Medium-and-low-temperature water-invasion-resistant low-density cement paste

Abstract

The invention provides medium and low temperature water-invasion-resistant low-density cement paste. The cement paste comprises the following components in parts by weight: 200-300 parts of low-temperature early strength cement, 200-300 parts of fly ash, 15-25 parts of silicon dioxide powder, 10-15 parts of a fluid loss agent, 4-8 parts of an expanding agent, 350-430 parts of water, 0.8-1 part of a water-invasion-resistant material and 0-50 parts of a lightening material. The low-temperature early-strength cement is adopted, the early-stage hydration process of the cement is promoted, the early-stage strength of a cement slurry system under the medium-low temperature condition is improved, the influence on cement hydration after a high-molecular water-invasion-resistant material is added is made up, the water-invasion-resistant performance of the low-density cement slurry system is improved, and the well cementation quality is guaranteed. A polyhydroxy high-molecular polymer is adopted as a water invasion resistant material, hydroxyl groups on macromolecules and oxygen atoms on ether bonds are associated with water molecules to form hydrogen bonds, so that free water is changed into bound water, a net structure can be formed in a cement paste system, and the cement paste has certain scouring resistance and water non-dispersion performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil drilling engineering, and particularly relates to a low-density cement slurry with medium and low temperature water invasion resistance. Background Art

[0002] To ensure the sealing of the entire well section, low-density cement slurry with a density less than 1.75 g / cm 3 is generally used to seal the upper well section. The formation temperature of the upper layer is low (20 - 45 °C), the water-cement ratio of the low-density cement slurry system is large (0.6 - 0.9), the hydration rate of cement is slow, the transition time from liquid to plastic state is long, and the probability of invasion and channeling by formation water during the waiting for setting period is high. It is difficult to ensure the sealing quality of water-bearing and water-producing intervals.

[0003] In recent years, in response to the problems of water invasion and water channeling, the industry has paid increasing attention. Industry scholars have carried out a large number of studies on how to improve the cementing quality of aquifers and water-producing intervals.

[0004] The technical solution disclosed in CN202110401187.6, a modified natural cellulose fiber, its preparation method and water invasion resistant cementing slurry, starts from the perspective of oil well cement slurry. To improve the water invasion resistance of the cementing slurry system in high water cut formations, a water invasion resistant cementing slurry is developed by modifying natural renewable cellulose fibers, which has the advantages of environmental protection, low cost, non-dispersibility in water, strong water invasion resistance, excellent mechanical properties, and adjustable thickening time of the cement slurry according to construction requirements. However, when this cement slurry is used under medium and low temperature conditions, there are problems such as slow hydration rate of the cement slurry, long setting time, slow development of cement stone strength, and low early strength, resulting in an increased probability of oil, gas, and water channeling, seriously affecting the cementing quality.

[0005] Wang Jianyao et al. synthesized an anti-dispersion flocculant for oil well cement by free radical polymerization, which can meet the requirements that the cement slurry does not segregate or disperse under the action of water scouring at 80 °C (Wang Jianyao, Zeng Jianguo, Sun Fuquan, et al. An anti-dispersion flocculant for oil well cement [J]. Drilling Fluid & Completion Fluid, 2018, 35(2): 90 - 93). An anti-water invasion functional polymer material was introduced, but the synthesis process is relatively complex, no cement slurry system was formed, and it affects the early hydration reaction of cement, resulting in a decrease in the early strength of the cement stone, and it is not suitable for cementing water-bearing and water-producing intervals under medium and low temperature conditions.

[0006] Lu Haichuan et al. prepared a water-blocking and channeling-preventing material for cementing by mixing inorganic materials such as sepiolite and copolymers such as styrene sulfonic acid-maleic anhydride (Lu Haichuan, Liu Yong, Zhang Weibin, etc. A water-blocking and channeling-preventing material for cementing and its preparation method [P]. CN106701048A, 2017). The cement slurry system of this invention is a conventional cement slurry system, and the density range is not limited, and it needs to be synthesized with a complex process. The inorganic materials and hydrophobic materials of this water-blocking and channeling-preventing material have low hydration activity, which will affect the early strength of the cement stone; and this water-blocking and channeling-preventing material is a liquid material and is not suitable for dry-mixing operations. Summary of the Invention

[0007] The purpose of the present invention is to provide a low-temperature and water-invasion-resistant low-density cement slurry to overcome the above-mentioned technical problems existing in the prior art.

[0008] For this reason, the technical solution provided by the present invention is as follows: A low-temperature and water-invasion-resistant low-density cement slurry, comprising the following components in parts by weight: 200-300 parts of low-temperature early-strength cement, 200-300 parts of fly ash, 15-25 parts of silica powder, 10-15 parts of fluid loss reducer, 4-8 parts of expansive agent, 350-430 parts of water, 0.8-1 part of water-invasion-resistant material, and 0-50 parts of weighting material. The content of tricalcium silicate in the low-temperature early-strength cement is 60-67%, the content of tricalcium aluminate is 5-8%, the content of dicalcium silicate is 12-14%, and the content of tetracalcium aluminoferrite is 9-10%.

[0009] The fly ash is Class I or Class II fly ash conforming to B / T1596-2019.

[0010] The silica powder is selected as silica fine powder conforming to B / T 21236-2007, wherein the SiO2 content is ≥90%.

[0011] The water-invasion-resistant material is methyl cellulose ether, hydroxyethyl cellulose ether, hydroxyethyl methyl cellulose ether or hydroxypropyl methyl cellulose ether.

[0012] The fluid loss reducer is 2-acrylamide-2-methylpropanesulfonic acid, acrylamide, acrylic acid copolymer or polyvinyl alcohol-based fluid loss reducer.

[0013] The expansive agent is calcium oxide, aluminum oxide or calcium sulfate.

[0014] The weighting material is hollow glass microspheres, hollow ceramic microspheres, cenospheres or expanded perlite.

[0015] A low-temperature and water-invasion-resistant low-density cement slurry, 250 parts of low-temperature early-strength cement, 250 parts of fly ash, 20 parts of silica powder, 12.5 parts of fluid loss reducer, 5 parts of expansive agent, 400 parts of water and 1 part of water-invasion-resistant material.

[0016] A medium- and low-temperature water-invasion-resistant low-density cement slurry, comprising 250 parts of low-temperature early-strength cement, 250 parts of fly ash, 20 parts of silica powder, 12.5 parts of fluid loss reducer, 5 parts of expandant, 50 parts of lightening material, 400 parts of water, and 1 part of water-invasion-resistant material.

[0017] The beneficial effects of the present invention are as follows: The medium- and low-temperature water-invasion-resistant low-density cement slurry provided by the present invention adopts low-temperature early-strength cement, which promotes the early hydration process of the cement, improves the early strength of the cement slurry system under medium- and low-temperature conditions, makes up for the influence on cement hydration after adding the polymer water-invasion-resistant material, improves the water-invasion resistance of the low-density cement slurry system, and ensures the cementing quality.

[0018] The present invention uses a polyhydroxy polymer as the water-invasion-resistant material. The hydroxyl groups on the polymer and the oxygen atoms on the ether bonds form hydrogen bonds with water molecules, turning free water into bound water, and can form a network structure inside the cement slurry system, making the cement slurry have certain erosion resistance and non-dispersion performance in water. Description of the Drawings

[0019] Figure 1 is the determination of the composition of G-class cement; Figure 2 is the determination of the composition of low-temperature early-strength cement. Detailed Embodiments

[0020] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0021] The exemplary implementation manners of the present invention are now introduced. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary implementation manners shown in the drawings are not limitations on the present invention.

[0022] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the art. In addition, it can be understood that the terms defined in the commonly used dictionary should be understood to have a meaning consistent with the context of their related fields, and should not be understood as idealized or overly formal meanings.

[0023] Example 1 The present invention provides a medium- and low-temperature water-invasion-resistant low-density cement slurry, which comprises the following components in parts by weight: 200-300 parts of low-temperature early-strength cement, 200-300 parts of fly ash, 15-25 parts of silica powder, 10-15 parts of fluid loss reducer, 4-8 parts of expandant, 350-430 parts of water, 0.8-1 part of water-invasion-resistant material, and 0-50 parts of lightening material. The medium- and low-temperature water-invasion-resistant low-density cement slurry provided by the present invention adopts low-temperature early-strength cement to promote the early hydration process of the cement, improve the early strength of the cement slurry system under medium- and low-temperature conditions, make up for the influence on cement hydration after adding polymer water-invasion-resistant materials, improve the water-invasion resistance of the low-density cement slurry system, and ensure the cementing quality.

[0024] Example 2 On the basis of Example 1, the present example provides a medium- and low-temperature water-invasion-resistant low-density cement slurry. In the low-temperature early-strength cement, the content of tricalcium silicate is 60-67%, the content of tricalcium aluminate is 5-8%, the content of dicalcium silicate is 12-14%, and the content of tetracalcium aluminoferrite is 9-10%.

[0025] The composition comparison between the low-temperature early-strength cement and G-class cement is shown in Table 1. The component determination is shown respectively in Figure 1 and Figure 2 as shown.

[0026] Table 1 Cement composition table

[0027] From the above data, it can be seen that according to the chemical composition requirements for high sulfate resistance (HSR) in the GB10238-2015 standard, the content of tricalcium aluminate exceeds the standard requirements. Tricalcium aluminate is the mineral component with the fastest hydration reaction rate, and its content is the main factor determining the initial setting time and thickening time of the cement slurry. By increasing the content of tricalcium aluminate and the specific surface area of the cement, the hydration rate of the cement under medium- and low-temperature conditions can be effectively increased, and the initial setting time can be shortened. The increase in the content of tricalcium silicate in the low-temperature early-strength cement (about 5-15% increase) ensures the early strength and final strength of the cement.

[0028] The strength data comparison between the low-temperature early-strength cement and conventional G-class cement at 38°C is shown in Table 2.

[0029] Table 2 Strength comparison between low-temperature early-strength cement and conventional G-class cement

[0030] It can be seen from Table 2 that at 38°C, the strength development time of the low-temperature early-strength cement is at least 4 hours earlier. The early strength of the cement stone at 4h / 8h is also significantly higher than that of the conventional G-class oil well cement, and the strength at 7d / 28d is also higher than that of the conventional G-class oil well cement, indicating that after the adjustment of the cement components, both the early strength and the final strength of the cement stone have been improved.

[0031] Example 3 Based on Example 2, this example provides a medium and low temperature water invasion resistant low density cement slurry, including 300 parts of low temperature early strength cement, 200 parts of fly ash, 15 parts of silica powder, 10 parts of fluid loss reducer, 4 parts of expansive agent, 350 parts of water, and 0.8 parts of water invasion resistant material.

[0032] In this example, the content of tricalcium silicate in the low temperature early strength cement is 62.67%, the content of tricalcium aluminate is 6.83%, the content of dicalcium silicate is 13.27%, and the content of tetracalcium aluminoferrite is 9.88%. The specific surface area is 375 m 2 / Kg. The fly ash used is grade II fly ash from Guohua Power Plant Building Materials Co., Ltd. The basic factory performance indicators are shown in Table 3.

[0033] Table 3 Performance indicators of Guohua grade II fly ash

[0034] The water invasion resistant material is methyl cellulose ether; the fluid loss reducer is 2-acrylamide-2-methylpropanesulfonic acid; the expansive agent is calcium oxide.

[0035] Example 4 Based on Example 2, this example provides a medium and low temperature water invasion resistant low density cement slurry, including 250 parts of low temperature early strength cement, 250 parts of fly ash, 20 parts of silica powder, 12.5 parts of fluid loss reducer, 5 parts of expansive agent, 25 parts of lightening material, 400 parts of water, and 0.9 parts of water invasion resistant material.

[0036] In this example, the low temperature early strength cement and fly ash are the same as those in Example 3. The water invasion resistant material is methyl cellulose ether, hydroxyethyl cellulose ether, hydroxyethyl methyl cellulose ether or hydroxypropyl methyl cellulose ether. The fluid loss reducer is acrylamide and acrylic acid copolymer; the expansive agent is alumina. The lightening material is; the lightening material is hollow glass microspheres (density 0.38 - 0.42 g / cm 3 )

[0037] Example 5 Based on Example 2, this example provides a medium and low temperature water invasion resistant low density cement slurry, including 200 parts of low temperature early strength cement, 300 parts of fly ash, 25 parts of silica powder, 15 parts of fluid loss reducer, 8 parts of expansive agent, 50 parts of lightening material, 430 parts of water, and 1 part of water invasion resistant material.

[0038] In this example, the low temperature early strength cement and fly ash are the same as those in Example 3. The water invasion resistant material is hydroxyethyl methyl cellulose ether; the fluid loss reducer is polyvinyl alcohol based fluid loss reducer; the expansive agent is calcium sulfate; the lightening material is hollow ceramic microspheres (density 0.60 - 0.65 g / cm 3 )

[0039] The performance tests of the low-density cement slurries of Examples 3 to 5 were carried out at 20 °C, 30 °C, and 45 °C respectively.

[0040] I. Thickening experiment According to the preparation method of conventional density cement slurries in G / T19139-2012, the cement slurries were prepared according to the components and ratios of Examples 3 to 5, and then the thickening tests of the cement slurries were carried out respectively. The results are shown in Tables 4 to 6.

[0041] Table 4 Comprehensive performance at 20 °C

[0042] Table 5 Comprehensive performance at 30 °C

[0043] Table 6 Comprehensive performance at 45 °C

[0044] II. Water invasion resistance The water invasion resistance of the cement slurry systems of Examples 3 to 5 and the comparative example was evaluated by measuring the cement loss rate. The results are shown in Table 7. Among them, the composition of the comparative example: 250 parts of G-grade cement, 250 parts of fly ash, 20 parts of silica powder, 12.5 parts of fluid loss reducer, 5 parts of expansive agent, and 400 parts of water.

[0045] (1) Prepare the cement slurry according to the method specified in Chapter 5 of GB / T 19139-2012.

[0046] (2) Measurement of cement loss rate; 1) Stir the prepared cement slurry in an atmospheric thickening instrument at 45 ± 2 °C for 20 min, take it out and let it stand for 3 min.

[0047] 2) Place a beaker (beaker specification: 500 ml) containing 400 ml of tap water on the balance and zero it.

[0048] 3) Pour the standing cement slurry into the beaker. The cement slurry is slowly poured from the mouth of the beaker. The pouring time is 1 min - 2 min, and the pouring amount is 150 g ± 0.5 g.

[0049] 4) After pouring, let the beaker stand for 1 min, suck out 350 ml of the solution on the upper layer of the beaker with a straw, stir the sucked-out solution evenly, and measure the density ρ with a digital display liquid densitometer.

[0050] The calculation formula for the cement loss amount is: M = (ρ - 1) × 350 In the formula: M is the cement loss amount, g; ρ is the density of the cement slurry, g / cm3 。

[0051] The calculation formula for the cement loss rate is as follows: P = (M / 150) × 100% Table 7 Water invasion resistance performance

[0052] The data in Table 7 show that for the low-density cement slurry system prepared with low-temperature early-strength cement, the strength of the cement stone at 35°C is about twice that of the low-density system prepared with the conventional G-class cement system. The strength development time at this temperature is advanced by about 2 - 3 h, and the cement loss rate is reduced by 80.8%. It can effectively reduce the probability of formation water invasion and ensure the cementing quality.

[0053] The content of tricalcium silicate in the cement used in the present invention is 5% - 15% higher than that of the conventional G-class cement, the specific surface area is increased by 5% - 15%, the strength of the cement stone at 38°C is increased by 200%. The early strength of the formed low-density system is significantly improved under low-temperature conditions, and it is suitable for cementing in medium-low temperature water-bearing and water-producing horizons. No liquid additives are added, which is suitable for dry-mixing operation cementing requirements. The external admixtures and additives used are all common materials and do not need to be re-synthesized. No early-strength agents, accelerators and other additives are used to promote the hydration reaction of tricalcium silicate to improve the early strength of the cement stone, which does not affect the final strength of the cement stone and ensures long-term effective sealing of the annulus. The low-temperature early-strength cement can be mixed with the conventional G-class cement in any proportion without affecting the rheological properties of the system, which is convenient for on-site use and is significantly different from the sulfoaluminate cement.

[0054] The above examples are only illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. Any design identical or similar to the present invention falls within the protection scope of the present invention.

Claims

1. A medium- and low-temperature water-invasion resistant low-density cement slurry, characterized in that: It comprises the following components in parts by weight: 200 - 300 parts of low-temperature early-strength cement, 200 - 300 parts of fly ash, 15 - 25 parts of silica powder, 10 - 15 parts of fluid loss reducer, 4 - 8 parts of expansion agent, 350 - 430 parts of water, 0.8 - 1 part of water invasion resistant material, and 0 - 50 parts of lightening material.

2. The low-temperature and water-invasion-resistant low-density cement slurry according to claim 1, characterized in that: In the low-temperature early-strength cement, the content of tricalcium silicate is 60 - 67%, the content of tricalcium aluminate is 5 - 8%, the content of dicalcium silicate is 12 - 14%, and the content of tetracalcium aluminoferrite is 9 - 10%.

3. A medium and low temperature water invasion resistant low density cement slurry according to claim 1, characterized in that: The fly ash is grade I or grade II fly ash conforming to B / T1596 - 2019.

4. A medium-low temperature water-invasion resistant low-density cement slurry according to claim 1, characterized in that: The silica powder is selected as silica fume conforming to B / T 21236 - 2007, wherein the SiO2 content is ≥90%.

5. A medium-low temperature water-invasion resistant low-density cement slurry according to claim 1, characterized in that: The water invasion resistant material is methyl cellulose ether, hydroxyethyl cellulose ether, hydroxyethyl methyl cellulose ether or hydroxypropyl methyl cellulose ether.

6. The low-temperature and low-density cement slurry resistant to water invasion according to claim 1, wherein: The fluid loss reducer is 2 - acrylamide - 2 - methylpropanesulfonic acid, acrylamide, acrylic acid copolymer or polyvinyl alcohol - based fluid loss reducer.

7. A medium and low temperature water invasion resistant low density cement slurry according to claim 1, characterized in that: The expansion agent is calcium oxide, aluminum oxide or calcium sulfate.

8. A medium and low temperature water invasion resistant low density cement slurry according to claim 1, characterized in that: The lightening material is hollow glass microspheres, hollow ceramic microspheres, cenospheres or expanded perlite.

9. A medium and low temperature water invasion resistant low density cement slurry according to any one of claims 1-8, characterized in that: 250 parts of low-temperature early-strength cement, 250 parts of fly ash, 20 parts of silica powder, 12.5 parts of fluid loss reducer, 5 parts of expansion agent, 400 parts of water and 1 part of water invasion resistant material.

10. A medium-low temperature water invasion resistant low density cement slurry according to any one of claims 1-8, characterized in that: 250 parts of low-temperature early-strength cement, 250 parts of fly ash, 20 parts of silica powder, 12.5 parts of fluid loss reducer, 5 parts of expansion agent, 50 parts of lightening material, 400 parts of water and 1 part of water invasion resistant material.

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