Creation of Porosity in Tight Shales during Organic
Matter Maturation
It has been suggested that porosity and permeability are
created in tight shales during the organic matter maturation
process, i.e. kerogen conversion to oil and gas followed by oil cracking to gas. We have
tested this hypothesis by examining changes in porosity and permeability using
FIB-SEM in both artificially matured shales and by analysis of a variety of shales of varying maturities in the natural setting. Artificial
maturation
(laboratory pyrolysis) was carried out on low maturity samples of the Barnett
Shale by heating them in pressure vessels under argon for a sequence of times
and temperatures to induce oil generation and oil cracking. Porosity and
permeability were recorded at various stages of
maturation
. These experiments
were compared with results from a variety of naturally-matured shales of
varying maturities. Kerogen maturity and hydrocarbon generation were determined
by Rock-Eval pyrolysis. The extent of oil cracking to gas was measured by diamondoid analysis, i.e. quantitative measurements of nanometer-sized
hydrogen-terminated diamonds dissolved in the generated liquids. Our results
show that the process of organic matter
maturation
can produce porosity and
permeability in tight shales. Furthermore, the amount of porosity and
permeability creation differs in different shale types.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California