SU1432197A1 - Method of cementing wells - Google Patents

Description

The invention relates to the field of drilling wells, in particular to methods for their cementing.

The aim of the invention is to increase the efficiency of cementing oil wells containing absorbing horizons by reducing the possibility of fluid penetration while simultaneously ensuring targeted forced filtration of excess fluid from the cement slurry into the absorption horizons.

The drawing shows an approximating curve of the intensity of the cement slurry hanging.

 The method is carried out as follows.

The casing is lowered into the well with the stop ring without a non-return valve, the cement slurry is pumped into the annular space according to known technology, using cementing units. According to the drainage of the separator plug of the retaining ring, partial extraction of the cement slurry into the casing through its shoe is carried out. To do this, gradually open the valve on the discharge line of the cementing unit and take the specified amount of squeezing liquid into the measuring capacity of the latter and then close the valve. In this case, the partial extraction of the cement slurry into the casing is carried out at a pressure in the annulus above the pressure of the fluid. To do this, for example, adjust the volumetric rate of the liquid to be withdrawn so that the discontinuity of the cement slurry and the hydraulic impact on the productive formations above the permissible level do not occur.

The required volume of fluid withdrawn depends on the setting time of the cement slurry, the reservoir properties of the oil-bearing and aquifer formations, and the well design and is determined experimentally. The amount of mortar should be sufficient to re-feed the cement slurry into the annulus and create pressure for 30-40 minutes. In this case, the re-injection of the cement slurry into the annulus is carried out under a pressure P, determined from the expression

 P (. +

(P, -R) C1 .eit.

e),

(one)

0

five

0

five

0

where P is the total hydrostatic pressure from the cement slurry at the end of the flushing, MTIa;

R. - hydrostatic pressure at the bottom of a borehole from a mixing fluid of a motor solution, MPa; t is the duration of the process of decreasing the hydrostatic pressure of the tamponage column. a strong solution, with; e - the base of the natural logarithm;

v is an indicator of the degree of intensity of the decrease in the hydrostatic pressure of the cement slurry column (C; 0.00y-0.07j.

After the completion of the selection of cement slurry into the column, the solution begins to hang in the annular space.

The suspension of the cement slurry in the annulus is accompanied by a decrease in the hydrostatic pressure at the bottom of the borehole, respectively, the pressure reading also decreases on the monometer at the mouth of the column. The decrease in hydrostatic pressure at the bottom of the well is approximated by the function

35

WG V Pc-P

oii

(2)

0

five

0

five

where P is the hydrostatic pressure of the cement slurry at the bottom of the well through the hang up time t, J1a.

The type of the approximating curve of the intensity of the cement slurry hanging is shown in drawing 1 (curve 1).,

For a specific geological-technical condition of hardening of the cement slurry. The degree of intensity of the hang is determined by the formula

/ J..i &

V and id

where P- is the hydrostatic pressure on the bottomhole at a given time t,, MGa; t; - current hang time, s. According to the formula (3), the hang degree is determined. For which, with known t ;, P, P., they fix

hydrostatic pressure on the bottom after 0, 5, 10 min. rest after selection.

The higher the overpressure on the cement slurry, the less likely it is that fluid-conducting channels will form. At the same time, the pressure created from the bottom of the cement slurry should not drive the cement slurry in the upper part of the annulus, since 80-90% of the casing is cemented without sealing the annulus. Cement grouting solutions will not move in the upper part, if the pressure on it from the bottom will not exceed 2Pj.-P; Hence, the most optimal overpressure created on the cement slurry is determined by the dependence function (1) or curve 2 (drawing).

If this pressure is exceeded, the movement and movement of the cement slurry in the annulus may occur, which has a negative effect on the forming stone. In the event that the overpressure is much less than recommended, the pressure created is not enough to force the excess closure fluid to be filtered out of the cement slurry and speeds up the formation of the cement stone.

Consequently, the overpressure created on the cement slurry through the casing shoe is most optimal when as close as possible to function (1), curve 2 "The limitations of the overpressure created are the amount of hydraulic fracturing at the bottom of the well and the maximum allowable internal casing pressure columns.

Example.

Vertical depth

wells, m1202

Well bottom (sloping depth), m 1206

Oil spacing

seams, m

Lower aquifer interval, m

Oil reservoir pressure, Mlla

1131.1-187

1190-1202

11.8

0

five

0

five

0

five

0

0.25

Mating aquifer, Mlla12,1

Aquifer fracturing pressure,, 0

Hydrostatic pressure of cement slurry at the bottomhole, MPa 20.4 Hydrostatic pressure of the squeezing fluid at the bottomhole, MPa14, 4

Production column diameter, mm146 Depth of column shoe, m1206 Installation depth of thrust ring, m 1203 Volume of the selected solution in the column, m Duration of waiting for cement mortar to hang behind the column, min10 Duration of injection time of the selected solution through the column shoe, min 20 Re-injected solution volume in the bottom part of the annular space after the cement slurry hangs, m 0.2 Maximum pressure on the lower aquifers when the cement slurry is re-injected , 22.5 MPa gauge pressure of the pump unit P Cement ", MPa

in O min. rest 6.0 in 5 min. rest. 5.2 through 1U min. Quiet 4.0

Intensity coefficient of cement slurry hanging, min 0,026 Pressure on the manometer of a cementing pump when pumping the returned cement slurry volume P, j, MPa:

five

after 10 minutes of rest after 15 minutes of rest after 20 minutes of rest after 25 minutes of rest

7.0 7.9 8.7

Not higher than 9.4

51

Claims (1)

Invention Formula The method of cementing wells, which includes feeding the cement slurry into the annular space, partial extraction of the cement slurry into the casing through its shoe, and re-applying the selected hydraulic fluid into the casing under pressure, characterized in that, in order to increase the efficiency of cementing, the fluid is formed by the developers who differ from those in order to increase the efficiency of cementing fluid from the builders. containing absorbing horizons by reducing the possibility of fluid displays while ensuring the target forced filtration of excess fluid from cement slurry into absorbing horizons, partial extraction of cement slurry into the casing is carried out at a pressure in the annular space above the pressure of the survey fluid, and re-supply of the cement slurry to the annulus the space is realized under the pressure P, determined from the expression R PC + (PC-P) 1st -Y) where P is the total hydrostatic pressure from the bottom solution at the end of the propellant, Sha; P is the hydrostatic pressure at the bottom of the well from the grouting fluid, MPa; t is the duration of the process of decreasing the hydrostatic pressure of the cement slurry column, s; e - the basis of natural logarithm;   measure of the intensity of the decrease in the hydrostatic pressure of the column of cement slurry (C 0.009-0.07K R PC Pi V