Experimental and modeling studies on the asphaltene precipitation in degassed and gas-injected reservoir oils

The asphaltene precipitation in a Chinese crude oil has been studied experi mentally under normal-pressure and high-pressure conditions. The onset of a sphaltene precipitation was detected by using light transmission method. No rmal pentane and hexane were used as precipitating agents for studying the onset of asphaltene deposition in (asphaltene + toluene) and (degassed crud e oil + toluene) mixtures under normal pressure. A total of eighteen sets o f normal pressure data have been measured. For high-pressure gas-injected r eservoir oil systems, the effects of injection-gas concentration, temperatu re, pressure, and the presence of a coexisting aqueous electrolyte (brine) phase on the amount of asphaltene deposition were studied and a total of se ven sets of data have been measured. In the modeling part, a modified Hirsc hberg solubility model and a new solubility parameter correlation were prop osed. The model parameters determined from low-pressure precipitation data have been successfully extended to high-pressure systems. Extensive tests v s. the data measured in this work and literature data show that the propose d model is capable of giving reasonable calculation results for most cases. (C) 1999 Elsevier Science B.V. All rights reserved.