Tight sandstone reservoir type determination method based on pore connectivity

Abstract

The invention relates to a compact sandstone reservoir type determination method based on pore connectivity, comprising: constructing a pressure drop model, the number of pore radiuses in the pressure drop model being equal to the series of the pressure drop model, the pore radiuses comprising a maximum value, a minimum value and at least one intermediate value of the pore radius of a target reservoir section rock sample; when the difference value of at least one group of adjacent pore radiuses is less than or equal to 25nm, the corresponding pressure drop model is a final pressure drop model; and fitting the final pressure drop model with the pressure drop curve to obtain the pore pressure influence weight corresponding to each pore radius in the final pressure drop model, further solving to obtain a homogeneous coefficient, and obtaining the reservoir type according to the homogeneous coefficient. According to the method, the pore connectivity of the reservoir is quantified, the larger the homogeneity coefficient is, the stronger the pore connectivity is, and the better the physical property of the reservoir is, so that the fine division of the reservoir types is realized.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas engineering, and particularly to a method for determining the type of tight sandstone reservoir based on pore connectivity during the exploration and development process. Background Art

[0002] Tight oil and gas have become important resources for increasing reserves and production in each oilfield and supporting high-quality development, supporting the high-quality development of major oilfields, mainly distributed in large basins such as Ordos, Junggar, Songliao, Bohai Bay, and Sichuan Basin, with huge development potential. The type of reservoir is a key link in the exploration, development, and reserve implementation of each oilfield. Through a large number of actual core samplings and on-site detections in the oilfield, it is confirmed that continental tight gas reservoirs in China have strong heterogeneity, discontinuous sand bodies, developed alternating sand and mud deposits, and very dense pore throats, resulting in diverse and complex reservoir types. Even in the same development area, there are huge differences in reservoir types, which brings great challenges to the classification and evaluation of reservoir types.

[0003] Through extensive research and patent benchmarking, a large amount of work has been done on determining the type of reservoir at present. The main typical evaluation methods are as follows. (1) Xu Jingling et al. (Xu Jingling, Huo Jiaqing, Liu Shuanglian, etc. Method and system for predicting lithofacies sweet spots in shale reservoirs, Patent No.: CN202110232294.0). This method obtains the attribute parameters related to the daily oil production per meter based on the intersection relationship between the attribute parameters of the lithofacies of the shale reservoir and the daily oil production per meter, and establishes a comprehensive evaluation model for sweet spots based on the attribute parameters to intuitively evaluate the quality of the reservoir. It only considers the influencing factors of geological sweet spots and ignores engineering factors. (2) Zhang Shuxia et al. (Zhang Shuxia, Wang Zhenhua, Bai Fenfei, etc. A method for evaluating reservoir quality, Patent No.: CN202210571828.7). This method obtains reservoir parameters including porosity, oil saturation, cementation index, saturation index, shale content, and irreducible water saturation through downhole coring, further quantifies the reservoir quality factor, and classifies the reservoir to achieve a quantitative evaluation of reservoir quality. This method only considers reservoir quality parameters and does not consider the influence of engineering parameters of strongly heterogeneous reservoirs on reservoir quality. At the same time, to pursue the integration of geological and engineering sweet spots, engineering sweet spots have not been considered. The above typical methods are relatively single, and they evaluate reservoir quality and type classification through production parameters or geological parameter means. The considerations are simple and it is difficult to promote and apply. Therefore, it is necessary to establish a method for determining the type of tight oil and gas reservoir suitable for providing a reliable scientific basis for increasing reserves and production of tight oil and gas. Summary of the Invention

[0004] The present invention aims at the above problems and proposes a method for determining the type of tight sandstone reservoir based on pore connectivity.

[0005] The technical solution of the present invention lies in: A method for determining the type of tight sandstone reservoir based on pore connectivity ability is as follows: Construct a pressure drop model. The number of pore radii in the pressure drop model is equal to the number of stages of the pressure drop model. The pore radii include the maximum value, the minimum value, and at least one intermediate value of the pore radii of the rock samples in the target reservoir section. When the difference between at least one set of adjacent pore radii ≤ 25 nm, the corresponding pressure drop model is the final pressure drop model; Fit the final pressure drop model with the pressure drop curve to obtain the pore pressure influence weights corresponding to each pore radius in the final pressure drop model; Calculate the homogeneity coefficient of the rock samples in the target reservoir section through the following formula (7): (7) In the formula: HI is the homogeneity coefficient, dimensionless; n is the number of stages of the final pressure drop model, dimensionless; i is the number of pore radii in any pressure drop model, dimensionless; r ni is the pore radius of the final pressure drop model, nm; a ni is r ni the corresponding pore pressure influence weight, dimensionless; a nmax is a ni the maximum value of, dimensionless; r nmax is a nmax the corresponding pore radius, nm; If 0.65 < HI ≤ 1, the reservoir type is grade I; If 0.30 < HI ≤ 0.65, the reservoir type is grade II; If 0 < HI ≤ 0.30, the reservoir type is grade III.

[0006] Preferably, the calculation formula of the pressure drop model is: (6) b ki = π ( r ki × 10 -4 ) 2 / (96 μcL 2 ) (1) In the formula:P t is the pressure drop model, dimensionless; k is the order of the pressure drop model, taking values from 3 - n ; r ki is k the pore radius of the - order pressure drop model, nm; a ki is r ki the corresponding pore pressure influence weight, dimensionless; b ki is r ki the corresponding pore pressure drop rate, s -1 ; μ is the gas viscosity, cP ; c is the gas compressibility, psi -1 ; L is the length of the rock sample in the target reservoir section, cm.

[0007] Preferably, the specific obtaining process of the final pressure drop model is as follows: Construct k the - order pressure drop model, and obtain the k pore pressure drop rate corresponding to the pore radius r ki in the - order pressure drop model, b ki and fit it with the pressure drop curve to obtain the k pore pressure influence weight corresponding to the pore radius r ki in the - order pressure drop model; a ki ; Take k the maximum value of the pore pressure influence weight in the - order pressure drop model a kmax and the corresponding pore radius r kmax for pore classification. If the maximum value of the pore pressure influence weight a kmax is a maximum or minimum value, then the classified pore radius r (k+1)g is calculated by the following formula (3); otherwise, the classified pore radius r (k+1)g is calculated by the following formula (4): r (k+1)g =( r kmax+ r kl ) / twenty three) r (k+1)g =( r kmax + r kv ) / twenty four) Where: r (k+1)g is the graded pore radius, nm; r kmax for k Maximum value of pore pressure influence weight in stage pressure drop model a kmax Corresponding pore radius, nm; r kl For r kmax adjacent pore radius, nm; r kv For r kmax Adjacent and pore pressure affects weight a ki Larger pore radius, nm; The graded pore radius r (k+1)g Insert to k In the stage pressure drop model, construct k +1 level pressure drop model, when the difference between at least one set of adjacent pore radii is ≤25nm, the corresponding k The +1 level pressure drop model is the final pressure drop model.

[0008] More preferably, it also includes, if k In the +1 level pressure drop model, the difference between all adjacent pore radii is > 25 nm. k The +1-level pressure drop model continues to perform pore classification until there is at least one set of adjacent pore radii with a difference of ≤25 nm, and the final pressure drop model is obtained.

[0009] More preferably, the specific process of obtaining the final pressure drop model is: Construct a three-level pressure drop model. The pore radius in the three-level pressure drop model r 3i The maximum, minimum and first intermediate value of the pore radius of the target reservoir section rock sample are used to obtain the pore radius of each layer in the three-level pressure drop model. r 3i The corresponding pore pressure drop rate b 3i, the pore radius in the three - stage pressure drop model is obtained by fitting with the pressure drop curve r 3i corresponding to the pore pressure influence weight a 3i ; The pore radius corresponding to the maximum value of the pore pressure influence weight in the three - stage pressure drop model a 3max is used for the first pore classification. If the maximum value of the pore pressure influence weight r 3max is the maximum or minimum value, the first - stage classified pore radius a 3max is calculated by r 4g =( r 4g + r 3max ) / 2; Otherwise, the first - stage classified pore radius r 3l is calculated by r 4g =( r 4g + r 3max + r 3v ) / 2; The calculated first - stage classified pore radius r 4g is inserted into the three - stage pressure drop model to construct a four - stage pressure drop model, and it is judged whether the four - stage pressure drop model is the final pressure drop model; If the four - stage pressure drop model is not the final pressure drop model, then for the pore radius corresponding to the maximum value of the pore pressure influence weight in the four - stage pressure drop model a 4max a second pore classification is carried out to obtain the second - stage classified pore radius r 4max ; r 5g ; Similarly, a five - stage and above pressure drop model is constructed until there is at least a group of adjacent pore radius differences ≤ 25 nm, and the corresponding pressure drop model at this time is the final pressure drop model.

[0010] Preferably, the pressure drop curve is obtained by conducting a pressure drop test experiment on the rock sample of the target reservoir section, and according to the pressure data values of the rock sample of the target reservoir section at different time points, the pressure drop curve is plotted.

[0011] More preferably, the specific preparation process of the rock sample of the target reservoir section is as follows: The core taken from the target reservoir section is made into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm, placed in an ultrasonic cleaner, and cleaned with an ethanol solution for 30 minutes to remove surface impurities; then it is put into a constant temperature oven and dried at 105 °C for 24 hours to make the pores free of moisture, thereby making the rock sample of the target reservoir section.

[0012] More preferably, the pressure drop test experiment is carried out in an experimental test device for the pore connectivity of a tight sandstone reservoir; the experimental test device for the pore connectivity of a tight sandstone reservoir includes a constant speed and constant pressure pump, an intermediate container, a vacuum pump and a core holder connected in sequence, and the core holder contains the rock sample of the target reservoir section; the intermediate container is also connected with a pressure gauge.

[0013] More preferably, the specific process of the pressure drop test experiment is as follows: Place the rock sample of the target reservoir section in the core holder; First, use the constant speed and constant pressure pump to inject gas into the intermediate container until the pressure gauge shows the designed value and then stop; Carry out vacuum treatment on the core holder through the vacuum pump. After the vacuum treatment is completed, the gas in the intermediate container is introduced into the core holder, and at the same time, record the data points of the pressure and time in the pressure gauge until the pressure in the pressure gauge is stable, and end the experiment.

[0014] More preferably, the gas is nitrogen.

[0015] The technical effect of the present invention is as follows: The present invention proposes a method for determining the type of tight sandstone reservoir based on pore connectivity. Calculate the homogeneity coefficient of the rock sample of the target reservoir section according to the pore radius and the influence weight of pore pressure in the final pressure drop model, quantify the pore connectivity of the reservoir, the larger the homogeneity coefficient, the stronger the pore connectivity, and the better the reservoir physical properties, so as to realize the fine classification of reservoir types; The data source of the present invention is the actual core experiment test in the oilfield. The data is accurate and reliable, and the test method is simple and easy to operate. It can be quickly applied to the classification of reservoir types in the oilfield, greatly reducing the costs of a large number of core sampling, logging level testing and interpretation in the oilfield, and has good application prospects and promotion value for the determination of the types of similar sandstone reservoirs. Description of the Drawings

[0016] Figure 1 This is the experimental device diagram for the pressure drop test.

[0017] Figure 2 This is the fitting diagram of the pressure drop curve and the three-stage pressure drop model in a specific experimental case.

[0018] Figure 3 This is the fitting diagram of the pressure drop curve and the four-stage pressure drop model in a specific experimental case.

[0019] Figure 4 It is the fitting graph of the pressure drop curve and the five - stage pressure drop model in a specific experimental case.

[0020] Figure 5 It is the fitting graph of the pressure drop curve and the six - stage pressure drop model in a specific experimental case.

[0021] Figure 6 It is the fitting graph of the pressure drop curve and the seven - stage pressure drop model in a specific experimental case.

[0022] Reference numerals: 1. Constant - speed and constant - pressure pump; 2. Outlet valve of the constant - speed and constant - pressure pump; 3. Intermediate container; 4. Outlet valve of the intermediate container; 5. Vacuum pump; 6. Inlet valve of the vacuum pump; 7. Rock sample of the target reservoir section; 8. Pressure gauge; 9. Core holder. Detailed implementation manners

[0023] Example 1 A method for determining the type of tight sandstone reservoir based on pore connectivity ability is as follows: Construct a pressure drop model. The number of pore radii in the pressure drop model is equal to the number of stages of the pressure drop model. Its pore radii include the maximum value, the minimum value, and at least one intermediate value of the pore radii of the rock sample in the target reservoir section. When the difference between at least one group of adjacent pore radii ≤ 25 nm, the corresponding pressure drop model is the final pressure drop model; Fit the final pressure drop model with the pressure drop curve to obtain the pore pressure influence weights corresponding to each pore radius in the final pressure drop model; Calculate the homogeneity coefficient of the rock sample in the target reservoir section through Equation (7); If 0.65 < HI ≤ 1, the reservoir type is grade I; If 0.30 < HI ≤ 0.65, the reservoir type is grade II; If 0 < HI ≤ 0.30, the reservoir type is grade III.

[0024] Example 2 Based on Example 1, it further includes: The calculation formula of the pressure drop model is: (6) b ki = π ( r ki × 10 -4 ) 2 / (96 μcL 2 ) (1).

[0025] Example 3 On the basis of Embodiment 2, it further includes: The specific process of obtaining the final pressure drop model is as follows: Construct k the stage pressure drop model, and extract k the pore radius r ki corresponding to the pore pressure drop rate b ki in the stage pressure drop model, and fit it with the pressure drop curve to obtain k the pore pressure influence weight r ki corresponding to the pore radius a ki in the stage pressure drop model; Take k the maximum value of the pore pressure influence weight a kmax corresponding to the pore radius r kmax in the stage pressure drop model for pore classification. If the maximum value of the pore pressure influence weight a kmax is the maximum or minimum value, then the classified pore radius r (k+1)g is calculated by the following formula (3); otherwise, the classified pore radius r (k+1)g is calculated by the following formula (4): r (k+1)g =( r kmax + r kl ) / 2 (3) r (k+1)g =( r kmax + r kv ) / 2 (4); Insert the classified pore radius r (k+1)g into the k stage pressure drop model to construct k the +1 stage pressure drop model. When the difference between at least one group of adjacent pore radii ≤ 25 nm, the corresponding k +1 stage pressure drop model is the final pressure drop model; if k the difference between all adjacent pore radii in the +1 stage pressure drop model is > 25 nm, then continue to perform pore classification on the k +1 stage pressure drop model until there is at least one group of adjacent pore radii with a difference ≤ 25 nm to obtain the final pressure drop model.

[0026] The specific process is as follows: Construct a three - level pressure drop model. In the three - level pressure drop model, the pore radius r 3i is the maximum value, minimum value, and the first intermediate value of the pore radius of the rock sample in the target reservoir section. Extract the pore pressure drop rate r 3i corresponding to each pore radius b 3i in the three - level pressure drop model, and fit it with the pressure drop curve to obtain the pore pressure influence weight r 3i corresponding to each pore radius a 3i ; Take the pore radius a 3max corresponding to the maximum value of the pore pressure influence weight in the three - level pressure drop model for the first pore classification. If the maximum value of the pore pressure influence weight r 3max is the maximum value or the minimum value, the first - stage classification pore radius a 3max is calculated by r 4g =( r 4g + r 3max + r 3l ) / 2; otherwise, the first - stage classification pore radius r 4g is calculated by r 4g =( r 3max + r 3v ) / 2; Insert the calculated first - stage classification pore radius r 4g into the three - level pressure drop model to construct a four - level pressure drop model, and determine whether the four - level pressure drop model is the final pressure drop model; If the four - level pressure drop model is not the final pressure drop model, then for the pore radius a 4max corresponding to the maximum value of the pore pressure influence weight in the four - level pressure drop model r 4max conduct the second pore classification to obtain the second - stage classification pore radius r 5g ; Similarly, a pressure drop model for five levels and above is constructed until there is at least one set of differences in adjacent pore radii ≤ 25 nm. At this time, the corresponding pressure drop model is the final pressure drop model.

[0027] Example 4 Based on Example 3, it further includes: the pressure drop curve is obtained by conducting a pressure drop test experiment on the rock sample of the target reservoir section, and according to the pressure data values of the rock sample of the target reservoir section at different time points, the pressure drop curve is plotted; The specific preparation process of the rock sample of the target reservoir section is as follows: The core taken from the target reservoir section is made into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm, placed in an ultrasonic cleaner, and cleaned with an ethanol solution for 30 minutes to remove surface impurities; then placed in a constant temperature oven and dried at 105 °C for 24 hours to make the pores free of moisture, thereby making the rock sample of the target reservoir section; The pressure drop test experiment is carried out in a test device for the pore connectivity ability of a tight sandstone reservoir; the test device for the pore connectivity ability of a tight sandstone reservoir includes a constant speed and constant pressure pump 1, an intermediate container 3, a vacuum pump 5, and a core holder 9 connected in sequence, and the core holder 9 is internally provided with a rock sample 7 of the target reservoir section; the intermediate container 3 is also connected with a pressure gauge 8; The specific process of the pressure drop test experiment is as follows: Place the rock sample 7 of the target reservoir section in the core holder 9; First, use the constant speed and constant pressure pump 1 to inject gas into the intermediate container 3 until the pressure gauge 8 shows the designed value and then stop; Carry out vacuum treatment on the core holder 9 through the vacuum pump 5. After the vacuum treatment is completed, the gas in the intermediate container 3 is introduced into the core holder 9, and at the same time, record the data points of the pressure and time in the pressure gauge 8 until the pressure in the pressure gauge 8 is stable, and the experiment ends; The gas is nitrogen.

[0028] Specific experimental case YP is the main development area of typical tight sandstone reservoirs in China. Vertically, it is divided into three main sub-layers YP1~YP3. YY1 is an evaluation well in this area. Downhole coring has been carried out in the three main sub-layers in the early stage. In this specific experimental case, YP1 is taken as the target reservoir section, and the method proposed by the present invention is used to evaluate the reservoir type of the YP1 main sub-layer.

[0029] A method for determining the type of tight sandstone reservoir based on pore connectivity ability is as follows: Step 1: Take a core from the YP1 target reservoir section to make a rock sample SH-1 of the target reservoir section (the minimum value of the pore radius of the core of the YP1 target reservoir section is 5 nm, and the maximum value is 500 nm), conduct a pressure drop test experiment to obtain a data point set of pressure changing with time, and further obtain a pressure drop curve; The specific process of the pressure drop test experiment is as follows: Place the rock sample 7 of the target reservoir section in the core holder 9; First, close all valves except the outlet valve 2 of the constant rate and constant pressure pump, and use the constant rate and constant pressure pump 1 to inject gas into the intermediate container 3 until the pressure gauge 8 shows the designed value, then stop the constant rate and constant pressure pump 1 and close the outlet valve 2 of the constant rate and constant pressure pump; Open the inlet valve 6 of the vacuum pump, and perform vacuum treatment on the core holder 9 through the vacuum pump 5. After the vacuum treatment, close the inlet valve 6 of the vacuum pump, then open the outlet valve 4 of the intermediate container, and introduce the gas in the intermediate container 3 into the core holder 9. At the same time, record the data points of the pressure in the pressure gauge 8 and the corresponding time until the pressure in the pressure gauge 8 is stable, and end the experiment.

[0030] Step 2: Establish a three - stage pressure drop model; The pore radius of the three - stage pressure drop model is r 31 = 5nm, r 32 = 100nm and r 33 = 500nm. Calculate the pore pressure drop rate corresponding to each pore radius according to formula (1) respectively. The calculation results are shown in Table 1; The abscissa of the established three - stage pressure drop model is the pore radius, and the ordinate is the corresponding pore pressure drop rate. Table 1 Three - stage pressure drop model - Pore pressure drop rate ; Fit the three - stage pressure drop model with the pressure drop curve. The fitting diagram is shown in Figure 2 ; Obtain the influence weights of each pore pressure a 3i , and the results are shown in Table 2; Table 2 Three - stage pressure drop model - Influence weights of pore pressure ; As can be seen from Table 2, among the influence weights of pore pressure a 3i the maximum value of the influence weight of pore pressure a 3max = a 33 , and the corresponding pore radius r 3max = r 33 = 500nm. Since 500nm is the maximum value, use formula (3) for the first pore classification to obtain the first - stage classified pore radius r 4g =(100 + 500) / 2 = 300nm.

[0031] Step 3: Establish a four - stage pressure drop model - final pressure drop model in sequence; Insert the first-stage pore radius r 4g = 300 nm into the pore radius of the three-stage pressure drop model to form the pore radius of the four-stage pressure drop model, which are successively: r 41 = 5 nm, r 42 = 100 nm, r 43 = 300 nm and r 44 = 500 nm; Calculate the pore pressure drop rate corresponding to the pore radius r 43 = 300 nm according to formula (1) b 43 is 1.2337 s -1 ; Fit the four-stage pressure drop model with the pressure drop curve, and the fitting diagram is shown in Figure 3 ; Obtain the influence weights of each pore pressure a 4i , and the results are shown in Table 3; Table 3 Four-stage pressure drop model - Influence weights of pore pressure ; As can be seen from Table 3, among the influence weights of pore pressure a 4i , the maximum value of the influence weight of pore pressure a 4max = a 43 , and the corresponding pore radius r 4max = r 43 = 300 nm. Since 300 nm is not the maximum or minimum value, the second pore classification is carried out using formula (4), and the pore radii adjacent to r 43 are r 42 and r 44 , and the corresponding a 42 < a 44 , so the second-stage pore radius r 5g = ( r 4max + r 4v ) / 2 = ( r 43 + r 44) / 2 = (300 + 500) / 2 = 400 nm; Insert the second-stage pore radius r 5g = 400 nm into the pore radius of the four-stage pressure drop model to form the pore radius of the five-stage pressure drop model, which are successively: r 51 = 5 nm, r 52 = 100 nm, r 53 = 300 nm, r 54 = 400 nm and r 55 = 500 nm; Calculate the pore pressure drop rate corresponding to the pore radius r 54 = 300 nm according to formula (1) b 54 = 2.1932 s -1 ; Fit the five-stage pressure drop model with the pressure drop curve. The fitting graph is shown in Figure 4 ; Obtain the influence weights of each pore pressure a 5i , and the results are shown in Table 4; Table 4 Five-stage pressure drop model - Influence weights of pore pressure ; As can be seen from Table 4, among the influence weights of pore pressure a 5i , the maximum value of the influence weight of pore pressure a 5max = a 53 , and the corresponding pore radius r 5max = r 53 = 300 nm. Since 300 nm is not a maximum or minimum value, the third-stage pore grading is carried out using formula (4), and the pore radii adjacent to r 53 are r 52 and r 54 , and the corresponding a 52 < a 54 , so the third-stage pore radius r 6g = ( r 5max + r 5v) / 2=( r 53 + r 54 ) / 2=(300 + 400) / 2 = 350 nm; Insert the third - stage pore radius r 6g = 350 nm into the pore radius of the five - stage pressure - drop model to form the pore radius of the six - stage pressure - drop model, which are successively: r 61 = 5 nm, r 62 = 100 nm, r 63 = 300 nm, r 64 = 350 nm, r 65 = 400 nm and r 66 = 500 nm; Calculate the pore - pressure drop rate corresponding to the pore radius r 64 = 350 nm according to formula (1) b 64 = 1.6792 s -1 ; Fit the six - stage pressure - drop model with the pressure - drop curve. The fitting graph is shown in Figure 5 ; Obtain the influence weights of each pore pressure a 6i , and the results are shown in Table 5; Table 5 Six - stage pressure - drop model - influence weights of pore pressure ; As can be seen from Table 5, among the influence weights of pore pressure a 6i , the maximum value of the influence weight of pore pressure a 6max = a 63 , and the corresponding pore radius r 6max = r 63 = 300 nm. Since 300 nm is neither a maximum nor a minimum value, the fourth - stage pore classification is carried out using formula (4), and r 63 The adjacent pore radii are r 62 and r 64 , and the corresponding a 62 < a64 , so the pore radius of the fourth classification r 7g =( r 6max + r 6v ) / 2=( r 63 + r 64 ) / 2=(300 + 350) / 2 = 325 nm; Insert the pore radius of the fourth classification r 7g = 325 nm into the pore radius of the six - level pressure drop model to form the pore radius of the seven - level pressure drop model, which are successively: r 71 = 5 nm, r 72 = 100 nm, r 73 = 300 nm, r 74 = 325 nm, r 75 = 350 nm, r 76 = 400 nm and r 77 = 500 nm; It can be seen that r 73 = 300 nm and r 74 = 325 nm have a difference of 25 nm. Therefore, the seven - level pressure drop model is the final pressure drop model; Calculate the pore pressure drop rate corresponding to the pore radius r 74 = 325 nm according to formula (1) b 74 = 1.4479 s -1 ; Fit the seven - level pressure drop model with the pressure drop curve, and the fitting graph is shown in Figure 6 ; Obtain the influence weights of each pore pressure a 6i , and the results are shown in Table 6; Table 6 Seven - level pressure drop model - influence weights of pore pressure .

[0032] Step 4: Calculate the homogeneity coefficient of the rock sample in the target reservoir section according to Equation (7) HI = 0.621. Therefore, it is determined that the reservoir type of the main sub - layer of YP1 is Class II, and the reservoir physical properties are medium.

[0033] Traditionally, the permeability is generally used to calculate the traditional pore connectivity coefficient; the average permeability of the main sub-layer YP1 is known to be 0.288, and the permeability range in its similar reservoirs is generally 0.010 mD - 0.500 mD; the traditional pore connectivity coefficient is expressed in the same form as the oil and gas reservoir index using the following formula: HII =( h s - h smin ) / ( h smax - h smin ) = 0.567; In the formula: HII is the traditional pore connectivity coefficient, dimensionless; h s is the average permeability of the reservoir, mD; h smax is the maximum permeability of the similar reservoir, mD; h smin is the minimum permeability of the similar reservoir, mD; HII is 0.567, and according to the reservoir classification rules in this application, it is also a Class II reservoir.

Claims

1. A method for determining the type of tight sandstone reservoir based on pore connectivity, characterized in that: Here’s how: A pressure drop model is constructed, in which the number of pore radii is equal to the order of the pressure drop model, and the pore radius includes the maximum value, the minimum value and at least one intermediate value of the pore radius of the target reservoir section rock sample. When the difference between at least one group of adjacent pore radii is ≤25nm, the corresponding pressure drop model is the final pressure drop model; the final pressure drop model is fitted with the pressure drop curve to obtain the pore pressure influence weight corresponding to each pore radius in the final pressure drop model; The homogeneity coefficient of the target reservoir section rock sample is calculated by the following formula (7): （7） Where: HI is the homogeneity coefficient, dimensionless; n is the order of the final pressure drop model, dimensionless; i is the number of pore radii in any pressure drop model, dimensionless; r ni is the pore radius of the final pressure drop model, nm; a ni for r ni The corresponding pore pressure influence weight is dimensionless; a nmax for a ni The maximum value of , dimensionless; r nmax for a nmax The corresponding pore radius, nm; If 0.65< HI ≤1, the reservoir type is Class I; if 0.30< HI ≤0.65, the reservoir type is II; if 0< HI ≤0.30, the reservoir type is Class III.

2. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 1, characterized in that: The calculation formula of the pressure drop model is: （6） b ki = π ( r ki ×10 -4 ) 2 / (96 μcL 2 ) （1） Where: P t is the pressure drop model, dimensionless; k is the level of the pressure drop model, which takes a value of 3- n , dimensionless; r ki for k Pore ​​radius of the stage pressure drop model, nm; a ki for r ki The corresponding pore pressure influence weight is dimensionless; b ki for r ki The corresponding pore pressure drop rate, s -1 ; μ is the gas viscosity, cP ; c is the gas compressibility factor, psi -1 ; L is the length of the target reservoir section rock sample, cm.

3. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 2, characterized in that: The specific process of obtaining the final pressure drop model is as follows: Build k The pressure drop model is used to find k Pore ​​radius in the stage pressure drop model r ki The corresponding pore pressure drop rate b ki , which is fitted with the pressure drop curve k Pore ​​radius in the stage pressure drop model r ki Corresponding pore pressure influence weight a ki ; Will k Maximum value of pore pressure influence weight in stage pressure drop model a kmax The corresponding pore radius r kmax For pore classification, if the pore pressure affects the maximum weight a kmax is a maximum or minimum value, then the graded pore radius r (k+1)g It is calculated by the following formula (3); otherwise , graded pore radius r (k+1)g Calculated by the following formula (4): r (k+1)g =( r kmax + r kl ) / 2 （3） r (k+1)g =( r kmax + r kv ) / 2 （4） Where: r (k+1)g is the graded pore radius, nm; r kmax for k Maximum value of pore pressure influence weight in stage pressure drop model a kmax Corresponding pore radius, nm; r kl For r kmax adjacent pore radius, nm; r kv For r kmax Adjacent and pore pressure affects weight a ki Larger pore radius, nm; The graded pore radius r (k+1)g Insert to k In the stage pressure drop model, construct k +1 level pressure drop model, when the difference between at least one set of adjacent pore radii is ≤25nm, the corresponding k The +1 level pressure drop model is the final pressure drop model.

4. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 3, characterized in that: Also includes, if k In the +1 level pressure drop model, the difference between all adjacent pore radii is > 25 nm. k The +1-level pressure drop model continues to perform pore classification until there is at least one set of adjacent pore radii with a difference of ≤25 nm, and the final pressure drop model is obtained.

5. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 4, characterized in that: The specific process of obtaining the final pressure drop model is as follows: Construct a three-level pressure drop model. The pore radius in the three-level pressure drop model r 3i The maximum, minimum and first intermediate value of the pore radius of the target reservoir section rock sample are used to obtain the pore radius of each layer in the three-level pressure drop model. r 3i The corresponding pore pressure drop rate b 3i , and the pore radius in the three-level pressure drop model is obtained by fitting with the pressure drop curve r 3i Corresponding pore pressure influence weight a 3i ; The maximum value of the pore pressure influence weight in the three-level pressure drop model a 3max The corresponding pore radius r 3max Perform the first pore classification. If the pore pressure affects the maximum weight a 3max is a maximum or minimum value, then the first classification pore radius r 4g pass r 4g =( r 3max + r 3l ) / 2; otherwise, the first grade pore radius r 4g pass r 4g =( r 3max + r 3v ) / 2 is calculated; The calculated first-class pore radius r 4g Insert it into the three-level pressure drop model, construct a four-level pressure drop model, and determine whether the four-level pressure drop model is the final pressure drop model; If the four-level pressure drop model is not the final pressure drop model, the maximum value of the pore pressure influence weight in the four-level pressure drop model is a 4max The corresponding pore radius r 4max Perform the second pore classification to obtain the second classification pore radius r 5g ; Similarly, five-level and above pressure drop models are constructed until there is at least one set of adjacent pore radii with a difference of ≤25nm. At this time, the corresponding pressure drop model is the final pressure drop model.

6. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 1, characterized in that: The pressure drop curve is obtained by conducting a pressure drop test experiment on a target reservoir section rock sample and plotting the pressure drop curve according to the pressure data values ​​of the target reservoir section rock sample obtained at different time points.

7. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 6, characterized in that: The specific preparation process of the target reservoir section rock sample is as follows: the rock core taken from the target reservoir section is made into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm, placed in an ultrasonic cleaning machine, and cleaned with an ethanol solution for 30 minutes to remove surface impurities; then placed in a constant temperature oven and dried at 105°C for 24 hours to remove moisture in the pores, thereby making the target reservoir section rock sample.

8. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 7, characterized in that: The pressure drop test experiment is carried out in a tight sandstone reservoir pore connectivity test device; the tight sandstone reservoir pore connectivity test device comprises a constant speed constant pressure pump (1), an intermediate container (3), a vacuum pump (5) and a core holder (9) connected in sequence, the core holder (9) having a target reservoir section rock sample (7) built therein; the intermediate container (3) is also connected to a pressure gauge (8).

9. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 8, characterized in that: The specific process of the pressure drop test experiment is as follows: a target reservoir section rock sample (7) is placed in a core holder (9); first, a constant speed constant pressure pump (1) is used to pump gas into an intermediate container (3) until the pressure gauge (8) displays a designed value and then stops; a vacuum treatment is performed on the core holder (9) by a vacuum pump (5); after the vacuum treatment is completed, the gas in the intermediate container (3) is passed into the core holder (9), and the data points of pressure and time in the pressure gauge (8) are recorded at the same time, until the pressure of the pressure gauge (8) is stable, and the experiment is ended.

10. The method for determining the type of tight sandstone reservoir based on pore connectivity according to claim 9, characterized in that: The gas is nitrogen.

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