RU2241819C1 - Method for stepped cementation of well in highly penetrable gas-saturated collectors - Google Patents

Abstract

FIELD: oil and gas extractive industry.

SUBSTANCE: device for stepped cementation is mounted on casing column above collector ceiling. Cementing head is mounted. Lower portion of casing column is cemented. Cementing solution is pushed in. Moment of its exit into behind-column space is registered. Two-phase foam is pumped into the latter. Cementing windows are opened with following feeding of excesses of cementing solution. Upper portion of casing column is cemented by pumping non-aerated cementing solution. During that floating hydraulic solution is formed in the well by pumping suspension into behind-column space, which contains liquid phase and filler. Height and hardness of floating hydraulic solution is determined from mathematical formulae. As liquid phase of suspension backward hydrocarbon-water emulsion is used. Mass portion of said emulsion, for one mass portion of said filler, is determined from mathematical formula. After forming of floating hydraulic solution well mouth is sealed. As buffer liquid viscous-resilient solution is used. As first portion of cementing solution - aerated cementing solution. As second portion - non-aerated cementing solution. After pumping of second portion of cementing solution backward hydrocarbon-water emulsion is pumped. Density of two-phase foam is determined form mathematical formula. When aerated cementing solution reaches sole of said collector mouth pressure in behind-column space is smoothly lowered to atmospheric level. After pushing in cementing solution mouth pressure is formed in casing column enough for packing behind-column space. Cementing of upper portion of casing column is started without delay for hardening of cementing solution. After pumping of non-aerated cementing solution viscous-resilient solution is pumped in amount providing for filling of behind-column space with height selected according to boundary condition.

EFFECT: higher efficiency.

3 cl, 1 ex, 1 tbl

Description

The invention relates to the field of construction of oil and gas wells and is used for cementing wells in highly permeable gas-saturated reservoirs.

Analysis of the current level of technology showed the following.

There is a method of stepwise cementing of wells in highly permeable gas-saturated reservoirs, which consists in sequentially carrying out three stages of cementing (see. Fixing wells in conditions of absorption and gas development / K.M. Tagirov, A.P. Migulya, V.I. Nifantov, A.M. Likhushin // Gas industry. 2001 G. No. 3. - p. 48). The first stage is filling the casing with three-phase foam as a buffer fluid before injecting the cement slurry to clog the foam with partial absorption zones located below the specified collector, direct cementing the casing in the interval from the shoe to the sole of the highly permeable gas-saturated manifold. The second stage is bringing the well-reservoir system into equilibrium by creating a floating hydraulic shutter (three-phase foam), which displaces gas into the indicated collector throughout the annular space, and meets cementing through the annular space. The third stage is the filling of the annular space from the upper boundary of the cement ring obtained in the previous stage to the mouth after the period of OZC with free filling with grouting mortar.

The disadvantage is the low cementing efficiency, which is explained by the following

the three-phase foam used as a floating hydraulic shutter is unstable, changes its properties over time. Upon contact with formation water, the liquid phase of the foam dissolves in it, and the foam collapses, which leads to disruption of the well-formation balance and contamination of the formation water. It is also necessary to add foam to the well after a certain time. Foam has a low gradient of gas breakthrough, because of which it is pumped into the well to the mouth;

it is difficult to ensure accurate installation of a floating hydraulic shutter in a predetermined interval above a highly permeable gas-saturated manifold due to the violation of the stability of the foam in contact with formation water;

the method has increased terms of work, since the absence of a step cementing sleeve does not allow to determine the required exact volume of cement slurry for each cementing interval, therefore, after direct cementing through the casing, several operations of adding cement slurry to the annular space may be required, since in one operation - this cannot be done due to acquisitions;

it is not possible to ensure the effectiveness of cementing, since there is no separation between the highly permeable gas-saturated reservoir and the mouth when topping up grouting mortar, because of which, after reducing the active pressure of the grouting grout, gas can penetrate into the grouting fluid and form gas-developing channels. The implementation of topping without selling does not allow to ensure the continuity of the cement ring, and upon contact with formation water in the annulus, a cement stone with low strength and high permeability is formed;

as a prototype, a method of stepwise cementing of a well in highly permeable gas-saturated reservoirs was taken (see clause 2188302, class E 21 B 33/14 of 09/19/2000. Method of stepwise cementing of a well under conditions of abnormally low reservoir pressure in the absorption zone, Aut .: Nersesov S.V., Mosienko V.G., Gasumov R.A. et al .; publ. BIPM - 2002. - No. 24.). A device for step cementing is installed (a step cementing clutch) in the casing over the roof of the specified collector, a cement head is mounted, the lower stage of the casing is cemented by pumping a buffer liquid, two portions of the cement slurry of different densities in the volume, ensuring filling the annular space from the casing shoe devices for step cementing, forcing cement slurry with squeezing fluid, fixing moment e on exit in the annulus and pumping in the latter two-phase foam, open windows cementing followed by washout of excess cement slurry and cement slurry after hardening cement upper stage of the casing through the apparatus for stage cementing. As the first portion, a non-aerated cement slurry is pumped in a volume that ensures filling the annular space from the sole of a highly permeable gas-saturated reservoir to a step cementing coupling. The second portion is an aerated cement slurry with a calculated degree of aeration in a volume that ensures filling the annular space in the interval from the casing shoe to the sole of a highly permeable gas-saturated reservoir. Two-phase foam is pumped into the annulus with a calculated degree of aeration to displace the liquid therein into a highly permeable gas-saturated reservoir.

The disadvantage of this method is the low efficiency of cementing, due to the following reasons:

the absence of a floating hydraulic shutter does not allow to lower the casing into the well without complications, since the wellhead is not isolated from the highly permeable gas saturated reservoir and when the casing is lowered, gas can freely escape from the well to the surface, which is unacceptable and reduces the efficiency of the method;

strong absorption may occur and part of the annular space may be uncemented due to the fact that the first portion of the grout is pumped and forced into the annular space in the area from the bottom of the collector to the step cementing unaerated coupling, which significantly reduces the cementing efficiency;

when cementing the upper interval of the casing string during the GAS period, gas from a highly permeable gas-saturated reservoir due to unreliable sealing can be introduced into the cement slurry with the formation of gas-conducting channels, which also affects the efficiency of well cementing;

the technology is complicated due to the fact that when pumping an aerated cement slurry into the well, it is necessary to constantly adjust its degree of aeration;

the casing string cementing works are being extended due to the fact that it is necessary to withstand the time for hardening the cement slurry used for cementing the lower stage.

The technical result that can be obtained by implementing the proposed technical solution is as follows:

increasing the efficiency of well cementing due to

- creating a high-quality and durable floating hydraulic shutter with an increased gradient of gas breakthrough and its precise installation in a predetermined interval over a highly permeable gas-saturated manifold;

- Improvement of annular space sealing, providing separation of a highly permeable gas-saturated reservoir from the wellhead;

- simplification of technology and reduction in the timing of work.

The technical result is achieved using the known method of stepwise cementing of a well in highly permeable gas saturated reservoirs, including installing a device for stepwise cementing in a casing string over the roof of a specified collector, mounting a cementing head, cementing the lower stage of a casing string by pumping a buffer fluid and two portions of a cement slurry of different densities into volume ensuring filling annular space from the casing shoe to a device for step cementing, forcing cement slurry with squeezing liquid, fixing the moment of its entry into the annulus and injecting two-phase foam into the last, opening cementing windows with subsequent washing out of excess cement slurry and cementing the upper casing string through the step cementing device by pumping non-oil solution.

We offer

previously form a floating hydraulic shutter in the well by pumping into the annulus a suspension with a density of less than 1000 kg / m ³ containing a liquid phase and a filler;

the height of the floating hydraulic shutter is determined by the formula

where N _s - the height of the floating hydraulic shutter, m;

P _PL - pressure in a highly permeable gas-saturated reservoir, MPa;

K is the coefficient of excess of hydrostatic pressure in the well over pressure in a highly permeable gas-saturated reservoir equal to 1.04-1.15;

Δ P is the gradient of gas breakthrough through a floating hydraulic shutter equal to 0.005-0.011 MPa / m, according to experimental studies;

the density of the floating hydraulic shutter is determined by the formula

where ρ _z - the density of the floating hydraulic shutter, kg / m ³ ;

ρ _W - fluid density in the well with a steady level after absorption, kg / m ³ ;

N _to - the depth of the highly permeable gas-saturated reservoir (roof), m;

h is the fluid level in the well, established after absorption, m;

as a liquid phase, use a reverse hydrocarbon-water emulsion with a viscosity of 150-300 MPa · s;

as a filler - gas-filled microspheres or expanded vermiculite;

the mass part of the specified emulsion per one mass part of the specified filler is determined by the formula

where m _e is the mass part of the inverse hydrocarbon-water emulsion per 1 mass part of the filler;

ρ _e - the density of the specified emulsion, kg / m ³ ;

ρ _n - the density of the filler, kg / m ³ ,

after the formation of a floating hydraulic shutter to seal the wellhead;

use a packer coupling as a device for step cementing;

use a viscoelastic solution as a buffer fluid;

as the first portion of the grout, use aerated grout, injected in a volume that ensures filling the annulus from the sole of a highly permeable gas-saturated manifold to the packer sleeve;

as a second portion - unaerated cement slurry injected in a volume that ensures filling the annular space from the casing shoe to the bottom of a highly permeable gas-saturated reservoir;

after injecting the second portion of the cement slurry, pump the reverse hydrocarbon-water emulsion in the volume necessary to fill the casing to the device for step cementing;

and the density of two-phase foam is determined by the formula

where ρ $\genfrac{}{}{0ex}{}{\text{wed}}{\text{P}}$ - the average required density of the foam in the range from the roof of a highly permeable gas-saturated reservoir to the wellhead, kg / m ³ ;

g is the acceleration of gravity, m / s ² ;

R _y - wellhead pressure in the casing, MPa,

at the moment of reaching the sole of the indicated collector with an aerated grouting mortar, the wellhead pressure in the annulus is gradually reduced to atmospheric;

and after forcing the cement slurry to create wellhead pressure in the casing, sufficient to pack annular space;

proceed to cementing the upper stage of the casing without waiting for the hardening of the cement slurry used to cement the lower stage of the casing;

after pumping the unaerated cement slurry used for cementing the upper stage of the casing, pump the visco-elastic mortar in a volume that ensures filling the annular space with a height selected from the condition

L <h _p <2L,

where h _p is the height of the column of viscoelastic solution in the annulus, m;

L is the length of the device for step cementing, m;

as the inverse hydrocarbon-water emulsion to use the following composition, wt.%:

Hydrocarbon Liquid 15-25

Fatty acids, or their salts, or their bottoms 0.5-1.5

Calcium Chloride 1.0-2.0

Water Else

as a viscoelastic solution, use the following composition, wt.%:

Sodium Chloride 1.0

Polyacrylamide 1.0

Chrompeak 0.8

Sodium Hyposulfide 0.8

Barite 15.0

Rubber crumb 5.0

Water Else

A floating hydraulic shutter (PGZ) is installed in the well before the casing is run in order to prevent the escape of gas from a highly permeable gas-saturated reservoir to the day surface, since additional pressure in the well and displacement of the liquid located in the annulus and gas mixing with liquid may come to the surface.

The height of the floating hydraulic shutter is determined taking into account the gas pressure in the highly permeable gas-saturated manifold and the gradient of gas breakthrough through the floating hydraulic shutter, which is obtained experimentally taking into account specific well conditions and the composition of the PGZ suspension (see table). GWP must withstand gas pressure from the specified reservoir without a breakthrough at the mouth.

Moreover, according to the requirements of the rules (“Safety Rules in the Oil and Gas Industry”, Moscow, 1998, p. 37, clause 2.7.3.3.), A coefficient for exceeding the hydrostatic pressure in the well over the well is introduced into the formula for calculating the height of the floating hydraulic shutter pressure in a highly permeable gas saturated reservoir equal to k = 1.04-1.15 (1.10-1.15 for wells up to 1200 m deep, 1.05-1.10 for wells up to 2500 m deep, 1.04 -1.07 - for wells with a depth of more than 2500 m).

The required (calculated) density of the PGZ suspension should ensure its installation over a highly permeable gas-saturated reservoir and depends directly on the density of the fluid in the well, its height above the roof of the specified reservoir and inversely on the calculated height of the PGZ, i.e., the PGZ should exert the same hydrostatic pressure at the level the roof of a highly permeable gas-saturated reservoir, as well as a column of fluid established in the well after catastrophic absorption.

After a catastrophic absorption during the opening of a highly permeable gas-saturated reservoir, the washing liquid is completely absorbed and mixed with produced water. Since the volume of produced water is much greater than the volume of absorbed flushing fluid, the density of the fluid established in the well after a catastrophic absorption will be close to the density of produced water. This density must be taken into account when determining the required density of a floating hydraulic shutter and taking into account which it will be installed in a given interval in the well.

A reverse hydrocarbon-water emulsion with a viscosity of less than 150 MPa · s does not provide sedimentation stability of a suspension with a filler, and with a viscosity of more than 300 MPa · s, it is difficult to prepare a suspension with the introduction of a filler and pumping it.

The reverse hydrocarbon-water emulsion has a density of 920-940 kg / m ³ , which is less than the density of water and allows the emulsion in the well to be on the surface of the water. However, the calculated (required) density of the PGZ suspension may be less than the density of the emulsion itself. Therefore, to reduce the density, a filler having a density of 200 to 600 kg / m ³ gas-filled microspheres or expanded vermiculite is used. Since the density of the filler is less than the density of the emulsion, and the Archimedean force of repulsion of particles is almost balanced by gravity (mass of particles), the prepared suspension has a high sedimentation stability.

The required density of the floating hydraulic shutter can also be provided due to the necessary ratio between the liquid and solid phases of the PGZ suspension.

This ratio will depend on the density of the inverse hydrocarbon-water emulsion, the density of the PGZ and the filler.

A floating hydraulic shutter formed by the proposed method has a high sedimentation stability and retains its properties for a long time, sufficient to perform the required technological operations. This is ensured by the fact that it as a liquid phase contains a reverse hydrocarbon-water emulsion with increased viscosity (150-300 mPa · s), which has high sedimentation stability and durability, is hydrophobic, does not break down and is not diluted with water.

The emulsifier of the inverse hydrocarbon-water emulsion are fatty acids, saponified with calcium chloride. If sodium, potassium or amine salts of fatty acids are used as an emulsifier, then in the process of preparation these cations are replaced by calcium and the calcium salts of fatty acids become an emulsifier, due to which the emulsion does not delaminate, is not diluted with water. Due to its high viscosity and increased surface tension, the gas practically does not dissolve in it, and the floating hydraulic shutter has an increased gradient of gas breakthrough.

The reverse hydrocarbon-water emulsion is hydrophobic due to the content of hydrocarbon liquid in it, is highly viscous and has low filtration (3-5 cm ³ in 30 min) and high sedimentation stability, therefore, when it comes in contact with wet walls of the well, it does not wet them, does not give the filtrate to collector and therefore does not cause their destruction.

When lowering the casing, the generated dynamic stresses can disturb the well-reservoir balance and change the installation interval of the floating hydraulic shutter, therefore, the wellhead is sealed, providing a more reliable separation between the highly permeable gas-saturated reservoir and the wellhead.

The use of a viscoelastic solution as a buffer fluid during cementing of the lower stage of the casing is selected from the condition of reliable separation of the cement slurry and fluid in the annulus of the borehole of large diameter, because the use of a low-viscosity buffer fluid leads to the formation of high mixing zones of the cement slurry and fluid in the annulus significantly reduces the quality of cementing and, therefore, the efficiency of the process.

The use of aerated cement slurry to fill the annulus in the zone of a highly permeable gas-saturated reservoir when cementing the lower stage of the casing ensures a decrease in its losses and more uniform filling of the annulus by creating an equilibrium between the pressure in the highly permeable gas-saturated reservoir and the pore pressure of the gas of the aerated cement.

The second portion of non-aerated cement slurry provides reliable fastening and isolation of annular space below the highly permeable gas-saturated reservoir by obtaining a low-permeability high-strength cement stone.

The reverse hydrocarbon-water emulsion injected into the well is designed to transfer the selling pressure to the second portion of the grout during cementing of the lower stage of the casing string. The inventive volume is selected from the condition of filling the annulus from the top of the cement cup left in the casing to the device for step cementing. The use of an emulsion between the squeezing fluid and the grout due to its hydrophobicity eliminates the formation of mixing zones.

The average density of the two-phase foam injected into the annulus when cementing the lower stage of the casing is selected from the condition that the column exerts the same hydrostatic pressure on the roof of the highly permeable gas-saturated reservoir as the liquid column established in the well after catastrophic absorption taking into account wellhead pressure in the annulus space or pillar of a floating hydraulic shutter.

The injected two-phase foam displaces the liquid from the annulus located above the roof of the highly permeable gas-saturated manifold together with a floating hydraulic shutter into the absorption zone, which subsequently reduces the pressure of the grout grout.

When cementing the lower stage of the casing string while pushing the aerated cement slurry and reaching it in the annular space of the sole of a highly permeable reservoir, the wellhead pressure in the annular space is gradually reduced to atmospheric. In this case, the balance is disturbed in the well. Two-phase foam is poured out of the annulus of the well, due to which the hydrostatic pressure on the roof of the highly permeable collector is significantly reduced, the grouting pressure is reduced, and favorable conditions are created for more complete filling of the annulus in the interval of the absorption zone with aerated grout. This also contributes to its expansion while reducing pressure in the well, that is, in the presence of depression of a gas-saturated reservoir. Suspended by two-phase foam into the absorption zone, a suspension of a floating hydraulic shutter prevents the penetration of aerated cement slurry. Due to this, the efficiency of well cementing is increased.

The use of a PDM-type packer coupling with an upper cementing plug and a lower combined “ball-plug” as a device for step cementing allows for pushing cement slurry into the annulus to cement the lower stage of the casing, reliably pack the annulus and cement the upper stage of the casing without waiting for the hardening of the cement slurry used for cementing the lower stage of the casing, since etsya rise aerated cement slurry to the device for stage cementing and packer in turn, reliably separates the annulus.

When cementing the upper stage of the casing, a viscoelastic solution is pumped into the well after an unaerated cement slurry in order to create a “liquid packer” over the step cementing device, which prevents gas from breaking out of a highly permeable gas-saturated reservoir at the mouth in case of poor packing of annular space. The height of its installation in the annular space is selected from the conditions for obtaining a high-quality “liquid packer”.

An analysis of the inventive step showed the following:

It is known to create a hydraulic shutter (foam-liquid barrier) that is pre-installed before the column is lowered, eliminating the contact of high-pressure gas and oil directly with the wellbore and representing the possibility of securing the work in the wells (see AS No. 874977, class E 21 V 33 / 13 dated January 17, 1980, published on October 23, 81, OB No. 39);

It is known to create a hydraulic shutter (a water-hydrocarbon emulsion containing a surfactant) that penetrates a collector with a high gas factor to block pores and act as a gas dispersant (see No. 2047745, class E 21 V 43/12 of January 27, 1992). , publ. 10.11.95, OB №31);

it is known to block the absorbing formation by injecting the three-phase foam used during opening as washing liquid, two-phase foam and foam cement mortar (see Amiyan V.A. et al. Increasing oil and gas recovery by improving their opening and development. M .: VNIIOENG, 1977 . - p. 38);

There is a method of isolating annular gas flows, including pumping a viscoelastic composition into annular space to create insulating jumpers to prevent gas breakthrough (see No. 2126880 according to class E 21 V 33/13 of 02.27.98, publ. 02.27.99, OB №6);

it is known in the method of completion that the injection of a viscoelastic composition with stable properties between portions of cement mortar (see paragraph No.868629, class E 21 B 33/13 from 10/29/90, publ. 08/30/94, OB No. 16). A viscoelastic composition is placed above the reservoir to ensure tightness of annular space;

It is known that to clog the collector and prevent the penetration of flushing fluid into it before the production string is lowered into the productive horizon zone, a foaming liquid with a filler is transported (see Tagirov K.M., Gasumov R.A., Pereima A.A., Nifantov V. I. Mounting wells at the opening of the reservoir // Gas industry. - 1998. - No. 10. - p. 42).

Based on the foregoing, we have not identified technical solutions that are based on features that match all the distinguishing features of the claimed technical solution. Thus, the latter does not follow explicitly from the analyzed prior art, i.e. has an inventive step.

Diesel fuel is used as a hydrocarbon liquid according to GOST 305-82, fatty acids according to TU 10-191-032-01-86, calcium chloride according to GOST 4460-87, expanded vermiculite according to GOST 26137-82, gas-filled microspheres MS - A9 according to TU 6 -48-108-94.

The content in the reverse hydrocarbon-water emulsion is a hydrocarbon liquid of less than 15 wt.%. it does not provide its sedimentation stability, and more than 25 wt.% - the viscosity of the emulsion will be less than 150 MPa · s, which will lead to the emergence of the filler and the deterioration of the properties of the suspension; a fatty acid content of less than 0.5 wt.% does not provide high-quality sedimentation stability, and more than 1.5 wt.% is not required, since the emulsion obtained already has the required properties; a content of calcium chloride of less than 1.0 wt.% does not provide complete saponification of the emulsifier to obtain the calcium salt of fatty acids, and more than 2.0 wt.% is not required, since complete saponification of the emulsifier is already provided.

The choice of the composition of the inverse hydrocarbon-water emulsion is due to the need to obtain a viscosity of 150-300 MPa · s and the stability of the emulsion.

The choice of the composition of the viscoelastic solution is due to the composition with the highest degree of crosslinking of polyacrylamide.

In more detail, the essence of the proposed method is described by the following example.

Example. A step cementing of the well of the Peschano-Umetsky UGS facility is carried out.

Initial data:

High permeability pressure

gas saturated manifold, R _pl 0.72MPa

The gradient of gas breakthrough through

floating

hydraulic shutter (at

plastic viscosity

emulsions

150.0 MPa · s), Δ Р 0.00677 MPa / m

Recommended Ratio

excess

hydrostatic

well pressure above

high permeability pressure

gas saturated manifold, K 1.10

Well fluid density

with steady level after

absorption, ρ _w 1000 kg / m ³

Depth of highly permeable

gas saturated collector:

- roof, N _to 232 m

- sole, N _p 262 m

Fluid level in the well,

settled after

absorption, h 165 m

Wellhead pressure created in

behind the casing

space, P _at 0.2MPa

Casing Diameter:

- outer, D _n 245 mm

- internal, D _in 225 mm

The diameter of the bit, which

drilling was carried out

under 245 mm

column, D _d 295.3 mm

Packer installation depth

couplings type PDM-245, N _m 224 m

Packer Coupling Length

type PDM-245, L 3.3 m

Casing Descent Depth

columns, L _approx. 400 m

Foam density

liquid, ρ _AMPs 1080 kg / m ³

Depth of descent 324 mm

conductor, L _to 229 m

Inner diameter

conductor, D _sn 0.304 m

Before the casing string is lowered, a floating hydraulic shutter is formed in the well containing a liquid phase and a filler. The height of the shutter is determined by the formula

Moreover, its density is determined from the expression

As the liquid phase of a floating hydraulic shutter, a reverse hydrocarbon-water emulsion with a viscosity of 300 MPa · s and density ρ _E = 938 kg / m ^{3 is used} .

As a filler, gas-filled microspheres with a density ρ _N = 280 kg / m ^{3 are used} .

The mass part of the inverse hydrocarbon-water emulsion per one mass part of the specified filler is determined by the formula

To form a hydraulic shutter, a suspension in volume is required

The mass of the floating hydraulic shutter is

Q _pgs = V _s ρ _e ,

Q _PGZ = 8.7 · 560 = 4872 kg.

The required mass of filler

The mass of the inverse hydrocarbon-water emulsion is

Q _e = Q _PGZ -Q _n = 4872-1392 = 3480 kg,

and its volume is equal

V _e = Q _e : ρ _e = 3480: 938 = 3.7 m ³ .

In the averaging tank, 3.7 m ^{3 of} inverse hydrocarbon-water emulsion of the following composition is prepared, wt.%:

Hydrocarbon fluid

(diesel) 20.0

Calcium Chloride 2.0

Fatty Acid 1.0

Water (technical) 77.0

1392 kg of gas-filled microspheres are introduced into this emulsion and, after thorough mixing, the suspension obtained is pumped into the well. Injection is carried out by the CA-320M unit in 2nd gear engaged. Moreover, its flow rate is Q = 3.16 l / s (with a sleeve diameter of 115 mm), pumping time T = V _s / Q = 8.7 / 0.0036 = 2416.7 s = 40.3 min.

After the formation of a floating hydraulic shutter in the well, a sealant is installed at the wellhead under the casing and it is lowered into the well with a device for step cementing installed on it, which is used as a PDM packer coupling. The latter is installed on the casing so that at the time the casing is lowered, it is 5 m higher than the shoe of the previous casing (in this case, the conductor lowered to a depth of 229 m).

A cementing head is installed with a lower combined “ball-plug” and an upper cementing plug.

For cementing the lower stage of the casing string, sequentially is pumped: buffer fluid (viscoelastic solution with a density of 1000 kg / m ³ ), the first and second portions of the grouting mortar.

A viscoelastic solution of the following composition is prepared in the averaging tank, wt.%:

Sodium Chloride 1.0

Polyacrylamide 1.5

Chrompeak 0.8

Sodium Hyposulfide 0.8

Water 95.9

Visco-elastic solution is pumped in volume

where 1 _BJ is the height of the column of buffer fluid in the annulus (in accordance with the instructions for fastening oil and gas wells RD 39-00147001-767-2000, 1 _BJ = 150-200 m), take 1 _BJ = 175 m.

As the first portion, an aerated cement slurry is used (with a degree of aeration in the bottomhole conditions α = 1.5-2) in a volume that ensures filling the annular space from the sole of a highly permeable gas-saturated manifold to the packer sleeve

where k _p - coefficient taking into account the increase in the volume of cement slurry absorbed by a highly permeable gas-saturated reservoir.

The second portion of the cement slurry (unaerated) is pumped in volume

where 1 _C - the height of the cement glass left in the casing, equal to: 1 _C = 15 m

The total volume of cement slurry for cementing the lower stage is V _ac + V _c1 = 0.8 + 3.54 = 4.34 m ³ .

The time for pumping the total volume of cement slurry is (two TsA-320M, at 3rd speed, with a sleeve diameter of 115 mm)

T _c1 = (V _ap + V _c1 ) / Q = 4.34 / 0.00598 · 2 = 362.9 s ≈ 6 min

Before forcing portions of the cement slurry, a reverse hydrocarbon-water emulsion is pumped into the casing to fill the casing in a volume from the casing shoe to the packer sleeve

After pumping the reverse hydrocarbon-water emulsion into the well, the lower combined “ball-ball” is released and forced.

The volume of the squeezing fluid for forcing the cement slurry and the inverse hydrocarbon-water emulsion is

The time for pushing the cement slurry of the lower stage is (two TsA-320M, at 3rd speed, with a sleeve diameter of 115 mm)

T _p1 = (V _p1 + V _e ) / Q = (8.9 + 6.4) / 0.00598 · 2 = 1279.3 s = 21.3 min

At the time of aeration of the cement slurry beyond the casing, determined by the volume of displacement fluid

V = V _Tr - (V _AC + V _C1 ) -V _e = 0.785 · 0.225 ² · 400- (0.8 + 3.54) -6.4 = 5.2 m ³ ,

biphasic foam with an average density determined by the formula is pumped into the annulus from the wellhead

To ensure a given density of a two-phase foam, its degree of aeration should be

where α is the degree of aeration;

ρ $\genfrac{}{}{0ex}{}{\text{wed}}{\text{P}}$ - the average required density of the foam in the fastening interval, kg / m ³ ;

_AMPs ρ - density of the foaming liquid, kg / m ^3;

ρ _g - gas density at atmospheric pressure, kg / m ³ ;

P ₀ - atmospheric pressure (P ₀ = 0.1 MPa);

P _PL - pressure in a highly permeable gas-saturated reservoir (P _PL = 0.72 MPa);

T is the maximum temperature in a highly permeable gas-saturated reservoir, T = 303K;

T ₀ - average normal temperature, T ₀ = 295K.

When pumping two-phase foam, the wellhead pressure in the annulus is equal to P _y = 0.2 MPa.

When the aerated cement slurry reaches the sole of a highly permeable gas-saturated manifold, which is determined by the flow rate of the squeezing fluid in the annular space from the casing shoe to the sole of a highly-permeable gas-saturated manifold

wellhead pressure in the annulus is gradually reduced to atmospheric.

After landing of the “plug-ball” on the saddle of the lower sleeve of the packer clutch, the central channel is blocked. Create a wellhead pressure in the casing equal to 5 MPa, while the lower sleeve moves down to the stop of the shear elements and the annulus is packaged. With a further increase in pressure to 6.0 MPa, cement windows open through which the annular space is cemented above the packer clutch.

A non-aerated cement slurry is injected for cementing the upper stage of the casing string in volume

where D _VP - the inner diameter of the previous casing,

The time for pumping the unaerated cement slurry of the upper stage is (two TsA-320M, at the 3rd speed, with a _sleeve diameter of 115 mm) T _c1 = V _c2 / Q = 5.7 / 0.00598 · 2 = 476.6 s≈ 8 minutes

In the averaging tank, a viscoelastic solution of the following composition is prepared in advance, wt.%:

Sodium Chloride 1.0

Polyacrylamide 1.0

Chrompeak 0.8

Barite 15.0

Rubber crumb 5.0

Sodium Hyposulfide 0.8

Water 76.4

After pumping the non-aerated cement slurry of the upper stage, a viscoelastic solution is pumped into the casing in volume

V _p = 0.785 $\genfrac{}{}{0ex}{}{\text{2}}{\text{kp}}$ -D $\genfrac{}{}{0ex}{}{\text{2}}{\text{n}}$ ) H _p ,

where h _p is the height of the viscoelastic solution, m, is selected from the condition

L <h _p <2L,

3.3 <h _p <6.6

take h _p = 5 m

V _p = 0.785 · (0.304 ² -0.245 ² ) · 5 = 0.13 m ³

After pumping 5.7 m ^{3 of} non-aerated cement slurry and 0.13 m ^{3 of} viscoelastic mortar into the well, the upper cement plug is released and forced. In this case, the volume of the squeezing liquid (process water) will be equal to

The time for grouting the grouting mortar is (two TsA-320M, at 3rd speed, with a sleeve diameter of 115 mm)

T _p1 = V _p2 / Q = 8.9 / 0.00598 · 2 = 744.15 s = 12.4 min

After punching and closing the cementing windows with the top cork hole, the well is left to wait for the hardening of the grouting mortar (BSC) for 24 hours.

After the expiration of the time of the WPC, the upper cementing plug, the combined “ball-plug”, cement cup and saddle of the lower sleeve of the packer coupling are drilled.

In the process, a floating hydraulic shutter was installed in a predetermined interval; a high-quality separation of a highly permeable gas-saturated reservoir from the wellhead was achieved, as evidenced by the absence of gas phenomena during casing running and during cementing. In addition, when performing the method, the operation of waiting for the hardening of the cement slurry used to cement the lower stage of the casing is excluded.

The grouting mortar is raised to the design height.

Method for stepwise cementing of a well in highly permeable gas-saturated reservoirs

Claims (3)

1. A method of stepwise cementing a well with a highly permeable gas-saturated reservoir, including installing a device for stepwise cementing in a casing over the roof of a specified collector, mounting a cementing head, cementing the lower stage of a casing by pumping a buffer fluid and two portions of a cement slurry of different densities in a volume that allows filling annular space from the casing shoe to the device for step cementing, sold grouting cement slurry with a squeezing fluid, fixing the moment of its entry into the annulus and pumping two-phase foam into the last, opening cementing windows with subsequent washing out of excess cement slurry and cementing the upper stage of the casing string through a cementing device by pumping a non-aerated cement slurry, while a floating hydraulic shutter is formed by pumping the suspension tightly into the annulus less than 1000 kg / m ³ containing the liquid phase and the filler, the height of the floating hydraulic shutter is determined by the formula

where N _s - the height of the floating hydraulic shutter, m; P _PL - pressure in a highly permeable gas-saturated reservoir, MPa; K is the coefficient of excess of hydrostatic pressure in the well over pressure in a highly permeable gas-saturated reservoir equal to 1.04-1.15; ΔР is the gradient of gas breakthrough through a floating hydraulic shutter equal to 0.005-0.011 MPa / m, according to experimental studies, and the density of the floating hydraulic shutter is determined by the formula

where ρ _z - the density of the floating hydraulic shutter, kg / m ³ ; ρ _W - fluid density in the well with a steady level after absorption, kg / m ³ ; N _to - the depth of the roof of a highly permeable gas-saturated reservoir, m; h is the fluid level in the well, established after absorption, m, in this case, a reverse hydrocarbon-water emulsion with a viscosity of 150-300 mPa · s is used as the liquid phase of the suspension, gas-filled microspheres or expanded vermiculite are used as the filler, the mass part of the specified emulsion per one mass part of the specified filler is determined by the formula

where m _e is the mass part of the inverse hydrocarbon-water emulsion per 1 mass part of the filler; ρ _e - the density of the specified emulsion, kg / m ³ ; ρ _n - the density of the filler, kg / m ³ , and after the formation of a floating hydraulic shutter, the wellhead is sealed, while a packer sleeve is used as a device for step cementing, a viscoelastic solution is used as a buffer fluid, and an aerated cement slurry is pumped in the first portion of the grout, which is pumped in a volume that ensures filling annular space from the sole of a highly permeable gas-saturated manifold to a packer coupling; as a second portion, an unaerated cement slurry pumped into a filling that ensures filling the annulus from the casing shoe to the sole of a highly permeable gas-saturated reservoir, and after pumping a second portion of the cement slurry, the reverse hydrocarbon-water emulsion is pumped in the volume necessary to fill the casing to the step cementing device, and the density of the two-phase foam is determined by the formula

where ρ $\genfrac{}{}{0ex}{}{\text{wed}}{\text{P}}$ - the average required density of the foam in the range from the roof of a highly permeable gas-saturated reservoir to the wellhead, kg / m; g is the acceleration of gravity, m / s ² ; R _y - wellhead pressure in the casing, MPa, moreover, at the moment of reaching the sole of the indicated collector with an aerated grouting mortar, the wellhead pressure in the annulus is gradually reduced to atmospheric pressure, and after the grouting mortar is pressed, wellhead pressure is created in the casing sufficient to pack the annulus, and cementation of the upper stage of the casing is started without waiting for the cementing to solidify the solution used to cement the lower stage of the casing, while after pumping neaerirov of the cement slurry used for cementing the upper stage of the casing, a viscoelastic solution is pumped in a volume that ensures filling the annulus with a height selected from the condition L <h _p <2L, where h _p is the height of the column of viscoelastic solution in the annulus, m; L is the length of the device for step cementing, m 2. The method according to claim 1, characterized in that as the reverse hydrocarbon-water emulsion using the following composition, wt.%: Hydrocarbon Liquid 15-25 Fatty acids, or their salts, or their bottoms 0.5-1.5 Calcium Chloride 1.0-2.0 Water Else 3. The method according to claim 1, characterized in that the following composition is used as a viscoelastic solution, wt.%: Sodium Chloride 1.0 polyacrylamide 1.0 Chrompeak 0.8 Sodium Hyposulfide 0.8 barite 15.0 Rubber crumb 5.0 Water Else