A method for determining the limit well spacing

Abstract

The invention relates to a method for determining a limit well spacing. The method obtains the cumulative percentage of pore throat volume of different pore throat radii by performing a series of processing on rock sample capillary pressure experimental data. Since the cumulative percentage of pore throat volume reflects the control or production degree of oil reservoir geological reserves, the corresponding pore throat radius can be determined by establishing a relationship between the pore throat radius and the cumulative percentage of pore throat volume, combined with the control or production degree to be achieved by the designed well; then, the relationship between the pore throat radius and the limit oil drainage radius is deduced by using the relationship between the permeability and the pore throat radius, combined with the relationship between the known permeability and the limit oil drainage radius; using the relationship, combined with the determined pore throat radius, a reasonable limit oil drainage radius can be calculated, and then a reasonable limit well spacing can be determined, thereby improving the effective control or production degree of the well network and helping to reduce the development cost.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas reservoir exploration and development or shale oil and gas reservoir, and in particular relates to a method for determining a limit well spacing. Background Art

[0002] For the development of tight oil reservoirs, reasonable well pattern and well spacing are the key technologies for efficient reservoir development. At present, there are many methods for determining the limit well spacing, but they all have various problems. For example, in the mine, the limit oil drainage radius formula is generally derived from Darcy's law, and the arithmetic mean or median of the rock sample permeability is substituted into the limit oil drainage radius formula, and the limit well spacing is calculated based on the obtained limit oil drainage radius.

[0003] However, due to the large range of permeability values ​​of the target reservoir layer, once the permeability parameter is not selected reasonably, the determined extreme well spacing is also unreasonable. When using this extreme well spacing parameter for reservoir development, due to the heterogeneity of the reservoir, if the permeability of a certain layer of the reservoir is low, the area between the wells will be unable to be used, and an oil stagnation zone will be formed. If the reserves of this part of the oil layer need to be used, new adjustment wells must be drilled to effectively use it. In addition, the well spacing will be too small to a large extent, and the number of wells corresponding to the same area will increase, which will increase the development cost and reduce the development efficiency.

[0004] In the prior art, there are other methods for calculating the limit well spacing, for example, the Chinese invention patent application with publication number CN107832540A and titled "A method for determining the technical limit well spacing of a tight oil reservoir", which includes: collecting, sorting, and selecting calculation parameters of tight oil reservoirs, using the mathematical model of the technical limit production well spacing when the tight oil reservoir is produced at a fixed rate, calculating the limit oil leakage radius of the production well when the crude oil flows in the easy-flow area, and the limit oil leakage radius of the production well when the crude oil flows in the difficult-flow area; confirming the technical limit production well spacing of the tight oil reservoir; and calculating the technical limit injection and production well spacing according to the well layout method of the tight oil reservoir. This patent comprehensively considers the unstable flow laws of the linear and nonlinear seepage laws of tight oil, and derives a mathematical model for calculating the technical limit production well spacing under the conditions of fixed-rate production in tight oil reservoirs, which can provide a theoretical basis and technical support for determining the reasonable well spacing of tight oil reservoirs and evaluating the development and production effects. However, the implementation steps of this method are relatively complicated and cannot provide the degree of control of the wells over the reservoir reserves. This may result in the reserves within the well network being controlled on the surface, but not being able to be fully effectively controlled from the perspective of microscopic pore channels, resulting in the reserves being unable to be effectively utilized to form production capacity.

[0005] For example, the Chinese invention patent application with the publication number "CN108920852A" and the name "A method for determining the injection-production well spacing in an ultra-low permeability oil reservoir" determines the injection-production well spacing by calculating the pressure distribution around the water injection well and the limit water injection radius. The sum of the limit water injection radius and the limit oil leakage radius is the injection-production well spacing. The injection-production well spacing obtained fully considers the seepage characteristics of the ultra-low permeability oil reservoir and the actual production of water injection development, providing a reliable basis for oil field development. However, the disadvantage of this method is that the steps are relatively complicated, and it also cannot provide the degree of control of the wells over the oil layer reserves. It may cause the reserves within the well network to be controlled on the surface, but from the perspective of microscopic pore roar, they cannot be fully effectively controlled, resulting in the inability to effectively mobilize the reserves to form production capacity. Summary of the invention

[0006] The purpose of the present invention is to provide a method for determining a limit well spacing, which is used to solve the problem of increased development costs caused by unreasonable design of limit well spacing in existing methods, and the problem of ineffective utilization of reserves caused by low effective control or utilization of well networks.

[0007] Based on the above purpose, a technical solution for determining a limit well spacing is as follows:

[0008] Step 1, obtaining data of capillary pressure test of rock samples of target layer, i.e. rock sample test data, including well number, layer, sampling point depth, rock sample number, permeability, pore throat radius, pore volume, and mercury saturation;

[0009] Step 2: Screen out the rock sample experimental data of the oil-bearing sample through the rock sample lithology analysis description, and sort the rock sample experimental data of the same rock sample from large to small according to the pore throat radius;

[0010] Step 3, according to the order in step 2, the cumulative pore throat volumes corresponding to the first i pore throat radii are calculated in turn according to the product of the pore volume and the mercury saturation, i = 1, 2, ..., n, where n is the number of pore throat radii of the rock sample;

[0011] Step 4, calculating the pore throat volume corresponding to the i+1th pore throat radius according to the difference between the cumulative pore throat volumes corresponding to the first i and first i+1 pore throat radii in step 3;

[0012] Step 5, among the rock sample experimental data of all oil-bearing samples, re-arrange the rock sample experimental data according to the pore throat radius and permeability, that is, first sort them from large to small according to the pore throat radius, and for the rock sample test analysis data with the same pore throat radius value, sort them from large to small according to the permeability;

[0013] Step 6: Calculate the cumulative pore throat volume of the entire sample corresponding to the first k pore throat radii according to the reordering results of step 5. The calculation formula is as follows:

[0014]

[0015] Where Vc k V is the cumulative pore throat volume of the whole sample corresponding to the first k pore throat radii, j = 1, 2, ..., k; C1 ,…,V Ck is the volume of the first k pore throats in the re-ranking results;

[0016] Step 7, according to the cumulative pore throat volumes of each full sample obtained in step 6, calculate the cumulative mercury injection volume percentage, that is, the cumulative percentage of pore throat volume, and the calculation formula is as follows:

[0017]

[0018] Where, X k Vc is the cumulative mercury volume percentage of the cumulative pore throat volume of the kth sample, k is the cumulative pore throat volume of the whole sample, V C总 It is the sum of the cumulative pore throat volumes of all samples;

[0019] Step 8, according to the cumulative percentages of the pore throat volumes determined in step 7 and the pore throat radius corresponding to each cumulative percentage of the pore throat volume, fitting the relationship between the pore throat radius and the cumulative percentage of the pore throat volume, substituting the control or producing degree of the set reservoir geological reserves as the cumulative percentage of the pore throat volume into the above relationship, and obtaining the corresponding pore throat radius;

[0020] Step 9, according to the sorting result of step 2, the pore throat radius and permeability of each rock sample are obtained, and the relationship between the pore throat radius and the permeability is fitted;

[0021] Step 10, obtaining the relationship between the limit oil drainage radius and the permeability, combining the relationship between the pore throat radius and the permeability in step 9, and obtaining the relationship between the limit oil drainage radius and the pore throat radius;

[0022] Step 11, using the relationship between the limit oil drainage radius and the pore throat radius determined in step 10, combined with the corresponding pore throat radius obtained in step 8, the corresponding limit oil drainage radius is calculated, and the limit well spacing of the target reservoir is calculated based on twice the limit oil drainage radius.

[0023] The beneficial effects of the above technical solution are:

[0024] The method of the present invention firstly performs a series of processing on the capillary pressure experimental data of the rock sample to obtain the cumulative percentage of the pore throat volume of different pore throat radii. Since the cumulative percentage of the pore throat volume reflects the control or production degree of the geological reserves of the oil reservoir, the corresponding pore throat radius can be determined by establishing the relationship between the pore throat radius and the cumulative percentage of the pore throat volume in combination with the set control or production degree; then, the relationship between the pore throat radius and the limit oil drainage radius is deduced by using the relationship between the permeability and the pore throat radius in combination with the relationship between the known permeability and the limit oil drainage radius; using the relationship in combination with the determined pore throat radius, a reasonable limit oil drainage radius can be calculated, and then a reasonable limit well spacing can be determined, thereby improving the effective control or production degree of the well network and helping to reduce the development cost.

[0025] In order to improve the accuracy of determining the limit well spacing, further, the pore throat radius in step 9 is the pore throat radius of the initial mercury injection when the capillary pressure test is performed on the rock sample, that is, the maximum pore throat radius.

[0026] In order to improve the accuracy of determining the critical well spacing, the permeability in step 9 is further calculated as the average permeability corresponding to the maximum pore throat radius, and the calculation formula is as follows:

[0027] K=(k1+k2+, .., +k m ) / m

[0028] Where K is the average permeability corresponding to the maximum pore throat radius, m is the number of rock samples with the same maximum pore throat radius, k1, k2, …, k m is the permeability of each rock sample.

[0029] Furthermore, in step 9, the relationship between the pore throat radius and the permeability is a linear relationship or a nonlinear relationship.

[0030] Specifically, the calculation formula for the cumulative pore throat volume corresponding to the first i pore throat radii in step 3 is as follows:

[0031]

[0032] Where V i is the cumulative pore throat volume corresponding to the first i pore throat radii, cm 3 ; is the mercury saturation corresponding to the i-th pore throat radius, %; V p is the pore volume of the rock sample, cm 3 .

[0033] Specifically, the calculation formula for the pore throat volume corresponding to the i+1th pore throat radius in step 4 is as follows:

[0034] Vc i+1 =V i+1 -V i

[0035] Where Vc i+1 is the pore throat volume corresponding to the i+1th pore throat radius, cm 3 ; i is an integer greater than 0; V i+1 is the cumulative pore throat volume corresponding to the first i+1 pore throat radii, cm 3 ; V i is the cumulative pore throat volume corresponding to the first i pore throat radii, cm 3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flow chart of a method for determining a limit well spacing in an embodiment of the present invention;

[0037] Figure 2 is a relationship diagram of the cumulative distribution of pore throat volume, pore throat volume, pore throat volume percentage and pore throat radius distribution in the embodiment of the present invention;

[0038] Figure 3 is a relationship diagram between the pore throat radius and the corresponding average permeability fitted in an embodiment of the present invention;

[0039] Figure 4 It is a diagram of the limit oil drainage radius under different pore throat radii and production pressure difference conditions in the embodiment of the present invention. DETAILED DESCRIPTION

[0040] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0041] This embodiment proposes a method for determining a limit well spacing. The overall process is as follows: Figure 1 As shown, the following takes a target reservoir as an example to introduce the specific implementation steps of this method:

[0042] Step 1: Obtain capillary pressure test data of rock samples at the target layer.

[0043] Specifically, seven coring wells were drilled in the target oil reservoir, and the Bayingebi Formation was subdivided into two sections and five sand groups. There were 129 effective capillary pressure samples, and capillary pressure tests were carried out on each rock sample using conventional pressure-gon method to obtain rock sample experimental data, including: sampling point depth, rock sample number, porosity, permeability, pore throat radius, pore volume, mercury saturation, etc.

[0044] The stratigraphic position of the rock sample (i.e., the target layer) is determined by the depth position of the rock sample in the coring section and the geological stratification, and the rock sample experimental data of the target layer is screened out.

[0045] Each rock sample has multiple experimental data records. For a rock sample, since each rock sample has several pore throat radii of different sizes, taking the rock samples numbered 11-22 as an example, the experimental data records of the rock samples are given, as shown in Table 1.

[0046] Step 2, through the rock sample lithology analysis description, filter out the rock sample test analysis data of the oil-bearing samples, the oil-bearing samples include oil trace, oil immersion and oil spot samples, among which each rock sample has multiple experimental data records. For a rock sample, since each rock sample has several pore throat radii of different sizes, a capillary pressure experiment can obtain multiple experimental data records.

[0047] For multiple experimental data records of the same rock sample, the experimental data records of each rock sample are sorted according to the pore throat radius from large to small. Taking the rock samples numbered 11-22 as an example, the experimental data records of each rock sample after sorting are given, as shown in Table 1.

[0048] Table 1

[0049]

[0050]

[0051] Step 3: According to the above ranking, calculate the cumulative mercury injection volume corresponding to each pore throat radius in each rock sample, that is, the cumulative pore throat volume, and the calculation formula is as follows:

[0052]

[0053] In formula (1), V i is the cumulative mercury injection volume corresponding to the first i pore throat radii when the pore throat radii in the rock sample analysis data are sorted from large to small, cm 3 ; where i = 1, 2, ..., n, n is the number of pore throat radii of a rock sample; is the mercury injection saturation (i.e., mercury injection saturation) corresponding to the i-th pore throat radius, %; 0.01 is the conversion coefficient, which is used to convert the mercury injection saturation from a percentage to a decimal; V p is the pore volume of the rock sample, cm 3 ;

[0054] The cumulative mercury injection volume corresponding to the pore throat radius is added to the experimental data of each rock sample. Taking rock samples numbered 4 and 8 as examples, the rock sample experimental data are shown in the following table:

[0055] Table 2

[0056]

[0057] Step 4: According to the difference between the cumulative pore throat volumes corresponding to the first i and first i+1 pore throat radii in step 3, the mercury injection volume corresponding to the i+1 pore throat radius, i.e., the pore throat volume, is calculated as follows:

[0058] Vc i+1 =V i+1 -V i (2)

[0059] In formula (2), V i is the cumulative mercury injection volume corresponding to the first i pore throat radii, cm 3 ; where i = 1, 2, ...; V i+1 is the cumulative mercury injection volume corresponding to the first i+1 pore throat radii, cm 3 ; Vc i+1 is the mercury injection volume corresponding to the i+1th pore throat radius, cm 3 ; and the first pore throat volume Vc1 = V1.

[0060] The pore throat volumes calculated above are added to the experimental data of each rock sample, as shown in Table 2. In Table 2, the first pore throat volume Vc1=V1=0.013, according to formula (2), the second pore throat volume Vc2=V2-V1=0.118-0.013=0.105; the third, fourth, ..., nth pore throat volumes can be obtained in turn according to formula (2), and this step will not be repeated.

[0061] Step 5: among all the rock sample experimental data, re-arrange the rock sample experimental data in descending order according to the pore throat radius; for the rock sample experimental data with the same pore throat radius value, sort them in descending order according to the permeability.

[0062] The data sorting in this step is different from the data sorting in step 2. In step 2, the test data belonging to the same rock sample are sorted, and the experimental data belonging to the same rock sample are sorted together according to the size of the pore throat radius, while the sorting in this step is for all rock sample experimental data records. According to the sorting method of pore throat radius from large to small and permeability from large to small, after sorting, as shown in Table 3:

[0063] Table 3

[0064]

[0065] Step 6: According to the re-ranking results in step 5 above, sort the pore throat radii from large to small in all rock sample experimental data, and calculate the sum of the mercury injection volumes corresponding to the first j pore throat radii, that is, the cumulative pore throat volume of the whole sample. The calculation formula is as follows:

[0066]

[0067] Where Vc k is the cumulative mercury injection volume corresponding to the first k pore throat radii, that is, the cumulative pore throat volume of the whole sample, j = 1, 2, ..., k; the calculation results of the cumulative pore throat volume of the whole sample are shown in Table 3. Table 3 shows that the cumulative pore throat volume of the first whole sample is 0.061 cm 3 The cumulative pore throat volume of the first two samples is 0.107 cm 3 , which is the sum of the first two pore throat volumes; and so on, the cumulative pore throat volume of the first k samples is the sum of the first k pore throat volumes.

[0068] Step 7, based on the cumulative pore throat volume of the whole sample obtained in step 6, calculate the cumulative mercury injection volume percentage, that is, the cumulative percentage of pore throat volume, and the calculation formula is as follows:

[0069]

[0070] In the formula, X k Vc is the cumulative mercury volume percentage of the kth data record, %; 总 The total volume of mercury inflow recorded in all data, cm 3 The calculation results of the cumulative percentage of pore throat volume are shown in Table 3. There are 1809 data records in total. Due to the large amount of data, Table 3 shows only part of the data. Vc 总 The total pore throat volume of 111 rock samples with a total of 1809 data records is 153.622 cm 3 .

[0071] In this step, the cumulative percentage of pore throat volume objectively represents the control or utilization degree of geological reserves of the reservoir. The principle is that when the conventional mercury injection method is used to perform mercury injection on each rock sample, since the order of mercury injection in each throat of all rock samples is carried out in the order from large pore throat radius to small pore throat radius, in step 5, the experimental data of all strip rock samples are re-ordered in the order from large pore throat radius to small pore throat radius. Moreover, the law of this order is consistent with the law of oil production in the formation. Oil is also produced in the formation in the order from large pore throat radius to small pore throat radius. Therefore, the mercury injection volume percentage calculated according to this order objectively represents the control or utilization degree of geological reserves of the reservoir.

[0072] Step 8: According to the rock sample experimental data, the relationship between the pore throat radius and the cumulative percentage of the pore throat volume is fitted, such as Figure 2 As shown, Figure 2 What is shown is the relationship between the cumulative distribution of pore throat volume, pore throat volume, pore throat volume percentage and pore throat radius distribution, with pore throat radius as the horizontal axis and the cumulative distribution of pore throat volume, pore throat volume and pore throat volume percentage as the vertical axis.

[0073] Since the cumulative percentage of pore throat volume represents the control or utilization degree of reservoir geological reserves, the corresponding pore throat radius interval is determined to be 0.063-0.25 μm, and the corresponding cumulative percentage of pore throat volume is 82.3%-64.3%, according to the requirement that the well network control degree should generally be between 60% and 80%. That is, the smaller the selected pore throat radius, the larger the corresponding cumulative percentage of pore throat volume, and thus the greater the well network control degree.

[0074] Step 9, according to the sorting results determined in step 2, the pore throat radius of each rock sample at the time of initial mercury injection (i.e., the largest pore throat radius among several pore throat radii of each rock sample) and the permeability of the rock sample are obtained. The pore throat radius of the rock sample at the time of initial mercury injection and the permeability of the rock sample are shown in Table 4.

[0075] Table 4

[0076]

[0077] According to the pore throat radius sorting results, the arithmetic mean of the permeability corresponding to each pore throat radius is calculated as follows:

[0078] K=(k1+k2+, .., +k m ) / m

[0079] Where K is the average permeability corresponding to the maximum pore throat radius, m is the number of rock samples with the same maximum pore throat radius, k1, k2, …, k m is the permeability of each rock sample. According to the above formula, the relationship between pore throat radius and average permeability is shown in Table 5.

[0080] Table 5

[0081] Pore ​​throat radius Permeability (μm) (mD) 25.000 15.892 16.000 10.944 10.000 5.761 6.300 3.748 4.000 3.169 2.500 1.936 1.600 1.029 1.048 0.952 1.000 0.683 0.630 0.326 0.400 0.137 0.160 1.347 0.063 0.064

[0082] Step 10: According to the arithmetic mean of the permeability corresponding to each pore throat radius in step 9, a linear regression is performed between the pore throat radius and the corresponding average permeability. The relationship between the pore throat radius and the corresponding average permeability is shown in the figure below: Figure 3 The linear relationship is as follows:

[0083] k=0.6439r 孔喉 (6)

[0084] Where k is the average permeability, mD; r 孔喉 is the pore throat radius, μm; the correlation coefficient is 0.9887.

[0085] In this embodiment,

[0086] Step 11, substitute the linear relationship in step 10 above into the formula (7) of the limit oil leakage radius to calculate the limit oil leakage radius, which is as follows:

[0087]

[0088] In the formula, r 极限 is the limit oil leakage radius, m; ΔP is the production pressure difference, MPa; k is the reservoir air permeability (i.e., average permeability) determined in step 10, mD; μ is the underground viscosity of crude oil, 0.348 mPa.s.

[0089] According to the pore throat radius interval of 0.063-0.25 μm determined in step 8, formula (6) and formula (7) are combined to calculate the limit oil leakage radius of 17.8-40.7 m when the production pressure difference is 20 MPa, and the corresponding pore throat volume cumulative distribution percentage is 82.3%-64.3%.

[0090] As another implementation method, when the production pressure difference is adjusted differently, the calculated limit oil drainage radius is also different. The calculation results of the limit oil drainage radius under different pore throat radii and production pressure difference conditions are shown in Table 6.

[0091] Table 6

[0092]

[0093] Using the above data, a relationship chart showing the relationship between the maximum oil drainage radius, the cumulative distribution percentage of pore throat volume and the pore throat radius is fitted, as shown in Figure 4 As shown, the relationship diagram can be used to illustrate:

[0094] (1) When the production pressure difference is constant, the limit oil drainage radius is positively correlated with the pore throat radius. The larger the pore throat radius, the larger the limit oil drainage radius.

[0095] (2) When the pore throat radius is constant, the limit oil drainage radius is positively correlated with the production pressure difference. The greater the production pressure difference, the greater the limit oil drainage radius.

[0096] (3) Since the cumulative distribution percentage of pore throat volume is calculated from large pore throats to small pore throats, the cumulative distribution percentage of pore throat volume is negatively correlated with the pore throat radius.

[0097] Since the limit well spacing is twice the limit oil drainage radius, according to the limit oil drainage radius corresponding to the production pressure difference of 20MPa, the optimal range of the limit well spacing is calculated to be 36-81m. Of course, according to the control or utilization requirements of the specific reservoir geological reserves, the specific pore throat radius can be determined in the relationship between the pore throat radius and the cumulative percentage of the pore throat volume determined in step 8, and the value is substituted into formula (6) to calculate the specific average permeability value, and the value is substituted into formula (7) to calculate the final limit oil drainage radius in combination with other specific parameters, and then the final limit well spacing is determined.

[0098] The method of the present invention can realize accurate prediction of the limit well spacing, and its principle is:

[0099] When using conventional mercury injection method to do capillary pressure, after the rock sample is pressurized with mercury, the mercury first enters the large throat space of the rock sample. As the pressure increases, the mercury continuously enters the smaller throat radius space. As the test pressure increases, the greater the pressure, the smaller the throat radius of the mercury enters, and the higher the mercury saturation. The throat radius space that mercury can enter is the effective storage space and migration channel of oil and gas. Therefore, the product of the mercury saturation of the rock sample and the pore volume of the rock sample can calculate the cumulative pore throat volume of the first i pore throat radii from large to small for a single sample, and then calculate the pore throat volume corresponding to each pore throat radius of the single sample.

[0100] During the production process of oil reservoirs or oil wells, the reservoir pressure gradually decreases, and the crude oil in the rock first flows out from the large throat, and then gradually flows out from the small throat. Using this rule, all samples are sorted from large to small according to the pore throat radius, and the permeability is also sorted from large to small, and then the cumulative pore throat volume of the whole sample is calculated, and the cumulative distribution percentage of the pore throat volume is calculated. Among them, the cumulative pore throat volume of the whole sample represents the oil volume of the rock sample, which is equivalent to the geological reserves of the reservoir for the oil reservoir. The cumulative distribution percentage of the pore throat volume represents the volume control or utilization degree of the rock sample, which is equivalent to the control or utilization degree of the geological reserves of the reservoir for the oil reservoir. According to the control or utilization degree of the well network requirements, combined with the relationship between the pore throat radius and the cumulative distribution percentage of the pore throat volume, the corresponding pore throat radius can be determined.

[0101] Then, the positive correlation between permeability and maximum pore throat radius is utilized, that is, the larger the pore throat radius, the higher the permeability, and the smaller the pore throat radius, the smaller the permeability. By establishing the relationship between permeability and maximum pore throat radius (5), combined with the relationship between the limit oil drainage radius and permeability (6), the relationship between the limit oil drainage radius and the pore throat radius is established. Combined with the above-determined pore throat radius, the limit oil drainage radius can be calculated, and then the accurate limit well spacing can be calculated.

[0102] As another embodiment, since the permeability also has a positive correlation with the non-maximum pore throat radius (relatively speaking, the positive correlation between the permeability and the maximum pore throat radius is stronger), when fitting the relationship between the permeability and the pore throat radius, the fitting data is not limited to the maximum pore throat radius, and the non-maximum pore throat radius can also be included.

[0103] In this embodiment, there are multiple rock samples with the same pore throat radius and different permeabilities. In order to increase the fitting accuracy, multiple permeability values ​​of the same pore throat radius are averaged. As another implementation method, several permeabilities k1, k2, ..., k mThe median value is taken as the permeability for fitting with the pore throat radius; or without considering the fitting speed, multiple permeability values ​​of the same pore throat radius are retained to directly fit the relationship between permeability and pore throat radius.

[0104] In this embodiment, the relationship between permeability and pore throat radius is a linear relationship, such as Figure 3 As shown, as another implementation, a nonlinear relationship, such as a monotonically increasing exponential relationship, etc., can also be fitted.

[0105] In this embodiment, by analyzing and processing the test data of a large number of coring wells in the target oil reservoir, samples of the oil-bearing layer are screened to facilitate the subsequent steps. For an oil reservoir, as long as there are samples in the plane interval and different oil layers in the vertical direction, and they are representative, the more samples there are, the stronger the representativeness is, the more representative it is of the entire oil reservoir, and the more reliable and accurate the result of finally determining the limit well spacing is.

[0106] The method for determining the limit well spacing of the present invention can effectively combine the cumulative distribution percentage of the pore throat volume (which is actually the control degree of the geological reserves of the reservoir) with the microscopic pore throat radius, and can effectively improve the utilization degree of the geological reserves, effectively utilize the geological reserves to the maximum extent, form oil production capacity, and improve efficiency; the method for determining the limit well spacing of the present invention can calculate the reasonable limit well spacing corresponding to different pore throat radii, and know the effective volume control or utilization degree that can be achieved by the determined reasonable limit well spacing, overcome the disadvantages of the existing limit well spacing design method, improve the reliability and accuracy of the well spacing design, enhance the effective control or utilization degree of the well network on the oil layer, avoid the problem of the formation of oil stagnation zone caused by the inability to mobilize the area between wells due to unreasonable well spacing design, and the problem of ineffective injection and production due to the determination of too large well spacing, and improve the effective control or utilization degree of the well network.

[0107] The application prospect of the method for determining the limit well spacing of the present invention is very broad, especially for low permeability reservoirs (permeability 10-50×10 -3 μm 2 ), especially for ultra-low permeability reservoirs (permeability 1-10×10 -3 μm 2 ) and ultra-low permeability reservoirs (permeability 0.1-1×10 -3 μm 2 ) is more practical and provides a reliable basis for the well spacing demonstration in reservoir engineering.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for determining a critical well spacing, characterized in that: The following steps are involved: Step 1, obtaining data of capillary pressure test of rock samples of target layer, i.e. rock sample test data, including well number, layer, sampling point depth, rock sample number, permeability, pore throat radius, pore volume, and mercury saturation; Step 2: Screen out the rock sample experimental data of the oil-bearing sample through the rock sample lithology analysis description, and sort the rock sample experimental data of the same rock sample from large to small according to the pore throat radius; Step 3, according to the order in step 2, the cumulative pore throat volumes corresponding to the first i pore throat radii are calculated in turn according to the product of the pore volume and the mercury saturation, i = 1, 2, ..., n, where n is the number of pore throat radii of the rock sample; Step 4, calculating the pore throat volume corresponding to the i+1th pore throat radius according to the difference between the cumulative pore throat volumes corresponding to the first i and first i+1 pore throat radii in step 3; Step 5, among the rock sample experimental data of all oil-bearing samples, re-arrange each rock sample experimental data according to the pore throat radius and permeability, that is, first sort them from large to small according to the pore throat radius, and for the rock sample experimental data with the same pore throat radius, sort them from large to small according to the permeability; Step 6: Calculate the cumulative pore throat volume of the entire sample corresponding to the first k pore throat radii according to the reordering results of step 5. The calculation formula is as follows: Where Vc k V is the cumulative pore throat volume of the whole sample corresponding to the first k pore throat radii, j = 1, 2, ..., k; C1 ,…,V Ck is the volume of the first k pore throats in the re-ranking results; Step 7, according to the cumulative pore throat volumes of each full sample obtained in step 6, calculate the cumulative mercury injection volume percentage, that is, the cumulative percentage of pore throat volume, and the calculation formula is as follows: Where, X k Vc is the cumulative mercury volume percentage of the cumulative pore throat volume of the kth sample, k is the cumulative pore throat volume of the whole sample, V C总 It is the sum of the cumulative pore throat volumes of all samples; Step 8, according to each pore throat volume cumulative percentage determined in step 7, and the pore throat radius corresponding to each pore throat volume cumulative percentage, fitting the relationship between the pore throat radius and the pore throat volume cumulative percentage, taking the set control or production degree of the reservoir geological reserves as the pore throat volume cumulative percentage, substituting it into the relationship between the pore throat radius and the pore throat volume cumulative percentage, and finding the corresponding pore throat radius; Step 9, according to the sorting result of step 2, the pore throat radius and permeability of each rock sample are obtained, and the relationship between the pore throat radius and the permeability is fitted; Step 10, obtaining the relationship between the limit oil drainage radius and the permeability, substituting the relationship between the pore throat radius and the permeability in step 9 into the relationship between the limit oil drainage radius and the permeability, and obtaining the relationship between the limit oil drainage radius and the pore throat radius. The relationship between the limit oil drainage radius and the permeability is as follows: In the formula, r 极限 is the limit oil leakage radius, △P is the production pressure difference, k is the permeability, and μ is the underground viscosity of crude oil; Step 11, using the relationship between the limit oil drainage radius and the pore throat radius determined in step 10, combined with the corresponding pore throat radius obtained in step 8, the corresponding limit oil drainage radius is calculated, and the limit well spacing of the target reservoir is calculated based on twice the limit oil drainage radius.

2. The method for determining the limit well spacing according to claim 1, characterized in that: The pore throat radius in step 9 is the pore throat radius of the initial mercury injection when the capillary pressure test is performed on the rock sample, that is, the maximum pore throat radius.

3. The method for determining the limit well spacing according to claim 1 or 2, characterized in that: The permeability in step 9 is the average permeability corresponding to the maximum pore throat radius, calculated as follows: K=(k1+k2+、..、+k m ) / m Where K is the average permeability corresponding to the maximum pore throat radius, m is the number of rock samples with the same maximum pore throat radius, k1, k2, …, k m is the permeability of each rock sample.

4. The method for determining the limit well spacing according to claim 1, characterized in that: The relationship between the pore throat radius and the permeability in step 9 is a linear relationship or a nonlinear relationship.

5. The method for determining the limit well spacing according to claim 1, characterized in that: The calculation formula for the cumulative pore throat volume corresponding to the first i pore throat radii in step 3 is as follows: Where V i is the cumulative pore throat volume corresponding to the first i pore throat radii, cm 3 ; is the mercury saturation corresponding to the ith pore throat radius, %; V p is the pore volume of the rock sample, cm 3 .

6. The method for determining the limit well spacing according to claim 1, characterized in that: The calculation formula for the pore throat volume corresponding to the i+1th pore throat radius in step 4 is as follows: You i+1 =V i+1 -V i Where Vc i+1 is the pore throat volume corresponding to the i+1th pore throat radius, cm 3 ; i is an integer greater than 0; V i+1 is the cumulative pore throat volume corresponding to the first i+1 pore throat radii, cm 3 ; V i is the cumulative pore throat volume corresponding to the first i pore throat radii, cm 3 .

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