Diagenetic evolution and implications for the reservoir properties of selected shallow marine and aeolian sandstones.
Three sandstones of varying complexity have been examined with the aim of quantifying
the effects of compaction and quartz cementation upon their diagenetic evolution. Emphasis has
been placed on the scales of heterogeneity, determination of the physical controls on cement
distribution, porosity and permeability.
The shallow marine, Fontainebleau Sandstone provides a relatively simple system in
which to examine progressive porosity and permeability reduction as a result of compaction and
quartz cementation. Cement was precipitated as lenses in response to ground water outflow
during the recent morphological development of the Paris Basin. Conventional modal and
textural analyses using transmitted light proved difficult, because grain/overgrowth boundaries
are poorly defined. However, combined SEM BSE CL and image analysis enabled accurate
quantification of detrital and authigenic quartz, minus-cement porosity and intergranular porosity.
Analyses indicate an extremely mature sand in terms of both mineralogy (100% quartz) and
texture (Fine Upper, Well Sorted). Minus-cement porosity values are high (-33%bv) indicating
that cementation occurred at a shallow depth. The degree of silicification is the dominant variable
control on permeability. Helium porosity and liquid permeability measurements are in the range of
8.6% and 114mO to 26% and 60, the data agree with predicted values.
The distribution of quartz cement, in relation to the Eden Valley Basin structure and
stratigraphy, for the Penrith Sandstone has been examined via literature review, fieldwork and
aerial photographs. Quartz cement is found dominantly north of Cliburn and towards the top of
the formation; the base of the formation lacks quartz cement and has undergone greater pressure
solution. Models for convective fluid flow are proposed to account for the distribution of cement
The Bowscar dune study examines how quartz cement influences dune-scale diagenetic
evolution within a transverse aeolian dune. The Locharbriggs dune is used to compare porosity
and permeability characteristics. SystematiC sampling of cores cut parallel to lamination and
collected horizontally and vertically over the preserved dunes ensured adequate and unbiased
sampling. Modal and textural analysis of the Bowscar dune indicate that dune-scale controls on
quartz cement distribution include effects of primary depOSitional fabric, detrital mineralogy and
compaction. Porosity and permeability measured from the cores give a three-dimensional (3-~)
analysis and demonstrates lateral and vertical variations associated with the distribution of
lamination types within the dunes.
At the lamina scale, 3-D geometrical quantification of detrital framework, quartz cement,
minus-cement and intergranular porosity networks has been achieved using preciSion serial
grinding/polishing, coupled with SEM BSE CL imaging and 3-~ reconstruction techniques.