A method of estimating a wettability characteristic of a rock and fluid system includes acquiring a sample of the rock material, performing a first nuclear magnetic resonance (NMR) measurement of the sample when the sample is in a full water saturation condition, and measuring a first T2 distribution, performing a second NMR measurement of the sample when the sample is in a second partial saturation condition, and measuring a second T2 distribution. The method also includes separating a hydrocarbon component of the second T2 distribution from a water component of the second T2 distribution, applying a fluid substitution model to the water component of the second T2 distribution to generate a computed T2 distribution, and calculating a wettability index (WI) based on a difference between the first T2 distribution and the computed T2 distribution.

A method includes deriving spatial permeability along a core axis by saturating the rock with an aqueous solution, performing T.sub.2 NMR on the saturated rock to detect spatial NMR data along the core axis, desaturating the rock, performing T.sub.2 NMR on the desaturated rock to detect spatial NMR data along the core axis, determining the spatial cutoff data for the saturated and desaturated rock along the core axis, and analyzing the spatial NMR data. The method further includes deriving spatial permeability along a second core axis by additionally performing T.sub.2 NMR on the saturated rock to detect spatial NMR data along a second core axis, performing T.sub.2 NMR on the desaturated rock to detect spatial NMR data along a second core axis, and determining the spatial cutoff data for the saturated and desaturated rock along the second core axis.

System and methods for nuclear magnetic resonance (NMR) fluid substitution are provided. NMR logging measurements of a reservoir rock formation are acquired. Fluid zones within the reservoir rock formation are identified based on the acquired measurements. The fluid zones include water zones comprising water-saturated rock and at least one oil zone comprising rock saturated with multiphase fluids. Water zones having petrophysical characteristics matching those of the oil zone(s) within the formation are selected. NMR responses to multiphase fluids resulting from a displacement of water by hydrocarbon in the selected water zones are simulated. A synthetic dataset including NMR T2 distributions of multiphase fluids is generated based on the simulation. The synthetic dataset is used to train a machine learning (ML) model to substitute NMR T2 distributions of multiphase fluids with those of water. The trained ML model is applied to the NMR logging measurements acquired for the oil zone(s).

A method for predicting formation permeability by measuring diffusional tortuosity in several directions by pulse gradient NMR. The method comprises evaluating an anisotropic diffusion coefficient by pulsed gradient NMR, determining diffusional tortuosity from the restricted diffusion data, supplementing the NMR results with resistivity and sonic logging data, measuring anisotropic tortuosity and porosity by resistivity and sonic data and combining all components in a single fitting model. The 11-coefficient model is trained to recognize the true values of permeability by comparing the real oil permeabilities measured in a library of oil-carrying rock cores with the NMR, resistivity and sonic correlates. The fitting coefficients are extracted by minimizing the discrepancy between the laboratory measured permeabilities and the predicted values combining all rapid logging information components with the agreement-maximizing weights.

A nuclear magnetic resonance (NMR) sensor and methods and systems for use are provided. The method comprises disposing a nuclear magnetic resonance (NMR) sensor into a borehole, the NMR sensor comprising a magnet assembly to create a static magnetic field and a first transversal-dipole antenna having an azimuthally selective response function. The method further comprises, while rotating the NMR sensor, initiating azimuthally selective NMR excitation in at least one sensitivity region at a first frequency using the first transversal-dipole antenna and the magnet assembly, wherein the at least one sensitivity region is determined by the static magnetic field and the RF magnetic field. The method then comprises acquiring one or more azimuthally selective NMR signals at the first frequency using the first transversal-dipole antenna.

A method for predicting formation permeability by measuring diffusional tortuosity in several directions by pulse gradient NMR. The method comprises evaluating an anisotropic diffusion coefficient by pulsed gradient NMR, determining diffusional tortuosity from the restricted diffusion data, supplementing the NMR results with resistivity and sonic logging data, measuring anisotropic tortuosity and porosity by resistivity and sonic data and combining all components in a single fitting model. The 11-coefficient model is trained to recognize the true values of permeability by comparing the real oil permeabilities measured in a library of oil-carrying rock cores with the NMR, resistivity and sonic correlates. The fitting coefficients are extracted by minimizing the discrepancy between the laboratory measured permeabilities and the predicted values combining all rapid logging information components with the agreement-maximizing weights.

A method for predicting formation permeability by measuring diffusional tortuosity in several directions by pulse gradient NMR. The method comprises evaluating an anisotropic diffusion coefficient by pulsed gradient NMR, determining diffusional tortuosity from the restricted diffusion data, supplementing the NMR results with resistivity and sonic logging data, measuring anisotropic tortuosity and porosity by resistivity and sonic data and combining all components in a single fitting model. The 11-coefficient model is trained to recognize the true values of permeability by comparing the real oil permeabilities measured in a library of oil-carrying rock cores with the NMR, resistivity and sonic correlates. The fitting coefficients are extracted by minimizing the discrepancy between the laboratory measured permeabilities and the predicted values combining all rapid logging information components with the agreement-maximizing weights.

A method for evaluating drilling fluid includes making an NMR measurement of a sample of the drilling fluid and inverting the measurements to compute a corresponding T1T2 plot. The T1T2 plot is in turn evaluated to characterize the drilling fluid. In one embodiment, a stability index of the fluid may be computed from multiple NMR measurements made while aging the sample.

Methods and logging systems for performing nuclear magnetic resonance (NMR) logging in downhole operations are described. The methods include performing a scout logging acquisition operation using an NMR logging tool to determine NMR logging parameters of a formation interval, setting an NMR logging acquisition mode based on the NMR logging parameters from the scout logging acquisition operation, and performing an NMR data logging operation to determine properties of the formation interval based on the set NMR logging acquisition mode.

A method and microfluidic device to perform reservoir simulations using pressure-volume-temperature (“PVT”) analysis of wellbore fluids.