Fracturing Fluids - Then and Now

Abstract

Summary Fracturing fluid provides the means by which the hydraulic fracturing process can take place. All applications of well stimulation by fracturing must include selection of fracturing fluid in the initial phases of fracture design and treatment planning. Fracturing fluid has two important purposes:to provide sufficient viscosity to suspend and transport proppant deep into the created fracture system andto decompose, or break, chemically to a low viscosity to allow flowback of a major part of the fluid to the surface for fracture cleanup after the treatment is completed. Because of the importance of its rheological properties and behavior in the fracture under reservoir conditions during (and immediately after) the treatment, service company research laboratories have spent millions of dollars on R&D of fracturing fluids. Historical Advances, Pre-1960 Since the introduction of hydraulic fracturing for well stimulation in 1948, fracturing fluids have enjoyed a fascinating history. The first several hundred fracturing treatments consisted of relatively small volumes of oil-based fluids to carry graded sand into the created fracture. Initial treatments were conducted with lease crude to ensure compatibility of the fluid with the producing formation. Because of its availability following World War II and the applicability of the gelled-fluid technology to the hydraulic fracturing process, napalm became the first "second-generation" fracturing fluid. With careful mixing and proper timing (before the napalm could set up as a gelatinous solid), many successful fracturing treatments were conducted. The lower pump pressures with higher effective viscosity and proppant transport obtained with the gelled diesel or kerosene marked early acceptance of gelled-fracturing-fluid technology. Variations in the quality of the gelling agent used to prepare the napalm-based gel caused inconsistent gelling rates and gel properties, which made the system extremely difficult to use. In the early 1950's, another gelled-oil system was developed by adding fatty acids and caustic to lease crudes and diesel oil. This use of the saponification (soap making) process to gel oils was widespread among the service companies of the day and allowed further advances in application of hydraulic fracturing. Although this method of gelation provided more dependable fluid characteristics than the napalm system, the saponification process was very sensitive to the presence of water in the lease crude being gelled.