RU2599150C1 - Composition for preventing formation of salt deposits during oil and gas extraction - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention relates to oil and gas industry. Composition for preventing formation of salt deposits in downhole equipment contains, wt%: oxyethylidene diphosphonic acid 1-3; hydrochloric acid 7-10; ammonium bifluoride 1-2; nonionic surfactant 0.1-0.2; water -balance.

EFFECT: technical result is higher efficiency of preventing precipitation of salts in a long period of time of well operation due to reduced surface tension at oil-inhibiting solution boundary and formation of strong silicate films, including inhibitor, on surface of rock-forming minerals.

1 cl, 5 dwg

Description

The invention relates to the oil and gas industry and can be used to prevent the formation of salt deposits during oil and gas production from wells.

Known composition for the prevention of carbonate, sulfate, iron oxide deposits (patent RU No. 2146232, publ. 03/10/2000), as well as the destruction of deposits of carbonate salts on heat and mass transfer surfaces. The composition contains, by weight. %: hydroxyethylene diphosphonic acid (OEDP) 15-40, zinc compound 0.1-7.0, sodium lignosulfonate 10-30 and water. In addition to effectively preventing the formation of salt deposits and inhibiting corrosion, the composition prevents the ion exchange of iron with the acid part of the reagent.

The disadvantage of the composition is the high freezing temperature, and therefore, the complexity of its use in regions of a cold climate, as well as insufficiently high heat resistance.

A known composition for preventing the loss of salts (patent RU No. 2122981, publ. 10.12.1998), containing, by weight. %: hydroxyethylidene diphosphonic acid 8-16, alkanolamine 6-8, ethylene glycol 20-42, water the rest.

The disadvantage of the composition is that when oil is extracted from reservoirs with low permeability or at high rock pressure, a depth dispenser must be used for its dosage. When using a depth dispenser with a limited volume and a large production rate of the production well, i.e. with a large consumption of inhibitory composition, the container must be filled 1-3 times a quarter. This is due to the ascent and descent of deep equipment, which is quite expensive and economically inexpedient.

A known composition for preventing the loss of salts (patent RU No. 2230766, publ. 06/20/2004), containing, wt.%: 0.1-0.125 polyaminomethylphosphonic acid, 0.375-0.9 sodium salt of polyacrylic acid, the rest is water. In the present invention, polyaminomethylphosphonic acid is a 13A PAP inhibitor.

The disadvantage of the composition is that the effectiveness of this mixture does not exceed 70%.

The closest solution taken as a prototype is the composition (patent RU No. 2070910, publ. 12/27/1996), which contains nitrilotrimethylene phosphonic acid (NTP), hydrofluoric acid (KFVK) and hydrochloric acid. The hydrofluoric acid obtained by the interaction of CPVC with hydrochloric acid interacts with silicate and aluminosilicate minerals, increasing the roughness of the rock during chemical interaction and thereby increasing the contact surface of the inhibitor with the rock.

However, a drawback of the composition is that hydrofluoric acid, which is hazardous to use, is used.

The technical result of the invention is to prevent the precipitation of salts during a long time of operation of the well by reducing interfacial tension at the oil-inhibitory interface and the formation of strong silicate films, including an inhibitor, on the surface of rock-forming minerals.

The technical result is achieved by the fact that the composition for preventing the formation of salt deposits in downhole equipment containing hydrochloric acid additionally contains hydroxyethylidene diphosphonic acid, ammonium bifluoride, nonionic surfactant surfactant, in the following ratios of components, wt. %:

Hydroxyethylidene diphosphonic acid 1-3 Hydrochloric acid 7-10 Ammonium bifluoride 1-2 Nonionic surfactant  0.1-0.2 Water  Rest

The composition for preventing the formation of salt deposits during oil and gas production is illustrated by the following figures:

FIG. 1 - The results of determining the interfacial tension at the border "oil - acid solution" of solutions of ammonium bifluoride and hydrochloric acid.

FIG. 2 - Interfacial tension at the border "oil - acid solution" with a different content of HEDP.

FIG. 3 - Evaluation of the effectiveness of scale inhibitors.

FIG. 4 - Change in the concentration of the inhibitor solution during adsorption on the formation.

FIG. 5 - Change in the concentration of the inhibitor solution during desorption.

To improve the sorption properties of scale inhibitors on the rock, it is recommended that they be injected in a mixture with weak acid solutions that expose the hydrophobized oil film surface with an increase in its area for contact with the inhibitor. So, the treatment of the NTF layer is carried out in a mixture with hydrochloric acid. Thanks to the acid reagent, film oil is rejected from the rock surface due to a decrease in interfacial tension in the "rock - oil - inhibitory solution" system. Hydrochloric acid interacts with carbonate minerals, and thus the adsorption area of the inhibitor on the rock increases.

The effectiveness of the claimed composition was evaluated in laboratory conditions. The development and testing of the composition in laboratory conditions was carried out in several stages. Initially, the interfacial tension was determined at the interface “oil - acid solutions” and the optimum content in the solution of hydrochloric acid and ammonium bifluoride was selected. At the second stage, the concentration of HEDP was determined, which provided the necessary decrease in interfacial tension at the oil – acid solution interface.

In laboratory conditions, the concentration range of ammonium bifluoride 0-5% in acid solutions was studied, and the content of hydrochloric acid varied within 3-15%, i.e. within the values recommended for the treatment of terrigenous and carbonate reservoirs.

The results of laboratory determinations of the interfacial tension of the solutions at the oil-acid solution interface are shown in the table in FIG. one.

Increasing the concentration of reagents reduces the magnitude of interfacial tension, and hydrochloric acid has a greater effect on this. The most optimal concentrations are 0.5-2% ammonium bifluoride and 7-10% hydrochloric acid. With these combinations, the interfacial tension of the composition at the oil-acid solution interface is 6.89-3.98 mN / m.

Adding HEDP to solutions allows an additional reduction in interfacial tension. For injection into a CCD, it is recommended to use a 1-5% OEDP solution. In order to identify the degree of decrease in the interfacial tension of the solution when adding HEDP, the following concentrations of components were taken: ammonium bifluoride with a content of 0.5-2%, hydrochloric acid with a content of 7-10% and HEDP in the range of 0.5-5%. In the table of FIG. Figure 2 shows the results of determining the interfacial tension of a solution at the oil-acid solution interface with different OEDP contents.

From FIG. Figure 2 shows that even insignificant concentrations of HEDP lead to a significant decrease in interfacial tension. This effect is noticeable to the content in the OEDP solution in an amount of 3%. Thus, the OEDP content of 1-3% is accepted as the optimal concentration. A further decrease in interfacial tension was achieved by the addition of a nonionic surfactant (nonionic surfactant) to the inhibitory solution.

According to the results, the following compositions No. 1 and No. 2, respectively, were studied as reagents for injection into the reservoir:

1) 3% HEDP + 1% NH4F + 7% Hcl + 0.1% nonionic surfactants + water - the rest;

2) 1% HEDP + 2% NH4F + 10% Hcl + 0.1% nonionic surfactants + water - the rest.

Evaluation of the effectiveness of the compositions by the ability to prevent sedimentation was carried out according to the standard NACE TM 0374-2007 in a liquid solution of an averaged model of produced water.

The tests were carried out at a temperature of 25 ° C, the exposure time was 24 hours. Water used in the experiments had the following model ionic composition: Ba ²⁺ = 410 mg / l, SO ^2- ₄ = 470 mg / l, Na ⁺ = 11910 mg / L, Cl ^- = 18200 mg / l. The experimental results are presented in the table in FIG. 3.

To determine the adsorption-desorption characteristics of inhibitory compositions, filtration studies were performed. Filtration experiments to simulate an oil well were conducted on natural cores.

Given the fact that the initial concentrations of organophosphorus reagents in the inhibitory compositions are different, only the dynamics of the relative concentrations of the solutions can be compared. In this case, the relative concentration is determined by the ratio of their current concentration to the initial one.

In FIG. Figure 3 shows the results of determining the relative concentrations of organophosphorus reagents in inhibitory compositions during adsorption.

Laboratory studies have shown that ultimate adsorption is achieved by pumping nine pore volumes for compositions No. 1 and No. 2.

Comparing the relative concentrations of the reagents during adsorption, we can conclude that adsorption proceeds faster when using inhibitory compounds under No. 1 and No. 2. More uniform adsorption is observed in the composition under No. 2.

After the core was left for 24 hours to establish adsorption equilibrium, formation water was pumped through it to displace the inhibitory composition. In FIG. 4 shows the results of determining the relative concentrations of the compositions during desorption.

The maximum concentration of HEDP to prevent the deposition of salts is 5-10 mg / l, it corresponds to a relative concentration of 0.0001 units

According to FIG. 5 when using the composition under No. 1, effective protection against loss of salts under similar conditions is maintained when pumping 46 pore volumes of water, and the composition under No. 2 - when pumping 42 pore volumes of water.

The effectiveness of the developed composition is explained by the mechanism of action on the rock by the acid additives that make up its composition.

Ammonium bifluoride, dissolving in hydrochloric acid, partially neutralizes it and as a result of this reaction, hydrofluoric acid and ammonium chloride are formed.

The reaction proceeds as follows:

Hydrogen fluoride is able to react with silicate and aluminosilicate minerals, with intense contact surface corrosion. Hydrofluoric acid interacts most actively with aluminosilicates present in kaolinic clays, mudstones and other rocks.

The hydrofluoric acid resulting from the interaction of hydrochloric acid with ammonium bifluoride reacts with quartz and kaolin, which are part of terrigenous reservoirs according to the following scheme:

Subsequently, the interaction of the formed silicon fluoride SiF ₄ with water occurs:

The resulting CPK - H ₂ SiF ₆ reaction remains in solution, and the silicon hydrate Si (OH) ₄ can turn from a sol into a gel-like gel as the acidity of the solution decreases. The resulting gel, in turn, can very easily seal the pores of the formation, thereby reducing the permeability of the rock. To prevent this, a mixture of fluoride and hydrochloric acid is used in the treatment of terrigenous reservoirs. Hydrochloric acid is necessary to maintain an increased acidity of the medium and to retain silicic acid in solution, preventing the formation of a gel from silica hydrate. In addition, if calcium and magnesium carbonates are contained in the formation rocks, then in the process of their reaction with fluoric acid, sparingly soluble calcium and magnesium fluorides are formed. This is prevented by hydrochloric acid. Hydrochloric acid is also able to change the wettability of a rock by cleaning its surface from an oil film. Due to this, a uniform and more complete adsorption of the scale inhibitor is achieved.

Due to the erosion of the surface of silicate rocks by hydrofluoric acid, an increase in their area and, accordingly, degree of adsorption on this surface of the chemical composition is ensured. The inhibitory solution will penetrate the composition of silicate sols, which cover the contact surface of the inhibitor with silicate minerals. Due to this, it will be slower to desorb from the formation, since the silicate films of the sol in the composition with the inhibitor are much more resistant to leaching. Which leads to the fact that the desorption period increases, and from this we can conclude that the effectiveness of the use of scaling inhibitor also increases.

Thus, the inventive multicomponent composition to obtain the greatest inhibitory effect against inorganic salts is very promising. The hydrofluoric acid formed as a result of the interaction of ammonium bifluoride with hydrochloric acid reacts with the silicate of the reservoir rock and makes it possible to increase the contact of the inhibitor with its surface, and in combination with a surfactant, significantly reduce the interfacial tension at the oil - inhibitory solution interface. Thus, the adsorption-desorption ability of the composition is increased. Since the reaction products are silicate sols, this interaction leads to an increase in the roughness of the rocks, the formation of strong silicate films and, consequently, to an increase in the surface area of the adsorbent, which increases the adsorption of complexones. In addition, the gel-like consistency formed during the reaction promotes uniform and slow desorption of the inhibitor. Nonionic surfactant allows in addition to the action of acid additives to reduce interfacial tension in the system "rock - oil - inhibiting solution". In addition, the presence of surfactants in waters prone to scaling has a positive effect on the inhibition of the process of aggregation of insoluble crystals from supersaturated solutions.

The objects for the treatment are production wells, complicated by the formation of salt deposits in underground equipment and reservoir.

Claims (1)

Composition for preventing the formation of salt deposits in downhole equipment containing hydrochloric acid, characterized in that it further comprises hydroxyethylidene diphosphonic acid, ammonium bifluoride, nonionic surfactant surfactant in the following ratios of components, wt.%:
Hydroxyethylidene diphosphonic acid 1-3 Hydrochloric acid 7-10 Ammonium bifluoride 1-2 Nonionic surfactant 0.1-0.2 Water rest

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