Phosphoaluminate cement, cement paste, application and well cementation method

Abstract

The invention relates to the technical field of well cementation in petroleum and natural gas drilling engineering, and discloses phosphoaluminate cement, cement paste, application and a well cementation method. The phosphoaluminate cement is prepared from aluminate, apatite powder, phosphate, aluminum oxide, mineral soil powder and auxiliaries, relative to 100 parts by weight of aluminate, the content of the apatite powder is 20-50 parts by weight, the content of the phosphate is 5-20 parts by weight, the content of the aluminum oxide is 5-30 parts by weight, the content of the mineral soil powder is 10-40 parts by weight, and the content of the auxiliary agent is 10-20 parts by weight. The cement stone formed by hydrating the cement has excellent CO2 corrosion resistance and sulfate corrosion resistance, has the advantage of stable strength at high temperature, and can well meet the requirements of well cementation operation in high-temperature and / or high-CO2-content geological environments.

Description

Technical Field

[0001] This invention relates to the field of cementing technology in oil and gas drilling engineering, and particularly to a phosphoaluminate cement, cement slurry, and its application and cementing method. Background Technology

[0002] In oil and gas drilling, cementing is a crucial step in ensuring drilling safety and improving oil and gas recovery. The selection and use of cementing materials are paramount during the cementing process. While traditional silicate cement is widely used, its performance is limited under certain geological conditions. For example, when downhole temperatures exceed 300°C, the cement sheath formed by the cement slurry solidifies exhibits significant strength degradation. Furthermore, in environments containing acidic media (such as CO2), the acidic media can severely corrode the cement sheath, affecting the cementing effect.

[0003] Therefore, there is an urgent need to develop new cementing materials to meet the cementing operation requirements in geological environments with high temperature and high CO2 content. Summary of the Invention

[0004] This invention addresses the problems of unsatisfactory CO2 corrosion resistance and severe strength degradation of existing oil well cement rings formed during cementing at temperatures exceeding 300°C. It provides a phosphoaluminate cement, cement slurry, and its application and cementing method.

[0005] To achieve the above objectives, the first aspect of the present invention provides a phosphaaluminate cement, the phosphaaluminate cement comprising: aluminate, apatite powder, phosphate, alumina, mineral clay powder and additives; relative to 100 parts by weight of the aluminate, the apatite powder is 20-50 parts by weight, the phosphate is 5-20 parts by weight, the alumina is 5-30 parts by weight, the mineral clay powder is 10-40 parts by weight, and the additives are 10-20 parts by weight.

[0006] A second aspect of the present invention provides a cement slurry comprising: cement, a water loss reducing agent, a retarder, and water; wherein, relative to 100 parts by weight of the cement, the water loss reducing agent is 2-8 parts by weight, the retarder is 0.5-5 parts by weight, and the water is 40-100 parts by weight.

[0007] Wherein, the cement is the phosphoaluminate cement described in the first aspect above;

[0008] The water loss reducing agent is a multi-component copolymer obtained by polymerization of raw materials containing at least three of AM monomer, AMPS monomer, NVP monomer and DMAA monomer.

[0009] The retarder contains element B and / or element P.

[0010] The third aspect of this invention provides the application of the cement slurry described in the second aspect above in cementing oil and gas wells.

[0011] A fourth aspect of the present invention provides a method for cementing wells, the method comprising: injecting the cement slurry described in the second aspect above downhole, solidifying it to form a cement sheath, and using the cement sheath for cementing wells;

[0012] The temperature of the formation where the cement sheath is located is 300-600℃, and the CO2 content in the formation is 0-15%.

[0013] Through the above technical solution, the phosphoaluminate cement provided by this invention is a thermodynamically CO2-resistant gel material. The cement stone formed after hydration exhibits excellent CO2 corrosion resistance in high CO2 environments (the weight loss of the cement stone is no more than 10% after 28 days of corrosion at 300℃ and a CO2 partial pressure of 5 MPa). It also possesses good sulfate corrosion resistance and the advantage of stable strength at high temperatures, maintaining stable strength at temperatures not lower than 300℃, and achieving a compressive strength of not less than 30 MPa at a maximum temperature of 600℃. Compared with conventional silicate cement and its cement slurry, the phosphoaluminate cement and cement slurry provided by this invention have significantly enhanced comprehensive performance in terms of CO2 corrosion resistance and high-temperature resistance, which can significantly improve cementing efficiency and well meet the cementing operation requirements in high-temperature and / or high-CO2 content geological environments. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] The first aspect of the present invention provides a phosphaaluminate cement, the phosphaaluminate cement comprising: aluminate, apatite powder, phosphate, alumina, mineral clay powder and additives; relative to 100 parts by weight of the aluminate, the apatite powder is 20-50 parts by weight, the phosphate is 5-20 parts by weight, the alumina is 5-30 parts by weight, the mineral clay powder is 10-40 parts by weight, and the additives are 10-20 parts by weight.

[0016] According to the present invention, in the phosphoaluminate cement, the components, while satisfying the above-mentioned proportional relationships, preferably comprise, relative to 100 parts by weight of the aluminate, 30-35 parts by weight of apatite powder, 10-15 parts by weight of phosphate, 10-15 parts by weight of alumina, 15-20 parts by weight of mineral clay powder, and 10-15 parts by weight of the additives. This allows the cement stone formed after hydration of the phosphoaluminate cement to have better CO2 corrosion resistance and high-temperature resistance.

[0017] According to the present invention, in the phosphoaluminate cement, the aluminate component can improve the thermodynamic stability of the cement stone formed after the phosphoaluminate cement has cured at high temperatures (e.g., 300-600°C). In some embodiments of the present invention, the aluminate may be selected from at least one of calcium aluminate, calcium hexaaluminate, and calcium sulfoaluminate.

[0018] According to a preferred embodiment of the present invention, the aluminate is calcium aluminate.

[0019] According to the present invention, in the phosphoaluminate cement, the apatite powder component can provide the crystalline linking skeleton for the high-temperature resistant and corrosion-resistant cement stone formed after the phosphoaluminate cement is cured.

[0020] According to the present invention, in the phosphoaluminate cement, the phosphate component can improve the CO2 corrosion resistance of the cement stone formed after the phosphoaluminate cement has cured. In some embodiments of the present invention, the phosphate may be selected from at least one of sodium phosphate, sodium polyphosphate, sodium dihydrogen phosphate, sodium hexametaphosphate, ammonium hydrogen phosphate, potassium phosphate, and potassium dihydrogen phosphate.

[0021] According to a preferred embodiment of the present invention, the phosphate is sodium phosphate.

[0022] According to the present invention, in the phosphoaluminate cement, the alumina component can improve the high-temperature resistance and corrosion resistance of the cement stone formed after the phosphoaluminate cement has cured. In some embodiments of the present invention, the alumina can take various forms, including but not limited to at least one of calcined α-alumina powder, corundum powder, alumina micro powder, and activated alumina micro powder.

[0023] In this invention, the calcined α-alumina powder refers to α-alumina powder with a D50 of 1-10 μm obtained by calcining the transition phase alumina formed by dehydration of aluminum hydroxide at temperatures above 1100°C and grinding the calcined product after cooling.

[0024] In this invention, the corundum powder refers to alumina powder with a D50 of 10-40 μm obtained by dehydrating diaspore (formed by dehydrating trihydrate alumina) to form a transition phase alumina, then heating it above 800°C, and grinding the resulting product after cooling.

[0025] In this invention, the alumina micro powder refers to a powder with a D50 of 40-80 μm formed by grinding alumina minerals.

[0026] In this invention, the activated alumina micro powder refers to a powder with a D50 of 10-80 μm obtained by directly forming α-alumina from boehmite after dehydration (without forming a transition phase alumina during the formation of α-alumina), followed by a phase transformation at 400°C, and then grinding the resulting product after cooling.

[0027] According to a preferred embodiment of the present invention, the alumina is calcined α-alumina powder.

[0028] According to the present invention, in the phosphoaluminate cement, the mineral clay powder can increase the bonding ability of the aluminate, apatite powder, and phosphate during the hydration process, thereby improving the strength of the skeleton. In some embodiments of the present invention, the mineral clay powder may be selected from at least one of metakaolin powder, mullite powder, periclase powder, and volcanic ash.

[0029] According to a preferred embodiment of the present invention, the mineral soil powder is metakaolin powder.

[0030] According to the present invention, in the phosphoaluminate cement, the additive can improve the ability of the cement stone formed after the phosphoaluminate cement has cured to form a densely packed aggregate. In some embodiments of the present invention, the additive may be selected from at least one of blast furnace slag, fly ash, and diatomaceous earth.

[0031] According to a preferred embodiment of the present invention, the additive is blast furnace slag.

[0032] In this invention, the phosphoaluminate cement contains the aforementioned specific components and satisfies a specific component ratio. These components work synergistically, resulting in cement stone formed after hydration of the phosphoaluminate cement exhibiting excellent CO2 corrosion resistance, good sulfate corrosion resistance, and very good high-temperature resistance. Specifically, the cement stone, after 28 days of corrosion at 300℃ and a CO2 partial pressure of 5 MPa, shows a weight loss of no more than 10%. The cement stone maintains stable strength at temperatures no lower than 300℃, and can maintain a compressive strength of no less than 30 MPa at a maximum temperature of 600℃. Compared to conventional silicate cement, the cement stone formed by the phosphoaluminate cement provided by this invention exhibits better durability under high temperature and high CO2 content conditions, maintaining high strength. It demonstrates significant performance advantages in cementing operations under high-temperature and / or high-CO2 content geological environments, effectively improving cementing results. When the components in the cement and the ratio between the components are not within the above-mentioned limits, it is impossible to obtain phosphoaluminate cement that meets the comprehensive performance requirements of this invention.

[0033] According to a preferred embodiment of the present invention, the phosphaaluminate cement comprises calcium aluminate, apatite powder, sodium phosphate, calcined α-alumina powder, metakaolin powder, and blast furnace slag, wherein, relative to 100 parts by weight of calcium aluminate, the apatite powder is 33-35 parts by weight, the sodium phosphate is 13-15 parts by weight, the calcined α-alumina powder is 13-15 parts by weight, the metakaolin powder is 18-20 parts by weight, and the blast furnace slag is 13-15 parts by weight. The cement stone formed after hydration of the cement of this preferred embodiment has further improved resistance to CO2 corrosion and high-temperature performance.

[0034] In this invention, the phosphoaluminate cement can be obtained by fully mixing its components, and can be prepared using processes known in the field of cement preparation, which will not be elaborated here.

[0035] A second aspect of the present invention provides a cement slurry comprising: cement, a water loss reducing agent, a retarder, and water; wherein, relative to 100 parts by weight of the cement, the water loss reducing agent is 2-8 parts by weight, the retarder is 0.5-5 parts by weight, and the water is 40-100 parts by weight.

[0036] Wherein, the cement is the phosphoaluminate cement described in the first aspect above;

[0037] The water loss reducing agent is an AM-AMPS-NVP-DMAA quaternary copolymer;

[0038] The retarder is selected from at least one of boric acid, borax and hydroxyphosphonic acid.

[0039] The cement slurry provided by this invention contains specific cement, which, in combination with other components, gives the cement slurry a wide density range, a wide thickening time range, and low water loss. Furthermore, the cement stone formed after hydration has excellent resistance to CO2 corrosion, good resistance to sulfate corrosion, and excellent high-temperature resistance.

[0040] According to the present invention, in addition to satisfying the above-mentioned proportions, the components in the cement slurry preferably have 3-5 parts by weight of the water loss reducing agent, 1-2 parts by weight of the retarder, and 50-60 parts by weight of water relative to 100 parts by weight of the cement, thereby achieving further improved comprehensive performance.

[0041] According to the present invention, the specific fluid loss reducing agent in the cement slurry can effectively reduce the amount of water lost to the formation during the cement slurry system during injection. In this invention, the fluid loss reducing agent can be a multi-component copolymer obtained by polymerizing at least three of the following raw materials: AM monomer, AMPS monomer, NVP monomer, and DMAA monomer. Preferably, the fluid loss reducing agent can be selected from an AM-AMPS-NVP-DMAA quaternary copolymer, or a ternary copolymer obtained by polymerizing three of the following monomers: AM monomer, AMPS monomer, NVP monomer, and DMAA monomer. More preferably, it is a fluid loss reducing agent with the brand name GWF-500L (manufacturer: Cementing Company of China National Petroleum Corporation Great Wall Drilling Engineering Co., Ltd.).

[0042] According to the present invention, the specific retarder in the cement slurry enables the cement slurry to have a thickening time that meets the construction requirements at the bottom hole circulation temperature. In the present invention, the retarder contains element B and / or element P. Preferably, the retarder can be selected from at least one of boric acid, borax, and hydroxyphosphonic acid, and more preferably a retarder with the grade GWR-500S (manufacturer: Cementing Company of China National Petroleum Corporation Great Wall Drilling Engineering Co., Ltd.).

[0043] According to the present invention, the cement slurry further includes a defoamer and, optionally, a drag-reducing agent.

[0044] In this invention, the definition of the defoamer is broad; various defoamers suitable for cement slurry can be used. They can be prepared in-house using conventional methods or commercially available products. Preferably, the defoamer can be selected from at least one of silicone-based defoamers, butyl phosphate defoamers, and nonionic surfactant defoamers. More preferably, a silicone-based defoamer can be used; for example, defoamer with the brand name GWX-1L (manufacturer: Cementing Company of China National Petroleum Corporation Great Wall Drilling Engineering Co., Ltd.) can be used.

[0045] According to the present invention, in the cement slurry, preferably, the defoamer is 0.2-1 parts by weight relative to 100 parts by weight of the cement.

[0046] In this invention, the drag-reducing agent can adjust the rheological properties of the cement slurry system, and those skilled in the art can flexibly decide whether to add it based on the actual construction conditions. The drag-reducing agent is broadly defined in this invention; various drag-reducing agents suitable for cement slurry can be used. It can be prepared using conventional methods or a commercially available product. Preferably, the drag-reducing agent can be selected from at least one of sulfonated aldehyde-ketone polymer drag-reducing agents, polycarboxylic acid drag-reducing agents, and polynaphthalene drag-reducing agents, and is more preferably a sulfonated aldehyde-ketone polymer drag-reducing agent. For example, a drag-reducing agent with the brand name GWD-1S (manufacturer: Cementing Company of China National Petroleum Corporation Great Wall Drilling Engineering Co., Ltd.) can be used.

[0047] According to the present invention, in the cement slurry, preferably, the drag-reducing agent is 0-2 parts by weight relative to 100 parts by weight of the cement.

[0048] According to the present invention, the cement slurry may also contain other conventional cement slurry reagents, including but not limited to weighting agents, lightening agents, expansion agents or toughening agents, etc. These reagents can all adopt conventional material selection and addition ratios in the art, which will not be elaborated here.

[0049] According to the present invention, the cement slurry has a wide density range. Preferably, the density of the cement slurry is 1.75-1.95 g / cm³. 3 .

[0050] According to the present invention, the cement slurry has good fluidity. Preferably, the fluidity of the cement slurry (at a temperature of 27°C and a pressure of 0.1 MPa) is 18-24 cm.

[0051] In this invention, the fluidity of the cement slurry is determined according to the method specified in GB / T 8077-2012.

[0052] According to the present invention, the cement slurry has a wide thickening time range. Preferably, the thickening time of the cement slurry at 60°C and 30MPa is 90-180 min.

[0053] In this invention, the thickening time of the cement slurry is determined according to the method specified in GB / T 19139-2012.

[0054] According to the present invention, the cement slurry has good filtration properties. Preferably, the cement slurry loses 15-50 mL of water at 60°C, 6.9 MPa, and 30 min.

[0055] In this invention, the water loss of the cement slurry is determined according to the method specified in GB / T 19139-2012.

[0056] The cement stone formed by the curing of the cement slurry provided by the present invention has excellent CO2 corrosion resistance. When the cement stone is corroded for 28 days under corrosion conditions of 300℃ and CO2 partial pressure of 5MPa, the weight loss of the cement stone is no more than 10%.

[0057] The cement stone formed by the curing of the cement slurry provided by the present invention has excellent high temperature resistance. The cement stone can maintain stable strength at a high temperature of not less than 300°C and can have a compressive strength of not less than 30MPa at a maximum temperature of 600°C.

[0058] In this invention, the compressive strength of cement stone is determined according to the method specified in GB / T 19139-2012.

[0059] According to the present invention, the cement slurry can be prepared by fully mixing its components, and can be prepared using processes known in the field of cement slurry preparation, which will not be described in detail here.

[0060] In this invention, the content of each component in the cement slurry can be determined based on the amount of material fed during preparation.

[0061] The cement slurry provided by this invention features a wide density range, a long thickening time, and low water loss, effectively ensuring the smooth progress of cementing operations. The cement stone formed after curing exhibits excellent resistance to CO2 corrosion, good resistance to sulfate corrosion, and outstanding high-temperature resistance. Compared to cement slurries prepared with conventional silicate cement, its comprehensive performance in terms of CO2 corrosion resistance and high-temperature resistance is significantly enhanced, significantly improving cementing effectiveness. It can well meet the cementing operation requirements in high-temperature and / or high-CO2 content geological environments, such as acidic gas reservoirs, geothermal wells, and heavy oil thermal recovery wells.

[0062] The third aspect of this invention provides the application of the cement slurry described in the second aspect above in cementing oil and gas wells.

[0063] According to the present invention, the cement slurry has a wide density range, a wide thickening time, and low water loss. The cement stone formed after hydration has excellent resistance to CO2 corrosion, good resistance to sulfate corrosion, and excellent high temperature resistance, making it particularly suitable for cementing operations in geological environments with high temperature and / or high CO2 content.

[0064] A fourth aspect of the present invention provides a method for cementing wells, the method comprising: injecting the cement slurry described in the second aspect above downhole, solidifying it to form a cement sheath, and using the cement sheath for cementing wells;

[0065] The temperature of the formation where the cement sheath is located is 300-600℃, and the CO2 content in the formation is 0-15%.

[0066] According to the present invention, in the cementing method, preferably, the working temperature of the cement slurry in the downhole formation is 40-120°C.

[0067] The cementing method provided by this invention uses the specific cement slurry of this invention. When cementing operations are carried out in geological environments with high temperature and / or high CO2 content, this method has a significantly improved cementing effect compared with cement slurry prepared with conventional silicate cement.

[0068] The present invention will be described in detail below through examples. In the following preparation examples, embodiments, and comparative examples,

[0069] Fluid loss reducer: Brand name GWF-500L, purchased from Cementing Company of China National Petroleum Corporation Great Wall Drilling Engineering Co., Ltd.

[0070] Retarder: GWR-500S, purchased from Cementing Company of China National Petroleum Corporation Great Wall Drilling Engineering Co., Ltd.

[0071] Defoamer: Brand name GWX-1L, purchased from Cementing Company of China National Petroleum Corporation Great Wall Drilling Engineering Co., Ltd.

[0072] Water: Municipal tap water.

[0073] Preparation Example 1

[0074] This preparation example illustrates the preparation of phosphoaluminate cement:

[0075] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium aluminate, 35 parts by weight of apatite powder, 15 parts by weight of sodium phosphate, 15 parts by weight of calcined α-alumina powder, 20 parts by weight of metakaolin powder, and 15 parts by weight of blast furnace slag to obtain phosphoaluminate cement (denoted as C1).

[0076] Preparation Example 2

[0077] This preparation example illustrates the preparation of phosphoaluminate cement:

[0078] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium aluminate, 32 parts by weight of apatite powder, 12 parts by weight of sodium phosphate, 12 parts by weight of calcined α-alumina powder, 18 parts by weight of metakaolin powder, and 12 parts by weight of blast furnace slag to obtain phosphoaluminate cement (denoted as C2).

[0079] Preparation Example 3

[0080] This preparation example illustrates the preparation of phosphoaluminate cement:

[0081] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium aluminate, 30 parts by weight of apatite powder, 10 parts by weight of sodium phosphate, 10 parts by weight of calcined α-alumina powder, 15 parts by weight of metakaolin powder, and 10 parts by weight of blast furnace slag to obtain phosphoaluminate cement (denoted as C3).

[0082] Preparation Example 4

[0083] This preparation example illustrates the preparation of phosphoaluminate cement:

[0084] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium hexaaluminate, 20 parts by weight of apatite powder, 5 parts by weight of sodium dihydrogen phosphate, 5 parts by weight of corundum powder, 10 parts by weight of mullite powder, and 16 parts by weight of fly ash to obtain phosphoaluminate cement (denoted as C4).

[0085] Preparation Example 5

[0086] This preparation example illustrates the preparation of phosphoaluminate cement:

[0087] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium hexaaluminate, 25 parts by weight of apatite powder, 20 parts by weight of sodium hexametaphosphate, 30 parts by weight of corundum powder, 10 parts by weight of periclase powder, and 18 parts by weight of fly ash to obtain phosphoaluminate cement (denoted as C5).

[0088] Preparation Example 6

[0089] This preparation example illustrates the preparation of phosphoaluminate cement:

[0090] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium sulfoaluminate, 40 parts by weight of apatite powder, 5 parts by weight of ammonium hydrogen phosphate, 30 parts by weight of alumina micro powder, 40 parts by weight of periclase powder, and 20 parts by weight of fly ash to obtain phosphoaluminate cement (denoted as C6).

[0091] Preparation Example 7

[0092] This preparation example illustrates the preparation of phosphoaluminate cement:

[0093] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium sulfoaluminate, 45 parts by weight of apatite powder, 20 parts by weight of potassium phosphate, 5 parts by weight of activated alumina micro powder, 10 parts by weight of volcanic ash, and 16 parts by weight of diatomaceous earth to obtain phosphoaluminate cement (denoted as C7).

[0094] Preparation Example 8

[0095] This preparation example illustrates the preparation of phosphoaluminate cement:

[0096] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium sulfoaluminate, 50 parts by weight of apatite powder, 5 parts by weight of potassium dihydrogen phosphate, 30 parts by weight of activated alumina micro powder, 40 parts by weight of volcanic ash, and 20 parts by weight of diatomaceous earth to obtain phosphoaluminate cement (denoted as C8).

[0097] Comparative Preparation Example 1

[0098] Commercially available oil well grade G high sulfur-resistant cement (purchased from Dalian Cement Plant in Liaoning Province) was used, denoted as DC1.

[0099] Comparative Preparation Example 2

[0100] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium sulfoaluminate, 10 parts by weight of apatite powder, 4 parts by weight of ammonium hydrogen phosphate, 4 parts by weight of alumina micro powder, 5 parts by weight of periclase powder, and 5 parts by weight of fly ash to obtain cement (denoted as DC2).

[0101] Comparative preparation example 3

[0102] This preparation example illustrates the preparation of phosphoaluminate cement:

[0103] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium sulfoaluminate, 5 parts by weight of potassium dihydrogen phosphate, 30 parts by weight of activated alumina powder, 40 parts by weight of volcanic ash, and 20 parts by weight of diatomaceous earth to obtain phosphoaluminate cement (denoted as DC3).

[0104] Comparative preparation example 4

[0105] This preparation example illustrates the preparation of phosphoaluminate cement:

[0106] The following dry ash components are thoroughly mechanically mixed: 100 parts by weight of calcium sulfoaluminate, 50 parts by weight of apatite powder, 5 parts by weight of potassium dihydrogen phosphate, 40 parts by weight of volcanic ash, and 20 parts by weight of diatomaceous earth to obtain phosphoaluminate cement (denoted as DC4).

[0107] Example 1

[0108] Cement slurry was prepared according to the method specified in GB / T19139-2012, using the above-mentioned cement C1, water loss reducing agent, retarder, defoamer, and water; wherein,

[0109] The cement paste (denoted as F1) is prepared by mixing cement C1, water loss reducer, retarder, defoamer, and water in a weight ratio of 100:4:1.5:0.5:55.

[0110] Examples 2-8

[0111] Cement slurry was prepared according to the method of Example 1, except that cement C1 was replaced with equal weights of C2-C8, and all other conditions were the same as in Example 1, and cement slurry (denoted as F2-F8) was obtained.

[0112] Comparative Example 1

[0113] Cement slurry was prepared according to the method of Example 1, except that cement C1 was replaced with an equal weight of DC1, and all other conditions were the same as in Example 1, to obtain cement slurry (denoted as DF1).

[0114] Comparative Example 2

[0115] Cement slurry was prepared according to the method of Example 1, except that cement C1 was replaced with an equal weight of DC2, and all other conditions were the same as in Example 1, and cement slurry (denoted as DF2) was obtained.

[0116] Comparative Example 3

[0117] Cement slurry was prepared according to the method of Example 1, except that cement C1 was replaced with an equal weight of DC3, and all other conditions were the same as in Example 1, and cement slurry (denoted as DF3) was obtained.

[0118] Comparative Example 4

[0119] Cement slurry was prepared according to the method of Example 1, except that cement C1 was replaced with an equal weight of DC4, and all other conditions were the same as in Example 1, and cement slurry (denoted as DF4) was obtained.

[0120] Test case

[0121] 1. Cement slurry density, thickening time, water loss, fluidity, and 24-hour strength tests.

[0122] The density, thickening time (BHTC: 60℃, pressure: 30MPa), water loss (BHTC: 60℃, pressure: 6.9MPa, time: 30min), fluidity (BHTC: 27℃, pressure: 0.1MPa), and 24h strength (BHTC: 60℃, pressure: 0.1MPa) of the above cement slurries F1-F8 and DF1-DF4 were tested respectively. The results are shown in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] As can be seen from the data in Table 1, the cement slurry prepared by the phosphoaluminate cement provided by the present invention has a wide range of density and thickening time, low water loss, and high strength of cement stone after curing. The 24-hour strength of the cement stone formed under the above test conditions is higher than 25 MPa.

[0127] 2. CO2 corrosion resistance test

[0128] The cement stones (referred to as S1-S8 and DS1-DS4) obtained by curing the above cement slurries F1-F8 and DF1-DF4 under the same conditions (curing at 50℃ for 48h) were cured at 300℃ and CO2 partial pressure of 5MPa for different ages. The weight loss of the cement stones before and after corrosion was tested, and the results are shown in Table 2.

[0129] Table 2

[0130]

[0131]

[0132] As can be seen from the data in Table 2, the cement slurry prepared with the phosphoaluminate cement provided by the present invention, when cured under the above conditions, yields cement stones S1-S8 with a weight loss rate of less than 7% after 7 days of corrosion at 300℃ and a CO2 partial pressure of 5MPa, less than 8% after 14 days of corrosion, less than 9% after 21 days of corrosion, and less than 10% after 28 days of corrosion. The CO2 corrosion resistance is significantly better than that of cement stones DS1-DS4 formed after cement curing in Comparative Examples 1-4.

[0133] 3. Sulfate corrosion resistance test

[0134] The above-mentioned cement stones (S1-S8, DS1-DS4) were immersed in a 20% by weight sodium sulfate aqueous solution, and the weight loss of the cement stones before and after corrosion was tested. The results are shown in Table 3.

[0135] Table 3

[0136]

[0137]

[0138] As can be seen from the data in Table 3, the cement slurry prepared by the phosphoaluminate cement provided by the present invention, when cured under the above conditions, resulted in cement stones S1-S8 with a weight loss rate of less than 7% after 7 days of corrosion in a 20% by weight sodium sulfate aqueous solution, less than 7.5% after 14 days of corrosion, less than 8.5% after 21 days of corrosion, and less than 9.5% after 28 days of corrosion. The resistance to sulfate corrosion is significantly better than that of DS1-DS4.

[0139] 4. High-temperature resistance test

[0140] The high-temperature resistance of the above cement stone (S1-S8, DS1-DS4) under 300℃ and 600℃ conditions are shown in Table 4.

[0141] Table 4

[0142]

[0143]

[0144] As can be seen from the data in Table 4, the cement slurry prepared by the phosphoaluminate cement provided by the present invention, when cured under the above conditions, yields cement stones S1-S8 with higher strengths than DS1-DS4 after calcination at 300℃ and 600℃ for 24 hours. The strength of the cement stone after calcination at 600℃ for 24 hours is not less than 30MPa, demonstrating excellent high-temperature resistance.

[0145] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A phosphoaluminate cement, characterized in that, The phosphoaluminate cement comprises: aluminate, apatite powder, phosphate, alumina, mineral clay powder, and additives; relative to 100 parts by weight of the aluminate, the apatite powder is 20-50 parts by weight, the phosphate is 5-20 parts by weight, the alumina is 5-30 parts by weight, the mineral clay powder is 10-40 parts by weight, and the additives are 10-20 parts by weight.

2. The phosphoaluminate cement according to claim 1, wherein, Relative to 100 parts by weight of the aluminate, the apatite powder is 30-35 parts by weight, the phosphate is 10-15 parts by weight, the alumina is 10-15 parts by weight, the mineral clay powder is 15-20 parts by weight, and the additives are 10-15 parts by weight.

3. The phosphoaluminate cement according to claim 1 or 2, wherein, The aluminate is selected from at least one of calcium aluminate, calcium hexaaluminate, and calcium sulfoaluminate.

4. The phosphoaluminate cement according to claim 1 or 2, wherein, The phosphate is selected from at least one of sodium phosphate, sodium polyphosphate, sodium dihydrogen phosphate, sodium hexametaphosphate, ammonium hydrogen phosphate, potassium phosphate, and potassium dihydrogen phosphate.

5. The phosphoaluminate cement according to claim 1 or 2, wherein, The alumina is selected from at least one of calcined α-alumina powder, corundum powder, alumina micro powder, and activated alumina micro powder.

6. The phosphoaluminate cement according to claim 1 or 2, wherein, The mineral powder is selected from at least one of metakaolin powder, mullite powder, periclase powder, and volcanic ash.

7. The phosphoaluminate cement according to claim 1 or 2, wherein, The additive is selected from at least one of blast furnace slag, fly ash and diatomaceous earth.

8. A cement grout, characterized in that, The cement slurry comprises: cement, a water loss reducing agent, a retarder, and water; relative to 100 parts by weight of the cement, the water loss reducing agent is 2-8 parts by weight, the retarder is 0.5-5 parts by weight, and the water is 40-100 parts by weight. Wherein, the cement is the phosphoaluminate cement according to any one of claims 1-7; The water loss reducing agent is a multi-component copolymer obtained by polymerization of raw materials containing at least three of AM monomer, AMPS monomer, NVP monomer and DMAA monomer. The retarder contains element B and / or element P.

9. The cement grout according to claim 8, wherein, Relative to 100 parts by weight of the cement, the water loss reducing agent is 3-5 parts by weight, the retarder is 1-2 parts by weight, and the water is 50-60 parts by weight.

10. The cement grout according to claim 8 or 9, wherein, The cement grout also includes a defoamer and, optionally, a drag-reducing agent; The defoamer is 0.2-1 parts by weight relative to 100 parts by weight of the cement; The drag-reducing agent is 0-2 parts by weight relative to 100 parts by weight of the cement.

11. The cement grout according to any one of claims 8-10, wherein, The density of the cement slurry is 1.75-1.95 g / cm³. 3 ; And / or, the fluidity of the cement slurry is 18-24 cm; And / or, the thickening time of the cement slurry at 60℃ and 30MPa is 90-180min; And / or, the water loss of the cement slurry at 60°C, 6.9MPa, and 30min is 15-50mL.

12. The application of the cement slurry according to any one of claims 8-11 in cementing oil and gas wells.

13. A cementing method, characterized in that, The method includes: injecting the cement slurry according to any one of claims 8-11 downhole, solidifying it to form a cement ring, and using the cement ring for well cementing; The temperature of the formation where the cement sheath is located is 300-600℃, and the CO2 content in the formation is 0-15% by weight.

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