With the oil and gas industry looking ever deeper for hydrocarbons, well control and completion have become important challenges to overcome. Ultra-deep wells usually have pressured or over-pressured formations and require heavyweight brines to control hydrostatic pressures. Completions that once used fresh water or sea water are no longer feasible due to the much higher pressure requirements, which surface treating equipment cannot sustain. Consequently, the industry has started using heavyweight brines as a base for fracturing fluids. However, the practice is limited by the polymer and the base brine. The most commonly used systems employ NaBr, usually in the range of 11.0 to 12.5 ppg, with a modified guar, buffer, crosslinker and other additives. The systems are finicky and hard to break, and the NaBr brines along with calcium and zinc brines, have increased in cost, prompting a search for alternative, inexpensive solutions.

A newly developed system will viscosity any brine from 11.0 to 19.2 ppg with only gellant and breaker added to the base brine. No buffer, crosslinker or other additives are necessary, which greatly enhances operational efficiency, especially offshore. The unique polymer system creates an association with the salt solution to generate viscosity. The system can be used with lower-cost brine blends such as NaCl/NaBr, CaCl2 and CaBr2. The resulting fluid is very elastic and has excellent proppant transport characteristics. The system can be broken efficiently to achieve good regain conductivity. This paper will present the chemistry and results of complete laboratory testing to evaluate the fluid for fracturing applications.

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