RU2269563C1 - Composition for treating well bottom zone of carbonate formation wells - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: invention relates to oil production technology involving use of hydrochloric acid-based chemicals via complex hydrochloric acid effect on well bottom zone to intensify oil production and may be specifically used to increase oil recovery of viscous oil-saturated low-permeable carbonate reservoirs. Composition contains 22-28% of 20 vol % aqueous HCl solution, 7-8% of 98% aqueous acetic acid solution, and 65-70% of solvent based on light pyrolysis tar obtained as secondary product from petroleum processing enterprises.

EFFECT: increased well bottom zone treatment efficiency due to improved quality of treatment composition, in particular stability and dipping depth into formation.

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Description

The proposal relates to the field of the oil industry, in particular to the technology of oil production using chemicals based on hydrochloric acid by complex hydrochloric acid exposure to the bottomhole zone of wells in an oil reservoir for the purpose of stimulation, and can be used to increase oil recovery of low-permeability carbonate reservoirs saturated with highly viscous oil (BBH).

A known composition for processing a carbonate formation (SCR) based on hydrochloric acid [see Loginov B.G. et al. Guide to acid treatment of wells. M .: Nedra, 1966, p.41-56].

The disadvantage of the composition is that hydrochloric acid has a high reaction rate with the formation rock, as a result of which its penetration depth into the formation is small.

In addition, often after treatment of the bottom-hole zone (BHP) with hydrochloric acid, the injectivity of wells decreases, since solutions of hydrochloric acid are characterized by an increased content of iron ions due to corrosion of equipment, which are deposited in the form of hydroxide on the rock. All this leads to a decrease in the effectiveness of the treatments.

There is also known a method for treating a carbonate formation based on concentrated acetic acid [see Amiyan V.A. and others. Physicochemical methods to increase well productivity. M .: Nedra, 1970, p.262].

The composition allows to reduce the reaction rate with the formation rock.

The disadvantage of the composition is the limited use due to the high cost.

The closest in technical essence and the achieved result to the proposed composition for the SCR of the carbonate formation is the composition [see author St. USSR No. 1170127, class E 21 In 43/27, 1985], containing a solution of hydrochloric and acetic acids, and as an additional moderator of the reaction rate with carbonate rock, liquid pyrolysis products from C ₅ and higher with the following ratios of components,% vol:

hydrochloric acid (20%)  4-20 acetic acid (98%)  9-67 liquid pyrolysis products - a mixture of condensates hydrocarbons C ₅ and higher rest.

When using the composition for SCR, the reaction rate with the formation rock decreases and its filterability increases under conditions of low-permeability reservoirs with asphalt-resin-paraffin deposits (AFS).

The disadvantage of the composition is the low efficiency of reducing the reaction rate with the formation rock and the low efficiency of removing paraffin from a low permeable porous medium due to the low technological effectiveness of the composition and the depth of penetration into the carbonate formation, the emulsion of an aqueous solution of hydrochloric and acetic acids in liquid pyrolysis products does not differ in time stability. In addition, the efficiency of the SCR remains low due to the rapid flooding of well production.

The disadvantage of the composition is also the limited use due to the specificity of the use of additives - pyrolysis products from C ₅ and above.

The technical result of the invention is to increase the efficiency of the SCR by increasing the manufacturability of the composition, namely the stability and penetration depth into the carbonate formation, as well as expanding the range of acid compositions for the SCR of low-permeable carbonate formations saturated with high-viscosity oil.

The technical result is achieved by the fact that the composition for processing the bottom-hole zone of the wells of the carbonate formation, containing 20% aqueous hydrochloric acid solution, 98% aqueous acetic acid solution and a solvent based on secondary products of oil refineries - light LPS pyrolysis resin, contains these components in the following ratio ,% vol .:

acetic acid solution 7-8 LPS 65-70 hydrochloric acid solution 22-28

The conducted experimental studies showed that the proposed composition allows you to:

- increase the filtration characteristics of the bottom-hole zone by expanding existing and creating new fluid-conducting channels during the dissolution of the mineral component of the formation;

- slow down, in comparison with basic solutions of acids, the dissolution rate of carbonates to increase the radius of their impact.

It has a low value of surface tension to improve their penetrating ability deep into low-permeability channels and to facilitate the return of the spent compounds into the wellbore. The composition has a high dissolving ability with respect to paraffin deposits, a low rate of metal corrosion and the compatibility of individual components with each other and with highly mineralized formation water.

The combined effect on the carbonate rock of the formation and hydrocarbon deposits (AFS) is solved by selecting a hydrocarbon solvent, a dispersant, capable of dissolving in acid solutions using a co-solvent. Acetic acid is such a co-solvent, which is the link between the other components and imparts phase stability to the entire system.

Of the available sources of patent and scientific and technical literature, we do not know the claimed combination of distinctive features.

Therefore, the proposed composition meets the criteria of the invention "inventive step".

The following materials were used to prepare the compositions:

- 20% hydrochloric acid (GOST 857-88);

is introduced into the composition in solutions as a rock solvent, transferring resin-paraffin deposits (ARPD) to a free state, followed by its bulk dispersion.

- 98% acetic acid (GOST 61-75);

is introduced into the acid composition as a complexing agent of iron ions and as a co-solvent, which is a connecting link between the individual components, which imparts phase stability to the entire system.

- light pyrolysis resin (LPS) TU 38.10285-83;

-introduced into the composition as a solvent based on secondary products of oil refineries, affecting the degree of washing of paraffin wax and allowing to increase the permeability of the rock.

For the experiments used:

- produced water - density 1.113-1.156, g / cm ³ , total salinity 195.1-236.7, g / l;

- core material - air permeability of 0.0010-0.0032 μm ² ,

- porosity 6.3-11.6%, calcite content 93.32-98.96, dolomites 2.6-5.21%;

- ferric chloride (FeCl ₃ ) - TU 4147-74.

The preparation of the compositions was carried out as follows.

Concentrated hydrochloric acid was diluted with fresh water to a 20% concentration by volume. Then, LPS and acetic acid were successively added to it, after which the contents were mixed.

All formulations are time-stable (7-9 days) and homogeneous liquids. The mixing order of the individual components does not affect the characteristics of the composition. The compounds are compatible with water. The characteristics of the compositions are shown in table No. 1.

Table 1 No. of acid composition. Composition Components Volume content,% vol. Density,
g / cm ³ Viscosity, MPa · s Surface tension, mN / m one 2 3 four 5 6 one 98% CH ₃ COOH 34 LPS 57 20% HCL 9 0.952 3.3 36.9 2 98% CH ₃ COOH 7 LPS 65 20% HCL 28 0.948 3.8 36,4 3 98% CH ₃ COOH 10 LPS 70 20% HCL twenty 0.945 4.2 36,2 four 98% CH ₃ COOH 9 LPS 71 20% HCL twenty 0.941 4.3 36.0 5 20% HCl one hundred 67.4 6 15% HCl one hundred 72.0

From table 1 it is seen that a decrease in surface tension occurs in all formulations compared with hydrochloric acid, which provides high penetration into the reservoir. The proposed compositions having a higher density compared with the density of highly viscous oil in reservoir conditions (0.874-0.908 g / cm ³ ) and lower viscosity compared to it (dynamic viscosity of VVN in reservoir conditions varies from 35.6 to 81.3 MPa · s ), due to the positive effect of the compositions during injection into the reservoir and oil displacement from the reservoir.

The complexing ability of acidic compounds with respect to iron ions was determined by pre-dosing 40% iron chloride solution (FeCl ₃ ) in them. After that, the compositions were neutralized to pH = 3, the process of precipitation of iron hydroxide was recorded visually (Methodology from the works of Christian M. et al. Increasing the productivity of injectivity of wells / Transl. Kn. - M .: Nedra, 1985).

Studies have shown that all the compounds are complexing agents of iron ions. Acetic acid in combination with other components included in the composition stabilizes the dissolved iron from its repeated precipitation.

The density of the compositions was measured by pycnometers, dynamic viscosity on a Rheo-Viskometer; open porosity according to OST 39181-85; permeability according to OST 39161-83; surface tension was determined by the stalagmometric method.

The rate of dissolution of the carbonate rock was determined as follows: the core was weighed to an accuracy of 0.01 g, its surface area was measured and lowered into a glass with the test composition, after 5 minutes it was removed from the composition, washed with water and dried in an oven at t = 100 ° С to constant weight and again weighed with initial accuracy. The difference in weight was determined by the dissolution efficiency.

The research results are shown in table 2.

table 2 The main components of the composition The content of components,% vol. The surface area of the core, m ² The duration of the reaction, min Core weight before processing, g Core weight after processing, g The dissolution rate, g / (m ² · s) one 2 3 four 5 6 7 98% CH ₃ COOH 34 LPS 57 20% HCL 9 0.0018 21 9,742 6,496 1.42 98% CH ₃ COOH 7 LPS 65 20% HCl 28 0.0018 26 9,769 6,494 1.16 98% CH ₃ COOH 10 LPS 70 20% HCl twenty 0.0018 thirty 9,740 6,490 1.00 98% CH ₃ COOH 9 LPS 71 20% HCl twenty 0.0018 31 9,743 6,480 0.97 20% HCl one hundred 0.0013 12 5,265 0.398 5.2 15% HCl one hundred 0.0013 17 5,290 0.649 3,5

From table 2 it is seen that all the studied compounds have a dissolving ability. All of them have a low dissolution rate of carbonates compared with hydrochloric acid, which contributes to a deep SCR formation.

The degree of dispersion of the ARPD by the proposed method was determined by the method of "cold cylinder". The technique is as follows.

A cylinder was lowered into oil heated to 30 ° C, the temperature of which was maintained at 15 ° C by adding ice to it. When the oil was stirred for 30 minutes, as a result of the difference in its temperature from the temperature of the “cold” cylinder, an ASA precipitate formed on the surface of the cylinder.

The cylinder with the precipitate formed was removed from the tank with oil and after its complete draining from it, it was weighed and transferred to a glass with a test composition of a certain concentration, the temperature of which was also maintained at 30 ° C. Then, the test composition was gradually stirred for 3 minutes, while the precipitate was separated from the surface of the “cold” cylinder. After that, the cylinder was re-weighed and in relation to the weight of the initially formed precipitate, the washing ability of the test composition of a given concentration was determined by the formula:

E = Q ₂ / Q ₁ · 100%,

where Q ₁ is the mass of sediment formed on the surface of the "cold cylinder", g;

Q ₂ - the mass of the washed precipitate, g

The research results are shown in table 3.

Table 3 The main components of the composition The content of components,% vol. The mass of the empty cylinder, g The mass of the cylinder with paraffin washing before washing, g ASPO weight, g The mass of the cylinder with AFS after washing, g The degree of washing,% wt. one 2 3 four 5 6 7 98% CH ₃ COOH 34 7,440 7,720 0.280 7,592 54,2 LPS 57 20% HCl 9 98% CH ₃ COOH 7 7,440 7,605 0.175 7,578 78.8 LPS 65 20% HCl 28 98% CH ₃ COOH 10 7,440 7,595 0.155 7,565 80.6 LPS 70 20% HCl twenty 98% CH ₃ COOH 9 7,440 7,595 0.155 7,559 76.7 LPS 71 20% HCl twenty

From table 3 it is seen that all the investigated compounds have a washing ability in relation to paraffin. The highest washing ability possess compositions containing 65% and 70% LPS.

In laboratory conditions, a series of experiments was carried out to determine the permeability of core material depending on the porosity of the core material and the number of washes.

The research results are shown in table 4.

Table 4 The main components of the working solution. The content of components,% vol. The porosity of the core,% Permeability, μm ² Source After processing / magnification first pore volume The second pore volume third pore volume one 2 3 four 5 6 7 98% CH ₃ COOH 34 LPS 57 0.0021 0.0036 0.0055 20% HCL 9 10.6 0.0018 1,1 2.7 4.2 98% CH ₃ COOH 7 LPS 65 0.0038 0.0072 0,022 20% HCL 28 10.7 0.0017 1.9 3.4 13,4 98% CH ₃ COOH 10 LPS 70 0.0048 0.012 0,029 20% HCL twenty 11.0 0.0019 2,5 6.5 15,2 98% CH ₃ COOH 9 LPS 71 0.0048 0.012 0,029 20% HCL twenty 11.0 0.0018 1,6 4,5 12,2

From table 4 it is seen that the permeability of the core increases after pumping one volume of the proposed compositions and continues to increase significantly with increasing pumping volume, the compositions are able to simultaneously dissolve carbonate rocks and paraffin deposits, have a high penetrating and leaching ability, dissolve in water of any mineralization, increase the permeability of the rock in an average of 4.2 to 15.2 times.

Studies of the phase state and stability of the system showed that the composition is a stable homogeneous liquid for seven nine-days with the following ingredients,% vol:

98% acetic acid 6-9 light pyrolysis resin 64-71 20% hydrochloric acid solution rest

With a decrease in LPS values, the system passes into an emulsion, which reduces the effectiveness of SCR.

The data shown in tables 1-4 show that the composition containing the following components,% vol .:

98% acetic acid solution (CH ₃ COOH) 7-10 light pyrolysis resin 65-70 20% hydrochloric acid solution (HCL) rest,

has low surface tension at the boundary with the rock and interfacial at the oil-composition boundary, which contributes to its high filterability in the low permeable oil-saturated part of the reservoir; high solubility in relation to paraffin, which contributes to the depth of penetration and increase coverage over the thickness of the reservoir; slower dissolution rate with respect to carbonates, which also contributes to deep formation SCR; maximizes the permeability of the rock, which under commercial conditions will lead to an increase in the injectivity of injection wells and, as a consequence, to an increase in the coefficient of oil displacement.

Studies have shown that increasing the LPS content above 70% leads to a decrease in the content of the hydrochloric acid phase in the solution and reduces the effectiveness of the SCR. Reducing the lower limit of the LPS content also reduces the effectiveness of the SCR.

The technical and economic efficiency of the proposed compositions for the SCR of the carbonate formation is composed by increasing the efficiency of the SCR, i.e. increasing the manufacturability of the composition, namely stability and penetration depth in the carbonate formation, as well as expanding the range of acid compositions for the SCR of low-permeable carbonate formations saturated with high-viscosity oil.

Claims (1)

The composition for processing the bottom-hole zone of the wells of a carbonate formation containing a 20% aqueous solution of hydrochloric acid, 98% aqueous solution of acetic acid and a solvent based on secondary products of oil refineries - light LPS pyrolysis resin, characterized in that it contains these components at their following ratio, vol.%: Acetic acid solution 7 - 8 LPS 65 - 70 Hydrochloric acid solution 22 - 28