BJORLYKKE, K., F. A. CHUHAN, O. LAUVRAK
Department of Geology, University of Oslo, Norway
Abstract: Constraints on Advective Mass Transfer during Burial Diagenesis
Transport of solids in pore water can be calculated
as a function of the solubility of ions in equilibrium with the most Important
mineral phases. Dissolution and precipitation due to fluid flow is then
a function of the fluid flux and the solubility/temperature gradient. Integrated
fluxes over time exceeding 106m3/m2 are
required to precipitate 10% quartz cement. In the case of aluminum the
required flux for significant mineral dissolution or precipitation is several
order of magnitude
higher. These fluxes are much higher than can be obtained
from compaction driven flow unless the flow is focused by 3-4 orders of
magnitude
. It is therefore no known mechanism which can explain large scale
dissolution or precipitation by advective flow except perhaps increase
of extreme focusing. Mass transfer is difficult to calculate from petrographic
observations and the advective component can not be distinguished from
precipitation and dissolution due to diffusion. Changes in composition
of sandstones and shales with depth can also be due to lateral facies changes.
New data from Jurassic sequences from Haltenbanken and the North Sea show
that precipitation of illite depend on the local availability of K-feldspar
and kaolinite which are the main precursor minerals. The amount of quartz
cement is a function of the temperature and the surface area available
for quartz precipitation. In sandstone with grain coatings of chlorite
or bitumen quartz cementation has been effectively prevented or reduced.
Reservoir quality is therefore linked to provenance and early diagenesis
and there is no evidence that fluid flow play a significant role.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas