Study on Evaluating Effects of Biocides in Fracturing Fluids with Optical Fiber Tweezer Method

In summer fracturing operation, microorganisms such as bacteria can cause the guar gum fracturing fluids to spoil and lose their effectiveness. Bactericides have thus to be used in the fracturing fluids to kill the bacteria. Presently there is no technical means of evaluating the performance of the bactericides. In this study a method based on optical fiber tweezer (OFT) is presented to evaluate the performance of the bactericides. The saprophytic bacteria are first captured before and after adding a bactericide into a fracturing fluid with a conical OFT, the movement pattern of the bacteria is then analyzed at microscopic scale, and this process can be used to invert the effect of the bactericides. Experimental results show that this method can be used to effectively evaluate the activity of the saprophytic bacteria. After adding bactericides into a fracturing fluid, the cells of the saprophytic bacteria become inactive and the movement distance of the saprophytic bacteria is greatly reduced to about only 0.8 – 0.9 μm. For saprophytic bacteria without contacting with bactericides, the movement distance is generally about 12.1 μm. The study proves that the OFT method is effective in evaluating the performance of bactericides, and it provides a reliable theoretical base for the direct evaluation of the performance of bactericides.