Development of Antifreeze Fracturing Fluid Systems for Tight Petroleum Reservoir Stimulations

Most newly developed oil fields worldwide are ultralow permeability reservoirs, especially the Bakken and Eagle in North America as well as the Erdos and Jimusar in China. Therefore, the technology of stimulated reservoir volume (SRV) has become a critical method to improve hydrocarbon production. However, field operations in the winter season are usually confronted with numerous difficulties. For instance, conventional water-based fracturing fluid and liquid additives are easy to freeze up, and therefore, the gelation performance will be compromised. Accordingly, based on the application performance analysis of current antifreeze additive application status in many fields, several different inorganic salts and alcohols as antifreeze additives were selected. In this study, the formula of the antifreeze fracturing fluid system was designed and optimized based on the evaluations of the addition of different types of antifreeze candidates on the fracturing fluid performance. Results showed that when the environmental temperature was above -15 degrees C, alcohols (e.g., tetraethylene glycol) and inorganic salts with low concentrations could be employed as an antifreeze and they had nearly no negative effect on the viscosity and the cross-linking performance of the fracturing fluid. In this circumstance, the optimum composition was 0.2% hydrocarbon propyl guar gum, 0.2% borax, 1%MJ-1, and 0.5% tetraethylene glycol. In addition, when the environmental temperature is below -20 degrees C, the freezing resistance in the aqueous solution of alcohols was limited. At this time, NaCl with mass ratio higher than 15% showed the best antifreezing effect. However, the large amount of addition of inorganic salts would significantly reduce the viscosity of the fracturing fluid. The optimal concentration of guar gum in the antifreeze fracturing fluid system should increase to 0.4%, and the optimal concentration of borax was 0.3%. In addition, 0.1-0.5% tetraethylene glycol can also be used as an antifreeze if the operation time is less than 6 h. The development of this antifreeze fracturing fluid can further elongate the current fracturing time in winter. Moreover, the experimental results can provide a guide for the field fracturing fluid operation and application.