Nuclear magnetic resonance gas isotherm technique to evaluate reservoir rock wettability

A system comprising:

• a nuclear magnetic resonance (NMR) sample cell configured to receive a reservoir rock sample comprising a plurality of porous regions distributed along a longitudinal axis of the reservoir rock sample, wherein the plurality of porous regions have a respective plurality of wettabilities, each wettability representing a quality of each porous region to absorb water;
• a pressure delivery system connected to the NMR sample cell, the pressure delivery system configured to apply a plurality of pressures to the reservoir rock sample in the NMR sample cell;
• a NMR control system connected to the NMR sample cell, the NMR control system configured to, at each pressure of the plurality of pressures, apply a spin-echo single-point imaging (SE-SPI) pulse sequence to the plurality of porous regions distributed along the longitudinal axis of the reservoir rock sample;
• and
• a computer system connected to the NMR control system and the pressure delivery system, the computer system including a non-transitory computer-readable storage medium storing executable instructions to cause the computer system to perform operations comprising:
• constructing a nuclear magnetic resonance (NMR) gas isotherm curve for the reservoir rock sample in response to applying the plurality of pressures and, at each pressure of the plurality of pressures, applying the SE-SPI pulse sequence to the plurality of porous regions distributed along the longitudinal axis of the reservoir rock sample;
• determining the plurality of wettabilities for the plurality of porous regions based on the NMR gas isotherm curve, each wettability of the plurality of wettabilities including a value representing the quality of each porous region to absorb water;
• and
• providing the plurality of wettabilities.

A method comprising:

• constructing a nuclear magnetic resonance (NMR) gas isotherm curve for a three-dimensional reservoir rock sample in response to applying a plurality of pressures to the reservoir rock sample and, at each pressure of the plurality of pressures, applying a NMR pulse sequence to a plurality of porous regions distributed along a longitudinal axis of the reservoir rock sample, wherein the plurality of porous regions have a respective plurality of wettabilities, each wettability representing a quality of each porous region to absorb water;
• determining the plurality of wettabilities for the plurality of porous regions based on the NMR gas isotherm curve, each wettability of the plurality of wettabilities including a value representing the quality of each porous region to absorb water;
• and
• providing the plurality of wettabilities for the plurality of porous regions.