:

• The unified inversion framework provides a robust solution for annular cement density determination.
• The methodology enhances the accuracy of formation density and porosity evaluations in cased holes.
• Accurate cement evaluation is critical for optimizing hydrocarbon recovery and reservoir management.