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.