THE EFFECT OF OIL-WATER-ROCK PARTITIONING ON THE OCCURRENCE OF ALKYLPHENOLS IN PETROLEUM SYSTEMS

Low molecular weight (C-0-C-3) alkylphenols are ubiquitous constituent s of crude oils and formation waters of petroleum systems, and they re present legislatively monitored pollutants in produced oils and waters from offshore petroleum facilities. Their origin and the controls on their abundance are uncertain. Analysis of forty-four oils from variou s petroleum provinces, together with laboratory partitioning experimen ts, has provided further information on these controls. Although pheno ls are clearly partitioned between oil and water in petroleum systems, the consistency of most nondegraded petroleum phenol distributions (d espite the apparent decrease of phenol concentrations in petroleums wi th increasing secondary migration distance) requires phenol partitioni ng between petroleum, water, and solid phases-chiefly kerogen in the c arrier bed. The retention of significant phenol concentrations in petr oleums that have migrated tens of kilometres does indicate that petrol eum typically only equilibrates with minor volumes of rock and associa ted waters. Laboratory experiments indicate that oils which have migra ted similar to 25 km in the North Sea Tampen Spur through Jurassic san dstones may have equilibrated with less than 20 vol of rock and water, and possibly much less than 1 vol, depending on the sorbing phases wi thin the rock (i.e., mineral or organic matter) and the wetting phase (oil or water). We conclude, supporting the hypothesis of Ioppolo-Arma nios et al. (1995), that although ortho-substituted isomers dominate t he phenol distributions of many petroleums, this reflects catalytic al kylation/isomerisation of unknown alkylphenol precursors in source roc ks, rather than selective removal of meta- and para-substituted alkylp henol isomers from petroleum by water washing. Copyright (C) 1997 Else vier Science Ltd.