FULL WAVEFORM INVERSION ON BEKAPAI FIELD: A GAME-CHANGER TECHNOLOGY FOR OUR SEISMIC IMAGING WORKFLOWS

摘要

Seismic imaging of the geological structure of thernBekapai field is challenging. The complex shallowrngeology of the overburden, including fault networksrnin unconsolidated sediments, overshadowed by gasrnclouds, causes several imaging challenges. Largernlateral velocity variations, absorption, shadowingrnzone and push down effects, are hurdles difficult torntackle with conventional depth imaging workflow.rnTotal in-house Full Waveform Inversion technologyrnis addressing some of these challenges. The latestrnhigh-fold long-offset wide-azimuth Ocean BottomrnCable acquisition over the Bekapai field, acquiredrnin 2012, provides a favorable seismic dataset for thernsuccessful application of this technology. FullrnWaveform Inversion is a data-matching waveequation-rnbased tomographic method. The methodrnconstructs a high-resolution velocity model capablernof explaining and characterizing the complex nearsurfacernstructures and properties of the overburden.rnFull Waveform Inversion provides new evidencernwhich reinforces and improves our understanding ofrnthe geology of the Bekapai field. Some of therngeological features, such as relatively thinrncarbonates patches, were already known andrninterpreted on seismic images, but are observed forrnthe first time in a velocity model. The main findingsrnare the extension and thickness of the shallow gasrnanomalies within the gas cloud area, and lowrnvelocity anomalies linked to gas trapped beneathrnshallow normal faults. These latter anomalies werernnever detected before.rnThese low velocities anomalies characterizationrnenables Full Waveform Inversion to resolve somerncomplex image push-downs and concomitantly to improve deeper targets reservoirs imagery. Thernprevious model building methodology which reliedrnon reflection tomography, could not correct forrnthese push-downs. Therefore, Full WaveformrnInversion also constrains the deeper velocity modelrnwhich will be updated by reflection tomography.rnThe integration of Full Waveform Inversion into thernmodel building workflow is the key to its successrnand encourages this approach on similar explorationrnand development projects.