Quantitative evaluation method for stability of tight oil reservoir cement sheath

Abstract

The invention discloses a quantitative evaluation method for the stability of a tight oil reservoir cement sheath, which comprises the following steps: 1) acquiring well cementation cement, measuring basic parameters of main substances in the well cementation cement, carrying out an underground cement well cementation simulation experiment, and measuring basic parameters of a cement sheath sample after reaction; 2) taking the particle size as a separation point, dividing the cement substance into an unreacted inclusion and a full-reacted body, calculating the average thickness of the outer ring of the unreacted inclusion, obtaining a thickness-diameter curve, calculating the ratio of the thickness to the particle size of the unreacted inclusion with different particle sizes, and re-representing the large-particle-size combination distribution state of the substance after the cement reaction; and 3) calculating the filling degree of the small-particle-size substances according to the porosity and the effective porosity of the cement sample, defining the unfilled small-particle-size substances and the unreacted inclusion substances as free substances, and calculating a stability coefficient according to the composition state of the free substances to evaluate the well cementation quality. The stability is determined according to the particle distribution state before and after the cement sheath reaction, and the method is more scientific and economical.

Description

Technical Field

[0001] This invention relates to the field of oil and gas engineering, and in particular to a quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs during exploration and development. Background Technology

[0002] Cement sheath stability is a core factor affecting cementing quality and is crucial for ensuring normal production, successful implementation of fracturing techniques, and reservoir stimulation in oil and gas wells. Extensive field experience has demonstrated that large-scale volumetric fracturing is necessary to create hydraulic fractures and establish high-permeability channels within the reservoir. The high displacement, high fluid volume, and high pressure of these operations pose significant challenges to wellbore integrity. Cement sheath stability is a prerequisite for successful volumetric fracturing; substandard cementing quality can lead to the abandonment of the entire well, resulting in substantial economic losses. Therefore, post-drilling cement sheath stability monitoring and accurate evaluation are extremely important for optimizing subsequent well production and reservoir stimulation strategies.

[0003] In the existing technology, some scholars have conducted research on the stability evaluation of cement sheath after drilling in tight reservoirs, including: (1) Chinese patent with patent number CN202010941907.3 discloses a method for establishing cementing quality evaluation index and a cementing quality evaluation method. The method conducts a well section cement slurry curing simulation experiment to obtain the well section cement stone corresponding to the well section and obtains the compressive strength of cement stone in each well section; according to the quantitative relationship between the compressive strength of cement stone with a predetermined density and the relative acoustic amplitude, the relative acoustic amplitude corresponding to each well section is obtained from the compressive strength of cement stone in each well section, and the cementing quality evaluation standard at different well depths is established based on the relative acoustic amplitude. (2) Chinese Patent CN202011102002.3 discloses a method and apparatus for determining cementing quality. This method acquires the original single-pole waveform of the acoustic logging-while-drilling instrument measured at a set measurement depth, determines the drill collar wave velocity and the casing wave velocity; calculates the propagation time difference between the drill collar wave and the casing wave over a first distance based on the drill collar wave velocity and the casing wave velocity, determines the casing wave energy within the corresponding time window, and then determines the cementing quality parameters at the current measurement depth based on the casing wave energy. The above two methods mainly rely on a comprehensive evaluation of cementing quality through indoor experiments and field testing, i.e., cement sheath stability evaluation. Field testing relies on the precision of the testing instruments and the accuracy of the interpretation results, resulting in relatively large errors and high testing costs. In contrast, indoor experimental testing is a more convenient and feasible method. However, current methods do not combine the material properties and distribution state of the cement sheath itself for quantitative evaluation of its stability. Summary of the Invention

[0004] To address the shortcomings of current technologies, this invention proposes a quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs. This method overcomes the deficiencies of existing technologies by characterizing the stability of cement sheaths through the distribution of large-particle-size material after cement reaction, thus providing a new method for quantitative evaluation of cement sheath stability.

[0005] This invention proposes a quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs, characterized by the following steps:

[0006] 1) Obtain the cement before it reacts, measure the basic parameters of the main substances in it, and then simulate the temperature and pressure conditions of the tight oil reservoir to carry out a downhole cement cementing simulation experiment and measure the basic parameters of the cement sheath sample after the reaction.

[0007] 2) Using particle size as the dividing point, cement material is divided into unreacted inclusions and fully reacted inclusions. The average thickness of the outer ring of the unreacted inclusions is calculated, the thickness-diameter curve is obtained, and the ratio of the thickness of the unreacted inclusions to the particle size is calculated. The distribution state of large particle size binding of cement material after reaction is re-characterized.

[0008] 3) Calculate the filling degree of small-diameter materials based on the porosity and effective porosity of cement samples. Define unfilled small-diameter materials and unreacted inclusions as free materials. Calculate the stability coefficient based on the composition state of the free materials. Evaluate the cementing quality through the stability coefficient.

[0009] Furthermore, the basic parameters of the main substances before reaction in step 1) include the percentage content of the substances, particle size distribution, and porosity.

[0010] The basic parameters of the cement ring sample after the reaction include the percentage content of the material, porosity, and effective porosity.

[0011] Furthermore, in step 1), an X-ray diffractometer is used to test the percentage content of the substance;

[0012] Furthermore, in step 1), a laser particle size analyzer is used to test the particle size distribution;

[0013] Furthermore, in step 1), an automatic helium porosity analyzer is used to test porosity-related parameters;

[0014] Furthermore, step 1) also includes the following steps:

[0015] Standardize the basic data of cement samples before and after reaction.

[0016] Furthermore, the method for unifying the basic data is as follows:

[0017] The method for standardizing the cement foundation data before the reaction is as follows:

[0018]

[0019] K newi =K oldi ·(1-L new (2)

[0020]

[0021] In the formula: L new To standardize porosity, %; L k For testing porosity, %; J hs The water-cement ratio is dimensionless; K newi To standardize the percentage content of substances, %; K oldi To test the percentage content of a substance, %; J news To standardize the water percentage, %; n represents the number of minerals, in species;

[0022] The method for standardizing the basic data of the cement ring samples after the reaction is as follows:

[0023] KS newj =KS oldj (1-LS) (4)

[0024] T newk =T oldk (1-LS) (5)

[0025] Where: KS newj To standardize the percentage content of cementing materials in cement samples, %; KS oldj The percentage of material in the cementing sample is %; LS is the porosity of the cementing sample, %; T newk To standardize the particle size distribution of cementing samples, %; T oldk To test the particle size distribution, %; the cement sample contains a total of m types of substances.

[0026] Furthermore, in step 2), the cement material is divided into unreacted inclusions and fully reacted particles with a particle size of 10 micrometers as the dividing point;

[0027] Furthermore, the method for determining the average thickness of the outer ring of the unreacted inclusions in step 2) is as follows:

[0028]

[0029]

[0030]

[0031] Where: H pT represents the percentage of the encapsulated material in the encapsulated body, in %; g T represents the average particle size in the average thickness, in micrometers; H The average thickness of the outermost layer of the coating is in micrometers; m represents the number of different types of substances after the cement-water mixture has stabilized.

[0032] Furthermore, in step 2), the ratio of the thickness to the particle size of unreacted inclusions of different particle sizes is calculated using the following method:

[0033]

[0034] In the formula: OP k It is a ratio, dimensionless; T c Target particle size, in micrometers;

[0035] Furthermore, the method for calculating the filling degree of small-particle-size materials in step 3) is as follows:

[0036]

[0037] In the formula: S e For small particle size material packing density, dimensionless; LS u Effective porosity, %;

[0038] Furthermore, the method for calculating the stability coefficient in step 3) is as follows:

[0039]

[0040] In the formula: W e This is the stability coefficient, which is dimensionless.

[0041] The present invention also provides an electronic device, including a memory, a processor, and a program stored in the memory and running on the processor, characterized in that the processor executes the program to implement the steps of the above-described quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs.

[0042] The present invention also provides a computer-readable storage medium, characterized in that the computer-readable storage medium stores instructions that, when the instructions are executed on a terminal device, cause the terminal device to perform the steps of the above-described quantitative evaluation method for the stability of the cement sheath in tight oil reservoirs.

[0043] The beneficial effects of this invention include at least the following: Based on the basic parameters of cement ring sample material measurement obtained under reservoir conditions, this invention divides cement material into unreacted inclusions and fully reacted bodies with particle size as the dividing point, thereby characterizing the large particle size binding distribution state of cement material after reaction, and determining the stability of cement ring by the particle size distribution state of cement ring, which is more scientific and economical. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below.

[0045] Figure 1 A schematic diagram of the method flow of this invention. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0047] like Figure 1 As shown, this invention provides a quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs, characterized by comprising the following steps:

[0048] 1) Obtain the cement before it reacts, measure the basic parameters of the main substances in it, and then simulate the temperature and pressure conditions of the tight oil reservoir to carry out a downhole cement cementing simulation experiment and measure the basic parameters of the cement sheath sample after the reaction.

[0049] Specifically, the steps include:

[0050] 11) Testing cementing material composition: X-ray diffractometer can be used to test the main cementing materials and obtain their percentage content, and test the percentage content of the cementing sample in step 13).

[0051] 12) Testing the particle size distribution of cementing materials: The particle size distribution can be obtained by using a laser particle size analyzer. The particle size range is 0.1 μm-0.5 μm, 0.5 μm-1 μm, 1 μm-2 μm, 2 μm-4 μm, 4 μm-7 μm, 7 μm-10 μm, 10 μm-20 μm, 20 μm-40 μm, 40 μm-60 μm, and 60 μm-100 μm.

[0052] 13) Obtaining cement samples after cementing reaction: Conduct cementing simulation under tight oil reservoir temperature and pressure conditions to obtain cement samples after cementing. The specific details are as follows:

[0053] ① Pour the cementing material into the intermediate container of the constant speed and pressure pump and mix it with water.

[0054] ② Use a vacuum pump to purge the air from the pipeline and the reactor. After purging, close the vacuum pump inlet valve and use a constant speed and constant pressure pump to pump the cementing material from the intermediate container in step ① into the clamp.

[0055] ③ Determine the experimental loading temperature and confining pressure based on the reservoir confining pressure and reservoir temperature parameters.

[0056] ④ Use a heating jacket to heat the cementing material and clamp to the experimental temperature determined in step ③, and use a confining pressure pump to apply the confining pressure determined in step ③ to carry out a cementing simulation experiment under reservoir temperature and pressure conditions.

[0057] ⑤ Step 4: 48 hours after the cementing simulation experiment, retrieve the cement sample from the holder.

[0058] 14) Porosity measurement: The porosity of cement before reaction and the porosity and effective porosity of cement after reaction with water are measured using an automatic helium porosity meter.

[0059] 15) Standardization of cementing data before reaction: Due to inconsistencies in the overall material composition of various test data from previous steps, this step standardizes the composition by recalculating the percentage content of each component using a unified denominator. The calculation formula is as follows:

[0060]

[0061] K newi =K oldi ·(1-L new (2)

[0062]

[0063] In the formula: L k For testing porosity, %; L new To standardize porosity, %; J hs The water-cement ratio is dimensionless; K oldi To test the percentage content of a substance, %; K newi To standardize the percentage content of substances, %; J news To standardize the water percentage, %; n represents the number of minerals, in species.

[0064] 16) Standardize the cementing data after reaction: Similarly to step 15), standardize the cementing samples after reaction and calculate the percentage content of each part. The calculation formula is as follows:

[0065] KS newj =KS oldj (1-LS) (4)

[0066] T newk =T oldk(1-LS) (5)

[0067] Where: KS oldj To test the percentage content of cementing materials in the cement sample, %; KS newj To standardize the percentage content of cementing materials in cement samples, %; LS represents the porosity of the cementing samples tested, %; T oldk For testing particle size distribution, %; T newk To standardize the particle size distribution of cementing samples, %; the total number of substances in the cementing samples is m.

[0068] 2) Using particle size as the dividing point, cement material is divided into unreacted inclusions and fully reacted inclusions. The average thickness of the outer ring of the unreacted inclusions is calculated, the thickness-diameter curve is obtained, and the ratio of the thickness of the unreacted inclusions to the particle size is calculated. The distribution state of large particle size binding of cement material after reaction is re-characterized.

[0069] 21) Cement material classification: Cement materials are divided into unreacted inclusions and fully reacted inclusions, with a particle size of 10 micrometers as the dividing point.

[0070] 22) Calculate the average thickness of the outer layer of the unreacted inclusions: Assuming all particles are spherical, the thickness is calculated using the percentage of unreacted substances and the percentage of newly formed substances. The formula is as follows:

[0071]

[0072]

[0073]

[0074] Where: H p T represents the percentage of the encapsulated material in the encapsulated body, in %; g T represents the average particle size in the average thickness, in micrometers; H denoted as the average thickness of the outer rim of the coating, in micrometers; m represents the number of different types of substances after the cement-water mixture has stabilized.

[0075] 23) Calculate the ratio of the thickness of large-diameter particle inclusions to the unreacted material within the inclusions: This is calculated using the average thickness and particle size distribution, using the following formula:

[0076]

[0077] In the formula: OP k It is a ratio, dimensionless; T c The target particle size is in micrometers.

[0078] 3) Calculate the filling degree of small-diameter materials based on the porosity and effective porosity of cement samples. Define unfilled small-diameter materials and unreacted inclusions as free materials. Calculate the stability coefficient based on the composition state of the free materials. Evaluate the cementing quality through the stability coefficient.

[0079] It should be noted that before and after the cement reaction, for example, the minerals before the reaction are A and B, and the product after the reaction is C. The unreacted inclusion is the inclusion in which the pre-reaction substances such as A and B are still present inside, and the product C is wrapped on the outside. The whole reactant is entirely composed of the product C.

[0080] 31) Filling degree of small-diameter minerals: The filling degree of small-diameter minerals can be determined by utilizing the relationship between effective porosity and porosity. The calculation formula is as follows:

[0081]

[0082] In the formula: LS u Effective porosity, %; S e This represents the filling degree of small-particle-size minerals and is dimensionless.

[0083] 32) Calculation of the stability coefficient: The stability of the cement ring can be determined by combining the thickness relationship of large-diameter minerals and the filling relationship of small-diameter minerals. The larger the value, the stronger the stability of the cement ring. Based on the inventor's experimental comparison results, it is divided into three levels according to its value. When the stability coefficient is 0... <W e When the stability coefficient is less than or equal to 0.30, the stability is weak; when the stability coefficient is 0.30... <W e When the stability coefficient is less than or equal to 0.50, it indicates moderate stability; when the stability coefficient is 0.50... <W e When <= 1.0, it represents strong stability, calculated using the following formula:

[0084]

[0085] In the formula: W e T is the stability coefficient, dimensionless. c The value is taken as the middle particle size value within the corresponding particle size range, in micrometers.

[0086] Example 1

[0087] The following describes in detail the specific implementation of the present invention using geological data of a tight gas reservoir in a certain block as an example.

[0088] The quantitative evaluation method for the stability of the cement sheath in tight oil reservoirs provided in this example is as follows:

[0089] 1) Obtain the unreacted cement, measure the basic parameters of its main components, then simulate the temperature and pressure conditions of a tight oil reservoir to conduct a downhole cement cementing simulation experiment, and measure the basic parameters of the cement sheath sample after reaction. The specific details are as follows:

[0090] 11) Testing the composition of cementing materials: The main materials of cement were tested using an X-ray diffractometer, and the percentage content of the cementing materials in step 13) was also tested. The test results are shown in Table 1.

[0091] Table 1 Basic Table of Cementing Composition

[0092]

[0093] 12) Testing the particle size distribution of cementing materials: The particle size distribution was obtained by using a laser particle size analyzer. The analyzed particle size ranges were 0.1 μm-0.5 μm, 0.5 μm-1 μm, 1 μm-2 μm, 2 μm-4 μm, 4 μm-7 μm, 7 μm-10 μm, 10 μm-20 μm, 20 μm-40 μm, 40 μm-60 μm, and 60 μm-100 μm, as shown in Table 2.

[0094] Table 2 Cement Particle Size Distribution

[0095]

[0096] 13) Obtain cement samples after cementing reaction: Conduct cementing simulation under tight oil reservoir temperature and pressure conditions, obtain cement samples after cementing, and mineral tests are shown in Table 1.

[0097] 14) Porosity measurement: The porosity of cement before reaction and the porosity and effective porosity of cement after reaction with water were measured using an automatic helium porosity analyzer, as shown in Table 1.

[0098] 15) Standardization of cement data before reaction: Since the total material content of the various test data in the previous steps is inconsistent, the total material content will be standardized here, and the percentage content of each part will be calculated. The calculation results are shown in Table 3.

[0099] Table 3 Data Standardization Table

[0100]

[0101] 16) Data standardization of cementing after reaction: Similarly to step 15), the cementing samples after reaction are standardized and the percentage content of each part is calculated. The results are shown in Table 3 and the particle size distribution is shown in Table 4.

[0102] Table 4 Cement Particle Size Redistribution Table

[0103]

[0104] 2) Using particle size as the dividing point, cement material is divided into unreacted inclusions and fully reacted inclusions. The average thickness of the outer ring of the unreacted inclusions is calculated, and the thickness-diameter curve is obtained. The ratio of the thickness of the unreacted inclusions to the particle size is calculated for different particle sizes. The distribution state of large-particle-size cement material after reaction is re-characterized. The specific content is as follows:

[0105] 21) Cement material classification: Cement material is divided into unreacted inclusions and fully reacted inclusions based on a particle size of 10 micrometers. The percentage of particles smaller than 10 micrometers is 19.28%, and the percentage of particles larger than 10 micrometers is 34.31%.

[0106] 22) Calculate the average thickness of the outer layer of the unreacted inclusions: Assuming all particles are spherical, the solution is obtained from the percentage of unreacted substances and the percentage of newly formed substances. First, calculate... The value is 36.44%, which falls between 20 and 40 micrometers, therefore T g The calculation formula is selected from the second row, and H is calculated. P The value is 0.1761, T g The value is 54.89 micrometers, therefore, the average thickness T of the outer ring of the package is... H It is 11.92 micrometers.

[0107] 23) Calculate the ratio of the thickness of large-diameter particle inclusions to the unreacted material within the inclusions: This is calculated using the average thickness and particle size distribution, expressed as the function expression.

[0108] 3) The filling degree of small-diameter materials is calculated based on the porosity and effective porosity of the cement sample. Unfilled small-diameter materials and unreacted inclusions are defined as free materials. The stability coefficient is calculated based on the composition of the free materials, and the cementing quality is evaluated through the stability coefficient. The specific details are as follows:

[0109] 31) Filling degree of small-diameter minerals: The filling degree of small-diameter minerals can be determined by the relationship between effective porosity and porosity. The value calculated by formula (10) is 0.5408.

[0110] 32) Calculate the stability coefficient: The stability of the cement ring can be determined by combining the thickness relationship of large-diameter minerals and the filling relationship of small-diameter minerals. The value calculated by formula (11) is 0.6708. According to the cement ring stability level classification standard in step 3), the cement ring is evaluated as having a strong stability.

[0111] This invention provides a quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs. First, the main materials of the cement are obtained, and their percentage content, particle size distribution, and porosity are tested. Downhole cementing simulations are conducted under simulated tight oil reservoir temperature and pressure conditions to obtain corresponding cement samples, and their porosity, effective porosity, and material percentage content are tested. Second, using particle size as a dividing point, the cement material is divided into unreacted inclusions and fully reacted inclusions. The average thickness of the outer ring of the unreacted inclusions is then calculated to obtain a thickness-diameter curve. Furthermore, the ratio of the thickness to the particle size of unreacted inclusions of different sizes is calculated, thereby re-characterizing the large-particle-size combination distribution state of the cement-reacted material. Finally, the filling degree of small-particle-size material is calculated based on the porosity and effective porosity of the cement samples. Unfilled small-particle-size material and large-particle-size unreacted inclusions are defined as free material. A stability coefficient is calculated based on the composition state of the free material; the larger the value, the stronger the stability of the cement sheath, thus achieving the purpose of quantitative evaluation. Compared with extensive monitoring in mines, the method provided by this invention is more economical. It is simple and feasible to operate, and can quantitatively evaluate the stability of the cement sheath in any well, providing a basis for efficient exploration and development of tight oil reservoirs in the later stages.

[0112] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs, characterized in that, Includes the following steps: 1) Obtain the cement before it reacts, measure the basic parameters of the main substances in it, and then simulate the temperature and pressure conditions of the tight oil reservoir to carry out a downhole cement cementing simulation experiment and measure the basic parameters of the cement sheath sample after the reaction. 2) Using particle size as the dividing point, cement material is divided into unreacted inclusions and fully reacted inclusions. The average thickness of the outer ring of the unreacted inclusions is calculated, the thickness-diameter curve is obtained, and the ratio of the thickness of the unreacted inclusions to the particle size is calculated. The distribution state of large particle size binding of cement material after reaction is re-characterized. 3) Calculate the filling degree of small-diameter materials based on the porosity and effective porosity of cement samples. Define unfilled small-diameter materials and unreacted inclusions as free materials. Calculate the stability coefficient based on the composition state of the free materials. Evaluate the cementing quality through the stability coefficient.

2. The quantitative evaluation method for the stability of cement sheath in tight oil reservoirs according to claim 1, wherein the basic parameters of the main substances before reaction in step 1) include the percentage content of the substances, particle size distribution and porosity. The basic parameters of the cement ring sample after the reaction include the percentage content of the material, porosity, and effective porosity.

3. The quantitative evaluation method for the stability of cement sheath in tight oil reservoirs according to claim 1, wherein in step 1), an X-ray diffractometer is used to test the percentage content of the substance; Particle size distribution was tested using a laser particle size analyzer; Porosity-related parameters were tested using an automatic helium porosity analyzer.

4. The quantitative evaluation method for the stability of the cement sheath in tight oil reservoirs according to claim 1, step 1) further includes the step of: The basic data of cement samples before and after reaction were standardized.

5. In the quantitative evaluation method for the stability of cement rings in tight oil reservoirs according to claim 1, in step 2), the cement material is divided into unreacted inclusions and fully reacted inclusions with a particle size of 10 micrometers as the dividing point.

6. The quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs according to claim 1, wherein step 2) calculates the ratio of the thickness to the particle size of unreacted inclusions of different particle sizes, the method being: In the formula: OP k It is a ratio, dimensionless; T c The target particle size is in micrometers.

7. The quantitative evaluation method for the stability of the cement sheath in tight oil reservoirs according to claim 1, wherein the calculation method for the filling degree of small-particle-size material in step 3) is as follows: In the formula: S e For small particle size material packing density, dimensionless; LS u Effective porosity, %.

8. The quantitative evaluation method for the stability of the cement sheath in tight oil reservoirs according to claim 1, wherein the stability coefficient is calculated in step 3) as follows: In the formula: W e This is the stability coefficient, which is dimensionless.

9. An electronic device comprising a memory, a processor, and a program stored in the memory and running on the processor, characterized in that, When the processor executes the program, it implements the steps of a quantitative evaluation method for the stability of cement sheaths in tight oil reservoirs as described in any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions that, when executed on a terminal device, cause the terminal device to perform the steps of a method for quantitatively evaluating the stability of a cement sheath in a tight oil reservoir as described in any one of claims 1 to 8.

Images