Freshwater sensitivity of glauconitic hydrocarbon reservoirs

Freshwater sensitivity tests were conducted on four glauconite/smectite mixed-layer clays (G/S) with 10–20% smectite content in order to determine whether G/S with low expandability has the potential to swell on contact with fresh water. Tests showed that three of the G/S samples underwent no visible swelling when immersed for up to 4 days in fresh water. In contrast, one sample was freshwater sensitive because, in addition to non-swelling G/S with low expandability, it contained a small component of highly smectitic G/S that rapidly swelled on contact with fresh water. These results indicate that the presence of G/S with low expandability in a hydrocarbon reservoir should not render the reservoir freshwater sensitive, but that individual reservoirs can contain a compositionally-heterogeneous population of G/S grains that may include a highly freshwater-sensitive, smectitic component.