Abstract

Virtually all of the world’s crude oils contains asphaltenes. Our studies and the technical literature show that when crude oil migrates through a reservoir, some asphaltenes are irreversibly adsorbed on rock surfaces. A method has been developed to detect and measure these asphaltenes. The method involves chemical treatment of a sample of core or drill cuttings. The treatment results in an enhancement of the ESR signal universally characteristic of asphaltenes. This enables their detection in the presence of vanadium, manganese, iron, and immature hydrocarbons whose ESR signals are not enhanced by the treatment.

This new technology makes it possible to determine if a crude oil has migrated through a subsurface formation in the geological past. Adsorbed asphaltenes serve as “footprints” for the study of migration pathways. Signals are observed on samples which give no odor, stain, fluorescence, or other indication of petroleum. Vertical migration may be distinguishable from lateral migration. An important application is to forecast updip accumulations from the downdip measurements. The method is rapid and it can be used at the well site during drilling operations. Seven case studies illustrating the use of ESR signal enhancement to answer petroleum exploration questions are given in this paper.