RU2291948C1 - Method for cementing oil and gas wells and device for realization of said method - Google Patents

Abstract

FIELD: oil and gas extractive industry.

SUBSTANCE: in accordance to method, well is prepared, casing string is lowered into it, drill mud is removed from annular space by means of replacing it with buffer liquid with following replacement of buffer liquid by forcing cementing solution into tubular hollow and its following forcing into annular space of well with pressurization of circular space between casing string and walls of well borehole. Casing string is subjected to vibration effect with frequency equal to or divisible by resonance frequency of casing string at stages of removal of drill mud from annular space and its replacement with buffer liquid, filling of well borehole with cementing solution with its following forcing into annular space and during stiffening stage of cementing solution. For accelerated growth of durability and for fast restoration of structural connections in cementing solution at last stage intensiveness of vibration effect is decreased. Device contains vibration excitation device built on above-ground section of casing string, frequency transformer for powering the vibration excitation device and basic frequency generator for controlling aforementioned frequency transformer. Vibration excitation device consist of two unbalance electromechanical vibrators, made with parallel shafts with possible opposite rotation, mounted on above-ground section of casing string immediately below cementing head by means of vertically positioned supporting plates enveloping the casing pipe.

EFFECT: increased cementing quality.

2 cl, 2 dwg

Description

The invention relates to the field of oil and gas production, and more specifically to the technique and technology of cementing wells in order to prevent behind-the-casing fluid flows and gas emissions at the mouth.

The accumulation of oil and gas in the bowels of the earth occurs in a sedimentary cover in well-permeable porous structures of the crystalline framework of the reservoir, which serve as natural reservoirs for fluids. Under natural conditions, natural reservoirs are limited along the roof and sole by impermeable rocks that impede inter-reservoir fluid flows.

Productive formations currently under development lie at depths of several hundred to three thousand meters or more. There is a steady tendency to develop deeper horizons. The average depths of oil wells in Western Siberia are 2500-3000 meters. The field development strategy currently adopted provides for drilling at the deepest productive site (reservoir). Naturally, in this case, all intermediate reservoir strata with different fluid filling are opened by the well.

In the process of drilling, inter-reservoir flows and flowing of fluids are eliminated by the use of weighted drilling fluids. After completion of drilling and lowering the casing string, the well is cemented and cemented. Currently, cementing is considered the main and best way to grout the well. The grouting mortar must have reliable contact and tightly fill all the gaps between the walls of the well and the casing. At the same time, three tasks are simultaneously solved:

- increases the strength of the well, reduces the possibility of crushing, fracture or curvature of the casing;

- elimination of annular communication channels of reservoirs, interstratal fluid flows through annular annular space, gas occurrences at the mouth, the occurrence of "secondary" oil and gas deposits;

- penetration of fluid through the shoe into the well, creating a reliable base under the shoe in weak rocks.

A known method of cementing wells, which is based on the injection of cement slurry into the casing, followed by forcing it into the annulus developed by Earl Hallibarton and first used by him in 1919 in Oklahoma.

In principle, two methods of cementing wells were developed:

1. The Perkins method - with two plugs separating the grouting composition as it moves along the casing from other fluids (flushing - using the bottom plug and squeezing - using the top plug).

2. Cementing without separation plugs.

The Perkins method quickly gained recognition among oil specialists and in 1924 it was already used even at the Baku oil fields in the USSR (see, for example, the Handbook of the oil business. Part 1. Edited by I.M. Gubkin. Scientific and Publishing Bureau Council of the Oil Industry. M., 1925. S.948).

The Perkins method has been surprisingly viable and with some unprincipled variations has been used to date (see A.I. Bulatov Oil and gas well cementing technology. M: Nedra, 1973, p.297).

As is known, the casing string cementing process includes two stages: the injection of grouting mortar into the pipe cavity and its subsequent pushing into the annulus of the well. At the same time, there is inevitably a time gap between the injection and the squeeze, associated with the need to unpin the cement plug, wash and connect the hydraulic units to the injection of the squeezing fluid.

The quality of cementing is determined by the adhesion of the cement stone to the casing and the walls of the well, ensuring the uniformity of the grouting composition, the absence of bulk defects and microcracks of the cement stone.

To improve the quality of cementing, casing pacing and rotation are traditionally used (see A.I. Bulatov. Cementing technology for oil and gas wells. Mineral resources. M .: 1973, p.297., Art Bonnet, Demos Pafitis Gas Migration - a look into the problem ./ Oil and Gas Review, Schlumberger. Spring. 1998. P.18-33). Walking is a periodic ups and downs of a column filled with cement slurry with an amplitude of 5-10 meters. It is known that pacing and rotation contribute to the destruction of the static shear stress of the drilling fluid, facilitating its removal. The destruction of the structure of the pinched clay mortar in combination with the presence of scrapers on the outer surface of the casing ensure the cleaning of the walls of the well and the contact of the grout with the rocks.

However, pacing in addition to the technical problems of its implementation raises a number of fundamental problems. The rise of the column, filled with cement slurry or displacing fluid, leads to a piston decompression effect, accompanied by the formation of degassing bubbles and, subsequently, volumetric defects in the cement stone. When lowering the casing string, there is an increased (even compared to the forcing pressure) pressure at the bottom and in the annulus, which under certain conditions can lead to hydraulic fracturing and absorption of drilling and grouting fluids. Casing rotation is not applicable for deviated wells (see Kilan Adamson et al. Well construction at high bottomhole pressures and temperatures. / Oil and Gas Review. Schlumberger. Autumn, 1999. Pages 42-57).

The main types of complications when cementing casing strings in deep wells are:

- lack of cement slurry;

- hydraulic fracturing;

- annular gas and oil manifestations;

- absorption of drilling and grouting solutions.

All of these complications usually occur due to premature thickening and setting of grouting mortar.

Fundamentally new approaches to improving the quality of cementing are to ensure the circular circulation of grouting mortar (US Pat. RF 2235860, E 21 V 33/14) and the method of exposure to cement mortar with ultrasonic vibrations using a downhole submersible source (US Pat. RF 2166063, E 21 V 33 / 14, 04/27/01).

Almost all the methods considered are based on the use of the phenomenon of thixotropy - the ability of process fluids to reversibly liquefy under sufficiently intense mechanical stresses.

The closest in technical essence to the proposed one is a method of cementing a casing pipe in a well by feeding cement slurry into the annulus and impacting the solution with hydroshock pulses with a frequency of 20-150 Hz generated by synchronized wellhead and bottomhole sources (SU 1523653 A1, “Casing cementing method in boreholes. ”Auth. R.Sh. Rakhimkulov).

The disadvantages of this method are:

- the use of two hydraulic vibrators, including the bottomhole;

- the dependence of the frequency of hydroshock pulses on the flow rate of the cement slurry;

- the need to synchronize the frequency of the wellhead and downhole hydraulic vibrators.

The objective of the invention is to create a method that significantly improves the quality of cementing while simplifying its technical implementation.

The solution to this problem is achieved using the following physical laws.

Almost all of the main process fluids used in drilling and cementing wells are suspensions or colloidal solutions (i.e., suspension of small solid particles in a liquid medium), which are fundamentally different from classical (Newtonian) fluids. Their main difference is that these solutions have the ability to maintain tangential stresses in a static state, which is typical for solids. This property leads, for example, to the fact that the free surface of the cement slurry can have a slope, not being in motion, it can have a suspended solid in it that has a higher density than the mortar, the mortar does not flow out of the tube with free ends placed vertically .

In addition to the above abnormal mechanical properties, colloidal solutions have a unique feature that has received the term “thixotropy” in the physical literature. The first mention of thixotropy was made by Kune, and this effect was examined in detail by Barus in 1893, who discovered a faster drop of steel balls in a gelatin solution after mixing. Currently, as a result of an in-depth study of the elastic-viscous-plastic properties of structured dispersed systems, thixotropy is defined as the ability of some dispersed systems to reversibly liquefy under sufficiently intense mechanical stresses. A little later, the phenomenon of reopexy was discovered, which consists in increasing the strength and structuring of disperse systems at low strain rates. Thus, mechanical action is a highly effective means of operational reversible control of the effective viscosity of structured dispersed systems such as drilling and cement slurries and flushing fluids.

Vibration exposure as a method of compaction and molding of concrete mixtures is widely used in the building materials industry (0.3 billion m ^{3 of} concrete per year). The method has been well studied and provides good filling of molds, effective compaction and increase in strength characteristics (Savinov OA, Lavrinovich EV Vibration technique of compaction and molding of concrete mixtures. - L .: Stroyizdat. Leningrad. Department. 1986).

A method for cementing oil and gas wells is proposed, including preparing a well, lowering the casing into it, removing drilling fluid from the annulus by replacing it with buffer fluid, then replacing the buffer fluid by pumping the grout into the pipe cavity and then forcing it into the annulus of the well with sealing the annular space between the casing and the walls of the wellbore, at the stages of removing the drilling fluid from the annulus and replacing it buffer fluid, filling the wellbore with grouting mortar, then forcing it into the annulus of the well and at the stage of setting the grouting mortar, the casing is subjected to vibration.

In the cementing process at the stages:

- removal of drilling fluid from the annulus and its replacement with a buffer fluid;

- filling the wellbore with grouting mortar;

- pushing the cement slurry from the well into the annulus, vibrating on the casing is carried out in the mode of breaking structural bonds of process fluids, and at the stage of setting the grouting cement, the intensity of vibration exposure is reduced to achieve the reopexy regime, which contributes to an accelerated increase in strength and a quick restoration of structural bonds in the grouting solution.

In order to increase the oscillation amplitude of the casing string, the vibrational frequency is set equal to or a multiple of the resonant frequency of the casing string.

Due to resonant vibrations, the vibration source transmitting the vibration energy to the process fluids is the entire inner and outer surface of the casing.

A device for cementing oil and gas wells is proposed, which contains a vibration exciter and a frequency converter, while the vibration exciter consists of two unbalanced electromechanical vibrators mounted on the above-ground part of the casing directly under the cementing head using vertically located support plates covering the casing.

To implement the method, a well is prepared, a casing is lowered into it, the drilling fluid is removed from the annulus by replacing it with buffer fluid and the buffer fluid is replaced with grouting fluid with sealing the annulus between the casing and the borehole walls, characterized in that at the stages of grouting injection into the pipe cavity and its subsequent pushing into the annulus of the well, the casing string is exposed to vibration.

What is new is that the vibrational effect on the cement slurry located both in the casing barrel and in the annulus is transmitted by the entire inner and outer surface of the casing, in which resonant vibrations are excited. To excite casing vibrations on the surface immediately below the wellhead grouting head on the outer surface of the casing are attached two unbalanced electromechanical vibration exciters. To increase the amplitude of oscillations of the casing and reduce power consumption using a frequency-controlled drive, the power frequency of the electromechanical vibration exciters is changed to achieve a resonant setting.

The proposed device (Figure 1) for cementing oil and gas wells consists of two unbalanced electromechanical vibration exciters (1), which are mounted on the above-ground part of the casing (3) directly under the cementing head using vertically located support plates (2) connected by tie rods (4) and forming a yoke (Figure 2). Each of the base plates (1) is a segment of a channel of a standard profile having special V-shaped cutouts in the shelves covering the casing. The design makes it easy to install vibration exciter on casing pipes of various diameters. The vibration exciter (1) is a commercially available product consisting of two asynchronous electric motors with unbalances installed on the ends of the rotor shaft. Imbalances, rotating with the rotor shaft, create a centrifugal (forcing) force. To generate directional vibrations, the exciter consists of two of the same type of vibrators with parallel oppositely rotating shafts. Power exciter is carried out from the frequency Converter (Figure 3). To increase the amplitude of the forced vibrations of the casing string, a resonant exciter is tuned. For this, the frequency converter is switched on in the mode of slow linear increase in frequency and the minimum current consumption is fixed. This frequency corresponds to resonant conditions and is set in the frequency converter setting. Achieving resonance even with a low-powered vibro-exciter is well fixed visually and visually.

In the process of cementing, vibration at the resonant frequency of the casing is carried out at the following stages:

- at the stage of removing the drilling fluid from the annulus and replacing it with buffer fluid - in order to destroy the clay crust on the rocks that form the walls of the well, removing the mud from the caverns;

- at the stage of filling the wellbore with grouting mortar - to reduce the effective viscosity and hydraulic resistance;

- at the stage of forcing the grouting mortar from the well into the annulus — to reduce the effective viscosity, hydraulic resistance, creating reliable contact with the rock and the outer wall of the casing, and vibrating the grouting grout.

At these stages, the intensity of vibration exposure ensures thixotropy in the corresponding process fluids.

At the stage of setting cement slurry, the intensity of vibration exposure is reduced to achieve the rheopexy regime, which contributes to an accelerated increase in strength and a quick restoration of structural bonds in the cement slurry.

Due to the vibration effect on the casing, a significant improvement in the quality of cementing is achieved, since this helps to clean the walls of the well from the mud cake, remove the clay mortar from the caverns, create reliable contact of the cement slurry with the rock and the outer wall of the casing, and vibro-seal the grout.

All these factors contribute to the achievement of high tightness of annular space, which ultimately will reduce the volume of repair and insulation work, reduce the likelihood of interstratal flows and protect the subsoil and the environment.

The method simplifies the technology of cementing, improves its quality, eliminates the likelihood of fractures, allows you to effectively control the viscosity of the cement slurry without the use of special chemicals.

Claims (2)

1. A method of cementing oil and gas wells, including preparing the well, lowering the casing into it, removing the drilling fluid from the annulus by replacing it with buffer fluid, followed by replacing the buffer fluid by pumping the grout into the pipe cavity and then forcing it into the annulus of the well with sealing the annular space between the casing and the walls of the wellbore, characterized in that the casing is subjected to vibration at a frequency equal to or a multiple of the resonant frequency of the casing, at the stages of removing the drilling fluid from the annulus and replacing it with buffer fluid, filling the wellbore with grouting fluid and then forcing it into the annulus and at the stage of setting the grouting cement, for accelerated growth strength and rapid restoration of structural bonds in the cement slurry at the last stage reduce the intensity of vibration exposure. 2. A device for cementing oil and gas wells, comprising a vibration exciter mounted on the above-ground part of the casing, characterized in that it comprises a frequency converter for supplying a vibration exciter and a driving generator for controlling the frequency converter, the vibration exciter consists of two unbalanced electromechanical vibrators made in parallel with the possibility of the opposite rotation of the shafts mounted on the aerial part of the casing directly under the cement with the help of a head with vertically arranged support plates covering the casing.

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