Methods for determining effective sandstone reservoirs

Abstract

The present invention provides a method for determining an effective sandstone reservoir. The method comprises: Step S10: obtaining a skeleton density value ρ of the sandstone reservoir in the target area ma ; Step S20: Obtain conventional logging data of the sandstone reservoir in the target area; Step S30: According to the skeleton density value ρ in step S10 ma Using the conventional well logging data from step S20, the density porosity #imgabs0# and neutron porosity #imgabs1# of the conglomerate reservoir are obtained. Step S40: Based on the density porosity #imgabs2# and neutron porosity #imgabs3# from step S30, a first crossplot of the neutron and density porosity difference #imgabs4# and the density porosity #imgabs5# is plotted. Step S50: Based on the first crossplot, the conglomerate reservoir is classified and the distribution range of the first and / or second reservoir types is determined. The method of the present invention can accurately classify conglomerate reservoir types and determine the distribution range of effective reservoirs using conventional well logging data.

Description

Technical Field

[0001] The present invention relates to the field of well logging technology, and in particular to a method for determining an effective sandstone reservoir. Background Art

[0002] To improve exploration efficiency and reduce development risks in new exploration areas, it is often necessary to understand the distribution of high-quality reservoirs and identify "sweet spots" before implementing development measures in new exploratory wells. This involves identifying effective sandstone and conglomerate reservoirs (in other words, evaluating reservoir effectiveness) so that development and trial production can be conducted in these high-quality reservoirs. Therefore, identifying effective sandstone and conglomerate reservoirs plays a crucial role in reducing development risks.

[0003] Currently, methods for identifying effective conglomerate reservoirs primarily focus on evaluating the pore structure of the target reservoir using new logging technologies such as nuclear magnetic resonance (NMR) and microresistivity scanning imaging logging. While these pore structure-based methods have proven highly applicable, in practice, they primarily utilize indirect pore structure parameters derived from NMR and microresistivity scanning imaging logging, rather than direct use of actual measured logging data. Consequently, the accuracy of these indirect parameters can directly impact the precision of determining effective conglomerate reservoirs.

[0004] Therefore, in the existing technology, when using new logging data such as nuclear magnetic resonance and micro-resistivity scanning imaging logging to determine the effective reservoir of sandstone and conglomerate, there is a problem that the effective reservoir of sandstone and conglomerate cannot be accurately determined. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for determining effective conglomerate reservoirs, which can accurately classify conglomerate reservoir types and determine the distribution range of effective reservoirs using conventional well logging data.

[0006] In order to achieve the above-mentioned object, the present invention provides a method for determining an effective sandstone reservoir, the method comprising: Step S10: obtaining a skeleton density value ρ of the sandstone reservoir in the target area ma ; Step S20: Obtain conventional logging data of the sandstone reservoir in the target area; Step S30: According to the skeleton density value ρ in step S10 ma The density porosity of the sandstone reservoir is obtained by combining the conventional logging data in step S20. and neutron porosity Step S40: According to the density porosity in step S30 and neutron porosity Plotting Neutron and Density Porosity Differences Porosity and density step S50: according to the first cross-plot, the types of sandstone reservoirs are classified to determine the distribution range of the first type of reservoir and / or the second type of reservoir.

[0007] Furthermore, the density porosity of the sandstone reservoir Satisfies the following formula: in, is the density porosity, in %; ρ b is the bulk density of the sandstone reservoir, in g / cm 3 ρ f is the density of the pore fluid in g / cm 3 ρ ma is the skeleton density of sandstone, in g / cm 3 .

[0008] Furthermore, the density of the pore fluid ρ f The value range is 1.0g / cm 3 to 1.1 g / cm 3 .

[0009] Furthermore, neutron porosity Satisfies the following formula: in, is the neutron porosity, in %; CNL is the neutron logging value of the conglomerate reservoir, in %.

[0010] Furthermore, the first type of reservoir is neutron and density porosity difference Density Porosity The corresponding reservoir.

[0011] Furthermore, the second type of reservoir is neutron and density porosity difference Density Porosity The corresponding reservoir.

[0012] Furthermore, the neutron and density porosity differences Density Porosity The corresponding area is a dry layer; or, the neutron and density porosity are poor Density Porosity The corresponding area is the mudstone layer.

[0013] Furthermore, the neutron and density porosity differences satisfy the following formula: Where, is the difference between neutron and density porosity, in %; is the density porosity, in %; is the neutron porosity, in %.

[0014] Furthermore, step S10 includes: step S11: obtaining the core porosity and bulk density values ​​of the sandstone; step S12: drawing a second cross-plot of the porosity and bulk density values ​​with porosity as the abscissa and bulk density as the ordinate; step S14: obtaining the skeleton density value ρ of the sandstone reservoir ma .

[0015] Furthermore, after step S12, the method further includes step S13 of obtaining a linear relationship between porosity and bulk density using a linear regression method, wherein when the porosity is 0, the bulk density is the skeleton density value ρ of the sandstone reservoir ma .

[0016] Applying the technical solution of the present invention, the skeleton density value ρ of the sandstone reservoir in the target area is obtained. ma and conventional logging data of sandstone reservoirs, and the skeleton density value ρ ma The density and porosity of the conglomerate reservoir can be calculated using conventional logging data. and neutron porosity Then, the neutron and density porosity differences are further calculated Then combined with neutron and density porosity difference and density porosity The first intersection map drawn can be used to classify the types of sandstone and conglomerate reservoirs, so as to achieve the purpose of determining the distribution range of effective sandstone and conglomerate reservoirs using conventional logging data. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0018] Figure 1 A schematic flow chart of a method for determining an effective sandstone reservoir according to an embodiment of the present invention is shown;

[0019] Figure 2 A schematic diagram showing a process of obtaining the skeleton density value ρma of a sandstone reservoir in a target area according to an embodiment of the present invention is shown;

[0020] Figure 3 A second cross-plot showing porosity and bulk density of a conventional core analysis of a sandstone reservoir according to an embodiment of the present invention;

[0021] Figure 4 The present invention is used to determine the neutron and density porosity difference of the effective reservoir of the sandstone. Porosity and density The first intersection plate of

[0022] Figure 5 The figure shows the effect of determining the effective sandstone reservoir using the method of the present invention. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] The methods known to the inventors for determining effective sandstone reservoirs using new logging data such as nuclear magnetic resonance and microresistivity scanning imaging logging mainly rely on new logging data such as nuclear magnetic resonance and microresistivity scanning imaging logging and supporting core analysis data. This results in the method being applicable only to a limited number of exploratory wells, and is not applicable to most development wells that have only measured conventional logging data and not nuclear magnetic resonance and microresistivity scanning imaging logging data.

[0025] Therefore, when using new logging technology data such as nuclear magnetic resonance and microresistivity scanning imaging logging to determine effective sandstone reservoirs, there is still a problem that it cannot be applied to development wells.

[0026] It should be noted that, in the present invention and in the embodiments of the present invention, effective reservoir refers to a reservoir with a high oil content (commonly known as a high-quality reservoir), for example, the first type reservoir and the second type reservoir in this embodiment.

[0027] like Figure 1 As shown, the embodiment of the present invention provides a method for determining an effective sandstone reservoir. The method comprises: Step S10: obtaining the skeleton density value ρ of the sandstone reservoir in the target area ma ; Step S20: Obtain conventional logging data of the sandstone reservoir in the target area; Step S30: According to the skeleton density value ρ in step S10 ma The density porosity of the sandstone reservoir is obtained by combining the conventional logging data in step S20. and neutron porosity Step S40: According to the density porosity in step S30 and neutron porosity Plotting Neutron and Density Porosity Differences Porosity and density step S50: according to the first cross-plot, the types of sandstone reservoirs are classified to determine the distribution range of the first type of reservoir and / or the second type of reservoir.

[0028] In the above technical solution, when obtaining the skeleton density value ρ of the sandstone reservoir in the target area ma and conventional logging data of sandstone reservoirs, and the skeleton density value ρ maThe density and porosity of the conglomerate reservoir can be calculated using conventional logging data. and neutron porosity Then, the neutron and density porosity differences are further calculated Then combined with neutron and density porosity difference and density porosity The first intersection plot can be used to classify the types of conglomerate reservoirs, thereby determining the distribution range of effective conglomerate reservoirs using conventional logging data. Compared to existing technologies that primarily rely on indirect pore structure parameters obtained from nuclear magnetic resonance and microresistivity scanning imaging logging, this method directly uses actual conventional logging data to more accurately determine effective conglomerate reservoirs (i.e., this scheme has a higher accuracy in evaluating conglomerate reservoirs), thereby improving exploration efficiency and reducing development risks.

[0029] Furthermore, the method for determining an effective sandstone reservoir according to an embodiment of the present invention can also be directly applied to the evaluation of development wells.

[0030] Specifically, in an embodiment of the present invention, conventional well logging data includes density logging data and neutron logging data. Conventional well logging instruments include density logging instruments and neutron logging instruments. Density logging data is derived from density logging curves acquired by density logging instruments, while neutron logging data is derived from neutron logging curves acquired by neutron logging instruments.

[0031] Preferably, in the embodiment of the present invention, by obtaining multiple sandstone cores from the sandstone reservoir in the target area and performing conventional physical property analysis on the multiple sandstone cores, the skeleton density value ρ of the sandstone reservoir in the target area can be obtained. ma .

[0032] Specifically, if Figure 1 As shown, in the embodiment of the present invention, the skeleton density value ρ of the sandstone reservoir in the target area is obtained. ma There is no sequential relationship between step S10 and step S20 of obtaining conventional logging data of the sandstone reservoir in the target area, that is, step S10 can be performed first and then step S20; or step S20 can be performed first and then step S10.

[0033] Preferably, in the embodiment of the present invention, the abscissa of the first cross-plot is the neutron and density porosity difference The vertical axis of the first intersection plot is density porosity In this way, the types of sandstone reservoirs can be divided more intuitively based on the first intersection plate.

[0034] In the embodiment of the present invention, the density porosity of the sandstone reservoir is Calculated using the following formula: in, is the density porosity, in %; ρ b is the bulk density of the sandstone reservoir, in g / cm 3 ρ f is the density of the pore fluid in g / cm 3 ρ ma is the skeleton density of sandstone, in g / cm 3 .

[0035] The above formula is used to calculate the volume density ρ of the sandstone reservoir b , the skeleton density value ρ obtained in step S10 ma and the density of the pore fluid ρ f Through processing, the density porosity of the sandstone reservoir can be obtained

[0036] In the above technical solution, the volume density of the sandstone reservoir ρ b and skeleton density value ρ ma Directly substitute the density logging value obtained by conventional density logging instrument into the above formula to calculate the density porosity Compared with the prior art which uses a fixed skeleton density value ρ ma In terms of the calculation method, the skeleton density value ρ obtained by actual core experiment is ma The method of substituting into the calculation formula can more accurately determine the density porosity of sandstone This improves the identification accuracy of effective sandstone reservoirs.

[0037] Specifically, in the embodiment of the present invention, the bulk density ρ of the conglomerate reservoir is b The density logging data obtained in step S20 is obtained by a density logging curve measured by a density logging tool.

[0038] In the embodiment of the present invention, the density of the pore fluid ρ f The value range is 1.0g / cm 3 to 1.1 g / cm 3 .

[0039] Preferably, the density of the pore fluid, ρ f The value is 1.0g / cm 3 .

[0040] In the embodiment of the present invention, the neutron porosity Satisfies the following formula: in, is the neutron porosity, in %; CNL is the neutron logging value of the conglomerate reservoir, in %.

[0041] In the above technical solution, the neutron logging value CNL is processed using the above formula to obtain the neutron porosity

[0042] In the above technical solution, the neutron logging value (CNL) obtained using conventional neutron logging instruments is a directly obtained parameter. Compared with the indirect pore structure parameters obtained from nuclear magnetic resonance and microresistivity scanning imaging logging in the existing technology, the directly obtained parameter is more accurate. Moreover, the CNL parameter can be directly obtained in both exploration wells and development wells, thereby more accurately determining the effective sandstone reservoir and thus improving exploration efficiency.

[0043] Specifically, in the embodiment of the present invention, the neutron logging value CNL is the neutron logging data obtained in step S20, and is obtained from a neutron logging curve measured by a neutron logging instrument.

[0044] It should be noted that, in the embodiments of the present invention, the neutron logging value CNL refers to the neutron value (ie, hydrogen content) of the reservoir, and its value can generally be used as an estimated value of the neutron porosity of the reservoir.

[0045] In an embodiment of the present invention, the neutron and density porosity difference satisfies the following formula: Where, is the difference between neutron and density porosity, in %; is the density porosity, in %; is the neutron porosity, in %.

[0046] In the above technical solution, the density porosity is calculated using the above formula and neutron porosity Calculation is performed to obtain the neutron and density porosity differences and plotting the neutron and density porosity differences Porosity and density In this way, the types of sandstone and conglomerate reservoirs can be divided according to the first cross-plate, so as to achieve the purpose of using conventional logging data to determine the distribution range of effective sandstone and conglomerate reservoirs, thereby improving exploration efficiency and reducing development risks.

[0047] Preferably, in the embodiment of the present invention, the neutron and density porosity difference Neutron porosity and density porosity The absolute value of the difference.

[0048] The first intersection plate can be used to divide the sandstone reservoir in a certain area. The specific division criteria are as follows:

[0049] like Figure 4 As shown, in the embodiment of the present invention, the first type of reservoir is neutron and density porosity difference Density Porosity corresponding reservoir area.

[0050] Through the above classification, the distribution range of the first type of reservoir can be effectively determined, and the effectiveness of the sandstone reservoir can be determined, thereby improving exploration efficiency and reducing development risks. and density porosity The distribution range of the first type of reservoir can be determined quickly and accurately.

[0051] Preferably, in an embodiment of the present invention, the daily liquid production of the first type of reservoir is greater than or equal to 6 tons.

[0052] like Figure 4 As shown, in the embodiment of the present invention, the second type of reservoir is neutron and density porosity difference Density Porosity The corresponding reservoir.

[0053] Through the above division, the distribution range of the second type of reservoir can be effectively determined.

[0054] Preferably, in an embodiment of the present invention, the daily liquid production of the second type of reservoir is less than 6 tons.

[0055] It should be noted that, in the embodiments of the present invention, the daily liquid production refers to the sum of the daily oil and gas equivalent production and the daily water production.

[0056] like Figure 4 As shown, in the embodiment of the present invention, the neutron and density porosity difference Density Porosity The corresponding area is the dry layer.

[0057] Through the above division, the distribution range of the dry layer can be effectively determined, unnecessary mining can be avoided, waste of resources can be reduced, and development risks can be lowered.

[0058] Preferably, in an embodiment of the present invention, the daily liquid production of the dry layer is equal to 0.

[0059] like Figure 4 As shown, preferably, in the embodiment of the present invention, the neutron and density porosity difference Density Porosity The corresponding area is the mudstone layer, and the mudstone layer is a non-reservoir layer.

[0060] like Figure 2 and Figure 3As shown, in the embodiment of the present invention, step S10 includes: step S11: obtaining the porosity and bulk density values ​​of the sandstone core; step S12: drawing a second cross-plot of the porosity and bulk density values ​​with porosity as the abscissa and bulk density as the ordinate; step S14: obtaining the skeleton density value ρ of the sandstone reservoir ma .

[0061] In the above technical solution, the porosity and bulk density values ​​of the conglomerate cores can be obtained by performing conventional physical property analysis (i.e., core experiments) on multiple conglomerate cores. Then, a second intersection chart is drawn with porosity as the abscissa and bulk density as the ordinate, and the value at the intersection of the curve in the second intersection chart and the ordinate is obtained to obtain the skeleton density value ρ of the conglomerate reservoir. ma In this way, the skeleton density value ρ of the sandstone reservoir can be clearly and intuitively obtained. ma .

[0062] like Figure 2 and Figure 3 As shown, in the embodiment of the present invention, after step S12, the method further includes a step S13 of obtaining a linear relationship between porosity and bulk density by using a linear regression method, wherein when the porosity is 0, the bulk density is the skeleton density value ρ of the sandstone reservoir ma .

[0063] In the above technical solution, after step S12 and before step S14, the linear regression method can also be used to obtain the linear relationship between porosity and bulk density, and then the porosity equal to 0 is substituted into the above relationship to obtain the skeleton density value ρ of the sandstone reservoir. ma , that is, the bulk density of the sandstone reservoir is the skeleton density value ρ ma , so that the skeleton density value ρ can be accurately obtained ma .

[0064] Based on conventional physical property analysis data of 266 representative cores taken from a sandstone reservoir in the target area and oil testing data of 17 intervals, a specific embodiment of the present invention is described:

[0065] Use Figure 1 A method for determining an effective sandstone reservoir is shown in the following steps:

[0066] Step 1: Conduct routine physical property tests on 266 representative cores to obtain experimental data on core porosity and bulk density. Use core porosity as the linear abscissa and bulk density as the linear ordinate to make a second intersection chart to determine the skeleton density value ρ of the sandstone reservoir. ma , the result is as follows Figure 3 According to the experimental results, the volume density ρ of the sandstone reservoir is determinedma =2.672g / cm 3 .

[0067] Step 2: Based on step 1, density and neutron logging data were collected using conventional logging instruments. The density and neutron logging data of 17 test oil layers were processed using the following formula to calculate the density and porosity of the sandstone reservoir. and neutron porosity

[0068]

[0069]

[0070] Among them, ρ b The reservoir bulk density is measured using conventional density logging tools, in g / cm 3 ; CNL is the neutron logging value measured using conventional neutron logging instruments.

[0071] Step 3: Based on step 2, calculate the neutron and density porosity differences of the 17 test intervals using the following formula:

[0072]

[0073] Step 4: Neutron and density porosity difference is the linear abscissa, with density porosity Make the first intersection diagram for the linear ordinate and obtain the division diagram of the effective reservoir of sandstone and conglomerate. The result is as follows: Figure 4 shown.

[0074] Step 5: According to Figure 4 As shown in the diagram of the division of effective glutenite reservoirs, the glutenite reservoirs in the target area can be divided into four types, and the corresponding reservoir type division standards are:

[0075] Type I reservoir: and and the daily liquid production of the first type of reservoir is greater than 6 tons;

[0076] The second type of reservoir: and and the daily liquid production of the second type of reservoir is less than 6 tons;

[0077] Dry layer: and And the daily liquid production of the dry layer is equal to 0;

[0078] Mudstone layer: and Moreover, the mudstone layer is a non-reservoir layer.

[0079] The method for determining effective sandstone reservoirs using conventional logging data provided by the embodiment of the present invention is applied to a sandstone formation in an exploratory well in the target area. The density and neutron logging data actually measured are processed to obtain Figure 5 The effect diagram of determining the effective reservoir of sandstone is shown. Figure 5 The effect diagram shown is divided into four parts. Figure 5 The first track includes the natural gamma ray (GR) curve, the spontaneous potential (SP) curve, and the caliper (CAL) curve; the second track includes the deep lateral (RT), shallow lateral (RI), and flushing zone (RXO) resistivity curves; the third track includes the density log (DEN), neutron log (CNL), and acoustic transit time (AC) logs; and the fourth track, CCLX, represents the sandstone and conglomerate reservoir types continuously identified using the method described in this embodiment. To visually display the reservoir effectiveness classification results, the CCLX value for the first type of reservoir is set to 1, the CCLX value for the second type of reservoir is set to 2, the CCLX value for the dry layer is set to 3, and the CCLX value for the mudstone layer is set to 4.

[0080] It should be noted that the vertical axis is the depth of the well section; the horizontal axis in the fourth channel is the CCLX value.

[0081] from Figure 5 The results show that the 3297.0-3354.0 m interval is mainly a Type I reservoir, except for a very small amount of mudstone interlayers. The intervals above 3297.0 m and below 3354.0 m are mudstone layers. This identification result is confirmed by the oil test data. The oil test results of the 3297.0-3335.0 m interval show that after fracturing, the daily oil production is 8.92 tons and the daily gas production is 0.021×10 4 m 3 , which was confirmed to be the first type of reservoir, verifying the reliability of the method of using conventional logging data to determine the effective sandstone reservoir shown in the present invention.

[0082] From the above analysis, it can be seen that the method for evaluating the effectiveness of sandstone conglomerate reservoirs of the present invention can accurately classify the reservoir types, which is conducive to improving the subsequent mining efficiency.

[0083] From the above description, it can be seen that the embodiment of the present invention achieves the following technical effects: in obtaining the skeleton density value ρ of the glutenite reservoir in the target area, ma and conventional logging data of sandstone reservoirs, and the skeleton density value ρ ma The density and porosity of the conglomerate reservoir can be calculated using conventional logging data. and neutron porosity Then, the neutron and density porosity differences are further calculated Then combined with neutron and density porosity difference and density porosity The first intersection plot can be used to classify the types of conglomerate reservoirs, enabling the use of conventional well logging data to determine the distribution range of effective conglomerate reservoirs, thereby improving exploration efficiency and reducing development risks. Furthermore, the method for determining effective conglomerate reservoirs in embodiments of the present invention can also be directly applied to the evaluation of development wells.

[0084] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for determining an effective sandstone reservoir, characterized in that: The method comprises: Step S10: Obtain the skeleton density value of the sandstone reservoir in the target area ρ ma ; Step S20: acquiring conventional logging data of the sandstone reservoir in the target area; Step S30: According to the skeleton density value in step S10 ρ ma The density porosity of the sandstone reservoir is obtained by combining the conventional logging data in step S20. φ D and neutron porosity φ N ; Step S40: According to the density porosity in step S30 φ D and the neutron porosity φ N , plotting the neutron and density porosity differences φ N_D Porosity with the density φ D The first intersection plate; Step S50: classifying the types of the sandstone reservoir according to the first intersection plate, and determining the distribution range of the first type of reservoir and / or the second type of reservoir; The step S10 includes: Step S11: obtaining the core porosity and bulk density values ​​of the sandstone; Step S12: using the porosity as the abscissa and the volume density as the ordinate, drawing a second cross-plot of the porosity and the volume density values; Step S14: Obtaining the skeleton density value of the sandstone reservoir ρ ma .

2. The method for determining an effective sandstone reservoir according to claim 1, characterized in that: The density porosity of the conglomerate reservoir φ D Satisfies the following formula: ； in, φ D is the density porosity, unit is %; ρ b is the bulk density of the sandstone reservoir, in g / cm 3 ; ρ f is the density of the pore fluid in g / cm 3 ; ρ ma is the skeleton density of sandstone, in g / cm 3 .

3. The method for determining an effective sandstone reservoir according to claim 2, characterized in that: The density of the pore fluid ρ f The value range is 1.0 g / cm 3 Up to 1.1 g / cm 3 .

4. The method for determining an effective sandstone reservoir according to claim 1, wherein: The neutron porosity φ N Satisfies the following formula: φ N =CNL; in, φ N is the neutron porosity, in %; CNL is the neutron logging value of the conglomerate reservoir, in %.

5. The method for determining an effective sandstone reservoir according to any one of claims 1 to 4, characterized in that: The first type of reservoir is the neutron and density porosity difference φ N_D ≤14%, the density porosity φ D ≥8% corresponding reservoir.

6. The method for determining an effective sandstone reservoir according to any one of claims 1 to 4, characterized in that: The second type of reservoir is the neutron and density porosity difference φ N_D ≤14%, the density porosity φ D <8% corresponding reservoir.

7. The method for determining an effective sandstone reservoir according to claim 5, characterized in that: The neutron and density porosity differences φ N_D >14%, the density porosity φ D ≤6% corresponds to a dry layer; or, the neutron and density porosity difference φ N_D >14%, the density porosity φ D The area corresponding to >6% is mudstone layer.

8. The method for determining an effective sandstone reservoir according to any one of claims 1 to 4, characterized in that: The neutron and density porosity differences satisfy the following formula: ； Where, φ N_D is the difference between neutron and density porosity, in %; φ D is the density porosity, unit is %; φ N is the neutron porosity, in %.

9. The method for determining an effective sandstone reservoir according to claim 1, wherein: After step S12, the method further includes step S13 of obtaining a linear relationship between the porosity and the bulk density using a linear regression method, wherein when the porosity is 0, the bulk density is the skeleton density value of the sandstone reservoir. ρ ma .

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