Method for evaluating sand body structure of tight sand gas reservoir

Abstract

The application discloses a method for evaluating sand body structure of a tight sand gas reservoir, and comprises the following steps: combining single-factor characteristic parameters obtained by different scale experimental methods such as well logging curve shape, macroscopic physical property, casting thin section, high-pressure mercury injection, constant-speed mercury injection and nuclear magnetic resonance, picking up well logging curve dentation rate, surface porosity standard deviation, high-pressure mercury injection index and other parameters such as key parameters of nuclear magnetic, constant-speed and phase permeability heterogeneity, constructing a radar chart for evaluating sand body structure heterogeneity, and finally forming a comprehensive evaluation standard for sand body structure heterogeneity with strong operability. The application can accurately quantitatively evaluate the sand body structure heterogeneity of the tight sand gas reservoir, and increases the precision of quality identification of the sand body structure of the tight sand gas reservoir.

Description

Technical Field

[0001] This invention belongs to the technical field of natural gas exploration and development methods, specifically relating to a method for evaluating the sand body structure of tight sandstone gas reservoirs. Background Technology

[0002] With conventional natural gas reservoirs becoming increasingly depleted and nearly exhausted, unconventional reservoirs, including carbonate rocks, tight sandstone, and shale gas reservoirs, have become the most important targets for exploration and development. Tight sandstone reservoirs are characterized by well-developed secondary porosity and strong lateral heterogeneity. Sand body structure evaluation is a powerful tool for the exploration, development, and reservoir evaluation of tight sandstone gas reservoirs, and it has great application potential.

[0003] The patent "Quantitative Differentiation Method and Device for Main Blocky Sandstone in Phase-Controlled Sandbody Structure" (Publication No.: CN201811234260.X; Publication Date: CN109298465A) published by China National Petroleum Corporation discloses a quantitative differentiation method and device for main blocky sandstone in phase-controlled sandbody structure. The method mainly includes dividing the sand body into sub-layers and using the comprehensive interpretation results of well logging as the object of sandbody structure research. However, it does not discuss the compatibility of other relevant experimental parameters of the reservoir.

[0004] The patent published by Northwest University, titled "A Quantitative Identification Method for Lithology and Sand Body Structure of Tight Sandstone Reservoirs" (Publication No.: CN202010061166.X; Publication Date: CN111487691A), discloses a quantitative identification method for lithology and sand body structure of tight sandstone reservoirs. It mainly uses well logging methods to identify and compensate for the lack of identification methods for sandstone reservoirs inside source rocks. However, it also lacks the matching of other relevant experimental parameters of the reservoir. Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating the sand body structure of tight sandstone gas reservoirs, which is beneficial for the accurate evaluation of the heterogeneity of the sand body structure of tight sandstone gas reservoirs and the effective assessment of the corresponding optimal selection of tight sandstone gas reservoirs.

[0006] The technical solution adopted in this invention is a quantitative evaluation method for the sand body structure of tight sandstone gas reservoirs, comprising the following steps: Step 1: Using the lowest GR value of the sand body structure well logging reservoir as the reservoir baseline, define the curve above the reservoir baseline as negative teeth and the curve below the reservoir baseline as positive teeth. Subtract the negative teeth from the number of positive teeth and divide by the sand body thickness to obtain the toothing rate T. Step 2: Collect the porosity, number of sections, and mean porosity of thin sections of sand body core castings to obtain the standard deviation S of porosity of the thin sections. Step 3: Collect mercury removal efficiency and mercury removal saturation from high-pressure mercury intrusion in sand body cores. Multiply the mercury removal saturation by the mercury removal efficiency to obtain the comprehensive parameter E for evaluating the pore structure of tight reservoirs. Step 4: Collect the maximum mercury saturation in the throat, the maximum mercury saturation in the pores, the maximum mercury ingress pressure, and the displacement pressure from the constant-rate mercury intrusion test of the sand body core. Analyze the morphological characteristics of the constant-rate mercury intrusion curves and use Mc, the heterogeneous parameter that is comprehensively affected by the parameters in the constant-rate mercury intrusion test data, as one of the indicators for evaluating the sand body structure. Step 5: Collect nuclear magnetic resonance experimental data of sand body structure cores, use nuclear magnetic resonance T2 spectrum and cumulative porosity spectrum distribution map, apply normal probability curve graphical method to analyze the characteristic parameters of pore throat size, and calculate the mean, standard deviation and nuclear magnetic heterogeneity coefficient T for quantitative characterization.

[0007] Step 6: Construct a comprehensive radar chart for evaluating microscopic heterogeneity to comprehensively determine the heterogeneity of the sand body structure.

[0008] The invention is further characterized in that, The formula for calculating the standard deviation S of the face rate in step 2 is as follows: (1) In equation (1), P i The face rate of sample i : Mean porosity of n thin sections of a sand body structure, where n is the number of thin sections; The formula for calculating E, the product of mercury removal saturation and mercury removal efficiency in step 3, is as follows: E=S W ×S E ×100 (2) In equation (2), E is the reservoir pore structure pore evaluation parameter, and S W For mercury removal efficiency, S E This refers to the mercury saturation level.

[0010] The formula for calculating the heterogeneity parameter Mc in step 4 is as follows: (3) In equation (3), Mc is the dispersion index of larynx size, and S Hg P represents the maximum mercury saturation level in the throat. max For the maximum mercury inlet pressure, P d To relieve driving pressure.

[0011] In step 5, when the NMR T2 spectrum shows a bimodal shape, the NMR heterogeneity coefficient T is 1 when the right peak is higher than the left peak. When the spectrum shows a bimodal shape, the NMR heterogeneity coefficient T is 2 when the left peak is higher than the right peak. When the spectrum shows a unimodal shape, the NMR heterogeneity coefficient T is 3 when the peak value is biased to the right. When the spectrum shows a unimodal shape, the NMR heterogeneity coefficient T is 4 when the peak value is biased to the left. The higher the NMR heterogeneity coefficient T value, the stronger the heterogeneity.

[0012] Step 6 requires parameters for constructing the radar chart, including the serration rate T of the sand body structure, the standard deviation of the porosity, the Mc index, and the high-pressure mercury intrusion index.

[0013] In step 6, the more fully the radar image is filled, the stronger the heterogeneity of the sand body structure.

[0014] The beneficial effect of this invention is that it can accurately and quantitatively evaluate the heterogeneity of the structure of dense sandstone, thereby increasing the accuracy of quality identification of dense sandstone. Attached Figure Description

[0015] Figure 1 This is a structural analysis diagram of the sand body in well y47 of Example 4 in the tight sandstone gas reservoir sand body structure evaluation method of the present invention; Figure 2 This is a correlation graph of porosity standard deviation S-index and permeability in Example 4 of the tight sandstone gas reservoir sand body structure evaluation method of the present invention; Figure 3 This is a radar image of the heterogeneity evaluation of the multi-parameter sand body structure of well x in Example 4 of the sand body structure evaluation method for tight sandstone gas reservoirs of the present invention. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0017] Example 1 Step 1: Collect drilling logging data. Due to different sand body stacking relationships, the logging curve shapes vary. The sand body structure is most intuitively reflected in the shape of the logging curves. Based on the observation and statistics of the logging curve shapes in the study area, the concept of toothing rate is introduced for quantitative evaluation of sand body structure. Toothing rate refers to finding the reservoir baseline on the logging curve, which is the lowest GR value of the reservoir interpreted by logging in this area. Then, curves above the reservoir baseline are defined as negative teeth, and curves below the reservoir baseline are defined as positive teeth. The toothing rate T is obtained by subtracting the negative teeth from the positive teeth and dividing by the sand body thickness. Statistical data shows that the greater the deviation of T from 0, the stronger the heterogeneity of the sand body structure.

[0018] Step 2: Collect relevant thin-section data of the sand body structure. Based on the experimental statistics and geostatistics of thin sections, the heterogeneity of the porosity is a kind of numerical dispersion from a statistical perspective. Probability statistics uses standard deviation to quantitatively evaluate the dispersion of a series of data. Therefore, the standard deviation of the porosity can be used as the porosity standard deviation S. The calculation formula is as follows: (1) In equation (1), P i The face rate of sample i : Mean porosity of n thin sections of a sand body structure, where n is the number of thin sections; Analysis of the correlation between the standard deviation of porosity (S) and reservoir porosity and permeability shows a negative correlation between the standard deviation of porosity and porosity; the larger the standard deviation of porosity, the lower the permeability. The porosity-permeability characteristics represented by the standard deviation of porosity indicate that the larger the standard deviation, the worse the reservoir properties and the stronger the heterogeneity.

[0020] Step 3: Collect relevant mercury injection experimental data on sandstone structure. Through reservoir pore throat studies, it was found that the correlation between characteristic parameters and mercury removal efficiency and saturation is generally weak, especially with mercury removal efficiency, where the correlation is even lower. Previous proposed reservoir pore structure characteristic evaluation parameters are mostly for medium- and high-permeability reservoirs. These methods have good adaptability and application effects for medium- and high-permeability reservoirs. For tight sandstone reservoirs, this invention adopts the product of mercury removal saturation and mercury removal efficiency, E, as a comprehensive parameter for evaluating the pore structure of tight reservoirs. The calculation formula is as follows: E=S W ×S E ×100 (2) In equation (2), E is the reservoir pore structure pore evaluation parameter, and S W For mercury removal efficiency, S E This refers to the mercury saturation level.

[0021] Based on the relationship between E and physical properties and pore throat parameters, E is most closely related to the maximum mercury saturation, showing a certain correlation, while E has a weak positive correlation with porosity. This indicates that the influencing factors of E are complex and can represent the complex pore structure characteristics of sand bodies.

[0022] Step 4: Collect constant-rate mercury intrusion test data of sand body structure cores, analyze the morphological characteristics of the curves, and use the heterogeneity parameter Mc, which is comprehensively affected by parameters such as the maximum mercury saturation in the throat, the maximum mercury saturation in the pores, the maximum mercury intrusion pressure and the displacement pressure in the constant-rate mercury intrusion test data, as one of the indicators for evaluating sand body structure. The smaller the Mc index, the stronger the heterogeneity of the sand body structure.

[0023] (3) In equation (3), Mc is the dispersion index of larynx size, and S Hg Maximum mercury saturation in the throat, P max For the maximum mercury inlet pressure, P d To relieve driving pressure.

[0024] Step 5: Collect nuclear magnetic resonance experimental data of sand body structure cores. Using the nuclear magnetic resonance T2 spectrum and cumulative porosity spectrum distribution map, the characteristic parameters of pore throat size are analyzed by applying the normal probability curve graphical method. The mean, standard deviation, nuclear magnetic heterogeneity coefficient T and other parameters can also be quantitatively characterized. When the spectrum shows a bimodal shape with the right peak higher than the left peak, the T value is 1. The higher the T value, the stronger the heterogeneity. The sand body has very poor heterogeneity.

[0025] Step 6: In actual production research, using as many experimental methods as possible to select relevant heterogeneity evaluation indices can more accurately evaluate the heterogeneity of sand body structures.

[0026] Step 7: In order to demonstrate the interrelationships of various parameters and their influence on the heterogeneity of sand body structure, based on the main controlling factors of microscopic heterogeneity and the single-factor characteristic parameters obtained from experiments at different scales, key parameters of heterogeneity and pore throat structure heterogeneity such as the serration rate T, porosity standard deviation, Mc index, high-pressure mercury intrusion index, and other parameters such as NMR, constant velocity, and phase infiltration are selected to construct a comprehensive radar chart for evaluating microscopic heterogeneity. The distribution characteristics of the radar chart can be used to comprehensively judge the heterogeneity of sand body structure. The fuller the radar chart is, the stronger the heterogeneity of sand body structure.

[0027] Example 2 Step 1: Collect drilling logging data. Due to different sand body stacking relationships, the logging curve shapes vary. The sand body structure is most intuitively reflected in the shape of the logging curves. Based on the observation and statistics of the logging curve shapes in the study area, the concept of toothing rate is introduced for quantitative evaluation of sand body structure. Toothing rate refers to finding the reservoir baseline on the logging curve, which is the lowest GR value of the reservoir interpreted by logging in this area. Then, curves above the reservoir baseline are defined as negative teeth, and curves below the reservoir baseline are defined as positive teeth. The toothing rate T is obtained by subtracting the negative teeth from the positive teeth and dividing by the sand body thickness. Statistical data shows that the greater the deviation of T from 0, the stronger the heterogeneity of the sand body structure.

[0028] Step 2: Collect relevant thin-section data of the sand body structure. Based on the experimental statistics and geostatistics of thin sections, the heterogeneity of the porosity is a kind of numerical dispersion from a statistical perspective. Probability statistics uses standard deviation to quantitatively evaluate the dispersion of a series of data. Therefore, the standard deviation of the porosity can be used as the porosity standard deviation S. The calculation formula is as follows: (1) In equation (1), P i The face rate of sample i : Mean porosity of n thin sections of a sand body structure, where n is the number of thin sections; Analysis of the correlation between the standard deviation of porosity (S) and reservoir porosity and permeability shows a negative correlation between the standard deviation of porosity and porosity; the larger the standard deviation of porosity, the lower the permeability. The porosity-permeability characteristics represented by the standard deviation of porosity indicate that the larger the standard deviation, the worse the reservoir properties and the stronger the heterogeneity.

[0030] Step 3: Collect relevant mercury injection experimental data on sandstone structure. Through reservoir pore throat studies, it was found that the correlation between characteristic parameters and mercury removal efficiency and saturation is generally weak, especially with mercury removal efficiency, where the correlation is even lower. Previous proposed reservoir pore structure characteristic evaluation parameters are mostly for medium- and high-permeability reservoirs. These methods have good adaptability and application effects for medium- and high-permeability reservoirs. For tight sandstone reservoirs, this invention adopts the product of mercury removal saturation and mercury removal efficiency, E, as a comprehensive parameter for evaluating the pore structure of tight reservoirs. The calculation formula is as follows: E=S W ×S E ×100 (2) In equation (2), E is the reservoir pore structure pore evaluation parameter, and S W For mercury removal efficiency, S E This refers to the mercury saturation level.

[0031] Based on the relationship between E and physical properties and pore throat parameters, E is most closely related to the maximum mercury saturation, showing a certain correlation, while E has a weak positive correlation with porosity. This indicates that the influencing factors of E are complex and can represent the complex pore structure characteristics of sand bodies.

[0032] Step 4: Collect constant-rate mercury intrusion test data of sand body structure cores, analyze the morphological characteristics of the curves, and use the heterogeneity parameter Mc, which is comprehensively affected by parameters such as the maximum mercury saturation in the throat, the maximum mercury saturation in the pores, the maximum mercury intrusion pressure and the displacement pressure in the constant-rate mercury intrusion test data, as one of the indicators for evaluating sand body structure. The smaller the Mc index, the stronger the heterogeneity of the sand body structure.

[0033] (3) In equation (3), Mc is the dispersion index of larynx size, and S Hg Maximum mercury saturation in the throat, P max For the maximum mercury inlet pressure, P d To relieve driving pressure.

[0034] Step 5: Collect NMR experimental data of the sand body structure core. Using the NMR T2 spectrum and cumulative porosity spectrum distribution map, analyze the characteristic parameters of pore throat size using the normal probability curve graphical method. Calculate parameters such as mean, standard deviation, and NMR heterogeneity coefficient T for quantitative characterization. The spectrum shows a bimodal shape, with the left peak higher and the right peak lower. The T value is 2. The higher the T value, the stronger the heterogeneity. This sand body has poor heterogeneity.

[0035] Step 6: In actual production research, using as many experimental methods as possible to select relevant heterogeneity evaluation indices can more accurately evaluate the heterogeneity of sand body structures.

[0036] Step 7: In order to demonstrate the interrelationships of various parameters and their influence on the heterogeneity of sand body structure, based on the main controlling factors of microscopic heterogeneity and the single-factor characteristic parameters obtained from experiments at different scales, key parameters of heterogeneity and pore throat structure heterogeneity such as the serration rate T, porosity standard deviation, Mc index, high-pressure mercury intrusion index, and other parameters such as NMR, constant velocity, and phase infiltration are selected to construct a comprehensive radar chart for evaluating microscopic heterogeneity. The distribution characteristics of the radar chart can be used to comprehensively judge the heterogeneity of sand body structure. The fuller the radar chart is, the stronger the heterogeneity of sand body structure.

[0037] Example 3 Step 1: Collect drilling logging data. Due to different sand body stacking relationships, the logging curve shapes vary. The sand body structure is most intuitively reflected in the shape of the logging curves. Based on the observation and statistics of the logging curve shapes in the study area, the concept of toothing rate is introduced for quantitative evaluation of sand body structure. Toothing rate refers to finding the reservoir baseline on the logging curve, which is the lowest GR value of the reservoir interpreted by logging in this area. Then, curves above the reservoir baseline are defined as negative teeth, and curves below the reservoir baseline are defined as positive teeth. The toothing rate T is obtained by subtracting the negative teeth from the positive teeth and dividing by the sand body thickness. Statistical data shows that the greater the deviation of T from 0, the stronger the heterogeneity of the sand body structure.

[0038] Step 2: Collect relevant thin-section data of the sand body structure. Based on the experimental statistics and geostatistics of thin sections, the heterogeneity of the porosity is a kind of numerical dispersion from a statistical perspective. Probability statistics uses standard deviation to quantitatively evaluate the dispersion of a series of data. Therefore, the standard deviation of the porosity can be used as the porosity standard deviation S. The calculation formula is as follows: (1) In equation (1), P i The face rate of sample i : Mean porosity of n thin sections of a sand body structure, where n is the number of thin sections; Analysis of the correlation between the standard deviation of porosity (S) and reservoir porosity and permeability shows a negative correlation between the standard deviation of porosity and porosity; the larger the standard deviation of porosity, the lower the permeability. The porosity-permeability characteristics represented by the standard deviation of porosity indicate that the larger the standard deviation, the worse the reservoir properties and the stronger the heterogeneity.

[0040] Step 3: Collect relevant mercury injection experimental data on sandstone structure. Through reservoir pore throat studies, it was found that the correlation between characteristic parameters and mercury removal efficiency and saturation is generally weak, especially with mercury removal efficiency, where the correlation is even lower. Previous proposed reservoir pore structure characteristic evaluation parameters are mostly for medium- and high-permeability reservoirs. These methods have good adaptability and application effects for medium- and high-permeability reservoirs. For tight sandstone reservoirs, this invention adopts the product of mercury removal saturation and mercury removal efficiency, E, as a comprehensive parameter for evaluating the pore structure of tight reservoirs. The calculation formula is as follows: E=S W ×S E ×100 (2) In equation (2), E is the reservoir pore structure pore evaluation parameter, and S W For mercury removal efficiency, S E This refers to the mercury saturation level.

[0041] Based on the relationship between E and physical properties and pore throat parameters, E is most closely related to the maximum mercury saturation, showing a certain correlation, while E has a weak positive correlation with porosity. This indicates that the influencing factors of E are complex and can represent the complex pore structure characteristics of sand bodies.

[0042] Step 4: Collect constant-rate mercury intrusion test data of sand body structure cores, analyze the morphological characteristics of the curves, and use the heterogeneity parameter Mc, which is comprehensively affected by parameters such as the maximum mercury saturation in the throat, the maximum mercury saturation in the pores, the maximum mercury intrusion pressure and the displacement pressure in the constant-rate mercury intrusion test data, as one of the indicators for evaluating sand body structure. The smaller the Mc index, the stronger the heterogeneity of the sand body structure.

[0043] (3) In equation (3), Mc is the dispersion index of larynx size, and S Hg Maximum mercury saturation in the throat, P max For the maximum mercury inlet pressure, P d To relieve driving pressure.

[0044] Step 5: Collect nuclear magnetic resonance experimental data of sand body structure cores. Using nuclear magnetic resonance T2 spectrum and cumulative porosity spectrum distribution map, the characteristic parameters of pore throat size are analyzed by applying the normal probability curve graphical method. The mean, standard deviation, nuclear magnetic heterogeneity coefficient T and other parameters can also be quantitatively characterized. The spectrum shows a single peak with the peak value to the right. The T value is 3. The higher the T value, the stronger the heterogeneity. This sand body has strong heterogeneity.

[0045] Step 6: In actual production research, using as many experimental methods as possible to select relevant heterogeneity evaluation indices can more accurately evaluate the heterogeneity of sand body structures.

[0046] Step 7: In order to demonstrate the interrelationships of various parameters and their influence on the heterogeneity of sand body structure, based on the main controlling factors of microscopic heterogeneity and the single-factor characteristic parameters obtained from experiments at different scales, key parameters of heterogeneity and pore throat structure heterogeneity such as the serration rate T, porosity standard deviation, Mc index, high-pressure mercury intrusion index, and other parameters such as NMR, constant velocity, and phase infiltration are selected to construct a comprehensive radar chart for evaluating microscopic heterogeneity. The distribution characteristics of the radar chart can be used to comprehensively judge the heterogeneity of sand body structure. The fuller the radar chart is, the stronger the heterogeneity of sand body structure.

[0047] Example 4 This will be further illustrated by a specific example of the He8 section reservoir in a certain area of ​​a basin.

[0048] The average permeability of the He 8 section in this area is concentrated between 0.1 and 1 mD, with reservoirs having an average permeability of less than 0.5 mD being the main type. These reservoirs are characterized by poor physical properties, low porosity, low permeability, and are tight. This embodiment provides an evaluation method for the sandstone structure of the aforementioned tight sandstone gas reservoir, which includes the following steps: Step 1: Due to different sand body stacking relationships, the logging curve morphology varies. The most intuitive manifestation of sand body structure is in the morphology of the logging curve. Based on the observation and statistics of logging curve morphology in the study area, this invention introduces the concept of toothing rate for quantitative evaluation of sand body structure. Toothing rate refers to finding the reservoir baseline on the logging curve, i.e., the lowest GR value of the reservoir interpreted by logging in that area. Then, curves above the reservoir baseline are defined as negative teeth, and curves below the reservoir baseline are defined as positive teeth. The toothing rate T is obtained by subtracting the negative teeth from the positive teeth and dividing by the sand body thickness. Statistical data shows that the greater the deviation of T from 0, the stronger the heterogeneity of the sand body structure. Figure 1 The analysis of the sand body structure in well Y47 shows that there are two sand body segments: the upper segment (2480m-2490m) and the lower segment (2497m-2506m). The thickness of the two sand body segments is basically similar. By calculating the toothedness of the sand body structure, it can be found that the upper segment is 0 and the lower segment is 0.38, which confirms that the upper sand body segment is relatively more homogeneous.

[0049] Step two: Based on the statistical analysis of thin section experiments in the study area, the reservoir in the study area has undergone long-term diagenesis, mainly developing intergranular pores, dissolution pores, and a small number of intercrystalline pores and microfractures. The porosity distribution of the reservoir samples in the study area is extremely uneven, with strong numerical dispersion. According to geostatistical principles, porosity heterogeneity is a form of numerical dispersion from a statistical perspective. Probability statistics uses standard deviation to quantitatively evaluate the dispersion of a series of data. Therefore, the standard deviation of porosity can be used as the porosity standard deviation S, calculated as follows: (1) In equation (1), P i The face rate of sample i : Mean porosity of n thin sections of a sand body structure, where n is the number of thin sections; According to such Figure 2 The correlation diagram shown illustrates the relationship between the standard deviation of porosity (S) and reservoir porosity and permeability. The diagram reveals a negative correlation between the standard deviation of porosity and porosity; a larger standard deviation indicates lower permeability. The porosity-permeability characteristics represented by the standard deviation of porosity indicate that a larger standard deviation suggests poorer reservoir properties and stronger heterogeneity. In this sand body structure, the standard deviation of porosity (S) is 1.6, indicating a moderate level of heterogeneity.

[0051] Step three, through the study of reservoir pore throats, revealed that the correlation between characteristic parameters and mercury removal efficiency and mercury removal saturation is generally weak, especially with mercury removal efficiency, where the correlation is even lower. Previous proposed reservoir pore structure characteristic evaluation parameters are mostly for medium- and high-permeability reservoirs. These methods have good adaptability and application effects for medium- and high-permeability reservoirs. For tight sandstone reservoirs, this invention adopts the product E of mercury removal saturation and mercury removal efficiency as a comprehensive parameter for evaluating the pore structure of tight reservoirs. The calculation formula is as follows: E=S W ×S E ×100 (2) In equation (2), E is the reservoir pore structure pore evaluation parameter; S W For mercury removal efficiency, S E This refers to the mercury saturation level.

[0052] The factors influencing E are complex and can represent the complex pore structure characteristics of sand bodies.

[0053] Step four involves analyzing the morphological characteristics of the constant-rate mercury intrusion (CRI) curves. Various experimental parameters can effectively characterize the microscopic pore-throat features of the reservoir. For constant-rate mercury intrusion experiments on tight sandstone reservoirs, the Mc heterogeneity index uses the maximum mercury saturation in the throat, the maximum mercury saturation in the pores, the maximum mercury intrusion pressure, and the displacement pressure as parameters to evaluate the heterogeneity of the tight reservoir. A Mc index of 0.005 indicates strong heterogeneity in the sandstone structure.

[0054] Step five, in addition to the qualitative analysis of the NMR T2 spectrum curve morphology and the multi-component porosity component identification method, this study, based on the graphical characteristic model and empirical distribution model of the normal distribution of pore structure, used the NMR T2 spectrum and cumulative porosity spectrum distribution map, and applied the normal probability curve graphical method to analyze the characteristic parameters of pore throat size, calculating parameters such as mean, standard deviation, and NMR heterogeneity coefficient T for quantitative characterization. The spectrum shows a single peak with the peak value skewed to the right, and the T value is 3, indicating that the heterogeneity of the sand body structure is moderate.

[0055] Step Six: To demonstrate the interrelationships of various parameters and their impact on the heterogeneity of the sand body structure, this embodiment, based on the main controlling factors of microscopic heterogeneity and single-factor characteristic parameters obtained from experiments at different scales, extracts key parameters of heterogeneity and pore-throat structural heterogeneity in this gas layer, such as the standard deviation of porosity, property fit, Mc index, high-pressure mercury intrusion index, and (NMR, constant velocity, phase permeability) parameters, and constructs a model as follows: Figure 3 The radar chart shown here is a comprehensive assessment of microscopic heterogeneity. The distribution characteristics of the radar chart can be used to comprehensively determine the heterogeneity of the sand body structure. Figure 3 The sand body is relatively full, therefore the structure is evaluated as highly heterogeneous.

Claims

1. A quantitative evaluation method for the sandbody structure of tight sandstone gas reservoirs, characterized in that, Includes the following steps: Step 1: Using the lowest GR value of the sand body structure well logging reservoir as the reservoir baseline, define the curve above the reservoir baseline as negative teeth and the curve below the reservoir baseline as positive teeth. Subtract the number of negative teeth from the number of positive teeth and divide by the sand body thickness to obtain the toothing rate T. Step 2: Collect the porosity, number of sections, and mean porosity of thin sections of sand body core castings to obtain the standard deviation S of porosity of the thin sections. The formula for calculating the standard deviation S of the face rate in step 2 is as follows: （1） In equation (1), P i The face rate of sample i : Mean porosity of n thin sections of a sand body structure, where n is the number of thin sections; Step 3: Collect mercury removal efficiency and mercury removal saturation from high-pressure mercury intrusion in sand body cores. Multiply the mercury removal saturation by the mercury removal efficiency to obtain the comprehensive parameter E for evaluating the pore structure of tight reservoirs. The formula for calculating E, the product of mercury removal saturation and mercury removal efficiency, in step 3 is as follows: E=S W ×S E ×100 (2) In equation (2), E is the reservoir pore structure pore evaluation parameter, and S W For mercury removal efficiency, S E Mercury saturation; Step 4: Collect the maximum mercury saturation in the throat, the maximum mercury saturation in the pores, the maximum mercury ingress pressure, and the displacement pressure from the constant-rate mercury intrusion test of the sand body core. Analyze the morphological characteristics of the constant-rate mercury intrusion curves and use Mc, the heterogeneous parameter that is comprehensively affected by the parameters in the constant-rate mercury intrusion test data, as one of the indicators for evaluating the sand body structure. The formula for calculating the heterogeneity parameter Mc in step 4 is as follows: （3） In equation (3), Mc is the dispersion index of larynx size, and S Hg P represents the maximum mercury saturation level in the throat. max For the maximum mercury inlet pressure, P d To relieve driving pressure; Step 5: Collect nuclear magnetic resonance experimental data of sand body structure cores, use nuclear magnetic resonance T2 spectrum and cumulative porosity spectrum distribution map, apply normal probability curve graphical method to analyze the characteristic parameters of pore throat size, and calculate the mean, standard deviation and nuclear magnetic heterogeneity coefficient T for quantitative characterization. In step 5, when the NMR T2 spectrum shows a bimodal shape, the NMR heterogeneity coefficient T is 1 when the right peak is higher than the left peak. When the spectrum shows a bimodal shape, the NMR heterogeneity coefficient T is 2 when the left peak is higher than the right peak. When the spectrum shows a unimodal shape, the NMR heterogeneity coefficient T is 3 when the peak value is biased to the right. When the spectrum shows a unimodal shape, the NMR heterogeneity coefficient T is 4 when the peak value is biased to the left. The higher the NMR heterogeneity coefficient T value, the stronger the heterogeneity. Step 6: Construct a comprehensive radar chart for evaluating microscopic heterogeneity to comprehensively assess the heterogeneity of the sand body structure; The parameters required for constructing the radar chart in step 6 include the serration rate T of the sand body structure, the standard deviation of the porosity, the Mc index, and the high-pressure mercury intrusion index. In step 6, the more fully the radar image is filled, the stronger the heterogeneity of the sand body structure.

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