Claudia Zoccarato

The role of sedimentation and natural compaction in a prograding delta: insights from the mega Mekong delta, Vietnam

The Vietnamese Mekong Delta was formed by rapid transgression during the second half of the Holocene by deposition of mainly unconsolidated, fine-grained (clayey) sediments undergoing high compaction rates. The natural subsidence can seriously impact the already vulnerable delta plain as its low elevation exposes the delta to global sea level rise, flooding, salinization. Human activities such as groundwater pumping, infrastructural loading, sand mining and dam construction have exacerbated the effects of natural consolidation. Here we present a novel modeling study that has allowed to reproduce the formation and evolution of the Mekong delta over the past 4000 years. Using an adaptive finite-element mesh, the model properly simulates accretion and natural consolidation characterizing the delta evolution. Large soil grain motion and the delayed dissipation of pore-water overpressure are accounted for. We find that natural compaction of Holocene deposits following delta evolution exceeds predicted values of absolute sea level rise. The unprecedented high rates (up to ~20 mm/yr) threaten the lower delta plain with permanent inundation and inevitably reduce the designed service life of flood defense structures along the coast. Total subsidence and sediment delivery to the delta plain will determine its future elevation and vulnerability to relative sea level rise.

Geomechanical Characterization of Storage Reservoirs by Assimilation of Surface Displacements

Gas injection into the subsurface is becoming increasingly popular worldwide in connection with Underground Gas Storage (UGS) and CO2 sequestration (CCS) projects. Depleted oil/gas fields or saline aquifers are strategically used to cope with the growing demand of energy and the planned reduction of the greenhouse efflux into the atmosphere. Due to the pressure increase caused by gas injection, porous rock formations expand and land surface rises. The surface displacements, when accurately measured for example by SAR interferometry, can be effectively used to evaluate the petrophysical and geomechanical properties of the injected formation. In this study, an Ensemble Smoother (ES) data assimilation technique is applied to reduce the uncertainty on the constitutive parameters characterizing the geomechanical model of a UGS field situated in the Po River basin, north of Italy. The assimilation has been implemented using vertical and East-West displacements measured by an advanced satellite technology based on Radarsat scenes collected between 2003 and 2008.