Catalytic Aquathermolysis Used for Viscosity Reduction of Heavy Crude Oils: A Review

The catalytic aquathermolysis becomes an important area for investigation to solve some of the problems during exploration of heavy crude oil. It has been reported in 1982 by Hyne et al. that metals can accelerate the aquathermolysis and thereafter the uses of several catalysts on this reaction have been studied. It is believed that superheated water passes heat to the hydrocarbon, and some asphaltene molecules are broken down by thermal heat to small molecules. Hence the viscosity as well as flow properties of heavy oil are improved. Moreover, the added heat provides driving force or pressure so that the viscous oils can flow easily and increases the oil production. When the catalyst is present on this reaction system, the viscosity is reduced very deeply. In general the catalysts employed for aquathermolysis are mineral, water-soluble, oil soluble, and dispersed catalyst. The viscosity reduction with these catalysts is in the order of mineral < water-soluble catalyst < oil-soluble catalyst < dispersed catalyst. It has also been found that during aquathermolysis, the saturates and aromatics increase while the amount of asphaltene and resin decreases. The use of different hydrogen donors on aquathermolysis also improves the quality of the heavy crude oil. The most commonly used hydrogen donor is tetralin. Moreover, when tetralin is used with a catalyst, the viscosity is also reduced more effectively. The use of catalysts in the real oil field indicates that the catalysts can substantially reduce viscosity and hence the catalytic aquathermolysis process can be used successfully for exploration of heavy crude oils. However, the oil soluble and dispersed catalysts are slightly more active than the water-soluble catalyst. The cost of the former two types of catalysts may be higher than the preparation cost of simple water-soluble catalysts. Therefore, more research is needed so that the catalysts can be used for this process more economically. Another problem is the efficiency of these catalysts in the oil field. The activity of the catalysts depends on the homogeneity of the temperature in the oil floor. When the superheated water is injected into the oil reservoir, the oil surface temperature is high. However, temperature is gradually lower on the depth of the oil floor, and hence the catalyst loses its activity. So, further investigation is also necessary to address this aspect.