The micro-scale simulation of maturation: outline of a new technique and its potential applications

Abstract

A micro-analytical technique has been developed for artifically maturing sedimentary organic matter and then quantifying the major components generated during this process in a single analytical step. Such a capability is well-suited for examining the compositional relationships between kerogens and petroleums, determining reaction kinetics and making precursor-product mass balances. According to this technique, simulations are made using sealed glass capillary tubes (heated here for three days at 300 °C, 330 °C and 350 °C). Pyrolysis products are then released directly into a combined thermovaporisation/pyrolysis-GC instrument and the major components of the entire C1 yto C35 range can be quantified in a single step using gas chromatography. Alkene yields are very low and pyrolysates are oil-like. This is exemplified by the fact that the n-C9-C19 alkane distribution range of simulated whole petroleum chromatograms, from originally immature Gloeocapsamorpha-typz alginite A, resembles that seen in crude oils generated from this same kerogen type in nature. Sealed tube experiments using Botryococcus type alginite A generated a »high wax« pyrolysate. The relative abundance of n-alkanes in the C2-C32 range of many kerogen pyrolysates does not appear to change significantly despite an approximately fifteen-fold difference in n-alkane yield between the 300 °C and 350 °C experiments. Kerogens which are »paraffinic« oil-prone, and whose pyrolysates are very rich in n-alkanes might therefore generate petroleums in nature with a fixed wet gas (C2-C4) to oil (C5+) ratio. Alginite B in a Greenland shale is much more thermally labile than either Botryococcus-type alginite A or Gloeocapsamorpha-type alginite A. The mass balance capabilities of the technique have been tested using Alum Shale kerogen. Two gas chromatograms were obtained, one for the free compounds generated during simulation, and one for the high temperature pyrolysate of the kerogen residue, for each heating experiment. Precursor-product relationships were qualitatively assessed, and dead carbon formation was quantified in this exercise. © 1989 Ferdinand Enke Verlag Stuttgart.