A practical application of pressure transient analysis (PTA) and 4D seismic for monitoring movement of flood fronts and determination of hydrocarbon saturations in a waterflooded reservoir is presented. A novel workflow for quantitatively integrating 4D seismic data with PTA is described. At the injectors, pressure falloff tests were analyzed to reveal the progression of the flood fronts by using analytical radial composite models. Seismic interpretations of flood fronts were incorporated and refined in the numerical PTA model to examine flood front anisotropies. Sensitivity analysis with numerical PTA of the 4D interpreted flood fronts reduced uncertainties in their size, shape and location. Analytical and numerical PTA techniques were used to determine the range of pressure-saturation conditions in the reservoir at the time of the monitor seismic survey that could explain the lack of 4D signal around the producers. Unique multiphase effects were observed in producers -like the appearance of artificial "humps" in the derivative -which were explained by means of numerical models with gas saturation gradients. Results from the integrated 4D-PTA approach reduced uncertainties in the predicted pressure and saturations around the injectors and producers. The results from these techniques can be used to improve reservoir characterization and reduce uncertainties in remaining reserves. The integrative workflow can lead to upgrades in the reservoir-management strategies, increasing the realized economic value of both PTA and 4D technologies. Application of the integrated PTA-4D techniques allow for early field intervention and optimized placement of development wells.

Strongly absorptive geologic bodies in the near surface, particularly from gas trapped beneath hydrates, have been a significant seismic challenge for the accurate identification and interpretation of deeper oil and gas reservoirs. In this case history, we show how the inverted Q model can compensate for the effects of amplitude loss, phase distortion and velocity dispersion seen in the recently acquired time-lapse ocean bottom node (OBN) surveys. The results of the inverted Q model are located at the same position as the low velocity anomalies derived from full waveform inversion (FWI) and align with the bright shallow structures, giving us confidence in the image compensation using this Q model. The compensation results show that the events become sharper and the structures more coherent for both Q-Kirchhoff PSDM and Q-RTM (Reverse Time Migration) imaging. We also show the impact on the 4D interpretation of the baseline and monitor 4D OBN surveys. Early interpretation results indicate the Q compensated data gives a much closer match between the 4D results and the earth model predictions.

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