Abstract: Class Ⅲ super-heavy oil reservoirs are featured by high crude oil viscosity, low permeability and well-developed interlayers. In the production with steam-assisted gravity drainage (SAGD), there are slow steam chamber expansion, high oil drainage resistance, low production and low oil-steam ratio. In order to solve these problems, a carbamide-assisted SAGD technology was proposed. Its working principle was discovered and key parameters were optimized by the combination of laboratory tests and numerical simulation. The study showed that the carbamide injected into the steam chamber could bed emulsified to reduce the viscosity, enhance oil displacement efficiency and improve water sensitivity. On the basis of the geological conditions and recovery percent, reservoir selection standards were developed and a test well cluster was selected for Well Block Z in Fengcheng Oilfield. An optimal design was developed, with carbamide injection concentration of 60%, injection temperature of 60-100 ℃, injected amount of 42 t, shut-in duration of 60min for injection well, and subsequent steam displacement slug of 10 t. SAGD was then conducted in the production well after 90 min shut-in. Compared with SAGD with pure steam, the average daily oil production increased by 3.8 t/d during the one-year period, the oil-steam ratio was increased by 0.04, the input-output ratio was 1∶5 at an oil price of 1 988 yuan/t in the calculation stage, and the predicted final recovery efficiency was increased by 9.4 percentage points to reach 55.7%. The study results are of great significance to improve the SAGD development effect of Class Ⅲ super-heavy oil reservoirs.

Key words: Class Ⅲ super-heavy oil reservoir, SAGD, carbamide, oil displacement efficiency, recovery efficiency