A NEODYMIUM ISOTOPIC STUDY OF CRUDE OILS AND SOURCE ROCKS - POTENTIAL APPLICATIONS FOR PETROLEUM-EXPLORATION

Neodymium isotope compositions were measured in source rocks, hydrous pyrolysate and crude oils from several different oil producing basins. The Sm-Nd characteristics of the source rocks suggest that there are sufficient differences in the Nd-143/Nd-144 ratio of potential source rocks to distinguish them from one another on both a regional and local scale. The Nd isotope ratio of the hydrous pyrolysate is identical to that of its source rock, suggesting that the Nd of the source rock kerogen is in isotopic equilibrium with the inorganic portion of the rock. Sm and Nd concentrations in crude oils are low, reflecting a retention of organically associated metals in source rocks during primary migration, possibly caused by a lack of appropriate chelating sites in the expelled hydrocarbons. Oils that have undergone extensive secondary migration have higher Sm/Nd ratios than do their source rocks and oils which have not undergone appreciable secondary migration. The reason for this apparent fractionation of Sm from Nd is not known. The previously hypothesized genetic relationship of two presumed source rock-oil pairs is supported by matching initial Nd isotope ratios. Although the results from this work are preliminary, the data show promise that Nd isotope ratios may serve as a correlation tool in matching crude oils with their source rocks.