Cementing fluid for casing and method for cementing casing

Abstract

The application discloses a casing-in-casing well fracture plugging fluid and a casing-in-casing well cementing method, the fracture plugging fluid comprises the following components in parts by weight: water: 100 parts, polypropylene fiber: 0.4-1 parts, walnut shell: 4-9 parts, pH response hydrophobic association plugging agent: 2-5 parts, and defoaming agent: 1-4 parts. The fracture plugging fluid is pumped to the bottom of the well; after the well is closed, the plugging fluid is continuously positively squeezed into the formation fracture until the pump pressure reaches 5-6 MPa; then, the well cementing slurry is pumped into the casing annulus of the well, so that the well cementing slurry is in contact with the plugging fluid in the fracture and reacts until the well cementing slurry is solidified. The fracture plugging fluid is simple in composition, low in cost, short in construction period, extremely simple in operation, low in cost and good in plugging effect.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well technology, specifically to a casing-in-casing cementing well fracture plugging fluid and a casing-in-casing cementing method. Background Technology

[0002] Shale gas reservoirs are characterized by low porosity, low permeability, and no natural production capacity. Their efficient development requires large-scale hydraulic fracturing to create artificial fractures and provide seepage channels for production. However, this process suffers from rapid production decline and a short period of stable production after the initial fracturing. Therefore, it is necessary to install small casing in the original wellbore, cement the casing, and then perform repeated fracturing to revive shale gas well productivity.

[0003] The technique of cementing old shale gas wells by running small casings is called casing-in-casing cementing. Because old shale gas wells contain original fractures from the initial fracturing, these original fractures need to be sealed before cementing operations to prevent cement slurry leakage into the fractures and affecting cementing safety. The original fractures formed during the initial fracturing are numerous, deep, and have low pressure, making plugging operations difficult. Traditional bridging plugging materials are insufficient to form a tight sealing layer in the fractures, resulting in unsatisfactory plugging effects. Therefore, researching and developing plugging fluid systems with good sealing capabilities is of great significance.

[0004] For wells requiring de-plugging of lost circulation fluid in fractures after cementing, using water-absorbing resin as the main agent in the plugging fluid offers significant advantages. When de-plugging is needed, peroxidizers (such as ammonium persulfate) can be used to decompose the water-absorbing resin and release the plug. Although water-absorbing resin has significant advantages in de-plugging, to improve its sealing ability, sodium hydroxide alkaline solution needs to be injected after the plugging fluid is injected into the fracture, and cementing can only proceed after 24 hours or longer, resulting in prolonged construction time and increased costs. For wells that do not require de-plugging after plugging, developing a plugging fluid and method with good sealing effect and short construction cycle is of great significance. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems and provide a casing-solidified well fracture plugging fluid that is simple in composition, low in cost, and has a good sealing effect.

[0006] This invention also provides a simple, easy-to-operate, effective, and short-cycle method for cementing inner casing wells.

[0007] The casing-type well fracture plugging fluid of the present invention comprises the following components in parts by weight: water: 100 parts, polypropylene fiber: 0.4-1 parts, walnut shell: 4-9 parts, pH-responsive hydrophobic associative plugging agent: 2-5 parts, and defoamer: 1-4 parts.

[0008] The pH-responsive hydrophobic associative blocking agent is prepared by uniformly mixing 100 parts water, 16 parts acrylic acid, 4 parts methacrylic acid, 4.75 parts vinylpyridine, 0.25 parts dodecyl methacrylate, 1 part urea, and 0.3 parts ammonium persulfate, curing at 60°C for 4 hours, and then drying and pulverizing.

[0009] The defoamer is a polyether-type defoamer or an organosilicon-type defoamer.

[0010] The length of the polypropylene fiber is 0.8-1.2 mm.

[0011] The walnut shells mentioned have a particle size of 2-3 mm.

[0012] The present invention relates to a casing cementing method, in which the aforementioned fracture plugging fluid is pumped to the bottom of the well; after shutting in the well, the plugging fluid is continuously pumped into the formation fractures until the pump pressure reaches 5-6 MPa; then, cementing slurry is pumped into the downhole casing annulus, so that the cementing slurry comes into contact with the plugging fluid in the fractures and reacts until the cement slurry solidifies.

[0013] The aforementioned crack plugging fluid is pumped to the bottom of the well and then pumped to a depth of 200-500m above the leaking layer before shutting in the well.

[0014] The cementing slurry is pumped into the downhole casing annulus until it returns to the preset position.

[0015] The cementing slurry is silicate cement slurry.

[0016] In response to the problems existing in the background technology, and for wells that do not require unplugging after plugging, a solid casing well fracture plugging fluid that can be quickly plugged is designed. Among them, (1) the walnut shell and fiber in the plugging fluid work together to bridge and seal in the perforation hole and formation fracture. The reason for using the combination of the two is that the walnut shell has high strength and can play a good supporting and bridging role in the fracture. The fiber can fill the gap between the walnut shell particles. Compared with using them alone, the combination can achieve better efficient sealing of the fracture. (2) A pH-responsive hydrophobic associative plugging agent is introduced into the solid technology, so that the plugging fluid containing the plugging agent has thixotropic properties. It contains a large number of carboxylic acid groups and has low viscosity under acidic conditions. Therefore, it has good fluidity when pumped and can be quickly delivered to the well and smoothly enter the fracture. After sealing the fracture and perforation hole, the cement slurry subsequently delivered is alkaline. After contact with it, the viscosity of the pH-responsive hydrophobic associative plugging agent will increase rapidly and significantly under neutral and alkaline conditions, thereby effectively enhancing the plugging effect and ensuring the cementing quality. Using the above principle, after injecting the plugging fluid, there is no need to wait for a long time. Cementing slurry can be injected directly for cementing construction, which greatly shortens the construction cycle; (3) The carboxylic acid groups in the pH-responsive hydrophobic associative plugging agent will also undergo cross-linking under the action of calcium ions, so that the pH-responsive hydrophobic associative plugging agent cross-links to form a gel, which is very beneficial to improving the plugging ability of the plugging fluid. Among them, the amount of pH-responsive hydrophobic associative plugging agent added should be controlled at 2-5 parts. Too much will make it difficult to meet the construction requirements for the amount of leakage of the plugging fluid, while too little will result in poor thixotropy.

[0017] This invention adds a pH-responsive hydrophobic associative plugging agent to the plugging fluid and cleverly combines it with cementing slurry. This ensures both the flowability of the plugging fluid during pumping and significantly improves the leak-proof capability during plugging, ensuring the cementing quality of casing-in-casing wells. After plugging, cementing can be carried out directly. The cementing method of this invention has a short construction cycle, is extremely simple to operate, has low cost, and has a good plugging effect. Detailed Implementation

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the embodiments or the prior art will be briefly described below. Obviously, the following description is only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these embodiments without creative effort. All parts in the following embodiments are parts by weight.

[0019] Example 1

[0020] Leakage sealing agent preparation: Prepare the leakage sealing solution according to the following formula: 100 parts water, 0.4 parts polypropylene fiber, 4 parts walnut shell, 2 parts pH-responsive hydrophobic associative sealing agent, and 1 part defoamer.

[0021] The pH-responsive hydrophobic associative blocking agent is prepared by mixing 100 parts water, 16 parts acrylic acid, 4 parts methacrylic acid, 4.75 parts vinylpyridine, 0.25 parts dodecyl methacrylate, 1 part urea, and 0.3 parts ammonium persulfate, curing at 60°C for 4 hours, and then drying and pulverizing.

[0022] Experiment: The initial viscosity of the prepared sealing fluid was 10 Pa·S. After adding 3 parts of cement, the viscosity of the sealing fluid was 195 Pa·S.

[0023] In a shale gas well with a depth of 3800 meters, before cementing operations were carried out, plugging fluid was pumped to the bottom of the well using coiled tubing. The well was shut in 200 meters above the leaking layer. After shutting in, the plugging fluid was continuously pumped into the formation fractures until the pump pressure reached 5 MPa. Cement slurry was then pumped into the downhole casing annulus until the cement slurry returned to the preset position.

[0024] Subsequent well logging calculations showed that the lost cement slurry was 0.1 m. 3 The cement slurry leakage was minimal, and the cementing operation proceeded smoothly.

[0025] Example 2

[0026] Leakage sealant preparation: 100 parts water, 0.7 parts polypropylene fiber, 6 parts walnut shell, 4 parts pH-responsive hydrophobic associative sealant, and 2 parts defoamer; the preparation of the pH-responsive hydrophobic associative sealant is the same as in Example 1.

[0027] Experiment: The viscosity of the prepared sealing fluid was 15 Pa·S in its initial state. After adding 3 parts of cement to the sealing fluid, the viscosity of the sealing fluid was 290 Pa·S.

[0028] In a shale gas well with a depth of 3900 meters, before cementing operations were carried out, plugging fluid was pumped to the bottom of the well using coiled tubing. The well was shut in 500 meters above the leaking layer. After shutting in, the plugging fluid was continuously pumped into the formation fractures until the pump pressure reached 6 MPa. Cement slurry was then pumped into the downhole casing annulus until the cement slurry returned to the preset position.

[0029] Subsequent well logging calculations showed that the lost cement slurry was 0.1 m. 3 The cement slurry leakage was minimal, and the cementing operation proceeded smoothly.

[0030] Example 3

[0031] Leakage sealing agent preparation: Prepare a leakage sealing solution by using 100 parts water, 1 part polypropylene fiber, 9 parts walnut shell, 5 parts pH-responsive hydrophobic associative sealing agent, and 3 parts defoamer; the preparation of the pH-responsive hydrophobic associative sealing agent is the same as in Example 1.

[0032] The initial viscosity of the prepared sealing fluid was 18 Pa·S. After adding 3 parts of cement to the sealing fluid, the viscosity of the sealing fluid was 335 Pa·S.

[0033] In a shale gas well with a depth of 4200 meters, before cementing operations were carried out, plugging fluid was pumped to the bottom of the well using coiled tubing and pumped to 400m above the leaking layer before shutting in the well. After shutting in the well, plugging fluid was continuously pumped into the formation fractures until the pump pressure reached 6MPa. Cement slurry was then pumped into the downhole casing annulus until the cement slurry returned to the preset position.

[0034] Subsequent logging calculations showed that the lost cement slurry was 0.06 m. 3 The cement slurry leakage was minimal, and the cementing operation proceeded smoothly.

[0035] Comparative Example 1

[0036] Leak-sealing agent preparation: Prepare the leak-sealing solution according to the following proportions: 100 parts water, 0.4 parts polypropylene fiber, 4 parts walnut shell, 3 parts polyacrylamide, and 1 part defoamer.

[0037] Experiment: The initial viscosity of the prepared sealing fluid was 10 Pa·S. After adding 3 parts of cement to the sealing fluid, the viscosity of the sealing fluid was 12 Pa·S.

[0038] A shale gas well, 3800 meters deep, was constructed using the same method as in Example 1.

[0039] Subsequent well logging calculations indicated a cement slurry loss of 3m. 3 The leakage is significant, which is very detrimental to cementing operations.

[0040] Comparative Example 2

[0041] Leak-sealing agent preparation: Prepare the leak-sealing solution according to the following formula: 100 parts water, 0.8 parts polypropylene fiber, 6 parts walnut shell, 4 parts polyacrylamide, and 1 part defoamer.

[0042] Experiment: The initial viscosity of the prepared sealing fluid was 13 Pa·S. After adding 3 parts of cement to the sealing fluid, the viscosity of the sealing fluid was 15 Pa·S.

[0043] A shale gas well, 3900 meters deep, was constructed using the same method as in Example 2.

[0044] Subsequent well logging calculations showed that the lost cement slurry was 2m. 3 The leakage is significant, which is very detrimental to cementing operations.

[0045] Comparative Example 3

[0046] Leakage sealing agent preparation: Prepare the leakage sealing solution according to the following formula: 100 parts water, 0.8 parts polypropylene fiber, 6 parts walnut shell, 7 parts pH-responsive hydrophobic associative sealing agent, and 1 part defoamer.

[0047] Excessive addition of pH-responsive hydrophobic associative sealant resulted in excessively high viscosity of the sealing solution, making it difficult to prepare and impossible to pump.

Claims

1. A plugging fluid for fractures in a casing-bonded well, characterized in that, The components include the following parts by weight: water: 100 parts, polypropylene fiber: 0.4 to 1 part, walnut shell: 4 to 9 parts, pH-responsive hydrophobic associative sealing agent: 2 to 5 parts, and defoamer: 1 to 4 parts; The pH-responsive hydrophobic associative blocking agent is prepared by uniformly mixing 100 parts water, 16 parts acrylic acid, 4 parts methacrylic acid, 4.75 parts vinylpyridine, 0.25 parts dodecyl methacrylate, 1 part urea, and 0.3 parts ammonium persulfate, curing at 60°C for 4 hours, and then drying and pulverizing. The defoamer is a polyether-type defoamer or an organosilicon-type defoamer; the length of the polypropylene fiber is 0.8-1.2 mm.

2. The casing-solidified well fracture plugging fluid as described in claim 1, characterized in that, The walnut shells mentioned have a particle size of 2-3 mm.

3. A method for cementing a casing within a casing, characterized in that, Pump the fracture plugging fluid as described in claim 1 or 2 to the bottom of the well; after shutting in the well, continue to pump the plugging fluid into the formation fracture until the pump pressure reaches 5-6 MPa; then pump the cementing slurry into the downhole casing annulus to allow the cementing slurry to contact and react with the plugging fluid in the fracture until the cement slurry solidifies.

4. The casing-in-casing cementing method as described in claim 3, characterized in that, The aforementioned crack plugging fluid is pumped to the bottom of the well and then pumped to a depth of 200-500m above the leaking layer before shutting in the well.

5. The casing-in-casing cementing method as described in claim 3, characterized in that, The cementing slurry is pumped into the downhole casing annulus until the cementing mud returns to the preset position.

6. The casing-in-casing cementing method according to any one of claims 3-5, characterized in that, The cementing slurry is silicate cement slurry.