Integration of Deep Crustal Seismic Imaging With Measured Heat-Flow Data Significantly Improves Thermal Maturation Modeling, Offshore Brazil and Uruguay

Abstract

More than 12,000 line kilometers of 16-second record length 2D seismic data were recorded in the offshore Oriental del Plata and Punte del Este basins, Uruguay, and in the offshore Pelotas basin, Brazil. Processed through PSDM, these data resulted in 40 km depth images in which the Mohorovic discontinuity (“Moho”) was reliably defined and crustal type and thickness could be determined. Crustal type and thickness data were integrated with measured heat-flow data to establish crustal thickness/heat-flow relationships. Independently, Bouger gravity data were correlated with the same heat-flow data. These relationships allowed heat flow to be mapped over a 700,000 km² area. Heat-flow maps resulting from both relationships were consistent, thereby providing a robust tool by which present-day source-rock thermal maturity could be mapped regionally. Results indicate that: 1. Thermal maturity is driven by crustal heat flow, and that maturation rate is driven by the rate of Cretaceous and Tertiary deposition; 2. Late Cretaceous strata are present-day thermally mature for gas generation in the Rio Grande Cone depocenter, and are thermally mature for oil generation in the area surrounding the Rio Grande Cone depocenter; 3. Early Cretaceous syn-rift strata are present-day thermally mature for gas generation throughout most the study area; and 4. Reservoirs in thermally immature areas to the west (landward) and east (seaward, overlying oceanic crust) could be charged if laterally extensive carrier beds are present. Fluid inclusion stratigraphy (FIS) data, showing paleo-oil columns and probable residual migrated oil, are consistent with independently developed maturity and migration models. Available bottom-hole temperature data also are consistent with maturity and migration models. This study illustrates the value of deep crustal seismic imaging in reliably predicting regional source rock thermal maturation, particularly in areas where geothermal gradient data are absent or sparse.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015