Proto-solid bitumen in petroleum altered by thermochemical sulfate reduction

Thermochemical sulfate reduction (TSR) involves a complex series of redox reactions whereby petroleum is oxidized by sulfate forming H2S and CO2. A highly aromatic, sulfur rich carbonaceous residue, which we define as TSR-solid bitumen, is commonly seen in reservoir rocks where TSR has occurred. Using atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry, we find that TSR altered oils and condensates contain highly condensed polynuclear aromatic and naphthenoaromatic species with 0-3 S atoms. These chemical species are not present in petroleum fluids of equivalent maturity that have not experienced TSR and must have been formed by the TSR process. We call these species proto-solid bitumen as they represent the type of organic compounds that could easily precipitate from the TSR altered oils with slight chemical alteration or changes in reservoir conditions. (C) 2011 Elsevier Ltd. All rights reserved.