RU2568198C1 - Method for cementing auxiliary string at well workover - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention suggests method for cementing auxiliary string with stages whereat geophysical survey of the well is performed in order to indentify state of the production string, location of disturbed intervals and perforated intervals; assembly of auxiliary string is run in and set at depth identified by results of geophysical survey of the well; grout injection equipment for is run in to the well; design volume of cement grout is prepared and injected to auxiliary string; displacing fluid is injected to the auxiliary string so that cement grout fills tubing-casing annulus; the well is withhold for waiting-on-cement time. At that according to results of geophysical survey length of cemented auxiliary string, quantity and mounting locations for sealing devices at the auxiliary string are determined on the basis of their next position at distance of 8-12 m higher and lower than disturbed intervals and at distance of 8-12 m over the upper boundary of perforated interval. The auxiliary string is assembled by installation of sealing devices in compliance with data obtained at the stage of mounting locations identification for sealing devices and by mounting positive centralizers above and below the sealing devices, at that installation of sealing devices is performed in the following way: the upper limiting ring, self-sealing rubber cup, cone-shaped thrust with lobes and gaps allowing passage of cement grout are put onto the auxiliary string bottom-up, at that limiting ring and cone-shaped thrust are fixed rigidly at the auxiliary string.

EFFECT: improved efficiency of well workover.

3 cl, 2 dwg

Description

The invention relates to the field of oil production, and, in particular, to the repair of oil wells by lowering an additional column and its subsequent cementing.

The production casing (EC) of wells that have been in operation for more than 10 years is most prone to leakage. The existing method of sealing the production casing with cement filling does not allow for long-term operation of the well, and therefore, wells with two or more disruptions are required to run and cement the additional casing. The introduction of an additional column restores the well’s working capacity and ensures the tightness of the EC for more than 10 years.

A known method of repairing a production casing by lowering it into a well and cementing an additional casing (Amirov A.D., Karapetov K. Л., Lemberansky F.D. and others. A reference book on the current and overhaul of oil and gas wells. M., Nedra 1979, p. 207). After the additional column is lowered into the well, grouting is performed to raise the cement slurry behind the additional column.

However, when the cement ring is formed behind the additional column 1 according to the known method (Fig. 1), a water belt is formed in the well due to the filtration of the liquid phase of the cement in violation of EC, as well as in the perforation intervals. The formation of a water belt violates the monolithicity of the cement ring and thereby reduces the bearing capacity of the cement stone. Uncontrolled filtration of the liquid phase of the cement mortar in violation of EC and during the perforation intervals, which occurs during the initial period of the cementing process (waiting for the cement to harden) under the influence of the weight of the cement mortar column, entails an insufficient height of the cement mortar rise behind the additional column, thereby exposing the upper part of the additional column 1 (see Fig. 1), and degrades the quality of grouting.

The objective of the present invention is to perform well repair by lowering an additional column and its subsequent cementing.

The problem is solved by the method of cementing an additional column, which includes stages in which:

- conduct geophysical studies of the well to determine the state of the EC, the location of the intervals of violations and intervals of perforation;

- on the basis of the results of geophysical studies determine the length of the cemented additional column, the number and location of the installation of sealing devices on the additional column based on their subsequent location above and below the violation intervals and above the upper boundary of the perforation interval;

- they complete the assembly of the additional column by installing sealing devices in accordance with the data obtained at the stage of determining the installation locations of the sealing devices, and by installing hard centralizers above and below the sealing devices, and the installation of sealing devices is as follows: put on the upper column from the bottom snap ring, self-sealing rubber seal, tapered stop with rigid tabs and clearances, both sintering the passage of the cement slurry, the restrictive ring and conical stop rigidly fixed to an additional column;

- lower and install the layout of the additional column into the well to a depth determined in accordance with the results of geophysical studies;

- lower into the well equipment for pumping cement;

- carry out the preparation of the estimated volume of cement mortar and pump it into an additional column;

- carry out the injection into an additional column of squeezing fluid so that the cement mortar fills the annular space;

- leave the well for the time of the OZZ (waiting for the hardening of cement).

The technical result is to increase the efficiency of well repair.

In FIG. 1 shows a case of cementing an additional column according to the prior art.

In FIG. 2 shows a case of cementing an additional column according to an embodiment of the present invention.

One embodiment of the method comprises the following steps.

Geophysical studies of the well are carried out to determine the technical condition of the EC, the locations of the intervals of violations of the EC and the intervals of perforation. Research is carried out by known methods, including: thermometry, debitometry, gamma (GC) and neutron logging (NGC) and others.

Further, on the basis of the results of geophysical studies, the length of the cemented additional column 1, the number and location of the sealing devices 2 on the additional column 1 are determined. The length of the cemented additional column 1 is determined by the length of the untight portion of the EC, the technical condition of the column. The number of sealing devices 2 to be installed on the additional column 1 depends on the number and location of the intervals of violations and perforation intervals located in the EC interval to be repaired. The installation location of the sealing devices 2 is determined so that after installing the layout of the additional casing in the well, the said sealing devices 2 are located above and below the fault intervals and above the upper boundary of the perforation interval. Other mounting options for sealing devices are also possible. Preferably, said sealing devices 2 should be located at a distance of 8-12 m above and below the fault intervals. More preferably, said sealing devices 2 should be located at a distance of 10 m above and below the fault intervals. It is also preferable that the sealing device 2 should be located above the upper boundary of the perforation interval at a distance of 8-12 m. More preferably, the sealing device 2 should be located above the upper boundary of the perforation interval at a distance of 10 m. It is worth noting that the mentioned preferred distance of the location of the sealing devices from the intervals of violations and perforation intervals may vary depending on specific conditions in the well, i.e. depending on the number of intervals of violations, on their relative position, on the length of the leaky section of the EC, etc.

In the embodiment of FIG. 2, there is one perforation interval and one perforation interval. Thus, it is necessary to install three sealing devices 2 on the additional column. Two of the mentioned sealing devices 2 must be installed above and below the violation interval, and the third sealing device 2 above the perforation interval.

Then complete the assembly layout of the additional columns. The assembly is carried out by installing sealing devices 2 on an additional column 1 in accordance with the data obtained at the stage of determining the installation locations of sealing devices 2. Direct centralizers are installed directly above and below the sealing devices 2. The use of rigid centralizers allows you to avoid displacements when installing the layout of an additional column in the well. The installation of sealing devices 2 comprises the steps of putting an upper restrictive ring, a rubber sealing collar of a self-sealing type, a cone-shaped stop with rigid lobes and gaps allowing cement passage to pass from below onto an additional column 1. The restrictive ring and conical emphasis are rigidly fixed to the additional column with special wedges.

The layout of the additional column is lowered and set into the well to a depth determined in accordance with the results of geophysical studies.

The cement slurry injection equipment is lowered into the well.

The calculated volume of cement mortar is prepared and pumped into an additional column 1. The volume of cement mortar is calculated so as to completely fill the space behind additional column 1, while mixing losses with well and flow fluid, losses in averaging capacity, etc., should be taken into account. .

Then carry out the injection into an additional column 1 squeezing liquid. The injection must be carried out in such a way that the cement mortar fills the annular space. At the same time, in order to avoid the penetration of diluted cement mortar into the annular space, the volume of displacement fluid must be reduced by 0.1 m ³ in comparison with the calculated one.

During the injection of the squeezing fluid and the OZC, the possibility of uncontrolled filtration of the liquid phase of the cement mortar in violation of the EC due to the installed sealing devices 2 is eliminated due to the installed sealing devices 2. The rubber sealing cuff of the self-sealing type of sealing devices 2 passes the cement mortar through itself to the calculated height of the EC when the cement mortar is pushed through with the squeezing fluid, and then, by sealing the rubber elements under the influence of the weight of the column of cement mortar, it isolates EC disturbances. The sealing device 2, installed above the violation interval and the perforation interval, prevents the cement slurry from being filtered at said intervals under the influence of the weight of a column of cement located above said intervals. The sealing device 2, installed below the violation interval, prevents the cement slurry from going down in the annulus, thereby ensuring reliable cementing of the interval of violation EC.

Thus, the solution is avoided in the intervals of disturbances and perforations and the necessary height of the cement is ensured behind the additional column 1. Then, the well is left for the time of the borehole test.

Claims (3)

1. The method of cementing an additional column, which includes stages in which:
- conduct geophysical studies of the well to determine the state of the EC, the location of the intervals of violations and intervals of perforation;
- based on the results of geophysical studies determine the length of the cemented additional column, the number and location of the installation of sealing devices on the additional column based on their subsequent location at a distance of 8-12 m above and below the intervals of violations and at a distance of 8-12 m above the upper boundary of the perforation interval;
- they complete the assembly of the additional column by installing sealing devices in accordance with the data obtained at the stage of determining the installation locations of the sealing devices, and by installing hard centralizers above and below the sealing devices, and the installation of sealing devices is as follows: put on the upper column from the bottom snap ring, self-sealing rubber seal, tapered stop with rigid tabs and clearances, both sintering the passage of the cement slurry, the restrictive ring and conical stop rigidly fixed to an additional column;
- lower and install the layout of the additional column into the well to a depth determined in accordance with the results of geophysical studies;
- lower into the well equipment for pumping cement;
- carry out the preparation of the estimated volume of cement mortar and pump it into an additional column;
- carry out the injection into an additional column of squeezing fluid so that the cement mortar fills the annular space;
- leave the well while waiting for the cement to harden. 2. The method according to claim 1, wherein the sealing devices are located at a distance of 10 m above and below the intervals of violations. 3. The method according to p. 1, and the sealing device is located above the upper boundary of the perforation interval at a distance of 10 m

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