Method for evaluation of permeability anisotropy using NMR diffusion measurements for oil and gas wells

A method of determining permeability anisotropy of a hydrocarbon-containing geological formation, comprising:

• a) determining a first 1H self-diffusion coefficient (Db) of bulk water in a portion of the hydrocarbon-containing geological formation where the water is present outside of the pores, by exposing the out of the pore portion of the hydrocarbon-containing geological formation to an NMR pulse gradient along an axis Z of the portion of the hydrocarbon-containing geological formation;
• wherein the out-the pore portion comprises brine flooding the borehole, wherein the brine is measured by NMR prior to flooding, post-flooding samples of the brine extracted from the borehole;
• b) determining a second 1H self-diffusion coefficient (DR) of water in a portion of the hydrocarbon-containing geological formation in a restricted porous environment by an NMR sequence with the magnetic pulse gradient along the axis Z;
• c) selecting the timescale of performing the NMR sequence in (a) and (b) such that the timescale corresponds to the asymptotic minimal values of the restricted diffusion coefficients for the entire pore size distribution;
• d) calculating a diffusion tortuosity value τz as τz=Db/DR;
• e) repeating steps (a)-(d) with the magnetic pulse gradient along any directions in a plane XY perpendicularly to the axis Z of the hydrocarbon-containing geological formation and computing a diffusion tortuosity metric τxy;
• f) determining the permeability of the hydrocarbon-containing geological formation based on a ratio of a plurality of diffusional tortuosity values measured in different directions.