Global heavy oil (μ > 100 CP in situ) resources in carbonate rocks are estimated at:
1.6×10 12 BBL [250×10 9 m 3];  one-third is in the Middle East.
Iran has over 50×10 9 BBL [8× 10 9 m3 ], comprising > 40% of Iran's proven oil reserves, mostly in naturally fractured carbonate rocks (limestone and dolomite). Most reported Iranian heavy oil is mobile at reservoir conditions, implying μ < 2000 CP; several have cold-flow tested oils of 6-18°API. Current heavy oil contribution to national production is negligible, partly because appropriate technologies have yet to be implemented. New technologies developed in the last 20 years in Canada constitute a true revolution for heavy oil production, but are not yet applied widely to fractured carbonates. For Iran, assuming ultimate R F of 20% for heavy oil and 30% for conventional oil, heavy oil reserves comprise about 30% of the total recoverable oil.

In this paper, occurrence, geological and reservoir engineering properties in selected heavy oil reserves in Iran are discussed. These selected reserves are technically evaluated for the implementation of several commercialized heavy oil production technologies. Results from this feasibility study show a promising future for some technologies in Iranian heavy oil reservoirs. However, final selection of the most appropriate production technologies requires more detailed reservoir evaluation and technical screening. A complementary research program is recommended for the next stage of technical production technology evaluation for Iranian heavy oil reservoirs in fractured carbonates.