A new hydraulic fracturing system has been developed and tested in both oil and gas wells. The fluids used are viscous polymer emulsions made from commonly available lease fluids such as crude oil and brine. By varying the oil and polymer content, the properties of the system can be easily controlled. Relative to other viscous fluid systems, for comparable results the costs are much less.
Summary and Conclusions
In the past 5 years, viscous fracturing fluids have been shown to have advantages over conventional, low-viscosity gelled-water fluids. Many viscous fluid systems were developed and tested with various degrees of success. The main limitations of those fluids are their high cost and, in some instances, the difficulty of removing the fluid from the formation.A new hydraulic fracturing system has been developed and tested under a variety of field conditions in both oil and gas wells. Fluids used in this system are viscous emulsions prepared with a lease crude, refined oil, condensate or liquefied petroleum gas as the internal phase, and water, brine, or acid containing a water-soluble polymer and a surfactant as the external phase. This adaptable fluid system is inexpensive, its properties can be controlled, and it breaks readily after the treatment, permitting the injected fluids to be easily produced from the formation.Properties of these emulsion fluids are controlled by varying the polymer concentration in the water and the volume of oil in the emulsion. Sufficient polymer is used to provide the aqueous phase with an polymer is used to provide the aqueous phase with an apparent viscosity from 10 to 100 cp at 75 degrees F and at a shear rate of 511 sec(-1). The concentration of the dispersed oil phase is maintained between 50 and 80 volume percent.For field applications, the preferred emulsion contains from 60 to 75 volume percent oil and from 1 to 2 lb of guar per barrel of water or brine. This composition is generally chosen since it can be emulsified easily and allows for a margin of mixing error. The fluid viscosity will be too low if the oil content is 50 percent or less, and the emulsion may become unstable or too viscous if the oil content is greater than 80 percent.A surface-active emulsifier capable of forming an oil-in-water emulsion is added to the aqueous phase at a concentration of about 0.5 percent by weight to help form the emulsion and temporarily stabilize its properties. The two basic types of surfactants used properties. The two basic types of surfactants used for this application are sodium tallate (for fresh water) and a quaternary amine (for brine; i.e., water containing more than 10,000 ppm chlorides). A fluid loss additive (FLA) - normally a mixture of silica flour and a commercial additive composed of particles coated with a water-soluble polymer - may be added at a concentration of 20 to 40 lb per 1,000 gal of emulsion.Polymer emulsion fracturing resulted in an average production increase of 3.4 for 97 Exxon Co. U.S.A. production increase of 3.4 for 97 Exxon Co. U.S.A. oil and gas wells treated in 1971 and 1972. Clean-up after these treatments was rapid and most gas wells were placed back on production without swabbing.
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