Numerical investigations on T₁-T₂*-based petrophysical evaluation in shale oil reservoir with complex minerals

It is of great significance to evaluate the petrophysical properties in shale oil reservoir, which can contribute to geological storage CO₂. Two-dimensional nuclear magnetic resonance (2D NMR) technology has been applied to petrophysical characterization in shale oil reservoir. However, limitations of traditional 2D NMR (T₁-T₂ or T₂-D) in detecting short-lived organic matter and the complexity of mineral compositions, pose NMR-based petrophysical challenges. The organic pores were assumed saturated oil and the inorganic pores were assumed saturated water, and the numerical algorithm and theory of T₁-T₂* in shale oil reservoir were proposed, whose accuracy was validated through T_2, T₁-T₂ and T₂* experiments. The effects of mineral types and contents on the T₁-T₂* responses were firstly simulated by the random walk algorithm, revealing the NMR response mechanisms in shale oil reservoir with complex mineral compositions at different magnetic field frequency (f). The results indicate that when the pyrite content is 5.43%, dwell time is 4 μs, the f is 200 MHz, and echo spacing is 0.4 ms, the T₁-T₂*-based porosity is 2.39 times that of T₁-T₂-based porosity. The T_2LM* is 0.015 ms, which is 0.015 times that of T_2LM. The T_1LM is 8.84 ms, which is 0.63 times that of T_1LM. The T₁-T₂*-based petrophysical conversion models were firstly created, and the foundation of petrophysical conversion was laid at different f.