A method for determining the best logging time for evaluating cementing quality

Abstract

The present application relates to a kind of cementing quality evaluation optimal logging time determination method, belong to well logging exploration technical field.The present application utilizes the compressive strength of cement stone of reference point to calculate the logging theory amplitude value when completely cemented, and according to the requirement that the cementing quality evaluation standard within the set range is influenced by candidate setting time within the optimal time, the amplitude value corresponding to the upper limit of medium cementation of optimal logging time is determined;And the compressive strength of cement stone is deduced back with the amplitude value corresponding to the upper limit of medium cementation of this optimal logging time, if the deduced back compressive strength reaches the set threshold, then the optimal logging time is the final optimal logging time, otherwise the time when compressive strength value reaches the set threshold is the optimal logging time.The present application can obtain reasonable cementing quality evaluation optimal logging time according to the characteristics of cement slurry system and downhole environment, significantly improve the accuracy and rationality of cementing quality evaluation, and effectively shorten construction cycle.

Description

TECHNICAL FIELD

[0001] The application relates to a method for determining the optimal logging time for evaluating cementing quality, and belongs to the technical field of well logging exploration. BACKGROUND

[0002] With the continuous development of cementing technology and cementing process, in order to cope with the complex and diverse downhole environment, various types of cement slurry systems have been developed, such as low-temperature cementing cement slurry system, high-temperature cementing cement slurry system, low-density cement slurry system and high-density cement slurry system. However, due to the addition of a large amount of density adjusting agent, retarder or accelerator and other additives in these systems, the hydration rate and strength change law of the cement have changed greatly, which brings great difficulty to the reasonable determination of the optimal time. The optimal logging time for evaluating cementing quality needs to consider the logging accuracy, downhole safety and time cost.

[0003] The current standard "SY / T 6592-2016: Cementing Quality Evaluation Method" gives the guidance that the conventional density cementing cementing time is not less than 24h for shallow wells, not less than 48h for deep wells, not less than 72h for ultra-deep wells, and the low-density cementing cementing time is not less than 48h. However, with the change of cement slurry system and downhole environment and the requirement of cost reduction and efficiency increase of drilling, this standard cannot be completely applicable. The main problems are as follows: (1) The influence of temperature on the optimal logging time for evaluating cementing quality is not considered. Temperature is the main factor affecting the speed of cement hydration reaction. For example, the low temperature condition faced by deep water cementing will lead to the reduction of cement hydration rate, the increase of cement slurry setting time and the slow development of cement strength, so that the annular cement sheath cannot provide enough shear stress to suspend the casing in a short time. At the same time, due to the short setting time, the sound amplitude value obtained by the cementing quality logging evaluation cannot reflect the real cementing quality, which will cause wrong evaluation results and even unnecessary remedial measures. Similarly, for high-temperature wells, the cement hydration rate is fast, and the cement stone can reach a very high strength in a short time. Therefore, the setting time can be appropriately reduced to shorten the well construction period according to the actual situation. (2) For low-density cement slurry system and ultra-low-density cement slurry system (density less than 1.30g / cm3), the cement content is low, and the cement strength is low. If the setting time is short, the cementing quality evaluation logging result may not reflect the real cementing quality, and the types and amounts of additives will also have some influence on the logging result. (3) The influence of the types and amounts of additives on the logging time is not considered. Retarder, accelerator and strength enhancer can greatly affect the early hydration reaction and strength change law of the cement stone. The acoustic logging response reflected by different logging times will change greatly. SUMMARY

[0004] The application aims to provide a method for determining the optimal logging time for cementing quality evaluation, so as to solve the problem of inaccurate determination of the optimal logging time.

[0005] The application provides a method for determining the optimal logging time for cementing quality evaluation, which comprises the following steps:

[0006] 1) Obtain the compressive strength value of the cement stone under the set curing condition, take the compressive strength value as the reference point strength value, and determine the longitudinal wave speed and the transverse wave speed of the cement stone corresponding to the reference point according to the relationship between the compressive strength value and the longitudinal wave speed and the transverse wave speed of the cement stone;

[0007] 2) Calculate the logging theoretical amplitude value at the time of complete cementation under the set curing condition according to the longitudinal wave speed and the transverse wave speed of the cement stone corresponding to the reference point;

[0008] 3) Calculate the upper limit value of the medium cementation according to the logging theoretical amplitude value at the time of complete cementation, and determine the amplitude value corresponding to the upper limit of the medium cementation at the optimal logging time according to the requirement that the cementing quality evaluation standard within the optimal time is affected by the setting time within the set range;

[0009] 4) Take the upper limit amplitude value of the medium cementation corresponding to the optimal logging time as the upper limit value of the medium cementation, and inversely deduce the logging theoretical amplitude value at the time of complete cementation;

[0010] 5) Determine the longitudinal wave speed, the transverse wave speed and the compressive strength value of the cement stone according to the inversely deduced logging theoretical amplitude value at the time of complete cementation;

[0011] 6) Judge whether the obtained compressive strength value is greater than the set threshold value, if yes, the optimal time determined is the optimal logging time; otherwise, the time when the compressive strength value reaches the set threshold value is the optimal logging time.

[0012] The application calculates the logging theoretical amplitude value at the time of complete cementation by using the compressive strength of the cement stone of the reference point, determines the amplitude value corresponding to the upper limit of the medium cementation at the optimal logging time according to the requirement that the cementing quality evaluation standard within the optimal time is affected by the setting time within the set range, inversely deduces the compressive strength of the cement stone by using the upper limit amplitude value of the medium cementation corresponding to the optimal logging time, and if the inversely deduced compressive strength reaches the set threshold value, the optimal logging time is the final optimal logging time, otherwise, the time when the compressive strength value reaches the set threshold value is the optimal logging time. The application can obtain a reasonable optimal logging time for cementing quality evaluation according to the characteristics of the cement slurry system and the downhole environment, significantly improves the accuracy and rationality of the cementing quality evaluation, and effectively shortens the construction cycle.

[0013] Further, in order to ensure the accuracy of the reference point selection, the curing conditions in the step 1) include that the curing temperature is 75 degrees Celsius and the curing time is 10 days.

[0014] Further, the calculation formula of the well logging theoretical amplitude value in the step 2) is as follows:

[0015]

[0016]

[0017] wherein, α T is the attenuation rate of the leakage Lamb wave in the casing to the casing wave, dB / m; A J is the received amplitude, that is, the well logging theoretical amplitude value, %; A f is the amplitude emitted by the transmitter, %; l is the well logging source distance, m; ρ is the density of the cement slurry, g / cm 3 ; h is the thickness of the casing, m.

[0018] Further, in order to ensure that the selected optimal time can meet the requirement that the influence of the setting time is within 5%, the upper limit value of the medium cementation in the step 3) refers to the received theoretical amplitude value when the cementation index is 0.6.

[0019] Further, the calculation formula of the upper limit value of the medium cementation is as follows:

[0020]

[0021] wherein, A f0.6 is the received theoretical amplitude value when the cementation index is 0.6, %; A0 is the emitted theoretical amplitude value when the cementation is complete, %; α T is the attenuation rate of the leakage Lamb wave in the casing to the casing wave, dB / m; l is the well logging source distance, m.

[0022] Further, the set range in the step 3) is 5%.

[0023] Further, the upper limit amplitude value of the medium cementation corresponding to the optimal well logging time determined in the step 3) is 1.05A f0.6 , A f0.6 is the received theoretical amplitude value when the cementation index is 0.6.

[0024] Further, the set threshold is 3.45 MPa.

[0025] Further, the relationship between the compressive strength value in the step 1) and the longitudinal wave speed and the transverse wave speed of the cement stone is obtained through experimental data fitting. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a flow chart of the method for determining the best logging time for cementing quality evaluation of the present application;

[0027] Figure 2 is a schematic diagram of the relationship between the compressive strength and the curing time (70℃) in Example 1 of the present application, wherein the cement slurry system is 1.25 g / cm 3 is a schematic diagram of the relationship between the longitudinal and transverse wave velocities of the cement slurry system and the curing time (70℃);

[0028] Figure 3 is a schematic diagram of the relationship between the compressive strength and the curing time (70℃) in Example 1 of the present application, wherein the cement slurry system is 1.25 g / cm 3

[0029] Figure 4 is a schematic diagram of the relationship between the compressive strength and the longitudinal and transverse wave velocities in Example 1 of the present application;

[0030] Figure 5 is a schematic diagram of the effect of the density on the best logging time in Example 2 of the present application;

[0031] Figure 6 is a schematic diagram of the effect of the retarder on the best waiting-on-cement time for cementing quality evaluation in Example 3 of the present application;

[0032] Figure 7 is a schematic diagram of the effect of the temperature on the best logging time in Example 4 of the present application. DETAILED DESCRIPTION

[0033] The specific embodiments of the present application will be further described in conjunction with the accompanying drawings.

[0034] The logging response for cementing quality evaluation is influenced by a variety of factors, including the casing size, the type of well fluid in the casing, the instrument eccentricity, the waiting-on-cement time, the bottom hole environment, the cement formulation, the cementing condition, etc. The effect of the logging time on the logging response mainly manifests in that, if the logging time is too early, the cement stone velocity and strength have not been fully developed, resulting in a high casing wave amplitude and a false interpretation result; if the logging time is too late, unnecessary downtime will be caused, increasing the construction cost. Therefore, the reasonable determination of the best logging time is to control the influence of the waiting-on-cement time on the logging response for cementing quality evaluation and the evaluation standard within a certain range. The general engineering allowable error is 5%, so the best logging time can be defined as that within the best time, the influence of the waiting-on-cement time on the cementing quality evaluation standard is within 5%, i.e. the influence of the waiting-on-cement time on the casing wave amplitude is within 5% when the cementing is good (the cementing index BI = 0.8) and when the cementing is poor (the cementing index BI = 0.6).

[0035] ​Therefore, the application proposes a method for determining the best logging time for evaluating the cementing quality according to the change law of the strength and acoustic characteristics of the cement stone corresponding to each density cement slurry system, in combination with the downhole acoustic field analysis of the casing well, so as to obtain the reasonable best logging time for evaluating the cementing quality, significantly improve the accuracy and rationality of the cementing quality evaluation, effectively shorten the construction cycle, and remarkably improve the economic benefit. The implementation process of the method is shown in Figure 1 The specific calculation process is as follows.

[0036] 1. Determine the relationship between the acoustic and strength characteristics of the cement to be evaluated.

[0037] According to the experimental analysis, the longitudinal and transverse wave velocities of the cement stone have corresponding exponential relationships with the compressive strength, so the expression of the quantitative relationship between the longitudinal wave velocity and the compressive strength of the cement stone is as follows:

[0038]

[0039] The expression of the quantitative relationship between the transverse wave velocity and the compressive strength of the cement stone is as follows:

[0040]

[0041] wherein P is the compressive strength of the cement stone to be checked; v p is the longitudinal wave velocity of the cement stone to be checked; v s is the transverse wave velocity of the cement stone to be checked; and a, b, c and d are respectively coefficients obtained through experimental data fitting.

[0042] 2. Determine the compressive strength of the cement stone of the reference point and the corresponding longitudinal and transverse wave velocities of the cement stone.

[0043] Obtain the compressive strength value of the cement stone under the set curing condition, and take the compressive strength value as the reference point strength value.

[0044] Determine the logging response of the reference point corresponding to the cementing quality evaluation standard.

[0045] Through the investigation of the status quo of the similar technologies at home and abroad and the analysis of the experimental results, it is known that the longitudinal and transverse wave velocities of the cement stone and the compressive strength increase with the increase of the curing time, but will tend to be stable when the increase reaches a certain degree. The application takes the compressive strength at the time of tending to be stable as the reference point compressive strength. In this embodiment, the compressive strength of the cement stone is measured under the curing temperature of 75℃ and the curing time of 10 days, and the compressive strength is taken as the reference point compressive strength. The reference point compressive strength is substituted into the formula (1) and the formula (2) to obtain the longitudinal and transverse wave velocities of the cement stone corresponding to the reference point.

[0046] 3. Calculate the logging theoretical amplitude value when the reference point is completely cemented.

[0047] The present application determines the logging theoretical amplitude value when the cement stone is completely cemented according to the cement stone longitudinal and transverse wave speed values corresponding to the obtained reference points.

[0048] That is, the present application brings the cement stone longitudinal and transverse wave speed values (curing condition: 75℃, 10 days) corresponding to the obtained reference points into formula (3) and formula (4) to obtain the logging theoretical amplitude value when completely cemented under the curing condition:

[0049]

[0050]

[0051] α T is the attenuation rate of the casing wave caused by the leakage Lamb wave in the casing, dB / m; A J is the sound amplitude received by the receiver, i.e. the logging theoretical amplitude value when completely cemented, %; A f is the sound amplitude emitted by the transmitter, %; l is the logging source distance, m; ρ is the density of the cementing slurry, g / cm 3 ; h is the thickness of the casing, m.

[0052] 4. Determine the theoretical amplitude values of the upper and lower limits of the medium cementation according to the logging theoretical amplitude value when the reference point is completely cemented.

[0053] The present application selects the cementation index between 0.6-0.8 as medium cementation, takes the cementation index 0.6 as the upper limit of the medium cementation, and takes the cementation index 0.8 as the lower limit of the medium cementation, and calculates the sound amplitude values corresponding to the upper and lower limits of the medium cementation according to the α T determined by formula (3), and the formula used is:

[0054] Lower limit of medium cementation:

[0055] Upper limit of medium cementation:

[0056] In the formula, A f0.6 is the theoretical sound amplitude value received when the cementation index is 0.6, %; A f0.8 is the theoretical sound amplitude value received when the cementation index is 0.8, %; A0 is the theoretical sound amplitude value emitted when completely cemented, %; α T is the attenuation rate of the casing wave caused by the leakage Lamb wave in the casing, dB / m; l is the logging source distance, m.

[0057] 5. Determine the upper limit sound amplitude value of the medium cementation corresponding to the optimal logging time point.

[0058] Through comparative analysis, A f0.8 , A f0.6Both change with the speed of sound, but a comparison shows that A f0.6 The percentage change is higher. Therefore, according to the requirement that the cementing quality evaluation standard within the optimal time is affected by the waiting time by less than 5%, it can be known that the acoustic amplitude value corresponding to the upper limit of medium cementation when the optimal logging time is reached is 1.05A. f0.6 .

[0059] 6. Based on the upper limit acoustic amplitude value of medium cementation corresponding to the optimal logging time point, inversely infer the theoretical acoustic amplitude value of the well and determine the corresponding compressive strength.

[0060] First, the acoustic amplitude value corresponding to the upper limit of medium cementation at the optimal logging time point is used as the updated acoustic amplitude value corresponding to the upper limit of medium cementation, i.e., 1.05A. f0.6 As A in formula (6) f0.6 Substituting this into formula (6) allows us to recalculate the corresponding α. T Then the obtained α T Substituting into formula (3), the longitudinal wave velocity and transverse wave velocity of the cement stone can be deduced. Finally, by substituting the obtained longitudinal wave velocity and transverse wave velocity of the cement stone into formula (1) and formula (2), the corresponding compressive strength of the cement stone can be calculated. The compressive strength of the cement stone is the compressive strength of the cement stone corresponding to the optimal logging time.

[0061] 7. Determine the optimal logging time based on the obtained compressive strength of the cement stone.

[0062] If the compressive strength corresponding to the optimal logging time is greater than 3.45 MPa, meeting the requirements for continuing drilling, it means that after the logging operation is completed, if the cementing quality is found to be acceptable, subsequent drilling operations can proceed. In this case, the optimal logging time is the final optimal logging time. If the compressive strength is less than 3.45 MPa, then the final optimal logging time should be based on the time when the strength reaches 3.45 MPa. The curing environment should be set according to the actual downhole conditions at the construction site, and the time corresponding to when the compressive strength reaches the required value is the optimal logging time.

[0063] To further illustrate the effects of the present invention, the method of the present invention will now be applied to specific examples for analysis.

[0064] Example 1

[0065] Taking the ultra-low density cement slurry system with a density of 1.25 g / cm³ commonly used in the Dongsheng Gas Field as an example, its cement slurry system formula is: Jiahua G-grade oil well cement + 25% cenosphere 1 + 22% cenosphere 2 + 20% microsilica + 140% water + 4% early strength agent + 3.5% fluid loss reducer + 0.20% drag reducer. The longitudinal and transverse wave velocities and compressive strength of the cement were measured through indoor tests, and their variation over time was obtained as shown in the attached figure. Figure 1 and attached Figure 2 As shown.

[0066] By the attached Figure 2 and attached Figure 3 It can be seen that with the increase of curing time, the longitudinal and transverse wave velocity of cement stone and compressive strength are constantly increasing, and the growth rate is faster within 72h, and the growth rate is slow after 72h, and gradually tends to be stable. This is because the cement in the early stage of calcium silicate hydration generates hydrated calcium silicate gel and calcium hydroxide crystals, which has a fast reaction speed, forms early strength and generates early hydration heat. The hydration of dicalcium silicate generates hydrated calcium silicate gel and calcium hydroxide crystals, which has a slow reaction speed, plays a key role in the development of cement late strength.

[0067] At the same time, the compressive strength and longitudinal and transverse wave velocity of the cement stone are fitted and analyzed, which satisfies a good exponential relationship, as shown in the attached Figure 4 .

[0068] The relationship between the longitudinal and transverse wave velocity and the compressive strength can be expressed as:

[0069]

[0070]

[0071] According to the actual site, the calculation parameters are introduced as follows: logging source distance 0.914m, casing wall thickness 10.36mm, casing density 7.85g / cm 3 , casing longitudinal wave velocity 5900m / s. According to the compressive strength of 14MPa at 10 days and the aforementioned steps, the compressive strength of 8.1MPa is calculated to meet the best waiting time, which is greater than 3.45MPa, so the node when the compressive strength reaches 8.1MPa is selected as the best waiting time. Therefore, the best waiting time of the cement slurry system under the condition of 70℃ is 36.0h.

[0072] Example 2:

[0073] The best logging time of each density cement slurry under the condition of 70℃ curing is calculated according to the above method, and the relationship is shown in the attached Figure 5 .

[0074] From the attached Figure 5 It can be seen that the best logging time decreases with the increase of density. When the density of the cement system is 1.10g / cm 3 , the corresponding best waiting time is 80h, and when the density of the cement system is 1.90g / cm 3 , the corresponding best waiting time is only 18h. The reason for the above phenomenon is that density is an important factor affecting the best waiting time of cementing quality evaluation. The higher the density of the cement, the more the cement content in the cement stone, the higher the compressive strength, and the faster the hydration reaction speed, and the corresponding best waiting time will be relatively shorter.

[0075] Example 3:

[0076] According to the above method, two different retarders are selected to be added into the 1.25g / cm 3 ultra-low density cement slurry formula, and the curing temperature is designed to be 70℃ for the convenience of comparison. Figure 6

[0077] As shown in the attached Figure 6 , the best logging time increases with the increase of the retarder dosage, but the increase range is different between different retarders. This is because the retarders are different, the mechanism is also different, and the influence on the development of the acoustic velocity of the cement stone is also different.

[0078] Example 4:

[0079] Temperature is an important factor affecting the best logging time. The curing temperature is selected to be 25℃, 40℃, 50℃, 70℃ and 80℃, and the density of the cement slurry is 1.25g / cm 3 . The longitudinal and transverse wave velocities and the compressive strength of the cement stone under each temperature condition are measured, and the best logging time under each temperature condition is obtained according to the foregoing method, as shown in the attached Figure 7

[0080] As shown in the attached Figure 7 , for the same density of the cement slurry system, the best standing time decreases with the increase of the temperature, which is related to the influence of the temperature on the development of the compressive strength and acoustic characteristics of the cement stone. The higher the temperature, the faster the early strength of the cement stone changes, and the shorter the corresponding best standing time will be.

[0081] The method for determining the best logging time for well cementing quality evaluation proposed in the present application fully considers the change rule of logging response, is related to the change rule of the compressive strength and acoustic velocity of the cement stone, and is closely related to the parameters such as density, temperature, retarder dosage, etc. The best logging time obtained according to the method is more accurate, which on the one hand improves the accuracy of the well cementing quality evaluation, and on the other hand, reduces the well cementing standing time as much as possible and shortens the construction period. The method for determining the best logging time for well cementing quality evaluation proposed in the present application has a clear calculation process, the required calculation parameters are easy to obtain, the operation is simple, and it is easy to implement and execute on site.​​

Claims

1. A method for determining the optimal logging time for evaluating cementing quality, characterized in that, The method comprises the following steps: 1) obtaining the compressive strength value of the cement stone under the set curing condition, taking the compressive strength when the compressive strength tends to be stable as the reference point, and determining the longitudinal wave speed and the transverse wave speed of the cement stone corresponding to the reference point according to the relationship between the compressive strength value and the longitudinal wave speed and the transverse wave speed of the cement stone; 2) calculating the logging theoretical amplitude value at complete cementation under the set curing condition according to the longitudinal wave speed and the transverse wave speed of the cement stone corresponding to the reference point, and determining the upper limit value of the medium cementation by the same; 3) determining the upper limit amplitude value of the medium cementation corresponding to the best logging time according to the requirement that the cementing quality evaluation standard within the set range is affected by the setting time within the best time, and taking the upper limit amplitude value as the final upper limit value of the medium cementation; 4) inversely deducing the logging theoretical amplitude value at complete cementation by using the final upper limit value of the medium cementation; 5) determining the longitudinal wave speed, the transverse wave speed and the compressive strength value of the cement stone according to the inversely deduced logging theoretical amplitude value at complete cementation; 6) judging whether the obtained compressive strength value is greater than the set threshold value, if yes, it is indicated that the determined best time is the best logging time; otherwise, taking the time when the compressive strength value reaches the set threshold value as the best logging time.

2. The method of determining the optimal logging time for evaluating cement job quality according to claim 1, characterized in that, The set curing condition in the step 1) comprises that the curing temperature is 75 degrees Celsius and the curing time is 10 days.

3. The method of determining the optimal logging time for evaluating cement job quality according to claim 1, characterized in that, The calculation formula of the logging theoretical amplitude value in the step 2) is: Wherein, α T is the attenuation rate of casing wave caused by casing leakage Lamb wave, dB / m; A J is the sound amplitude received by the receiver, i.e. the theoretical sound amplitude value of logging, %; A f is the sound amplitude emitted by the transmitter, %; l is the logging source distance, m; ρ is the density of cement slurry for cementing, g / cm 3 ; h is the thickness of the casing, m.

4. The method of determining the optimal logging time for evaluating cement job quality according to claim 3, characterized in that, The upper limit value of the medium cementation in the step 3) refers to the received theoretical amplitude value when the cementation index is 0.

6.

5. The method of determining the optimal logging time for evaluating cement job quality according to claim 4, characterized in that, The calculation formula of the upper limit value of the medium cementation is: wherein A f0.6 is the theoretical amplitude of the received sound, %; A0is the theoretical amplitude of the emitted sound, %; a T is the attenuation rate of the casing wave caused by the leakage Lamb wave in the casing, dB / m; and l is the logging source distance, m.

6. The method of determining the optimal logging time for evaluating cement job quality according to claim 1, wherein, The set range in the step 3) is 5%.

7. The method of determining the optimal logging time for evaluating cement job quality according to claim 6, characterized in that, The upper limit of the medium cementation corresponding to the optimal logging time determined in step 3) is 1.05A f0.6 , A f0.6 is the theoretical amplitude value received when the cementation index is 0.

6.

8. The method of determining the optimal logging time for evaluating cement job quality according to claim 1, characterized in that, The set threshold value is 3.45Mpa.

9. The method of determining the optimal logging time for evaluating cement job quality according to claim 1, wherein, The relationship between the compressive strength value and the longitudinal wave speed and the transverse wave speed of the cement stone in the step 1) is obtained by fitting experimental data.

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