API RP 39:1998 pdf download

API RP 39:1998 pdf download.Recommended Practices on Measuring the Viscous Properties of a Cross-linked Water-based Fracturing Fluid.
1.1.1 Fracturing fluids play a critical role in thc hydrauJic fracturing process for increasing the production of oil and gas in porous media such as sandstones, carbonates, and coal seams. Fracturing fluids must have sufficient viscosity to mitiate and propagate hydraulic fractures, and to suspend and transport propping agcnts deep into the created fracture.
1.1.2 Fracturing fluids should possess the following rheologically associated properties:
a. Sufficient viscosity to create wide fractures and carry propping agents at high concentrations deeply into the producing formation through the fracture.
b. Low treating pipe friction to allow high injection rates in the well tubulars while minimizing surface injection pits.sures and horsepower requiremcnts.
c. Shear stability over the range of shear rates experienced in the pumps, flow lines, weilbore conduits, perforations, and the hydraulic fracture.
d. Thermal stability over the range of temperatures experienced during the treatment.
e. Low to moderate fluid loss properties so that fluid volumes used to create the desired fracture dimensions are minimized, but with sufficient fluid leak-off to allow the fracture to close at the end of pumping.
f. Controlled degradability to allow for moderate to high viscosity during pumping, then breaking to a low viscosity as the fracture closes to allow the fracture fluid to flow back and clean-up.
1.1.3 Water-based, cross-linked fluids are commonly used to fracture treat oil and gas reservoirs. The properties of these fluids can be controlled well enough to provide many of the characteristics desired in a fracturing fluid. For example, cross-linked fracture fluids provide high viscosity at low shear rates in the fracture, but have relatively low friction pressures under the high shear rates in the welibore during pumping. The high viscosity of the cross-linked gels can be reduced (broken) to much lower viscosities at the completion of the fracturing treatment to allow fluid flowback and fracture clean-up.
1.1.4 Typically, the base polymers for preparing cross- linked gels are the following:
a. Guar gum.
b. Hydroxypropyl guar (HPG).
1.1.7 With a given set of additives, the viscous properties of a gel depend on the shear rate, shear history, and thermal history that the fluid has experienced during the mixing and pumping processes. The viscous properties of a cross-linked water-based fluid will be directly related to how the gel is mixed and tested.
1.1.8 The industry has discovered that the viscous properties of a cross-linked water-based fluid vary widely as a function of test procedures. Consequently, to develop rheological models and reproducible laboratory test methods, standardized testing procedures must be used to ensure that the tests fairly represent the typical fluid behavior duiing a fracturing treatment, and the tests can be run with repeatable results in a laboratory.
1.1.9 The industry also needs well developed field procedures for testing cross-linked fracturing gels on location prior to and during the fracture treatment. These tests are necessary for quality control monitoring of the fluids that are actually mixed and pumped during a treatment.