Synthetic mudstone compaction trends and their use in pore pressure prediction

We have compared compaction trends for synthetic mudstones to well logs in order to predict pore pressure in shallow mudstone sequences in the northern North Sea and Vøting Basin, offshore Norway. Well log data showing intervals of higher porosity and lower density than the experimental data may indicate significant overpressure development. The variability found within mudstone compaction trends indicates that mechanical compaction of mudstones varies over a wide range depending on clay mineral type (smectite, kaolinite, chlorite, illite, etc.), particle size, the total amount of clays, sand and silt particles (quartz, feldspar, mica, etc.), nature of pore fluids, and pore pressure. Smectite has low compressibility, velocity, and permeability compared to other clay minerals. The key to successful application of compaction trends to pore pressure prediction, therefore, must be lithological and textural characterization of the individual mudstones. These parameters are predominantly controlled by provenance, facies, and depositional history. This study demonstrates that experimental compaction trends of well characterized synthetic mudstones can be a useful tool to predict pore pressure during shallow burial where mechanical compaction is the dominant process.