Acid-soluble cement paste with high strength and high acid solubility and preparation method thereof

Abstract

The invention provides acid-soluble cement paste with high strength and high acid solubility and a preparation method of the acid-soluble cement paste, and relates to the technical field of petroleum engineering well cementation. The acid-soluble cement paste comprises the following components: 100 parts of oil well Portland cement, 40-70 parts of an acid-soluble hard filler, 4-6 parts of a fluid loss agent, 0.5-1 part of a retarder and 50-70 parts of water, wherein the acid-soluble hard filler consists of the following three fillers with different meshes in parts by weight: 5.8-10.1 parts of 325-mesh fillers, 26.6-46.8 parts of 600-mesh fillers and 7.6-13.1 parts of 3000-mesh fillers. On the basis of ensuring the strength of set cement, the acid solubility of the cement paste system can be improved to the maximum extent, the damage to the stratum is small, and the cement paste has wide application value in the fractured leakage stratum.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum engineering cementing, and in particular to a high-strength, high-acid-solubility acid-soluble cement slurry suitable for oil and gas well fracture leakage and a preparation method thereof. Background Art

[0002] During the drilling and completion process of low-pressure and leaky oil and gas reservoirs in China, due to the existence of complex natural fractures, the drilling and completion working fluid is seriously lost, causing serious damage to the reservoir and seriously affecting the production capacity. In response to this, the oil field proposed to use cement slurry as a plugging agent to fill the natural fractures. Since cement slurry has natural solidification properties, the solidified cement slurry blocks the natural fractures and prevents further leakage of other working fluids. The solidified cement slurry also blocks the oil and gas seepage channel, and acidization operations are required to increase oil and gas production. However, acidization operations are difficult to effectively dissolve conventional cement stone, reducing oil and gas production efficiency.

[0003] During cementing operations in low-permeability oil and gas reservoirs, cement slurry enters the pores of the oil and gas reservoir, causing reservoir pollution. The conventional approach is acid fracturing operations, but the acid solubility of conventional cement stone is limited by acid fracturing operations. In addition, the low acid solubility also has a certain impact on the subsequent fracturing initiation pressure and fracture diversion.

[0004] At present, the conventional practice is to fill cement with acid-soluble materials to increase the acid solubility of the cement paste system. However, excessive acid-soluble materials will reduce the strength of cement paste. In order to improve the strength of cement paste, reinforcing agents such as calcium oxide and magnesium oxide are usually added to the cement paste system. The addition of reinforcing agents causes certain disadvantages in the cement paste system in terms of mixing and performance control. Summary of the invention

[0005] One of the purposes of the present invention is to provide an acid-soluble cement slurry with high strength and high acid solubility, which is mainly used for cementing construction of natural fractured and leaking formations, and subsequent acidizing operations are required. The cement stone in the natural fractures is acid-dissolved and discharged out of the well, opening up oil and gas seepage channels, providing a basic guarantee for increasing the production of oil and gas reservoirs. In addition, the acid dissolves the cement ring of the cementing well and removes the cement that is blocked near the well wall, thereby increasing the permeability of the reservoir, which is beneficial to subsequent fracturing construction.

[0006] The second object of the present invention is to provide a method for preparing the high-strength, high-acid-solubility acid-soluble cement slurry.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] In a first aspect, the present invention provides an acid-soluble cement slurry with high strength and high acid solubility, comprising the following components in parts by weight: 100 parts of oil well silicate cement, 40-70 parts of acid-soluble hard filler, 4-6 parts of fluid loss reducer, 0.5-1 part of retarder, and 50-70 parts of water, wherein the acid-soluble hard filler is composed of three fillers of different mesh sizes in the following parts by weight: 5.8-10.1 parts of 325 mesh, 26.6-46.8 parts of 600 mesh, and 7.6-13.1 parts of 3000 mesh.

[0009] The following is a detailed description:

[0010] In some embodiments, the oil well silicate cement is one or more of grade A, grade G and grade H, preferably grade G silicate cement.

[0011] The grade of the oil well silicate cement is defined according to GB10238-98 standard.

[0012] The weight proportion of oil well silicate cement is 100 parts.

[0013] In some embodiments, the acid-soluble hard filler is calcium carbonate or magnesium carbonate.

[0014] The present invention adopts three kinds of acid-soluble hard fillers (such as calcium carbonate) with mesh sizes: 325 mesh, 600 mesh and 3000 mesh respectively. The three kinds of calcium carbonate with mesh sizes are composed according to the following weight proportions: 5.8-10.1 parts, 26.6-46.8 parts and 7.6-13.1 parts.

[0015] Typical but non-limiting weight portions of acid-soluble hard fillers are, for example, 40, 42, 45, 46, 48, 50, 52, 55, 56, 58, 60, 62, 65, 66, 68, and 70 parts, among which the typical but non-limiting weight portions of 325 mesh filler are, for example, 6, 6.2, 6.5, 6.6, 6.8, 7, 7.5, 8, 8.5, 9, 9.5, and 10 parts, the typical but non-limiting weight portions of 600 mesh filler are, for example, 27, 27.5, 28, 28.5, 29, 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, and 46 parts, and the typical but non-limiting weight portions of 3000 mesh filler are, for example, 8, 9, 10, 11, 12, and 13 parts.

[0016] In some embodiments, the fluid loss additive is a vinyl polymer, preferably polyvinyl alcohol.

[0017] Typical but non-limiting weight amounts of the fluid loss additive are, for example, 4, 5, or 6 parts.

[0018] In some embodiments, the retarder is an acrylamide polymer.

[0019] Typical but non-limiting weight parts of the retarder are, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1 part.

[0020] In some embodiments, the water is distilled water.

[0021] Typical but non-limiting parts by weight of water are, for example, 50, 52, 55, 56, 58, 60, 62, 65, 66, 68, 70 parts by weight.

[0022] The inventors found that in order to improve the acid solubility, the amount of acid-soluble materials must be increased, but the small particle size of the acid-soluble materials limits the strength of the cement slurry, which makes the acid solubility and strength form a contradiction. In order to effectively solve this problem, the inventors continuously explored through experiments and compressible stacking model design, and selected 3 kinds of acid-soluble materials (calcium carbonate) with specific mesh sizes to coordinate with a certain amount and ratio, which can play a role that ordinary acid-soluble materials cannot achieve. The cement slurry system formed not only has a high acid solubility rate, but also maintains a high level of strength.

[0023] In a second aspect, the present invention provides a method for preparing a high-strength, high-acid-solubility acid-soluble cement slurry, comprising the following steps:

[0024] The oil well silicate cement and the acid-soluble hard filler (325 mesh acid-soluble hard filler, 600 mesh acid-soluble hard filler and 3000 mesh acid-soluble hard filler) are mixed uniformly to obtain a dry powder;

[0025] Stir water, fluid loss reducer and retarder at low speed to form a mixed liquid;

[0026] Add the dry powder into the mixed liquid, cover the mixer lid, and stir at high speed to obtain an acid-soluble cement slurry system.

[0027] In some embodiments, the low-speed stirring speed is 4000±200 r / min, and the stirring time is 2-3 min.

[0028] In some embodiments, the high-speed stirring speed is 12000±500 r / min, and the stirring time is 45-60 s.

[0029] Beneficial effects:

[0030] The present invention can improve the acid solubility of the cement slurry system to the maximum extent on the basis of ensuring the strength of cement stone, has little damage to the formation, and has wide application value in fractured leakage formations.

[0031] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0033] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0034] Oil well silicate grade G cement comes from Dalian Cement Group Co., Ltd.;

[0035] The fluid loss reducer used in the embodiment is polyvinyl alcohol, which comes from the cementing company of Changcheng Drilling Engineering Co., Ltd.;

[0036] The retarder used in the embodiment is acrylamide polymer, which is GWR-100L retarder from the cementing company of Great Wall Drilling Engineering Co., Ltd.

[0037] Example 1

[0038] Weigh 100 parts of oil well silicate grade G cement, 40 parts of calcium carbonate (wherein the amounts of 325 mesh, 600 mesh, and 3000 mesh calcium carbonate are 5.8 parts, 26.6 parts, and 7.6 parts, respectively), 5 parts of fluid loss reducer, 0.7 parts of retarder, and 65 parts of distilled water.

[0039] The preparation method is as follows:

[0040] Weigh oil well silicate grade G cement, 325 mesh calcium carbonate, 600 mesh calcium carbonate, and 3000 mesh calcium carbonate, and mix them evenly to obtain dry powder;

[0041] Measure water, weigh the fluid loss reducer and retarder, stir the water, fluid loss reducer and retarder at a low speed (4000r / min) for 2 minutes to form a mixed solution, slowly add the mixed dry powder into the mixed solution, cover the mixer lid, and stir at a high speed (12000r / min) for 45s.

[0042] Example 2

[0043] Weigh 100 parts of oil well silicate grade G cement, 50 parts of calcium carbonate (wherein the amounts of 325 mesh, 600 mesh, and 3000 mesh calcium carbonate are 7.3 parts, 33.2 parts, and 9.5 parts, respectively), 5 parts of fluid loss reducer, 0.7 parts of retarder, and 68.2 parts of distilled water.

[0044] The preparation method is the same as that of Example 1.

[0045] Example 3

[0046] Weigh 100 parts of oil well silicate grade G cement, 60 parts of calcium carbonate (wherein the amounts of 325 mesh, 600 mesh, and 3000 mesh calcium carbonate are 8.8 parts, 39.8 parts, and 11.4 parts, respectively), 5 parts of fluid loss reducer, 0.7 parts of retarder, and 69 parts of distilled water.

[0047] The preparation method is the same as that of Example 1.

[0048] Example 4

[0049] Weigh 100 parts of oil well silicate grade G cement, 70 parts of calcium carbonate (wherein the amounts of 325 mesh, 600 mesh, and 3000 mesh calcium carbonate are 10.1 parts, 46.8 parts, and 13.1 parts, respectively), 5 parts of fluid loss reducer, 0.7 parts of retarder, and 70 parts of distilled water.

[0050] The preparation method is the same as that of Example 1.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that the amount of calcium carbonate used is 30 parts, wherein the amounts of 325 mesh, 600 mesh, and 3000 mesh calcium carbonate are applied evenly, namely 10 parts, 10 parts, and 10 parts, respectively.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 1 is that the amount of calcium carbonate used is 80 parts, wherein the amounts of 325 mesh, 600 mesh, and 3000 mesh calcium carbonate are 11.7 parts, 53.4 parts, and 14.9 parts, respectively.

[0055] Comparative Example 3

[0056] The difference between this comparative example and Example 1 is that the amount of calcium carbonate used is 51 parts, wherein the amounts of 325 mesh, 600 mesh and 3000 mesh calcium carbonate are 17 parts, 17 parts and 17 parts respectively.

[0057] Comparative Example 4

[0058] The difference between this comparative example and Example 1 is that the amount of calcium carbonate used is 40 parts, wherein the amounts of 325 mesh, 600 mesh, and 3000 mesh calcium carbonate are 20 parts, 20 parts, and 0 parts, respectively. That is, two kinds of calcium carbonate with different mesh sizes are used.

[0059] The acid solubility test of the cement slurry system in the embodiment was carried out using 15% hydrochloric acid, and the compressive strength of the cement paste was tested according to GB / T19139-2012 "Test Methods for Oil Well Cement". The specific method is as follows:

[0060] 1. Acid solubility rate:

[0061] Place the cement slurry in a cylindrical mold of Φ25.4mm×50.8mm, and place the mold in a high-temperature and high-pressure curing kettle, set the curing temperature to 60℃, the curing pressure to 20MPa, and the curing time to 24h.

[0062] After the curing is completed, the mold is disassembled and a cement stone cylindrical specimen is prepared. The cement stone cylindrical specimen is dried and weighed, and the mass is recorded as m1.

[0063] Place the cement stone cylindrical specimen in a glass beaker. Prepare 12% hydrochloric acid and fill the high temperature acid dissolving cup containing the cement stone cylindrical specimen with the 12% hydrochloric acid. Place an O-ring on the top of the high temperature acid dissolving cup, cover the cup tightly, and place it in an oven.

[0064] Heat the oven to the experimental temperature of 60℃. After acid dissolving for t hours (60min, 2h), disassemble the high-temperature acid dissolving cup, take out the cement stone debris after acid dissolution, rinse it with clean water, dry it, weigh it and record the mass as m2.

[0065] The acid solubility rate η was calculated according to the following formula:

[0066]

[0067] 2. Compressive strength:

[0068] Place the cement slurry in a cubic mold of 50.8mm×50.8mm×50.8mm, and place the mold in a high-temperature and high-pressure curing kettle. Set the curing temperature to 60°C, the curing pressure to 20MPa, and the curing time to 24h.

[0069] After the curing is completed, the mold is disassembled and cement stone cube specimens are prepared.

[0070] The compressive strength of cement stone cube specimens was tested using a universal material testing machine.

[0071] The results are shown in Table 2:

[0072]

[0073]

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A high-strength, high-acid-solubility acid-soluble cement slurry, characterized in that: The invention comprises the following components in parts by weight: 100 parts of oil well silicate cement, 40-70 parts of acid-soluble hard filler, 4-6 parts of fluid loss reducer, 0.5-1 part of retarder and 50-70 parts of water, wherein the acid-soluble hard filler is composed of fillers of three different mesh sizes in the following parts by weight: 5.8-10.1 parts of 325 mesh, 26.6-46.8 parts of 600 mesh and 7.6-13.1 parts of 3000 mesh.

2. The acid-soluble cement slurry according to claim 1, characterized in that: The oil well silicate cement is one or more of grade A, grade G and grade H, preferably grade G silicate cement.

3. The acid-soluble cement slurry according to claim 1, characterized in that: The acid-soluble hard filler is calcium carbonate or magnesium carbonate.

4. The acid-soluble cement slurry according to claim 1, characterized in that: The fluid loss additive is an ethylene polymer.

5. The acid-soluble cement slurry according to claim 1, characterized in that: The retarder is acrylamide polymer.

6. The acid-soluble cement slurry according to claim 1, characterized in that: The water is distilled water.

7. A method for preparing the acid-soluble cement slurry according to any one of claims 1 to 6, characterized in that: The following steps are involved: Mixing oil well silicate cement and acid-soluble hard filler evenly to obtain dry powder; Stir water, fluid loss reducer and retarder at low speed to form a mixed liquid; Add the dry powder into the mixed liquid, cover the mixer lid, and stir at high speed to obtain an acid-soluble cement slurry system.

8. The preparation method according to claim 7, characterized in that: The low-speed stirring speed is 4000±200r / min, and the stirring time is 2-3min.

9. The preparation method according to claim 7, characterized in that: The high-speed stirring speed is 12000±500r / min, and the stirring time is 45-60s.

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