Economic Benefits of Gas Injection in Steam-Assisted Gravity Drainage (SAGD) Wind Down

PTAC Petroleum Technology Alliance Canada

March 31, 2016

 

Executive Summary

SAGD is the dominant technology for in situ oil sands production. After approximately 10 years, the production from a well pair (injection and production wells) will decline and eventually become uneconomical. SAGD operations would then proceed to a wind down phase whereby the well pair would be taken off steam injection and production. However, several issues may arise that would require attention. For example, the steam chamber of a shutdown well pair may act as a thief zone and affect production and steam to oil ratio (SOR) in neighboring producing well pairs. Also, buffer zones between well pairs or projects in the same oilfield may be as wide as 200 meters, resulting in a loss of reserves. Furthermore, enhanced recovery may be possible with in situ combustion in order to recover the oil-in-place not recoverable by SAGD, but only if the flue gas from in situ combustion would not negatively impact adjacent well pairs that are still producing in SAGD mode.Recognizing the challenges posed by the SAGD Wind Down process (i.e. the end of life of a SAGD well pair), Petroleum Technology Alliance Canada (PTAC) proposed the project “Technical and Economic Benefits of Gas Injection in Steam-Assisted Gravity Drainage (SAGD) Wind Down” for ecoEII funding. The Project was awarded $97.5K from ecoEII to study the SAGD Wind Down process, generate reservoir engineering information and find solutions that will minimize negative environmental and cost impact of depleted SAGD reservoirs on adjacent producing SAGD well pairs.
The Project was undertaken by PTAC in collaboration with Devon Energy, Husky Energy, Nexen, Statoil Canada, Suncor Energy, Alberta Innovates Technology Futures (AITF), and Computer Modelling Group (CMG). To set the stage for the Project, a workshop was held to discuss the merits of various technologies in SAGD Wind Down and maintenance modes. The workshop was attended by oil sands operators and provided a unique opportunity for attendees to discuss various strategies to maximize value from old and mature SAGD reservoirs, including the injection of NCG (air, O2, CO2, CH4), or electrical heat to maintain pressure in depleted areas.

 

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