Experimental method and application of thickening of cement slurry with large temperature difference

Abstract

The application provides an experimental method for thickening of large-temperature-difference cementing slurry, wherein temperature and pressure in the experimental method are set as four stages, (1) temperature and pressure are increased from normal temperature and normal pressure to temperature and pressure simulating well bottom circulation; (2) the temperature and pressure are kept for 10-30 min; (3) temperature and pressure are decreased from the temperature and pressure simulating well bottom circulation to sealing temperature and sealing pressure; (4) the sealing temperature and sealing pressure are kept until the cementing slurry is thickened; wherein the sealing temperature and sealing pressure are respectively temperature and pressure of a static state at 1 / 2 of the cementing sealing section. The experimental method reasonably controls the hydration reaction rate of the top cementing slurry, and improves the early strength and overall sealing performance of the top cementing slurry.

Description

Technical Field

[0001] This invention relates to the field of measurement technology of thickening time of cement slurry for cementing, and specifically to experimental methods and applications for thickening cement slurry with large temperature difference. Background Technology

[0002] According to the definition of the thickening curve of oil well cement slurry in standard SY / T 5313-2006 "Drilling Engineering Terminology", the curve representing the change in cement slurry consistency over time under a specific temperature and pressure change program represents the thickening process that the cement slurry undergoes over time during heating or pressurization. Here, "specific temperature and pressure change program" refers to the process of raising the temperature (pressure) from its initial value to its final value at a specified heating (pressurization) rate. This program is set based on the requirements of experimental conditions to ensure that the temperature and pressure changes realistically simulate the on-site cementing conditions.

[0003] The API definition of cement slurry thickening time is the time elapsed from the start of heating and pressurization until the cement slurry reaches a specified consistency value (typically 100 Bc). This time indicator is commonly used to determine the cementing time during field cementing operations. If the thickening time is too short, it may lead to a "sausage-filling" accident during the injection process, affecting operational safety. If the thickening time is too long, the cement slurry may not solidify within the specified time, affecting the normal progress of subsequent drilling work.

[0004] In oil and gas well cementing engineering, the "leading slurry sealing section" refers to the well section sealed using a specific formula cement slurry (i.e., "leading slurry"). Leading slurry is typically used to seal the shallow or top areas of the wellbore, and its design must meet the following characteristics: 1) Ensure the sealing of the top or shallow section of the wellbore to prevent formation fluid cross-flow; 2) Provide early strength support to ensure the safety of subsequent drilling or completion operations.

[0005] In cementing operations in high-temperature deep wells, the current design of cement slurry thickening time is mainly based on the following principle: the thickening time of the slurry from injection into the wellhead casing to the bottom of the casing, and then back to the wellhead, plus an additional 120-180 minutes to cope with various situations that may occur during construction (such as equipment failure). The experimental method uses the bottom hole circulation temperature as the experimental temperature and the bottom hole fluid column pressure as the experimental pressure, conducting experiments under these temperature and pressure conditions. In the experiment, a high-temperature retarder is added for constant temperature and pressure thickening experiments. However, in actual construction, when the cement slurry is pumped from the bottom hole to the surface, there is a temperature difference of more than 50°C between the bottom hole and the surface, resulting in slow growth of the compressive strength at the top of the cement slurry, sometimes failing to reach the required strength of 7 MPa within 72 hours. Existing cement slurry designs are usually optimized only based on the bottom hole temperature, neglecting the significant impact of the low temperature at the top on the cement slurry's setting time and strength development. This neglect of the low temperature at the top leads to excessive retarder addition, resulting in over-retarded setting of the cement slurry at the top, severely affecting cementing quality.

[0006] The main reasons for the slow increase in compressive strength at the top of the cement slurry in the existing technology are as follows:

[0007] (1) Temperature difference affects the hydration reaction of cement slurry. Because the temperature at the bottom of the well is relatively high (usually exceeding 120°C), the hydration reaction rate of cement slurry at the bottom of the well is relatively fast. However, when the cement slurry returns to the wellhead or the top sealing section, the temperature drops sharply to below 50°C, the hydration reaction slows down significantly, and affects the early strength development of cement slurry.

[0008] (2) Excessive retarder affects strength development. Existing cement slurry designs are mainly optimized for bottom hole temperature, resulting in a higher amount of retarder added to ensure that the bottom hole construction time meets the requirements. However, in the low temperature environment at the top, excessive retarder slows down the hydration process of the cement slurry, making it impossible for the top cement slurry to reach the design strength for a longer period of time.

[0009] (3) The phenomenon of super-retarded setting of cement slurry at the top: Due to the low temperature environment at the top, the hydration reaction rate of cement slurry is significantly reduced. Some cement slurry may remain in an incompletely hydrated state for a long time, and even super-retarded setting may occur, making it impossible to reach the compressive strength requirement of 7MPa within 72 hours.

[0010] (4) Delayed Strength Development of Cement Slurry: In high-temperature deep well environments, the strength development of cement slurry is affected by the crystallization rate of hydration products and the dissolution rate of cement particles. The top cement slurry is located in a lower temperature region, and the hydration reaction kinetics are insufficient, resulting in delayed early strength formation and affecting the sealing effect.

[0011] Therefore, there is an urgent need for an experimental method for thickening cement slurry with large temperature difference in order to overcome the above-mentioned defects in the existing technology. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of the existing technology and provide an experimental method for thickening cement slurry with large temperature difference cementing. This experimental method can reasonably control the hydration reaction rate of the top cement slurry and improve the early strength and overall sealing performance of the top cement slurry.

[0013] To achieve the above objectives, the first aspect of the present invention provides an experimental method for thickening cement slurry in cementing with large temperature difference, characterized in that: the temperature and pressure in the experimental method are set into four stages: (1) increasing the temperature and pressure from normal temperature and pressure to the temperature and pressure of simulated bottom hole circulation; (2) maintaining the temperature and pressure for 10-30 minutes; (3) decreasing the temperature and pressure from the temperature and pressure of simulated bottom hole circulation to the sealing temperature and sealing pressure; (4) maintaining the sealing temperature and sealing pressure until the cement slurry thickens; wherein the sealing temperature and sealing pressure are the static temperature and pressure at 1 / 2 of the cementing section.

[0014] This invention ensures the accurate performance of cement slurry in simulated high-temperature bottom and low-temperature top environments by rationally controlling the temperature and pressure during heating, pressurization, constant temperature and pressure, and cooling and depressurization processes, and by employing precise temperature and pressure control methods. It also makes the hydration process of cement slurry at different depths conform to actual cementing conditions, and prevents insufficient strength at the top of the cement slurry caused by excessive addition of retarder while ensuring construction safety.

[0015] In high-pressure thickening experiments, temperature control stability is crucial. Current high-temperature, high-pressure thickening instruments may continue to heat up after reaching the target temperature, resulting in temperature fluctuations of 3-5°C, before returning to the target temperature. Immediately cooling down after reaching the target temperature can lead to uncontrolled temperature fluctuations, affecting the accuracy of experimental data. Therefore, to ensure system temperature stability, a 10-30 minute isothermal phase should be set after reaching the target temperature, followed by gradual cooling to ensure the consistency and repeatability of experimental data. To accurately assess the development of the cement slurry's top strength, the experimental temperature and pressure should be reduced to the static temperature and pressure at the middle half of the cementing section. This temperature and pressure more accurately reflect the thermal environment of the cement slurry during cementing operations, avoiding localized errors that may result from relying solely on the lowest temperature and pressure.

[0016] In some embodiments of the present invention, the bottom-hole circulation temperature is determined based on surface temperature, geothermal gradient, and bottom-hole vertical depth: T button =(T Top +Geothermal Gradient × D) * coefficient;

[0017] Among them, T button Temperature of the wellbore circulation (°C); T Top: Surface temperature (°C); Geothermal Gradient: Geothermal gradient (°C / 100m), i.e., the increase in temperature per 100 meters of depth; D: Vertical depth at the bottom of the well (m); The coefficient is an empirical value, ranging from 0.5 to 1.00.

[0018] In some embodiments of the present invention, the bottom hole circulation pressure is determined based on the drilling fluid density and the vertical depth of the bottom hole: P button =ρ liquid ×D×0.0098;

[0019] Among them, P button : Bottom hole circulation pressure (MPa); ρ liquid Drilling fluid density (g / cm³) 3 D: Vertical depth at the bottom of the well (m).

[0020] In some embodiments of the present invention, the temperature range of the bottom hole circulation is 90°C-200°C; the pressure range of the bottom hole circulation is 40-200 MPa.

[0021] In some embodiments of the present invention, the cooling rate is determined based on the bottom hole circulation temperature, the sealing temperature, and the running time of the cement slurry in that section: Cooling rate = (T button -T top,static ) / t run ;

[0022] Among them, T button Temperature of the wellbore circulation (°C); T top,static Sealing temperature (°C); t run : The running time (min) of cement slurry in this section.

[0023] In some embodiments of the present invention, the pressure reduction rate is determined based on the bottom hole circulation pressure, the sealing pressure, and the running time of the cement slurry in that section: Pressure reduction rate = (P button -P top,static ) / t run ;

[0024] Among them, P button : Bottom hole circulation pressure (MPa); P top,static Sealing pressure (MPa); t run : The running time (min) of cement slurry in this section.

[0025] This invention uses a gradual cooling and depressurization method to ensure that the hydration process of the cement slurry at different depths conforms to the actual cementing conditions, preventing uneven solidification caused by excessively rapid cooling and depressurization, and improving the stability and overall sealing performance of the cement slurry.

[0026] In some embodiments of the present invention, the amount of early strength agent added is 0.5-1% of the cement weight.

[0027] In some embodiments of the present invention, the compressive strength of the slurry within 48 hours is ≥7MPa.

[0028] A second aspect of the present invention provides an application of the above-described experimental method in vertical or directional wells.

[0029] A third aspect of the present invention provides an application of the above-mentioned experimental method in a horizontal well, the experimental method further comprising the following steps: in step (2), the duration for which the temperature and pressure are kept stable is consistent with the actual running time of the cement slurry in the horizontal section, and then step (3) is performed to cool down and depressurize.

[0030] In horizontal well experiments, since the cement slurry naturally forms a constant temperature state during its flow in the horizontal section, the duration of this constant temperature stage should match the residence time of the cement slurry from the casing outlet to a position where the well inclination angle is less than 80°.

[0031] The technical solution provided by this invention has the following beneficial effects:

[0032] (1) This invention achieves the real performance of cement slurry in simulated high temperature bottom and low temperature top environments by reasonably controlling the temperature and pressure during the heating and pressurization, constant temperature and pressure and cooling and pressurization processes, and adopting precise temperature and pressure control methods, thereby improving the accuracy of experimental data; making the hydration process of cement slurry at different depths conform to the actual cementing working conditions, and preventing insufficient strength at the top of cement slurry caused by excessive addition of retarder under the premise of ensuring construction safety.

[0033] (2) In high-pressure thickening experiments, the stability of temperature control is crucial. Current high-temperature high-pressure thickeners may continue to heat up after reaching the target temperature, resulting in temperature fluctuations of 3-5℃, before returning to the target temperature. If the temperature is immediately lowered after reaching the target temperature, it may lead to uncontrolled temperature fluctuations, affecting the accuracy of experimental data. Therefore, to ensure system temperature stability, a 10-30 minute isothermal phase should be set after reaching the target temperature, followed by gradual cooling to ensure the consistency and repeatability of experimental data.

[0034] (3) In order to accurately assess the development of the strength at the top of the cement slurry, the experimental temperature and pressure should be reduced to the static temperature and pressure at the middle half of the cementing section. This temperature and pressure can more accurately reflect the thermal environment of the cement slurry during the cementing process and avoid local errors that may be caused by relying solely on the lowest temperature and pressure. Attached Figure Description

[0035] Figure 1 A schematic diagram of the high-temperature and high-pressure thickening experimental method for vertical wells, directional wells, and horizontal wells;

[0036] Figure 2(a) shows the thickening experiment diagram of Comparative Example 1 with temperature, pressure and time.

[0037] Figure 2(b) shows the thickening experiment of Example 1 under temperature, pressure and time. Detailed Implementation

[0038] To make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the materials used in the embodiments are commercially available products or conventional products that can be synthesized by known methods.

[0039] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0040] Example 1: High-Temperature and High-Pressure Thickening Experiment and Compressive Strength Test in Vertical Wells

[0041] This embodiment uses a vertical well as an example, with the following specific parameters:

[0042] Well depth: 5000m

[0043] Drilling fluid density: 1.40 g / cm³ 3

[0044] Geothermal gradient: 3℃ / 100m

[0045] Surface temperature: Ignore (calculated directly using the geothermal gradient)

[0046] Bottom hole circulation temperature calculation:

[0047] T button =3×5000 / 100×0.8=120℃

[0048] Bottom hole pressure calculation:

[0049] P button =1.40×5000×0.0098=68.6MPa.

[0050] Sealing temperature: Static temperature at 1 / 2 of the grout sealing section (static temperature corresponding to a depth of 1500m):

[0051] T top,static=120℃-(5000m-1500m)×3℃ / 100m=45℃

[0052] Sealing pressure: Static liquid column pressure at 1 / 2 of the grout sealing section:

[0053] P top,static =1.40×1500×0.0098=20.58MPa

[0054] Cooling rate = (120℃ - 45℃) / 75min = 1.0℃ / min

[0055] Pressure drop rate = (68.6 MPa - 20.58 MPa) / 75 min = 0.64 MPa / min

[0056] The control instrument was cooled and depressurized to the target value at a rate of 1.0℃ / min and 0.64MPa / min, and then kept at constant temperature and pressure until the end of the experiment.

[0057] The time when the thickening time reaches 100 Bc is recorded as the baseline thickening time T. According to construction requirements, T must meet the following conditions: annular volume (150 m³ / s). 3 ) + casing internal volume (57.8m 3 Divide by the construction discharge volume (1.4m) 3 The retarder loading time is 148 min ( / min), with a stopper loading time of 10 min. The final reference thickening time range is 158-188 min. If the experimental results do not meet the requirements, adjust the amount of retarder and retest.

[0058] The experimental method for thickening cement slurry with large temperature difference is described, with the temperature and pressure in the experimental method set in four stages: (1) increasing the temperature and pressure from room temperature and pressure to 120℃ and 68.6MPa; (2) setting the temperature to 120℃ and the pressure to 68.6MPa, and conducting a constant temperature and pressure thickening experiment; (3) cooling down to 45℃ and depressurizing to 20.58MPa at rates of 1.0℃ / min and 0.64MPa / min; (4) maintaining 45℃ and 20.58MPa until the cement slurry thickens. The thickening experimental process is shown in Figure 2(b).

[0059] Strength test: The adjusted cement slurry sample was placed in a high temperature and high pressure curing autoclave and treated according to the above temperature rise and fall procedure (120℃×68.6MPa constant temperature for 20 minutes, then cooled to 45℃×20.7MPa).

[0060] After curing at 45℃ and 20.7MPa for 48 hours, the compressive strength of the cement paste is tested. If the strength is ≥7MPa, the formula is qualified; otherwise, an early strength agent (0.5-1% of the cement weight) needs to be added, and the test should be repeated until the standard is met.

[0061] Experimental results:

[0062] The standard thickening time is 172 min (meets the requirement of 158-188 min); the heating and cooling thickening time is 11 hours and 45 minutes (meets the requirement of ≥158 min); the compressive strength is 8.2 MPa after 48 hours (≥7 MPa, qualified).

[0063] Example 2: High-Temperature and High-Pressure Thickening Experiment and Compressive Strength Test of Horizontal Wells

[0064] For horizontal wells, the experimental procedures are as follows:

[0065] Constant temperature and pressure stage:

[0066] The bottom circulation temperature was set to 120℃ and the pressure to 68.6MPa, and the temperature was maintained for 30 minutes (simulating the residence time of cement slurry in the horizontal section).

[0067] Cooling and depressurization phase:

[0068] Based on the cooling rate (1.0℃ / min) and pressure reduction rate (0.64MPa / min) of the vertical well, the temperature is reduced to a static temperature of 45℃ and a pressure of 20.58MPa at 1 / 2 of the slurry sealing section.

[0069] Strength test:

[0070] The curing conditions were the same as those for the vertical well, and the compressive strength was 7.5 MPa after 48 hours, which met the requirements.

[0071] Example 3: Synergistic optimization of retarder and accelerator

[0072] If the compressive strength does not meet the standard (e.g., the strength is 6.0 MPa after 48 hours), adjust the formula:

[0073] Early strength agent addition: Add 0.8% by weight of nano-silica-based early strength agent to the cement slurry.

[0074] Repeat the experiment:

[0075] The adjusted baseline thickening time is 180 min, the heating and cooling thickening time is 12 hours, and the compressive strength is increased to 7.9 MPa after 48 hours.

[0076] Example 4: Verification of Dynamic Cooling Program for Directional Wells

[0077] For directional wells, the method for calculating the cooling rate has been adjusted:

[0078] For well sections with an inclination angle of 80°: the cement slurry running time is extended by 10%, the cooling rate is adjusted to 0.9℃ / min, and the pressure reduction rate is 0.58MPa / min.

[0079] Experimental results: Compressive strength 7.3 MPa, which meets the requirements.

[0080] Comparative Example 1

[0081] This comparative example uses traditional cementing test methods, conducting isothermal and isobaric experiments based solely on bottom hole temperature, without simulating the temperature rise and fall process. Specific parameters are as follows:

[0082] Well depth: 5000m

[0083] Experimental temperature: 120℃ (bottom hole circulation temperature)

[0084] Experimental pressure: 68.6 MPa (bottomhole hydrostatic pressure)

[0085] Experimental conditions: The cement slurry was kept at a constant temperature and pressure until its consistency reached 100 Bc, and then cured at 120℃ and 68.6 MPa for 48 hours to test its strength. The thickening experiment process is shown in Figure 2(a).

[0086] Experimental results:

[0087] Reference thickening time: 150 min (meets construction time requirements)

[0088] Compressive strength (at bottom hole temperature): 14.5 MPa (qualified)

[0089] Compressive strength (at a static temperature of 45°C at the top): 5.0 MPa (<7 MPa, unqualified)

[0090] Experimental instruments and data recording

[0091] Equipment: High-temperature and high-pressure thickening apparatus (accuracy ±1℃, ±0.5MPa), curing autoclave (temperature control accuracy ±2℃), universal pressure testing machine.

[0092] Data acquisition: Temperature, pressure, thickening time, and intensity development curves are recorded in real time through an online monitoring system.

[0093] The performance parameters of Examples 1-4 and Comparative Example 1 are shown in Table 1.

[0094] Table 1

[0095]

[0096] A comparison of Examples 1-4 with Comparative Example 1 shows that:

[0097] 1) Thickening time and construction safety:

[0098] The comparative benchmark has a short thickening time (150 min), which meets the requirements for bottom hole construction, but does not take into account the actual time consumption of the heating and cooling process, which poses a construction risk.

[0099] The heating and cooling thickening time (11.5-12h) in Examples 1-4 is dynamically simulated to ensure that the cement slurry remains stable during the operation time from the bottom to the top of the well by simulating real well conditions, thus avoiding problems such as "sausage filling" or delayed solidification.

[0100] 2) Compressive strength and sealing quality:

[0101] The comparative example showed a compressive strength of only 5.0 MPa at a low temperature (45°C) at the top, which is far below the requirement of 7 MPa, leading to the risk of sealing failure.

[0102] The example demonstrates how optimizing the formulation through temperature rise and fall experiments (such as adding 0.8% early strength agent) can increase the top strength to 7.3-8.2 MPa, effectively solving the problem of ultra-retarded setting.

[0103] 3) Retarder dosage and cost:

[0104] The comparison requires 100% retarder dosage to control the thickening time at the bottom of the well, but the top of the well has an excessive amount of retarder due to a sudden drop in temperature, which exacerbates the insufficient strength.

[0105] The example demonstrates how dynamic temperature control and synergistic optimization reduce the amount of retarder to 70-75%, lowering costs while increasing top strength.

[0106] 4) Adaptability verification:

[0107] Comparative models are only applicable to single well bottom conditions and cannot adapt to large temperature differences or complex well types (such as horizontal wells and directional wells).

[0108] The implementation examples adjust experimental parameters for different well types (e.g., adding a constant temperature section for horizontal wells and adjusting the cooling rate for directional wells) to ensure the universality of the method.

[0109] A comparison is made between the conventional method (Comparative Example 1) and Embodiment 1 of the present invention, as shown in Figures 2(a) and 2(b):

[0110] Thickening curve: The traditional method has a short thickening time (226 min) under constant temperature conditions, but after temperature rise and fall simulation, the thickening time is extended to 11 h 45 min, which is closer to the actual working conditions.

[0111] Strength curve: Traditional methods show slow strength growth at top temperature (only 5.0 MPa after 48 hours), while the method of this invention achieves 5.8 MPa in 24 hours and stabilizes at ≥7 MPa after 48 hours.

[0112] As can be seen from the comparison, the present invention significantly solves the problem of insufficient top strength caused by ignoring the temperature gradient in traditional methods through dynamic temperature control simulation and formula optimization, while reducing the amount of retarder by 20-30%, thereby improving cementing quality and economic benefits.

[0113] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. An experimental method for thickening cement slurry under large temperature differences, characterized in that: The temperature and pressure in the experimental method are set into four stages: (1) increasing the temperature and pressure from room temperature and pressure to the simulated bottom hole circulation temperature and pressure; (2) maintaining the temperature and pressure for 10-30 minutes; (3) decreasing the temperature and pressure from the simulated bottom hole circulation temperature and pressure to the sealing temperature and sealing pressure; (4) maintaining the sealing temperature and sealing pressure until the cement slurry thickens; wherein the sealing temperature and sealing pressure are the static temperature and pressure at 1 / 2 of the slurry sealing section.

2. The experimental method according to claim 1, characterized in that: The bottom-hole circulation temperature (T) is determined based on surface temperature, geothermal gradient, and vertical depth at the bottom of the well. button =(T Top +Geothermal Gradient × D) * coefficient; Among them, T button Temperature of the wellbore circulation (°C); T Top : Surface temperature (°C); Geothermal Gradient: Geothermal gradient (°C / 100m), i.e., the increase in temperature per 100 meters of depth; D: Vertical depth at the bottom of the well (m); The coefficient is an empirical value, ranging from 0.5 to 1.

00.

3. The experimental method according to claim 1, characterized in that: Determine the bottom hole circulation pressure based on drilling fluid density and vertical depth at the bottom of the well: P button =ρ liquid ×D×0.0098; Among them, P button : Bottom hole circulation pressure (MPa); ρ liquid Drilling fluid density (g / cm³) 3 D: Vertical depth at the bottom of the well (m).

4. The experimental method according to claim 1, characterized in that: The temperature range of the bottom hole circulation is 90℃-200℃; the pressure range of the bottom hole circulation is 40-200MPa.

5. The experimental method according to any one of claims 1-4, characterized in that: The cooling rate is determined based on the bottom hole circulation temperature, sealing temperature, and the running time of the cement slurry in this section: Cooling rate = (T button -T top,static ) / t run ; Among them, T button Temperature of the wellbore circulation (°C); T top,static Sealing temperature (°C); t run : The running time (min) of cement slurry in this section.

6. The experimental method according to any one of claims 1-4, characterized in that: The pressure reduction rate is determined based on the bottom hole circulation pressure, sealing pressure, and the running time of the cement slurry in that section: Pressure reduction rate = (P button -P top,static ) / t run ; Among them, P button : Bottom hole circulation pressure (MPa); P top,static Sealing pressure (MPa); t run : The running time (min) of cement slurry in this section.

7. The experimental method according to claim 1, characterized in that: The amount of early strength agent added is 0.5-1% of the cement weight.

8. The experimental method according to claim 1, characterized in that: The compressive strength of the slurry within 48 hours is ≥7MPa.

9. The application of the experimental method according to any one of claims 1-8 in vertical or directional wells.

10. The application of the experimental method according to any one of claims 1-8 in a horizontal well, the experimental method further comprising the following steps: In step (2), the temperature and pressure are maintained for the same duration as the actual running time of the cement slurry in the horizontal section, and then step (3) is performed to cool down and depressurize.

Images