Tangleflags project is a highly successful example of a Steam Assisted Gravity Drainage (SAGD) process operated by Canadian Natural Resources Limited. The original reservoir conditions were unfavourable for steam injection : the reservoir has a small gas cap and an active bottom water, which made the primary production very unattractive. However, a judicious application of steam injection with horizontal producers made it a show case project.

This study examines the Tangleflags type of projects from the point of view of future applications (screening and design) of the SAGD process. A thermal simulator (STARS) was used, to achieve a history match of six-years' performance. Predictions for 15 years showed continued encouraging operations.

The second phase of the study involved examination of reservoir parameters and operating conditions that would lead to a successful project. For example, it was found that without using conditions of a steam trap, the steam-oil ratios would be high. Pools with oil viscosities higher than 35,000 mPa.s, and oil zone thicknesses less than 15 m were found to be unattractive. Vertical injectors (rather than horizontal), appeared to be more desirable, with an improvement in performance as the injectors are placed farther from the horizontal producer. Optimal well spacing in such a scheme, seemed to be dependent on the mobility of oil in the reservoir. Presence of an active aquifer below the formation results in severe water coning after a few years from the start of steam injection.

The results of this study are expected to be helpful in planning a Tangleflags type operation in heavy oil pools containing mobile oil, where vertical steam injectors are used around horizontal producers.

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