SU1002526A1 - Method of cementing wells - Google Patents

Description

The invention relates to the fastening of oil and gas wells, in particular to the cementing of columns in wells with non-isolated low pressure zones. A well-known method of cementing wells, including low-pressure uninsulated zones, involves the use of lower density cement slurries using fillers, for example expanded perlite sand or diatom sand or perlite or plasmilon, etc. til The disadvantage of the known method is that the use of lightweight additives It significantly complicates the production of cement mixtures for dwelling and logging, in addition, they significantly reduce the strength of the resulting cement stone. Closest to the invention is a method of cementing wells, including the descent of casing strings into a well filled with washing liquid and injection of cement slurry into the annulus to the calculated height C2. However, this method is limited in use, as for those; nevertheless, it is still necessary to create in the annulus a hydrostatic pressure exceeding the permissible pressure during drilling. Indeed, at the initial moment of cementing, when cement mortar is pumped in, the well is completely filled and every 100 m of cement mortar causes an increase in the static pressure of about 7 kgf / cm g, since the difference in density of the flushing fluid and cement slurry of normal density is 0.7 g / cm. Therefore, even before pushing with flushing fluid, such an excess of pressure (which can cause hydraulic fracturing, up to catastrophic absorption) is possible. Therefore, the known method is possible only with small amounts of cement used. The purpose of the invention is to increase the efficiency of cementing wells with non-isolated low pressure zones when using cement slurries of normal density. The goal is achieved by the fact that in the method of cementing

wells, including casing in a well filled with flushing fluid, and pumping the cement slurry into the annulus to the calculated height, before pumping the cement slurry into the annulus, reduce the level of propella fluid by an amount of hydrostatic pressure equal to the pressure difference caused by the difference in well density cement slurry, and the level of washing fluid) is reduced by bypassing it from the annulus into the casing, which During the descent, partially filled up, leaving the volume of the empty part of the column / equivalent to the volume of the annular space from the mouth to the depth of decrease of the flushing liquid, the volume of the empty part of the column is cut off with a diaphragm, which is installed in the column during its descent, and before flushing the washing liquid from the annular space in the casing diaphragm destroy.

FIG. 1-4 depict the sequence of operations for the proposed method.

A casing is put into the well L with a depth of L for a length L and a blind cast-iron diaphragm disengaging the lower part of the cavity from the upper one is installed in the internal cavity of the pipes. In the future, the rest of the upper part of the column of pipes L2 is allowed, leaving it unfilled with a washing liquid (Fig. 1). At the same time, the volume of the empty cavity should be equal to the volume of the well at a length equal to the required reduction in the annulus space (minus the volume of the pipe body at the same length).

An empty column dumps a steel rod, which, falling on the diaphragm, destroys it. The tube space communicates with the annular (ring and) and the level in the latter decreases to a depth H (Fig.

A cement slurry of normal density, occupying the required height H, is pumped into the annular space. When the composite pressure of the cement slurry and washing fluid in the annulus with a height L - (H + H2) is equal to the pressure of the washing fluid in the fully filled pipes on the length L, i.e. equal to the hydrostatic pressure, tolerance of the emoma during drilling (Fig. 3).

B. The annular space is injected with a squeezing fluid, with an equal flushing fluid density of

the volume of the rinse fluid of the annular space from the baimak column to the lower boundary of the cement slurry in its position in FIG. In this case, the flushing fluid from the 5 tubes is constantly squeezed out, and the level in the annulus is maintained at H (according to the law of communicating vessels).

After injection of the estimated amount of the squeezing fluid, the cementing solution enters the casing shoe, the pressure in the pipe (washing liquid) and the annular (the composite column of cement and the washing liquid) is equal and the cementing process ends (Fig. 4),

If a rise in cement slurry is required to the mouth, after hardening the cement stone injected in the first stage, but without being pumped with washing liquid, the second cementing stage is carried out, in which the missing amount of cement slurry is pumped into the open and unfilled ring.

An example. The production column with a diameter of 146 mm, which overlaps a low-pressure reservoir with a diameter of 215.9 mm in the wellbore zone at a depth of 1500 m and maintains the hydrostatic pressure of the flushing fluid with a density of 1.15 g / cm while drilling, is cemented. Cementation is carried out with a cement solution of Portland cement with a density of 1.85 g / cm with a rise of 500 m from the column shoe.

0 Determine the pressure drop from the difference in density between the cement slurry and the washing liquid at the height of the cement slurry behind the column.

5 lR 0.1 (1.85 - 1.15) -500 35 kgf / cm, I

The decrease in the level of flushing fluid in the annulus is determined, compensating for the pressure drop from filling 500 m of the annulus with cement slurry.

10-35

 300 m

H

T7G5

The length of the upper part of the casing string (above the diagram) is determined, the internal cavity of which is not filled with the flushing fluid during the descent into the well (wall thickness

casing 10 mm).

- 3000, (0, 0.126) Lgr0.12ё

Claims (2)

 780 m. Therefore, after the descent of 720 casing pipes (L) a diaphragm is installed in their internal cavity, and the upper 780 m are lowered empty. After the descent of the column to the slab 1500 m dump the rod, the diaphragm collapses, and fluid from the annulus flows into Noah's pipes. The level in the annulus decreases by 300 m. 12.4 tons of cement is required to fill the 500 m annular space to fill it, on the basis that about 1.85 tons of cement is required to prepare a 1.m cement slurry with a density of 1.85 g / cm3. Q 0., 785- (0, 0.146) 5.00-1.25 12.4 tf. The cement slurry is pumped into the annulus and its upper layer occupies the level in the annulus at a distance of 300 m from the mouth. At the same time, during the entire injection, the hydrostatic pressure in the annular gas does not exceed the hydrostatic pressure of the flushing fluid in the pipes and, consequently, what happened during the drilling. Pumped into the annulus 14 m squeezing fluid density of 1.15 g / cm at the rate of .f L. jb j av / l. f l, l / ti. J 4, v-x. X V 0.785- (O ,, 146) .700 14 m. In this case, the tampon solution moves in the annular space to the required interval (lower limit to the column shoe, and upper one to a height of 500 m from the shoe) . The level of the production fluid in the annular space remains at a depth of 300 m from the mouth, the hydrostatic pressure in the pipes and in the annular space becomes equal, and the cementing process ends. Thus, the application of the proposed method allows cementing to be carried out without exceeding the hydrostatic pressure on the low pressure formation against that which occurred during the drilling of wells. In turn, this allows to eliminate complications (absorption, fracturing) when cementing low pressure formations using cement slurries of normal density and contributes to an increase in the quality of attachment. Claim 1. The method of cementing wells, including the descent of casing in a well filled with flushing fluid, and injection of cement slurry into the annular space to the calculated height, so that, with the aim of improving the efficiency of cementing wells low-pressure non-isolated zones when using normal-density cement solutions, before injection of cement slurry in the annular space, reduce the level of washing liquid by the amount of hydrostatic pressure It is equal to the pressure drop caused by the difference in the densities of the well fluid and the T 1 slurry solution, and the level of flushing fluid is reduced by bypassing it from the annulus to the casing, which is partially filled during descent, leaving the volume of the unfilled portion equivalent to Set to the depth of the flushing fluid level. 2. A method according to claim 1, characterized in that the volume is uncapitalized; The core of the column is cut off with a diaphragm, which is installed in the column during its descent, and before re-running the washing liquid from the annular space into the outer column, the diaphragm is destroyed. Sources of information taken into account during the examination 1.N. Lutsenko and others. Tampon solutions of low density. M., Nedra, 1972, p. 5-13. 2. Authors certificate of the USSR: 594300, cl. E 21 V 33/14, 1978 (prototype). dJvi.f Fe / g. y  I