A method for determining the type of tight sandstone reservoir based on pore connectivity

Abstract

The present invention relates to a method for determining the type of tight sandstone reservoir based on pore connectivity ability. A pressure drop model is constructed, and 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; the final pressure drop model is fitted with the pressure drop curve to obtain the pore pressure influence weights corresponding to each pore radius in the final pressure drop model, and then the homogeneity coefficient is solved, and the reservoir type is obtained according to the homogeneity coefficient. The present invention quantifies the pore connectivity ability of the reservoir. The larger the homogeneity coefficient, the stronger the pore connectivity ability and the better the reservoir physical properties, thereby realizing the fine classification of reservoir types.

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 and supporting high-quality development in each oilfield, supporting the high-quality development of major oilfields. They are mainly distributed in large basins such as Ordos, Junggar, Songliao, Bohai Bay, and Sichuan Basin, with great 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 sand-mud interbedding, and very dense pore throats, resulting in diverse and complex reservoir types. There are also huge differences in reservoir types in the same development area, 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 the lithofacies sweet spot of 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 the sweet spot 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 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, in order 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 to provide a reliable scientific basis for increasing reserves and production of tight oil and gas. Summary of the Invention

[0004] The present invention aims to address 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:

[0006] A method for determining the type of tight sandstone reservoir based on pore connectivity ability is as follows:

[0007] 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;

[0008] Calculate the homogeneity coefficient of the rock samples in the target reservoir section through the following formula (7):

[0009] (7)

[0010] In the formula: HI is the homogeneity coefficient, dimensionless;

[0011] n is the number of stages of the final pressure drop model, dimensionless;

[0012] i is the number of pore radii in any pressure drop model, dimensionless;

[0013] 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;

[0014] 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.

[0015] Preferably, the calculation formula of the pressure drop model is:

[0016] (6)

[0017] bki = π ( r ki ×10 -4 ) 2 / (96 μcL 2 ) (1)

[0018] In the formula: P t is the pressure drop model, dimensionless;

[0019] k is the order of the pressure drop model, with a value of 3 - n ;

[0020] 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.

[0021] Preferably, the specific obtaining process of the final pressure drop model is as follows:

[0022] Construct k -order pressure drop model, and obtain k the pore pressure drop rate r ki corresponding to the pore radius b ki in the -order 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 ;

[0023] Take k the maximum value of the pore pressure influence weight a kmax corresponding to the pore radius r kmaxPerform pore grading. If the maximum value of the pore pressure influence weight a kmax is a maximum or minimum value, then the graded pore radius r (k+1)g is calculated by the following formula (3); otherwise, the graded pore radius r (k+1)g is calculated by the following formula (4):

[0024] r (k+1)g =( r kmax + r kl ) / 2 (3)

[0025] r (k+1)g =( r kmax + r kv ) / 2 (4)

[0026] In the formula: r (k+1)g is the graded pore radius, nm;

[0027] r kmax is k the maximum value of the pore pressure influence weight in the a kmax -level pressure drop model corresponding pore radius, nm; r kl is the pore radius adjacent to r kmax , nm;

[0028] r kv is the pore radius adjacent to r kmax and with a relatively large pore pressure influence weight a ki , nm;

[0029] Insert the graded pore radius r (k+1)g into the k -level pressure drop model to construct the k +1-level pressure drop model. When the difference between at least one set of adjacent pore radii ≤ 25 nm, the corresponding k +1-level pressure drop model is the final pressure drop model.

[0030] More preferably, it also includes that if k in the +1-level pressure drop model, the differences between all adjacent pore radii are > 25 nm, then fork The +1 level pressure drop model continues pore classification until there is at least one set of adjacent pore radius differences ≤ 25 nm, obtaining the final pressure drop model.

[0031] More preferably, the specific obtaining process of the final pressure drop model is as follows:

[0032] Construct a three - level pressure drop model, where the pore radii in the three - level pressure drop model r 3i are the maximum value, minimum value, and first intermediate value of the pore radii of the rock sample in the target reservoir section. Obtain the pore pressure drop rates r 3i corresponding to each pore radius b 3i in the three - level pressure drop model, and fit with the pressure drop curve to obtain the pore pressure influence weights r 3i corresponding to each pore radius a 3i ;

[0033] 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, then the first - stage classified pore radius a 3max is calculated by r 4g =( r 4g =( r 3max + r 3l ) / 2; Otherwise, the first - stage classified pore radius r 4g is calculated by r 4g =( r 3max + r 3v ) / 2;

[0034] Insert the calculated first - stage classified 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;

[0035] If the four - level pressure drop model is not the final pressure drop model, then for the maximum value of the pore pressure influence weight in the four - level pressure drop model a4max The corresponding pore radius r 4max Perform the second pore classification to obtain the second classified pore radius r 5g ;

[0036] Similarly, construct a pressure drop model for five levels and above until there is at least one set of adjacent pore radius differences ≤ 25 nm. At this time, the corresponding pressure drop model is the final pressure drop model.

[0037] Preferably, the pressure drop curve is obtained by conducting a pressure drop test experiment on the rock sample of the target reservoir section, and based on the pressure data values of the rock sample of the target reservoir section at different time points obtained, the pressure drop curve is plotted.

[0038] 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 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.

[0039] More preferably, the pressure drop test experiment is carried out in a test device for the pore connectivity of a tight sandstone reservoir; the 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.

[0040] 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; perform 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 then end the experiment.

[0041] More preferably, the gas is nitrogen.

[0042] The technical effect of the present invention is as follows:

[0043] 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, and the larger the homogeneity coefficient, the stronger the pore connectivity and the better the reservoir physical properties, thereby realizing the fine classification of reservoir types;

[0044] The data source of the present invention is the actual core experiment and test in the mine field. 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 mine field, greatly reducing the costs of a large number of coring, logging level testing and interpretation in the mine field, and having good application prospects and promotion value for determining the same type of sandstone reservoir types. Description of the Drawings

[0045] Figure 1 It is a diagram of the experimental device for the pressure drop test.

[0046] Figure 2 It is a fitting diagram of the pressure drop curve and the three - stage pressure drop model in a specific experimental case.

[0047] Figure 3 It is a fitting diagram of the pressure drop curve and the four - stage pressure drop model in a specific experimental case.

[0048] Figure 4 It is a fitting diagram of the pressure drop curve and the five - stage pressure drop model in a specific experimental case.

[0049] Figure 5 It is a fitting diagram of the pressure drop curve and the six - stage pressure drop model in a specific experimental case.

[0050] Figure 6 It is a fitting diagram of the pressure drop curve and the seven - stage pressure drop model in a specific experimental case.

[0051] Reference Signs: 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 Embodiments

[0052] Embodiment 1

[0053] A method for determining the type of tight sandstone reservoir based on pore connectivity ability is as follows:

[0054] 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, 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;

[0055] Calculate the homogeneity coefficient of the rock sample in the target reservoir section through Equation (7);

[0056] If 0.65 <HI ≤1, the reservoir type is Class I; if 0.30 < HI ≤0.65, the reservoir type is Class II; if 0 < HI ≤0.30, the reservoir type is Class III.

[0057] Example 2

[0058] Based on Example 1, it further includes: The calculation formula of the pressure drop model is:

[0059] (6)

[0060] b ki = π ( r ki ×10 -4 ) 2 / (96 μcL 2 ) (1).

[0061] Example 3

[0062] Based on Example 2, it further includes: The specific obtaining process of the final pressure drop model is:

[0063] Construct k -level pressure drop model, extract the k -level pressure drop model of the pore radius r ki corresponding pore pressure drop rate b ki , and fit it with the pressure drop curve to obtain the k -level pressure drop model of the pore radius r ki corresponding pore pressure influence weight a ki ;

[0064] Take k the maximum value of the pore pressure influence weight in the -level pressure drop model a kmax corresponding pore radius r kmax 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):

[0065] r (k+1)g =( r kmax + r kl ) / 2 (3)

[0066] r (k+1)g =( r kmax + r kv ) / 2 (4);

[0067] Insert the graded pore radius r (k+1)g into k the - level pressure drop model to construct k the +1 - level pressure drop model. When the difference between at least one set of adjacent pore radii ≤ 25 nm, the corresponding k +1 - level pressure drop model is the final pressure drop model; if k all the differences between adjacent pore radii in the +1 - level pressure drop model are > 25 nm, then for the k +1 - level pressure drop model, continue pore grading until there is at least one set of adjacent pore radii with a difference ≤ 25 nm to obtain the final pressure drop model.

[0068] The specific process is as follows:

[0069] Construct a three - level pressure drop model. The pore radii r 3i in the three - level pressure drop model are the maximum value, minimum value, and the first intermediate value of the pore radii of the rock sample in the target reservoir section. Obtain the pore pressure drop rates r 3i corresponding to each pore radius b 3i in the three - level pressure drop model, and fit with the pressure drop curve to obtain the pore pressure influence weights r 3i corresponding to each pore radius a 3i in the three - level pressure drop model;

[0070] Take the pore radius a 3max corresponding to the maximum pore pressure influence weight r 3max in the three - level pressure drop model for the first pore grading. If the maximum pore pressure influence weight a 3max is the maximum value or the minimum value, then the first - graded pore radius r 4g is obtained through r4g =( r 3max + r 3l ) / 2 is calculated; otherwise, the first-stage pore radius r 4g is obtained through r 4g =( r 3max + r 3v ) / 2 is calculated;

[0071] The calculated first-stage 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;

[0072] If the four-stage pressure drop model is not the final pressure drop model, then for the maximum value of the pore pressure influence weight a 4max corresponding to the pore radius r 4max a second pore classification is performed to obtain the second-stage pore radius r 5g ;

[0073] Similarly, a five-stage and higher-stage pressure drop model is constructed until there is at least one set of differences between adjacent pore radii ≤ 25 nm, and the corresponding pressure drop model at this time is the final pressure drop model.

[0074] Example 4

[0075] On the basis of 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 the pressure drop curve is drawn according to the pressure data values of the rock sample of the target reservoir section at different time points;

[0076] 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, and thus the rock sample of the target reservoir section is made;

[0077] The pressure drop test experiment is carried out in the experimental test device for the pore connectivity of tight sandstone reservoirs; the experimental test device for the pore connectivity of tight sandstone reservoirs 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 a core sample 7 of the target reservoir section is arranged inside the core holder 9; the intermediate container 3 is also connected with a pressure gauge 8;

[0078] The specific process of the pressure drop test experiment is as follows: place the core 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; perform vacuum treatment on the core holder 9 through the vacuum pump 5, and after the vacuum treatment is completed, introduce the gas in the intermediate container 3 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 end the experiment; the gas is nitrogen.

[0079] Specific experimental case

[0080] 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 of the three main sub-layers was carried out in the early stage. In this specific experimental case, YP1 is taken as the target reservoir section, and the reservoir type of the YP1 main sub-layer is evaluated by using the method proposed by the present invention.

[0081] A method for determining the type of tight sandstone reservoir based on pore connectivity is as follows:

[0082] Step 1: Take a core from the YP1 target reservoir section to make a core sample SH-1 of the target reservoir section (the minimum pore radius of the core in the YP1 target reservoir section is 5 nm, and the maximum is 500 nm), carry out a pressure drop test experiment to obtain a data point set of pressure changing with time, and further obtain a pressure drop curve;

[0083] The specific process of the pressure drop test experiment is as follows:

[0084] Place the core sample 7 of the target reservoir section in the core holder 9; first, close all valves except the outlet valve 2 of the constant speed and constant pressure pump, 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, then stop the constant speed and constant pressure pump 1 and close the outlet valve 2 of the constant speed and constant pressure pump; open the inlet valve 6 of the vacuum pump, perform vacuum pumping treatment on the core holder 9 through the vacuum pump 5, close the inlet valve 6 of the vacuum pump after the vacuum treatment, then open the outlet valve 4 of the intermediate container, introduce the gas in the intermediate container 3 into the core holder 9, and at the same time record the data points of the pressure and the corresponding time in the pressure gauge 8 until the pressure in the pressure gauge 8 is stable, and end the experiment.

[0085] Step 2: Establish a three-level pressure drop model;

[0086] The pore radius of the three - stage pressure drop model is r 31 = 5 nm, r 32 = 100 nm and r 33 = 500 nm. According to formula (1), the pore pressure drop rates corresponding to each pore radius are calculated respectively, and 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;

[0087] Table 1 Three - stage pressure drop model - Pore pressure drop rate

[0088] ;

[0089] The three - stage pressure drop model is fitted with the pressure drop curve, and the fitting diagram is shown in Figure 2 ; The influence weights of each pore pressure are obtained a 3i , and the results are shown in Table 2;

[0090] Table 2 Three - stage pressure drop model - Influence weight of pore pressure

[0091] ;

[0092] It can be seen from Table 2 that 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 = 500 nm. Since 500 nm is the maximum value, the first pore classification is carried out using formula (3), and the first - stage classified pore radius r 4g =(100 + 500) / 2 = 300 nm.

[0093] Step 3: Establish the four - stage pressure drop model - final pressure drop model in sequence;

[0094] Insert the first - stage classified 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 in sequence: r 41 = 5 nm, r 42 = 100 nm, r 43= 300 nm and r 44 = 500 nm; The pore radius is calculated according to formula (1) r 43 The pore pressure decline rate corresponding to b 43 = 300 nm is 1.2337 s -1 ;

[0095] The four - stage pressure decline model is fitted with the pressure decline curve. The fitting diagram is shown in Figure 3 ; The influence weights of each pore pressure are obtained a 4i , and the results are shown in Table 3;

[0096] Table 3 Four - stage pressure decline model - Influence weights of pore pressure

[0097] ;

[0098] 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). The pore radii adjacent to r 43 are r 42 and r 44 . The corresponding a 42 < a 44 , so the second - stage classification pore radius r 5g = ( r 4max + r 4v ) / 2 = ( r 43 + r 44 ) / 2 = (300 + 500) / 2 = 400 nm;

[0099] Insert the second - stage classification pore radius r 5g = 400 nm into the pore radius of the four - stage pressure decline model to form the pore radius of the five - stage pressure decline 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; The pore radius is calculated according to formula (1) r 54 The pore pressure decline rate corresponding to = 300 nm b 54 = 2.1932 s -1 ;

[0100] The five - level pressure decline model is fitted with the pressure decline curve, and the fitting diagram is shown in Figure 4 ; The influence weights of each pore pressure are obtained a 5i , and the results are shown in Table 4;

[0101] Table 4 Five - level pressure decline model - Influence weights of pore pressure

[0102] ;

[0103] 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 The corresponding pore radius r 5max = r 53 = 300 nm, 300 nm is not the maximum or minimum value. Therefore, the third - level pore classification 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 - level classified pore radius r 6g =( r 5max + r 5v ) / 2 =( r 53 + r 54) / 2=(300 + 400) / 2 = 350nm;

[0104] Insert the third - stage pore radius r 6g = 350nm 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 in turn: r 61 = 5nm, r 62 = 100nm, r 63 = 300nm, r 64 = 350nm, r 65 = 400nm and r 66 = 500nm; Calculate the pore - pressure drop rate corresponding to the pore radius r 64 = 350nm according to formula (1) b 64 = 1.6792s -1 ;

[0105] 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;

[0106] Table 5 Six - stage pressure - drop model - Influence weights of pore pressure

[0107] ;

[0108] 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 = 300nm. Since 300nm is neither a maximum nor a minimum value, the fourth - stage pore classification is carried out using formula (4),

[0109] and r 63 The adjacent pore radii are r 62 and r 64 , and the corresponding a62 < a 64 , 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;

[0110] 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; According to formula (1), calculate the pore pressure drop rate corresponding to the pore radius r 74 = 325 nm b 74 = 1.4479 s -1 ;

[0111] Fit the seven - level pressure drop model with the pressure drop curve, and the fitting diagram is shown in Figure 6 ; Obtain the influence weights of each pore pressure a 6i , and the results are shown in Table 6;

[0112] Table 6 Seven - level pressure drop model - influence weights of pore pressure

[0113] .

[0114] Step 4: Calculate the homogeneity coefficient of the rock sample in the target reservoir section according to Equation (7)HI = 0.621, so it is determined that the reservoir type of the main sub-layer YP1 is Class II, and the reservoir physical properties are medium.

[0115] 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 accumulation index using the following formula:

[0116] HII =( h s - h smin ) / ( h smax - h smin ) = 0.567;

[0117] 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;

[0118] 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 ability, characterized in that, The method 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 by 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 The pore radius of the final pressure decline model, nm; is r ni The corresponding pore pressure influence weight, dimensionless; is The maximum value of, dimensionless; is 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 Class II; if 0 < HI ≤ 0.30, the reservoir type is Class III; Among them, the calculation formula of the pressure drop model is: （6） b ki =π(r ki ×10 -4 ) 2 / (96 μL 2 ) (1) Where: P t is the pressure drop model, dimensionless; k is the number of stages of the pressure drop model, taking values from 3 - n, dimensionless; r ki Pore radius for the k - level pressure drop model, nm; For r ki Corresponding pore pressure influence weight, dimensionless; b ki For r ki 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.

2. The method for determining the tight sandstone reservoir type based on pore connectivity ability according to claim 1, wherein The specific obtaining process of the final pressure drop model is: Construct a k-level pressure drop model, and obtain the pore radius r in the k-level pressure drop model ki The corresponding pore pressure drop rate b ki , and fit it with the pressure drop curve to obtain the pore pressure influence weight corresponding to the pore radius r in the k-level pressure drop model ki ;​ The maximum pore pressure influence weight in the k-level pressure drop model The corresponding pore radius Perform pore classification. If the maximum pore pressure influence weight Is a maximum or minimum value, 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): （3） （4） where: r (k+1)g is the hierarchical pore radius, nm; The maximum value of the pore pressure influence weight in the k-level pressure drop model The corresponding pore radius, nm; r kl Is related to The adjacent pore radius, nm; r kv To be adjacent to and the pore pressure influence weight is larger, pore radius, nm; Insert the graded pore radius r (k+1)g into the k - level pressure drop model to construct the (k + 1)-level pressure drop model. When the difference between at least one set of adjacent pore radii ≤ 25 nm, the corresponding (k + 1)-level pressure drop model is the final pressure drop model.

3. The method for determining the tight sandstone reservoir type based on pore connectivity ability according to claim 2, wherein It also includes that if the difference between all adjacent pore radii in the (k + 1)-stage pressure drop model is > 25 nm, then continue to perform pore grading on the (k + 1)-stage pressure drop model until there is at least one set of adjacent pore radii with a difference ≤ 25 nm to obtain the final pressure drop model.

4. The method for determining the tight sandstone reservoir type based on pore connectivity ability according to claim 3, characterized in that The specific obtaining process of the final pressure drop model is: Construct a three - stage pressure drop model. In the three - stage 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 b 3i corresponding to each pore radius r 3i in the three - stage pressure drop model, and fit with the pressure drop curve to obtain the pore pressure influence weight 3i corresponding to each pore radius r ; The maximum pore pressure influence weight in the three-stage pressure drop model The corresponding pore radius Perform the first pore classification. If the maximum pore pressure influence weight is a maximum or minimum value, the first classification pore radius r 4g is obtained through calculation; otherwise, the first classification pore radius r 4g is obtained through calculation; Insert the calculated first-stage pore radius r 4g into the three-stage pressure drop model to construct a four-stage pressure drop model, and determine whether the four-stage 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 maximum value of the pore pressure influence weight in the four - level pressure drop model corresponding pore radius perform a second pore classification to obtain the second - classified pore radius r 5g ; Similarly, construct a pressure drop model with five or more stages until there is at least one set of adjacent pore radii with a difference ≤ 25 nm. At this time, the corresponding pressure drop model is the final pressure drop model.

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

6. The method for determining the tight sandstone reservoir type based on pore connectivity ability according to claim 5, characterized in that The specific preparation process of the rock samples in the target reservoir section is: Make the core taken from the target reservoir section into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm, place it in an ultrasonic cleaner, and clean it with an ethanol solution for 30 minutes to remove surface impurities; Then put it into a constant temperature oven and dry it at 105 °C for 24 hours to make the pores free of moisture, and then make the rock samples in the target reservoir section.

7. The method for determining the tight sandstone reservoir type based on pore connectivity ability according to claim 6, wherein 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. The core holder (9) contains the rock samples (7) in the target reservoir section; The intermediate container (3) is also connected to a pressure gauge (8).

8. The method for determining the tight sandstone reservoir type based on pore connectivity ability according to claim 7, characterized in that, 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 a constant rate 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; Use a vacuum pump (5) to conduct vacuum treatment on the core holder (9). After the vacuum treatment is completed, introduce the gas in the intermediate container (3) 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) stabilizes, and then end the experiment.

9. The method for determining the tight sandstone reservoir type based on pore connectivity ability according to claim 8, characterized in that The gas is nitrogen.

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