Previous TalksWednesday February 10th, 2010
The normal compaction of clay rocks is fundamental for understanding overpressure
Philip D. Heppard, ConocoPhillips Company, Houston Abstract Porosity reduction during the burial of clay rocks, compaction, has
been a subject of interest for many years (Athy, 1930, Mondol et. al.,
2007). Besides just the normal curiosity of geologists and
geophysicists about how rocks get to their present state, being able to
predict their properties has practical applications for log analysis,
interpreting seismic data and seismic rock properties, and more
recently shale as a hydrocarbon reservoir, but also is fundamental for
interpreting the presence and magnitude of overpressure. In
overpressured shale we expect porosity to be higher than normal which
should be reflected in the well log response or seismically detected
velocity. Our processes for estimating overpressure in the industry
depend one way or the other on predicting how clay rocks or shale
should behave as a result of varying confining and pore pressure
environments usually summarized by discussion about a normal compaction
trend (compaction prediction). In the published literature interest in
this subject commonly includes the sensible comparison of a number of
normal compaction trends derived by other workers from many basins as
well as the results from compaction studies conducted in a laboratory.
These comparisons show a wide range of compaction trends with the only
commonality being increasing compaction with depth but at any depth a
very wide scatter daunting to anyone who needs to predict this
behavior. An unfortunate consequence can be a general notion that it
is so variable due to a dependence on a large number of geologic
factors that any interpretation of overpressure can be supportable with
plausible explanations. This presentation shows that in most clastic
dominated basins that clay rock compaction is actually fairly well
constrained and predictable. A brief review of the published
compaction trends suggests that outliers are from basins that have
undergone a complicated geologic history and are now out of place and
not at maximum burial depth. Our work supports recent evaluations of
clay rock compaction which indicates, however, that the composition of
the clay rock does significantly affect the rate of compaction.
Lahann, (2002, 2004), Katahara (2003), and Alberty and McLean (2003)
support a similar conclusion that smectite-rich clay rocks will compact
at a much slower rate then illite- or mixed-clay rich clay rocks or
shale. Speaker BiographyPhilip D. Heppard is a principal geologist with ConocoPhillips
in Houston, Texas. Since 1988 Philip has been a pore pressure expert
supporting worldwide exploration and development efforts encompassing
most known petroleum basins and has been a lecturer on pore pressure
for AAPG and related professional organizations. In 2003 he won the
AAPG best international poster award for “Using shear and Vp/Vs to
predict overpressure in petroleum basins” with his four co-authors.
His interest has been the integration of well and seismic data to
predict overpressure in the subsurface for well planning and the
evaluation of seal quality, as well operational support for drilling
wells. He has worked as a development geologist for the Permian Basin,
Texas, and Trinidad, West Indies. Philip received his B.S. in geology
from Juniata College, Pennsylvania, and his M.S. in geology from the
University of Akron, Ohio, some time ago. He joined Amoco Production
Co. in 1979 and then BP after the merger of the two in 1999. He joined
ConocoPhillips Company in February 2006 to become a leading member of
their GeoPressure team within the Subsurface Technology group in
Houston. |