RU2070963C1 - Method for intensification of operation of oil-gas-producing wells - Google Patents

Abstract

FIELD: production of liquid and gaseous minerals, for instance, oil and natural gas, including gas-condensate. SUBSTANCE: to increase the efficient radius of pore channels in reservoir cement and to remove colloid and solid products of reaction to bottom-hole formation zone, injected successively is solution alkali metal hydroxide and acid solution with concentration calculated to provide for dissolving alkali- and acid-soluble minerals in reservoir cement and between them, buffer solution to prevent mixing of the two first solutions. Buffer solution is used in form of solutions of chlorides, nitrates, fluorides or their mixtures. Concentration of alkali metal hydroxide is taken equal to 10-50 mas.%, and acid solution concentration of 12-30 mas.%. EFFECT: higher efficiency. 3 cl, 2 tbl

Description

 The invention relates to the production of liquid and gaseous minerals, for example, oil and natural gas, including gas condensate.

Known methods for intensifying the inflows of oil and gas wells by acidizing their bottom zones to increase the permeability of the latter, expanding the pore filtration channels by dissolving part of the collector minerals, in which one or a mixture of several (usually two) strong acids, for example, hydrochloric, is pumped into the bottom hole or hydrochloric with hydrofluoric (clay acid). The peculiarity of these methods is that after the acid solution is pushed into the bottomhole zone, it is left in it to react under pressure for 4 36 hours, and various reaction inhibitors and stabilizers are introduced into it to maintain the dissolving ability of the solution [1]
The disadvantages of these methods are as follows:
acids, with the exception of hydrofluoric acid, when interacting with minerals of the silicate and aluminosilicate groups, give a large amount of volumetric hydrogel of silicic acid, and even the presence of hydrofluoric acid is unable to completely remove it, since the fraction of the latter is from 20 to 35% of the active substance, in addition to hydrofluoric acid acid when interacting with calcium-containing minerals and solutions gives sparingly soluble fluorite (calcium fluoride), i.e. acidic solutions can form large quantities of colmatants, reducing boiling and sometimes precluding efficiency intensification;
acidic solutions have low permeability, especially in terrigenous reservoirs, and increase the viscosity of the formation fluid, which leads to the need to create high pressures to push them into the formation, often approaching the fracture pressures;
due to the described feature and the ability to easily dissolve the binder components of the sealing cement stone, they often destroy it and go not into the formation, but into the annulus, which leads to the occurrence of annular flows of water and gas without increasing the productivity of the well in the main mineral.

Closest to the claimed solution is a method of intensification of oil and gas wells, including the injection into the bottomhole zone of an alkali metal hydroxide solution [2]
The disadvantage of the prototype is the same as the above methods.

 The inventive method consists in the fact that three solutions are successively pumped into the well and its bottomhole zone: the first alkaline aqueous solution of an alkali metal hydroxide, for example sodium (caustic soda), the purpose of which is to dissolve alkali-soluble minerals in the cement of the reservoir and thereby increase the permeability to acid, a decrease in the viscosity of the formation fluid and its displacement into the remote bottomhole zone, and with the return movement, the removal of colloidal and solid reaction products of the acid solution; the second buffer, designed to prevent mixing of alkaline and acid solutions and the neutralization reaction between them; a third acidic, for example, hydrochloric acid or mixture of acids for dissolving acid-soluble minerals of cement in the reservoir, as well as solid and colloidal reaction products of an alkaline solution. The buffer solution is necessarily a solution of salt or salts used in the processing of acid (s) and base. The volume of solutions is determined by the usual method based on the selected conventional radius of the bottom hole treatment, the effective reservoir thickness and porosity of the reservoir, and the concentration of working alkaline and acid solutions from the amount of alkali and acid-soluble minerals in the cement of the reservoir. The concentration of the buffer solution is calculated so that its density is intermediate between the densities of alkaline and acid solutions. Thus, the proposed method provides an individual approach to the stimulation of each well.

 Well development is carried out immediately after the complete complete injection of the acid solution into the bottomhole zone, since exposure to the reaction does not make sense, since in the pore space of the formation, the active components of the solutions are completely consumed at a high reaction rate.

An example of calculating concentrations per 1 m ^{3 of} collector (conditional data):
Effective (open) porosity of the reservoir 20% pore volume filled with cement 15% including alkali-soluble minerals (opal-ST, halloysite) 40% of the filled pore volume, acid-soluble silicates and aluminosilicates (montmorillonite, chlorite) 45% iron hydroxides 10% carbonates (calcite, dolomite) 5% Reagents NaOH, HCl, NaCl buffer solution. Density of minerals (taking into account the friability of cement aggregates): carbonates 2.75; iron hydroxides 3.0; acid soluble silicates 1.8; opal-ST 1.9; halloysite 1.9. The mass of minerals in 1 m ^{3 of the} collector: carbonates 20.6 kg; iron hydroxides 45.0 kg; acid soluble silicates 121.0 kg; Opal-ST 60.0 kg; halloysite 60.0 kg. According to experiments, dissolution occurs in about half of the visible filled pores, and the rest, for various reasons, are not available for acid solutions, therefore, a coefficient of 0.5 is used in calculating the amount of acid. With this in mind, the consumption of Hcl for the dissolution of carbonates is 7.9 kg, iron hydroxides 15.3 kg, acid-soluble silicates 55.3 kg, the required excess of acids to maintain a pH <2.5 1.0 kg, and only 79.5 kg. The volume of open pores is 200 l, and taking into account the increase in pore space with a partial dissolution of cement 300 l Hence, the concentration of the acid solution should be 22 mass. The concentration of the alkaline solution takes into account the alkali consumption for the dissolution of opal-CT 40.0 kg and halloysite 32.6 kg. In addition, in the reaction of acid with silicates, 44.3 kg of silicic acid hydrogel are formed, and 40.3 kg of alkali are needed for the reaction with them. Given the excess alkali to maintain a pH> 12 (1.0 kg), its total amount is 112.9 kg. The volume of open pores is 200 l, and taking into account the partial dissolution of cement minerals in the process of movement of an alkaline solution, 220 l. Then the concentration of alkaline solution is equal to 50 wt. The acid solution of the calculated concentration has a density of 1.14 t / m ³ and alkaline 1.4 t / m ³ , respectively, the buffer solution should have a density of 1.2 t / m ³ , which corresponds to a NaCl concentration of 20 wt.

Before feeding into the well, it is advisable to warm the alkaline solution to a temperature of 25–80 ^° C depending on the formation temperature and the temperature of the outside air: at the formation temperature of 70–80 ^° C, heating is minimal, and at lower temperatures, since the dissolution occurs only in hot alkalis.

 Everything in the claimed method of the substance is known, all of them are used for the same or similar purposes, however, their use in one process, the sequence of administration, functionality and interaction, as well as concentration and method of their calculation significantly distinguish the claimed solution from the known ones, including the prototype allows to conclude that the criteria of "inventive step" and "novelty" are met.

The inventive method is tested by laboratory experiments and tested in an industrial environment at three wells of the Urengoy field. Laboratory experiments consisted of sequential pumping through water- and kerosene-saturated samples in reservoir or close conditions (Robzh 20.0 30.0 MPa; Pbx 17.0 24.0 MPa; P 0.3 1.0 MPa, t 70 80 ^o C) solutions of NaOH with a concentration of 10 to 50 wt. NaCl and NaCl + NaNO ₃ with a total concentration of 12 to 20 wt. HCl + NaNO ₃ solutions with a concentration of 15 to 22 wt. followed by reversal (reverse movement of the spent solutions) and measuring the permeability of water or kerosene before and after the experiment. As a result, permeability increased by 20 100% or more. As a result of industrial treatments according to the proposed method, two wells that were previously idle due to low flow rates were put into fountain mode, and one increased productivity 3 times.

 The table below shows the test results of the proposed method in the conditions of the Urengoy field.

Claims (3)

 1. The method of intensification of oil and gas wells, including the injection into the bottom-hole zone of an alkali metal hydroxide solution, characterized in that after the injection of the metal hydroxide solution into the bottom-hole zone, buffer and acid solutions are successively pumped.  2. The method according to p. 1, characterized in that as a buffer solution using solutions of chlorides, nitrates, fluorides or mixtures thereof.  3. The method according to p. 1, characterized in that the concentration of alkali metal hydroxide is taken equal to 10 50 wt. and the concentration of the acid solution is 12 to 30 wt.

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