FRENCH group CGGVeritas has revealed that it has perfected a seismic monitoring solution for managing steam-assisted gravity drainage (SAGD) production of heavy oil.
Time-lapse seismic reservoir monitoring can be used in conjunction with production well data to improve understanding of reservoir behaviour and to optimise hydrocarbon recovery.
But in heavy oil reservoirs produced using steam-assisted gravity drainage, the reservoir can vary significantly over a few weeks. Furthermore, crucial SAGD production effects may be rapid, but also small, requiring highly sensitive acquisition in this noisy environment.
This is where a seismic monitoring system originally devised for an equally unconventional and challenging application – underground gas storage monitoring – comes into play.
The original system was developed by CGGVeritas, Gaz de France and the Institut Francais de Petrol (IFP) via a joint industry project to provide high-resolution continuous seismic monitoring of a natural reservoir used for the seasonal storage of methane.
CGGVeritas has now reworked the original concept for heavy crude. Moreover, it is designed to be autonomous and utilises buried receiver arrays and a novel piezoelectric vibrator source.
Known as SeisMovie, it is said to be flexible and versatile and capable of a variety of receiver configurations to achieve different monitoring objectives. For aerial coverage over a large target, long arrays or grids of buried geophones can be installed. To increase the vertical sensitivity of the system, arrays of sensors (two, three or four component) can be installed vertically in boreholes to provide vertical seismic profiling (VSP-style) datasets.
The first heavy oil pilot project was conducted in 2005 in Canada. A single buried source and a grid of 397 receivers were used to monitor a shallow, unconsolidated tar sand reservoir for a one-month period of steam injection. Recording was near-continuous, with 240 records per hour being acquired. These were pre-processed automatically onsite and transferred to the office via an internet link for analysis.
The data generated a seamless “movie” of the reservoir and showed the progressive effects of steam injection in unprecedented detail. In particular, the transit time maps revealed the irregular nature of the steam propagation into the reservoir and the corresponding effectiveness of the individual injection wells.
Despite high levels of noise generated by the adjacent steam plant and nearby drilling operations, CGGVeritas claimed the SeisMovie results showed good signal content and bandwidth. There was also good correlation with the available well data, and detailed QC of the continuous seismic record ensured that anomalies could be easily identified and the results validated. Because of the Canadian success, similar monitoring projects are under way in Brazil, Russia and Venezuela.