Anomalous concentrations of specific alkylaromatic and alkylcycloparaffin components in West Texas and Michigan crude oils

Abstract

Crude oils produced from a Midland Basin, West Texas reservoir and a Michigan Basin reservoir contain anomalous concentrations of specific members in several alkylaromatic and alkylcyclohexane, homologous series. These components include C 15-alkylated benzene, toluene, xylene, cyclohexane, methylcyclohexane, and dimethylcyclohexane; C 11-alkylated napthalene, methylnapthalene, and tetralin; and C 12-alkylated indane. All compounds have been identified by GC-MS analysis of the oils and separated fractions. In nearly all cases, these anomalous components are several times more abundant than their adjacent homologs, as shown by mass fragmentograms. The consistent domination of C 15-alkylated species through the substituted benzene ( m/ z 92), toluene ( m/ z 106) and xylene ( m/ z 119) series in both oils suggests that these components were all derived from alkylation by a n-C 15 group rather than through ring closure of a higher carbon number compound. The same relationships were observed among alkycyclohexanes as well as alkylbenzenes in the Michigan oil; it showed an additional dominance of C 17-alkylated single ring components. However, the dominant C 11-alkyl substitutent in alkylnapthalenes, alkyl-methylnaphthalenes, and alkyltetralins, plus a dominance of C 12-alkylindane suggest the second ring is formed by ring closure of a C 15-alkylated single ring compound. A series of heating experiments designed to simulate naturally-occurring reactions demonstrated that benzene, toluene, and cyclohexane can be alkylated by long-chain primary alcohols in the presence of kerogen. The effect of kerogen on alkylation appears to be more relevant to the formation of anomalous alkylated species than does the effect of catalytically-active clays.