Acid fracturing

On the other hand, the length of the fracture is shorter, because the acid reacts with the formation and therefore is spent. If traces of fluoride are in the hydrochloric acid, then insoluble calcium fluoride is precipitated out. Therefore plugging by the precipitate can jeopardize the desired effect of stimulation. 

Fluid loss limits the effectiveness of acid fracturing treatments. Therefore formulations to control fluid loss have been developed and characterized 

in particular, and etching agents, in general, may be mixed with a gelling agent and encapsulated with oils and polymers [713,714]. 

A particulate gel breaker for acid fracturing for gels crosslinked with titanium or zirconium compounds is composed of complexing materials such as fluoride, phosphate, sulfate anions, and multicarboxylated compounds. The particles are coated with a water-insoluble resin coating, which reduces the rate of release of the breaker materials of the particles so that the viscosity of the gel is reduced at a retarded rate [205]. 

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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. 

In addition to hydraulic fracturing, there are other stimulation techniques such as acid fracturing or matrix stimulation. Hydraulic fracturing finds use not only in the stimulation of oil and gas reservoirs, but also in coal seams to stimulate the flow of methane from there. 

M. E. Gonzalez and M. D. Looney. The use of encapsulated acid in acid fracturing treatments. Patent WO 0075486A, 2000. 

H. Mukheijee and G. Cudney. Extension of acid fracture penetration by drastic fluid-loss control. SPE Unsolicited Paper, 1992. 

B. D. Sanford, C. R. Dacar, and S. M. Sears. Acid fracturing with new fluid-loss control mechanisms increases production. Little Knife field. North Dakota. In Proceedings Volume, pages 317-324. SPE Rocky Mountain Reg Mtg (Casper, WY, 5/18-5/21), 1992. 

D. J. White, B. A. Holms, and R. S. Hoover. Using a unique acid-fracturing fluid to control fluid loss improves stimulation results in carbonate formations. In Proceedings Volume, pages 601-610. SPE Permian Basin Oil Gas Recovery Conf (Midland, TX, 3/18-3/20), 1992. 

In the third type of acidizing, fracture acidizing, acid is injected above the parting or fracture pressure of the formation. The acid reacts with the minerals on the exposed fracture face in a process called etching. With sufficient etching, the fracture does not reseal when normal well production or injection operations are resumed. 

High fluid injection rates are often required. For this reason, friction reducers are often used in acid fracturing. These include polyacrylamide and acrylamide copolymers, guar gum, hydroxyethyl cellulose, and karaya gum (108)... 

Most of these reservoirs have natural permeabilities below 10 mD, and the stimulation of their production is achieved through acid fracturing operations. Viscosified hydrochloric acid is pumped into wells at pressures larger than formation parting pressure. Irregular etching of the fracture walls by the acid is expected to create highly... 

Pabley, A.S. and Holcomb, D.L. "A New Method of Acidizing or Acid Fracturing Crosslinked Acid Gels," 1980 Proc. Annu. Southwest. Pet. Short Course, Lubbock, April 17-18, 31 38. 

Katona, J., Udovecz, G, and Vas, A. "Acidic Fracturing Fluid for Geological Strata," Chemical Abstracts. 105(18) 155989q(1986). 

Graves, G. and Fellin, E. "Automated Rheology Equipment Facilitates Acid Fracturing Fluid Characterization," Presented at the SPE Computer Technology Symposium, Texas Tech University, Lubbock, March 6, 1986. 

Acid fracturing, friction reducers, 15 Acid hydrolysis, lignin, 173 Acid injection into carbonate reservoir, 610-611 Acid-rock reactions, rate, 15,16 Add wormholing in carbonate reservoirs, 608-620 in carbonate rocks, 610-611 Acidity-controlled redox reactions, 141-142 Addization... 

Foamed Acid Fracturing. The goal of add fracturing is to create a fracture within the reservoir and to etch the sides of the fradure face. Etching of the fracture face with add dissolves a portion of the fradure face and allows a conductive path to be created after the fradure has closed. The further the live add can reach into the fracture, the longer the conductive channel will increase well productivity. 

HMPEOs are soluble in concentrated mineral acids and exhibit superior resistance to thermal degradation in solution 4). Because these copolymers are of low molecular weight, they are less shear-sensitive than high molecular weight commercial poly(ethylene oxide), which can lose 90-95% of its solution viscosity when subjected to high shears at room temperature for 5 min. By contrast, HMPEOs lose no more than 30% of their viscosity in water or acid solution. These unique properties of HMPEOs make them ideal candidates for applications in petroleum recovery via acid fracturing. 

Dextran sulfate sodium fracturing fluids Naphthenic acid fracturing, hydraulic Bauxite fragrance... 

Acid fracturing is an oil well stimulation process in which acid (HCl or HF, depending on the rock structure) is injected into an oil well at sufficiently high pressure to fracture the porous media or to widen existing natural fractures. Various principles of surface chemistry are employed in this process in order to avoid excessive and costly fluid loss, and to decrease the rate of acid spent. 

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