Adsorptive interaction between nitrogen compounds and organic and/or mineral phases in subsurface rocks. Models for compositional fractionation of pyrrolic nitrogen compounds in petroleum during petroleum migration

Abstract

SummaryThe results are reported of a range of laboratory chromatographic fractionation experiments with synthetic model compounds and a petroleum pyrrolic nitrogen fraction. Reversed phase separation of pyrrolic nitrogen compounds was governed mainly by the number of carbon atoms in the molecule, with little selectivity toward different positional isomers, whereas normal phase separation of the compounds could be explained in terms of steric effects related to alkylation position. Comparison of experimental results from model compounds with observations made previously using sets of natural samples taken from sedimentary basins clearly suggests adsorptive interactions between organic and mineral phases are involved in the compositional fractionation of pyrrolic nitrogen compounds in petroleum during migration. Detailed studies of the effects of petroleum migration on the molecular distribution of petroleum pyrrolic nitrogen compounds may provide useful, quantifiable, migration-related geochemical parameters.

Reservoir geochemistry: methods, applications and opportunities

“…There is strong experimental and empirical evidence both for the adsorption of N species onto minerals and for the fractionation of individual N compounds during petroleum migration (Charlesworth 1986;Bonilla &Engel 1988;Brothers et al 1991;Yamamoto 1992;Li et al 1992Li et al , 1995see Krooss et al 1992, for a review of geochromatography in general). Further, enhanced concentrations of some NSO species are found in migration pathways (Miles 1990).…”

“…The experiments also suggest that for a typical fraction such as the carbazoles, adsorption onto rock minerals can be described in terms of normal phase chromatographic fractionation with variable, irreversible adsorption of different isomers (i.e. adsorption from a mobile, low polarity organic phase onto a more polar solid phase; Li et al 1994). Fractionation is chiefly controlled by steric effects related to the alkylation position relative to the active pyrrole functionality (Fig.…”

“…1,8-dimethylcarbazole) are adsorbed less strongly than compounds in which the pyrrole functionality is exposed (e.g. 3,4-dimethylcarbazole;Li et al 1995;Fig. 10).…”

“…Further, enhanced concentrations of some NSO species are found in migration pathways (Miles 1990). Experimental work suggests that pyridinic N compounds adsorb more strongly than pyrrolic compounds (Li & Larter 1993), and that the extent to which individual pyrrolic compounds are adsorbed from a moving organic phase onto a polar surface is determined by steric effects related to the alkylation position relative to the active pyrrole functionality. Compounds in which the pyrrole functionality is shielded by adjacent methyl groups (e.g.…”

Mathematical models of the distribution of geotracers during oil migration and accumulation

“…Kinetic adsorption without diffusion leakage. For some geotracers, like benzocarbazoles, the partition coefficient is negligibly low, <0.00001 (Li et al 1994;Stoddart 1994;Van Duin & Larter 1998). In these cases, the tracer concentration in the pore water is negligibly low and the diffusion of tracers out of the migration channel can be neglected.…”