Interpretation of NMR relaxometry in organic-rich mudrocks still remains a challenge for petrophysicists. A reliable numerical simulation of NMR response in these rocks helps in better understanding of the NMR relaxometry data and the corresponding petrophysical properties (e.g., the wettability and fluid distribution in the pore space). The hydrocarbon-wetting or mixed-wetting characteristics of organic-rich mudrocks have significant impacts on hydrocarbon recovery from the rocks, but quantification of wettability using conventional well-log interpretation methods remains a conundrum. The objectives of this paper are (a) to introduce a NMR two-phase simulation method to model the NMR responses in organic-rich mudrocks and (b) to investigate the effects of wettability alteration and fluid distribution on NMR relaxometry using numerical simulations.
We simultaneously simulate the NMR responses from both water and hydrocarbon phases in organic-rich mudrocks using a random-walk algorithm. The main input to this two-phase NMR simulator is a digital rock matrix reconstructed from 3D pore-scale images of organic-rich mudrock samples, including water, inorganic grains, hydrocarbon, and kerogen. The pore-scale digital images are obtained from FIB-SEM (Focused Ion Beam Scanning Electron Microscope) images. The output of the NMR simulator is the NMR transverse magnetization decay in the rock matrix. The NMR
We successfully simulated NMR