RU96114896A - METHOD FOR DISSOLUTION OF DEPOSITS IN EDUCATIONS CONTAINING NUMEROUS PRODUCTIVE LAYERS - Google Patents

Claims (11)

1. The method of dissolving deposits in the formation containing numerous productive layers, including:
a) directing the first liquid composition of known density into the perforated borehole to dissolve the alkaline earth metal sulfate scale deposit from the perforations and productive layers in communication with said borehole; and
b) the direction in the borehole, on the upper surface of the first liquid composition, of the second liquid composition for dissolving the deposition of alkaline earth metal sulfate in the upper perforated layer of the borehole, which communicates with the productive layers in which the second liquid composition has a density lower than the density of the first liquid composition.  2. The method according to claim 1, wherein in step (c), the density of the second liquid composition is reduced by adding a saline solution of an alkali or alkaline earth metal having a lower density.  3. The method of claim 1, wherein in step (c), the density of the second liquid is reduced by adding an aqueous or hydrocarbon-containing solution containing an alkali or alkaline earth metal salt in an amount sufficient to obtain a density that is at least 0.1 wt.% less than the density of the first liquid composition.  4. The method according to claim 3, in which the aqueous or hydrocarbon-containing solution contains bromides or chlorides.  5. The method according to claim 2, 3 or 4, in which the solution is selected from a member of the group consisting of sodium chloride, potassium chloride, zinc chloride, sodium bromide, potassium bromide or zinc bromide.  6. The method according to any preceding paragraph, in which the density of the first liquid composition is from 11.5 to 12.0 pounds / gallon (from 0.955 to 1.00 kg / dm).  7. The method according to any preceding paragraph, in which the density of the second liquid composition is from 10.5 to 11.0 pounds / gallon (from 0.872 to 0.914 kg / dm).  8. The method according to any preceding paragraph, in which subsequent fluids are added to the borehole over the first and second fluids, the density of each of which is at least 0.1 wt.% Lower than the density of the last fluid added, the addition being carried out until all desired productive salts and perforations in contact with them are treated with a dissolving solution.  9. The method according to any one of claims 1 to 7, in which, after step (c), a third liquid composition for dissolving the deposit is sent to the borehole, which has a density of 9.5 to 10.00 pounds / gallon (0.789 to 0.831 kg / dm).  10. The method according to claim 9, in which, after stage (c), a fourth liquid composition for dissolving deposits is sent to the borehole, which has a density of 8.5 to 9.0 pounds / gallon (0.706 to 0.748 kg / dm). 11. The method according to any preceding paragraph, in which the first and second liquid compositions contain an aqueous solution having a pH of from 8 to 14, with each solution containing:
i) aminocarboxylic acid or polyamine chelate compounds, salts and mixtures thereof in an amount of from 0.1 to 1.0 M; and
ii) a catalyst in an amount of from 0.01 to 0.5 M, which is a member selected from the group consisting of fluoride, oxalate, persulfate, dithitonate, hypochlorite, formate, thio, amino, and oxyacetate anions, whereby a solution is obtained which can dissolves substantially more deposits over a substantially shorter time period than is possible with only one chelate compound mentioned.