--> Abstract: Maturity-Dependent Biomarker Transformations--A Critical Re-examination, by D. A. Wavrek; #91012 (1992).

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ABSTRACT: Maturity-Dependent Biomarker Transformations--A Critical Re-examination

WAVREK, DAVID A., University of Tulsa, Tulsa, OK

Biomarkers are widely used to establish oil and source rock maturities even though there are significant gaps in our understanding of the actual reaction mechanisms. In this study, three carefully selected crude oils have been artificially matured in 48 separate experiments since the use of oil avoids complications due to generation from kerogen. The pyrolysates were analyzed using GC-FID and quantitative GC-MS for a wide range of compounds. In addition to evaluating the apparent biomarker transformations of isomerization, aromatization, and side chain cleavage, the processes of differential thermal destruction, secondary sulfurization, rearrangement to adamantanes, and predicted fragmentation (formation of the most stable radicals or ions) were evaluated. Data from the laboratory sim lations were complimented by a natural data set.

Experimental results show that nearly all of the maturity-dependent biomarker transformations proceed by differential thermal destruction. Interestingly, the apparent transformations did not appear to proceed until one species was depleted by at least 50% and did not evolve rapidly until depletions reached 80% or more (corresponding to reaction temperatures greater than or equal to 330 degrees C). An exception to this trend occurs when reaction products are derived by a predicted fragmentation. It was also established that the rearrangement to adamantanes and the formation of sulfurized biomarker analogs were insignificant and that elemental sulfur promotes the thermal degradation reactions. Additional data indicate that the occurrence of apparent maturity reversals are a function of ery low biomarker concentrations at advanced maturity levels and that quantitative biomarker concentrations can be used as maturation indicators in laboratory simulations and natural data sets.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)