A potential NMR-based wettability index using free induction decay for rocks.

Area of Science:

• Geosciences
• Petroleum Engineering
• Analytical Chemistry

Background:

• Rock wettability significantly impacts petrophysics and oil recovery efficiency.
• Heterogeneous wettability in rocks arises from minerals with varying surface properties.
• Nuclear magnetic resonance (NMR) is sensitive to variations in sample composition.

Purpose of the Study:

• To propose and validate a novel method for estimating rock wettability using magnetic susceptibility contrasts.
• To investigate wettability alteration in reservoir rocks before and after ageing.
• To develop a refined NMR wettability index correlated with traditional methods.

Main Methods:

• Theoretical analysis of magnetic susceptibility contrast between rock and fluids.
• Employing internal magnetic field gradients to assess wettability changes.
• Utilizing free induction decay measurements on artificial sandstone samples.
• Correlating the new NMR wettability index with Amott wettability tests.

Main Results:

• Observed distinct internal gradients for water and oil in aged rock pores due to magnetic susceptibility differences.
• Acquired magnetic susceptibility contrasts for intermediate-wet artificial sandstone.
• Presented a refined NMR wettability index.
• Demonstrated a strong correlation between the new index and Amott tests.

Conclusions:

• The proposed NMR method using magnetic susceptibility contrast is a feasible approach for determining rock wettability.
• This technique offers a valuable tool for understanding wettability alteration and its impact on oil recovery.
• The refined NMR wettability index provides a reliable alternative to conventional methods.