Petroelastic Modelling as Key Element of 4D History Matching: A Field Example

4D (or time-lapse) seismic is sensitive to changes in reservoir pressure and saturation. It allows monitoring of a reservoir during production, helps define areas of unswept hydrocarbons, and aids planning of infill drilling or pressure support solutions. By improving the reservoir model, 4D reservoir monitoring can improve the accuracy of reserves evaluation and help with the optimisation of reservoir management. This paper describes the preliminary work carried out as part of an ongoing project on 4D reservoir monitoring. The ultimate aim of the project is to history match a field flow model using both production and 4D seismic data. The proposed approach, based on the integration of a reliable petroelastic model (PEM) with a dynamic flow simulator, uses an iterative, gradient-based optimisation method to adjust the initial reservoir parameters. This paper focuses on the assessment of the impact of petroelastic modelling within the framework of 4D quantitative history matching. It shows the results of the procedure that was followed to validate the PEM for the Girassol field in offshore Angola. It addresses the problems of scale usually encountered within a 4D workflow. It also illustrates the results of the sensitivity analysis carried out on the acoustic properties predicted by the PEM when applied to the dynamic flow simulator. In view of the application of the full 4D history matching loop to the field example, possible ways of determining the acoustic parameters and the areas of the reservoir that are most sensitive to 4D effects were assessed and are presented herein. This paper highlights the importance of deriving a reliable PEM when dealing with 4D reservoir monitoring and suggests a way forward for integration with computer-aided history matching processes using both production and seismic data