Virtual Outcrop Models and Subsurface Investigation Resolutions: Lessons Learned from Lodève Triassic Deposits (South of France)

Flavia Girard¹, Richard Labourdette¹, and Michel Lopez^2
1TOTAL S.A./Montpellier 2 University, Pau, France
²DESTEEM, Montpellier 2 University, Montpellier, France

Conventional subsurface acquisitions, including borehole or geophysical methods in fluvial systems, are difficult to interpret in terms of sedimentary structures and extensions. Classically, the only direct calibration is available from cores, which only provide one-dimensional information. In this study, subsurface data are interpreted directly with a nearby Triassic outcrop from Lodève area (South of France).

This outcrop was studied in detail in order to characterize sandstone reservoir heterogeneities. Three main paleogeographical units were interpreted from conventional outcrop descriptions, i.e. facies, architectural element geometries and bounding surfaces identification. The units represent (i) braided channel deposits, (ii) meandering sinuous channel deposits and (iii) lagoonal deposits.

Geophysical methods i.e. ground penetrating radar, seismic hammer and borehole acquisitions were performed on a three-dimensional area of 200x100x30m. The integration and spatial positioning of subsurface measurements and outcrop analysis provide the basis for a three-dimensional reconstruction of sedimentary heterogeneities at different scales. Architectural element and facies distributions are achieved according to the spatial coherence of the various acquisition methods.

Interpretations derived from the different acquisitions, are then compared to each other, in order to quantify the degree of determination achieved on sedimentary architectures. This thorough data integration, incorporating outcrop analog description, geophysical acquisitions and borehole investigation methods provide a better understanding of fine-scale sedimentary heterogeneity distributions as well as an estimation of correlation reliability according to subsurface tool resolutions.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas