Measurement Strategies and Techniques for Seismic Reservoir Monitoring
Authors: Holberg Olav 
Published: October 2008

Seismically driven reservoir monitoring is an emerging technology which can be expected to have a substantial impact on the E&P industry. The present paper addresses technical issues controlling the success of reservoir monitoring projects, and briefly discusses the relative merits of different seismic data acquisition techniques in the context of offshore field monitoring.

Critical factors for technical success in a seismic reservoir monitoring project include: repeatability in the time-lapse 3D "measurement" of a seismic attribute set which must be sufficiently large to avoid ambiguity in the interpretation, well calibration, and the incorporation of geological and production data.

Seabed seismic data acquisition offers significant advantages for seismically driven reservoir characterization and monitoring of offshore fields, both from a conventional data quality point of view, and because seabed data allow for the measurement of multicomponent data. Permanently installed seismic receiver systems can be expected to represent a particularly cost-effective technique for detailed monitoring of limited areas of critical importance.

Introduction

The E&P challenge has intensified as the most easily exploitable reserves have been found and are being produced. New resources are increasingly found in smaller traps in geologically complex areas, or in subtle traps, not easy to identify and evaluate. Petroleum reserves have thus become progressively more difficult to discover and develop, financial risks have increased, and economic margins have decreased. These factors combine to make optimization a central concern of the oil and gas industry.

For today's producing fields the reliability of reservoir simulation and production forecasting is often limited by the accuracy of the reservoir description. Many failures in pilot and field-wide EOR projects can be attributed to the poor quality of the reservoir model used to simulate the process; the decision to go ahead with the project had been based on over optimistic forecasts of reservoir performance, which were mainly the result of an inadequate description of reservoir heterogeneity.

Seismic measurements are the main source of information on the reservoir away from wellbores. It is a continuing trend to extract reservoir-related information from seismic, in addition to the usual structural information. Of particular interest today is seismic reservoir monitoring, or 4D where the fourth dimension is the time-lapse of the 3D seismic surveys. See I for a review of the state of the art of seismically driven reservoir monitoring

Staging 3-D seismic surveys over time to monitor a producing reservoir not only can establish where fluids are today versus yesterday, but also can be used to more accurately predict future fluid movement. They also help to identify bypassed oil and hydraulic barriers, and can reduce the risk of early breakthrough and lost wells. Field operations can thus be modified more efficiently to maximize reservoir productivity (more production from fewer wells) and percentage of recovery.

The 4D seismic technique is a natural one for fields about to enter production. The opportunity to conduct a baseline survey over a field prior to initiating production opens many possibilities for using the surveys that follow to optimize reservoir management.