A fracturing fluid system concentrate has been developed for hydraulic fracturing operations. The concentrate contains a hydrated polymer, a clay-control additive, a surfactant, and buffers. It can be combined readily with water to provide the proper base gel viscosity for the desired application. The stored mixing water that is added to the concentrate can be fresh water or seawater. Hydration is instant; therefore, no work tanks are required. Cleanup is simplified because all of the additives are in the concentrate, and the mixing water that is added to the concentrate remains unchanged. Therefore, the unused water can be disposed of without environmental concern.

The concentrate reduces the amount of materials required on location and offers greater flexibility in increasing or decreasing the polymer load during a treatment. The concentrate can be prepared in advance and transported to a location to be used for a treatment. This eliminates the need to mix fluids from dry materials on location and the potential waste of those fluids if the treatment is delayed. The concentrate is stable for long periods of time, and it can be returned or used at another location if necessary.

The ability to change the fluid system viscosity and to stop fluid mixing provides new flexibility in designing hydraulic fracturing treatments and eliminating waste on location if extensive delays occur.

During offshore operations, operators can realize significant cost savings by using readily available seawater instead of freshwater, which must be transported to the site, as a base component for fracturing fluids. Operators in the Gulf of Mexico have successfully used seawater in many fracpack treatments. Using an optimized low-gel (LG), borate-crosslinked fracturing fluid and catalyzed oxidizing breaker instead of conventional borate-crosslinked fluids, operators can increase oil and gas production.1 

The fracturing gel composition can be mixed with seawater, as well as fresh water, to help reduce logistical costs. In a typical treatment, seawater and gel are mixed on-the-fly using the liquid gel concentrate. This process allows operators to run jobs of any size without incurring the tank-cleaning charges associated with batch-mixed jobs. The use of seawater minimizes completion and downtime rig costs by allowing the stimulation vessel to obtain water at sea instead of having to travel back to shore to take on fresh water between fracpack treatments.

Because seawater is more plentiful than fresh water in offshore drilling operations, and because seawater does not have to be shipped to offshore sites, the LG fluid system has been adapted for use with seawater. Seawater contains high concentrations of calcium and magnesium, which precipitate in high-pH fracturing fluids. Previously, large amounts of a caustic agent were added to conventional borate-crosslinked fluids to help stabilize fracturing fluids made from seawater. In solutions with a pH of 10 or greater (levels characteristic of most conventional borates), seawater precipitates solids called hydroxides. The precipitation of these hydroxides consumes the caustic agent added to the fluid. To counter the formation of hydroxides, researchers lowered the pH level of the LG fluid slightly. This lower pH has proved effective in prohibiting hydroxide precipitation.

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et al. 
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Gulf of Mexico Frac-and-Pack Treatments Using a New Fracturing Fluid System
paper SPE 39897 presented at the 1998 International Petroleum Conference and Exhibition of Mexico
Villahermosa, Mexico
March 3-5