Procedure for casing cementing and device for its implementation

IPC classes for russian patent Procedure for casing cementing and device for its implementation (RU 2513581):

E21B33/13 - Methods or devices for cementing, for plugging holes, crevices, or the like (dump bailers E21B0027020000; chemical compositions therefor C09K0008000000)

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FIELD: oil and gas industry.

SUBSTANCE: invention relates to construction of oil and gas wells, in particular to procedures of casing cementing. Method of casing cementing includes treatment of the well bore, casing running, washing of the well with flush fluid, pumping of displacement fluid and cement slurry and their squeezing to annular space. Herewith, in order to increase cohesion of cement stone with the outer surface of the casing string and rock of the well surface during cement slurry preparation, a monoelectret with positive or negative charges is added to the slurry in a fine disperse state with weight up to 1%. The solution is mixed up thoroughly and squeezed to annular space. Thereafter the casing string at the well head is connected in respect to the monoelectret charge to positive or negative terminals of direct-current source with voltage of 10 - 24 V and withhold under voltage until cement stone hardens.

EFFECT: improving leak tightness of annular space.

2 dwg

The invention relates to the construction of oil and gas wells, and in particular to a method of cementing casing, and can be used in the oil and gas industry.

There is a method of cementing wells with cement grouting composition [1], containing in its composition of cement - 100 weight units, acetylcellulose 0.3 to 0.5 units, eliminatethe product of 0.5-1.0 units, water - 40-50%

The disadvantages of this method is that the apparent shrinkage of the cured stone, has low adhesion to the surface of the casing and the borehole walls, insufficient bending strength, etc. together form channels for the flow of fluids on them.

There is a method of cementing using polymer cement slurry [2].

The disadvantages of this method are the following: at operating temperatures in the range of 20-55°C curing of the composition occurs with shrinkage of 2.5-3.5%, which reduces the insulating properties of the cement slurry; start time setting cement slurry is more than 8 hours that do not meet state standards 26798.1-96.

A known method for vibration cementing casing in wells [3]. This method comprises applying to the outer surface of the casing layer of rare earth element with magnetostriction and properties. Lower the casing into the borehole. Then pumped into the casing cement grout and push it into the annulus. On the layer of rare earth element transmit voltage with a frequency equal to the natural frequency of the column. While the cement slurry is heated to a temperature of 40-50°C. the Frequency of natural oscillations of the column agree with the frequency of natural oscillations of cement. The excitation of vibrations of the casing is carried out in a period of time in which the strength of the stone in the annulus based on the cement reaches 0,5 its normative strength.

The disadvantages of this method are the complexity of its execution and appreciation of the preparatory work for no apparent advantages over traditional methods.

Closest to the present invention is a method of cementing wells [4] cement solution, prepared by electrochemically activated catholyte fresh water.

The disadvantages of this method is, as in traditional methods, not a tight fit of cement to the outer surface of the casing and the surface of the well, which leads to the existence of channels through which fluids flow.

The objective of the invention is to eliminate the disadvantages mentioned in the above ways, including the prototype.

An object of the invention is to develop a method of cementing wells, providing a good sealing of the annulus and thus the absence of annular gas pressure, which reduces the leakage of gas from the well and increase the safety of its operation.

Practice shows [5]that a significant amount of gas, gas condensate and oil wells in the fields and underground gas storage (UGS) in Russia and abroad have annular pressure (MCD) and cross flows (CMP). So 30-50% of the wells (in some fields up to 80%) are operated with MCD various sizes. Operation of wells with MCD accompanied by a loss of natural gas, which is approximately up to 2 billion m³methane per year. The main cause of MCD is weak contact cement surface casing and education in these places filtration channels. Therefore, improving the contact between the cement stone, the outer surface of the casing and the surface of the wells will provide the best sealing the annular space.

The invention consists in that, to increase the adhesion of the cement to the outer surface of the casing and rock in cement mortar, when it is cooking, add nanoelectric with the advantages of the m or minus sign of the charge or bipolar electret in minced to disperse state, weighing up to 1%, thoroughly mixed, and forced into the annulus, after which the casing at the wellhead is connected to the negative (opposite to the sign of the charge of electret terminal of the source of direct current voltage from 10 to 24 In and hold it under tension until the solidification of the cement stone.

The electrets are dielectric materials, capable of a long time to be in the excited state after removal of the external influence that caused the polarization [6]. In addition to conventional electrets with opposite signs of the charges from different sides (bipolar electrets), known so-called nanoelectrode, representing, for example, a polymeric film (plate) with a charge of the same sign on both sides. Stability charge electrets can reach tens of years.

Originally electret material is crushed to the dispersed state, and then electrify into electret (nanoelectric or bipolar electret). And in this state it is added to cement slurry during its preparation.

Because the charge of the particles electret - positive (took nanoelectric), and the casing has a negative charge (connected to the negative terminal of the DC electric the CSOs current), the particles electret (positive) will move to the surface casing (negative). This movement is due to the small particle size of nanoelectrode in cement mortar (can travel). Casing is not able to move, because its mass is huge compared with particles of electret (like the gravity of the subject to the Ground, and not Vice versa). When your moving particles electret will bring and particles of the solution. Approaching surface of the casing, pieces of electret firmly stick to it (neutralized through the piece gives an insulating layer formed of cement slurry between the particle and the surface of the casing under the action of electric Coulomb forces. These forces will act on the particles electret during the time of connecting the casing to a source of direct electric current, i.e., before the solidification of the cement stone. In the process of hardening particles electret will not be removed from the surface of the casing when the shrinkage of the cement stone, and will remain stuck to the surface under the action of electric forces. This will ensure a tight seal cement mortar with the outer surface of the casing. The same thing will occur on the surface of a rock formation on n the surface of the well. Because the Earth has a negative electric charge [7], between the surface of the well and particles electret located near to it, it will be the force of attraction of the particles are positively charged, and the surface of the well is negatively charged). The surface of the well to move is not possible, and will it to move particles electret, which will firmly stick to it, providing a tight seal cement surface casing and the surface of the well.

When using normal electret (bipolar electret) effect of adhesion of particles electret to the surface of the casing and the surface of the well will be less than nanoelectron, since the particles must be rotated around its center of mass so that the side with an electric charge opposite the casing string and the surface of the wells of the sign (positive charge) was sent to them. To do this will not all particles due to the viscosity of the solution and because of the uncertainty of the charge in the Central part of the space between casing and borehole wall.

New features with significant differences according to the method are:

1. The use of electrets for additives in cement mortar as electric charges.

2. Use the electric charges in cement and the casing opposite sign for the formation of the forces of attraction between them and moving charges in cement mortar to the outer surface of the casing string.

3. The use of electric charges in cement and in the rocks of the opposite sign for the formation of the forces of attraction between them and moving charges in cement mortar to the surface of the well.

4. Using adhering to the outer surface of the casing and to the surface of the wells of charged particles for the formation of a tight connection between the cement stone, casing and rock.

The essential distinguishing characteristics of the device are:

- the presence of a source of direct electric current;

- connection of DC electric current to the casing near its mouth;

- the presence of electrets in cement mortar;

- the presence of razmelchitel electret material;

- the presence of electristar - manufacturer electret.

The use of new signs ensures the achievement of the technical result of the invention, namely: the improvement of the adhesion strength of the cement stone with the outer surface of the casing and with the surface of the well, thereby ensuring better sealing annular space.

The invention is illustrated by drawings. Figure 1 shows a longitudinal section of the casing and the borehole at the time of cementation. Figure 2 shows the components of the device for cementing obsa the different columns of the proposed method.

On the longitudinal section of the borehole, figure 1 shows that at the time of cementing method proposed casing 1 is in position, when the displacement of cement slurry 3 in the annulus between the outer surface 4 of the casing and the surface of the bore 8. Prepared cement slurry, including its composition and the electrets a positive sign (the drawing shows nanoelectrode), the internal cavity of the casing under pressure, through the end of the casing is extruded in annular space 9, filling it. Casing 1 is connected to the negative terminal of the source of direct electric current 2, resulting casing is energized negative sign. The earth has a negative charge, therefore, the borehole wall bears on its surface electric charge of negative sign. In cement mortar are particles of electret 5, positively charged (in the example shown in the drawing). Under the action of the electric (Coulomb) forces these particles are concentrated on the surface of the casing and on the surface of the well, forming, respectively, more dense and impermeable layers 6 and 7. Casing 1 may be connected to the "positive" terminal of the source of the ICA constant electric current. But then particles electret 5 must be charged negatively. Figure 2 presents the components of the device for cementing casing of the proposed method. They include: razmelchitel electret material 10, which grinds the material to disperse state. And the smaller will be the grinding, the more vigorous will be the pieces of electret, the better the sealing of the annular space will be provided; electristar 11 - manufacturer electret. Electristar, affecting their electromagnetic fields on the electret material which is crushed, but the dielectric condition, turns it into electret, i.e. makes the charged particles (or equally - moelectric, or with opposite signs of bipolar electret); mixer 12 prigotovili cement slurry, which, after the selection of certain components, including electret, thoroughly mixes it, leading to a condition suitable for punching shear in the annulus; devices for produce cement slurry 13 into the annulus. Here are the traditional devices, the original device is not assumed; a source of direct electric current, which is connected to its "negative" (as shown in the drawing) or "put Inoi" terminal on the wellhead to the casing string.

Cementing the proposed method includes the following steps.

Before preparing a cement slurry is prepared electret. This is a crushing electret material razmelchitel to disperse state. Then crushed material is electrified (turns into electret). Sign electrification is determined in advance.

Electret may well be delivered in finished form, i.e. it is not necessary to grind and electrisave electret material around a well.

After preparing cement slurry, when all its components, including electric, together with the solvent are thoroughly mixed by a mixer and brought to a condition suitable for pressing into the annulus.

Further, known devices are bursting prepared cement slurry in the annulus. After this is included in the operating status of the source of direct electric current, connected to its terminal (in the drawing, for example, the "negative" terminal) to the casing at its mouth. And remains the current source 2 is turned on prior to the curing of cement 3. In this casing, having a negative charge that attracts of the cement slurry positively charged particles electret. As these partially is covered with a layer of cement mortar, between the outer surface of the casing and particles electret there is an insulating layer that does not allow you to move the electrons from the casing on these particles and to neutralize. Therefore, particles of electret closer to the external surface of the casing 1, are concentrated near the surface, held electric (Coulomb) forces, forming adjacent to the outer surface of the casing layer 6, more dense and has, due to gravity forces, the best adhesion with the surface of the casing. Depending on the voltage applied on the casing, will depend on the degree of adhesion. But, from the standpoint of personnel safety, to raise the voltage above 24 V is not advisable. Too low a voltage below 10 V, will not give the desired effect.

The same thing will occur on the surface of the well. However, since the electrical charge of the Earth is much less than that supplied to the casing, and the effect of formation of layer 7 near the surface of the well will be weaker than the surface casing. But, nevertheless, the adhesion of the cement stone with rock wells will be stronger than without the use of electret. When the cement stone has hardened, the source of direct electric current is switched off.

The proposed method cement is investing casing allows to significantly improve the tightness hardening annular space, to reduce manifestations of annular pressure and gas leakage.

Sources of information

1. RF patent №2149981, "Cement mortar".

2. RF patent №2319722, "Polymer cement solution".

3. RF patent "Method for vibration cementing casing in wells. The login. application number - 92012958. Publication number of patent - 2094590.

4. USSR author's certificate No. 1134699, "Method of cementing wells."

5. Ruban G.N., Nifontov V.I. and others, "Assessment of the technical condition of UGS wells and the requirements of the technology of their construction". The proceedings of the workshop "industrial safety of underground gas storage "Gazprom". The results of work in 2009, and progress in 2010 P. Krasnaya Polyana, March 2010): Gazprom. - P.34-39.

6. The electrets / Under the editorship of Sessler, - M.: Mir, 1983. - 487 S.

7. The electrical charge of the Earth, www.p-energy.ru/node/212.

Method of cementing casing, including the preparation of the borehole, the casing, rinse the wells with wash liquid, the injection of the buffer fluid and the cement slurry and displacement with them in the annulus, wherein for the purpose of increasing the adhesion of the cement to the outer surface of the casing and the rock surface wells in the cement slurry when it is cooking, add nanoelectric with PL the weighing or negative charges in the ground to disperse state as weighing up to 1%, carefully, this solution is stirred and forced into the annulus, after which the casing at the wellhead connected, respectively, to the charge of nanoelectrode, with "negative" or "positive" terminal of the source of direct current voltage from 10 to 24 and held under tension until the solidification of the cement stone.