Method and device for analyzing pore throat structure pattern based on fractal theory

Abstract

The invention relates to a pore throat structure style analysis method and device based on a fractal theory, and the method comprises the steps: obtaining a rock sample mercury injection curve through a mercury injection experiment, and obtaining mercury intrusion dynamic parameters of a plurality of test points; calculating a mercury intrusion dynamic parameter logarithm value according to the rock sample mercury intrusion curve; fitting the mercury intrusion dynamic parameter logarithm value to obtain a linear regression fitting straight line; calculating the pore fractal dimension of the rock according to the slope of the linear regression fitting straight line; and analyzing the pore throat structure style according to the pore fractal dimension to obtain an analysis result. The fractal theory and the mercury injection experiment are combined, and classification characterization and three-dimensional simulation of the reservoir complex pore throat structure style can be achieved through reservoir pore fractal dimension determination.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration and development, and in particular, to a method and device for analyzing pore-throat structure patterns based on fractal theory. Background Art

[0002] Pores are the spaces in rocks that are not filled with solid minerals, and are composed of two parts: pore channels and throats. Among them, the pore channels have a larger aperture and determine the fluid storage capacity; the throats are narrow channels connecting the pore channels, with a relatively smaller aperture, and control the fluid percolation capacity. The pore channels and throats are coupled and connected to each other to jointly form a complex spatial topological pore-throat network. Therefore, the essence of pores is a complex of pore channels and throats, with a pore-throat binary structure.

[0003] The property that the local part of a geometric object is similar to its whole in a certain form is called self-similarity. A geometric object with self-similarity is a fractal. A large number of studies have shown that rock pores have self-similarity and are natural fractals. Using fractal theory, characteristic parameters - pore fractal dimensions - that characterize the degree of irregularity of their structures can be obtained. Since the mercury injection method can directly measure the pore distribution characteristics of rock samples from the inside, the mercury injection curve method has become the most important method for calculating the pore fractal dimension of core samples. According to different pore simplification models, there are currently two main methods for determining the pore fractal dimension of rocks using mercury injection curves: the spherical formula method and the capillary formula method.

[0004] The spherical formula method simplifies pores into spheres and uses fractal power laws to derive a pore fractal formula with water saturation to calculate the pore fractal dimension; while the capillary formula method simplifies pores into equal-diameter curved tubular bodies and uses fractal power laws to derive a pore fractal formula with mercury saturation to calculate the pore fractal dimension. Whether it is a sphere or a tubular body, both have three-dimensional spatial topological properties.

[0005] Therefore, the numerical values of the pore fractal dimensions calculated by traditional methods (the spherical formula method and the capillary formula method) are between 2.0 and 3.0. The closer the value is to 2.0, the weaker the pore heterogeneity, the simpler the structure, and the smoother the surface; the closer it is to 3.0, the stronger the pore heterogeneity, the more complex the structure, and the rougher the surface. Although traditional methods can calculate the pore fractal dimension, assuming pores as a single sphere (closer to the pore channel morphology) or a tubular body (closer to the throat morphology) does not conform to the pore-throat binary structure characteristics of pores. Due to the over-simplification of the pore morphology, the calculation results of the pore fractal dimension cannot reflect the spatial topological structure of the pore throats. Summary of the Invention

[0006] The present invention provides a method and device for analyzing pore-throat structure patterns based on fractal theory to solve the defects of the prior art.

[0007] The first aspect of the present invention provides a method for analyzing pore-throat structure patterns based on fractal theory, including:

[0008] S1: Obtain the mercury intrusion curve of the rock sample through mercury intrusion experiments to obtain the mercury intrusion dynamic parameters at multiple test points;

[0009] S2: Calculate the logarithmic values of the mercury intrusion dynamic parameters according to the mercury intrusion curve of the rock sample;

[0010] S3: Fit the logarithmic values of the mercury intrusion dynamic parameters to obtain a linear regression fitting line;

[0011] S4: Calculate the pore fractal dimension of the rock according to the slope of the linear regression fitting line;

[0012] S5: Analyze the pore-throat structure pattern according to the pore fractal dimension to obtain the analysis result.

[0013] According to the method for analyzing pore-throat structure patterns based on fractal theory provided by the present invention, the mercury intrusion dynamic parameters in step S1 include:

[0014] Mercury injection pressure, mercury injection saturation;

[0015] The logarithmic values of the mercury intrusion dynamic parameters in step S2 include:

[0016] Logarithmic value of mercury injection pressure, logarithmic value of mercury injection saturation.

[0017] According to the method for analyzing pore-throat structure patterns based on fractal theory provided by the present invention, the expression of the linear regression fitting line in step S3 is:

[0018] lgS Hg = k·lgp c - A;

[0019] Where, lgS Hg Is the logarithmic value of mercury injection saturation, k is the slope of the linear regression fitting line, lgp c Is the logarithmic value of mercury injection pressure, and A is the intercept of the linear regression fitting line.

[0020] According to the method for analyzing pore-throat structure patterns based on fractal theory provided by the present invention, the expression of the pore fractal dimension in step S4 is:

[0021] D = k + 3;

[0022] Where, D is the pore fractal dimension, and k is the slope of the linear regression fitting line.

[0023] According to the method for analyzing pore-throat structure patterns based on fractal theory provided by the present invention, step S5 further includes:

[0024] S51: Combine the pore ball-stick model to decompose the pore fractal dimension into the pore throat fractal dimension and the throat fractal dimension, and obtain the decomposition result;

[0025] S52: Analyze the pore throat structure pattern according to the decomposition result to obtain the analysis result.

[0026] According to a method for analyzing pore throat structure patterns based on fractal theory provided by the present invention, the expression of the decomposition result in step S51 is:

[0027] D = D d + D t ;

[0028] where D is the pore fractal dimension, D d is the pore throat fractal dimension, and D t is the throat fractal dimension.

[0029] According to a method for analyzing pore throat structure patterns based on fractal theory provided by the present invention, step S52 specifically includes:

[0030] When the pore fractal dimension is greater than 4 and less than 6, the analysis result is that the pores have a 1-pore-1-throat structure;

[0031] When the pore fractal dimension is greater than or equal to 6, the analysis result is that the pores have a 1-pore-multi-throat structure;

[0032] When the pore fractal dimension is less than or equal to 4, the analysis result is that the pores have a capillary structure.

[0033] The second aspect of the present invention also provides an apparatus for analyzing pore throat structure patterns based on fractal theory, including:

[0034] An acquisition module: used to obtain the mercury intrusion curve of the rock sample through a mercury intrusion experiment to obtain the mercury intrusion dynamic parameters of multiple test points;

[0035] A logarithm calculation module: used to calculate the logarithm of the mercury intrusion dynamic parameters according to the mercury intrusion curve of the rock sample;

[0036] A fitting module: used to fit the logarithm of the mercury intrusion dynamic parameters to obtain a linear regression fitting line;

[0037] A dimension calculation module: used to calculate the pore fractal dimension of the rock according to the slope of the linear regression fitting line;

[0038] An analysis module: used to analyze the pore throat structure pattern according to the pore fractal dimension to obtain the analysis result.

[0039] The third aspect of the present invention provides an apparatus for analyzing pore throat structure patterns based on fractal theory, including:

[0040] A memory and at least one processor, with instructions stored in the memory;

[0041] At least one of the processors invokes the instructions in the memory to cause a pore-throat structure pattern analysis device based on fractal theory to execute a pore-throat structure pattern analysis method based on fractal theory as described in any one of the above.

[0042] The fourth aspect of the present invention provides a computer-readable storage medium, on which instructions are stored, and when the instructions are executed by a processor, a pore-throat structure pattern analysis method based on fractal theory as described in any one of the above is implemented.

[0043] Multiple types of pore-throat structures coexist inside the reservoir, but currently there is a lack of effective analysis methods for the patterns of various pore-throat structures. For this reason, the present invention proposes a pore-throat structure pattern analysis method, device, equipment and storage medium based on fractal theory. First, a new method - the ball-stick formula method - for determining the fractal dimension of rock pores based on the pore-throat binary structure is provided, breaking through the limitations of the traditional spherical formula method and capillary formula method. By considering the pore-throat binary structure and coordination number, the present invention simplifies the pores into ball-stick bodies (a combination of spheres and circular tubes), which is more in line with the true structural characteristics of the pores; secondly, the present invention uses fractal power law to derive a new pore fractal formula with mercury saturation, realizing the deep integration of the pore fractal dimension and the pore-throat topological structure, so that the calculated pore fractal dimension is no longer limited by 3.0 and can more accurately reflect the complex structure and irregularity of the rock pore-throat; and by performing logarithmic processing and linear regression fitting on the mercury injection curve data, the present invention can identify multiple scale-free regions existing inside the rock pores and determine the pore-throat structure type corresponding to each scale-free region, thus providing an important basis for the interpretation of the complex pore-throat structure inside the reservoir pores.

[0044] In addition, the operation of the present invention is simple and easy. It can not only judge various pore-throat structure patterns, but also evaluate the complexity of the pore-throat structure through the size of the pore fractal dimension, providing a scientific basis for reservoir evaluation and oil and gas development; the present invention enriches and improves the reservoir pore-throat fractal characterization theory, has important theoretical guidance and practical value for the classification characterization and three-dimensional simulation of the complex pore-throat structure of the reservoir, has a broad application prospect in the field of oil and gas exploration and development, and can provide technical support for improving the efficiency and recovery rate of oil and gas development. Description of the Drawings

[0045] To more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0046] Figure 1 Schematic flow chart of a pore throat structure pattern analysis method based on fractal theory provided by an embodiment of the present invention;

[0047] Figure 2 Schematic diagram of a pore simplification model provided by an embodiment of the present invention;

[0048] Figure 3 Schematic structural diagram of a pore throat structure pattern analysis device based on fractal theory provided by an embodiment of the present invention;

[0049] Figure 4 Schematic diagram of a mercury intrusion curve provided by an embodiment of the present invention;

[0050] Figure 5 Schematic diagram of linear regression fitting provided by an embodiment of the present invention. Detailed implementation manners

[0051] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. They should not be construed as limiting the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. In the description of the present invention, it should be understood that the terms used are only for the purpose of description and cannot be construed as indicating or implying relative importance.

[0052] To better understand the present invention, the following first explains in detail the basic principles on which the present invention is based.

[0053] According to fractal theory, the number of scale feature bodies accommodated by a fractal object and the linear scale of the measured feature body satisfy a power-law relationship, that is:

[0054] N(r) ∝ r -D ;

[0055] Wherein, N(r) is the number of scale feature bodies accommodated by the fractal object, r is the linear scale of the scale feature body, and D is the fractal dimension of the fractal object.

[0056] Considering the pore-throat binary structure and coordination number, the pore channels are simplified to spheres and the throat channels are simplified to equal-diameter curved circular tubes. At the same time, considering that the pore volume is the sum of the volumes of the pore channels and throat channels, N(r) is as follows:

[0057]

[0058] Among them, N(r) is the number of characteristic volumes accommodated by the pore volume, V is the pore volume, a1 is a constant related to the pore channel shape, a2 is a constant related to the throat channel shape, n is the pore-throat coordination number, R is the pore channel radius, r is the throat channel radius, and l is the throat channel length.

[0059] According to fractal theory, for self-similar pores or each scale-free region thereof, the pore channels, throat channels, or the whole pore-throat have statistical self-similarity, that is, characteristic parameters such as the pore-throat ratio, pore-throat coordination number, and throat channel length-radius ratio have statistical consistency. Therefore, combining the first two equations gives:

[0060]

[0061] Among them, c is the pore-throat ratio, d is the throat channel length-radius ratio, and e is the rewritten comprehensive coefficient.

[0062] It can be seen from the above equation that:

[0063] V∝r 3-D ;

[0064] And according to the Washburn equation, there is:

[0065]

[0066] Among them, P c is the capillary pressure, σ is the interfacial tension, and θ is the contact angle. According to the above two equations, it can be obtained that:

[0067]

[0068] Differentiating the above equation gives:

[0069]

[0070] Among them, f is a constant.

[0071] During the mercury injection experiment, as the capillary pressure increases (or the pore-throat radius decreases), the mercury injection volume gradually increases. Integrating the above equation accordingly gives:

[0072]

[0073] Among them, P min is the displacement pressure, and V(>r) represents the change from P min increasing to P cThe mercury intrusion volume at that time.

[0074] Similarly, it can be obtained that:

[0075]

[0076] Among them, P max is the maximum capillary pressure, and V is the total mercury intrusion volume when increasing from P min to P max at that time.

[0077] Combining the above two formulas, it can be obtained that:

[0078]

[0079] Among them, S Hg is the mercury intrusion saturation.

[0080] Since P max >>P min , the above formula is simplified to:

[0081]

[0082] Taking the logarithm of both sides of the above formula, it can be obtained that:

[0083] lgS Hg =(D - 3)lgP c -(D - 3)lgP max ;

[0084] The above formula shows that when taking the logarithm of the mercury intrusion pressure lgP c as the independent variable and the logarithm of the mercury intrusion saturation lgS Hg as the dependent variable, there is a linear relationship between the two, and the pore fractal dimension can be determined by using the slope of the straight line.

[0085] Based on the above principle, aiming at the problem that the traditional spherical or capillary formula method overly simplifies the pore morphology and cannot invert the pore throat structure, the present invention aims to provide a new method for determining the rock pore fractal dimension based on the pore throat binary structure, which is simple, easy to implement, and highly operable, breaks through the limitations of the traditional method, deeply integrates the pore fractal dimension with the pore throat topological structure, and provides an important basis for the interpretation of the complex pore throat structure inside the reservoir pores.

[0086] The embodiments of the present invention will be described below with reference to the drawings.

[0087] As Figure 1 shown, the first aspect of the present invention provides a method for analyzing the pore throat structure pattern based on the fractal theory, including:

[0088] S1: Obtain the mercury intrusion curve of the rock sample through the mercury intrusion experiment to obtain the mercury intrusion dynamic parameters of multiple test points.

[0089] Furthermore, the main principle of the mercury intrusion method is as follows: mercury is a non-wetting phase. Under high pressure, mercury is injected into the rock sample, and the capillary pressure and the volume of injected mercury in equilibrium with it are determined, thereby obtaining the relationship curve between the capillary pressure and the mercury saturation of the rock sample. Since the mercury intrusion method can directly measure the pore throat distribution characteristics of rock samples from the inside, it can be used to determine the pore fractal dimension.

[0090] During the mercury intrusion test of the rock sample, data such as the mercury injection pressure and mercury injection saturation, mercury withdrawal pressure and mercury injection saturation at each test point were completely recorded. The present invention first obtains and organizes these data. Among them, the data of mercury injection pressure and mercury injection saturation are mainly used.

[0091] Among them, the mercury intrusion dynamic parameters in step S1 include: mercury injection pressure, mercury injection saturation.

[0092] In step S1 of the present invention, the mercury intrusion curve data of the rock sample is obtained through a mercury intrusion experiment. The purpose is to measure the pore distribution characteristics of the rock sample. Specifically, the basic principle of the mercury intrusion experiment is to use mercury as a non-wetting phase fluid, and under high-pressure conditions, force the mercury liquid to invade the pore space of the rock sample and record the intrusion of the mercury liquid at different pressures. The mercury intrusion dynamic parameters described above are the key measurement indicators during the process of the mercury liquid invading the rock pores. The mercury injection pressure refers to the pressure value required to inject the mercury liquid into the pores of the rock sample, and the unit is usually MPa. According to the aforementioned Washburn equation, the mercury injection pressure is inversely proportional to the pore throat radius, so it can reflect the size characteristics of the rock pore throat. The mercury injection saturation refers to the percentage of the volume of the mercury liquid invading the pores of the rock sample to the total pore volume of the rock sample at a specific pressure, which reflects the mercury filling degree of the rock pores at a specific pressure.

[0093] S2: Calculate the logarithm values of the mercury intrusion dynamic parameters according to the mercury intrusion curve of the rock sample.

[0094] Among them, the logarithm values of the mercury intrusion dynamic parameters in step S2 include: the logarithm value of the mercury injection pressure, the logarithm value of the mercury injection saturation.

[0095] Furthermore, step S2 is a processing link for logarithmic conversion of the mercury intrusion dynamic parameters on the basis of obtaining the original experimental data. The purpose is to convert the data on the linear scale into the logarithmic scale to prepare for subsequent fractal analysis. The logarithm values of the mercury intrusion dynamic parameters are the key terms in this step. It refers to the result obtained by performing logarithmic operations on the mercury intrusion dynamic parameters obtained in S1, specifically including the logarithm value of the mercury injection pressure, that is, taking the common logarithm of the mercury injection pressure. The logarithmic processing compresses the pressure value from the range of several orders of magnitude to a narrower interval, which helps to identify the power-law relationship in subsequent analysis. The logarithm value of the mercury injection saturation is the common logarithm of the mercury injection saturation. Similarly, the conversion helps to linearize the fractal relationship.

[0096] According to fractal theory, when an object has fractal characteristics, there is usually a power-law relationship between its characteristic parameters. In step S2 of the present invention, through logarithmic transformation, the power-law relationship can be transformed into a linear relationship, providing the necessary mathematical basis for the linear regression analysis in the subsequent steps.

[0097] S3: Fit the logarithm values of the mercury intrusion dynamic parameters to obtain a linear regression fitting line.

[0098] Further, in step S3, based on the logarithm values obtained in S2, a linear regression analysis is performed on these logarithm values through statistical methods. The purpose is to determine the linear relationship between the logarithm value of the mercury injection pressure and the logarithm value of the mercury injection saturation, providing a basis for the subsequent calculation of the pore fractal dimension. The linear regression fitting line is a straight-line equation fitted from a series of data points through statistical techniques such as the least squares method.

[0099] Among them, the expression of the linear regression fitting line in step S3 is:

[0100] lgS Hg = k·lgp c - A;

[0101] Among them, lgS Hg is the logarithm value of the mercury injection saturation, k is the slope of the linear regression fitting line, lgp c is the logarithm value of the mercury injection pressure, and A is the intercept of the linear regression fitting line.

[0102] Further, in the above formula, the logarithm value of the mercury injection saturation is the dependent variable, representing the logarithm of the percentage of the pore volume of the mercury liquid intruding into the rock sample under a specific pressure to the total pore volume. The slope of the linear regression fitting line is directly used for the subsequent calculation of the rock pore fractal dimension, while the logarithm value of the mercury injection pressure is the independent variable, representing the logarithm of the pressure required to press the mercury liquid into the rock sample pores. The intercept of the linear regression fitting line is the constant term of the fitting equation.

[0103] S4: Calculate the pore fractal dimension of the rock according to the slope of the linear regression fitting line.

[0104] Among them, the expression of the pore fractal dimension in step S4 is:

[0105] D = k + 3;

[0106] Among them, D is the pore fractal dimension, and k is the slope of the linear regression fitting line.

[0107] The traditional spherical formula method simplifies pores into spheres, and uses the fractal power law to derive a pore fractal formula with water saturation to calculate the pore fractal dimension; while the capillary formula method simplifies pores into equal-diameter curved circular tubes, and uses the fractal power law to derive a pore fractal formula with mercury saturation to calculate the pore fractal dimension. Whether it is a sphere or a circular tube, it has a three-dimensional space topology attribute. However, the present invention reconsiders the pore-throat binary structure and coordination number, and simplifies pores into ball-stick bodies, that is, a combination of spheres and circular tubes. Specifically, the structure of the pore simplification model of the present invention is as Figure 2 shown.

[0108] That is, in step S4 of the present invention, based on the fractal power law and the pore-throat binary structure model, specifically, in the traditional spherical formula method or capillary formula method, the pore fractal dimension is usually limited between 2.0 and 3.0. However, the present invention breaks through this limitation by considering the pore-throat binary structure and coordination number.

[0109] When there are multiple scale-free regions inside the rock, each scale-free region will correspond to a linear regression fitting line. Therefore, multiple pore fractal dimension values can be calculated, indicating that there are multiple coexisting pore-throat structure patterns inside the rock. These different pore fractal dimensions reflect the structural characteristics of the rock in different scale ranges.

[0110] Therefore, in step S4, the present invention calculates the pore fractal dimension of the rock through the slope of the linear regression fitting line obtained in S3, and finally obtains the expression for calculating the pore fractal dimension as shown in the above expression, providing a key parameter for subsequent analysis of the pore-throat structure pattern of the rock.

[0111] S5: Analyze the pore-throat structure pattern according to the pore fractal dimension to obtain an analysis result.

[0112] Among them, step S5 further includes:

[0113] S51: Combine the pore ball-stick model to decompose the pore fractal dimension into the pore channel fractal dimension and the throat fractal dimension to obtain a decomposition result.

[0114] Among them, the expression of the decomposition result in step S51 is:

[0115] D = D d + D t ;

[0116] Among them, D is the pore fractal dimension, D d is the pore channel fractal dimension, and D t is the throat fractal dimension.

[0117] S52: Analyze the pore-throat structure pattern according to the decomposition result to obtain an analysis result.

[0118] Among them, step S52 specifically includes:

[0119] When the pore fractal dimension is greater than 4 and less than 6, the analysis result is that the pores have a 1-pore 1-throat structure; when the pore fractal dimension is greater than or equal to 6, the analysis result is that the pores have a 1-pore multi-throat structure; when the pore fractal dimension is less than or equal to 4, the analysis result is that the pores have a capillary structure.

[0120] For the pore channels, if they are regarded as spheres, they have three-dimensional topological properties, and the fractal dimension is between 2 and 3, that is, D d ∈(2, 3). For a single throat, if it is regarded as a circular tube, it can be arbitrarily twisted in three-dimensional space. Therefore, the fractal dimension of a single throat is also between 2 and 3, that is, D t,i ∈(2, 3), where i is the throat index value, and D t,i represents the throat fractal dimension of the i-th throat.

[0121] According to the simplified structural model of the present invention, for the throats in the pores, they are a collection of multiple throats. Therefore, the pore fractal dimension is closely related to the pore-throat coordination number. When the pore-throat coordination number is equal to 2, since 2 < D d < 3 and 2 < D t < 3, so 4 < D < 6. At this time, the pores have a 1-pore 1-throat structure; obviously, when the pore-throat coordination number is greater than 2, D ≥ 6, and the pores have a 1-pore multi-throat structure; in addition, when the pore-throat coordination number is less than 2, D ≤ 4. Since during the mercury injection experiment, the mercury liquid invades along the connected pore throats, the pore-throat coordination number is greater than or equal to 2. If the pore-throat coordination number is less than 2, it means that there is no difference between the pore channels and the throats, that is, the pores have a capillary structure.

[0122] According to the above corresponding principle between the pore fractal dimension and the pore-throat structure pattern, combined with the calculation result of the pore fractal dimension, the pore-throat structure pattern and its irregularity can be explained. Generally, the larger the pore fractal dimension, the more complex the pore-throat structure and the higher its irregularity.

[0123] As Figure 3 shown, the present invention also provides a pore-throat structure pattern analysis device based on fractal theory, including:

[0124] Acquisition module 100: used to obtain the mercury injection curve of the rock sample through the mercury injection experiment to obtain the mercury intrusion dynamic parameters of multiple test points;

[0125] Logarithmic calculation module 200: used to calculate the logarithm of the mercury intrusion dynamic parameters according to the mercury injection curve of the rock sample;

[0126] Fitting module 300: used to fit the logarithm of the mercury intrusion dynamic parameters to obtain a linear regression fitting line;

[0127] Dimension calculation module 400: used to calculate the pore fractal dimension of the rock according to the slope of the linear regression fitting line;

[0128] Analysis module 500: used to analyze the pore throat structure pattern according to the pore fractal dimension to obtain an analysis result.

[0129] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative labor.

[0130] The present invention also provides a pore throat structure pattern analysis device based on fractal theory, including:

[0131] A memory and at least one processor, wherein instructions are stored in the memory;

[0132] At least one of the processors invokes the instructions in the memory so that a pore throat structure pattern analysis device based on fractal theory executes a pore throat structure pattern analysis method according to any one of the above.

[0133] The present invention also provides a computer-readable storage medium, on which instructions are stored, and when the instructions are executed by a processor, a pore throat structure pattern analysis method according to any one of the above is implemented.

[0134] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence, or the part that contributes to the prior art can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disc, etc., including several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0135] Next, a pore throat structure pattern analysis method based on fractal theory provided by the present invention will be described in conjunction with specific embodiments.

[0136] This embodiment is based on an area of about 5000 km 2Taking the oilfield as an example, the main producing formation of the oilfield is the Chang 8 oil zone of the Yanchang Formation in the Triassic. It belongs to the delta front sedimentation. The average porosity of the reservoir is 12.1%, and the average permeability is 10 -3 μm 2 , belonging to the low-porosity and low-permeability reservoir.

[0137] Taking the mercury injection curve of the 6# rock sample (2064.1m) in Well X105 in the Chang 8 oil zone of the above-mentioned oilfield as an example, the basic data of the mercury injection experiment of this rock sample are shown in Table 1, and the measured mercury injection curve data are shown in Table 2. The corresponding mercury injection curve is as Figure 4 shown.

[0138] Table 1 Basic data table of mercury injection experiment of rock sample

[0139] Core number: 6# <![CDATA[Pore volume (cm 3 ):]]> 1.51 Sample weight (g): 30.02 Well number: West 105 <![CDATA[Sample volume (cm 3 ):]]> 12.17 Lithology: Grey oil-impregnated fine sandstone Well depth (m): 2064.1 Porosity (%): 12.47 Stratigraphic horizon: <![CDATA[Length 81]]> <![CDATA[Permeability (×10 -3 μm 2 ):]]> 0.216

[0140] Table 2 Data table of mercury injection curve of rock sample

[0141]

[0142]

[0143]

[0144] According to the above mercury injection curve data of the rock sample (mercury injection pressure and mercury injection saturation), calculate the logarithms of the mercury injection pressure and mercury injection saturation at multiple test points in the mercury injection curve of the rock sample. The calculation results are shown in Table 3.

[0145] Table 3 Calculation result table of logarithms of mercury injection pressure and mercury injection saturation of rock sample

[0146]

[0147]

[0148]

[0149] According to the logarithms of the mercury injection pressure and mercury injection saturation at multiple test points in the mercury injection curve of the rock sample, taking the logarithm of the mercury injection pressure lgp c as the independent variable and taking the logarithm of the mercury injection saturation lgS Hg as the dependent variable, plot the scatter diagram of lgp c and lgS Hg and perform linear regression fitting on the scatter diagram.

[0150] The specific fitting results are as Figure 5 shown. It can be seen from Figure 5 that there are three fitting lines for the 6# rock sample, and the expressions of the obtained fitting lines are respectively:

[0151] The first fitted line, and the first fitted line is the fitted line of the green marked points, with the expression:

[0152] y = 9.1785x + 2.9656;

[0153] R 2 = 0.9044;

[0154] The second fitted line, and the second fitted line is the fitted line of the blue marked points, with the expression:

[0155] y = 1.6764x + 0.1752;

[0156] R 2 = 0.996;

[0157] The third fitted line, and the third fitted line is the fitted line of the blue marked points, with the expression:

[0158] y = 0.2216x + 1.4696;

[0159] R 2 = 0.9576;

[0160] From the above three expressions, it can be seen that their slopes are 9.1785 → 1.6764 → 0.2216 in descending order. This shows that the pores of this rock sample exhibit a three-segment fractal characteristic, and there are three scale-free regions (low-pressure region, medium-pressure region, high-pressure region) inside the pores. Each scale-free region corresponds to a type of pore-throat structure. Therefore, the three types of pore-throat structures coexist inside the pores of the 6# rock sample in this embodiment, and the specific interpretation results are shown in Table 4.

[0161] Table 4 Interpretation results of the fractal dimension of the rock sample pores and the pore-throat structure patterns

[0162]

[0163] A method and device for analyzing pore-throat structure patterns based on fractal theory provided by the present invention, aiming at the limitations of traditional methods, reconsiders the pore-throat binary structure and coordination number, simplifies pores into ball-stick bodies (i.e., a combination of spheres and circular tube bodies), uses the fractal power law to derive a new pore fractal formula with mercury saturation, and constructs a new method for determining the fractal dimension of rock pores based on the pore-throat binary structure, the ball-stick type formula method. The present invention deeply integrates the pore fractal dimension with the pore-throat topological structure, so that the value of the calculated pore fractal dimension is not limited by 3.0 and can be used to explain the pore-throat structure and its irregularity of rocks. The present invention is simple and easy to implement, and has strong operability. It not only provides a new technical means for determining the fractal dimension of reservoir pores, but also provides a new idea for explaining the complex pore-throat structure inside reservoir pores, has important guiding significance for the classification characterization and three-dimensional simulation of the complex pore-throat structure of reservoirs, and has broad application prospects.

[0164] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for analyzing pore-throat structure patterns based on fractal theory, characterized in that, Comprising: S1: Obtain the mercury intrusion curve of the rock sample through mercury intrusion experiments to obtain the mercury intrusion dynamic parameters of multiple test points; S2: Calculate the logarithmic values of the mercury intrusion dynamic parameters according to the mercury intrusion curve of the rock sample; S3: Fit the logarithmic values of the mercury intrusion dynamic parameters to obtain a linear regression fitting line; S4: Calculate the pore fractal dimension of the rock according to the slope of the linear regression fitting line; S5: Analyze the pore throat structure pattern according to the pore fractal dimension to obtain an analysis result.

2. The pore-throat structure pattern analysis method based on fractal theory according to claim 1, wherein, The mercury intrusion dynamic parameters in step S1 include: Mercury injection pressure, mercury injection saturation; The logarithmic values of the mercury intrusion dynamic parameters in step S2 include: Logarithmic value of mercury injection pressure, logarithmic value of mercury injection saturation.

3. The pore-throat structure pattern analysis method based on fractal theory according to claim 1, characterized in that The expression of the linear regression fitting line in step S3 is: lgS Hg = k·lgp c -A; where, lgS Hg is the logarithm of the mercury intrusion saturation, k is the slope of the linear regression fitting line, lgp c is the logarithm of the mercury intrusion pressure, and A is the intercept of the linear regression fitting line.

4. The pore-throat structure pattern analysis method based on fractal theory according to claim 1, characterized in that The expression of the pore fractal dimension in step S4 is: D = k + 3; Where D is the pore fractal dimension and k is the slope of the linear regression fitting line.

5. A method for analyzing pore-throat structure patterns based on fractal theory according to claim 1, characterized in that Step S5 further includes: S51: Combine the pore ball-and-stick model to decompose the pore fractal dimension into the pore channel fractal dimension and the throat fractal dimension to obtain a decomposition result; S52: Analyze the pore throat structure pattern according to the decomposition result to obtain an analysis result.

6. The pore-throat structure pattern analysis method based on the fractal theory according to claim 5, characterized in that, The expression of the decomposition result in step S51 is: D = D d + D t ; Among them, D is the pore fractal dimension, D d is the pore-throat fractal dimension, D t is the throat fractal dimension.

7. The method for analyzing pore-throat structure patterns based on fractal theory according to claim 5, characterized in that, Step S52 specifically includes: When the pore fractal dimension is greater than 4 and less than 6, the analysis result is that the pores have a 1-pore 1-throat structure; When the pore fractal dimension is greater than or equal to 6, the analysis result is that the pores have a 1-pore multi-throat structure; When the pore fractal dimension is less than or equal to 4, the analysis result is that the pores have a capillary structure.

8. An apparatus for analyzing pore-throat structure patterns based on fractal theory, characterized in that, Comprising: Acquisition module: Used to obtain the mercury intrusion curve of the rock sample through mercury intrusion experiments to obtain the mercury intrusion dynamic parameters of multiple test points; Logarithmic calculation module: Used to calculate the logarithmic values of the mercury intrusion dynamic parameters according to the mercury intrusion curve of the rock sample; Fitting module: Used to fit the logarithmic values of the mercury intrusion dynamic parameters to obtain a linear regression fitting line; Dimension calculation module: Used to calculate the pore fractal dimension of the rock according to the slope of the linear regression fitting line; Analysis module: Used to analyze the pore throat structure pattern according to the pore fractal dimension to obtain an analysis result.

9. An analysis device for pore-throat structure patterns based on fractal theory, characterized in that Comprising: A memory and at least one processor, wherein instructions are stored in the memory; At least one of the processors invokes the instructions in the memory so that a pore throat structure pattern analysis device based on fractal theory executes a pore throat structure pattern analysis method according to any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, Instructions are stored on the computer-readable storage medium, and when the instructions are executed by the processor, a pore throat structure pattern analysis method according to any one of claims 1-7 is implemented.

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