Pyrolysis of Heavy Oil

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In Situ Upgrading

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In Situ Upgrading of Heavy Oil

Recently development has been accelerated in large heavy oil reservoirs in the Orinoco Tar Belt, Figure 1, which contains over a trillion barrels of oil.

While the deposit contains 9-11 API crude oil, many parts are deep enough, warm enough, and contain enough gas to have significant primary (cold) production. However, primary only recovers around 20% of the oil, a diluent is needed in the pipeline transporting the oil to the coast, and a multi-billion dollar refinery is needed to produce salable crude. All of this combines to reduce the value of the asset.

Figure 1 – Location of the Orinoco Tar Belt

Insitu Thermal Visbreaking (pyrolysis) has been studied for several decades, but is not important in most fields because the steam temperature is not high long enough to “crack” much crude. However, Orinoco reservoirs are deep enough, and are being developed with a large enough spacing for much of the oil to be above 540 ^oF (282 ^oC) at least ten years. Figure 2, (calculated from laboratory visbreaking data) suggests that these conditions will result in pyrolysis of a high fraction of the larger hydrocarbon molecules.

These half-lives agree with those calculated from pyrolysis observed in field projects like Peace River. The figure shows that 50 % of the heavy ends and asphaltenes should decompose in 17 years in the regions of a reservoir where the steam temperature is greater than 544 ^oF, i.e., steam pressure of 1,000 psi. At 1,300 and 1,400 psi, around the original reservoir pressure at Hamaca, 50 % pyrolyzes in just a few years.

Figure 2 – Half-Life of Heavy-Oil Molecules

This means that 8 to 15 percent of the heaviest oil components in a 50 Hectare Hamaca pattern pyrolyzes in simulations. Then most of the produced oil has an API gravity of 25 or more, and production almost doubles. Moreover, the oil is lighter, less viscous (transportable) and easier to refine. Results are shown in Figure 3.

Figure 3 – Calculated API Gravity of Crude Oil
Produced in 50 Hectare Models

Figure 3 shows first that steam injection without pyrolysis could produce around 25% of an 11 API crude. This is only slightly more than if the injection wells had been used for continued primary production.

However, if the oil can pyrolyze, and the reservoir pressure approaches 1,000 psi as production is restrained, the API gravity rises to between 20 and 25 API. If steam injection is increased to 1 PV, by injecting at the original reservoir pressure, over 40 % of the oil is produced. The API gravity rises above 25 as the reservoir pressure decreases late in the project. The simulations indicate that the pyrolyzed oil is produced and that coke is left behind. In a formation without too many barriers, injecting into a 50-hectare section can enhance production and API gravity of a 200-hectare section.

Figure 4 – Effect of Insitu Upgrading on Net Project Cash Flow

Moreover, one dollar per barrel is saved because the API gravity of the cracked-produced oil is high enough to not need diluent in the pipeline. In addition, the production of the coastal refineries can be increased, because the oil is already cracked. Finally, the leases should produce at least twice-as-much oil. So fewer wells are needed, total investment will be much less, and the return on investment for projects with integrated production-upgrading facilities could be very attractive.

This study is summarized more completely in SPE 62560. Copies are available through the Society of Petroleum Engineers, or from MK Tech Solutions.

To Discuss Possibilities Please Contact Us At

MK Tech Solutions, Inc. - Houston, Tx - Phone: 281 - 564 - 8851, ASKMKTS@MKTechSolutions.com