A plugging cement composition for drilling, a cement slurry system and a preparation method thereof

Abstract

The present invention relates to a plugging cement composition for drilling, a cement slurry system and a preparation method thereof, comprising a plugging cement main ingredient and an anti-water dispersing additive; the plugging cement main ingredient comprises oil well cement, the anti-water dispersing additive comprises an anti-dispersing flocculant and an anti-dispersing regulator, wherein the amount of the anti-dispersing flocculant used per 100 parts of oil well cement is 4-7 parts, and the amount of the anti-dispersing regulator is 0.1-0.5 parts; the anti-dispersing flocculant is an acrylamide fluid loss additive; and the anti-dispersing regulator is a naphthalenesulfonic acid formaldehyde condensate. The cement composition of the present invention reduces the filtration loss of the cement slurry by the anti-dispersing flocculant, maintains a relatively stable flocculation state between cement particles, improves the water-isolating effect of the cement slurry in cracks and caves, and ensures that the plugging cement slurry resides in the cracks; and adjusts the speed of the flocculation state of the plugging cement slurry by the anti-dispersing regulator, effectively solving the problem that the plugging materials of the prior art are difficult to reside in alkaline water and have poor sealing effect.

Description

Technical Field

[0001] The invention relates to a plugging cement composition for drilling, a cement slurry system and a preparation method thereof, and belongs to the field of petroleum drilling technology and well cementing. Background Art

[0002] The deep layers of the Anpeng Depression in the Henan Oilfield are home to dense tight sandstone reservoirs, making it a prime exploration area for tight sandstone oil and gas. Alkali layers are developed between 2,000 and 2,200 meters below the surface. Long-term exploitation of alkaline resources has resulted in large fractures and karst caves in this well section, leading to severe drilling fluid losses during drilling, with rates reaching 40 to 120 cubic meters per hour. Furthermore, this layer is filled with flowing alkaline water, making it difficult for plugging materials and slurries to remain in place, making plugging difficult and ineffective. This has begun to hinder oil and gas exploration in the area. Summary of the Invention

[0003] The first object of the present invention is to provide a plugging cement composition for drilling, so as to solve the problem that the plugging materials and plugging cement slurries in the prior art have poor retention effects and poor plugging effects.

[0004] The second object of the present invention is to provide a plugging cement slurry system for drilling to solve the problem in the prior art that the plugging materials and plugging cement slurry have poor retention effect and poor plugging effect.

[0005] The third object of the present invention is to provide a method for preparing a plugging cement slurry system for drilling, which has simple process, convenient operation, conciseness during on-site construction, and is easy to promote.

[0006] In order to achieve the above object, the technical solution of the drilling plugging cement composition in the present invention is:

[0007] A plugging cement composition for drilling comprises a plugging cement main ingredient and a water-resistant dispersing additive. The plugging cement main ingredient comprises oil well cement, and the water-resistant dispersing additive comprises an anti-dispersing flocculant and an anti-dispersing regulator. The amount of the anti-dispersing flocculant used per 100 parts of oil well cement is 4-7 parts, and the amount of the anti-dispersing regulator is 0.1-0.5 parts. The anti-dispersing flocculant is an acrylamide-based fluid loss additive, and the anti-dispersing regulator is a naphthalenesulfonic acid formaldehyde condensate.

[0008] The beneficial effect of the above technical solution is that the drilling plugging cement composition of the present invention is mainly composed of a plugging cement main ingredient and a water-resistant dispersible additive, the plugging cement main ingredient includes oil well cement, and the water-resistant dispersible additive is composed of an anti-dispersible flocculant and an anti-dispersible regulator. Among them, the anti-dispersible flocculant is used to reduce the filtration loss of the cement slurry, while maintaining a relatively stable flocculation state between the cement particles, so as to achieve the effect that the cement slurry in the water does not disperse and the cement slurry and water do not mix; the anti-dispersible regulator is used to adjust the speed of the formation of the flocculation state of the plugging cement slurry. The drilling plugging cement composition of the present invention can effectively improve the bearing capacity of the wellbore, provide a good wellbore environment for subsequent drilling and cementing construction, and provide technical support for solving the problems in the prior art of poor retention effect of plugging materials and plugging cement slurry, and poor effect after plugging.

[0009] As a further improvement, the main material of the plugging cement includes the following components: a thixotropic agent, a drag reducing agent, a fiber plugging agent, an early strength agent and an expansion agent.

[0010] The beneficial effects of the above technical solution are: the thixotropic agent is used to improve the thixotropic properties of cement slurry, so that the cement slurry has the ability of high shear and low viscosity, and low shear and high viscosity. The cement slurry can quickly form a certain structure after it is still, thereby improving the retention capacity of the plugging cement slurry; the drag reducer improves the rheological properties of the cement slurry and reduces the flow resistance; the fiber plugging agent is used to improve the bridging and adsorption of the cement slurry in cracks and holes, and gradually reduce the size of cracks and holes; the early strength agent is used to improve the early compressive strength of the cement stone and shorten the thickening time of the cement slurry, so that the cement slurry can quickly form a strong cement stone after entering the leaking formation; the expansion agent is used to reduce the volume shrinkage of the cement stone during the solidification process of the plugging cement slurry, improve the bonding strength of the interface between the plugging cement slurry and the cracks and caves, and improve the plugging effect.

[0011] As a further improvement, for every 100 parts of oil well cement, the corresponding dosage of thixotropic agent is 2-5 parts, the dosage of drag reducer is 0.5-1.0 parts, the dosage of fiber plugging agent is 2-4 parts, the dosage of early strength agent is 2-2.5 parts and the dosage of expansion agent is 1.5-2.0 parts.

[0012] As a further improvement, the thixotropic agent is a bentonite-type thixotropic agent; and the drag reducer is a polycarboxylic acid-type drag reducer.

[0013] The beneficial effect of the above technical solution is that: it has been verified that the use of bentonite thixotropic agent and polycarboxylic acid drag reducer in combination can improve the rheological properties of cold slurry without destroying the anti-dispersion structure of cement slurry under 30-100°C conditions. After the cement slurry has been stationary for more than 20s, the slurry can quickly form a water-resistant dispersion structure.

[0014] As a further improvement, the expansion agent is a gas expansion agent.

[0015] The beneficial effect of the above technical solution is that after the gas expansion agent is aerated, a large number of tiny bubbles are distributed in the cement slurry. When the volume of the cement slurry decreases or the slurry column pressure decreases, the potential energy of the tiny bubbles is released, increasing the resistance of the cement slurry to entering cracks and caves.

[0016] As a further improvement, the main ingredient of the plugging cement includes a defoamer, and the amount of the defoamer used is 0.1-0.2 parts per 100 parts of oil well cement.

[0017] The beneficial effect of the above technical solution is that the defoaming agent is used to eliminate bubbles generated during the slurry mixing process.

[0018] In order to achieve the above-mentioned object, the technical solution of the drilling plugging cement slurry system in the present invention is:

[0019] A plugging cement slurry system for drilling, comprising the above-mentioned plugging cement composition for drilling and water.

[0020] The beneficial effects of the above technical solution are as follows: the plugging cement slurry of the present invention is composed of oil well cement, thixotropic agent, anti-dispersion flocculant, anti-dispersion regulator, drag reducer, fiber plugging agent, early strength agent, gas expansion agent, defoaming agent and water. It has the characteristic of not dispersing in water, reducing the mixing and dilution of the plugging cement slurry by formation water during the plugging process, and effectively forming a water barrier; the cement slurry has high shear and low viscosity, low shear and high viscosity thixotropic properties. After the plugging cement slurry enters large cracks and caves, as the flow rate slows down, the viscosity increases, which can effectively improve the retention effect of the plugging cement slurry; a large number of fiber plugging materials are distributed in the plugging cement slurry, which can bridge and adsorb on the surface of cracks and caves, increase the resistance of the plugging cement slurry to enter cracks and caves, and further increase the retention effect of the plugging cement slurry; after the gas expansion agent in the cement slurry is gasified, a large number of tiny bubbles are distributed in the cement slurry. When the volume of the cement slurry decreases or the slurry column pressure decreases, the potential energy of the tiny bubbles is released, increasing the resistance of the cement slurry to enter cracks and caves. The plugging cement slurry of the present invention exhibits good non-dispersion stability in water at a temperature between 20 and 90° C., and the strength of the cement stone formed in water can reach more than 80% of the strength of the cement stone formed in air.

[0021] Preferably, the oil well cement is Grade G high sulfate resistance oil well cement.

[0022] Thixotropic agents are used to enhance the thixotropic properties of cement slurry, enabling it to achieve both high shear and low viscosity, or low shear and high viscosity. This allows the slurry to quickly form a structure after settling, improving its retention capacity for leak-proofing. Preferably, the thixotropic agent is bentonite, which must be prehydrated at least 24 hours in advance to enhance the thixotropic properties of the slurry.

[0023] Anti-dispersion flocculants reduce the filtration loss of cement slurry while maintaining a relatively stable flocculation state between cement particles. This prevents the slurry from dispersing and mixing with water when it leaks into water-containing cracks and caves, enhancing the slurry's water-isolating properties within cracks and caves and ensuring that the leak-proof slurry remains within the cracks. Preferably, the anti-dispersion flocculant is an acrylamide-based fluid loss additive; more preferably, the anti-dispersion flocculant is BCY-100A, a type of acrylamide-based fluid loss additive. BCY-100A is produced by Tianjin PetroChina Boxing Engineering Technology Co., Ltd.

[0024] Anti-dispersion modifiers are used to adjust the rate at which plugging cement slurries form flocculation. Preferably, the anti-dispersion modifier is a naphthalenesulfonic acid formaldehyde condensate; more preferably, the anti-dispersion modifier is BCY-100B oil well cement anti-dispersion modifier. The BCY-100B oil well cement anti-dispersion flocculant is produced by Tianjin PetroChina Boxing Engineering Technology Co., Ltd.

[0025] Drag reducers improve the rheological properties of cement slurry and reduce flow resistance. Preferably, the drag reducer is a polycarboxylic acid drag reducer; more preferably, the drag reducer is BCD-210L medium-temperature resistant drag reducer for oil well cement. The BCD-210L medium-temperature resistant drag reducer for oil well cement is produced by Tianjin PetroChina Boxing Engineering Technology Co., Ltd.

[0026] The fiber plugging agent is used to improve the bridging and adsorption of cement slurry in cracks and holes, and gradually reduce the size of cracks and holes as the plugging cement slurry enters the cracks. Preferably, the fiber plugging agent is a composite fiber material with a fiber length of 2-10mm.

[0027] Early strength agents are used to increase the early compressive strength of cement paste and shorten the thickening time of cement slurry, allowing the cement slurry to quickly form strong cement paste after entering the lost-flow formation. Preferably, the early strength agent is a composite early strength agent; further preferably, the early strength agent is XJQ-2 oil well cement early strength agent. The XJQ-2 oil well cement early strength agent is produced by Henan Xinxing Building Materials Co., Ltd.

[0028] Expansive agents are used to increase the flow resistance of plugging cement slurry in cracks and caves, reduce the volume shrinkage of cement paste during the solidification process of plugging cement slurry in cracks and caves, and improve the interfacial bond strength between the plugging cement slurry and cracks and caves, thereby enhancing the plugging effect. Preferably, the expansive agent is a gaseous expansive agent; more preferably, the expansive agent is QJ625 oil well cement gas expansive agent. This QJ625 oil well cement gas expansive agent is produced by Weihui Chemical Co., Ltd.

[0029] The defoamer is used to eliminate bubbles generated during the slurry mixing process. Preferably, the defoamer is a silicone oil defoamer; further preferably, the defoamer is D50 defoamer. The D50 defoamer is produced by Tianjin PetroChina Boxing Engineering Technology Co., Ltd.

[0030] As a further improvement, the density of the cement slurry system is 1.5-1.75 g / cm 3 .

[0031] The beneficial effect of the above technical solution is that the cement slurry system has a wide density distribution range and is widely used.

[0032] In order to achieve the above-mentioned object, the technical solution of the preparation method of the plugging cement slurry system for drilling in the present invention is:

[0033] A method for preparing a plugging cement slurry system for drilling comprises the following steps:

[0034] 1) Mixing the formulated amounts of oil well cement, early strength agent, plugging fiber agent, and gas expansion agent to obtain a mixture A;

[0035] 2) adding a thixotropic agent to an appropriate amount of water and pre-hydrating to obtain a mixture B, adding a formulated amount of an anti-dispersion flocculant, an anti-dispersion regulator, a drag reducer, and a defoaming agent to the mixture B and mixing uniformly to obtain a mixture C;

[0036] 3) Mix mixture A and mixture C.

[0037] The preparation method of the drilling plugging cement slurry system of the present invention has simple process and convenient operation. The prepared cement slurry system has stable performance. When used, the mixture A and the mixture C can be mixed and injected into the well at the same time, and the construction is simple.

[0038] In order to further improve the mixing uniformity and mixing efficiency, preferably, in step 2), the mixing is performed by adding mixture A to mixture C within 10-15 seconds at a rotation speed of 3800-4200 r / min. After mixture A completely enters mixture C, high-speed stirring is performed at 11500-12500 r / min for 35 seconds to obtain drilling plugging cement slurry. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with specific embodiments. It should be noted that, unless otherwise specified, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used are all commercially available or commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0040] The raw materials used in the following examples are all commercially available products. The oil well cement used was G-grade high-sulfate-resistant oil well cement, purchased from Sichuan Jiahua Enterprise (Group) Co., Ltd.; the thixotropic agent was drilling-grade bentonite, purchased from Xianyang Fenghua Mud Material Co., Ltd.; the anti-dispersion flocculant BCY-100A (a transparent liquid), the anti-dispersion regulator BCY-100B (a brown solid powder), and the drag reducer BCD-210L (a brown liquid), purchased from Tianjin PetroChina Boxing Engineering Technology Co., Ltd.; the gas expansion agent was QJ625 oil well cement expansion agent, purchased from Henan Xinxing Building Materials Co., Ltd.; the early strength agent was XJQ-2 oil well cement early strength agent, purchased from Henan Xinxing Building Materials Co., Ltd.; and the defoaming agent was D50 defoaming agent, purchased from Tianjin PetroChina Boxing Engineering Technology Co., Ltd.

[0041] 1. Specific examples of the drilling plugging cement composition and cement slurry system of the present invention are as follows:

[0042] Example 1

[0043] The drilling plugging cement composition of this embodiment is composed of the following components in parts by weight: 100 parts of G-grade high sulfate-resistant oil well cement (oil well cement), 2 parts of drilling-grade bentonite, 4 parts of BCY-100A anti-dispersion flocculant, 0.1 parts of BCY-100B anti-dispersion regulator, 0.5 parts of BCD-210L drag reducer, 2.5 parts of F27A fiber plugging agent, 2 parts of XJQ-2 early strength agent, 1.5 parts of QJ625 gas expansion agent, and 0.1 parts of D50 defoaming agent.

[0044] The plugging cement slurry system for drilling of this embodiment is composed of water and the cement composition of this embodiment; the mass ratio of water to the oil well cement in the cement composition is 60:100.

[0045] Example 2

[0046] The drilling plugging cement composition of this embodiment is composed of the following components in parts by weight: 100 parts of G-grade high sulfate-resistant oil well cement (oil well cement), 3 parts of drilling-grade bentonite, 4.5 parts of BCY-100A anti-dispersion flocculant, 0.2 parts of BCY-100B anti-dispersion regulator, 0.7 parts of BCD-210L drag reducer, 2.5 parts of F27A fiber plugging agent, 2 parts of XJQ-2 early strength agent, 1.5 parts of QJ625 gas expansion agent, and 0.1 parts of D50 defoaming agent.

[0047] The drilling plugging cement slurry system of this embodiment is composed of water and the cement composition of this embodiment; the mass ratio of water to the oil well cement in the cement composition is 80:100.

[0048] Example 3

[0049] The drilling plugging cement composition of this embodiment is composed of the following components in parts by weight: 100 parts of G-grade high sulfate-resistant oil well cement (oil well cement), 3.5 parts of drilling-grade bentonite, 5.5 parts of BCY-100A anti-dispersion flocculant, 0.4 parts of BCY-100B anti-dispersion regulator, 0.7 parts of BCD-210L drag reducer, 3.0 parts of F27A fiber plugging agent, 2.5 parts of XJQ-2 early strength agent, 2.0 parts of QJ625 gas expansion agent, and 0.1 parts of D50 defoaming agent.

[0050] The plugging cement slurry system for drilling of this embodiment is composed of water and the cement composition of this embodiment; the mass ratio of water to the oil well cement in the cement composition is 95:100.

[0051] Example 4

[0052] The drilling plugging cement composition of this embodiment is composed of the following components in parts by weight: 100 parts of G-grade high sulfate-resistant oil well cement (oil well cement), 4 parts of drilling-grade bentonite, 7 parts of BCY-100A anti-dispersion flocculant, 0.5 parts of BCY-100B anti-dispersion regulator, 0.8 parts of BCD-210L drag reducer, 3.5 parts of F27A fiber plugging agent, 2.5 parts of XJQ-2 early strength agent, 2.0 parts of QJ625 gas expansion agent, and 0.1 parts of D50 defoaming agent.

[0053] The plugging cement slurry system for drilling of this embodiment is composed of water and the cement composition of this embodiment; the mass ratio of water to the oil well cement in the cement composition is 107:100.

[0054] 2. Specific examples of the preparation method of the drilling plugging cement slurry system of the present invention are as follows:

[0055] Example 5

[0056] The preparation method of the drilling plugging cement slurry system of this embodiment comprises the following steps:

[0057] (1) Preparation of mixture A:

[0058] Mixture A was prepared by mixing grade G high sulfate resistance oil well cement (oil well cement), F27A fiber plugging agent, XJQ-2 early strength agent, and QJ625 gas expansion agent at room temperature using an oil well cement dry mixing device for 5 minutes.

[0059] (2) Preparation of mixture B:

[0060] At room temperature, pour the formulated amount of water into a water tank with a stirrer at 100 r / min, then add the formulated amount of drilling-grade bentonite while stirring. Continue stirring for 15 minutes after addition. Place the mixture in a beaker and hydrate for 24 hours to obtain mixture B.

[0061] (3) Preparation of mixture C:

[0062] At room temperature, the formulated amount of mixture B was injected into a water tank with a stirrer, the speed was set to 100 r / min, and then the formulated amount of BCY-100A anti-dispersion flocculant, 0.7 parts of BCD-210L drag reducer, and 0.1 parts of D50 defoamer were added in sequence while stirring. After the addition, stirring was continued for 5 minutes, and then 0.1 parts of BCY-100B anti-dispersion regulator was added. Stirring was continued for 5 minutes to obtain mixture C.

[0063] (4) Place the mixture C obtained above in a constant speed stirrer device and set the speed to 4000 r / min. Then, add the mixture A to the stirring device at a uniform speed within 15 seconds. After all the solid materials disappear, set the speed to 12000 r / min and continue stirring for 35 seconds to obtain the plugging cement slurry for drilling.

[0064] The drilling plugging cement slurry systems of Examples 2-4 can be prepared accordingly with reference to the method of Example 5.

[0065] Based on the preparation method of the drilling plugging cement slurry system of the present embodiment, in step (4), the rotation speed is set to 3800r / min-4200r / min, and mixture A is added to mixture C at a uniform speed for a time varying from 10 to 15s, and cement slurry with performance equivalent to that of the present embodiment can be obtained.

[0066] 3. Comparative Example

[0067] Comparative Example 1

[0068] The drilling plugging cement slurry system of this comparative example is composed of the following components in parts by weight: 100 parts of G-grade high sulfate-resistant oil well cement (oil well cement), 2 parts of drilling-grade bentonite, 4 parts of G303L fluid loss additive, 0.5 parts of BCD-210L drag reducer, 2.5 parts of F27A fiber plugging agent, 2 parts of XJQ-2 early strength agent, 1.5 parts of QJ625 gas expansion agent, 0.1 part of D50 defoaming agent and 60 parts of water.

[0069] The preparation method is basically the same as that of Example 5. Compared with the formula of Example 1, the difference is that no anti-dispersion material is added when preparing mixture C. The fluid loss additive G303L of this comparative example is a powder and is added when preparing mixture A.

[0070] Comparative Example 2

[0071] The drilling plugging cement slurry system of this comparative example is composed of the following components in parts by weight: 100 parts of G-grade high sulfate-resistant oil well cement (oil well cement), 2 parts of drilling-grade bentonite, 4 parts of A-PAM anti-dispersion material, 0.5 parts of BCD-210L drag reducer, 2.5 parts of F27A fiber plugging agent, 2 parts of XJQ-2 early strength agent, 1.5 parts of QJ625 gas expansion agent, 0.1 parts of D50 defoaming agent and 60 parts of water.

[0072] The preparation method is basically the same as that of Example 5. The difference relative to the formulation of Example 1 is that A-PAM anti-dispersion material is added when preparing mixture C.

[0073] Comparative Example 3

[0074] The drilling plugging cement slurry system of this comparative example is composed of the following components in parts by weight: 100 parts of G-grade high sulfate-resistant oil well cement (oil well cement), 2 parts of drilling-grade bentonite, 0.1 parts of BCY-100B anti-dispersion regulator, 0.5 parts of BCD-210L drag reducer, 2.5 parts of F27A fiber plugging agent, 2 parts of XJQ-2 early strength agent, 1.5 parts of QJ625 gas expansion agent, 0.1 parts of D50 defoaming agent and 60 parts of water.

[0075] The preparation method is basically the same as that of Example 5. The difference from the formulation of Example 1 is that BCY-100A anti-dispersion flocculant is not added when preparing mixture C.

[0076] Comparative Example 4

[0077] The drilling plugging cement slurry system of this comparative example is composed of the following components in parts by weight: 100 parts of G-grade high sulfate-resistant oil well cement (oil well cement), 2 parts of drilling-grade bentonite, 4 parts of BCY-100A anti-dispersion flocculant, 0.5 parts of BCD-210L drag reducer, 2.5 parts of F27A fiber plugging agent, 2 parts of XJQ-2 early strength agent, 1.5 parts of QJ625 gas expansion agent, 0.1 part of D50 defoaming agent and 60 parts of water.

[0078] The preparation method is basically the same as that of Example 5. The difference relative to the formula of Example 1 is that 0.1 part of BCY-100B anti-dispersion regulator is used when preparing mixture C.

[0079] IV. Experimental Examples

[0080] Experimental Example 1

[0081] This experimental example is to test the engineering performance and plugging performance of the plugging cement slurry systems for drilling of Examples 1-4 and Comparative Examples 1-4. The testing method is as follows:

[0082] Engineering performance testing: measured in accordance with the standard "GB / 19139-2012 Oil Well Cement Test Method".

[0083] Plugging performance test: The leakage loss and plugging effect are tested in accordance with the petroleum and natural gas industry standard SY / T5840-2007 "Indoor test method for bridging plugging materials for drilling fluids". A plugging simulation device with a seam width of 4 mm is used to test the plugging performance of the present invention. The test conditions are 90°C×35MPa×40min.

[0084] Leakage plugging performance test: Strength test is carried out in accordance with the oil well cement test method GB-T19139 standard; the test process of the strength of the underwater cement stone is as follows: conventional cement slurry is prepared, and a standard grinding tool (50.8mm) is poured into the submerged grinding tool. 3 The strength of cement stone was tested after it was placed in water at a predetermined temperature (65°C) for 24 hours. The strength test process of cement stone formed in air was as follows: conventional cement slurry was prepared and poured into a standard mold (50.8mm 3 The cement stone strength was tested after being placed in water at a predetermined temperature (65°C) for 24 hours.

[0085] The engineering properties and plugging properties of the drilling plugging cement slurry systems of Examples 1-4 and Comparative Examples 1-4 are shown in Table 1.

[0086] Table 1 Performance index of plugging cement slurry

[0087]

[0088]

[0089] It can be seen from Table 1 that the engineering performance of the drilling plugging cement slurry meets the needs of on-site construction and has a good plugging effect.

[0090] Experimental Example 2

[0091] This experimental example tests the actual application of the drilling plugging cement slurry of Examples 1-4. The basic test results are as follows:

[0092] The target well on site uses the plugging cement slurry system for drilling of Examples 1-4 to plug the alkaline water layer cave with an overflow rate of 40-60 cubic meters per hour (alkaline water pressure equivalent of 1.21g / cm 3 ).

[0093] The overflow layer of well 1# is located at 2230-2240m, with an overflow volume of 55m 3 / h, the plugging string is lowered into the technical casing, and 10m 3 Isolation fluid, inject 20m 3 Example 3 Cement slurry, then inject 20m3 In Example 1, the cement slurry is displaced by injecting clean water to 30 m above the overflow layer, so that the cement can improve the pressure bearing capacity of the formation near the wellbore in the overflow well section and the overflow layer;

[0094] The overflow layer of well 2# is located at 2310-2315m, with an overflow volume of 60m 3 / h, the plugging string is lowered to the technical casing, and 20m 3 Isolation fluid, inject 20m 3 Example 2 Cement slurry, then inject 30m 3 In Example 1, the cement slurry is displaced by injecting clean water to 30 m above the overflow layer, so that the cement can improve the pressure bearing capacity of the formation near the wellbore in the overflow well section and the overflow layer;

[0095] The overflow layer of well 3# is located at 2190-2200m, with an overflow volume of 42m 3 / h, the plugging string is lowered into the technical casing, and 10m 3 Isolation fluid, inject 15m 3 Example 4 Cement slurry, then inject 20m 3 Example 1: Cement slurry is displaced by injecting clean water to 30m above the overflow layer, so that the cement can improve the pressure bearing capacity of the formation near the wellbore in the overflow well section and the overflow layer.

[0096] 3 test wells were successfully plugged at one time, and no more overflow occurred after drilling out the remaining cement stone in the wellbore. 3 The cement slurry continued to drill without overflow or loss. After drilling was completed, 1.60g / cm 3 The cement slurry cementing process did not cause leakage, indicating that the plugging cement slurry has a good sealing effect and high pressure bearing capacity. At the same time, the on-site configuration process is simple and easy to construct.

[0097] In summary, the drilling plugging cement slurry provided by the present invention has the characteristics of a wide density distribution range, no dispersion after contact with water, good retention effect, high wellbore pressure bearing capacity, and good plugging effect. It shows good non-dispersion stability in water between 20-90°C, and the strength of the cement stone formed in water can reach more than 80% of the strength of the cement stone formed in air.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be based on the claims. Any equivalent structural changes made using the contents of the description of the present invention shall also be included in the scope of protection of the present invention.

Claims

1. A cement composition for plugging well drilling, characterized in that: The invention comprises a main ingredient of plugging cement and an anti-water dispersing additive; the main ingredient of the plugging cement comprises oil well cement and a drag reducer; the anti-water dispersing additive comprises an anti-dispersing flocculant and an anti-dispersing regulator; and in parts by weight, for every 100 parts of oil well cement, the amount of the anti-dispersing flocculant is 4-7 parts, the amount of the anti-dispersing regulator is 0.1-0.5 parts, and the amount of the drag reducer is 0.5-1.0 parts; the anti-dispersing flocculant is an acrylamide polymer; the anti-dispersing regulator is a naphthalenesulfonic acid formaldehyde condensate; and the drag reducer is a polycarboxylic acid drag reducer.

2. The drilling plugging cement composition according to claim 1, wherein: The main material of the plugging cement also includes the following components: a thixotropic agent, a fiber plugging agent, an early strength agent and an expansion agent.

3. The drilling plugging cement composition according to claim 2, wherein: In parts by weight, for every 100 parts of oil well cement, the corresponding amount of thixotropic agent is 2-5 parts, the amount of fiber plugging agent is 2-4 parts, the amount of early strength agent is 2-2.5 parts and the amount of expansion agent is 1.5-2.0 parts.

4. The drilling plugging cement composition according to claim 2, wherein: The thixotropic agent is a bentonite-type thixotropic agent.

5. The drilling plugging cement composition according to claim 2, wherein: The expansion agent is a gas expansion agent.

6. The drilling plugging cement composition according to claim 1, wherein: The main ingredient of the plugging cement also includes a defoamer. Calculated by weight, the amount of the defoamer is 0.1-0.2 parts per 100 parts of oil well cement.

7. A plugging cement slurry system for drilling, characterized by: The cement slurry system comprises the drilling plugging cement composition according to any one of claims 1 to 6 and water.

8. The plugging cement slurry system for drilling according to claim 7, characterized in that: The density of the cement slurry system is 1.5-1.75 g / cm 3 .

Images