RU2726754C1 - Cementing slurry - Google Patents

Abstract

FIELD: mining.SUBSTANCE: invention relates to construction of wells, in particular to cementing slurries for cementing of casing strings, gas condensate and oil wells, complicated by availability of loosely bound, perennial permafrost-susceptible to hydraulic fracturing. Cementing slurry containing cementing Portland cement PCT-1-50, expanding component and 4% aqueous calcium chloride solution is characterized by that it additionally contains poly-N-vinylpyrrolidone "Impiron" plasticiser and microsilica, and the expanding component used is calcium oxide in the following ratio of components, wt%: microsilica 8–12, calcium oxide 5–8, poly-N-vinylpyrrolidone 0.4–0.6, cementing Portland cement (PCT-1-50) – balance, and content of 4 % aqueous solution of calcium chloride in the cementing slurry ensures the ratio of the aqueous mixture to base from 0.5 to 0.55.EFFECT: improving strength and adhesion properties of the formed cement slurry while ensuring its pumping capacity by introducing a plasticiser reagent and reducing the amount of free water in the composition.1 cl, 1 tbl

Description

The invention relates to the field of construction and maintenance of wells, in particular to grouting slurries for cementing casing strings, gas condensate and oil wells, complicated by the presence of weakly bound, prone to hydraulic fracturing and collapses, permafrost.

Known oil well cement for low-temperature wells "Arccement" (RF Patent No. 2144977, published 01/27/2000), containing wt. %: Portland cement - from 48 to 80, alumina cement grade "400" - from 20 to 50, chloride salt of an alkali or alkaline earth metal - from 4 to 6, modified technical lignosulfonate plasticizer - LSTM (S-3, N-1) - from 0.15 to 0.7.

The disadvantage is low spreading and, accordingly, low pumping ability, which will not allow its effective use at low temperatures, as well as reduced strength of the cement stone.

Known polymer cement slurry for low-temperature wells (RF Patent No. 2370515, published 20.10.2009), containing Portland cement PCT-50-1-50, fluid loss reducer - CFL-117, adhesive additive - Concrepol, expanding additive NRS-1M and water, when the following ratio of components wt. %: Portland cement PTC-50-1-50 from 90 to 92, CFL-117 from 0.2 to 0.3, Concrepol - 1.0, NRS-1M from 8 to 10, water from 45 to 50.

The disadvantage of the solution is the low strength characteristics of the cement stone, due to the chemical reaction between the added polymers and Portland cement.

Known grouting solution (RF patent No. 2441897, published 02/10/2012) containing cement, hydroxyethyl cellulose, plasticizer, defoamer and additionally synthetic fibers with a diameter of 0.001 to 0.1 and a length of 1 to 20 mm, an expanding additive in the following ratio, wt. h: cement - 100; hydroxyethyl cellulose 0.2 to 0.4; plasticizer from 0.1 to 0.5; antifoam - 0.2; synthetic fibers from 0.1 to 4; expanding additive from 0.1 to 20; water from 49 to 51.

The disadvantage of this composition is the significant shrinkage of the cement stone during hardening, which leads to a deterioration in the quality of cementing wells and their surface layers.

Known grouting solution for casing wells and sidetracks with horizontal sections (RF Patent No. 2460754, published 09/10/2012), containing wt. %: caustic brucite powder - 43.86-47.36, magnesium sulfate - 8.32-13.81, water - the rest.

The disadvantage of this composition can be attributed to the low strength characteristics of the forming cement stone, as well as low adhesion of the plugging stone to the metal of the casing pipes and rocks.

Known grouting solution (RF patent No. 2471846, published 01/10/2013), including grouting Portland cement, fluid loss reducer, plasticizer and structurant, and as structurant the solution contains microsilica MK-85 and calcium chloride solution, as fluid loss reducer - natrosol 250 EXR, as a plasticizer - oxil-cm with the following ratio of components, wt. %: Portland oil well cement from 58.46 to 60.64; microsilica MK-85 from 1.19 to 1.24; CaCl2 solution 32.81 to 34.04; Natrosol 250 EXR 2.62 to 2.72; oxil cm from 1.36 to 4.92.

The disadvantage of this composition is the low level of adhesion of the stone with the column, leading to inter-column crossflows and reduced strength of the cement stone, as well as the lack of the required expansion coefficient of the plugging stone.

Known lightweight grouting solution (RF patent No. 2151271, published 06/20/2000), taken as a prototype, containing backfill Portland cement, lightening material - aluminosilicate hollow microspheres, expanding component - carboaluminate additive mixed with gypsum, water or 4% aqueous solution of CaCl ₂ . The grouting solution contains ingredients in the following ratio, wt. %: Portland oil-well cement from 36.47 to 57.34; hollow aluminosilicate microspheres from 6.47 to 17.65; carboaluminate additive from 1.18 to 2.67; gypsum 1.18 to 2.67; water or 4% calcium chloride solution - the rest. The composition has a density from 1240 to 1580 kg / cm3, a bending strength of the stone from 1.0 to 2.8 MPa.

The disadvantage of this solution is the gravitational phase separation during the solidification process, which leads to surface heterogeneity, and local destruction during subsequent well operation. An increase in sedimentation stability by reducing the water-cement ratio (W / C) or an increase in the content of microspheres leads to a deterioration in the rheological properties of the solutions and cracking in the cement stone along the surface of the well.

The technical result is to increase the strength and adhesive properties of the resulting cement slurry while ensuring the pumpability of the grouting composition and achieving optimal hardening times at low well temperatures, by reducing the amount of free water in the composition due to the introduction of a plasticizer reagent, which in turn increases the physical and mechanical properties cement stone, including in permafrost conditions.

The technical result is achieved by the fact that it additionally contains a plasticizer poly-N-vinylpyrrolidone "Impiron" and microsilica, and calcium oxide is used as an expanding component, with the following ratio of components, wt. %:

microsilica 8-12 calcium oxide 5-8 poly-N-vinylpyrrolidone 0.4-0.6 oil well Portland cement (PCT-1-50) - the rest,

and the content of a 4% aqueous solution of calcium chloride in the cement slurry provides the ratio of the aqueous mixture to the base from 0.5 to 0.55.

The claimed grouting composition includes the following reagents and commercial products containing them:

Microsilica from 8 to 12, produced in accordance with GOST R 56178-2014.

Calcium oxide from 5 to 8, produced in accordance with GOST 8677-76.

Poly-N-vinylpyrrolidone from 0.4 to 0.6, manufactured according to TU 9365-005-98540320-2014.

Backfill Portland cement PTC-1-50 - the rest, produced in accordance with GOST 1581-96.

4% aqueous solution of calcium chloride, produced in accordance with GOST 450-77, in the cement slurry provides the ratio of the aqueous mixture with the base from 0.5 to 0.55.

The selected composition of the grouting slurry for cementing wells in the permafrost zone increases the strength of the cement stone, while the proposed composition has increased sedimentation stability, frost resistance and the necessary spreadability. The proposed composition of the grouting slurry for casing strings in the permafrost zone meets the requirements for cement stone used for borehole casing in permafrost conditions.

The basis of the grouting solution for casing wells in the permafrost zone is the PTC-1-50 grouting Portland cement. As you know, Portland cements set and harden with a general decrease in volume. In construction, this problem is solved by the introduction of inert fillers and aggregates that allow cement to harden without shrinkage. In the present invention, calcium oxide is introduced as an expanding plugging material in an amount of 5 to 7 wt. %. The additive allows you to create crystallization pressure, which is formed during the crystallization of poorly soluble hydroxides during hydration, which prevents destructive processes in the formed cement stone. The most optimal content of calcium oxide in the grouting solution (to achieve maximum strength of the solution) is from 5 to 7% wt. With the introduction of calcium oxide less than 5% wt. the additive has a negligible effect on the setting time and strength of the cement. With the introduction of calcium oxide more than 7% wt. bending strength of the stone is significantly reduced.

Microsilica is added as a concentrate of nanostructures; its introduction increases the compressive and flexural strength of the cement stone, its frost resistance, and also decreases its permeability. The use of microsilica in the composition of the cement slurry for cementing wells in the cryolithozone leads to a significant compaction of the cement stone and a corresponding improvement in its mechanical properties. In addition, the modification of the microsilica material stabilizes the most important valence interactions Ca-Si-H (formed when the cement mixture is mixed with water and the clinker material is hydrated), which are responsible for the cohesion of concrete, reducing calcium leaching and increasing its moisture resistance. The addition of ultrafine silica to the grouting composition affects the increase in the strength properties of the cement stone.

The experiments made it possible to establish the most optimal content of microsilica in the grouting slurry (to achieve the maximum strength of the solutions) from 8 to 12% wt. Grouting slurry with microsilicon additives in the proposed range is characterized by sedimentation stability, and cement stone with microsilicic additives in the proposed range has low permeability. With the addition of microsilica, an increase in the density and a decrease in the porosity of the cement stone is also observed, which, as a result, leads to an improvement in its waterproofness and corrosion resistance. The addition of microsilica is less than 8% wt. insufficiently increases the strength of the cement slurry. When using a concentration of microsilica from 12 to 14% wt. the strength of the solution increases slightly. With an increase in the content of microsilica in the composition of the cement slurry more than 14% wt. and cracking of the samples occurs, while the frost resistance of the cement stone is significantly reduced.

A 4% aqueous solution of calcium chloride is added as a hardening accelerator. The content of a 4% aqueous solution of calcium chloride in the cement slurry provides the ratio of the aqueous mixture to the base from 0.5 to 0.55. The selected range of the ratio of the aqueous mixture to the base allows you to obtain a cement slurry without adversely affecting the strength characteristics of the forming cement stone, together with the use of a plasticizer reagent. The content of calcium chloride also has an effect as an accelerator of the setting time of grouting slurries, with a high rate of heat release at the beginning of the mixing reaction with a minimum amount of heat released in general, which is necessary when casing wells at low temperatures. The content of more than 4% calcium chloride in the grouting slurry can cause thawing of permafrost during its exothermic reaction.

"Impiron" is a water-polymer system based on an amorphous-linear polymer of poly-N-vinylpyrrolidone, viscous, transparent or slightly opalescent, colorless or slightly colored liquid, produced in accordance with TU 9365-005-98540320-2014 "Impiron", produced by LLC "Orgpolymersintez SPB" Saint-Petersburg, Russia).

The tasks performed by the plasticizer in the cement slurry are reduced to increasing the mobility (spreading) of the slurry and reducing its structural (plastic) viscosity. The addition of poly-N-vinylpyrrolidone to the grouting composition of an amorphous linear polymer leads to system stabilization. The filtration properties of the cement slurry improve, the mobility of the cement slurry increases. Due to the effective reduction of porosity, the compressive and flexural strength and adhesive properties of the cement stone are increased.

Grouting slurry with boundary values of calcium oxide from 5 to 8% wt., Microsilica from 8 to 12% wt., Poly-N-vinylpyrrolidone from 0.4 to 0.6 wt.%, Grouting Portland cement PTC-1-50, with a ratio an aqueous mixture with a base from 0.5 to 0.55, due to the addition of a 4% aqueous solution of calcium chloride, has a density of 1800 to 1820 kg / m ³ and is characterized by a significant increase in the strength of the cement stone formed from it.

Preparation of cement slurry with increased strength indices is carried out as follows. During the preparation of the grouting solution, calcium oxide and microsilica were mixed with Portland cement PCT-1-50 in dry form at various ratios. A 4% aqueous solution of calcium chloride was used as a mixing liquid. The plasticizer was added to the finished suspension. The mixing of the amponage suspension was carried out in accordance with GOST 1581-96. After that, the influence of the amount of introduced microsilica, calcium oxide and plasticizer on the density, spreadability, setting time of the cement slurry, strength and expansion of the formed from the non-cement stone was determined. The determination of the main properties of the grouting slurry and stone was carried out at a temperature of (20 ± 2) ° С in accordance with GOST 26798.1-96 “Grouting cements. Test methods ".

The method is illustrated by the following examples.

Example 1. For the preparation of 1 kg of plugging solution, 866 g (86.6 wt.% :) of plugging cement PTC-1-50 was used, then mixed with 50 g of calcium oxide (5 wt.%), And 80 g of microsilica (8 wt. .%), after which the dry mixture was added to the solution in a solution of 4% calcium chloride solution in an amount providing the ratio of the aqueous mixture to the base equal to 0.5. Then in the resulting suspension was added the plasticizer "Impiron" in the amount of 6 g (0.6 wt.%),

After that, the resulting composition was mixed for 3 minutes, then the density and spreadability of the cement slurry was determined. Then the solution was poured into molds to determine the setting time. The stone was tested for strength after 2, 7 and 14 days and for expansion after 2, 7 and 14 days.

Examples 2-8. Preparation and testing of the rest of the grouting solutions presented in table. 1 are similar.

Data on the composition of the studied grouting slurries and data on the properties of grouting slurries, mixed according to the claimed recipe, are shown in Table 1. As can be seen from the data in Table 1, the proposed grouting slurries are characterized by improved values of indicators of the main technological properties, namely, the strength of the cement stone and the expansion of the cement stone.

Thus, as shown in the above description of the invention, the technical result is achieved, which consists in increasing the strength of the resulting cement slurry while improving its operational characteristics, increasing the activity of the expanding component that increases the adhesive properties of the cement stone while ensuring the pumpability of the cement slurry and achieving optimal hardening times when low downhole temperatures, by reducing the amount of free water in the composition due to the introduction of a plasticizer reagent.

The proposed technical solution can be used for cementing casing strings of gas, gas condensate and oil wells, complicated by the presence of weakly bound permafrost rocks prone to hydraulic fracturing.

Claims (3)

Grouting slurry containing grouting Portland cement PCT-1-50, an expanding component and a 4% aqueous solution of calcium chloride, characterized in that it additionally contains a plasticizer poly-N-vinylpyrrolidone "Imiron" and microsilica, and calcium oxide is used as an expanding component with the following ratio of components, wt. %: Microsilica 8-12 Calcium oxide 5-8 Poly-N-vinylpyrrolidone 0.4-0.6 Backfill Portland cement PCT-1-50 Rest and the content of a 4% aqueous solution of calcium chloride in the cement slurry provides the ratio of the aqueous mixture to the base from 0.5 to 0.55.