Effect of Hydrogen Donors on Chemical Reactions Involved in the Aquathermolytic Treatment for Downhole Upgrading of Extraheavy and Heavy Oil Under Low Severity Conditions

Diego Sánchez, Cala Miranda**, Solange Rivero, and Yani C. Araujo
Gerencia Esquemas de Explotación, PDVSA Intevep, Apdo. 76343, Caracas 1070-A, Venezuela
** Escuela de Ingeniería de Petróleo, Facultad de Ingeniería, UCV, Caracas 1020-A, Venezuela
email: [email protected], [email protected], [email protected], [email protected]

Extraheavy and heavy oil are an important hydrocarbon resource that represents about three times the conventional oil in the world, especially in Venezuela, which contains the biggest world extraheavy and heavy oil reserves. The major difficulty in the production of these oils is its high viscosity. Thermal recovery techniques, such as steam injection, are effective in temporarily lowering the oil viscosity by heating. Other technologies such as emulsification could assist thermal production. Nevertheless, there are no radical changes in extraheavy and heavy oil molecular structures or components.

However, aquathermolytic technology could upgrade extraheavy and heavy oil downhole under low severity conditions. As a result, contents of heavy components are decreased, or molecular structures transformed, consequently, viscosity is reduced. Aquathermolytic treatment is a potential visbreaking process for extraheavy and heavy oil recovery. Researches on these oils aquathermolysis have been carried out in the past three decade by Hyne, Clark, Liu, Zhong et al. According to obtained results, they suggested that these oils appear to undergo competitive chemical transformations that affect viscosity in opposite ways during aquathermolysis. Either reactive fragments generated can polymerize and thus raise viscosity of these oils, or initiate a series of further reactions that result in generation products which can reduce viscosity even in relatively small amounts [1]. Hydrogen donors are potential to prevent reactive fragments or radical from polymerization according to Ovalles, Vallejos, et al.

In this work, using typical Venezuelan extraheavy oil, laboratory experiments were carried out under low severity conditions in order to investigate the effect of hydrogen donors on chemical reactions involved in the aquathermolytic treatment. As a result, it was observed an important viscosity reduction and an increase of API grades by adding a mixture of hydrogen donors. It was also observed a synergetic effect between hydrogen donors and water used as reactive in the aquathermolytic treatment. Additionally, chemical reactions involved in the process between hydrogen donors and water, according to gas, oil and coke analysis performed, were proposed (Figure 1).

References

[1] Hyne, J.B., Aquathermolysis of Heavy Oils. Second International Conference on Heavy Crude and Tar Sand 1982, Caracas - Venezuela, 25-30.

Figure 1. Proposal of chemical reactions involved in the aquathermolytic treatment with hydrogen donors.

AAPG Search and Discovery Article #90075©2008 AAPG Hedberg Conference, Banff, Alberta, Canada