Subjecting a heavy crude oil to mild thermal cracking conditions effects apermanent and significant reduction in its viscosity and specific gravity. Although all crudes are susceptible to cracking, the temperatures and timesrequired usually exceed those required to crack heavy crudes such as thosefound in the Athabasca tar sands. At temperatures below 1000°F, it has already been established that cracking of both pure hydrocarbons and petroleum can bedescribed by first-order kinetic equations. To use this fact, a reference mustbe established by which the amount of upgrading or conversion of crudeconstituents can be estimated. This was done by subjecting both the original crude and the ‘heat-treated’ oil to distillation under identical conditions.The residuum from the distillation of the treated oil was compared to that from the original crude to establish the ‘degree of upgrading.’
From such laboratory tests on a variety of crude oils, it has been possible to estimate the time-temperature history necessary to produce specific degrees of viscosity reduction for each. As a result, it is possible to estimate thefeasibility of utilizing heat in the reservoir to facilitate the production of heavy oil, or of using heat to facilitate the surface handling of oil alreadyproduced.
The permanent upgrading in physical properties occurs so slowly at 500°F that the use of temperatures below this level, as currently practiced with heated pipelines, will effect only a temporary improvement in oil fluidity. Attemperatures in excess of 700°F, coking may present serious operating problems unless residence times are kept very short.
Crude oils of low API gravity and crude oils having a high pour point present production problems both in and out of the reservoir. To overcomesurface handling problems, the oil industry currently practices extensive and expensive blending of light oils and LPG with heavy crudes to make them easily handled in pipelines and storage facilities. An alternative remedial technique involves thermal cracking. Thermal cracking, with its attendant lowering ofpour point and viscosity, was used in Russia many years ago to facilitate the pumping of heavy crudes (1). Egloff and Morrell (2) proposed, in 1926, toseverely crack a high-pour-point oil at the wellhead to eliminate the need for pipeline heaters and diluents.