Physical
Properties of Mudstones During Burial: A Comparison
Between Laboratory Investigations and Well Logs from the Northern North
Sea
and Vøring Basins, Offshore Norway
Mondol, Nazmul
Haque1, Øyvind Marcussen1, Christer B. Peltonen1, Knut
Bjørlykke1, Jens Jahren1 (1) University of Oslo, Oslo, Norway
Mudstones act as source rocks, seals and
permeability barriers in many reservoirs and determine fluid flow in
sedimentary basins. Their compaction behavior and physical properties varies
significantly with depth and have great importance for basin modelling, seismic and well log interpretation. This study
quantifies the compaction behavior and physical properties of mudstones as
functions of effective stress up to 50 MPa. Twelve
brine-saturated synthetic samples were compacted in the laboratory and their
physical properties were compared with well logs through Cenozoic muddy
sediments from the Northern North Sea and Vøring
basins, offshore Norway. Results show that the
physical properties of mudstones are strongly influenced by initial composition
and distribution of minerals, grain size, pore fluids and pore pressure. High smectite content in mudstones produce low permeability
which may generate overpressure thus preserving high porosity and low velocity
in shaley formations. Comparisons of experimental
results and well logs show a good agreement in compaction behavior and physical
properties of mudstones. Mudstones are not uniform lithologies
and may differ in physical properties as much as sandstones and limestones. Changes in density, porosity and velocity as a
function of stress/depth reflect the differences in lithology,
pore pressure and temperature. The default compaction curves provided by the
basin modeling packages may therefore not be a good proxy for the compaction
properties in sedimentary basins. Laboratory compaction trends in association
with well logs may improve prediction of porosity-density-velocity/depth trends
of mudstones, which are extensively used for basin modelling,
exhumation studies and to simulate pressure regime.