Mobil Oil Corporation

Richard L Morris

James M Paul

The present invention relates to the use of low frequency sonic energy within the range of 1.25 to 6.5 KHz, preferably less than 2.0 KHz and most preferably 1.25 KHz, for enhancing the dissolution of alkaline earth metal scales from well bores using a scale-removing solvent comprising an aqueous alkaline solution having a pH of about 8 to about 14 and containing EDTA or DTPA and a catalyst or synergist, preferably an oxalate anion. When the scale deposit is contacted with the scale removing solvent while simultaneously transmitting low frequency sonic energy through the solvent, substantially more scale is dissolved at a faster rate than previously possible.

Method for removing alkaline sulfate scale

A method and composition for removing barium and strontium sulfate scale deposits. The composition comprises an aqueous solution having a pH of about 8 to about 14, an EDTA or DTPA chelant, and a catalyst or synergist. Preferred chelants comprise diethylenetriaminepentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA or alkali salts thereof. Anions of organic and inorganic acids comprise the catalyst. Catalysts which can be used include fluoride, oxalate, persulfate, dithionate, hypochlorite and formate anions. When the solution containing the composition is contacted with a surface containing a scale deposit, the deposit dissolves substantially more scale quicker than heretofore possible.

Composition for removing an alkaline earth metal sulfate scale

Alkaline earth metal scales, especially barium sulfate scale deposits are removed from oilfield pipe and other tubular goods with a scale-removing composition comprising an aqueous alkaline solution having a pH of about 8 to about 14, a polyaminopolycarboxylic acid, preferably EDTA or DTPA and a catalyst or synergist comprising oxalate anion. When the scale-removing solution is contacted with a surface containing a scale deposit, substantially more scale is dissolved at a faster rate than previously possible.

Compositions for dissolution of sulfate scales

Barium sulfate scale is dissolved by contacting the scale with an aqueous solvent having a pH of about 10 to about 14, preferably about 12, and comprising a chelating agent comprising a polyaminopolycarboxylic acid or salt of such an acid, and a synergist anion. The solvent containing the dissolved scale is regenerated by acidifying the solvent in the presence of an anion which forms a precipitate of an insoluble salt of the alkaline earth metal of the dissolved scale. The precipitate is then removed from the solvent. Thereafter, the pH of the solvent is increased to a pH of about 10 to about 14, preferably about 12, to recover a regenerated solvent for reuse, in dissolving scale.

Method for regenerating scale solvent

Alkaline earth metal scales, especially barium sulfate scale deposits are removed from oilfield pipe and other tubular goods with a scale-removing composition comprising an aqueous alkaline solution having a pH of about 8 to about 14, preferably about 11 to 13, of a polyaminopolycarboxylic acid, preferably EDTA or DTPA and a catalyst or synergist comprising a monocarboxylic acid, preferably a substituted acetic acid such as mercaptoacetic, hydroxyacetic acid or aminoacetic acid or an aromatic acid such as salicylic acid. When the scale-removing solution is contacted with a surface containing a scale deposit, substantially more scale is dissolved at a faster rate than is possible without the synergist.

Sulfate scale dissolution

A liquid membrane method for removing scale deposits wherein a novel chelating composition is utilized. The composition used in the external and internal aqueous phases of said membrane comprises an aqueous solution having a pH of about 8 to about 14, and an aminocarboxylic acid or polyamine chelant. Additionally, a catalyst or synergist is used in the external phase only. Preferred chelants comprise diethylenetriamine pentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA) or alkali salts thereof. Anions of organic and inorganic acids comprise the catalyst used in the external phase. Catalysts which can be used include fluoride, oxalate, persulfate, dithionate, hypochlorite, formate, thio, amino and hydroxy acetate anions. When the solution containing the composition is contacted with a surface containing a scale deposit, the deposit dissolves substantially more scale quicker than heretofore possible.

Method for removing scale via a liquid membrane in combination with an

Alkaline earth metal scales, especially barium sulfate scale is removed from a well (the wellbore and the adjacent formation) by contacting the scale with a scale-removing solvent and thereafter sparging the solvent with air or insert gas to dissolve the scale. The sparging aids in achieving a flushing action by the solvent relative to the scale thereby enabling the solvent to more effectively dissolve the scale in the well. Temperature and caustic compatible surfactuants (anionic and non-ionic) may be used in the solvent to generate a column of foam which increases the extent of cleaning oil from the scale surfaces, enabling the solvent to more effectively remove the scale.

Method for scale removal in a wellbore

Barium sulfate scale is dissolved by contacting the scale with an aqueous solvent having a pH of about 10 to about 14, preferably about 12, and comprising a chelating agent comprising a polyaminopolycarboxylic acid or salt of such an acid, and a synergist anion. The solvent containing the dissolved scale is regenerated by acidifying the spent solvent with an acidic chelating agent such as EDTA or DTPA, preferably DTPA, that release alkaline earth cations which react with sulfate ions present in the solvent to form a precipitate of an insoluble salt of the alkaline earth metal. The precipitate is then removed from the solvent by settling/decanting, filtering, or centrifuging. Thereafter, caustic is added to increase the pH of the solvent to a pH of about 10 to about 14, preferably about 12, to recover a regenerated solvent for reuse, in dissolving scale. The amount of chelating agent added to acidify the spent solvent balances the total amount of dilution caused by adding the caustic thereby maintaining the activity of the chelating agent in the regenerated solvent at least equivalent to or greater than the activity in the spent solvent.

Method for reducing radioactivity of oilfield tubular goods contaminated

A method and composition for removing barium and strontium sulfate scale deposits. The composition comprises an aqueous solution having a pH of about 8 to about 14, an EDTA or DTPA chelant, and a catalyst or synergist. Preferred chelants comprise diethylenetriaminepentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA) or alkali salts thereof. Anions of organic and inorganic acids comprise the catalyst. Catalysts which can be used include Fluoride, oxalate, persulfate, dithionate, hypochlorite and formate anions also thio, amino, and hydroxy acetate anions. When the solution containing the composition is contacted with a surface containing a scale deposit, the deposit dissolves substantially more scale quicker than heretofore possible.

Method for removing an alkaline earth metal sulfate scale

Barium sulfate scale is dissolved by contacting the scale with an aqueous solvent having a pH of about 8 to about 14, containing a chelating agent comprising a polyaminopolycarboxylic acid or salt of such an acid, and a synergist anion. The aqueous solvent containing the dissolved scale is regenerated by first acidifying the aqueous solvent sufficiently to generate free alkaline earth metal ions. The aqueous solvent is then mixed with a liquid membrane emulsion enveloped around droplets of an internal aqueous phase containing an anion that forms an insoluble precipitate with the free alkaline earth metal ions. The scale-free aqueous solvent is separated from the emulsion by gravity and recovered for reuse. In another embodiment, the internal aqueous phase may contain a chelating agent to remove the free alkaline earth metal ions by forming a stable complex with the ions.

Natural gas processing equipment and sorption media such as charcoal, silica or alumina, contaminated with adherent scale deposits of alkaline earth metal sulfates may include radioactive components, especially radium sulfate and thorium sulfate, which render the equipment radioactive. The scale is removed from the processing equipment by washing with an aqueous chemical composition including a polyaminopolycarboxylic acid such as EDTA or DEPA as a chelant in combination with a synergist, preferably oxalate or monocarboxylate acid anion such as salicylate. The washing may be carried out with the equipment in place or by immersion of the equipment in a body of the solution in a suitable treatment tank.

Method for treating natural gas equipment

Alkaline earth metal scales, especially barium sulfate scale deposits are removed from oilfield pipe and other tubular goods with a scale-removing composition comprising an aqueous alkaline solution having a pH of about 8 to about 14, preferably about 11 to 13, of a polyaminopolycarboxylic acid, preferably EDTA or DTPA and a catalyst or synergist comprising thiosulfate or nitriloacetate anions. When the scale-removing solution is contacted with a surface containing a scale deposit, substantially more scale is dissolved at a faster rate than is possible without the synergist.

A liquid membrane method for removing scale deposits wherein a novel chelating composition is utilized. The composition used in the external and internal aqueous phases of said membrane comprises an aqueous solution having a pH of about 8 to about 14, and a polyaminopolycarboxylic acid chelant. Additionally, a catalyst or synergist is used in the external phase only. Preferred chelants comprise diethylenetriaminepentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA), salts, and mixtures thereof. The catalyst used in the external phase comprises an oxalate anion. When the solution containing the composition is contacted with a surface containing a scale deposit, the deposit dissolves substantially more scale quicker then heretofore possible.

Growing community of inventors

Duncanville, TX, United States of America

Richard L Morris