RU2312973C1 - Method to prevent gas flow via annulus during well cementing - Google Patents

Abstract

FIELD: oil and gas production, particularly methods or devices for cementing, for plugging holes, crevices, or the like.

SUBSTANCE: method involves securing casing pipes by cementing thereof with cement mortar up to level located over productive reservoir roof; arranging composition having viscoelastic properties over cement mortar; placing plugging composition having setting time exceeding that of cement mortar over viscoelastic composition, wherein the plugging composition has density providing creation of hydrostatic pressure exceeding gas pressure in productive reservoir before hardening of cement mortar supplied within productive reservoir interval. Viscoelastic composition is poured so that viscoelastic composition height is not less than 10 m. The viscoelastic composition is clayless viscoelastic composition.

EFFECT: increased cementing reliability.

4 cl, 1 ex

Description

The invention relates to the oil and gas industry and can be used in well construction, in particular when cementing annular space of both gas and oil wells with a large gas factor.

A well-known method of securing wells (RF Patent No. 2068489, class ЕВВ 33/13, 1996), which includes installing a hardening grouting material (a step in the process of securing the casing) in a given place in the annulus of the well and installing a non-hardening plastic grouting composition above it. Moreover, as a non-hardening plastic grouting composition, a hydrophobic non-hardening grouting material is used, consisting of diesel fuel and bitumen, acquiring the properties of a plastic body after feeding it into the well.

In the implementation of this known method, the viscosity of the non-hardening grouting material is controlled during preparation by introducing a thickener and additional heating to the viscosity of the hardening grouting material. The specified method is intended to increase the tightness of the lining.

However, this method is not without a number of disadvantages, namely:

- the use in this method of non-hardening grouting composition, including hydrocarbon fluid, requires additional fire safety measures and does not meet environmental requirements;

- the implementation of the known method is tied to the requirements of compliance with a certain temperature, which is not always possible to perform in a drilling environment.

The closest to the proposed technical solution for its intended purpose is a method of preventing gas migration through the annular space of oil and gas wells, as well as subsequent intercolumn gas displays and gas griffins at their mouths, including fixing casing strings with cementing with raising the cement slurry with a normal density above the gas (productive) roof formation to a height of up to 50 m and installation above a cement mortar of a composition with viscoelastic properties prepared from spent clay mortar and with sludge with the addition of powdered polyacrylamide, and the interval in permafrost rocks is filled with an ice-free solution from the wellhead and when the level of the indicated solution is reduced, it is pumped to provide hydrostatic pressure in the annulus above the cement ring above the reservoir ring (RF Patent No. 2235858, CL Е21В 33 / 14, from 2002).

The disadvantage of this known method is the absence during hardening of the cement mortar of sufficient hydrostatic pressure created by the composition with viscoelastic properties, as a result of which gas and formation fluid penetrate into the cement mortar and form channels in the cement stone, through which oil and gas flows are possible. This prevents reliable sealing annular space.

In addition, another disadvantage of this known method is that when it is carried out, it is filled with an ice-free solution (analogue of the drilling fluid) of the annulus. Drilling fluid is not a stable system and its complete destruction may occur over time. As a result, formation fluids can flow from overlying permeable formations into the well, which can subsequently lead to depressurization of the annulus.

The technical result achieved by the claimed invention is to increase the reliability of cementing by creating a guaranteed tight lining, as well as to increase the trouble-free life of the well.

The specified technical result is achieved by the proposed method for preventing gas migration through the annulus during well cementing, including fixing casing with cementing with raising a normal density cement mortar above the top of the reservoir and installing a composition with viscoelastic properties over the cement mortar, while the new is that over the composition with viscoelastic properties additionally place the grouting composition with a setting time longer than that of cement about the mortar, and with the necessary density, which ensures the creation of hydrostatic pressure above the gas pressure in the reservoir while waiting for the cement to solidify, delivered to the interval of the reservoir, and installation of a composition with viscoelastic properties over a cement mortar is performed at a height of at least 10 m, and as a composition with viscoelastic properties, a clayless viscoelastic composition is used.

In an advantageous embodiment, as a clayless viscoelastic composition, a composition with adjustable lifetimes is used.

A weighting agent may be introduced into it.

The lifetime of a clayless viscoelastic composition is determined by the time of its destruction, after which the weighting agent falls out.

The achievement of the specified technical result is ensured by the following.

Due to the fact that cement composition of the required density is additionally placed over a composition with viscoelastic properties and with a setting time longer than that of a cement mortar located in the interval of the productive formation, hydrostatic pressure is created above the reservoir pressure in the productive formation for the entire waiting period for the cement mortar to harden. located opposite the productive interval, which eliminates the formation of channels in the lining, and therefore increases its tightness and reliability spine.

Due to the fact that installation of a composition with viscoelastic properties over a cement mortar is carried out to a height of at least 10 m, a sufficient buffer is created between the cement mortar and the grouting composition, which also prevents the migration of gas into the cement mortar and overlying intervals.

Violation of the structure of the composition with viscoelastic properties (hereinafter WCS) when the weighting agent falls out at the end of the life of the WCS leads to the formation of a kind of plug, due to which additional annular space is sealed.

All this leads to a decrease in the likelihood of gas migration through the annulus, and therefore to an increase in the trouble-free life of the well.

The proposed method is simple to implement, because provides for the minimum number of reagents and operations used.

The proposed method is implemented as follows.

Example

Geological and technical characteristics are determined: well depth, bottomhole temperature, column diameter, reservoir interval, reservoir pressure, etc.

For example, it is necessary to cement a well with the following initial data:

- well depth (vertical) - 1400 m;

- column diameter - 168 mm;

- bit diameter - 215.9 mm;

- the interval of the reservoir - 1200-1400 m;

- reservoir pressure gradient - 0.0103 MPa / m;

- the density of the drilling fluid is 1080-1100 kg / m ³ ;

the density of the mixing fluid is 1000 kg / m ³ .

First, the well is prepared for cementing, for example, according to the method according to the patent of the Russian Federation No. 2137906. Then a cement slurry of normal density 1.82 g / cm ^{3 is} pumped into the well with a thickening time equal to Tc / 0.75 - presumably 2 hours (setting time 3 hours), and it is pressed above the top of the reservoir (in our case, a gas reservoir) ) to a height of 50-100 m from the roof of the specified gas reservoir. At the same time, a clay-free viscoelastic composition (hereinafter WCL) is prepared on the day surface. As the specified clay-free WCS with adjustable lifetimes, a composition known from the RF patent No. 2132458, the following component content, wt.%:

starch 5-10 NaOH 0.5-1 Surfactant 0.05-0.075 sodium tetraborate mixture and peroxide compound in the ratio of 1 ÷ 5 ÷ 1 0.7-1.5 water rest

The adjustable lifespan of specific formulations of these clay-free WCS is 3-4 hours.

To increase the efficiency, a weighting agent, for example, barite or hematite in the required amount, is additionally introduced into the specified WCS.

Calculate the required height of the WCS in the well above the cement mortar using the formula

H = 10 ⁵ · ΔP / ρ _WCS ,

where ρ _WCS - the density of the WCS, kg / m ³ ;

ΔР is the overpressure, MPa, necessary to balance the reservoir pressure P _{PL with the} hydrostatic column of the grout fluid R _PZ , determined by the formula

ΔP = P _PL -P _ZhZ .

In our case, the overpressure will be equal to

ΔP = 12.36-12.0 = 0.36 MPa.

According to the above formula, based on the density of the WCS = 1630 kg / m ³ , we determine the height of the installation of the WCS:

N = 10 ⁵ · 0.36 / 1630 = 22 m.

Next, install the WCS in the well above the cement slurry. Next, a portion of the grouting composition of the required density is pumped into the well with a thickening time of 3 hours (setting time is 3.5-4 hours), wt.h:

cement one hundred water fifty filtration reducer 0.3

As you can see, the thickening (setting) time of the specified grouting composition is longer than the thickening (setting) time of the cement mortar installed in the interval of the productive formation. This is necessary so that during the formation of cement stone from the cement mortar located in the interval of the reservoir, the hydrostatic pressure is maintained above the reservoir due to the portion of the grouting composition located above the WCS. This portion has a longer setting time and thereby, due to the creation of the necessary excess of hydrostatic pressure over the reservoir, the migration of gas through the cement mortar is prevented while waiting for the cement to harden (OZZ).

Thus, the cement slurry will not be affected by the gas coming from the gas reservoir.

The WCS, in turn, plays the role of a packer located in the annulus and prevents the migration of gas into the overlying intervals, thereby ensuring the formation of cement stone from the grouting composition of the upper portion without gas penetrating into it.

In addition, after cementing during cementing, the self-destruction of the slurry will occur (due to an adjustable lifespan), the weighting agent will precipitate and thereby create an impenetrable stopper that prevents the migration of gas into the grouting composition, due to which the latter will also provide a tight seal.

This technology allows you to qualitatively isolate both gas wells and oil wells with a high gas factor by preventing the migration of gas from the reservoir during the SSC and by creating guaranteed tight supports, and high-quality and reliable isolation of the well allows you to increase the trouble-free life of its operation.

Claims (4)

1. A method of preventing gas migration through annular space during well cementing, including mounting casing strings with cementing with raising a normal density cement slurry above the top of the reservoir and installing a composition with viscoelastic properties above the cement slurry, characterized in that cement slurry is additionally placed over the composition with viscoelastic properties composition with a setting time longer than that of the cement mortar, and with the necessary density, providing the creation of hydra the residual pressure is higher than the gas pressure in the reservoir while waiting for the cement to solidify, delivered to the interval of the reservoir, and a composition with viscoelastic properties is installed above the cement mortar to a height of at least 10 m, and a clayless viscoelastic composition is used as a composition with viscoelastic properties. 2. The method according to claim 1, characterized in that as a clay-free viscoelastic composition, a composition with adjustable life spans is used. 3. The method according to claim 1, characterized in that a weighting agent is additionally introduced into the clay-free viscoelastic composition with adjustable life spans. 4. The method according to claim 3, characterized in that the life time of a clayless viscoelastic composition is determined by the time of its destruction, after which the weighting agent falls out.