Development and study of a Visco-Elastic Gel with controlled destruction times for killing oil wells

Abstract

Well-killing operations remain the most complex of all wellbore operations (before proceeding with the workover operation). Using Visco-Elastic Gel (VEG) for well-killing efficiently preserves and reinstates the filtration characteristics of the bottom-hole formation zone. Since these methods exclude the possibility of penetration of well-killing fluids into the reservoirs, the natural permeability of the reservoir is retained. In this article, the authors have reported a new VEG with controlled fracture times that remains appropriate for killing oil wells associated with both terrigenous carbonate reservoir operations. A distinctive feature of the proposed technology using a VEG with adjustable degradation times (which can vary from 3 to 120 h) is that it requires a relatively smaller volume of the composition in comparison with that of the conventional technologies. As a result, a significant reduction in the negative impact on the reservoir is achieved, resulting from a relatively low penetrating ability of the proposed VEG. High structural properties of the VEG make it possible to block the overlapped reservoir interval reliably, excluding the penetration of process fluid into the reservoir. In addition, it also eliminates the flow of formation fluid from the reservoir, which is necessary for trouble-free repair work. It was found from the present study that the use of a breaker of a particular single type does not provide the desired results. The authors have deduced a relatively complex breaker based on peroxyhydrate and citric acid with a 1:1 ratio in the present study. The introduction of the encapsulated peroxyhydrate at the stage of preparation of the VEG ensures the monodispersity of its dispersion characteristics. The developed VEG was successfully tested in 32 wells of oil fields in the Perm Krai fields in Russia. The well-killing technology developed and described in this article using a VEG with adjustable destruction times has successfully been applied in the fields of the Perm Krai. The economic effect of applying this technology was $6.000 per well.