High Resolution Mass Spectrometry Compositional Comparison of the Heptane Precipitated Asphaltenes and Asphaltenes induced from Reduction of Pressure

Geoffrey C. Klein¹, Andrew Yen², Sam Asomaning ², Ryan P. Rodgers³ and Alan G. Marshall³

^1.  Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306.

^2.  Baker Petrolite, 12645 West Airport Blvd Sugar Land, TX 77478

^3. Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, Florida State University, 1800 E Paul Dirac Drive, Tallahassee, Florida 32310-4005.

Asphaltenes are typically defined by their solubility as benzene soluble and pentane or heptane insoluble. They are believed to exist in the oil as a colloidal suspension, and are stabilized by resins adsorbed on their surface. These components of crude oil are normally in equilibrium at reservoir conditions.  As crude oil is produced this equilibrium may be disrupted by a number of factors including pressure reductions, crude oil chemical composition changes, introduction of miscible gases and liquids, mixing with diluents and other oils, and during acid stimulation, hot oiling and other oilfield operations.

Electrospray ionization (ESI) provides selective ionization of polar N, S, and O containing compounds and combined with high resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) makes a powerful tool for the compositional analysis of petroleum-derived materials such as asphaltenes. In this work we compare the compositional differences between heptane precipitated asphaltenes and asphaltenes collected from live oil depressurization experiments.  The samples were observed by both negative and positive ion electrospray to compare both the acidic and basic species, respectively.  The results suggest that the heptane-precipitated asphaltenes contain a higher double bond equivalence (number of rings and double bonds) compared to the asphaltenes induced by pressure drop. On the other hand, the pressure drop sample seems to have a higher abundance of species containing sulfur.  This work was supported by the NSF National High Field FT-ICR Facility (CHE-99-09502), Florida State University, and the National High Magnetic Field Laboratory in Tallahassee, FL.