Mechanism of formation of chromium acetate(Cr3+)/ phenol-formaldehyde resin prepolymer(PRP) complex and its compound cross-linking reaction with polymer for conformance control

摘要

For the heterogeneous oil reservoir with high water cut, the conformance control by using polymer gels is good for increasing oil production and decreasing excessive water. However, facing the current situation of low oil prices, how to improve the exploitation efficiency and reduce the production cost in the maximum extent are still drawing the attention of petroleum engineers. Therefore, it is necessary to further study the polymer gels to achieve this purpose. Among the polymer gels, the polymer/Cr3+ system and polymer/phenolic-formaldehyde compounds system are the most common used, which are suitable for the low temperature reservoir and high temperature reservoir, respectively. Based on the properties of each other, the combination of Cr3+ and phenolformaldehyde resin prepolymer (PRP) as a type of cross-linking agent can not only improve the thermal stability of polymer/Cr3+ gel, but also enable polymer/PRP gel to be applied to low-medium temperature reservoirs, which can further improve the application effect of polymer gels. However, the mechanism of compound crosslinking reaction of Cr3+ -PRP and polymer is still unclear. In this paper, the properties of Cr3+-PRP solution is first tested and then the process of crosslinking reaction of Cr3+-PRP and polymer is study. In the Cr3+-PRP solution, a new polynuclear olation complex ion of chromium (Cr3+-PRP complex) is formed, of which the properties is different from PRP solution or chromium acetate solution. The cross-linking reaction of Cr3+-PRP complex and polymer is compound. During the compound reaction at the temperature of 45 degrees C, the reaction of Cr3+ and polymer has an impact on that of PRP and polymer, so that the reaction of Cr3+-PRP complex and polymer is different from the superposition of the two reaction processes of Cr3+/polymer system and PRP/ polymer system. The formed Cr3+-PRP complex can resist salt to 70,000 mg/L. The experimental results can provide a theoretical guidance for the high efficient practical application of conformance control by using polymer/Cr3+ system or polymer/phenolic-formaldehyde compounds system.