ECI / EEC Reservoir Management Reviews

1
Abstract
The understanding of clay, and its effects on
reservoir performance and log responses is
critical in shaly sands. Equally important as the
volume of clay is the mineralogy and habit or
distribution of the clays. For example, some
laminated reservoirs may have very high clay
volume in the detrital shales but still retain
excellent productivity. Other reservoirs may
have what appears to be an insignificant amount
of authigenic clay and yet the reservoir is
plagued by very low resistivity in the
hydrocarbon zones, or low permeability or
irreparable formation damage. Understanding the
type of clays and their distribution is critical
to establishing a comprehensive understanding of
any shaly sand reservoir. It has long been
observed that the shaly sands of the Malay Basin
present a boomerang-like pattern on a standard
Neutron Density Crossplot. Following on from the
initial work at EPMI by Kuttan et. al., many
companies have developed their own internal
processing to derive a number of reservoir
properties from this distinctive pattern. These
parameters include porosity, shale/clay volume,
permeability, SWIRR, rock strength, acoustic
impedance, cutoffs and petrofacies. This
presentation will attempt to review the history
of the interpretation models and de-mystify the
geological significance of this distinctive
pattern and show how it can be used to determine
all these reservoir attributes. Furthermore,
these clay-rich reservoir facies, in the presence
of fresh to brackish formation water, can result
in low contrast pay. This then increases the
uncertainty in resistivity derived saturation
calculations. An example is shown along with a
general scheme to manage uncertainty, data
acquisition and resources.
2
Bio
Grant Heavysege attended Concordia and McGill
Universities, both in his home town of Montreal,
Canada. After a brief stint in mineral
exploration he joined Imperial Oil in Calgary and
worked there for 10 years. His assignments
initially included plate tectonic reconstruction,
basin subsidence analysis, assessment and
regional geochemistry and stratigraphy of the
North Atlantic margin and the Canadian Arctic
Islands. He eventually evolved into a production
geologist in predominantly carbonate fields in
the Western Canadian Basin and the Williston
Basin. In 1992 he was asked to join the
petrophysics core group and was seconded into
ExxonMobil in Houston, thus starting his career
in petrophysics. Since then he has worked on a
number of development and exploration projects
worldwide, mostly in carbonate and shaly sand
reservoirs, most notably in the Malay Basin of
Malaysia, the North Field of Qatar, and the
Northwest Shelf of Australia. He recently
retired from IOL/ExxonMobil and joined PETRONAS
in Kuala Lumpur as Principal Petrophysicist. He
is a founding member of the FESM and is currently
serving as President.