RU2808959C1 - Backfill compound - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: cement mixtures intended for cementing oil and gas wells covering intervals of permeable formations at elevated temperatures. The cement composition includes cement, water and plasticizer. Saudi class G cement is used as well cement, and C-3 plasticizer is used as a plasticizer, while the composition additionally contains silica powder and nanoclay, with the following component ratio, wt.%: Saudi class G cement - 50, 40-50, 76, plasticizer C-3 - 0.40-0.41, silica powder - 17.64-17.77, nanoclay - 0.51-1.01, water - the rest.

EFFECT: increasing the efficiency of well casing under conditions of elevated temperatures.

1 cl, 6 tbl, 12 ex

Description

The invention relates to the oil and gas industry, in particular to cement mixtures intended for cementing oil and gas wells covering intervals of permeable formations at elevated temperatures.

A known composition for producing cement slurries (RU patent No. 2588066, published on June 27, 2016) contains aluminous cement and additionally contains quartz sand, quicklime, superplasticizer C-3, a stabilizer reagent and a fluid loss reducer - a 1% solution of hydroxyethylcellulose, a defoamer Penta-465 and water at the following ratio of components, wt.%: Portland cement - 55-65, aluminous cement - 10-20, quicklime - 5-10, quartz sand - 15-20, specified superplasticizer - 1-1.3 , hydroxyethylcellulose - 0.2-0.3, the specified defoamer - 0.05-0.1, water - the rest.

A disadvantage of the known composition is its ability to maintain the necessary strength only under normal temperatures. Cannot be used at elevated temperatures.

A known composition for producing cement slurries (RU patent No. 2761396, published 12/08/2021), containing cement-free Portland cement of high sulfate resistance PCTI-G-CC-1, ground pulverized quartz grade “B”, fly ash ZU KUK-B-3, condensed microsilica MK-85, plasticizer based on polycarboxylate polymers WellFix P-100, calcium chloride, aluminum powder PAP-1, Neonol AF 9-4, hydroxyethylcellulose, Natrosol 250 KR, 18% sodium chloride solution. This composition makes it possible to obtain cement stone that is resistant to the aggressive effects of very strong brines.

The disadvantage of this solution is the rapid loss of strength at high temperatures.

A known composition for producing cement slurries (RU patent No. 2504568, published on January 20, 2014), including cement cement, a finely dispersed inorganic additive, hydroxyethylcellulose, sodium chloride or potassium chloride and water in the following ratio of components, wt.%: cement cement 75.0- 85.0, finely dispersed inorganic additive 15.0-25.0, hydroxyethyl cellulose 0.3-0.6, specified salt additive 5.0-10.0, water 45.0-55.0. As a finely dispersed inorganic additive, the expanding cement composition contains natural technical dispersed chalk or ground powdered quartz, or finely ground siliceous filler.

The disadvantages of this composition are low compressive and bending strength at a temperature of 300°C.

A cementing composition is known (patent for invention RU No. 2617763, published on April 26, 2017), containing a cementing magnesia-carnallite mixture, including caustic magnesite powder, carnallite chlorinator sludge, sodium tripolyphosphate, water, characterized in that the mixture additionally contains urea and a finely dispersed inorganic additive with the following ratio of components, wt.%: caustic magnesite powder 22.88-37.29, carnallite chlorinator sludge 22.22-36.79, finely dispersed inorganic additive 6.35-11.43, sodium tripolyphosphate 0.32-0, 65, urea 1.27-3.27, water - the rest.

The disadvantage of the composition is the reduced strength of the cement stone at elevated temperatures, which has not been tested at temperatures above 150°C.

A well-known cement composition (patent for invention RU No. 2120538, published on December 27, 2014), adopted as a prototype, used for cementing oil and gas wells, containing cement cement, as a plasticizer, a polyelectrolyte complex of resorcinol-formaldehyde oligomers and polyethylene polyamine, stabilized by formaldehyde. The content of well cement in the solution is 69%, plasticizer 0.05-0.45%, water - the rest.

The disadvantage is low compressive and bending strength at a temperature of 300°C.

The technical result is to increase the efficiency of well casing under conditions of elevated temperatures.

The technical result is achieved by using Saudi class G cement as a well cement, and C-3 plasticizer as a plasticizer, while the composition additionally contains quartz flour and nanoclay, with the following component ratio, wt.%:

Saudi grade G cement 50.40-50.76 plasticizer S-3 0.40-0.41 quartz flour 17.64-17.77 nanoclay 0.51-1.01 water rest

The claimed cement composition for increasing the strength of cement stone for cementing wells includes the following reagents and commercial products containing them, %:

- Saudi class G cement – 50.40-50.76 wt.%, corresponding to API specification 10A (American Petroleum Institute);

- plasticizer S-3 – 0.40-0.41 wt.%, produced according to TU 5870-005-58042865-05;

- quartz flour – 17.64-17.77 wt.%, produced according to GOST 9077-82;

- nanoclay – 0.51-1.01 wt.%, produced in accordance with GOST R 59456-2021.

- water - the rest; produced in accordance with GOST 23732-79.

Saudi Class G cement is a product obtained by grinding Portland cement clinker primarily consisting of hydrous calcium silicates, usually containing one or more forms of calcium sulfate as a grinding additive. When producing class G oil well cement, no additives are added to the clinker during grinding or mixing, except calcium sulfate and water. Saudi Class G cement is the primary well cement in American Petroleum Institute specifications. Available in medium MSR and high HSR sulfate resistance grades.

Plasticizer S-3 is a special friction reducer - a mixture of different molecular weights of sodium salts of polymethylene naphthalene sulfonic acids, made in the form of a dark brown aqueous solution with a concentration of at least 32%. It has excellent plasticizing properties and an effective water-reducing effect. It is used to obtain highly fluid concrete mixtures without reducing the strength of concrete, as well as to increase the strength, water resistance and other quality indicators of concrete due to the water-reducing effect and obtaining a combined effect with partial use of the first two.

Quartz flour is a material consisting of more than 99% SiO ₂ and has a density of 2.64 g/cm ³ . This flour is produced by grinding vein chemically pure quartz. The degree of grinding of quartz flour is similar to the fineness of grinding Portland cement cements for elevated and moderate temperatures, passing through a sieve with a mesh with a diameter of 0.08 mm is at least 90%. The addition of quartz flour effectively slows down the setting time of cement, ensures the uniformity and stability of the solution, and increases the strength of the cement stone. at high temperatures.

The use of heat-resistant cements allows grouting work to be carried out in deep wells with elevated and high bottomhole temperatures from 101°C to 300°C, as well as in the range of moderate temperatures from 51°C to 100°C, ensuring high-quality fastening of casing strings throughout the entire interval of solution placement .

Nanoclay particles are montmorillonite particles modified by a cation exchange reaction, the density of nanoclay particles is 1.98 g/cm ³ .

The water must meet the requirements of technical water and not contain mechanical impurities.

The cement composition is prepared as follows. A dry mixture of Saudi class G cement, quartz flour and nanoclay is prepared. A dispersed mixture of liquid components of the C-3 plasticizer and water is prepared by mixing in an ultrasonic bath. Then the dispersed mixture of water and C-3 plasticizer is mixed with the dry mixture in the following order: the dispersed mixture of water and C-3 plasticizer is added to the dry mixture or the dry mixture is added to the dispersed mixture of water and C-3 plasticizer. The suspension is kept for 30 seconds to absorb water. Then mix at low speed from 135 to 145 rpm for 30 seconds, after which mixing is stopped and any dough that may have collected on the sides of the bowl in the batch is scraped down for 15 seconds. Mixing is then continued for 60 seconds at an average speed of 275 to 295 rpm.

Example 1. The cement composition is prepared as follows. A dry sample of Saudi class G cement is prepared in the amount of 68.76 wt. %. Plasticizer S-3 in an amount of 0.69 wt. %, which is 1% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The dispersed mixture is obtained by mixing water and C-3 plasticizer in an ultrasonic bath. Then the dispersed mixture of water and C-3 plasticizer is mixed with cement in the following order: the dispersed mixture of water and C-3 plasticizer is added to the cement or cement is added to the mixture. The suspension is kept for 30 seconds to absorb water. Then mix at low speed from 135 to 145 rpm for 30 seconds, after which mixing is stopped and any dough that may have collected on the sides of the bowl in the batch is scraped down for 15 seconds. Mixing is then continued for 60 seconds at an average speed of 275 to 295 rpm.

The resulting cement paste after mixing is tested for spreadability according to the AzNII method, then poured into cubic molds with edge sizes of 40 mm for testing compressive strength, cylindrical molds with a diameter of 38.1 mm and a length of 22.9 mm for testing tensile strength. Brazilian method and permeability. The molds are then immersed in a water bath at 25 ⁰ C for a specified time. To analyze each of the compositions, two temperature conditions were used: low temperature at 25°C and high temperature cyclically varying from 25°C to 300°C. Before testing the cement stone studied in low-temperature mode, the samples were immersed in a water bath for 7 and 28 days. Samples studied in high-temperature mode were placed in a water bath at a temperature of 25°C for 4 and 25 days, then for 3 days. in an autoclave were exposed to a temperature of 300°C to simulate the operating cycle of steam injection wells. These samples were then cooled and tested in the same way as for low temperature conditions. Table 1 shows the conditions for holding cement stone samples before testing.

Table 1 - Conditions for holding cement stone samples

Mode Sample storage time Ambient temperature low temperature 7 days in a water bath 25°C 28 days in a water bath 25°C high temperature – one thermal cycle 7 days:
4 days in a water bath
3 days in autoclave 25°C
300°C 28 days:
25 days in a water bath
3 days in autoclave 25°C
300°C

The prepared cement mortar has a density of 1.97 g/cm ³ .

The compositions of the inventive cement mixture are given in Table 2. The results of tests for spreadability are given in Table 3, strength tests - in Tables 4-5, permeability tests - in Table 6.

Table 2 - Concentrations of reagents used in the cement mixture, % wt.

No. Composition, wt. % Dry mixture, wt. % Liquid mixture, wt. % Saudi Grade G Cement Quartz flour Nanoclay Plasticizer S-3 Water 1 2 3 4 5 6 1 68.76 0.00 0.00 0.69 rest 2 68.83 0.00 0.00 0.62 rest 3 68.89 0.00 0.00 0.55 rest 4 51.14 17.90 0.00 0.41 rest 5 50.76 17.77 0.51 0.41 rest 6 50.40 17.64 1.01 0.40 rest 7 50.03 17.51 1.50 0.40 rest 8 49.67 17.39 1.99 0.40 rest 9 49.71 17.40 1.99 0.35 rest 10 49.75 17.41 1.99 0.30 rest eleven 49.82 17.44 1.99 0.20 rest 12 49.78 17.42 1.99 0.25 rest

Example 2. The cement mixture is prepared as follows. A dry sample of Saudi class G cement is prepared in the amount of 68.83 wt. %. Plasticizer S-3 in an amount of 0.62 wt. %, which is 0.9% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 3. The cement mixture is prepared as follows. A dry sample of Saudi class G cement is prepared in the amount of 68.89 wt. %. Plasticizer S-3 in an amount of 0.55 wt. %, which is 0.8% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 4. A dry mixture of Saudi class G cement is prepared in an amount of 51.14 wt. % and quartz flour in the amount of 17.90 wt. %, which is 35% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.41 wt. %, which is 0.8% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 5. A dry mixture of Saudi class G cement is prepared in an amount of 50.76 wt. %, quartz flour in the amount of 17.77 wt. %, which is 35% by weight of cement, and nanoclay in the amount of 0.51 wt. %, which is 1% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.41 wt. %, which is 0.8% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 6. A dry mixture of Saudi class G cement is prepared in an amount of 50.40 wt. %, quartz flour in the amount of 17.64 wt. %, which is 35% by weight of cement, and nanoclay in the amount of 1.01 wt. %, which is 2% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.40 wt. %, which is 0.8% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 7. A dry mixture of Saudi class G cement is prepared in an amount of 50.03 wt. %, quartz flour in the amount of 17.51 wt. %, which is 35% by weight of cement, and nanoclay in an amount of 1.50 wt. %, which is 3% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.40 wt. %, which is 0.8% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 8. A dry mixture of Saudi class G cement is prepared in an amount of 49.67 wt. %, quartz flour in the amount of 17.39 wt. %, which is 35% by weight of cement, and nanoclay in the amount of 1.99 wt. %, which is 4% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.40 wt. %, which is 0.8% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 9. A dry mixture of Saudi class G cement is prepared in an amount of 49.71 wt. %, quartz flour in the amount of 17.40 wt. %, which is 35% by weight of cement, and nanoclay in the amount of 1.99 wt. %, which is 4% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.35 wt. %, which is 0.7% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 10. A dry mixture of Saudi class G cement is prepared in an amount of 49.75 wt. %, quartz flour in the amount of 17.41 wt. %, which is 35% by weight of cement, and nanoclay in the amount of 1.99 wt. %, which is 4% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.30 wt. %, which is 0.6% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 11. A dry mixture of Saudi class G cement is prepared in an amount of 49.78 wt. %, quartz flour in the amount of 17.42 wt. %, which is 35% by weight of cement, and nanoclay in the amount of 1.99 wt. %, which is 4% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.25 wt. %, which is 0.5% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

Example 12. A dry mixture of Saudi class G cement is prepared in an amount of 49.82 wt. %, quartz flour in the amount of 17.44 wt. %, which is 35% by weight of cement, and nanoclay in the amount of 1.99 wt. %, which is 4% by weight of cement. The resulting composition is thoroughly mixed until a homogeneous mass is obtained. Plasticizer S-3 in an amount of 0.20 wt. %, which is 0.4% by weight of cement, is added to water in an amount ensuring the ratio of water to other components is equal to 0.44. The solution is prepared in the same way as in example 1.

The use of the proposed cement slurry will expand the scope of application of the cement mixture and ensure long-term reliable fastening of casing strings at normal, moderate and elevated temperatures and increase the strength of the adhesive adhesion of the cement mixture to rock and casing.

Table 3 - results of determining the spreadability of the cement mortar.

No. Spreadability of cement slurry, cm 1 26.33 2 25.83 3 24.42 4 23.5 5 22.25 6 21.25 7 20.25 8 19.58 9 18.83 10 17.42 eleven 16.92 12 15.83

Table 4 - results of strength tests for uniaxial compression.

No. Ultimate uniaxial compressive strength of cement stone, MPa 25°C 300°C 7 days 28 days 7 days 28 days 1 44 46.5 8.1 9.5 2 44.7 47.4 8.4 9.8 3 45 48.7 8.5 10.4 4 43.8 47.9 41.5 44 5 52.5 54.7 42 47.1 6 53 56.2 44.5 49.7 7 55.1 58.5 53 57.6 8 46.1 47.2 29 32.5 9 45.8 47.1 28 32.4 10 45.7 46.8 27.5 32.1 eleven 45.3 46.2 27.2 31.5 12 45.1 46.1 27 31.1

Table 5 - results of tensile strength tests.

No. Tensile strength of cement stone, MPa 25°C 300°C 7 days 28 days 7 days 28 days 1 5.6 5.73 2.2 1.93 2 5.8 5.81 2.31 2.11 3 5.9 5.91 2.32 2.15 4 5.59 5.64 5.32 5.4 5 6.1 6.1 5.61 5.4 6 6.63 6.71 6.22 6.35 7 6.57 6.81 6.64 6.65 8 6.06 6.4 4.11 4.65 9 5.96 6.3 4.1 4.63 10 5.88 6.1 4.02 4.6 eleven 5.76 5.8 3.99 4.5 12 5.70 5.7 3.78 4.35

Table 6 - results of permeability measurements.

No. Permeability of cement stone samples after storage for one thermal cycle at high temperature conditions, mD*10 ^-3 300°C 7 days 28 days 1 5.3 5.4 2 5.4 5.4 3 5.4 5.6 4 2.8 2.5 5 2.5 2.1 6 2.3 2 7 2.4 2.3 8 5.1 5.4 9 5.2 5.4 10 5.4 5.6 eleven 5.5 5.8 12 5.6 5.9

From Table 3, we note that the spreadability of samples 4 to 9 is in the range from 18 to 24 cm, which will ensure the delivery of cement slurry to the well casing interval; samples of mortar with a spreadability of less than 18 are thick and cannot be pumped; samples of mortar with a spreadability of more than 24 are thick. too runny. From Table 4 we note that samples 5 to 7 achieve a clear improvement in the compressive strength of cement stone at high temperatures, and also from Table 5 we note that samples 5 to 7 achieve a clear improvement in the tensile strength of cement stone at high temperatures, while while from Table 5 we note that samples 4 to 6 achieve a clear improvement in the permeability of cement stone at normal, medium and high temperatures. Thus, samples 5 to 6 represent the composition of the required cement, which will ensure the delivery of cement slurry to the well casing interval, will improve the quality of fastening and durability of wells at normal, medium and high temperatures and increase the strength of the adhesive adhesion of the cement mixture to the rock and casing.

Claims (2)

A grouting composition, including grouting cement, water, a plasticizer, characterized in that Saudi class G cement is used as a grouting cement, and C-3 plasticizer is used as a plasticizer, while the composition additionally contains quartz flour and nanoclay, with the following ratio of components, wt.%: Saudi grade G cement 50.40-50.76 plasticizer S-3 0.40-0.41 quartz flour 17.64-17.77 nanoclay 0.51-1.01 water rest