Cement paste and application thereof

Abstract

The invention relates to the technical field of oil and gas well cementation, in particular to cement paste and application thereof. The cement paste is prepared from the following raw materials in parts by weight: 100 parts of cement, 40-100 parts of a heat stabilizer, 0.5-4 parts of a toughening agent, 1-5 parts of a fluid loss agent, 0.5-3.5 parts of a retarder and 50-100 parts of water, wherein the heat stabilizer comprises washed kaolin, quartz sand and micro-silicon. The cement paste, the washed kaolin with different particle sizes and dosages, the quartz sand and the micro-silicon have a synergistic effect, the microstructure of the cement sheath can be changed, the compactness degree of the cement sheath structure is enhanced, the strength of the cement sheath at low temperature can be guaranteed, and the strength of the cement sheath can be prevented from declining at high temperature.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas well cementing, and in particular to a cement slurry and application thereof. Background Art

[0002] The high-temperature steam stimulation process is adopted in the exploitation of Chunguang heavy oil reservoir. Due to the periodic internal pressure and temperature changes in the steam stimulation well, the strength of conventional cement stone is easily degraded under the action of high temperature and high pressure, which may form annular gaps at the interface, leading to sealing failure and causing safety problems such as water seepage.

[0003] Adding quartz sand can reduce the calcium-silicon ratio of cement clinker and form tobermorite, which can improve the strength of high-temperature cement paste. However, practice shows that adding sand alone cannot make cement paste withstand 250-320℃ steam huff-and-puff construction. The compressive strength of commonly used silica sand cement paste after curing at 300℃ and 20MPa for 72h is only 3-4MPa, and the sealing effect will be lost after one cycle.

[0004] In CN201610215185.7, quartz sand, microsilicon, diatomaceous earth and fly ash of different mesh sizes (200 mesh, 400 mesh, 400 mesh, 800 mesh and 1000 mesh) are compounded. Although it can reduce the decay of cement paste, after being subjected to high temperature of 120°C-150°C, the strength of cement paste is reduced compared with that under low temperature conditions.

[0005] CN202010859052.X discloses a new type of high-temperature resistant cement slurry system for heavy oil thermal recovery wells, which uses a compound of silica sand, microsilicon and kaolin as a high-temperature enhancer. The prepared cement paste has long-term resistance to high-temperature strength decay. However, the strength of the cement paste after curing for 72 hours at 320°C and 21MPa is less than 20MPa.

[0006] Therefore, it is urgent to provide a cement slurry that can improve the compressive strength and sealing stability of cement paste at high temperatures. Summary of the invention

[0007] The purpose of the present invention is to solve the problems of weak pressure resistance and poor sealing effect of cement stone at high temperature in the prior art, and to provide a cement slurry and application thereof.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a cement slurry, wherein the raw materials for preparing the cement slurry include: 100 parts by weight of cement, 40-100 parts by weight of a heat stabilizer, 0.5-4 parts by weight of a toughening agent, 1-5 parts by weight of a fluid loss reducer, 0.5-3.5 parts by weight of a retarder and 50-100 parts by weight of water; wherein the heat stabilizer includes washed kaolin, quartz sand and microsilica.

[0009] A second aspect of the present invention provides an application of cement slurry in cementing, preferably in cementing of steam stimulation thermal recovery wells.

[0010] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0011] 1) The cement slurry provided by the present invention, the washed kaolin, quartz sand and micro-silicon with different particle sizes and dosages can synergistically change the microscopic morphology of the cement sheath and enhance the density of the cement sheath structure, which can not only ensure the strength of the cement sheath at low temperatures, but also prevent the strength of the cement sheath from declining at high temperatures;

[0012] 2) The use of chopped inorganic fibers in the cement slurry provided in the present invention can further improve the elastic-plasticity and thermal shock resistance of the cement sheath;

[0013] 3) The cement slurry provided in the present invention directly uses washed kaolin as a heat stabilizer, and there is no need to calcine the kaolin, which can greatly reduce energy consumption and is more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a SEM image of cement paste formed after the cement slurry in Example 1 of the present invention is cured after 7 rounds;

[0015] Figure 2 This is a SEM picture of cement stone formed after the cement slurry in Comparative Example 1 of the present invention is cured after 7 cycles. DETAILED DESCRIPTION

[0016] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0017] The first aspect of the present invention provides a cement slurry, wherein the raw materials for preparing the cement slurry include: 100 parts by weight of cement, 40-100 parts by weight of a heat stabilizer, 0.5-4 parts by weight of a toughening agent, 1-5 parts by weight of a fluid loss reducer, 0.5-3.5 parts by weight of a retarder and 50-100 parts by weight of water; wherein the heat stabilizer includes washed kaolin, quartz sand and microsilica.

[0018] Among them, in the present invention, the inventors have found through research that the addition of quartz sand and micro-silicon can reduce the calcium-silicon ratio in cement slurry. Washed kaolin does not need to be calcined. The synergistic effect of washed kaolin, quartz sand and micro-silicon can promote the secondary development of cement sheath strength at a high temperature of 300-350°C, making the microstructure of the cement sheath formed after the cement slurry solidifies more compact and dense, thereby improving the thermal shock resistance of the cement sheath, so that the strength of the cement sheath gradually increases after 7-10 steam cycles, and no cracking occurs.

[0019] In some embodiments of the present invention, the raw materials for preparing the cement slurry include: 100 parts by weight of cement, 60-70 parts by weight of heat stabilizer, 1.5-2.5 parts by weight of toughening agent, 2.5-3.5 parts by weight of fluid loss additive, 1.5-2.5 parts by weight of retarder and 65-75 parts by weight of water.

[0020] Among them, in the present invention, the inventors have found through research that when the amount of raw materials used in preparing cement slurry is limited within the above range, the compression resistance and sealing effect of the cement ring are optimal.

[0021] In some embodiments of the present invention, the cement is selected from one or more of Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement and composite Portland cement, preferably Portland cement, more preferably oil well G grade Portland cement.

[0022] In some embodiments of the present invention, in the thermal stabilizer, the mass ratio of washed kaolin, quartz sand and microsilicon is 1:1-5:0.05-0.5, preferably 1:2-4:0.15-0.35.

[0023] Among them, in the present invention, the inventors have found through research that by adding washed kaolin, the stability of the compressive strength of the cement ring at high temperature can be further improved and the sealing effect can be enhanced.

[0024] In some embodiments of the present invention, the washed kaolin is selected from one or more of washed sandy kaolin, washed hard kaolin, and washed soft kaolin, preferably washed sandy kaolin.

[0025] In some embodiments of the present invention, the average particle size of the washed kaolin is 10-120 μm, preferably 30-60 μm; the average particle size of the quartz sand is 10-120 μm, preferably 30-60 μm; the average particle size of the microsilicon is 0.02-0.5 μm, preferably 0.2-0.3 μm.

[0026] Among them, in the present invention, the inventors have found through research that the strength of cement paste can be further improved by controlling the particle size of washed kaolin, silica powder and microsilica powder.

[0027] In some embodiments of the present invention, the toughening agent is selected from short-cut fibers and / or long-cut fibers, preferably short-cut fibers.

[0028] In some embodiments of the present invention, the chopped fibers are chopped inorganic fibers, preferably one or more of chopped silicon carbide fibers, chopped carbon fibers, and chopped basalt fibers.

[0029] Among them, in the present invention, the short-cut inorganic fibers can withstand temperatures above 1000° C., can assist in enhancing the compressive strength of the cement sheath, and play a role in toughening and tensile strength.

[0030] In some embodiments of the present invention, the fluid loss additive is a polyacrylamide polymer. In the present invention, the polyacrylamide polymer includes but is not limited to AMPS copolymer (i.e., acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer); wherein the AMPS copolymer can be purchased, and the present invention will not be elaborated here.

[0031] In some embodiments of the present invention, the retarder is an acrylamide compound. In the present invention, the acrylamide polymer includes but is not limited to AMPS / IA copolymer (i.e., 2-acrylamide-2-methylpropanesulfonic acid / itaconic acid copolymer); wherein, AMPS / IA copolymer can be purchased, and the present invention will not be elaborated here.

[0032] In some embodiments of the present invention, the cement slurry may also contain other additives commonly used in the art, including but not limited to early strength agents, dispersants, defoamers, lubricants, drag reducers, suspension stabilizers, density regulators, and the like.

[0033] In some embodiments of the present invention, the density of the cement slurry is 1.8-1.9 g / cm 3 , preferably 1.85-1.9 g / cm 3 .

[0034] In some embodiments of the present invention, the method for preparing the cement slurry comprises: uniformly mixing cement, a heat stabilizer, a toughening agent, a fluid loss reducer, a retarder and water to obtain cement slurry.

[0035] The second aspect of the present invention provides an application of the cement slurry described in the first aspect of the present invention in cementing, preferably in cementing a steam-throwing thermal recovery well.

[0036] The cement stone formed after the cement slurry in the present invention is solidified can undergo secondary development in a steam environment, so that the strength of the cement ring is gradually increased to ensure that no cracking occurs.

[0037] The present invention will be described in detail below through examples. In the following examples and comparative examples: the fluid loss reducer is an AMPS copolymer, the retarder is an AMPS / IA copolymer, and the toughening agent is chopped silicon carbide fiber.

[0038] Example 1

[0039] 100g of oil well G grade cement, 60g of heat stabilizer (the mass ratio of washed kaolin with an average particle size of 45μm, quartz sand with an average particle size of 45μm and microsilicon with an average particle size of 0.2μm is 1:2:0.25), 2g of toughening agent, 3g of fluid loss reducer, 2g of retarder and 68g of water are mixed evenly to obtain a density of 1.90g / cm 3 of cement slurry.

[0040] Example 2

[0041] 100g of oil well G grade cement, 70g of heat stabilizer (the mass ratio of washed kaolin with an average particle size of 45μm, quartz sand with an average particle size of 45μm and microsilicon with an average particle size of 0.2μm is 1:4:0.35), 2.5g of toughening agent, 3.5g of fluid loss reducer, 2.5g of retarder and 75g of water are mixed evenly to obtain a density of 1.88g / cm 3 of cement slurry.

[0042] Example 3

[0043] 100g of oil well G grade cement, 80g of heat stabilizer (the mass ratio of washed kaolin with an average particle size of 45μm, quartz sand with an average particle size of 45μm and microsilicon with an average particle size of 0.2μm is 1:3:0.15), 1.5g of toughening agent, 2.5g of fluid loss reducer, 1.5g of retarder and 72g of water are mixed evenly to obtain a density of 1.85g / cm 3 of cement slurry.

[0044] Example 4

[0045] 100g of oil well G grade cement, 90g of heat stabilizer (the mass ratio of washed kaolin with an average particle size of 75μm, quartz sand with an average particle size of 45μm and microsilicon with an average particle size of 0.2μm is 1:5:0.1), 3.5g of toughening agent, 1g of fluid loss reducer, 3g of retarder and 85g of water are mixed evenly to obtain a density of 1.80g / cm 3 of cement slurry.

[0046] Example 5

[0047] 100g of oil well G grade cement, 50g of heat stabilizer (the mass ratio of washed kaolin with an average particle size of 45μm, quartz sand with an average particle size of 75μm and microsilicon with an average particle size of 0.2μm is 1:1:0.4), 1g of toughening agent, 4g of fluid loss reducer, 0.5g of retarder and 55g of water are mixed evenly to obtain a density of 1.90g / cm 3 of cement slurry.

[0048] Example 6

[0049] The same as Example 1, except that the washed kaolin with an average particle size of 45 μm is replaced by washed kaolin with an average particle size of 75 μm, and the quartz sand with an average particle size of 45 μm is replaced by quartz sand with an average particle size of 75 μm.

[0050] Comparative Example 1

[0051] The same as Example 5, except that the heat stabilizer is replaced by quartz sand with an average particle size of 45 μm.

[0052] Comparative Example 2

[0053] The same as Example 5, except that the washed kaolin is replaced by calcined kaolin in equal amount, wherein the calcined kaolin is a calcined product of washed kaolin calcined at 750° C. for 2 hours.

[0054] Test Example 1

[0055] The cement slurries prepared in Examples 1-6 and Comparative Examples 1-2 were poured into molds, placed in a pressurized curing kettle, cured at 50° C. for 72 hours, and demolded to obtain cement paste. The demolded cement paste was directly subjected to a compression test according to GB / T19139-2012 "Test Methods for Oil Well Cement", and an elastic modulus test was performed according to "NB / T 14004.2-2016 Shale Gas Cementing Engineering Part 2: Cement Slurry Technical Requirements and Evaluation Methods", and the test results are shown in Tables 1 and 2.

[0056] Under the same conditions, cement paste was re-prepared, and the demoulding cement paste was placed in a high-temperature and high-pressure curing kettle, with a set pressure of 21 MPa. In a water bath environment, the temperature was raised to 350°C at a rate of 1°C / min, kept constant for 7 days, and then cooled naturally to complete one cycle. The compressive strength and elastic modulus of the cement paste after completing 1, 3, and 7 cycles were tested, respectively, and the test results are shown in Tables 1 and 2.

[0057] Table 1

[0058]

[0059] Table 2

[0060]

[0061] As can be seen from Table 1, the cement paste formed after the cement slurry provided in the present invention is cured has a strength of >20 MPa at low temperatures. At a high temperature of 350°C, with the secondary development of the cement paste, the strength of the cement paste gradually increases, showing good thermal shock resistance.

[0062] By comparing Example 1 and Example 6, it can be seen that, within the range defined by the present invention, adjusting the particle sizes of washed kaolin and quartz sand can further improve the mechanical strength and elastic modulus of cement paste.

[0063] It can be seen from Comparative Example 1 that when only quartz sand is used as a heat stabilizer, the strength of the cement paste at low temperatures is poor. Under high-temperature treatment at 350°C, the strength first increases and then decreases, and finally declines.

[0064] It can be seen from Comparative Example 2 that although the calcined kaolin in Comparative Example 2 can improve the strength of cement stone at low temperature, it cannot maintain the long-term strength stability of cement stone at high temperature and is difficult to resist the thermal shock effect during steam huff and puff mining.

[0065] The cement stone after 7 cycles in Example 1 and Comparative Example 1 was characterized by SEM. The results are as follows: Figure 1 and Figure 2 shown.

[0066] in, Figure 1 is the SEM image of the cement paste in Example 1, Figure 2 It is the SEM picture of the cement paste in Comparative Example 1. Figure 1 It can be seen that after high-temperature steam treatment, the microstructure of the cement paste in Example 1 is still dense. Figure 2 It can be seen that after being treated with high-temperature steam, the microstructure of the cement paste in Comparative Example 1 is loose.

[0067] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A cement slurry, characterized in that: The raw materials for preparing the cement slurry include: 100 parts by weight of cement, 40-100 parts by weight of heat stabilizer, 0.5-4 parts by weight of toughening agent, 1-5 parts by weight of fluid loss reducer, 0.5-3.5 parts by weight of retarder and 50-100 parts by weight of water; wherein the heat stabilizer includes washed kaolin, quartz sand and microsilica.

2. The cement slurry according to claim 1, wherein: The raw materials for preparing the cement slurry include: 100 parts by weight of cement, 60-70 parts by weight of heat stabilizer, 1.5-2.5 parts by weight of toughening agent, 2.5-3.5 parts by weight of fluid loss reducer, 1.5-2.5 parts by weight of retarder and 65-75 parts by weight of water.

3. The cement slurry according to claim 1 or 2, wherein: The cement is selected from one or more of Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement and composite Portland cement, preferably Portland cement, more preferably oil well G grade Portland cement.

4. The cement slurry according to any one of claims 1 to 3, wherein: In the thermal stabilizer, the mass ratio of washed kaolin, quartz sand and microsilicon is 1:1-5:0.05-0.5, preferably 1:2-4:0.15-0.

35.

5. The cement slurry according to any one of claims 1 to 4, wherein: The average particle size of the washed kaolin is 10-120 μm, preferably 30-60 μm; the average particle size of the quartz sand is 10-120 μm, preferably 30-60 μm; the average particle size of the microsilicon is 0.02-0.5 μm, preferably 0.2-0.3 μm.

6. The cement slurry according to any one of claims 1 to 5, wherein: The toughening agent is selected from short-cut fibers and / or long-cut fibers, preferably short-cut fibers; Preferably, the chopped fibers are chopped inorganic fibers, preferably one or more of chopped silicon carbide fibers, chopped carbon fibers, and chopped basalt fibers.

7. The cement slurry according to any one of claims 1 to 6, wherein: The fluid loss reducer is a polyacrylamide polymer.

8. The cement slurry according to any one of claims 1 to 7, wherein: The retarder is an acrylamide compound.

9. The cement slurry according to any one of claims 1 to 8, wherein: The density of the cement slurry is 1.8-1.9 g / cm 3 , preferably 1.85-1.9 g / cm 3 .

10. Use of the cement slurry according to any one of claims 1 to 9 in cementing, preferably in cementing of steam stimulation thermal recovery wells.

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