Analysis of Chemical Compositions Injection Combined with Cyclic-Steam Stimulation

Abstract

The paper presents the analysis of cyclic steam stimulation (CSS) application results for producing wells on Permian-Carboniferous deposits of Usinskoye oilfield of high-viscosity oil, the Republic of Komi, Russia. The application of thermotropic chemical compositions for enhanced oil recovery combined with CSS is discussed. Data on treatment of more than 170 cyclic-stean wells for 2017, as well as statistical data on cyclic steam stimulation for 2014-2017 are given. Among the wells considered are both wells treated with steam only, and in combination with chemical compositions of two types, oil-displacing and flow-diverting. The compositions used are thermotropic, using the energy of the injected fluid to activate the necessary chemical reactions, such as gelling or the formation of an alkaline buffer system. Also, the effect of CSS for wells where this treatment is applied for the first time, with wells with multiple CSS (from two to ten cycles), is compared. Experimental curves of efficiency distribution are obtained, expressed in the increase in oil production rate after treatment, for different well groups. The analysis of the efficiency of the CSS on a large data set was carried out, the asymmetries in the efficiency distribution of the wells were revealed, where the CSS was used for the first time. The first CSS cycle, especially when the well is put into operation from inactivity or after drilling, is most effective, the average flow rate after treatment is 24.0 tons/day, with multiple treatments the efficiency is significantly reduced, a decrease to 5.5 tons/day is observed. The influence of chemical compositions of various functional purposes on the efficiency of cyclic steam stimulation has been studied. With repeated CSS, the use of the oil-displacing composition is efficient and reasonable, since one of the main declared functions of the composition is precisely the extra washing of the residual oil. The average yield for repeated treatments with a composition is 10.9 tons per day. The use of the gel-forming (flow-diverting) composition with the CSS reduces the water cut of the product by 30-40%, and stabilizes the average result of the treatments, both at low and high efficiencies, so that application of such a composition is undesirable in wells with a high oil production rate before the CSS, but is valid for highly watered wells. Based on the results of the analysis, it was concluded that for the new wells, the first cycle of CSS is most effective, and the use of chemical compositions is not necessary, but for subsequent cycles, it is recommended to use chemical compositions that will provide afterwashing of residual oil and reduced water cut. For old wells, where no CSS was previously used, it is necessary to evaluate the expediency of using chemical compositions in the first cycles based on the dynamics of the well and the initial water cut.