| CPC E21B 49/0875 (2020.05) [G01N 23/2258 (2013.01); G01N 33/241 (2013.01); E21B 49/10 (2013.01)] | 28 Claims |

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1. A method for subsurface characterization, comprising:
obtaining a formation fluid sample;
extracting an oil-water interface from the formation fluid sample;
preparing a solid-phase test sample from the oil-water interface extracted from the formation fluid sample;
configuring a time-of-flight secondary ion mass spectrometry instrument to analyze the solid-phase test sample to determine a mass spectrum of the solid-phase test sample; and
processing the mass spectrum of the solid-phase test sample to determine at least one property of the oil-water interface of the formation fluid sample,
wherein the solid-phase test sample includes surface-active species and solid adsorbed species of the oil-water interface, and
wherein the preparing the solid-phase test sample involves heating or drying the oil-water interface extracted from the formation fluid sample.
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