Fracturing fluids

As the term propping implies, the agent functions to prop or hold the fracture open. The fluid must have the proper viscosity and low friction pressure when pumped, it must break down and clean up rapidly when treatment is over, and it must provide good fluid-loss control (not dissipate). The fluid chemistry may be water, oil, or acid based, depending on the properties of the formation. Water-based fluids (slickwater) are the most widely used in shale formations because of their low cost, high performance, and ease of handling. 

Because the make-up of each fracturing fluid varies to meet the specific needs of each area, there is no one-size-fits-all formula for the volumes for each additive. In classifying fracturing fluids and their additives, it is important to realize that service companies that provide these additives have developed a number of compounds for different recipes with similar functional 

Source Based on data (2008) from ALL Consulting for a fracture operation in the Fayetteville Shale. 

Some fracturing fluids may include nitrogen and carbon dioxide to help foaming. Oil-based fluids find use in hydrocarbon-bearing formations susceptible to water damage, but they are expensive and difficult to use. Acid-based fluids use hydrochloric acid to dissolve the mineral matrix of carbonate formations (limestone and dolomite) and thus improve porosity the reaction produces inert calcium chloride salt and carbon dioxide gas. 

Proppants hold the fracture walls apart to create conductive paths for the natural gas to reach the wellbore. Silica sands are the most commonly used proppants. Resin coating the sand grains improves their strength. 

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Polyacrylamides are used in many other oilfield appUcations. These include cement additives for fluid loss control in well cementing operations (127), viscosity control additives for drilling muds (128), and fracturing fluids (129). Copolymers [40623-73-2] of acrylamide and acrylamidomethylpropanesulfonic acid do not degrade with the high concentrations of acids used in acid fracturing. 

Tetraalkyl titanates react with organic borates, B(OR )2, to give complexes of the general formula Ti(OR)4 B(OR )2, which are useful as catalysts and cross-linking agents (562). Mixtures of chelated organic titanates such as TYZOR TE and TYZOR LA with alkaU metal borates, such as borax, or boric acid can be used to produce shear-stable fracturing fluids (563). 

A more complete discussion of the rheology and molecular stmcture of HP Guar gels used in fracturing fluids has been pubUshed (564—566). 

Fluid loss additives are also called filtrate-reducing agents. Fluid losses may occur when the fluid comes in contact with a porous formation. This is relevant for drilling and completion fluids, fracturing fluids, and cement slurries. 

Static fluid loss measurements, which are the present standardized testing method, provide inadequate results for comparing fracturing fluid materials or for understanding the complex mechanisms of viscous fluid invasion, filter-cake formation, and filter-cake erosion [ 1806]. On the other hand, dynamic fluid loss studies have inadequately addressed the development of proper laboratory methods, which has led to erroneous and conflicting results. 

A fluid loss additive is described that consists of granular starch composition and fine particulate mica [337]. An application comprises a fracturing fluid containing this additive. A method of fracturing a subterranean formation penetrated by a borehole comprises injecting into the borehole and into contact with the formation, at a rate and pressure sufficient to fracture the formation, a fracturing fluid containing the additive in an amount sufficient to provide fluid loss control. 

A fluid loss additive is described [1849] that helps achieve a desired fracture geometry by lowering the spurt loss and leak-off rate of the fracturing fluid into the surrounding formation by rapidly forming a filter-cake with low permeability. The fluid loss additive is readily degraded after the completion... 

Hydroxypropylguar gum gel can be crosslinked with borates [1227], ti-tanates, or zirconates. Borate-crosslinked fluids and linear hydroxyethyl-cellulose gels are the most commonly used fluids for high-permeability fracture treatments. This is for use for hydraulic fracturing fluid under high-temperature and high-shear stress. 

A low-molecular-weight condensation product of hydroxyacetic acid with itself or compounds containing other hydroxy acid, carboxylic acid, or hydroxy-carboxylic acid moieties has been suggested as a fluid loss additive [164]. Production methods of the polymer have been described. The reaction products are ground to 0.1 to 1500 p particle size. The condensation product can be used as a fluid loss material in a hydraulic fracturing process in which the fracturing fluid comprises a hydrolyzable, aqueous gel. The hydroxyacetic acid condensation product hydrolyzes at formation conditions to provide hydroxyacetic acid, which breaks the aqueous gel autocatalytically and eventually provides the restored formation permeability without the need for the separate addition of a gel breaker [315-317,329]. 

Aq, Aqueous C, cementing Cb, clay based D, drilling fluids FF, fracturing fluids HP, high pressure application HT, high-temperature application LT, low temperature Ob, oil based S, seawater mud SB, salt and brine tolerant. 

A special problem is the refracturing of a previously fractured formation that is contaminated with bacteria. In such a case the fracturing fluid must be mixed with an amount of biocide sufficient to reach and to kill the bacteria contained in the formation. The refracturing of the formation causes the bactericide to be distributed throughout the formation and to contact and kill bacteria contained therein [1181]. 

Fracturing fluids are often classified into water-based fluids, oil-based fluids, alcohol-based fluids, emulsion fluids, and foam-based fluids. 

Fracturing fluids are injected into a subterranean formation for the following purposes ... 

A general review of commercially available additives for fracmring fluids is given in the literature [71]. Possible components in a fracturing fluid are listed in Table 17-2. 

In particular. Table 17-2 reflects the complexity of a fracturing fluid formulation. Some additives may not be used together reasonably, such as oil-gelling additives in a water-based system. More than 90% of the fluids are water based. Aqueous fluids are economical and can provide control of a broad range of physical properties as a result of additives developed over the years. 

Oil-gelling additives Same as crosslinkers for oil-based fracturing fluids... 

However, it has been established that an intense control of certain variables may improve the execution of a hydraulic fracturing job and the success of a stimulation. Therefore an intense quality control is recommended [552,553]. Such a program includes monitoring the breaker performance at low temperatures and measuring the sensitivity of fracturing fluids to variations in crosslinker loading, temperature stabilizers, and other additives at higher temperatures. 

The concentration of an oxidative gel breaker can be measured by colorimetric methods, by periodically or continuously sampling the gel [341]. The colorimetric reagent is sensitive to oxidizing agents. It contains iron ions and thiocyanate. Thus the quantity of breaker added to the fracturing fluid can be controlled. 

Naturally occurring polysaccharides and their derivatives form the predominant group of water-soluble species generally used as thickeners to impart viscosity to treating fluids [1092]. Other synthetic polymers and biopolymers have found ancillary applications. Polymers increase the viscosity of the fi ac-turing fluid in comparatively small amounts. The increase in fluid viscosity of hydraulic fracturing fluids serves for improved proppant placement and fluid loss control. Table 17 summarizes polymers suitable for fracturing fluids. 

Boron-crosslinked galactomannan fracturing fluids have an increased temperature stability. The temperature stability of fracturing fluids containing galactomannan polymers is increased by adding a sparingly soluble borate with... 

Acrylics, A copolymer of 2-ethylhexylacrylate and acrylic acid is not soluble either in water or in hydrocarbons. The ester units are hydrophobic and the acid units are hydrophilic. An aqueous suspension with a particle size smaller than 10 p can be useful in preparing aqueous hydraulic fracturing fluids [776]. 

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