RU2293838C2 - Casing column cementation method and device for realization thereof - Google Patents

Abstract

FIELD: well drilling technologies.

SUBSTANCE: in accordance to method casing column is lowered into well and cemented in suspended position and stretched state. Stretching load is created on lower end of casing column in the moment when its cementation ends due to pressure drop between inter-column and behind-column spaces at depth where stop-ring is positioned and following anchoring of casing column before perforation zone, at level where stop ring is positioned and above perforation zone beyond well walls by means of hydro-mechanical localizing anchors. Device contains shoe, shoe branch pipe, reverse valve, stop ring, signal ring, casing column with, mounted on it, turbulence promoters, spring or rigid localizers, cementing head with mounted cementing plug. Device is provided with not less than two hydro-mechanical localizing anchors, lower one of which is located below perforation zone, at the level of reverse valve, while other hydro-mechanical localizer anchors are mounted above perforation zone of casing column. Value of pressure drop needed for activation of hydro-mechanical localizing anchors is greater than value of pressure drop between hollows inside and outside column at depth where stop ring is positioned in the moment of "stop" pressure.

EFFECT: increased quality of fastening of well walls.

2 cl, 2 dwg

Description

The invention relates to the field of drilling, namely, for fastening the walls of the well.

A known method of cementing a casing string and a device [1], including a casing string with elements of technological equipment: a shoe, a shoe pipe, a non-return valve, a stop ring, a signal ring, rigid or spring centralizers, turbulators, scrapers, a cementing head with a cementing plug installed.

After preparing the wellbore, the casing with technological equipment elements (shoe, shoe pipe, check valve, stop ring, signal ring, rigid or spring centralizers, turbulators, scrapers) is lowered. A cementing head with an installed cementing plug is mounted on the upper casing pipe and the wellbore is washed. After flushing the well, the required amount of cement is pumped into the casing and the cement plug is dumped. Following the cement plug, a squeezing fluid is pumped (most often drilling mud), which is used to push the cement mortar into the annulus. Count the amount of squeeze fluid injected into the well.

When 1 ... 2 m ^{3 of} squeezing liquid remains, the intensity of its injection is reduced. The process is carried out before the cementing plug is planted on the stop ring. This moment is characterized by a sharp increase in pressure. The magnitude of the onset of a sharp increase in pressure is called “stop” pressure. After that, the pressure is increased above the “stop” pressure, taking into account the strength characteristics of the casing and leave it under excess pressure for a certain time. At the same time, the pressure gauge on the mouth is monitored. If the pressure value during this time at the mouth does not change, then the column is considered airtight. The overpressure in the sealed string is vented and the casing stays in this state until the cement stone is formed.

After the formation of the cement stone ring, the casing, cement stone and rock are perforated to create a hydrodynamic connection between the well and the formation.

In the case of using a buffer fluid, the latter is transported before and after grouting mortar. It is intended to prevent the mixing of drilling and cement slurries, to clean the wellbore and the wall of the well.

When cementing long casing strings, the signal to stop the cementing plug comes to the surface and is fixed with a manometer at the mouth with a delay of several seconds [2]. This is dangerous because the fluid continues to be pumped and the pressure rises, as a result of which the cement plug, stop ring and casing can be destroyed. Therefore, a signal ring is set up a certain distance from the stop ring. It is strengthened in the column using tared studs. As soon as the cement plug sits on the signal ring, the pressure in the column into which fluid injection continues continues to increase sharply. This pressure surge is fixed on the surface and pumping fluid will be stopped in a timely manner. After cutting the studs, the cement plug with the signal ring continues to move until it fits onto the stop ring.

The disadvantages of this method of cementing the casing string and the device for its implementation is that after bleeding off the overpressure in the string, its lower part is compressed under the action of the Archimedes force due to the differences in the densities of the annular squeezing fluid and the annular cement mortar, thereby worsening the conditions for centering the compressed part of the column relative to the axis of the well and obtaining a uniform cement stone in thickness in the interval of the compressed section of the column.

When the casing is perforated, impact energy is distributed through the casing, the wellbore fluid and the cement stone. However, the degree of attenuation of shock energy in cement stone and well fluid is higher than in the column. Therefore, most of the shock energy is transmitted through the casing, which contributes to the destruction of the cement stone ring, that is, the formation of microcracks in the cement stone.

The above disadvantages reduce the quality of the fastening of the walls of the borehole, which, in turn, increases the likelihood of the flow of fluids from the reservoir into the absorbing strata or onto the surface between the borehole wall and the casing.

The invention is aimed at obtaining a technical result, expressed in that the use of the invention allows to obtain a more uniform formation along the thickness of the cement stone along the entire length of the casing string and to reduce the degree of destruction of the cement stone ring behind the perforation zone of the casing string, that is, to improve the quality of fastening of the borehole walls.

The technical result is achieved by the fact that the casing is cemented in a suspended position and in its tensioned state by creating a tensile load on the lower end of the casing due to the pressure drop between the annular and annular spaces at the depth of the stop ring and subsequent anchoring of the casing at the location level stop rings for the walls of the borehole using a hydromechanical centralizer-anchor, which will eliminate the negative impact of the buoyancy force Ap Imeda the bottom of the casing and to ensure a better alignment of the casing with respect to the borehole axis.

Anchoring the casing below and above the perforation zone behind the borehole walls with hydromechanical centralizers-anchors will ensure the removal of part of the shock energy into the rock during perforation of the casing, which will reduce the degree of destruction of the cement stone behind the perforation zone.

The pressure drop across the hydromechanical anchor centralizers should be greater than the pressure drop between the casing and annular cavities at the depth of the stop ring at the stop pressure, taking into account the strength characteristics of the casing. This value of the pressure drop of the hydromechanical anchor centralizers makes it possible to create an additional tensile force of the casing and, at the same time, will allow the casing to be anchored to the borehole walls. In turn, the anchoring of the casing will provide a taut state and better centering it relative to the axis of the well.

When the casing is suspended in the conditions of the well, in order to ensure its stretched state along the entire length and to maintain the integrity of the cement stone behind the perforation zone, it is necessary to install at least two hydromechanical anchor centralizers on the string. This will create additional channels, made in the form of levers of a centralizer-anchor made of metal, to divert part of the shock energy to the rock during perforation of the casing, which will reduce the degree of destruction of cement stone.

Thus, high-quality centering of the casing relative to the axis of the well and a decrease in the degree of destruction of cement stone behind the perforation zone of the casing will provide better fastening of the walls of the well.

A device for implementing a method of cementing a casing string includes a shoe, a shoe pipe, a check valve, a stop ring, a signal ring, a cementing head with a cementing plug, a casing with turbulators, scrapers, spring or rigid centralizers installed on it, and at least two hydromechanical centralizers anchors located below and above the perforation zone of the casing string, with the lower hydromechanical centralizer-anchor installed at the level of the check valve.

Figure 1 shows the device in the transport position in the conditions of the well (longitudinal section); figure 2 shows the device in working condition.

The device comprises a shoe 1, shoe socket 2, check valve 3, stop ring 4, hydromechanical centralizers-anchors 5, casing 6, spring centralizers 7, cement head 8 with installed cement plug 9.

A device for cementing a casing string is as follows.

After preparing the wellbore, the casing with the elements of its technological equipment is lowered. A cementing head 8 with an installed cementing plug 9 is mounted on the upper casing string 6 and the wellbore is washed. After washing the well, the required amount of cement mortar is pumped into the casing 6 and the cement plug 9 is dumped. Following the cement plug 9, a squeezing fluid is pumped (most often drilling mud), which is used to push the cement mortar into the annulus. Count the amount of squeezing fluid injected into the well.

When 1 ... 2 m ^{3 of} squeezing liquid remains, the intensity of its injection is reduced. The process is carried out until the cementing plug 9 is planted on the stop ring 4. This moment is characterized by a sharp increase in pressure. The magnitude of the onset of a sharp increase in pressure is called “stop” pressure.

After that, the pressure in the string is increased above the “stop” pressure or to the pressure of the casing pressure testing taking into account the strength characteristics of the casing and the casing is left under excess pressure for a certain time. In this case, under the action of a pressure differential, a tensile force is created on the stop ring 4, which exceeds the buoyancy force of Archimedes in magnitude, which contributes to the elongation of the casing. At the same time, when a certain pressure drop arises between the casing and annular cavities, hydromechanical centralizers-anchors are successively activated from top to bottom, rigidly anchoring the casing over the borehole walls.

After a certain time, the overpressure in the casing is vented. In this case, the buoyancy force of Archimedes, perceived by the walls of the borehole through the lower hydromechanical centralizer-anchor, and the elasticity force of the casing from its extension, perceived by the walls of the borehole through all hydromechanical centralizers-anchors located on the casing, i.e. the casing, act on the lower end of the casing It is taut along the entire length. This condition of the casing string provides a better centering of it relative to the axis of the well, which in turn leads to a more uniform formation of cement stone along the thickness of the ring along the entire length of the casing string.

After the formation of the cement stone ring, the casing, cement stone and rock are perforated to create a hydrodynamic connection between the well and the formation. At the same time, part of the shock energy is absorbed by the walls of the well through the levers of hydromechanical centralizers-anchors installed behind the perforation zone. This arrangement of centralizers-anchors reduces the degree of destruction of cement stone beyond the perforation zone.

The formation of a more uniform cement stone thickness along the entire length of the casing and a decrease in the degree of destruction of the cement stone behind the perforation zone of the casing makes it possible to improve the quality of fastening of the borehole walls.

Information sources

1. Bulatov A.I. Grouting materials and well cementing technology: Textbook. for technical schools. - 4th ed., Revised. and add. - M .: Nedra, 1991 .-- 336 p. silt

2. Podgornov Yu.M. Production and exploratory drilling for oil and gas: Textbook. allowance for workers in the workplace. - M .: Nedra, 1988 .-- 325 s. silt

Claims (2)

1. The method of cementing the casing string, including the descent of the casing string into the well and cementing it in a suspended position and in tension, characterized in that a tensile load is created on the lower end of the casing string at the moment of completion of its cementing due to the pressure differential between the casing and annulus the depth of the location of the stop ring and the subsequent anchoring of the casing string below the perforation zone, at the level of the location of the stop ring and above the perforation zone beyond the borehole wall at hydro power centralizers, anchors. 2. A device for cementing a casing string comprising a shoe, a shoe pipe, a check valve, a stop ring, a signal ring, a casing string with turbulators installed thereon, spring or rigid centralizers, a cementing head with a cementing plug installed, characterized in that it is provided at least two hydromechanical anchor centralizers, the lower of which is located below the perforation zone, at the level of the check valve, and the following hydromechanical anchor centralizers are installed above the zones perforating the casing, wherein the actuation pressure drop centralizers, anchors hydromechanical greater than the pressure differential between annulus and vnutrikolonnoy cavities at a depth location of the stop ring when the pressure on the "stop".

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