Experimental Investigation of the Generation and Expulsion Characteristics of Different Source Rocks and the Impact Onto the Composition of Hydrocarbons

Abstract

Reservoir charging history, as well as petroleum composition and quality are highly affected by expulsion and migration, controlled by the nature of the organic matter (OM) and source-rock/reservoir lithology. Thus, studying expulsion and migration effects is essential to obtain an encompassing picture, from generation to reservoir charge, aiming calibration and enhancement of modelling calculations. For this purpose a newly designed apparatus, the “Expulsinator”, was developed and built by the Organic Geochemistry Unit at Kiel University in cooperation with and funded by ENI SpA. The Expulsinator is capable of performing a semi-open hydrous pyrolysis at elevated temperatures (up to 360 °C) by using an intact source rock (Ø 50 mm). The pyrolysis is conducted at pressure conditions (overburden- and pore-pressures) prevailing during catagenesis. Generated products (liquids and gas) are flushed out of the Expulsinator's high-pressure reactor in short intervals during an experiment and collected separately by an automated sampling system. To characterize generation, expulsion and primary migration properties of four different kerogen types and eight different source rock lithologies a standardized experimental approach was developed, simulating burial depths of ∼2000 m, ∼2500 m and ∼3000 m. In general, the source rocks used were of low maturity, with an initial Tmax between 411 °C and 439 °C. The generation/expulsion characterization of the different source rocks indicated that beside the nature of the OM various other factors influenced the expulsion properties of liquid products and gases. Lithology controlled effects, like diverging pressure response (e.g. ductile, brittle, sturdy) and permeability caused variations in product yields and expulsion efficiency. Moreover, molecular parameters were affected by the expulsion process. Molecular size (number of aromatic rings) caused different retention by geochromatography during the migration of the hydrocarbons, leading to fractionation. Molecular sieve adsorption affected the ratio of 2-methylphenanthrene (smaller diameter) versus 9-methylphenanthrene (larger diameter). In contrast, the trend of the pristane/n-C17 ratio were highly systematic for the different kerogen types. Generation effects, leading to a constant decrease with ongoing catagenesis, mainly controlled this ratio. Due to simultaneous generation and migration in most experiments, this ratio has proven to be a suitable expulsion indicator.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016