Acidizing stimulation method using viscoelastic gelling agent

Abstract

A method of acidizing a subterranean formation involves the use of a composition containing a solution of a viscoelastic amidoamine oxide surfactant and an HF-containing acidizing solution. The composition typically contains from about 0.1 to about 8 weight percent of surfactant solution and from about 92 to about 99.9 weight percent of HF-containing acidizing solution. The composition is pumped into the subterranean formation. As the acid reacts, the composition viscosifies and becomes a self-diverting agent created in-situ. When the acid is further spent, the fluid viscosity declines eventually returning to a low viscosity state, allowing for easy cleanup. The process allows for selective acidizing of less permeable zones of the formation and more uniform stimulation of the hydrocarbon bearing formulation.

Description

[0001] This application claims the benefit of U.S. patent application Ser. No. 60 / 530,577 filed on Dec. 18, 2003.FIELD OF THE INVENTION [0002] The present invention relates generally to the field of stimulating sandstone formations of oil and gas wells by use of an acidizing solution containing hydrofluoric acid and a viscoelastic gelling agent. BACKGROUND OF THE INVENTION [0003] Subterranean sandstone or siliceous formations in oil and gas wells have been treated in the past with acid treatments to increase their permeability, thus enhancing the flow of hydrocarbons to the wellbore, thereby increasing or improving production from the formation. As used herein the term “siliceous” refers to the characteristic of having silica and / or silicate. Most sandstone formations are composed of over 50-70% sand quartz particles, i.e. silica (SiO2) bonded together by various amounts of cementing material including carbonate (calcite or CaCO3) and silicates. [0004] Acidizing can cause the dissol...

AI Technical Summary

Benefits of technology

[0011] Typically, introduction of the composition of the invention into the formation is preceded by a preflush and, optionally followed by an overflush; the preflush and overflush generally consisting of hydrochloric acid and / or ammonium chloride. Other flush systems known in the art, such as acetic or formic acid solutions, may also be used. Other suitable preflushes, such as those disclosed in U.S. Pat. No. 6,443,230, herein incorporated by reference, contain citric acid and a phosphonate compound. One reason for pumping these flushes is to dissolve carbonate minerals within a certain distance of the wellbore, prior to injecting the composition of the invention, thereby minimizing the risk of damage that could be caused by precipitating insoluble calcium fluoride. Another reason is to maintain low pH conditions to remove protective films that can form on some formation minerals or to reduce iron hydroxide precipitation.

[0013] The fluid system of the invention is further void of polymers, thereby reducing any potential damage the fluid may do to the formation. For instance, the composition of the invention minimizes rock disaggregation at the interface of the acid and rock.

Problems solved by technology

Such attempts proved to be inefficient as the fluid would often react or spend too quickly; and therefore be incapable of penetrating deep into the formation, thereby limiting effectiveness to very near-wellbore applications.

The precipitation products plug pore spaces and reduce the porosity and permeability of the formation, thus impairing flow potential.

Because clays are normally a part of the cementitious material that holds the sand grains of sandstone formations together, the dissolution of clay also weakens and de-consolidates the sandstone matrix in the vicinity of the wellbore, thus causing damage to the formation.

While such methods allow the acid to penetrate slightly further into the formation, they do not eliminate precipitates from forming and clogging the matrix.

Often, however, such materials have difficulty in controlling the flow of the acidizing fluid.

For instance, in some applications, it has been noted that a control mechanism for diverting or forcing the acid from a higher permeability and / or water saturated sections of the formation to the lower permeability or oil bearing sections is lacking.

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