This paper describes how it is possible to reduce or eliminate the need for dilution of heavy oil before transport in pipelines by partially upgrading in the field with a new technology utilizing molten sodium metal as a scavenger of sulfur, metals and acidity. The paper further describes how the technology works, experimental findings, other benefits of the technology and the development status.
Heavy oil with high viscosity and specific gravity requires dilution with naphtha or condensate to meet pipeline transport specifications. Naphtha often must be transported to the oil production site at great expense. A new technology promises to enable economic partial upgrading at scales in the 1000 to 25, 000 barrel per day range. The process dramatically reduces specific gravity and viscosity enabling pipeline transportation with no or little diluent.
Molten sodium is brought into direct contact with sour heavy oil where it reacts with sulfur, metals and acid groups. The reaction is very fast enabling compact reactors. Sodium sulfide, a solid, is formed, separated and regenerated to sodium and elemental sulfur on site. All of the processes can be housed in pre-fabricated modular containers and transported to the production site for installation.
As mentioned, specific gravity decreases and API gravity increases, typically by 8-10 points. Viscosity is reduced by several orders of magnitude, especially at lower temperatures. Thus diluent requirements are reduced or eliminated, a logistical and financial benefit to producers. Asphaltene content is reduced. For example, pentane insoluble asphaltene is typically reduced by 60% and heptane insoluble asphaltene is reduced by 90%. There also is reduction in the resid fraction. The fraction boiling above 524°C typically is reduced by 35%. Sulphur levels are typically reduced by more than 90%. Metals such as nickel and vanadium are removed from the oil, typically over 98% and 99% respectively – and the metals are recoverable as elemental byproducts. In addition, the total acid number (TAN) is reduced nearly to 0, mitigating corrosivity in the pipeline and downstream processing units. All of these benefits occur typically with volumetric yield approaching 100%.
A key requirement of the process is ability to regenerate sodium from the sodium sulfide. Regeneration is conducted electrolytically at relatively low temperature, less than 150°C. Laboratory scale cells have operated over 13, 000 hours with no deterioration. Elemental sulfur is an additional byproduct produced. An environmental benefit of the entire process is the total absence of sulfur oxide emissions – since no sulfur plant is required.
The Molten Sodium Upgrading process is not complex. The capital intensity and operating costs are expected to be much less than a coker/hydrotreating facility – especially at smaller scales. Overall, this technology is particularly well suited to to improving the economics of producing sour heavy oil where diluent is normally required for transportation to market.