Practical Kerogen Typing for Petroleum Exploration

Brian Horsfield, Stephen R. Larter

The explorationist requires basic quantitative information on the size, gas-oil ratio (GOR), and timing of petroleum charges. Yet only a part of this crucial information is obtainable from the data currently used to define kerogen types. We describe here a practical approach and solution to this problem by defining kerogen type according to three fundamental criteria. One of these is total hydrocarbon-generating potential, as determined by Rock-Eval pyrolysis (S2). The other equally important criteria are source quality (GOR, wax content, etc), as determined by pyrolysis-gas chromatography (PY-GC), and thermal lability (response to thermal stress), as determined by PY-GC and microscale simulation pyrolysis techniques. With regard to source quality determination, paraffini oil-generating potential (both high wax and low wax), paraffinic-naphthenic-aromatic oil-generating potential (both high wax and low wax), and gas condensate-generating potentials are readily discernible and quantifiable. Concerning thermal lability, the influence of extreme maturation levels on source rock and petroleum composition has been assessed. In the case of some kerogens, bulk compositional features can be preserved to high levels of thermal stress. This means that original oil-generating potential can sometimes be discerned from the analysis of overmature kerogens.

The improved resolution of kerogen types described here offers the petroleum geoscientist the potential for constructing more exact organic facies models and for selecting the most appropriate calibration standards for maturation models. In addition, the measurement of primary GOR values for petroleum charges allows us to model more effectively the volumetric behavior of petroleum during secondary migration. Examples and case histories are presented on Tertiary nonmarine source rocks from Indonesia and the United States, lower Paleozoic source rocks from the United States and Scandinavia, and Mesozoic marine source rocks from northwestern Europe.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.