An appropriate fracturing fluid is one of the key elements for success of hydraulic fracturing treatments. In western Siberia, borate crosslinked polymer fluid has been widely used because of the high viscosity required for placement of large-size proppants. The first step to obtain the viscosity is to hydrate or dissolve a dry form of polymer and prepare a linear gel. This operation requires a minimum temperature of 25°C. Because the average temperature is below 20°C all year and as low as – 40°C in the winter (Fig. 1), this temperature requirement, coupled with the lack of freshwater sources in some locations, presents both logistical and operational challenges.
Figure 1

Average temperature in Tyumen Region, W. Siberia

Figure 1

Average temperature in Tyumen Region, W. Siberia

Water produced from the Cenoman formation is readily available in many locations in western Siberia (Blackbourn Report 2010). With temperatures ranging from 35 to 50°C, Cenoman water could be an ideal source for preparing fracturing fluids. However, the water contains boron and a high level of magnesium and calcium that cause undesirable instant crosslinking of linear gel and shear and thermal instability. To eliminate the impacts of those elements, we introduced a chelating additive to the water to sequester the cations species and optimized the initial fluid pH to improve thermal stability. The concentration of chelating agent is further adjustable to ensure consistency in crosslinking delay time and to provide shear insensitivity.

Using Cenoman water and equipment for continuous mixing of fracturing fluid has greatly improved the operational efficiency and service quality of fracturing treatments in western Siberia. The time to complete a single fracturing treatment was reduced from 2 days to less than 1 day. In some cases, two treatments were performed in 1 day. As of December 2008, more than 500 fracturing treatments had been performed using Cenoman water with an average of over 94% proppant-placement rate.

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