Weyburn Oil Field Seismic Survey Between Horizontal Wells Lays Foundation for CO₂ Injection Tracking  

A cross-well seismic survey was successfully completed in the Weyburn oilfield of southeast Saskatchewan in early September 2000. It recorded high-resolution seismic signals that will be used to help monitor a large-scale commercial carbon dioxide (CO₂) flood in the field operated by PanCanadian Petroleum Limited of Calgary, Alberta.

Two 1,000-meter-long horizontal wells, drilled in a Mississippian fractured carbonate reservoir 1,400 meters deep, were used as a source hole and a receiver hole, respectively. This survey, which is one of the first of this kind in the world, is a joint geophysical research project between PanCanadian Oil Company and Lawrence Berkeley National Laboratory. It is a first step in an comprehensive, multi-disciplinary, injection monitoring program, with the support of International Energy Agency (IEA) Weyburn CO₂ Sequestration Monitoring Research Initiative, the Office of Basic Energy Sciences Geosciences Research Program of the US Department of Energy and other industrial participants including TomoSeis Inc., Trican Well Service Ltd. of Calgary, and OYO Geospace.

A total of 56,000 seismic traces were recorded over 25 hours using 48-levels of hydrophones attached to a 2-3/8" coiled tubing 3,000 m long placed into the receiver well. The data acquisition was a technical success, which opens the door for wider applications of the cross-well seismic technology, which was used in the past only in vertical wells according to PanCanadian. The cross-well survey will be repeated again in the same well pair early next year, 4 to 5 months after CO₂ injection, in order to provide high-resolution time-lapse seismic pictures of how the injected CO₂ gas moves between the horizontal injector and producer, and the interaction of fractures with the various phases of fluids in the affected reservoir.

This sort of detailed monitoring information is critical to understand how the CO₂ is stored in the reservoir rocks during the course of long-term sequestration. In addition to the crosswell seismic monitoring surveys, other new geophysical technologies, including multi-component surface 4-D seismic, multi-component 4-D VSP, single-well sonic imaging in horizontal wells, and passive microseismic monitoring, are used in this field for the monitoring purpose

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