RU2120546C1 - Method of reagent demudding of wells - Google Patents

Abstract

FIELD: mining industry; may be used in well operation. SUBSTANCE: method includes formation in zone of perforation of the first bath of aqueous solution of acid salt of alkali metal, its holding and removal; formation of the second bath of aqueous solution of hydrochloric acid, its holding and removal. Added to aqueous solution of hydrochloric acid is potassium chloride with concentration of 0.2-2 wt.%. The first bath is removed by displacement and replacement with initial volume of aqueous solution of hydrochloric acid with potassium chloride in the course of formation of the second bath. Initial volume of aqueous solution of hydrochloric acid with potassium chloride after holding is displaced from perforation zone upward by injection of displacing fluid. Displacing fluid is used in the form of said aqueous solution of hydrochloric acid with potassium chloride. The solution is forced through perforation zone to bottom-hole formation zone and held there. The second bath is removed by washing. EFFECT: higher efficiency of demudding of wells and increased well production rate. 8 cl

Description

 The invention relates to the mining industry and can be used in the operation of wells.

 There are various methods of reagent wedging of wells, including the formation of acids in the perforation zone of the bath to increase the permeability of the bottomhole formation zone, not only due to the reaction of acids with carbonates, but also due to the dissolution of clay minerals [1].

 However, practical tests show a low efficiency of acid exposure to clay-containing collectors and collectors that are clogged by clay minerals during drilling, tapping, repair work, which is associated with the specificity of the interaction of clay minerals with acids. The main fundamental drawback of these methods is the lack of dispersion of clay minerals and, as a consequence, the low solubility of clay minerals with acids. In addition, when exposed to acids, the effect of clay swelling is not prevented when they interact with fresh waters. These limitations determine the low efficiency of acidic methods of influencing reservoirs containing clay minerals.

 The closest is the method of reagent wedging of wells, including the formation in the perforation zone of the first bath of an aqueous solution of an alkali metal acid salt, its exposure, removal, the subsequent formation in the same zone of the second bath of an aqueous solution of hydrochloric acid, its exposure, removal of the second bath and subsequent development of the well [2].

 During the formation of the second bath, hydrofluoric acid is additionally introduced into the solution. In this method, a two-stage process of destruction of clay mud formations is organized, due to which the filtration conductivity of the bottomhole zone of the well is increased. The advantages of this method include the fact that it allows, with a relatively low consumption of reagents, to transfer clay minerals, clogging productive formations and ultimately reducing the flow of oil to the well, into a finely dispersed state and thereby make their dissolution real, as well as removing reaction products from the filter formation zones. Ultimately, this leads to a significant increase in the flow rate of wells in comparison with methods involving injection of acids.

 However, the main limitation of this method is that the cleaning of clay materials is carried out only directly in the perforation zone. Clay minerals remain in the bottom-hole part of the formation even when fresh water enters these zones, for example, during repair work and water is injected into the formation in order to maintain reservoir pressure, clay minerals can swell, i.e., increase their volume and block filtration channels, reducing thereby the flow rate or injectivity of the well. In addition, when implementing this method in practice, between the installation of the first bath and the second bath, it is necessary to flush the well with water, which increases the flow of water and for which additional time is required.

 Thus, the known method has a low efficiency of restoring the initial hydraulic conductivity of the bottomhole zone, which is especially important for injection wells.

 The problem solved by the invention is to increase the effectiveness of wedging wells and increase their flow rate.

 The technical result that can be obtained by implementing the inventive method is to increase the hydraulic conductivity of the formation.

 To solve the problem in the known method of reagent wedging wells, including the formation in the area of the first bath of an aqueous solution of an alkali metal acid salt, its exposure, removal, the subsequent formation in the same area of the second bath of an aqueous solution of hydrochloric acid, its exposure, removal of the second bath and the subsequent well development, according to the invention, potassium chloride is added to an aqueous solution of hydrochloric acid in a concentration of 0.2 - 2 wt.%, the first bath is removed by its displacement and replacement with the original the volume of an aqueous solution of hydrochloric acid with potassium chloride in the specified concentration during the second bath, while the said initial volume of the aqueous solution of hydrochloric acid with potassium chloride in the specified concentration after exposure is displaced from the perforation zone by injection of the selling fluid, which is used as the above aqueous hydrochloric solution acids with potassium chloride in the specified concentration, push it through the perforation zone into the bottom-hole zone of the formation and stand, and the removal of the second bath is carried out pour by washing.

Additional embodiments of the method are possible, in which it is advisable that hydrofluoric acid with a concentration of 2-5 wt.% Is introduced into an aqueous solution of hydrochloric acid with potassium chloride in a concentration of 0.2-2 wt.%; a solution of sodium bicarbonate with a concentration of 5-15 wt.% was used as an aqueous solution of an alkali metal acid salt, and the first bath was aged for 8-10 hours; the second bath of an aqueous solution of hydrochloric acid with potassium chloride in a concentration of 0.2-2 wt.% was formed for 0.5-1 hours, while hydrochloric acid in a concentration of 6-10 wt.% would be used; the formation of the first and second baths was carried out by injection of solutions through a tubing string (NTK), lowered to the lower holes of the perforation zone, while the total volume Q of an aqueous solution of hydrochloric acid with potassium chloride at a concentration of 2-5 wt.% would be selected from the ratio
Q = (8 ÷ 13.5) πh (R ² -r ² ) + (1,5 ÷ 2) πhmR $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ ,
Where
h is the height of the filter, m;
R is the inner radius of the casing, m;
r is the outer radius of the tubing, m;
m is the coefficient of effective porosity;
R _p - radius adjacent to the well of the formation zone, m,
the initial volume of Q ₁ aqueous solution of hydrochloric acid with potassium chloride at a concentration of 0.2-2 wt.% was selected from the ratio
Q ₁ = (5 ÷ 10) πh (R ² -r ² ),
the volume of Q ₂ selling fluid, which is used as an aqueous solution of hydrochloric acid with potassium chloride at a concentration of 0.2-2 wt.%, was selected from the ratio
Q ₂ = (3 ÷ 3,5) πh (R ² -r ² ),
the volume of Q ₃ to fill the threshold space of the bottomhole formation zone with an aqueous solution of hydrochloric acid with potassium chloride at a concentration of 0.2-2 wt.% was chosen from the ratio
Q ₃ = (1.5 ÷ 2) πhmR $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ .
By introducing potassium chloride acid into the solution and performing the above operations with this solution, it is possible to maintain the hydraulic conductivity of the bottomhole formation zone.

 The indicated advantages, as well as the features of the present invention, are illustrated by the best embodiment with a specific example of the method and with reference to FIG. 1 and 2.

 In FIG. 1 shows the dependence of the degree of substitution of a solution of acids with potassium chloride φ on the volume of pumped liquid Q; in FIG. 2 - dependence of the degree of restoration of hydraulic conductivity of the bottomhole formation zone χ on the volume of pumped fluid Q.

 The essence of the proposed technical solution consists in processing clay particles initially, as in the known solution, with an aqueous solution of alkali metals, which in the first stage of the process leads to the dispersion of clay materials as a result of ion-exchange reactions and subsequent processing of clay particles located in the pore space of the bottomhole formation an aqueous solution of these acids with potassium chloride. The interaction of the proposed acid solution with potassium chloride leads to the penetration of potassium ions into the interplanar distance between the flakes of clay particles, as a result of which they flow through each other near each other. With the subsequent penetration of water with low salinity, which is usually the water injected into the formation, ion-exchange reactions practically do not occur, the clay does not swell and, thus, the hydraulic conductivity of the layers is preserved.

 As studies have shown, compared with the known method, when the content of potassium chloride in the acid solution is more than 0.2%, fresh water does not impair the hydraulic conductivity of the collector. An increase in the concentration of said salt above 2% leads to the appearance of a solid precipitate in the solution, which can cause blockage of the pore channels, and, consequently, reduce the flow rate or injectivity of the well.

 In practice, in the known method, prior to the installation of the second acid solution bath, it was necessary to wash the bottom-hole zone with water in order to remove clay minerals and reaction products. In the proposed method, the removal from the bottom zone of an aqueous solution of an acidic alkali metal salt with the products of the ion exchange reaction allows you to remove the products of the displacement reaction and thereby eliminate the additional washing operation.

 As in the known method, to dissolve the aluminosilicates in the second bath, hydrofluoric acid can be added in a concentration of 2-5 wt.%.

As an aqueous solution of an acid salt of an alkali metal, you can use a solution of soda NaHCO ₃ with a concentration of 5-15%, and exposure is carried out for 8-10 hours

 The injection of an aqueous solution of an acid salt of an alkali metal and the formation of the first and second baths, as in the known method, is carried out using a tubing string (tubing), lowered to the lower holes of the perforation zone. In this case, the required volume Q of an aqueous solution of acids with potassium chloride can be obtained from the following considerations.

The amount of potassium chloride acid solution must be such that its volume quantity Q is sufficient
a) the formation of a second bath with the aim of dissolving clay materials that have passed into a finely dispersed phase as a result of treatment with an alkali metal acid salt solution
Q ₁ = (5 ÷ 10) πh (R ² -r ² ),
Where
h is the height of the filter, m;
R is the inner radius of the casing, m;
r is the outer radius of the tubing, m;
Given the errors in measuring volumes during repair work on wells to prevent possible errors, in practice a 5 - 10-fold supply of acid solution is accepted with a thickness of opened productive formations from 5 to 15 m. For thinner formations this reserve can be selected and 30 - 50 times in order to deliberately position the bath against productive formations.

b) to remove from the perforation zone a solution containing the reaction products of acids with clay components (the operation of removing the solution by displacement)
Q ₂ = (3 ÷ 3,5) πh (R ² -r ² ),
what is obtained experimentally as a result of the study of the well model.

 As can be seen from FIG. 1, for this purpose, 3 to 3.5 volumes of the annulus in the well perforation zone are sufficient.

c) to fill the pore space of the bottomhole zone of the well in order to consolidate the clay and, therefore, prevent their swelling when interacting with water having a low salt concentration
Q ₃ = (1.5 ÷ 2) πhmR $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ ,
Where
m is the coefficient of effective porosity;
R _p - radius adjacent to the well of the formation zone, m;
The volume of pumped fluid for an effective degree of restoration of hydraulic conductivity of the bottomhole formation zone χ, as follows from FIG. 2 should be 1.5 to 2 pore volumes.

Typically, the coefficient of effective porosity is taken on average equal to 0.2, and the radius R _p equal to 0.5.

 As can be seen from FIG. 1 and 2, both dependences at certain specified values of the argument Q become almost constant.

Thus, the total required volume of a solution of acids with potassium chloride corresponds to (Q = Q ₁ + Q ₂ + Q ₃ )
Q = (8 ÷ 13.5) πh (R ² -r ² ) + (1,5 ÷ 2) πhmR $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ .
Installation of a bath from a solution of acids with potassium chloride for 0.5 - 1 h is selected from the level that during this period of the reaction of acid with fine particles of clay materials proceeds completely, and an increase in bath time can lead to additional unjustified corrosion of the pipes.

 Before removing the second bath, they pump into the well through a tubing string (tubing) with an open annular space of the squeezing liquid in the amount of 3 - 3.5 volumes of the annular space in the perforation zone, then close the annular space and squeeze the aqueous solution of acid with chloride potassium in the volume of 1.5 - 2 volume of the pore space of the rock adjacent to the perforation zone, after punching, hold for 0.5 to 1 hour. Closing the annulus after injection into The tubing of the squeezing fluid ensures that a solution of potassium chloride in acid containing no reaction products enters the bottomhole formation zone. The exposure time of 0.5 - 1 h is due to the time required for the binding of potassium ions to clay particles.

 An example implementation of the method.

A well equipped with a tubing string is connected to equipment for pumping working solutions and lowering and raising tubing. The tubing string is lowered below or to the lower holes of the casing filter. As equipment, you can use a cementing unit, for example, CA-320, in the tank of which a 6% NaHCO ₃ soda solution is poured, and an acid injection unit such as AzINMASH-30 with a solution containing a corrosion inhibitor, 10% HCl, 3% HF and 1% KCl. The well is pre-muffled and connected to the equipment installed on its mouth.

The first unit is pumped into the tubing string 4 m ³ of soda solution and, pushing it with water, is brought to the bottom. An installed bath of a soda solution is kept for 10 hours.

Next, a solution of 10% HCl, 3% HF and 1% KCl is pumped into the well. The total volume of the solution is calculated by the above formula. With a casing string with a diameter of 146 mm, a wall of 8 mm and a tubing string diameter of 73 mm, h = 10 m, with m = 0.2 and R _p = 0.5, we obtain
Q = (8 - 13.5) • 3.14 • 10 • (0.065 ² - 0.031 ² ) + (1.5 - 2) • 3.14 • 10 • 0.2 • 0.5 ²
Thus, the value of Q is in the range from 3.2 m ³ to 4.4 m ³ .

Take Q = 4 m ³ .

Next, the solution is added to the acid with potassium chloride by pumping with a washing liquid to the bottom of the well, displacing and replacing it with a salt solution without first washing the well, and form an acid bath in the annulus in accordance with the expression for Q ₁ in a volume of 0.5 m ³ for a period of 0 5 hours

Then, with an open annulus, squeezing fluid is pumped into the tubing string in a volume of Q ₂ corresponding to 0.3 m ³ for the selected example. In this case, the initial volume Q ₁ , contaminated by the reaction products of the action of clay-containing particles with acid, is displaced upward. After that, the annulus is closed and fluid is pumped into the tubing, thereby forcing acid with potassium chloride into the bottomhole formation zone, and the well is left for 0.5-1 hours. After that, the well is washed and mastered in the usual way.

 The tests showed that the increase in flow rate or injectivity is not less than 2 - 2.5 times.

 The most successfully claimed method of reagent claying of wells can be used in the mining industry when commissioning clay wells.

Sources of information
1. Patent of the Russian Federation N 2078203, E 21 B 43/27, publ. 04/27/97.

 2. Patent of the Russian Federation N 2055983, E 21 B 43/27, publ. 03/10/96.

Claims (6)

 1. The method of reagent wining of wells, including the formation in the perforation zone of the first bath of an aqueous solution of an alkali metal acid salt, its exposure, removal, the subsequent formation in the same zone of the second bath of an aqueous solution of hydrochloric acid, its exposure, removal of the second bath and subsequent development of the well, characterized in that potassium chloride is added to an aqueous solution of hydrochloric acid in a concentration of 0.2 to 2 wt.%, the first bath is removed by its displacement and the initial volume of the aqueous solution is replaced with hydrochloric acid acid with potassium chloride in the specified concentration during the formation of the second bath, while the said initial volume of an aqueous solution of hydrochloric acid with potassium chloride in the specified concentration after exposure is displaced from the perforation zone by injection of a selling fluid, which is used as the above aqueous solution of hydrochloric acid with chloride potassium in the specified concentration, push it through the perforation zone into the bottomhole formation zone and incubate, and the second bath is removed by washing.  2. The method according to claim 1, characterized in that in an aqueous solution of hydrochloric acid with potassium chloride in a concentration of 0.2 to 2 wt.% Injected hydrofluoric acid with a concentration of 2 to 5 wt.%.  3. The method according to claim 1, characterized in that a solution of sodium bicarbonate with a concentration of 5-15 wt.% Is used as an aqueous solution of an acidic alkali metal salt, and the first bath is aged for 8-10 hours.  4. The method according to claim 1, characterized in that the second bath of an aqueous solution of hydrochloric acid with potassium chloride in a concentration of 0.2 to 2 wt.% Form for 0.5 to 1 hour, using hydrochloric acid at a concentration of 6 - 10 wt.%. 5. The method according to p. 1, characterized in that the formation of the first and second baths is carried out by injection of solutions through a tubing string, lowered to the lower holes of the perforation zone, with the total volume Q of an aqueous solution of hydrochloric acid with potassium chloride in concentration of 2 to 5 wt.% choose from the ratio
Q = (8-13.5) πh (R ² -r ² ) + (1.5-2) πhmR $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ ,
where h is the height of the filter, m;
R is the inner radius of the casing, m;
r is the outer radius of the tubing, m;
m is the coefficient of effective porosity;
R _p - radius adjacent to the well of the formation zone, m 6. The method according to p. 5, characterized in that the initial volume Q _{1 of an} aqueous solution of hydrochloric acid with potassium chloride in a concentration of 0.2 to 2 wt.% Is selected from the ratio
Q ₁ = (5-10) πh (R ² -r ² ).
7. The method according to claim 5, characterized in that the volume Q _{2 of the} selling liquid, which is used as an aqueous solution of hydrochloric acid with potassium chloride in a concentration of 0.2 to 2 wt.%, Is selected from the ratio
Q ₂ = (3-3.5) πh (R ² -r ² ).
8. The method according to claim 5, characterized in that the volume of Q ₃ to fill the pore space of the bottomhole formation zone with an aqueous solution of hydrochloric acid with potassium chloride in a concentration of 0.2 to 2 wt.% Is selected from the ratio
Q ₃ = (1.5-2) πhmR $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ .P

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