Low friction resistance salt resistant high density oil well cement slurry and method of making same

Abstract

This invention relates to the field of cement slurry technology for oil and gas field cementing, and discloses a low-friction, salt-resistant, high-density oil well cement slurry and its preparation method. The low-friction, salt-resistant, high-density oil well cement slurry comprises the following components, added per 100 parts by weight of cement: 35-110 parts weighting agent, 0-15 parts fine aggregate, 1.5-5 parts fluid loss reducing agent, 0-1 part retarder, 0.5-3 parts drag reducing agent, and 0.2-0.6 parts defoamer; the density is 2.0-2.10 g / cm³. 3 The salt-resistant, low-temperature, anti-channeling, and tough cement slurry provided by this invention is based on a low-friction, high-density cement slurry system with iron ore powder weighting. The thickening time is adjustable, and the overall performance is good. It can maintain good performance under high temperature, high pressure, and high salt conditions.

Description

Technical Field

[0001] This invention relates to the field of cement slurry technology for oil and gas field cementing, specifically to a low-friction, salt-resistant, high-density oil well cement slurry and its preparation method. Background Technology

[0002] In oil and gas well cementing, high pore pressure, wellbore instability, and plastic flow formations all require control using high hydrostatic pressure. To maintain wellbore stability and safe operation, it is necessary to increase the density of the cement slurry. The frictional resistance during cementing injection has a very significant response to the equivalent circulating density. If the frictional resistance is high, it will generate enormous back pressure in the annulus between the casing and the formation, potentially leading to formation fracturing, circulation loss, and other well control problems. In small-diameter drilling technology, the reduced casing inner diameter increases the flow resistance and friction coefficient of the cementing system, resulting in increased pump pressure during cementing operations. Therefore, in situations with long open-hole sections, small annular spaces, large flow friction pressure drops, and high operating pressures, reducing the frictional resistance of the cement slurry is crucial for ensuring safe cementing operations.

[0003] In the western part of the Turpan-Hami Oilfield, the Tertiary N1t and Esh formations in the Yanmuxi, Shenquan, and Pubei blocks contain large sections of salt-gypsum layers. The total salinity of the drilling fluid filtrate in these formations is high, and using salt-resistant cement slurry can improve cementing quality and reduce costs. In ultra-deep well cementing operations, such as in the Keshen well area of ​​the Tarim Oilfield, due to the development of downhole salt-gypsum layers, narrow gaps, high pressure, high temperature, and large temperature differences, salt-resistant cement slurry systems can solve cementing problems and seal high-pressure brine layers, ensuring safe and efficient development. In areas such as the Missan Oilfield in Iraq, where high-pressure salt-gypsum layers are common at the well bottom and the pressure window is narrow, using salt-resistant high-performance cement slurry systems can solve problems such as cement slurry thickening and thixotropy that may occur due to high-salt mixed water preparation, while also improving the compressive strength of the cement stone. In cementing operations requiring the sealing of abnormally high-pressure gas layers and high-pressure brine layers, such as the Guanshen 1 well, an ultra-high-density cement slurry system is employed. This system boasts advantages such as good fluidity, high strength, high-temperature resistance, and strong anti-channeling capability, effectively addressing the practical difficulties of cementing. In cementing operations requiring the penetration or sealing of saline formations, ultra-deep wells, high-pressure salt-gypsum layers, and the sealing of high-pressure gas and brine layers, the stability and durability of the cement slurry are particularly crucial. Traditional high-density cement slurries are easily affected by salt in high-salt environments, leading to performance degradation and an inability to maintain the required cementing performance over the long term.

[0004] To address the aforementioned issues, this invention proposes a low-friction, salt-resistant, high-density cement slurry. The aim is to achieve lower friction, superior rheological properties and stability, and higher strength in cementing operations under complex environments such as high temperature, high pressure, and high salt content, through innovative formulation and preparation processes. Summary of the Invention

[0005] Based on this, the present invention proposes a low-friction, salt-resistant, high-density oil well cement slurry for unconventional oil and gas cementing and salt gypsum or brine layers, and its preparation method. This oil well cement slurry can maintain good performance under high temperature, high pressure, and high salt conditions.

[0006] According to a first aspect of the present invention, a low-friction, salt-resistant, high-density oil well cement slurry is provided, comprising the following components, added per 100 parts by weight of cement: 35-110 parts of weighting agent, 0-15 parts of fine aggregate, 1.5-5 parts of fluid loss reducing agent, 0-1 parts of retarder, 0.5-3 parts of drag reducing agent, and 0.2-0.6 parts of defoamer;

[0007] The density is between 2.0 and 2.10 g / cm³. 3 .

[0008] According to an embodiment of the present invention, the cement is Grade G high sulfate-resistant cement;

[0009] And / or, the water loss reducing agent is an AMPS synthetic polymer;

[0010] And / or, the retarder is a phosphonate;

[0011] And / or, the water is a semi-saturated or saturated saline solution.

[0012] According to an embodiment of the present invention, the weighting agent is one or more of barite, iron ore powder, hematite, ilmenite, and micro manganese powder;

[0013] The iron ore powder has a density of 4.8 g / cm³. 3 Or 7.2g / cm 3 ;

[0014] The density of the micro-manganese powder is 4.9 g / cm³. 3 .

[0015] According to an embodiment of the present invention, the fine aggregate is one or more of microsilica, quartz sand, and activated silica powder;

[0016] The particle size of microsilica is 100μm-300μm; the particle size of quartz sand is 0.25mm-0.5mm; and the particle size of activated silica is 0.05mm-0.15mm.

[0017] According to an embodiment of the present invention, the drag-reducing agent is a drag-reducing agent composed of a polycarboxylic acid polymer and an aldehyde-ketone condensate polymer.

[0018] According to an embodiment of the present invention, the defoamer is a mixture of tributyl phosphate and organosilicon;

[0019] The mass ratio of the tributyl phosphate to the organosilicon is 1:2 to 1:3.

[0020] According to an embodiment of the present invention, the weight ratio of the polycarboxylic acid polymer to the aldehyde-ketone condensate is 10:0.8 to 10:1.9.

[0021] According to an embodiment of the present invention, the polycarboxylic acid polymer is a polymer of small monomers and macromonomers;

[0022] The small monomer is composed of 4-7 parts by weight of maleic anhydride, 5-10 parts by weight of acrylic acid, and 3.5-6 parts by weight of sodium methyl allyl sulfonate.

[0023] The macromonomer is 20-25 parts by weight of allyl polyoxyethylene ether with a molecular weight of 2000 and 40-60 parts by weight of allyl polyoxyethylene ether with a molecular weight of 5000.

[0024] The molecular ratio of the macromonomer EPEG to the acrylic acid is 2.95:4.2.

[0025] According to a second aspect of the present invention, a method for preparing the above-mentioned low-friction, salt-resistant, high-density oil well cement slurry is provided, comprising the following steps:

[0026] Preparation of drag-reducing agents;

[0027] Weigh out 100 parts of cement, 35-110 parts of weighting agent, and 0-15 parts of fine aggregate according to the proportions, mix them evenly, and obtain a solid sample.

[0028] Add 1.5 to 5 parts of water loss reducing agent, 0 to 1 part of retarder, 0.5 to 3 parts of drag reducing agent, 0.2 to 0.6 parts of defoamer and water to the mixing cup and stir evenly to obtain a liquid sample;

[0029] Under low-speed stirring, the solid sample is added to the liquid sample, and after increasing the stirring frequency, the mixture is mixed evenly to obtain the low-friction, salt-resistant, high-density oil well cement slurry.

[0030] According to an embodiment of the present invention, the preparation of the drag-reducing agent includes:

[0031] Preparation of polycarboxylic acid polymer: Add 100 parts by weight of water to a beaker, weigh 20-25 parts of allyl polyoxyethylene ether with a molecular weight of 2000, 40-60 parts of allyl polyoxyethylene ether with a molecular weight of 5000, 4-7 parts by weight of maleic anhydride, and 5-10 parts by weight of acrylic acid, dissolve and stir; add sodium hydroxide to adjust the pH of the aqueous solution to 5-6, add 2-10 parts of hydrogen peroxide and 2-5 parts of vitamin C as initiators, and 0.02 parts of mercaptopropionic acid as a chain transfer agent, and continue the reaction to obtain the polymer;

[0032] The polymer was added to 3.5-6 parts of sodium methyl allyl sulfonate and sulfonated for 2 hours to obtain the final product, a polycarboxylic acid polymer.

[0033] The aldehyde-ketone condensate is added to the prepared polycarboxylic acid polymer in a certain proportion to form the drag-reducing agent.

[0034] As can be seen from the above technical solution, the anti-backflow oil-based drilling fluid plugging material and its preparation method provided by the present invention have the following beneficial effects:

[0035] Compared with existing technologies, this salt-resistant, low-temperature, anti-channeling, and tough cement slurry is applicable at temperatures up to 180℃. Based on a low-friction, high-density cement slurry system weighted with iron ore powder, the slurry density is 2.25-2.50 g / cm³. 3 The cement slurry flowability index n ≥ 0.7 and consistency coefficient K ≤ 0.8 Pa·s n It exhibits a reduction in friction coefficient of over 30%, a 24-hour compressive strength >20MPa, adjustable thickening time, and excellent overall performance. Based on a barite-weighted high-density cement slurry system, the cement slurry density is 2.05-2.25 g / cm³. 3 The flowability index of the cement slurry n ≥ 0.7, and the consistency coefficient K ≤ 1 Pa·s n 24h compressive strength >14MPa, thickening time is adjustable. Attached Figure Description

[0036] Figure 1 The TG results for the drag-reducing agent in this embodiment of the invention;

[0037] Figure 2 The thickening curve is shown in Example 2 of this invention;

[0038] Figure 3 The thickening curve is shown in Example 7 of this invention;

[0039] Figure 4 This is the thickening curve of Example 11 of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0041] According to a first aspect of the present invention, a low-friction, salt-resistant, high-density oil well cement slurry is provided, comprising the following components, added per 100 parts by weight of cement: 35-110 parts of weighting agent, 0-15 parts of fine aggregate, 1.5-5 parts of fluid loss reducing agent, 0-1 parts of retarder, 0.5-3 parts of drag reducing agent, and 0.2-0.6 parts of defoamer;

[0042] Density is between 2.0 and 2.10 g / cm³ 3 .

[0043] This low-cost, low-friction, salt-resistant, high-density cement slurry system does not use weighting agents; it achieves the required density (2.0–2.10 g / cm³) solely through the cement itself. 3 It's adjustable, which greatly reduces costs.

[0044] According to an embodiment of the present invention, the cement is Grade G high sulfate-resistant cement;

[0045] And / or, the water loss reducing agent is an AMPS synthetic polymer;

[0046] And / or, the retarder is a phosphonate.

[0047] According to embodiments of the present invention, the water is a semi-saturated or saturated saline solution, and the salt can be sodium chloride or other commonly used inorganic salts; the water can also be on-site brine, with a concentration that can reach saturation; the water can also be fresh water, reclaimed water, or on-site water; the water can also be experimental water, tap water, or distilled water.

[0048] According to an embodiment of the present invention, the weighting agent is one or more of barite, iron ore powder, hematite, ilmenite, and micro manganese powder;

[0049] The density of the iron ore powder is 4.8 g / cm³. 3 Or 7.2g / cm 3 ;

[0050] The density of the micro-manganese powder is 4.9 g / cm³. 3 .

[0051] According to an embodiment of the present invention, the fine aggregate is one or more of microsilica, quartz sand, and activated silica powder;

[0052] The particle size of microsilica is 100μm-300μm; the particle size of quartz sand is 0.25mm-0.5mm; and the particle size of activated silica is 0.05mm-0.15mm.

[0053] According to an embodiment of the present invention, the drag-reducing agent is a drag-reducing agent composed of a polycarboxylic acid polymer and an aldehyde-ketone condensate polymer.

[0054] According to an embodiment of the present invention, the aldehyde-ketone condensate can be a liquid drag reducer of the aldehyde-ketone condensate type, SGJS-3.

[0055] According to an embodiment of the present invention, the defoamer is a mixture of tributyl phosphate and organosilicon;

[0056] The mass ratio of tributyl phosphate to organosilicon is 1:2-1:3.

[0057] According to an embodiment of the present invention, the weight ratio of polycarboxylic acid polymer to aldehyde-ketone condensate is 10:0.8 to 10:1.9.

[0058] According to embodiments of the present invention, the polycarboxylic acid polymer is a polymer of small monomers and macromonomers;

[0059] The small monomers are 4-7 parts by weight of maleic anhydride, 5-10 parts by weight of acrylic acid, and 3.5-6 parts by weight of sodium methyl allyl sulfonate (SMAS).

[0060] The macromonomers are 20-25 parts by weight of allyl polyoxyethylene ether with a molecular weight of 2000 and 40-60 parts by weight of allyl polyoxyethylene ether with a molecular weight of 5000.

[0061] The molecular ratio of the macromonomer EPEG to acrylic acid is 2.95:4.2.

[0062] According to a second aspect of the present invention, a method for preparing the above-mentioned low-friction, salt-resistant, high-density oil well cement slurry is provided, comprising the following steps:

[0063] Preparation of drag-reducing agents;

[0064] Weigh out 100 parts of cement, 35-110 parts of weighting agent, and 0-15 parts of fine aggregate according to the proportions, mix them evenly, and obtain a solid sample.

[0065] Add 1.5 to 5 parts of water loss reducing agent, 0 to 1 part of retarder, 0.5 to 3 parts of drag reducing agent, 0.2 to 0.6 parts of defoamer and water to the mixing cup and stir evenly to obtain a liquid sample;

[0066] Under low-speed stirring, the solid sample is added to the liquid sample. After increasing the stirring frequency, the mixture is mixed evenly to obtain a low-friction, salt-resistant, high-density oil well cement slurry.

[0067] According to an embodiment of the present invention, the preparation of the drag-reducing agent includes:

[0068] Preparation of polycarboxylic acid polymer: Add 100 parts by weight of water to a beaker, weigh 20-25 parts of allyl polyoxyethylene ether with a molecular weight of 2000, 40-60 parts of allyl polyoxyethylene ether with a molecular weight of 5000, 4-7 parts by weight of maleic anhydride, and 5-10 parts by weight of acrylic acid, dissolve and stir; add sodium hydroxide to adjust the pH of the aqueous solution to 5-6, add 2-10 parts of hydrogen peroxide and 2-5 parts of vitamin C as initiators, and 0.02 parts of mercaptopropionic acid as a chain transfer agent, and continue the reaction to obtain the polymer;

[0069] The polymer was added to 3.5-6 parts of sodium methyl allyl sulfonate and sulfonated for 2 hours to obtain the final product, a polycarboxylic acid polymer.

[0070] Aldehyde-ketone condensates are added to the prepared polycarboxylic acid polymer in a certain proportion to form a drag-reducing agent.

[0071] The technical solution of the present invention will be described in detail below through preferred embodiments. It should be noted that the specific embodiments in the following text are for illustrative purposes only and are not intended to limit the present invention.

[0072] The cement slurry is composed of cement, weighting agent, fine aggregate, fluid loss reducer, retarder, drag reducer, defoamer, and saturated brine. The cement is Grade G high sulfate-resistant cement supplied by Shengwei Cement Plant, and the fluid loss reducer, retarder, and defoamer are BH-F201L fluid loss reducer, BH-R102L retarder, and BH-XP901L defoamer supplied by PetroChina Bohai Drilling Second Cementing Company.

[0073] Preparation methods include:

[0074] Add 100 parts by weight of water to a beaker, weigh out 20-25 parts of allyl polyoxyethylene ether with a molecular weight of 2000, 40-60 parts of allyl polyoxyethylene ether with a molecular weight of 5000, 4-7 parts by weight of maleic anhydride, and 5-10 parts by weight of acrylic acid, and dissolve and stir. Add sodium hydroxide to adjust the pH of the aqueous solution to 5-6, add 2-10 parts of hydrogen peroxide and 2-5 parts of vitamin C as initiators, and 0.02 parts of mercaptopropionic acid as a chain transfer agent, and continue the reaction to obtain the polymer.

[0075] The polymer was added to 3.5-6 parts of sodium methyl allyl sulfonate and sulfonated for 2 hours to obtain the final product, a polycarboxylic acid polymer.

[0076] Aldehyde condensates are added to the prepared polycarboxylic acid polymer in a certain proportion to form a drag-reducing agent.

[0077] Weigh out 100 parts of cement, 35-110 parts of weighting agent, and 0-15 parts of fine aggregate according to the proportions, mix them evenly, and obtain a solid sample.

[0078] Add 1.5 to 5 parts of water loss reducing agent, 0 to 1 part of retarder, 0.5 to 3 parts of drag reducing agent, 0.2 to 0.6 parts of defoamer and water to the mixing cup and stir evenly to obtain a liquid sample;

[0079] Under low-speed stirring, the solid sample is added to the liquid sample. After increasing the stirring frequency, the mixture is mixed evenly to obtain a low-friction, salt-resistant, high-density oil well cement slurry.

[0080] Example 1

[0081] The oil well cement slurry formula is as follows: 100 parts cement, 3 parts water loss reducer, 0.5 parts retarder, 1 part drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.00 g / cm³. 3 .

[0082] Example 2

[0083] The oil well cement slurry formula is as follows: 100 parts cement, 4 parts water loss reducer, 0.5 parts retarder, 2 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.05 g / cm³. 3 .

[0084] Example 3

[0085] The oil well cement slurry formula is as follows: 100 parts cement, 5 parts water loss reducer, 0.5 parts retarder, 3 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.10 g / cm³. 3 .

[0086] Example 4

[0087] The oil well cement slurry formula is as follows: 100 parts cement, 35 parts barite weighting agent, 2 parts fine aggregate silica, 3 parts water loss reducing agent, 0.5 parts retarder, 2 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.05 g / cm³. 3 .

[0088] Example 5

[0089] The oil well cement slurry formula is as follows: 100 parts cement, 65 parts barite weighting agent, 2 parts fine aggregate silica, 4 parts water loss reducing agent, 0.5 parts retarder, 2 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.15 g / cm³. 3 .

[0090] Example 6

[0091] The oil well cement slurry formula is as follows: 100 parts cement, 70 parts barite weighting agent, 2 parts fine aggregate silica, 4 parts water loss reducing agent, 0.5 parts retarder, 2 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.20 g / cm³. 3 .

[0092] Example 7

[0093] The oil well cement slurry formula is as follows: 100 parts cement, 70 parts iron ore powder weighting agent, 5 parts micro-manganese powder weighting agent, 3 parts water loss reducing agent, 0.5 parts retarder, 1.5 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.30 g / cm³. 3 .

[0094] Example 8

[0095] The oil well cement slurry formula is as follows: 100 parts cement, 70 parts iron ore powder weighting agent, 5 parts micro-manganese powder weighting agent, 3 parts water loss reducing agent, 0.5 parts retarder, 1.5 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.35 g / cm³. 3 .

[0096] Example 9

[0097] The oil well cement slurry formula is as follows: 100 parts cement, 80 parts iron ore powder weighting agent, 7 parts micro-manganese powder weighting agent, 2 parts microsilica, 3 parts water loss reducing agent, 0.5 parts retarder, 1.5 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.40 g / cm³. 3 .

[0098] Example 10

[0099] The oil well cement slurry formula is as follows: 100 parts cement, 85 parts iron ore powder weighting agent, 7 parts micro-manganese powder weighting agent, 2 parts microsilica, 3 parts water loss reducing agent, 0.5 parts retarder, 1.5 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.45 g / cm³. 3 .

[0100] Example 11

[0101] The formula for oil well cement slurry is: 100 parts cement, 110 parts 7.2 g / cm³ 3 The cement paste contains iron ore powder as a weighting agent, 10 parts of micro-manganese powder as a weighting agent, 60 parts of silica fume, 3 parts of microsilica, 3 parts of water loss reducing agent, 0.5 parts of retarder, 2 parts of drag reducing agent, and 0.5 parts of defoamer, with the balance being saturated brine. The density of the prepared cement paste is 2.50 g / cm³. 3 .

[0102] Comparative Example 1

[0103] The oil well cement slurry formula is as follows: 100 parts cement, 70 parts iron ore powder weighting agent, 5 parts micro-manganese powder weighting agent, 3 parts water loss reducing agent, 0.5 parts retarder, 1.5 parts drag reducer, and 0.5 parts defoamer, with the balance being saturated brine. The prepared cement slurry has a density of 2.35 g / cm³. 3 .

[0104] The only difference between Comparative Example 1 and Example 8 is the drag-reducing agent used; the drag-reducing agent used is Weihui's USZ sulfonated aldehyde-ketone drag-reducing agent.

[0105] Comparative Example 2

[0106] The oil well cement slurry formula is as follows: 100 parts cement, 70 parts iron ore powder weighting agent, 5 parts micro-manganese powder weighting agent, 3 parts water loss reducing agent, 0.5 parts retarder, 1.5 parts drag reducer, and 0.5 parts defoamer, with the balance being tap water. The prepared cement slurry has a density of 2.35 g / cm³. 3 .

[0107] The differences between Comparative Example 2 and Example 8 are as follows: 1. The drag-reducing agent used is different; the drag-reducing agent used is Weihui's USZ sulfonated aldehyde-ketone drag-reducing agent. 2. Tap water is used for mixing the slurry.

[0108] Experimental Example

[0109] The cement slurries prepared from Examples 1-11 and Comparative Examples 1-2 were tested for various properties according to API specifications.

[0110] (1) Rheology

[0111] The rheological properties of the cement slurries prepared in Examples 1-11 and Comparative Examples 1-2 at room temperature and after heat curing were measured respectively. The experimental results are shown in Table 1 and 2. Figure 1 As shown.

[0112] Table 1. Rheological results of high-density cement paste

[0113]

[0114] (Note: " / " indicates no reading at a certain speed; based on field application, the curing temperature for high-density cement slurry without weighting agent is 90℃; the curing temperature for high-density cement slurry with barite as weighting agent is 90℃; the curing temperature for high-density cement slurry with iron ore powder as weighting agent is 65℃.)

[0115] As shown in Table 1, the density range of the high-density cement slurry in this invention patent is 2.0 g / cm³. 3 ~2.50g / cm 3 It exhibits good rheological properties. A comparison of Examples 2 and 4 shows that the rheological indices of high-density cement slurry without weighting agents and high-density cement slurry weighted with barite are basically the same, indicating comparable rheological properties. However, from a cost perspective, the cost of the cement slurry is significantly reduced. A comparison of Example 8 and Comparative Examples 1-2 shows that the drag-reducing agent prepared from the low-friction, salt-resistant high-density cement slurry has excellent rheological properties and also exhibits resistance to saturated salt water, while the aldehyde-ketone polymer USZ-type drag-reducing agent does not possess salt resistance. From... Figure 1 It is known that the drag-reducing agent composed of polycarboxylic acid polymer and aldehyde-ketone condensate dispersant of the present invention has a temperature resistance of up to 221°C, as shown by TG-DTA analysis.

[0116] (2) Comprehensive performance evaluation of high-density cement paste

[0117] The comprehensive performance of the cement slurries prepared in Examples 1-11 and Comparative Examples 1-2 was measured respectively, and the experimental results are shown in Table 2.

[0118] Table 2. Comprehensive Performance Evaluation of High-Density Cement Slurry

[0119]

[0120] As shown in Table 1, with the increase of cement slurry density, all the indicators of the cement slurry meet the construction requirements. The compressive strength of the cement stone is greater than 25 MPa after 24 hours, the water loss of the cement slurry is ≤40 mL, the settling stability of the cement slurry density difference is almost 0, and the free liquid is 0, indicating good overall performance. As shown in Table 4, the rheological properties are excellent.

[0121] (3) Friction coefficient

[0122] Friction resistance of low-friction, salt-resistant, high-density cement slurry was studied according to SY / T 5480-2007 "Cementing Design Specification". Taking a 5.5-inch casing as an example, the flow velocity ν of the cement slurry is generally set to 1.1 m / s. The casing outer diameter D... w The inner diameter of the casing is 139.7 mm, and the wall thickness is 9.17 mm. i The diameter is 121.36 mm. Based on the inner diameter of the casing, the density of the cement grout, and the flow index n and consistency coefficient k of the cement grout, the Reynolds number R of the cement grout can be calculated. e Then, the friction coefficient of the cement grout is calculated. The Reynolds number R... e The formula is shown in equation (1): K RePL The value is 1.

[0123]

[0124] For turbulent flow, the proportion of the effect of the sidewall increases; at the same time, due to the limitations of the well structure, the discharge rate of cementing operations is relatively small, and there is a greater chance of being in the transition zone from laminar to turbulent flow. Therefore, the friction coefficient under turbulent flow is calculated using a method suitable for narrow gaps. Thus, we determine the values ​​of A and B according to turbulent flow. When the flow state is turbulent, the friction coefficient f is calculated as follows: regardless of the geometry in which the fluid flows, f is calculated according to the following formula (2).

[0125]

[0126] The values ​​of A and B are determined based on n, according to SY / T 5480-2007, as shown in Table 3 below:

[0127] Table 3. Values ​​of A and B

[0128] n A B 0.2 0.0646 0.349 0.3 0.0685 0.325 0.4 0.0712 0.307 0.6 0.074 0.281 0.8 0.076 0.263 1.0 0.0779 0.250

[0129] The comprehensive properties of the cement slurries prepared in Examples 1-11 and Comparative Examples 1-2 were measured respectively, and the experimental results are shown in Table 2.

[0130] Table 4. Rheological properties and friction coefficient of high-density cement paste

[0131]

[0132] (Note: " / " indicates that it cannot be calculated; based on the field application, the curing temperature of high-density cement slurry without weighting agent is 90℃; the curing temperature of high-density cement slurry with barite as weighting agent is 90℃; the curing temperature of high-density cement slurry with iron ore powder as weighting agent is 65℃.)

[0133] To ensure safe construction, according to cementing technology requirements, the friction coefficient of cement slurry should be <0.3, which is the minimum standard for safe cementing construction. Based on actual on-site construction needs and to meet various construction conditions, the friction coefficient of cement slurry in actual cementing processes is generally less than 0.15. According to practical cementing construction experience, the optimal friction coefficient for cement slurry is currently 0.08. The lower the friction coefficient of the cement slurry, the lower its rheological properties, which is more conducive to cement slurry return and better ensures cementing quality. Table 3 shows that the low-friction, high-density cement slurry of Examples 1-11 has a friction coefficient not exceeding 0.08, which is very low. The friction coefficient of the USZ type aldehyde-ketone polymer drag reducer in Comparative Examples 1-2 is around 0.11. The drag reducer formulated with the polycarboxylic acid polymer and aldehyde-ketone condensate dispersant of this invention significantly reduces the friction coefficient by more than 35.2%. The main mechanism is that the hydrogen bonds formed by the association of strongly hydrophilic polar groups such as carboxyl, hydroxyl, sulfonic acid, and ether bonds in this drag-reducing agent with water molecules can improve the wettability of cement particle surfaces, reduce friction between cement particles, and maintain the fluidity of cement concrete. Meanwhile, the low-friction, salt-resistant, high-density drag-reducing agent in this invention not only has good particle size distribution, but also exhibits very low friction and significant resistance to saturated salt water, making it suitable for a wide range of cementing applications.

[0134] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-friction, salt-resistant, high-density oil well cement slurry, characterized in that, The following components are added per 100 parts by weight of cement: 35-110 parts of weighting agent, 0-15 parts of fine aggregate, 1.5-5 parts of water loss reducing agent, 0-1 parts of retarder, 0.5-3 parts of drag reducing agent, and 0.2-0.6 parts of defoamer. The density is between 2.0 and 2.10 g / cm³. 3 .

2. The low-friction, salt-resistant, high-density oil well cement slurry according to claim 1, characterized in that, The cement is Grade G high sulfate-resistant cement; And / or, the water loss reducing agent is an AMPS synthetic polymer; And / or, the retarder is a phosphonate.

3. The low-friction, salt-resistant, high-density oil well cement slurry according to claim 1, characterized in that, The weighting agent is one or more of barite, iron ore powder, hematite, ilmenite, and micro manganese powder; The iron ore powder has a density of 4.8 g / cm³. 3 Or 7.2g / cm 3 ; The density of the micro-manganese powder is 4.9 g / cm³. 3 .

4. The low-friction, salt-resistant, high-density oil well cement slurry according to claim 1, characterized in that, The fine aggregate is one or more of microsilica, quartz sand, and activated silica powder.

5. The low-friction, salt-resistant, high-density oil well cement slurry according to claim 1, characterized in that, The drag-reducing agent is a drag-reducing agent composed of polycarboxylic acid polymers and aldehyde-ketone condensates.

6. The low-friction, salt-resistant, high-density oil well cement slurry according to claim 1, characterized in that, The defoamer is a mixture of tributyl phosphate and organosilicon; The mass ratio of the tributyl phosphate to the organosilicon is 1:2 to 1:

3.

7. The low-friction, salt-resistant, high-density oil well cement slurry according to claim 1, characterized in that, The weight ratio of the polycarboxylic acid polymer to the aldehyde-ketone condensate is 10:0.8 to 10:1.

9.

8. The low-friction, salt-resistant, high-density oil well cement slurry according to claim 1, characterized in that, The polycarboxylic acid polymer is a polymer of small monomers and macromonomers; The small monomer is composed of 4-7 parts by weight of maleic anhydride, 5-10 parts by weight of acrylic acid, and 3.5-6 parts by weight of sodium methyl allyl sulfonate. The macromonomer is 20-25 parts by weight of allyl polyoxyethylene ether with a molecular weight of 2000 and 40-60 parts by weight of allyl polyoxyethylene ether with a molecular weight of 5000. The molecular ratio of the macromonomer EPEG to the acrylic acid is 2.95:4.

2.

9. A method for preparing low-friction, salt-resistant, high-density oil well cement slurry according to any one of claims 1-8, characterized in that, Includes the following steps: Preparation of drag-reducing agents; Weigh out 100 parts of cement, 35-110 parts of weighting agent, and 0-15 parts of fine aggregate according to the proportions, mix them evenly, and obtain a solid sample. Add 1.5 to 5 parts of water loss reducing agent, 0 to 1 part of retarder, 0.5 to 3 parts of drag reducing agent, 0.2 to 0.6 parts of defoamer and water to the mixing cup and stir evenly to obtain a liquid sample; Under low-speed stirring, the solid sample is added to the liquid sample, and after increasing the stirring frequency, the mixture is mixed evenly to obtain the low-friction, salt-resistant, high-density oil well cement slurry.

10. The preparation method according to claim 9, characterized in that, The preparation of the drag-reducing agent includes: Preparation of polycarboxylic acid polymer: Add 100 parts by weight of water to a beaker, weigh 20-25 parts of allyl polyoxyethylene ether with a molecular weight of 2000, 40-60 parts of allyl polyoxyethylene ether with a molecular weight of 5000, 4-7 parts by weight of maleic anhydride, and 5-10 parts by weight of acrylic acid, dissolve and stir; add sodium hydroxide to adjust the pH of the aqueous solution to 5-6, add 2-10 parts of hydrogen peroxide and 2-5 parts of vitamin C as initiators, and 0.02 parts of mercaptopropionic acid as a chain transfer agent, and continue the reaction to obtain the polymer; The polymer was added to 3.5-6 parts of sodium methyl allyl sulfonate and sulfonated for 2 hours to obtain the final product, a polycarboxylic acid polymer. The aldehyde-ketone condensate is added to the prepared polycarboxylic acid polymer in a certain proportion to form the drag-reducing agent.

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