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When Nothing Works!-Prospects for New Geochemical Tools for Defining Petroleum System Properties in Ancient Complex Multicycle Basins-Progress and Prognosis

Steve Larter and Haiping Huang
PRG, Dept Geosciences, University of Calgary, Canada

Many challenges face petroleum systems analysts in old complex basins charged from Lower Paleozooic or Pre-Cambrian strata. In addition to commonly high maturity current source sections and fluids, and often complex, multiple phase tectonics with consequent cap rock failure and/or fluid remigration and mixing phases, such commonly structurally inverted petroleum systems challenge traditional geochemical methods based on the qualitative molecular marker approach or vitrinite reflectance methods.

Despite the obvious conclusion that petroleum mixing is common, petroleum geochemists have continued to use relative abundances of, in particular, saturated hydrocarbon and other biomarkers to a large degree in correlations and maturity and facies assessment of reservoired oils and gas/condensates. This is despite evidence that the concentrations of these compounds vary greatly between source rock types and greatly for single facies source rocks of differing maturities (Li et al ,1995; Wilhelms and Larter, 2004). We have suggested before, an alternative approach is needed which tracks the maturity/ petroleum mass fraction relationships for a reservoired oil (mass fraction maturity) in a more complex but realistic manner and we describe the practical barriers to implementing such a strategy.

In complex, multiple cycle basins being able to directly measure oil charge histories from inreservoir analysis would be a gamechanger in basin assessment, yet a practical method for dating oil field charging time from analysis of crude-oil does not exist. While forward basin models can provide estimates of oil charging times, they are unconstrained by any time dependent measurements that can be made on the crude oil. Nevertheless, age dating oilcharge is now an area of active research (Selby and Creaser, 2005; Larter et al, 2012) and here we review the developments in our group and in others towards this goal.

AAPG Search and Discovery Article #90175©2013 AAPG Hedberg Conference, Beijing, China, April 21-24, 2013