Many of the currently producing extra-heavy oil fields have entered the closing stage of development, so the correct ceasing of production is a matter of acute importance. This is particularly true for shallow heavy oil reservoirs developed by steam-assisted gravity drainage (SAGD) method involving continuous injection of large volumes of steam into a subsurface formation. The problem is that once the steam injection stops, the injected steam cools and condenses decreasing dramatically in volume and bringing about a sharp decrease of formation pressure. Considering that most of heavy oil reservoirs occur at shallow depths this may be detrimental to environment and can even alter the soil surface.
Various options to cease heavy oil production by example of a heavy oil reservoir in the Sheshminskian formation in Tatarstan developed by the SAGD method were analyzed. The laboratory experiment was modeled on a digital core, and a digital core twin was created to be used in the live reservoir model. Different production ceasing options were considered. A base case provided for steam injection till complete depletion of the reservoir, i.e. development going on in the normal course. Also, options providing for stop of steam injection in different years since start of development were considered and key performance parameters (steam-oil ratio (SOR), cumulative oil production, steam injection) were analyzed.
The paper presents recommendations on criteria for application of production ceasing strategies (stop of steam injection) to cut down steam generation costs, decrease SOR, and minimize oil losses.
References
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