RU2042807C1 - Method for treatment of bottom-hole formation zone - Google Patents

Abstract

FIELD: oil producing industry. SUBSTANCE: method for treatment of bottom-hole formation zone includes successive injection into formation of spacer fluid based on hydrocarbons in form of casing-head stabilized gasoline and isopropyl alcohol in ratio of (1-3):1, inhibited aqueous solution of hydrochloric acid, or mud acid in mixture with alcohol-containing product in ratio from 1:1 to 1:2. Then, the second spacer fluid is injected in form of stabilized casing-head gasoline presenting mixture of saturated hydrocarbons C_3+more. EFFECT: higher efficiency. 7 tbl

Description

 The invention relates to the oil and gas industry, in particular to methods for processing heterogeneous formations.

 A known method of processing the bottom-hole zone, including the injection of acid with a hydrocarbon fluid (1).

 This method involves reducing the injectivity of highly permeable intervals of a heterogeneous formation due to the high viscosity oil-acid emulsion and increasing the coverage of the thickness of the reservoir. However, if oil-acid composition is difficult to enter in highly permeable intervals, it is less likely that it will penetrate into low-permeability intervals of productive formations. Therefore, the effectiveness of acid treatment to a greater extent is ensured by neutralizing a pure acid solution and reducing the rate of its reaction with the rock, which means deeper processing of highly permeable intervals. But to ensure deeper processing during the injection of oil-acid compositions into the formation, it is necessary that they are stable at high temperatures, for which it is necessary to use highly resinous oils or heat-resistant emulsifiers. The latter, due to the presence of water in the acid solution simultaneously with the presence of water in the formation, can create the prerequisites for the formation of a water-oil emulsion with strong adsorption films at the phase boundaries, which is a significant obstacle for cleaning the bottomhole zone from reaction products during well development after acid treatment. Thus, the contradictions inherent in the known method in practice will lead to ambiguous results, depending on the extent to which this or that factor plays.

 There is also a method of treating the bottom-hole zone of a formation by pumping hydrocarbon-based liquid into the formation, then inhibited hydrochloric acid or clay acid (2).

 The disadvantage of this method is that, by pumping a hydrocarbon fluid and acid, which includes water, emulsions can also form in the reservoir during the reaction, and free water of the acid solution will contribute to clay swelling. These processes together will lead to a significant reduction in porosity and permeability of the reservoir. Due to the low viscosity of the inhibited acid, along with high surface tension at the phase boundaries of the acid solution with the hydrocarbon liquid, the acid will not penetrate well into low-permeability areas and, conversely, will easily move and absorb into a highly permeable part of an inhomogeneous formation. In addition, the method does not provide for the removal of highly resinous paraffin deposits (paraffin).

 The purpose of the invention is to increase the likelihood of acid solution penetrating into low-permeability areas and more complete removal of the spent solution from the formation, as well as cleaning the bottom-hole zone of asphalt-resin-paraffin deposits.

This is achieved by the fact that additionally after injection of an inhibited aqueous solution of hydrochloric acid or clay acid in a mixture with an alcohol-containing product in a ratio of 1: 1 to 1: 2, a second buffer liquid is injected, which is used as gas stable gasoline (BHS), which is a mixture saturated hydrocarbons With _{3 + higher} , while stable gasoline is used benzene gas stable and isopropyl alcohol (SIP) in the ratio (1-3): 1 as a buffer liquid on a hydrocarbon basis.

 The fact that as the first buffer liquid it is necessary to pump a mixture of hydrocarbon fractions (SFU) and isopropyl alcohol precisely in the ratio (1-3): 1, even for specialists it does not follow the prior art without additional studies to verify the degree of clay drying sample (table 4) and measurements of interfacial tension at the boundary of this buffer fluid with produced water (table 3). Only after carrying out these experiments it was found that the composition of SIP + BGS in a ratio of even 1: 3 almost equal to the commercial SIP drains moist clay samples, which is very important in terms of practical application, since it allows to significantly save the deficient SIP. And given that SFU is a waste and cheaper than self-supporting insulated wires, it is necessary to further reduce the costs of the process. In addition, a buffer liquid with a ratio of SFU: SIP equal to 3: 1, still quite effectively reduces interfacial tension at the border with formation water (up to 5 mN / m).

 As for alcoholic acid compositions, it is also only after a large amount of work has been done to study the solubility of sand and clay cores that their advantages (new properties) are compared with acid solutions, in particular, in reducing the reaction rate with polymictic sand cores by about 5- 35% (meaning a deeper treatment of the formation will be carried out), as well as alcohol-acid compositions, the interfacial tension at the border with kerosene is much less than conventional acid solutions (means the composition stumbled and in tight areas inhomogeneous reservoir).

 The injection of the second portion of the buffer fluid, namely BGS, aims not only to separate the alcohol-acid composition from the squeezing liquid, but also to clean the bottom-hole zone of asphalt-tar deposits during the reaction of the acid with the rock. It can be seen from Table 2 that, according to the solubility of the AFS, the GHS is not inferior to either GF or EBF, and if we take into account that GHS is more accessible to the November region of Western Siberia and without transportation costs, it is 2 times cheaper than GF and EBF is 7 times, from the point of view of practical application there is a significant savings.

 In the inventive method, each process fluid (the first buffer liquid, alcoholic acid solution and the second buffer liquid) exhibits additional functions with obtaining in the complex of an ultimately total effect.

 All chemicals used in the method are produced on an industrial scale. In the process of opening productive formations and throughout the life of wells, acidic solutions are periodically applied. Therefore, the inventive method is applicable, for example, in the oil and gas industry, geology at the present time.

 Technical hydrochloric acid HCl (TU 6-01-714-77) is supplied by industry to the November region, which is inhibited mainly by reagent KI-1 grade A 22-23%, grade B 20-23%.

 An inhibited mixture of hydrochloric and hydrofluoric acids (clay acid) is supplied by industry with a mass fraction of hydrogen chloride in the range of 20-25% and a mass fraction of hydrogen fluoride in the range of 3-5% (TU 6-01-14-78-88).

 KI-1 acid corrosion inhibitor and water repellent (TU 6-01-873-76) is a mixture of catapine-200, urotropine and water.

Isopropyl alcohol CIP (GOST 9805-84 or TU 39-576565-7-040-86) of a technical grade contains at least 87% of the main substance of isopropyl alcohol. The density of self-supporting insulated wires at 20 ^о С is 814-897 kg / m ³ , the boiling point is 82 ^о С.

Composition ERA (TU 2069635-001-90) is a mixture of spent solvent (mainly ethyl alcohol GOST 17299-78) manufactured SST-2 polymer with Neonol AF ₉ -6. Content of the basic substance (C ₂ H ₅ OH) in the composition ERA 55-85% Density at ²⁰ ° C 845-920 kg / m ^3.

Gasoline is a stable mixture of saturated C _{3 +} hydrocarbons _higher . According to TU 39-1340-89. The first two fractions of methane and ethane (C ₁ and C ₂ ) are not included in TU, since in most cases they are not included in the mixture and their concentrations actually vary respectively 0-0.09 and 0-0.17% 0.02- 0.09 vol. methane; 0.09-0.17 vol. ethane; 1.91-2.60 about. propane; 3.76-4.01 vol. isobutane; 7.38-8.65 vol. n-butane; 6.39-7.48 vol. isopentane; 8.51-9.58 vol. n-pentane; 68.51-70.85 about. the amount of hexanes; no solids; no water.

Physico-chemical properties of SFU: density at 20 ^о С 620-670 kg / m ³ ; initial boiling point 30-40 ^{° C;} boiling point temperature 120-200 ^о С; self-ignition temperature is above 380 ^{° C;} pour point of minus 95 ° ^C; explosive concentration of vapors mixed with air 1.4-8.0 vol.

The ethylbenzene fraction of EVF (TU 38-30225-81) is a mixture of aromatic hydrocarbons mixed with hexane. Density at 20 ° ^C 867 kg / m ^3.

 The hexane fraction GF (TU 38-10381-83) is produced by the Nizhnekamsk Petrochemical Plant.

 The method is as follows.

Pre-washed the interval of perforation and bottom hole through a deflated tubing from the accumulated sludge. After that, the first portion of the buffer fluid is pumped into the tubing, which consists of one part SIP and 1-3 parts of SFU pre-mixed in proportion, that is, 0.25 is taken to prepare 1 m ^{3 of} buffer solution in the SIP: SFU ratio of 1: 3, 0.25 m ³ SIP and 0.75 m ³ SFU. The volume of the first portion of the buffer fluid (SIP + SFU) is selected based on up to 5 m ³ per 1 m of the perforated part of the formation. Then a pre-mixed solution of commercial chemical products of inhibited hydrochloric acid or clay acid with an alcohol-containing product, for example SIP or ERA composition, is pumped in a ratio of 1: 1, that is, 0.5 m ^{3 of} clay acid and 0 are taken to prepare 1 m ^{3 of the} composition of clay + + SIP 5 m ³ SIW or, for example, 1/3 of hydrochloric acid + 2/3 of the composition of the ERA with a ratio of the latter 1: 2.

The volume of the alcoholic acid solution is taken from the calculation of up to 1 m ³ per 1 m of the perforated part of the formation. Next, a second portion of the buffer fluid is pumped into the tubing on the CBC. The volume of the second portion of the buffer fluid is selected based on a 2-3-fold excess of the casing filling volume in the perforation interval. Squeezing liquid, for example industrial water, saline or oil, is pumped over a second portion of the buffer liquid. After a portion of the first portion of the buffer fluid leaves the tubing and displaces the well fluid (oil) from the perforated zone, the annulus is closed at the mouth. Then they continue pumping and push the first portion of the buffer fluid (BGS + SIP) and the alcohol-acid solution into the productive formations, and the second portion of the buffer fluid (SFU) partially fills the bottomhole zone and the entire interior of the casing opposite the perforated part. The well is left to respond. After that, the annular space of the well is opened and, by backwashing with oil in a 1-2-fold volume of tubing, the reaction products are washed out of the wellbore. Then the well is mastered by the compressor by taking from it a liquid in an amount of at least 3 volumes of tubing.

 The effectiveness of the method is confirmed by laboratory studies.

 Firstly, in alcoholic acid solutions, the widely used acid corrosion inhibitor KI-1 does not lose its properties (Table 1). So, for example, the corrosion rate of the "D" grade steel tubing and the casing string most commonly used in the oil industry, when 1% KI-1 is added to an clay solution + SIP (or ERA) decreases by more than 2 times.

 The next important point is that the first portion of the BGS + SIP buffer liquid mixes well (is compatible) with oil, and the alcoholic acid solutions have low surface tension values measured with a stalagmometer at the interfaces between the oxygen and the hydrocarbon liquid (Table 5). Therefore, these process fluids will easily penetrate not only into highly permeable parts of heterogeneous formations, but also low permeability sections. This provides a more complete coverage of productive formations by treatment. In addition, the SFU + SIP alcohol-hydrocarbon buffer liquid has low interfacial tension values and at the border with water (Table 2, 3); therefore, it will also flow well into irrigated areas. From the data in Table 3, it can be seen that at SFU: SIP ratios of up to 3: 1, the interfacial tension at the boundary with formation water is still quite low 5 mN / m, but a further increase in the CW in the buffer fluid is undesirable.

 Thus, the first portion of the buffer fluid does not push the relict water deep into the reservoir, but mixes with it. Therefore, during the period of the reaction of the acid with the rock, drying (dehydration) of the bottomhole zone will occur. This is confirmed by the results presented in table 4. Samples of sifted clay powder with a diameter of 20 mm and a height of 32 mm were pressed for 5 min to determine the water absorption capacity of various media. Samples were weighed and immersed in 0.5% CMC solutions for 18 hours. Swollen samples were also weighed and placed in test compositions for 24 hours. Then, clay samples were weighed again and the degree of sample drying was judged by weight loss. Research results show that SFU has a weak water-absorbing property. At the same time, compositions containing SFU and SIP even in a ratio of 3: 1 have practically the same water-absorbing properties as pure SIP, at about 60%. Naturally, the alcohols included in alcoholic solutions will also contribute to dehydration bottomhole formation zone.

 In addition, from the data of Table 5 on the solubility of sand core of polymictic rocks, it can be seen that the percentage of dissolution in 60 minutes of the core of the Karamovskoye deposit in the compositions of clay acid + SIP and clay acid + ERA is approximately 25-35% less than just in a clay acid solution of that same concentration. Slowing down the reaction rate with the formation rocks will allow for deeper processing of the productive horizon.

 Table 6 shows the results of dissolution of clay core from well 422 of the Karamovskoye field. Since the carbonate content of the rocks in this field is very low, the core solubility in clay acid is about 4 times less. But if in the solution the clay-acid + SIP was less dissolved than in the solution of the clay-acid + water in the same proportion, then in the solutions of hydrochloric acid it is vice versa. So in the second case, the effect of not only dissolving the clay core with acid, but also its dehydration with a solution of hydrochloric acid + SIP was more pronounced. This allows us to conclude that during the reaction the pore space of the reservoir will be increased due to two factors: acid dissolution and dehydration of swollen rocks.

 In the table. 7 presents the results of studies of the solubility of asphalt-resin-paraffin deposits from different deposits with a second portion of SFU buffer fluid in comparison with the well-known and widely used HF and EBP. To assess the effectiveness, the “baskets” method was used with a mesh size of 1 mm and determination of the mass of the ARPD sample before and after dissolution and dispersion in a certain volume of buffer fluid. The studies were carried out in a dynamic mode, glasses with suspended baskets were mounted in cassettes rotating at a speed of 150-180 rpm. It was revealed that SFU is quite effective, at the level of the best solvents, it can remove paraffin from the bottomhole zone during the acid reaction period.

 Thus, an integrated approach to solving the problems of well repair will significantly increase the efficiency of the process. Since the proposed method uses relatively cheap and affordable compositions: with increased penetration, this increases the coverage of the formation by treatment; by slowing down the rate of reaction of the acid with the rock, it is able to conduct a deeper treatment; to dehydrate the reservoir and prevent the formation of oil-water emulsions; able to clear bottom-hole zone of paraffin; capable of easier and faster to remove reaction products from the pore space during well development.

Claims (1)

METHOD FOR PROCESSING A BOTTOM-HOLE ZONE OF A STRING by sequentially injecting a hydrocarbon-based buffer liquid into a formation and an inhibited aqueous solution of hydrochloric acid or clay acid, characterized in that, further, after injection of an inhibited aqueous solution of hydrochloric acid or clay acid in a mixture with an alcohol-containing product in a ratio of 1 to 1 up to 1 2, a second buffer liquid is pumped in, which is used gas stable gas, representing a mixture of saturated hydrocarbons C _{3 + higher} while in As a buffer liquid on a hydrocarbon basis, stable gasoline and isopropyl alcohol are used in the ratio of (1 3) 1, respectively.

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