SU1740631A1 - Formation isolation method - Google Patents

Abstract

Use: isolation of formations in drilling oil and gas wells. SUMMARY OF THE INVENTION: Between portions of the cement slurry, a buffer fluid is pumped, then a salt / polymer mixture, a portion of a crosslinking agent, and a buffer fluid. Polyacrylamide, for example, is used as a polymer. Sol-polymer mixture is placed over an insulated formation. The densities of the salt-polymer mixture and the crosslinking agent are equal to the density of the cement slurry. For example, berit is used to adjust the density. bentonite. The height of the crosslinking agent method is calculated according to the formula NesUZ / (1 + /) In + + 0.5 pb) / #, where / is the minimum required ratio of the volume of the suspension of the cross-linking agent to the volume of the salt-polymer mixture. 1P - packer length. he is the height of the column of buffer fluid, and is the value of the maximum relative residue of the suspension of the cross-linking agent. 2 ill., 4 tabl SL

Description

The invention relates to the drilling of wells, in particular, to methods for isolating formations with abnormally high formation pressures (AHF).

A known method for isolating AVPD formations involves pumping into the annulus during cementing the casing between portions of the cement slurry a gelling composition with placing it over an insulated formation.

The disadvantage of this method is its low efficiency in isolating layers with AVPD due to the use of a gel-forming composition that is not resistant to dilution. The decrease in the hydraulic pressure of the cement slurry to the formation fluid during ABC causes its inflow into the cement solution into the cement annulus, displacing its liquid phase into an overlying portion of the gelling composition that is diluted with the filtrate loses its insulating properties. As a result, behind-the-barrel fluid flow may occur.

The closest to the present invention is a method of isolating formations, which includes injection into the annulus between portions of the cement-mortar of a salt-polymer mixture (ATP) in the interval of the aquifer.

The disadvantage of this method is its low efficiency in the absence of aquifers over the insulated layer.

2

About About 00

since the incoming water from the aquifer in the ATP plays, in a known way, the main role in creating an insulating polymer tampon.

When there are no aquifers in the desired interval, the formation of a polymer tampon is possible only due to the influx of the liquid phase onto the bottom packet of cement slurry. However, in this case, the volume of the latter should be large enough so that an excess of its gate fluid is enough to fully react with the polymer.

For example, when using chromium sulphate per 1 m of ATP as the salt of the CA, about 2 m of the salt solution is required. Taking into account the water consumption for cement hydration, the volume of cement mortar of normal density (1700-18500 kg / m3) should be 4-5 m3. Such a minimum volume should precede the ATP volume and be located above the insulated formation. The length of the interval filled by it will be approximately 300–500 m. The tightness of this interval of the annular space will obviously be bad due to the considerable dehydration of the cement slurry and its saturation with formation fluid.

The aim of the invention is to increase the efficiency of isolation of formations with solar-polymer mixtures in the absence of aquifers in a section over an insulated formation by providing the polymer with the required volume of aqueous phase.

The goal is achieved by the fact that in the method of isolating formations, which include injection and a annular space between portions of the cement slurry, portions of the salt-polymer mixture with its placement over the insulated formation, a volume of suspension is pumped into the column after the solar-polymer mixture in an aqueous solution of a salt of a crosslinking agent.

The method is carried out as follows.

Before launching the casing, the selected interval for installing the liquid packer with a chisel or expander is carefully worked out, spring centralizers are installed on the casing at the limits of the interval for installing the liquid packer, and after the casing is lowered, the selected interval is carefully washed from the drilled rock.

Before cementing the column, the compositions of the gelling material are preliminarily selected in the form of a suspension of a salt – polymer mixture (ATP) and a suspension of a gel (in this case, barite) in a solution of a salt of a crosslinking agent — barite suspension (BS). Thus, so that their densities are equal to a given density of the cement slurry, and the spreadability is close to the lower permissible limit (16-18 cm). The densities of the SPS and BS suspensions are regulated by the addition of an emulsifier, the spreadability of the ATP by the addition of a polymer, and the deposition rate of the solid phase in them by the addition of bentonite. FIG. Tables 1 and 2 show the conventional isolation schemes and Table. Figures 1 and 2, respectively, show the dependence of the coefficient / 3 on the density of the salt-field5 and the measured mixture for various salts of CA and the consumption of materials for the preparation of 1 m of barite suspension on solution of CA. Table 3 gives examples of the sol-polymer phase by the addition of bentonite. In tab. 3 given

0 examples of a sol-polymer mixture of various densities.

In the installation interval of the liquid packer, during the cementing process, the casing is pumped between two portions of the cement slurry 1 portion of ATP 3 and BS 4. To decrease the possibility of ATP mixing with cement mortar and BS in the process of cementing the column, BS buffer (BZH) ) 0.5 m3 each — diesel fuel used with barite and grouting cement (or bentonite) to the density of the cement slurry. In addition to the separation role, the upper portion of the BZ in the annular space performs an additional function, which is that its constituent, precipitating, carries away the lighter polymer, accelerating the separation process.

0 At the end of the dispatch, the 2nd portions of the cement slurry fluid in the annular space is arranged in the order shown in FIG. one.

At rest, under the action of gravitational forces, the separation of the heavy and light components of the suspension occurs. Light hydrocarbon liquid moves upward relative to polymer that is carried along by the top portion

0 Buffer fluid down. At the same time, precipitation of the ut gels in BS 4 and the formation of barite cork 7 occur (see Fig. 2). The sludge solution of a salt of a crosslinking agent (CA) in BS is mixed with precipitating

5 into it with a polymer, forming a viscoelastic tampon.

The normal course of the deposition process depends not only on the presence of the necessary gap between the column and the well walls in the cementing interval, but also on its

uniformity, the lower layers should settle at a faster rate than the upper, then there will be no cork preventing the deposition and mixing of the entire volume of the polymer with the salt solution in the BS, therefore the rate of precipitation of barite in the BS should be slightly higher than the rate of deposition of the solid phase in the ATP and in the lower portions of the BZ.

An experimental assessment of the effectiveness of the recommended method compared to the selective method without the presence of an aquifer was carried out for all types of salts of the SA. For this, 1.5 m long glass tubes were used. In some cases, ATP, BZ and cement mortar were pumped in series without suspension of the CA salt, and in other cases with the suspension of the CA salt with barite improved. similar to that in cases of filling wells (see fig. 1). A general qualitative assessment of the results is given in Table. four.

The calculation of the required BS and ATP and BZ volumes is carried out in the following order.

Select the installation interval of the packer In (see Fig. 2). Calculate the height of the ATP column in the annular space (see Fig. 1) by the formula

hcnc 1p / (1 + ft, (1)

where / Vp / Vcnc is the ratio of the minimum required volume of salt solution to the volume of ATP, which is determined from the table.

Calculate the initial height of the BS column in the annular space by the formula

h6c 5 T + 7ln + ° 5Нб) (2)

and hp / pbs. where hp is the absolute value of SST, m,

the dog is the initial height of the suspension column in the measuring cylinder, m.

The required volumes of ATP and BS are calculated by the formulas

Vcnc 0.785 hcnc (dc2 - d /) (3)

V6c 0.785 h6c (dc2 - dK2) (4)

where dc is the diameter of the well specified after expansion in the packer installation interval, m,

dK - casing diameter, m

After that, the volumes of the lower and upper portions of the cement slurry are calculated.

PRI me R. A casing with a diameter of 0.178 m was launched into a well 3200 m deep and 0.214 m in diameter, which reveals the formation with AHPD. It is necessary to isolate the reservoir from AHPP, whose roof is located at a depth of 3000 m. The cement solution with a density of 1600 kg / m3 according to the project must be raised to the mouth.

We believe that in order to isolate the formation, it is necessary to install an ATP-based liquid packer above its roof. We take a 1% solution as a crosslinking agent

K2Sg207.

According to the table. 2 for a BS density of 1600 kg / m, we determine the consumption of components per 1 m3:

BS: 0,786 kg of 1% aqueous solution of KasgaO,

760 kg of barite and 80 kg of bentonite.

The relative value of the maximum settling of such a suspension is 0.75.

Packer Length Set In 100 m.

According to the table. 1 dl / Both 1600 kg / m we find / 3 0,64.

Calculate the height of the ATP column by the formula (1).

ten

hcnc

 61 k.

1 +0.64

Calculate the height of the column portion of the buffer fluid, taking its volume of 0.5

m

2l

he - 0.5 0.785 (0.244 - 0.1784

-05 & t 5

Calculate the height of the BS column by the formula (2).

1 (y frfp-100 + 0.545) 82m,

Bbs

0.75 M + 0.64

Calculate the volume of the ATP and BS by the formulas (3) and (4)

Vcnc 61 0,0111 6.8m3

V5C 82-0,0111 9.1 m3

The final volumes are increased by 10-20% (depending on the depth of the well), taking into account the losses during their injection into the well.

Claims (1)

Invention Formula A method of isolating formations, which involves injecting into the annular space between portions of a cement slurry a portion of a salt of a ro-polymer mixture, separated by portions of a buffer liquid, and placing a salt-polymer mixture over an insulated reservoir, characterized in isolation in the absence of aquifers in the isolation interval, inject the suspension of the cross-linking agent with a column height determined by the following formula NBS (° 5 where a is the value of the maximum relative residue of the suspension of the crosslinking agent; (3) the minimum necessary ratio of the volume of the suspension of the crosslinking agent to the volume of the sol – polymer mixture; ln - packer length, m; he is the height of the buffer fluid column, m, moreover, the density of the sol-polymer mixture and the suspension of the cross-linking agent are chosen to be equal to the density of the cement slurry. Dependence of the coefficient / on the ATP density for various CA salt solutions Consumption of materials for the preparation of 1 m of barite suspension on 1% solution of Cr2 (504) s or teCrzO and on 20% CuSO solution Examples of a sol-polymer mixture of various densities Table 1 table 2 Table 3 The results of the comparison of the effectiveness of the recommended and known methods of isolation layers - pressure gradient of water breakthrough through the tampon formed by the pressure of a tampon shear relative to the walls of a tube 18 mm in diameter. Table 4