Determining an uptake capacity of a core sample

A system for determining an uptake capacity of a core sample, comprising:

• a nuclear magnetic resonance (NMR) pressure cell, comprising:
• a test cylinder configured to hold a test fluid and a core sample;
• and
• an NMR coil positioned around the test cylinder and configured to measure NMR spectrum signals of the test cylinder;
• a control system communicably coupled to the NMR coil and configured to perform operations comprising:
• measuring a nuclear magnetic resonance (NMR) spectrum signal of a test fluid at a particular pressure and entrained in a core sample enclosed in a test cylinder of an NMR pressure cell such that an annulus is defined between the core sample and the test cylinder;
• deconvolving the NMR spectrum signal into a first NMR spectrum signal portion that is associated with a first portion of the test fluid in the annulus and a second NMR spectrum signal portion that is associated with a second portion of the test fluid entrained in the core sample;
• and
• determining a mass of the second portion of the test fluid based at least in part on the first and second NMR spectrum signals.