RU2352754C1 - Method of repairing wells of underground reservoirs - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: while implementing method, well is preliminary filled with saturated water solution of common salt with density 1180-1200 kg/m³ to base surface of artificial bottomhole, then lower part of flow string is perforated by making four diametrical openings of 20 mm diameter. The artificial bottomhole is set by means of pumping return emulsion, containing filler - polypropylene fiber- at amount of 0.03-0.05 wt % from the volume of return emulsion, and by pumping cement grout with density 900-1000 kg/m³, made on mineralised water, in volumes facilitating formation of columns 10 m each in an open borehole of the well; then the well is held for the period of cement hardening. An additional casing column is lowered and cemented to the well head. Before pumping the cement grout in the middle part of the interval of its location three circular grooves of 15 cm depth are made at the distance of 1 m one from another. After holding the well for cement hardening the borehole of the well is expanded and its diameter is increased in interval from the top of the artificial bottomhole to the base of the flow string. Tamping the lower part of the flow string is performed by supplying cement grout with density 1840-1900 kg/m³ made on mineralised water in volume calculated from formula. The well is held for cement hardening with following boring a cement column at a depth facilitating setting of the shoe of the additional casing column lower, than the shoe of the flow string.

EFFECT: upgraded quality of pressure tightness restoration of column.

2 cl

Description

The invention relates to the operation of underground reservoirs created in rock salt, and is intended to restore the integrity of the production string.

A known method of repairing a production well, including the installation of artificial slaughter from a viscoelastic composition and the supply of cement mortar through a pipe string (see p. Of the Russian Federation No. 2121559 of 03/27/98 according to CL E21B 33/13, publ. 10.11.98, OB No. 31). A viscoelastic solution is installed in the range below the lower boundary of the leakage of the production string, while the height is determined from the condition of ensuring the equilibrium of the hydrostatic pressure of the liquid column in the well and reservoir pressure.

The disadvantages of the method is the poor restoration of the tightness of the production casing of wells of underground tanks created in rock salt. The artificial slaughter from the WCS does not allow the creation of a durable cement stone in the shoe of the production casing, as the strength properties of the WCS will not ensure the installation of a large volume of cement mortar in a given interval. When a cement mortar is supplied in one portion, a discontinuity of the WCS can occur and, as a result, cement mortar leakage. The leakage of the latter can also occur at the contact of the WCS with the reservoir rock, since VUS is not inert to rock salt and will not provide high-quality adhesion to it. The method does not include the descent of the additional casing string, and in the case of the descent of the latter, artificial slaughter will not allow creating a high-quality cement ring between the production casing and the additional casing string, since the stresses arising during the operation may cause partial destruction or its creep due to the lack of adhesion of the used cement mortar to rock salt.

There is a method of repairing wells in underground tanks, including perforating the bottom of the production casing, installing artificial slaughter, plugging the bottom of the production casing, lowering the additional casing and cementing it to the wellhead (see RF No. 2211300 of 12/27/2001, according to cl Е21В 29 / 00, published on August 27, 2003, OB No. 24). As an artificial slaughter, a packer is installed. The plugging of the lower part of the production casing is carried out by pumping brine heated to 60-90 ° C into the well.

The disadvantage of this method is the poor restoration of the tightness of the production casing of wells of underground tanks created in rock salt. Underground tanks most often have large diameters and the use of packers in these cases is impossible. The used packer, blocking the space between the production casing (main) and the additional casing, does not allow isolation with normal density cement mortar in the shoe interval and create a strong and impermeable cement stone behind the production casing, where there may be cavities formed during erosion in the salts of the underground reservoir . The use of concentrated brine, for example, NaCl solution, heated to a temperature above the rock temperature (60-90 ° C), will not provide a qualitative restoration of the tightness of the production string, since when cooling in the well, salt crystals crystallize from the brine, which can clog only small cracks, but not able to clog large, and even more caverns. Well repair of underground reservoirs created in rock salt using this solution can only be carried out if viscoplastic clays are present in the annulus, which penetrate into the fracture zone in the annulus of cement during crystallization of the salt from the brine. And if there are no such clays, then it is impossible to achieve high-quality repair.

The technical result consists in improving the quality of restoring the tightness of the production string by creating a strong and impermeable cement stone in the interval of the shoe of the production string due to the possibility of using cement of normal density, ensuring its delivery to the area below the shoe of the string, eliminating interaction with the liquid in the well and the possibility additional sealing.

The technical result is achieved in that in a method of repairing wells of underground reservoirs, including perforating the bottom of the production string, installing artificial bottom, plugging the bottom of the production string, lowering the additional casing and cementing it to the wellhead.

According to the claimed method, the well is pre-filled with a saturated aqueous solution of sodium chloride with a density of 1180-1200 kg / m ³ to the bottom of the artificial bottom.

Perforation of the lower part of the operational casing string is carried out by making four diametrically arranged holes with a diameter of 20 mm.

Artificial slaughter is established by pumping a reverse emulsion into the well with a filler content of polypropylene fiber, in an amount of 0.03-0.05 wt.% Of the volume of the inverse emulsion, and a cement slurry with a density of 900-1000 kg / m ³ mixed with mineralized water, in volumes ensuring the creation by them of 10 m each columns in the open hole of the well, and the shutter speed of the well for the period of OZZ.

Before pumping the specified cement mortar in the middle part of the interval of its location, three annular grooves with a depth of 15 cm are performed at a distance of 1 m from each other.

After the well is kept for the period of the wet drilling cycle, the wellbore is expanded, increasing its diameter in the interval from the artificial bottom face to the casing shoe.

Tamponization of the lower part of the production casing is carried out by supplying a cement mortar with a density of 1840-1900 kg / m ³ , shut in mineralized water, in a volume calculated by the formula:

V ₁ = 0.785 * (K * D) ² * h ₁ + 0.785 * D _in ² * h ₂ ,

K is the coefficient of expansion of the wellbore;

D - nominal (initial to expansion) borehole diameter, m;

D _in - the inner diameter of the production casing, m;

h ₁ - the distance between the artificial slaughtering roof and the shoe of the production casing, h ₁ ≥10 m;

h ₂ - the height of the cement glass, m,

and exposure of the well for the period of the SSC with subsequent drilling of the cement nozzle to a depth that ensures the installation of the shoe of the additional casing string below the shoe of the production string.

As the reverse emulsion using the following composition, wt.%:

Hydrocarbon fluid 20-25 Chloride aqueous solution calcium density 1120 kg / m ³ 74-78.5 Cationic emulsifier 1.0-1.5

Thus, this technical solution meets the condition of novelty.

Wells of underground reservoirs created in rock salt were most often intended for the storage of liquid hydrocarbons, therefore, there were no special requirements for the tightness of the production casing string. When transferring the constructed underground tanks to underground gas storage, the requirements for tightness increased sharply.

The reason for the leakage of the production string is the poor adhesion of the cement stone to the casing and rock, especially in the salt bed. Through cracks and channels of annular space gas can leak to the surface. In many cases, when salts are washed away in the underground reservoir, the shoe of the production casing is bare, uncemented, with caverns. Another cause may be disruption to the production string.

Before carrying out repair work, the well of the underground reservoir is pre-filled with a saturated aqueous solution of sodium chloride with a density of 1180-1200 kg / m ³ to the bottom of the artificial bottom. This is required in order to install artificial slaughter on the surface of an aqueous solution of sodium chloride, including pumping an inverse emulsion with a filler and cement mortar with a density of 900-1000 kg / m ³ . The density of the aqueous solution of sodium chloride, inverse emulsion and cement slurry is chosen from the condition

ρ _W > ρ _e > ρ _p ,

where ρ _W - the density of a saturated aqueous solution of sodium chloride, kg / m ³ ;

ρ _e - the density of the inverse emulsion with a filler injected into the well, kg / m ³ ;

ρ _p - the density of the cement slurry, closed on saline water, kg / m ³ .

Such a ratio of the densities of an aqueous solution of sodium chloride, inverse emulsion and cement mortar is selected in order to ensure their sedimentation stability when injected into the well and to maintain consistent placement in the well, eliminating the substitution of each other.

Perforation of the lower part of the production casing is carried out by making four diametrically located holes with a diameter of 20 mm at a distance of 10 m above the shoe of this casing. The selected diameter and the uniform arrangement of holes around the circumference provide communication between the annular and annular space of the well, necessary for the passage of fluid from the annular space. Making holes with a diameter of more than 20 mm will cause a change in the flow rate, which will degrade the quality of filling the grouting channels. Making holes with a diameter smaller than the selected one will not provide a decrease in resistance when cementing the bottom of the production casing.

When installing artificial slaughter before pumping cement slurry with a density of 900-1000 kg / m ³ , closed on mineralized water, the implementation of three annular grooves in the middle of the interval of its location with a depth of 15 cm at a distance of 1 m from each other is necessary to increase the bearing capacity of artificial slaughter and preventing it from moving in contact with the rock (rock salt) after the cement slurry has solidified. The artificial slaughter created in this way withstands additional loading with cement mortar with a density of 1840-1900 kg / m ³ , ensuring its delivery to the zone below the column shoe.

The height of the artificial bottom depends on the bending strength of the cement stone based on the cement slurry with a density of 900-1000 kg / m ³ and the surface area of the artificial bottom (borehole diameter). The greater the strength of the cement stone and the smaller the surface area of the artificial face, the lower the height of the interval of location of the artificial face. The bending strength of a cement stone based on a cement mortar with a density of 900-1000 kg / m ³ after two days of hardening at a temperature of 20 ° C is not more than 1.0 MPa, therefore, the height of the interval for the location of the specified cement mortar is taken to be 10 m. The height of the inverse emulsion with the filler must be not less than the height of the cement slurry with a density of 900-1000 kg / m ³ to prevent their mutual substitution during the injection process. Therefore, the height of the column of the inverse emulsion with the filler is taken equal to 10 m

Cement mortar with a density of 900-1000 kg / m ³ for installation of artificial slaughter and cement mortar with a density of 1840-1900 kg / m ³ for cementing the bottom of the production casing are closed with mineralized water (NaCl) with a density of 1050-1100 kg / m ³ to prevent the dissolution of rock salt rocks in contact with the cement and the formation of channels for the passage of gas from the well.

The plugging of the lower part of the production casing provides annular space sealing in the interval of the casing shoe in the presence of uncemented channels or caverns and creates an insulating hermetic cement screen below the casing shoe. The height of this insulating screen, which is the distance between the shoe of the production casing and the artificial slaughtering roof, h ₁ , must be taken at least 10 m, which is associated with ensuring guaranteed isolation of the lower part of the production casing from a breakthrough from the gas well, as well as the quality of the cement stone for gas permeability and the quality of the contact of the cement stone with the rock - halite (rock salt).

In the interval from the artificial slaughtering roof to the shoe of the production casing, the wellbore is expanded with a mechanical expander, increasing its diameter. This diameter is limited by the characteristic of the mechanical expander itself. To perform this operation, you can use a hydraulic monitor, however, the use of a standard hydraulic monitor will not ensure uniform destruction of rock salt. The expansion of the trunk is required to prevent cracking of the cement stone when drilling a cement cup before lowering the additional casing. The thicker wall of the cement cup provides higher strength and resistance to cracking. The formula for calculating the volume of cement slurry density 1840-1900 kg / m ³ , closed on saline water, enter the coefficient of expansion of the wellbore K, which is defined as the ratio between the maximum possible expanded borehole diameter obtained using a mechanical expander and the nominal borehole diameter in extension run interval.

When installing artificial slaughter on the surface of a saturated aqueous solution of sodium chloride, a reverse emulsion is pumped into the well with a filler content of polypropylene fiber in an amount of 0.03-0.05 wt.% Of the volume of the inverse emulsion. The reverse emulsion acts as a separation fluid between an aqueous solution of sodium chloride and a cement mortar. Due to its hydrophobicity, the inverse emulsion does not mix with these liquids.

Reverse emulsion has structuring properties and contains polypropylene fiber as a filler. This filler in the proposed ratios practically does not affect the plastic viscosity, but significantly increases the ultimate dynamic shear stress and the thixotropy coefficient, which ensures the formation of the structure in a short time after injection into the well. When using polypropylene fiber in an amount of less than 0.03%, it is impossible to obtain the described properties. Use in an amount of more than 0.05% is impractical, since with an increase in its amount the properties of the emulsion do not significantly change.

Cement mortar is not diluted with well fluid, which ensures good quality of cement stone, primarily in terms of strength.

When used in the composition of a hydrocarbon liquid in an amount of less than 20 wt.%, The emulsion does not have sufficient sedimentation stability, and its addition of more than 25 wt.% Does not provide sufficient viscosity to keep the filler in suspension.

The addition of an aqueous solution of calcium chloride of less than 74 wt.% Does not allow to obtain a composition having a sufficient viscosity, and the addition of more than 78.5 wt.% Will not provide sedimentation stability of the emulsion.

The use of a cationic emulsifier in an amount of less than 1 wt.% Does not allow to obtain a composition with sufficient sedimentation stability, and more than 1.5 is not advisable, since the properties of the emulsion do not change.

The descent of the additional casing string below the shoe of the production string provides additional sealing annular space, which guarantees its quality. And cementing the additional string to the mouth eliminates violations (cracks, corrosion damage, wear) in the production string.

Thus, the set of essential features of the invention provides a durable and impermeable cement stone in the interval of the shoe of the production casing, which characterizes the high quality of restoration of the tightness of the production casing. From the scientific, technical and patent literature, we have not identified sources of information containing features that match the distinguishing features of the invention. The technical solution does not follow for the specialist explicitly from the prior art, therefore, has an inventive step.

The essence of the proposed method is illustrated by the following example.

Initial data:

Diameter of production casing, D, mm 324 Depth of descent of the production casing, L, m 803 Bore diameter wells in the range of 803-850 m, m 0.50-0.60 Open hole diameter in the range of 850-880 m, m 0.40-0.48 Depth of underground tank, m 1196 Saturated Density water solution salt filling the well, kg / m ³ 1200

According to the ACC, there are no cavities behind the production casing, but the quality of the contact of cement stone with the casing and the walls of the well is unsatisfactory. An underground tank was built to store hydrocarbon fluids. Currently, the task is set to transfer this underground reservoir to gas storage. For this, it is necessary to carry out repair work in order to increase the tightness of the lining (production casing) of the well.

Process fluids are prepared, for which the required volumes are calculated. To plug the bottom of the production casing, use cement slurry, sealed with mineralized water, with a density of 1900 kg / m ³ , volume V ₁ = 0.785 * (2.67 * 0.6) ² * 10 + 0.785 * 0.3 ² * 10 = 20.8 m ³ , while the distance between the artificial slaughtering top and the casing shoe is taken to be the minimum possible value, 10 m, and the borehole expansion coefficient 2.67 (the maximum possible size of the expanded borehole using a mechanical expander is 1.60 m) .

The diameter of the wellbore in the zone of location of a cement slurry with a density of 1000 kg / m, closed on saline water, and the inverse emulsion with polypropylene fiber are the same, so the volume required to create a column with a height of 10 m is V _lr = 0.785 * 0.6 ² * 10 = 2.83 m ³ .

The reverse emulsion has the following composition, wt.%:

Diesel fuel 25 Calcium Chloride Aqueous Solution 74 Emultal one

Diesel fuel according to GOST 305-82, calcium chloride according to GOST 4460-87, emulsion according to TU 6-14-1035-79.

In one container, 2.123 m ^{3 of an} aqueous solution of calcium chloride with a density of 1120 kg / m ³ (332.7 kg of anhydrous calcium chloride) is prepared, and 43 kg of emulsion in 0.707 m ^{3 of} diesel fuel are dissolved in another container. Both solutions are pumped through a tee and dispersant into a separate container and dispersed until a homogeneous emulsion is obtained (2-3 cycles). 1.42 kg of polypropylene fiber, which is 0.05 wt.% Of the volume of the emulsion, is introduced into the finished emulsion and mixed uniformly until a homogeneous mass is obtained.

Based on the above calculations, determine the required level of a saturated aqueous solution of sodium chloride. The level should be 833 m. An echo sounder in the borehole determines the level of sodium chloride solution filling the borehole and is added to the required level. The liquid level mark in the well is 835.4 m. The well is filled with a saturated aqueous solution of sodium chloride with a density of 1200 kg / m ³ , volume V = 0.785 * 0.6 ² * 2.4 = 1.13 m ³ . To prepare this volume of solution, 351.7 kg of crystalline salt is required.

The production string is perforated in the range of 10 m from the shoe, creating four diametrically located holes. The diameter of each hole is 20 mm. The calculated volume of the inverse emulsion with filler is pumped through the tubing. Using a mechanical expander at a depth of 817 m, 818 m and 819 m, circular grooves are made with a depth of 15 cm, after which a cement mortar with a density of 1000 kg / m ³ , pumped in mineralized water, is pumped. The well is maintained for 48 hours, after which the overlying interval of the wellbore is extended to the shoe of the production casing, increasing the diameter by 1.0 m. 20.8 m ^{3 of} grouting mortar grilled on mineralized water with a density of 1900 kg / m ^{3 are fed} . Withstand the well for 24 hours. Drill a cement cup, going deeper below the shoe of the production string by 10 m. Lower the additional casing and cement it to the mouth, pumping cement into the well with a density of 1900 kg / m ³ in a volume of V ₂ = 0.785 * (0.304 ² -0.245 ² ) * 803 + 0.785 * 0.225 ² * 10 = 20.42 + 0.4 = 20.82 m ³ .

After 24 hours, comprising the waiting time for cement hardening, an additional casing is tested for leaks. The tests were carried out successfully, which characterizes the high quality of the restoration of tightness and industrial applicability of the invention. The invention has an inventive step, is new and industrially applicable, therefore, meets the condition of patentability.

Claims (2)

1. A method of repairing wells in underground tanks, including perforating the bottom of the production casing, installing artificial slaughter, plugging the bottom of the production casing, lowering the additional casing and cementing it to the wellhead, characterized in that the well is pre-filled with saturated aqueous sodium chloride density 1180 -1200 kg / m ³ to artificial bottom sole and perforating the bottom of the production tubing is carried performing four diametrically aspolozhennyh holes 20 mm in diameter, the artificial slaughter adjusted by pumping into the well with an invert emulsion containing a filler -. polypropylene fibers in an amount of 0.03-0.05 wt% of the inverse emulsion and the cement slurry density of 900-1000 kg / m ³ , shut on mineralized water, in volumes that ensure that they create columns in the open borehole of 10 m columns each, and hold the well for the period of the BCP, while before pumping the specified cement mortar in the middle of the interval, it is located Three circular grooves 15 cm deep at a distance of 1 m from each other are performed, and after the well has been kept for the period of the test period, the wellbore is expanded, increasing its diameter in the interval from the artificial slaughtering roof to the production casing shoe, and the lower part of the production casing is plugged by feeding cement mortar with a density of 1840-1900 kg / m ³ , closed on mineralized water, in the volume calculated by the formula:
V ₁ = 0.785 · (K · D) ² · h ₁ + 0.785 · D _in ² · h ₂ ,
where K is the coefficient of expansion of the wellbore;
D - nominal (initial to expansion) borehole diameter, m;
D _in - the inner diameter of the production casing, m;
h ₁ - the distance between the roof of the artificial slaughter and the shoe of the production casing, h ₁ ≥10 m;
h ₂ - the height of the cement glass, m,
and exposure of the well for the period of the OZZ with subsequent drilling of the cement nozzle to a depth that ensures the installation of the shoe of the additional casing string below the shoe of the production string. 2. The method according to claim 1, characterized in that as the inverse emulsion using the following composition, wt.%:
Hydrocarbon fluid 20-25 Chloride aqueous solution calcium, density 1120 kg / m ³ 74-78.5 Cationic emulsifier 1.0-1.5