Reservoir Monitoring With Seismic Timeshifts: Geomechanical Modeling for ItsApplication in Stacked Pay

摘要

Production-induced depletion of hydrocarbon and waterrnreservoirs leads to deformation, compaction, displacements,rnand stress changes in the reservoir as well as in thernsurrounding rock. Shell's geomechanical finite-elementrncomputer program was used to simulate this for the depletionrnof stacked oil-saturated reservoir sands from the Mars basin inrnthe Deepwater Gulf of Mexico (GoM), USA. 3D Quantitativerninsight was obtained in the response and mechanicalrninteraction of depleting sands and surrounding mudstones as arnfunction of production. The calculated deformation and stressrnchange were used to model changes in two-way travel time ofrnvertically-propagating seismic P-waves. Comparison of ourrn3D-model results with repeat-seismic 2D field timeshift datarnshows reasonable agreement. This confirms the value ofrnintegrating geomechanics in forward models of seismicrntimeshifts related to depletion, and may find application inrnreservoir fluid-flow monitoring with time-lapse seismic.rnSystematic variation of the depletion pattern in stacked sandsrnof idealised lenticular shapes helped to understand some basicrnaspects of compaction-induced timeshifts, and revealed theirrnpotential and limitations in deep stacked-reservoir settings.rnOur Mars model of compaction-induced timeshifts needsrnfurther calibration to field data, and addition of the saltsedimentrngeomechanical interaction. However, already at thisrnstage, our study suggests that forward models of compactioninducedrnseismic timeshifts can help to better interpret fieldrnobservations of timeshifts, with a promise to detect undepletedrncompartments and fluid-flow barriers in producing reservoirs.