High-temperature-resistant thixotropic cement paste and application thereof

Abstract

The invention provides high-temperature-resistant thixotropic cement paste and application thereof. The cement paste comprises cement, first fly ash, slag, silica sand, a thixotropic agent, a fluid loss agent, a retarder and water.

Description

Technical Field

[0001] This invention relates to the fields of oilfield chemistry and oil and gas well cementing materials, specifically to a thixotropic cement slurry suitable for preventing gas channeling during cementing. Background Technology

[0002] The high-temperature, high-pressure gas wells in Shunbei have active gas layers that are difficult to stabilize, resulting in poor formation sealing quality. Multiple wells require secondary pressure testing, compromising safe production. While current wellbore structures prevent the sealing of high-pressure gas layers, the shortcomings in preventing gas channeling during cementing will inevitably constrain the drilling and development of high-pressure gas wells in Shunbei as the oilfield develops. Overcoming this bottleneck will bring about technological innovation. Stabilizing the gas layer directly affects the success or failure of cementing high-pressure gas layers. Seven cement slurry systems already in use, including those for high-temperature gas generation, elastic latex, brine granules, latex silica, and emulsion silica, have all failed to effectively stabilize the formation.

[0003] Research indicates that thixotropic cement slurry exhibits the characteristic of its gel structure being destroyed under shear stress and rapidly recovering after rest. The ability to quickly achieve high gel strength after pumping stops is the primary reason for preventing gas channeling. Furthermore, once it enters the transition state, the further development of gel strength also helps prevent mechanical deformation of the liquid column and the generation of air bubbles, thus achieving the goal of preventing gas channeling. However, a mature thixotropic cement slurry system is currently lacking, and the high temperatures of the northerly air layer, exceeding 170℃, pose significant challenges to the research of thixotropic cement slurry systems. Summary of the Invention

[0004] One aspect of the present invention provides a cement slurry comprising cement, first fly ash, slag, silica sand, thixotropic agent, water loss reducing agent, retarder, and water.

[0005] In one specific embodiment, the cement is Grade G oil well cement.

[0006] In one specific embodiment, the particle size of the first fly ash is 1000 to 1250 mesh.

[0007] In one specific embodiment, the slag has a particle size of 1000 to 1250 mesh.

[0008] In one specific embodiment, the silica sand has a particle size of 120 to 200 mesh.

[0009] In one specific embodiment, the slag is S95 grade slag and / or S105 grade slag.

[0010] In one specific embodiment, the thixotropic agent is formed by combining a second fly ash with a synthesized polymeric thixotropic agent, wherein the synthesized polymeric thixotropic agent is formed by polymerizing 2-acrylamide-2-methylpropanesulfonic acid and acrylamide, with a mass ratio of 2-acrylamide-2-methylpropanesulfonic acid to acrylamide of (3-4):(7-6). The crosslinking agent used in the synthesis of the polymeric thixotropic agent is N,N-methylenebisacrylamide (MBA), which is added at 0.5% to 3% of the total monomer mass. The initiator used is ammonium persulfate, which is added at 1% to 4% of the total monomer mass. The particle size of the second fly ash is 200 to 500 mesh, and its addition is 800% to 900% of the total monomer mass.

[0011] In one specific embodiment, the water loss reducing agent is SCF180 and / or BXF-200L.

[0012] In one specific embodiment, the retarder is DHZ-3.

[0013] In one specific embodiment, based on the total mass of cement, first fly ash, slag, and silica sand as 100%, the amount of cement is 40% to 50%, the amount of first fly ash is 15% to 25%, the amount of slag is 10% to 20%, the amount of silica sand is 15% to 25%, the amount of thixotropic agent is 4% to 6%, the amount of water loss reducing agent is 5% to 8%, and the amount of retarder is 5% to 6%.

[0014] In one specific embodiment, the water-to-solid ratio of the cement slurry is 0.44.

[0015] The second invention relates to the application of cement slurry according to any one of the first inventions in cementing high-temperature gas wells.

[0016] In one specific embodiment, the high temperature can be up to 180°C.

[0017] The beneficial effects of this invention are:

[0018] The high-temperature thixotropic cement slurry system of the present invention can achieve the purpose of maintaining good anti-gas channeling performance of cement slurry even under high temperature conditions of 180℃. It can be used for anti-gas channeling cementing of high temperature and high pressure gas wells in Shunbei, and has obvious good application and promotion prospects. Attached Figure Description

[0019] Figure 1 The thixotropic properties of the cement slurry prepared based on the formulation of Example 1 are shown in the test at 130°C.

[0020] Figure 2 The thixotropic properties of the cement slurry prepared based on the formulation of Example 2 are shown in the test at 170°C.

[0021] Figure 3 The thixotropic properties of the cement slurry prepared based on the formulation of Example 3 are shown in the test at 180°C.

[0022] Figure 4 The thixotropic properties of the cement slurry prepared based on the formulation of Comparative Example 1 are shown in the test at 140°C. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments. However, the embodiments of the present invention are merely illustrative examples and should not be construed as limiting the present invention under any circumstances.

[0024] The thixotropic agent is the one specified in CN202010736175.4, which is formed by combining fly ash with a synthetic polymer thixotropic agent. The synthetic polymer thixotropic agent is formed by polymerizing 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and acrylamide (AM), with a mass ratio of 2-acrylamido-2-methylpropanesulfonic acid to acrylamide of (3-4):(7-6). The crosslinking agent used in the synthesis of the polymer thixotropic agent is N,N-methylenebisacrylamide (MBA), which is added at 0.5% to 3% of the total monomer mass. The initiator used is ammonium persulfate, which is added at 1% to 4% of the total monomer mass. The particle size of the fly ash can be 200 to 500 mesh, and its addition is 800% to 900% of the total monomer mass.

[0025] One specific thixotropic agent was prepared as follows: 4 parts by mass of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), 6 parts by mass of acrylamide (AM), and 0.2 parts by mass of MBA were dissolved in 36 parts by mass of water to form a solution. Then, 0.2 parts by mass of ammonium persulfate was added to the solution to form solution I. 90 parts by mass of fly ash were added to solution I and stirred until homogeneous to form slurry I. Slurry I was reacted at 75°C for 2 hours, then dried and pulverized to obtain the thixotropic agent.

[0026] Example 1

[0027] Cement slurry was prepared according to GB / T10238-2015 standard: 4 parts by weight of G-grade oil well cement, 1.5 parts by weight of 1000-mesh fly ash, 2 parts by weight of S95-grade slag with a particle size of 1000 mesh, and 2.5 parts by weight of 120-mesh silica sand; the total mass of cement, fly ash, slag, and silica sand was taken as 100%, water loss reducer SCF180 5%, retarder DHZ-3 5%, and thixotropic agent 4%; then water was added to make the water-solid ratio 0.44.

[0028] The specific preparation process is as follows: the cementitious system (G-grade oil well cement, fly ash, slag and silica sand) and thixotropic agent are dry-mixed to obtain a dry-mix component; water, water loss reducer and retarder are wet-mixed to obtain a wet-mix component; the dry-mix component and the wet-mix component are mixed to form cement slurry SA.

[0029] Example 2

[0030] Cement slurry was prepared according to GB / T10238-2015 standard: 5 parts by weight of G-grade oil well cement, 2 parts by weight of 1250-mesh fly ash, 1 part by weight of S105-grade slag with a particle size of 1250 mesh, and 2 parts by weight of 200-mesh silica sand; the total mass of cement, fly ash, slag, and silica sand was taken as 100%, and water loss reducing agent BXF-200L 6%, retarder DHZ-3 6%, and thixotropic agent 5% were added; then water was added to make the water-solid ratio 0.44.

[0031] The specific preparation process is as follows: the cementitious system (G-grade oil well cement, fly ash, slag and silica sand) and thixotropic agent are dry-mixed to obtain a dry-mix component; water, water loss reducer and retarder are wet-mixed to obtain a wet-mix component; the dry-mix component and the wet-mix component are mixed to form cement slurry SB.

[0032] Example 3

[0033] Cement slurry was prepared according to GB / T10238-2015 standard: 5 parts by weight of G-grade oil well cement, 2.5 parts by weight of 1250-mesh fly ash, 1 part by weight of S105-grade slag with a particle size of 1250 mesh, and 1.5 parts by weight of 250-mesh silica sand; the total mass of cement, fly ash, slag, and silica sand was taken as 100%, water loss reducer SCF180 8%, retarder DHZ-3 8%, and thixotropic agent 6%; then water was added to make the water-solid ratio 0.44.

[0034] The specific preparation process is as follows: the cementitious system (G-grade oil well cement, fly ash, slag and silica sand) and thixotropic agent are dry-mixed to obtain a dry-mix component; water, water loss reducer and retarder are wet-mixed to obtain a wet-mix component; the dry-mix component and the wet-mix component are mixed to form cement slurry SC.

[0035] Comparative Example 1

[0036] Cement slurry was prepared according to GB / T10238-2015 standard: 5 parts by weight of G-grade oil well cement, 2 parts by weight of 1250-mesh fly ash, 1 part by weight of S105-grade slag with a particle size of 1250 mesh, and 2 parts by weight of 250-mesh silica sand; the total mass of cement, fly ash, slag, and silica sand was taken as 100%, water loss reducer SCF180 8%, and retarder DHZ-3 8%; then water was added to make the water-solid ratio 0.44.

[0037] The specific preparation process is as follows: dry-mix the cementitious system G-grade oil well cement, fly ash, slag and silica sand to obtain dry-mix components; wet-mix the water, water loss reducer and retarder to obtain wet-mix components; mix the dry-mix components with the wet-mix components to form cement slurry SD.

[0038] Cement grout performance testing

[0039] The on / off consistency increment method is the most direct way to observe the thixotropic properties of cement slurry under high temperature and high pressure conditions.

[0040] During the thickening experiment of cement slurry, stirring was stopped, and the cement slurry was allowed to stand. The slurry will develop thixotropic strength. After a certain period, the mixer was restarted, and the stirring blades began to operate. At this point, the cement slurry was sheared, breaking its thixotropic strength. This is reflected in the thickening curve as consistency fluctuations. However, thixotropy is a reversible gelling state, so after breaking the thixotropy, the consistency of the cement slurry recovers. Three start-stop cycles were performed to test the repeatability of thixotropy. Cement slurries prepared based on the formulations of Examples 1 to 3 and Comparative Example 1 were used. After preparing the cement slurry according to the GB / T10238-2015 standard, the thickening temperature was raised to the specified temperature, and the mixer was stopped and allowed to stand for 15 minutes. Then, the mixer was restarted, and the consistency increment method was used for testing. The more significant the consistency increment, the better the thixotropic properties of the cement slurry. The test results are as follows: Figures 1 to 4 As shown.

[0041] from Figure 1 It can be seen that at 130℃, the viscosity increase during switching on and off is about 20 Bc, and it can be repeatedly thixotropic 3 times, demonstrating excellent thixotropic performance.

[0042] from Figure 2 It can be seen that at 170℃, the viscosity increase during switching on and off is about 15 Bc, and it can be repeatedly thixotropic 3 times, demonstrating excellent thixotropic performance.

[0043] from Figure 3 It can be seen that at 180℃, the consistency increase between shut-off and start-up is about 10 Bc, and it can be repeatedly thixotropic 5 times. Within the test range, the cement slurry exhibits significant thixotropic properties, and its high-temperature thixotropic performance is also significant. Under 180℃ conditions, the thixotropic properties are good, and it can still recover its fluidity after repeated thixotropic cycles, and it also has excellent right-angle thickening performance.

[0044] from Figure 4 It can be seen that at 140℃, the consistency increase of cement slurry between turning the machine on and off is only about 5, indicating that the cementitious system has certain thixotropic properties, but the thixotropic properties are weak without the addition of a thixotropic agent.

[0045] While the present invention has been described with reference to specific embodiments, those skilled in the art will understand that various changes can be made without departing from the true spirit and scope of the invention. Furthermore, numerous modifications can be made to the subject, spirit, and scope of the invention to suit specific situations, materials, material compositions, and methods. All such modifications are included within the scope of the claims of the present invention.

Claims

1. A cement slurry comprising cement, first fly ash, slag, silica sand, thixotropic agent, water loss reducing agent, retarder, and water.

2. The cement grout according to claim 1, characterized in that, The cement is Grade G oil well cement.

3. The cement grout according to claim 1, characterized in that, The particle size of the first fly ash is 1000 to 1250 mesh; and / or The slag has a particle size of 1000 to 1250 mesh; and / or The silica sand has a particle size of 120 to 200 mesh.

4. The cement grout according to claim 1, characterized in that, The slag is S95 grade slag and / or S105 grade slag.

5. The cement grout according to claim 1, characterized in that, The thixotropic agent is formed by combining the second fly ash with a synthesized polymeric thixotropic agent. The synthesized polymeric thixotropic agent is formed by polymerizing 2-acrylamide-2-methylpropanesulfonic acid and acrylamide, with a mass ratio of 2-acrylamide-2-methylpropanesulfonic acid to acrylamide of (3-4):(7-6). The crosslinking agent used in the synthesis of the polymeric thixotropic agent is N,N-methylenebisacrylamide (MBA), which is added at 0.5% to 3% of the total monomer mass. The initiator used is ammonium persulfate, which is added at 1% to 4% of the total monomer mass. The particle size of the second fly ash is 200 to 500 mesh, and its addition is 800% to 900% of the total monomer mass.

6. The cement grout according to claim 1, characterized in that, The water loss reducing agent is SCF180 and / or BXF-200L.

7. The cement grout according to claim 1, characterized in that, The retarder is DHZ-3.

8. The cement grout according to claim 1, characterized in that, The total mass of cement, first fly ash, slag, and silica sand is taken as 100%, wherein the amount of cement is 40% to 50%, the amount of first fly ash is 15% to 25%, the amount of slag is 10% to 20%, the amount of silica sand is 15% to 25%, the amount of thixotropic agent is 4% to 6%, the amount of water loss reducing agent is 5% to 8%, and the amount of retarder is 5% to 6%.

9. The cement grout according to claim 1, characterized in that, The water-to-solid ratio of the cement slurry is 0.

44.

10. The application of the cement slurry according to any one of claims 1 to 9 in cementing high-temperature gas wells.

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