Integrating petrophysical, geological and geomechanical modelling to assess stress states, overpressure development and compartmentalisation adjacent to a salt wall, gulf of Mexico

Abstract

Multi-well pressure data from the Magnolia Field, located on a flank of the salt-bounded Titan passive mini-basin in the Garden Banks area of the continental slope of the Gulf of Mexico, indicate remarkably high overpressures that vary, at similar depths, by up to 10 MPa between sand bodies 1 km apart. In the present paper, we integrate geological and geophysical analysis with 2D forward hydro-mechanical evolutionary modelling to assess the contribution of both disequilibrium compaction and diapir-related tectonic loading to the observed overpressure and to understand controls on pressure compartmentalisation. The 2D finite element evolutionary model captured the sedimentation of isolated sand channels bounded by mud-dominated sediments close to a rising salt wall which led to tectonic loading on sediments. Comparison of results from the 2D and 1D models shows that disequilibrium compaction can explain most of the overpressure as a result of very rapid deposition of mainly mud-rich, low permeability sediments; tectonic loading contributes around 7% of the observed overpressure. The models also show that linked to the high sedimentation rates, small variations in the permeability and connectivity of the mud-rich sections that bound the channel sands result in highly compartmentalised pressure distributions in adjacent sand bodies.