4D Joint Stratigraphic Inversion of Prestack Seismic Data: Application to the CO2 Storage Reservoir (Utsira Sand Formation) at Sleipner Site

Abstract : Seismic monitoring is commonly used in the oil industry to follow the evolution of reservoir properties during production. We present a methodology of time-lapse (or 4D) stratigraphic inversion, which is able to provide an estimation of P- and S-wave impedance variations in the reservoir by inverting prestack time-lapse seismic data. The 4D inversion is implemented in the time domain and requires a time scaling law for each repeated seismic dataset in order to adjust the arrival times of homologous events observed in the so-called reference and monitor datasets. This operation is often referred to as the warping problem. The 4D inversion is a 3-step methodology. The first step consists in inverting each seismic vintage independently, thus providing as many P- and S-wave impedance distributions as datasets considered. The second step uses the available P-wave impedance information to solve the warping problem which is crucial to the third and final step: the joint inversion of all available seismic vintages.This 4D inversion sequence was applied to seismic datasets recorded on the Norwegian CO2 storage reservoir of Sleipner field located in the North Sea. The latter is becoming a reference industrial site for the long-term storage of carbon dioxide (CO2) in a saline aquifer, the Utsira sand formation. We focused our 4D inversion study on the 1994 and 2006 vintages acquired two years before and ten years after the beginning of CO2 injection, respectively. The warping correction resulted in a time-scaling law with a maximum pushdown effect of about 45 ms at the base of the Utsira aquifer. The joint 4D inversion results show more consistency than the single 3D inversion results: the 4D inversion notably provides P-wave impedances for the CO2 -saturated sandstones which are close to the values derived from rock physics studies.
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K. Labat, N. Delépine, V. Clochard, P. Ricarte. 4D Joint Stratigraphic Inversion of Prestack Seismic Data: Application to the CO2 Storage Reservoir (Utsira Sand Formation) at Sleipner Site. Oil & Gas Science and Technology - Revue d'IFP Energies nouvelles, Institut Français du Pétrole, 2012, 67 (2), pp.329-340. ⟨10.2516/ogst/2012006⟩. ⟨hal-01936477⟩

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