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.

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.

A nuclear magnetic resonance (NMR) downhole tool and method that may include a housing, a power source, a Radio Frequency (RF) pulse generator tank electrically connected to the power source, a power switch electrically disposed within the RF pulse generator tank and disposed in the housing, and an NMR signal acquisition tank electrically connected to the RF pulse generator tank and disposed in the housing. The method may include disposing the NMR downhole tool into a wellbore, charging a first capacitor with the power source that is electrically connected to the first capacitor, generating a RF pulse, disconnecting the first capacitor from the RF pulse generator tank, and storing energy from the inductive coil in the first capacitor. The method may further include connecting the inductive coil to an NMR signal acquisition tank using a decoupler switch and acquiring an NMR signal with the NMR signal acquisition tank.

A nuclear magnetic resonance (NMR) downhole tool and method that may include a housing, a power source, a Radio Frequency (RF) pulse generator tank electrically connected to the power source, a power switch electrically disposed within the RF pulse generator tank and disposed in the housing, and an NMR signal acquisition tank electrically connected to the RF pulse generator tank and disposed in the housing. The method may include disposing the NMR downhole tool into a wellbore, charging a first capacitor with the power source that is electrically connected to the first capacitor, generating a RF pulse, disconnecting the first capacitor from the RF pulse generator tank, and storing energy from the inductive coil in the first capacitor. The method may further include connecting the inductive coil to an NMR signal acquisition tank using a decoupler switch and acquiring an NMR signal with the NMR signal acquisition tank.

A method comprises determining a Nuclear Magnetic Resonance (NMR) response of a subsurface formation that is based on an NMR response signal that traversed through the subsurface formation and that is result of a magnetic field being emitted into the subsurface formation; determining an Archie cementation exponent for an Archie equation based on the NMR response; and determining a property of the subsurface formation based on the Archie cementation exponent.

Implementations described and claimed herein provide systems and methods for determining surfactant impact on reservoir wettability. In one implementation, a nuclear magnetic resonance T1 measurement of a sample is obtained before surfactant imbibition is applied to the sample, and a second nuclear magnetic T2 measurement of the sample is made after forced imbibition of the surfactant. Moreover, another nuclear magnetic resonance T1 measurement (e.g., omitting surfactant imbibition) can be obtained simultaneously with the nuclear magnetic resonance T2 measurement using a twin core sample. The nuclear magnetic resonance T1 measurement and the nuclear magnetic resonance T2 measurement are captured under simulated reservoir conditions. A fluid typing map is generated using the nuclear magnetic resonance T1 measurement and the nuclear magnetic resonance T2 measurement. An impact of the surfactant on fluid producibility is determined based on the fluid typing map.

Implementations described and claimed herein provide systems and methods for determining surfactant impact on reservoir wettability. In one implementation, a nuclear magnetic resonance T1 measurement of a sample is obtained before surfactant imbibition is applied to the sample, and a second nuclear magnetic T2 measurement of the sample is made after forced imbibition of the surfactant. Moreover, another nuclear magnetic resonance T1 measurement (e.g., omitting surfactant imbibition) can be obtained simultaneously with the nuclear magnetic resonance T2 measurement using a twin core sample. The nuclear magnetic resonance T1 measurement and the nuclear magnetic resonance T2 measurement are captured under simulated reservoir conditions. A fluid typing map is generated using the nuclear magnetic resonance T1 measurement and the nuclear magnetic resonance T2 measurement. An impact of the surfactant on fluid producibility is determined based on the fluid typing map.

A method for determining the concentration of asphaltenes in a solution is described. A model is first established for estimating the concentration of asphaltenes in a solution based on multiple samples of solutions of asphaltenes in the solvent in which the concentrations are known. The multiple samples have varying concentrations of asphaltenes. The diffusivity and relaxation time are measured for each sample using two-dimensional NMR. The ratio of diffusivity to relaxation time for each sample is then calculated. A linear equation is determined to fit the relationship between the ratio of diffusivity to relaxation time and the asphaltene concentration by weight for the multiple samples, thus creating the model. For a given solution sample for which the concentration of asphaltenes is desired to be determined, diffusivity and relaxation time are determined using two-dimensional NMR, and the ratio of diffusivity to relaxation time is calculated. This ratio is then used with the model, so that the linear equation can be solved for the asphaltene concentration in the given solution sample.

A method for determining the concentration of asphaltenes in a solution is described. A model is first established for estimating the concentration of asphaltenes in a solution based on multiple samples of solutions of asphaltenes in the solvent in which the concentrations are known. The multiple samples have varying concentrations of asphaltenes. The diffusivity and relaxation time are measured for each sample using two-dimensional NMR. The ratio of diffusivity to relaxation time for each sample is then calculated. A linear equation is determined to fit the relationship between the ratio of diffusivity to relaxation time and the asphaltene concentration by weight for the multiple samples, thus creating the model. For a given solution sample for which the concentration of asphaltenes is desired to be determined, diffusivity and relaxation time are determined using two-dimensional NMR, and the ratio of diffusivity to relaxation time is calculated. This ratio is then used with the model, so that the linear equation can be solved for the asphaltene concentration in the given solution sample.

This disclosure describes systems and methods to predict viscosity of heavy oil in a geological formation, even when the geological formation also contains water such as clay-bound water, using a downhole nuclear magnetic resonance (NMR) tool. The downhole NMR tools may obtain responses include distributions of a first relaxation time T1, a second relaxation time T2, or diffusion, or a combination of these. The responses of the NMR measurements that are due to water are separated from the responses of the NMR measurements that are due to heavy oil. The responses of the NMR measurements due to heavy oil are then related to likely values of viscosity of the heavy oil based on empirical or simulated measurements.