Etude géologique et modélisations sismiques d'une coupe de la bordure méridionale de la plate-forme urgonienne du Vercors ( France) ; Contribution à la caractérisation sismique d'un réservoir carbonaté.

摘要

The aim of this work is an integrated multi-disciplinary study conceming the seismic modeling and inversion of a realistic 2D geological mode!. The approach which involves an impedance model building, a pre-stack seismic modeling and seismic inversions, is based on the study of outcrops trom a carbonate platform. To build the geo logical model, we focused on the urgonian limestones (Barremian - lower Aptian) and their basement situated on the leeward side of the platforrn, on the south-western part of the Vercors mass if. The outcrops show a semi-continuous exposure of the stratal anatomy from the inner to the outer-slope of the platforrn. Stratal pattern study, associated with cartography and correlation of fifthorder cycles, allowed to build a 16 kilometers long and about 800 meters thick cross-section. By sampling the different Iithofacies, rock physic properties (Vp, Vs, porosity and density) were measured in laboratory. The measured velocities and porosity or clay-content are Iinearly related. The Iinear coefficients were determined and used to build impedance models from porosity values of a real reservoir. The Impedance contrasts will be localized at the top of ail the parasequence of the crosssection. The seismic modeling was perforrned with IWo approaches, a zero-offset ray tracing and a 2D finite differences scheme. The source frequency content was chosen to reproduce the frequency range of standard seismic profiles of oil exploration. Usual as weil as AVO processings were performed on the dataset modelised by fmite difference method to obtain a time migrated profile. The Interpretation of the seismic profiles is compared to the geological mode!. This comparison shows that the stratal pattern is difficult to recover from the interpretation ofthe seismic events in terrns of geometry and pinch-out. Stratigraphie inversion and seismic attributes analyses were carried out on a profile and results were compared to the model geological mode!. The stratigraphie inversion gives impedance profiles close to the original impedance mode!. A lithological prediction was made using the seismie impedance as an attribut and a instantaneous attribut. This attribut discriminate the lithology classes which show the same seismic impedance. After prediction, the lithological section are close to the geological crosssection.