Solid sandstone dissolver

Abstract

A dry solid composition is disclosed that, when added to an aqueous liquid, provides a slurry that can be used in sandstone acid fracturing. The slurry generates hydrofluoric acid downhole to etch the sandstone fracture faces created. The chemical and physical properties of the composition result in very uneven etching of the fracture faces, enhancing the fluid conductivity of the final fracture. Optionally, inert masking materials may be included in the dry composition, or added to the slurry, to increase the inhomogeneity of the etching and further increase the fluid conductivity.

Description

[0001] This application is a Continuation-in-Part of U.S. patent application Ser. No. 10 / 605,784, filed on Oct. 27, 2003, which claimed the benefit of U.S. Provisional Patent Application No. 60 / 421,696, filed on Oct. 28, 2002. This application is related to a U.S. patent application Ser. No. 10 / 941,384 entitled “Selective Fracture Face Dissolution,” filed on Sep. 15, 2004, inventors J. Ernest Brown, et al., and to a U.S. patent application Ser. No. 10 / 941,385 entitled “Differential Etching in Acid Fracturing,” filed on Sep. 15, 2004, inventors J. Ernest Brown, et al.BACKGROUND OF THE INVENTION [0002] The invention relates to stimulation of wells penetrating subterranean formations. In particular it relates to acid fracturing; more particularly it relates to methods of etching the fracture faces so that etching is minimal in some regions but a conductive path from the fracture tip to the wellbore is nonetheless created. Most particularly it relates to a solid additive that is added t...

AI Technical Summary

Benefits of technology

[0010] One embodiment is a water-free composition that contains particles of a solid acid-precursor and particles of a solid that releases hydrogen fluoride in the presence of aqueous acid. Examples of the solid acid-precursor are lactide, glycolide, polylactic acid, polyglycolic acid, copolymers of polylactic acid and polyglycolic acid, copolymers of glycolic acid with other hydroxy-, carboxylic acid-, or hydroxycarboxylic acid-containing moieties, copolymers of lactic acid with other hydroxy-, carboxylic acid-, or hydroxycarboxylic acid-containing moieties, and mixtures of these materials. The solid acid-precursor may be encapsulated or may be coated with an effective amount of a material that slows hydrolysis of the solid acid-precursor when it is contacted with

Problems solved by technology

There are generally three major problems encountered during this normal procedure.

First, in the pumping operation the acid is in contact with iron-containing components of the wellbore such as casing, liner, coiled tubing, etc.

Strong acids are corrosive to such materials, especially at high temperature.

Furthermore, acid corrosion creates iron compounds such as iron chlorides.

These iron compounds may precipitate, especially if sulfur or sulfides are present, and may interfere with the stability or effectiveness of other components of the fluid, thus requiring addition of iron control agents or iron sequestering agents to the fluid.

Second, if, as is usually the case, the intention is to use the acid to treat parts of the formation at a significant distance away from the wellbore (usually in addition to treating parts of the formation nearer the wellbore), this may be very difficult to accomplish because if an acid is injected from the surface down a wellbore and into contact with the formation, the acid will naturally react with the first reactive material with which it comes into contact.

At best this may be wasteful of acid; at worst this may make the treatment ineffective or even harmful.

In general, the higher the temperature the more reactive is the acid and the greater are the problems.

This is usually a severe problem when at least some of the formation is carbonate, which is typically very reactive towards acid.

Third, even when the acid has successfully been contacted with the desired region of the fracture face, there is sometimes a tendency for the acid to react evenly with the fracture faces, especially in localized regions, so that conductive channels along the fracture faces are not created by differential etching in such regions after fracture closure.

There are problems with these methods.

Although emulsified acids are popular and effective, they require additional additives and specialized equipment and expertise, and may be difficult to control.

A problem with the encapsulated acids is that the location and timing of release of the acid may be difficult to control.

Physical damage to the encapsulating material, or incomplete or inadequate coating during manufacture, could cause premature release of the acid.

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