Relationship Between the Petroleum Potential and Structural Evolution of Coals

VU Thi Anh, Tiem¹, Richard Sykes², H. J. Schenk³, Brian Horsfield⁴ (1) GFZ, Potsdam, Germany (2) Institute of Geological & Nuclear Sciences, Lower Hutt, New Zealand (3) FZ Jülich, Jülich, Germany (4) GeoForschungsZentrum-Potsdam, Potsdam, Germany

The New Zealand coal covering the complete maturity range from peat to high volatile bituminous (Suggate, 2000) has been studied in order to relate petroleum potential to its structural and compositional evolution. Both non-extracted and extracted coals, as well as the extracted bitumen itself were analyzed using Rock-Eval, infrared spectrometry and pyrolysis-gas chromatography.

The obtained data shows that New Zealand coal is classified as mixed gas- and oil-prone, HI values increase from 120 to 280 (mg hydrocarbons/g TOC) with increasing maturity. The subtracted-normalised yields between non-extracted and extracted coals were compared with direct yields based on the analysis of bitumen. The important role of bitumen in defining the petroleum generation potential was elucidated. Specially, second order reactions between kerogen and bitumen occurred which reduce the primary gas yield, but increase the potential secondary gas as well as oil yields. The comparative investigation with previously studied higher rank Carboniferous German coals (0.7- 6.1 R0%; Schenk and Horsfield, 1998) showed an excellent fit for both pyrolysis and infrared spectrometry data, suggesting that the New Zealand coals can be considered as natural precursors of the German coals.

References

Suggate, R. P., 2000. The Rank(Sr) scale: its basis and its applicability as a maturity index for all coals. New Zealand Journal of Geology & Geophysics 43: 521-553.

Schenk, H. J. and Horsfield, B., 1998. Using natural maturation series to evaluate the utility of parallel reaction kinetics models: and investigation of Toarcian shales and Carboniferous coals, Germany. Organic Geochemistry 29(1-3): 137-154.