Borehole neutron measurements are routinely used for in situ rock assessment in hydrocarbon reservoirs. We have used gadolinium oxide nanoparticles for enhancing the sensitivity of macroscopic thermal neutron absorption cross-section (Sigma) measurements of rocks. The gadolinium-based doping agent is used due to its exceptionally high neutron absorption cross section, low cost, and availability; it is also shown to preserve or enhance the differentiation between pore fluids. Injected from a pilot well, the doping agent could thus substantially improve the precision of Sigma-derived saturation measurements. Computational modeling verifies that modest gadolinium concentrations in the rock’s pore volume give rise to significant enhancement of reported Sigma: A concentration of 1750 weight ppm is shown to offer superior contrast enhancement across a wide range of rock solid and fluid compositions. Preliminary experimental work confirms the reported effects obtained with computational modeling of gadolinium doping in simulated porous rocks.

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