Eric Forgues

Modelling of 4D Seismic Data for the Monitoring of Steam Chamber Growth During the SAGD Process

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 formulae. 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. These modifications of the stress state may imply deformations that can, in turn, have an impact on reservoir production. These changes also have an influence on wave propagation into rocks and fluids and may consequently produce differences on seismic velocities and on the travel time. The objectives of this work are to evaluate the impact of reservoir heterogeneities on steam chamber growth and to improve the interpretation of 4D seismic data in steam-assisted production. The study is based on a heavy oil field of the Canadian Athabasca McMurray formation. Two periods of SAGD production are studied in detail: the early steam injection and later on when the steam chamber develops laterally and vertically toward the top of the reservoir.

Simultaneous active and passive seismic monitoring of steam-assisted heavy oil production

The world-class heavy oil reserves of Canada represent a significant resource for North America which is free from the geopolitical uncertainty currently affecting conventional oil supplies in some parts of the world. Energy security and the current sustained oil prices make heavy oil extraction an attractive proposition.

Continuous High-Resolution Seismic Monitoring of SAGD

We used a pre-existing buried geophone array located on a heavy oil SAGD (Steam-Assisted Gravity Drainage) pilot project in Alberta. This array has been used to evaluate the ability of a new seismic technique based on permanent sources and receivers to provide a fast indicator of steam motion. The high repeatability of this technique enabled observation of the steam’s progression over a period of one month.

Use of Ambient Noise to Enhance Low Frequencies Seismic Migration Images

In this study, we propose an example of body wave retrieval using ambient noise correlation. The correlated data are migrated using a Kirchhoff pre-stack time migration (PSTM) and then with the migration obtained with conventional active data. It allows to considerably broaden the final image spectrum toward the low frequencies.

4D Pre-stack Time Migration - Application to Thermal EOR Monitoring

In 4D seismic, the velocity model used for imaging and reservoir characterization can change over calendar time as the reservoir is produced. This is particularly true for heavy-oil reservoir produced by steam simulation (EOR). We propose an automatic 4D update of the 3D velocity model using an efficient technique based on 4D pre-stack time migration (4D-PSTM) that describes the pre-stack differential kinematic effects by matching the 4D dataset. On real continuous 4D seismic data, the 4D-PSTM allows us to quantify interval velocity variations that can be used to map temperature changes in the reservoir in agreement with petro-elastic model expectations.