Summary This paper presents an integrated workflow for the interpretation of 4D seismic data to monitor steam chamber growth during the steam-assisted gravity drainage recovery process (SAGD). Superimposed on reservoir heterogeneities of geological origin, many factors interact during thermal production of heavy oil and bitumen reservoirs, which complicate the interpretation of 4D seismic data: changes in oil viscosity, fluid saturations, pore pressure, and so on. The workflow is based on the generation of a geological model inspired by a real field case of the McMurray formation in the Athabasca region. The approach consists of three steps: the construction of an initial static model, the simulation of thermal production of heavy oil with two coupled fluid-flow and geomechanical models and the production of synthetic seismic maps at different stages of steam injection. The distribution of geological facies is simulated on a fine grid using a geostatistical approach, which honours all available well data. The reservoir's geomechanical and elastic properties are characterized by logs and literature at an initial stage before the start of production. Production scenarios are run to obtain pore pressure, temperature, steam and oil saturations on a detailed reservoir grid around a well pair at several stages of production. Direct coupling with a geomechanical model produces volumetric strain and mean effective stress maps as additional properties. These physical parameters are used to compute new seismic velocities and density for each stage of production according to Hertz and Gassmann formulas. Reflectivity is then computed, and a new synthetic seismic image of the reservoir is generated for each stage of production. The impacts of heterogeneities, production conditions and reservoir properties are evaluated for several simulation scenarios from the beginning of steam injection to 3 years of production. Results show that short-term seismic monitoring can help in anticipating early changes in steam injection strategy. In return, long-term periods allow the behaviour of the steam chamber to be monitored laterally and in the upper part of the reservoir. This study demonstrates the added value of 4D seismic data in the context of steam-assisted heavy oil production.
This work was presented at the EAGE workshop in Grenoble. Its purpose was to illustrate a stratigraphic modelling approach on a single schematic 2D case and to discuss which sedimentary features are imaged on synthetic seismic sections at different frequencies. The Vercors plateau carbonate sequence, deposited during the Barremian to Early Aptian, was considered. Modelling hypotheses constrained mainly the depositional time length and the geometry of each sequence. In addition, it was assumed that most of the carbonates were produced in situ . The stratigraphic modelling approach and lessons from the simulation results are presented, followed by a discussion of how stratigraphic modelling can be a helpful tool to validate or question the geological model. In order to reproduce the sequence geometries, rates of carbonate production needed to be changed between regressive and transgressive periods. Simulated sea-level changes do not match the geological estimations from field interpretation but they are in agreement with the magnitude of sea-level curve variations, with the exception of the early Barremian sequences. Qualitative and quantitative results from the model simulations help to question or validate the geological model. Stratigraphic modelling provides some insight into the way the carbonate system may have worked. Secondly, for a smaller 2D geological model, several synthetic seismic sections were computed using wavelets of different dominant frequencies. The seismic sections are compared to underline what is imaged mainly at the different frequencies. The presence of two characteristic facies were also analysed. Results show the importance of some thin beds inside thick sequences and that certain sequence boundaries may not be visible at all.
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