Well logging interpretation method for oil saturation of tight sandstone reservoir

Abstract

The invention relates to a tight sandstone reservoir oil saturation logging interpretation method, and belongs to the technical field of oil layer exploration and development. According to the method, a water saturation calculation formula is established by performing multiple regression analysis on parameters such as a water saturation value, natural gamma, deep induced resistivity, interval transit time, compensated neutrons, compensated density and logging oil and gas display level assignment of experimental analysis of a closed rock core section, and the method is direct, simple and reliable; meanwhile, influence factors such as rock electricity parameters, formation water resistivity or empirical values are eliminated, so that the confidence coefficient of oil saturation calculation of the tight sandstone reservoir and the reliability of reserve estimation are improved, dynamic and static data of an oil field are reasonably matched, and geological understanding is clearer.

Description

Technical Field

[0001] The invention belongs to the technical field of oil layer exploration and development, and in particular relates to a well logging interpretation method for oil saturation in tight sandstone reservoirs. Background Art

[0002] In 1942, Archie proposed a calculation formula for water saturation in formations based on the experimental results of cemented sandstone: Among them, F is the formation factor; φ is the porosity; S w is water saturation; RI is resistivity index; a and b are coefficients related to lithology; m is porosity index; n is saturation index; R t is the formation resistivity; R w is the resistivity of formation water. In the above formula, a and b are coefficients related to lithology, porosity index m, saturation index n, and R w The accuracy of these data directly affects the accuracy of water saturation calculation, and further affects the reliability of reserve estimation.

[0003] Archie's formula has a good description for pure sandstone formations with medium to high porosity and high permeability. However, tight sandstone reservoirs have the characteristics of poor physical properties, strong heterogeneity, and complex pore structure. Compared with conventional sandstone reservoirs, tight sandstones show great differences in reservoir characteristics and logging response characteristics. For example, tight sandstones with low porosity and low permeability have dual pore structures, large pores and micropores coexist in reservoir rocks, and the electrical response law is complex, resulting in a large number of "non-Archie" phenomena, that is, the resistivity increase multiple and water saturation show diverse variation characteristics in double logarithmic coordinates, and formation factors and porosity show nonlinear relationships in double logarithmic coordinates. According to the previous study on the influencing factors of rock electrical parameters, under the comprehensive influence of formation temperature, pressure, formation water salinity, pore structure, etc., the m and n values ​​are constantly changing under formation conditions. However, in the process of logging data processing and interpretation, it is inevitable to calculate geological parameters with relatively fixed m and n values. Inaccurate. In addition, the resistivity of formation water is affected by the mineralization of formation water, formation temperature, sampling time, etc., and its value also has a great influence on the calculation result of water saturation. The Chinese invention patent application document with application publication number CN113719277A discloses a method for calculating water saturation of low permeability reservoirs. This method calculates the water saturation value of the reservoir through the resistivity of mud and formation water, parameters reflecting the structure and connectivity of rock reservoirs, saturated rock conductivity, connected pore porosity, total porosity and mud content, and the ratio of the volume of movable formation water to that of immovable formation water in the reservoir. Although this method avoids the problem of changes in rock electrical parameters and the problem of reasonable value selection of formation water resistivity, it requires empirical value selection and optimization processing, and there is still uncertainty.

[0004] The Simondu formula is a conductive model for mixed shale sandstone, which has the function of shale correction and reduces the influence of shale content on the calculation results of water saturation. However, in actual application, due to model assumptions and parameter selection, the accuracy of saturation calculation is also limited: on the one hand, the Simondu formula does not distinguish between the additional conductivity of fine silt and clay in shale; on the other hand, some rock electrical parameters use empirical values, and some are obtained from core rock electrical experiments. For example, Zhao Peiqiang et al. published "A Joint Inversion Method for Saturation of Tight Sandstone Reservoirs Based on Dielectric Logging and Resistivity Logging" ["Logging Technology" (2022.04)], which is based on the dielectric dispersion model of shale sandstone, the complex refractive index model and the Simondu resistivity formula, to construct the parameter response equation of tight sandstone reservoirs, but the rock electrical parameters still need to be involved in the study. Summary of the invention

[0005] The purpose of the present invention is to provide a method for logging and interpreting oil saturation in tight sandstone reservoirs, so as to solve the problem of the variation characteristics of rock electrical parameters in tight sandstone reservoirs and the rationality of the value of formation water resistivity.

[0006] To achieve the above object, the solution of the present invention includes:

[0007] A technical solution of a method for logging and interpreting oil saturation in a tight sandstone reservoir of the present invention comprises the following steps:

[0008] 1) Collect well logging data, mud logging data and core test analysis data, and determine the target layer;

[0009] 2) Return the sealed core to its original position; calibrate the oil saturation and water saturation of the core experimental test; obtain the logging value of the core sample corresponding to the well depth based on the above logging data;

[0010] 3) Assign values ​​according to the oil and gas display levels based on core test analysis data;

[0011] 4) Based on the data from steps 2) and 3), multiple regression data analysis is performed on the core water saturation and the corresponding logging values ​​and oil and gas display values ​​to establish a water saturation calculation formula;

[0012] 5) Calculate the water saturation based on the logging data and the water saturation calculation formula;

[0013] 6) Combined with the correction in step 2), the oil saturation value of the tight sandstone reservoir is calculated based on the water saturation.

[0014] The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 1, characterized in that the logging data include natural gamma, deep induction resistivity, sonic time difference, compensated neutron and compensated density.

[0015] Furthermore, in step 2), the oil saturation and water saturation of the core experimental test are corrected to So+Sw=100; wherein So is the oil saturation and Sw is the water saturation; in step 6), the oil saturation value of the tight sandstone reservoir is calculated according to the formula So=100-Sw.

[0016] Furthermore, in the steps 2) and 4), if the deep induction resistivity is not tested during drilling, the logging value is replaced by the deep lateral resistivity or the array induction resistivity.

[0017] Furthermore, in step 4), various parameters including core water saturation, natural gamma, deep induction resistivity, acoustic wave time difference, compensated neutron, compensated density and oil and gas display assignment are subjected to multivariate regression data analysis in Excel in the office software.

[0018] Furthermore, in step 4), the water saturation calculation formula is:

[0019] Sw=b+k1AC+k2ILD+k3DEN+k4CNL+k5GR+k6YQ

[0020] Among them, b is a constant term, k1~k6 are regression coefficients, Sw is water saturation, AC is acoustic time difference, ILD is deep induction resistivity, DEN is compensated density, CNL is compensated neutron, GR is natural gamma, and YQ is oil and gas display assignment.

[0021] Furthermore, in the water saturation calculation formula, b=-111.8573, k1=-0.3461, k2=-0.1971, k3=94.8098, k4=0.9392, k5=0.3316, k6=-3.1020.

[0022] Furthermore, the oil and gas display levels in step 3) include fluorescence / no display, oil traces, oil spots, and oil immersion.

[0023] Furthermore, in step 3), the method of assigning values ​​according to the oil and gas display level includes:

[0024] According to the oil and gas display level, the corresponding oil saturation values ​​in the core experimental analysis data are counted, and the average oil saturation of the oil-trace core is taken as the base value, and the multiples of the average oil saturation of the oil-spot and oil-immersed cores to the oil-trace core are calculated; referring to the oil content grade classification standard of porous oil-bearing cuttings in the industry standard, the maximum value of the proportion of oil-bearing cuttings in oil-trace cuttings is set as the base value, and the multiples of the median proportion of the two types of oil-bearing cuttings and oil-immersed cuttings to the oil-trace cuttings are calculated.

[0025] Furthermore, the four oil and gas display levels of fluorescence / no display, oil stains, oil spots, and oil immersion are assigned values, which are Y1=0, Y2=1, Y3=5, Y4=11, and Y5=17 respectively.

[0026] In order to solve the influencing factors such as rock electrical parameters, formation water resistivity or empirical values ​​in the well logging interpretation of oil saturation of tight sandstone reservoirs in the above-mentioned background technology, the present invention establishes a water saturation calculation formula by performing multivariate regression analysis on the water saturation value and its natural gamma, deep induction resistivity, acoustic wave time difference, compensated neutron and compensated density, and logging oil and gas display level assignment parameters obtained through experimental analysis of closed core sections. The method is direct, simple and reliable, and at the same time eliminates the influencing factors such as rock electrical parameters, formation water resistivity or empirical values, thereby improving the confidence of oil saturation calculation of tight sandstone reservoirs and the reliability of reserve estimation, making the dynamic and static data of the oil field reasonably matched and the geological understanding clearer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of a method for logging interpretation of oil saturation in a tight sandstone reservoir in an embodiment of the method of the present invention;

[0028] Figure 2 It is a comprehensive well logging interpretation diagram of the closed coring section of the XX37P40 well in the embodiment of the method of the present invention;

[0029] Figure 3 It is a comprehensive logging interpretation diagram of the closed coring section of Well XX162 in the embodiment of the method of the present invention;

[0030] Figure 4 It is a comprehensive logging interpretation diagram of the closed coring section of Well XX168 in the embodiment of the method of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0032] Example 1 of the method for interpreting the oil saturation of tight sandstone reservoirs:

[0033] The main idea of ​​the present invention is to construct a relatively direct and simple calculation formula related to the water saturation of tight sandstone reservoirs by performing multivariate regression data analysis on water saturation of closed core experiments, logging data (including natural gamma, acoustic wave time difference, compensated neutron and compensated density), and logging data (including oil and gas display level), avoiding the uncertainty influencing factors of rock electrical parameters and formation water resistivity in Archie's formula, and quickly and accurately identifying the type of oil layer through logging and logging data, so that the dynamic and static data of the oil field are better matched, the geological understanding is improved, and the data foundation for increasing reserves and building production in tight sandstone oil reservoirs is consolidated.

[0034] Specifically, the method for interpreting the oil saturation of a tight sandstone reservoir according to the present invention is as follows: Figure 1 The process shown includes the following steps:

[0035] 1) Collect well logging data, mud logging data, core experimental analysis and other data of the closed coring wells in the study area and the "Oil and Gas Well Geological Logging Specification" (SY / T 5788.3-2014) to determine the target layer; well logging data include natural gamma, deep induction resistivity, acoustic wave time difference, compensated neutron and compensated density; core data include core logging display and experimental analysis data;

[0036] 2) Return the sealed core to its original position; calibrate the oil saturation (So) and water saturation (Sw) of the core experimental test; read the natural gamma, deep induction resistivity, acoustic wave time difference, compensated neutron and compensated density logging values ​​of the core sample corresponding to the well depth;

[0037] 3) According to the oil and gas display levels such as fluorescence / no display, oil trace, oil spot, and oil immersion, the corresponding core experimental analysis oil saturation values ​​are counted. Taking the average oil saturation of the oil trace core as the base value, the multiples of the average oil saturation of the oil spot and oil immersion core to the oil trace core are calculated; according to the oil grade classification standard of porous oil-bearing cuttings in the "Oil and Gas Well Geological Logging Specifications", taking the maximum value of 5% of the oil-bearing cuttings in the oil trace cuttings as the base value, the multiples of the median proportion of oil-bearing cuttings such as oil spot, oil immersion, and oil-rich to the oil trace cuttings are calculated; after comprehensive comparative analysis, the oil and gas display levels such as fluorescence / no display, oil trace, oil spot, oil immersion, and oil-rich are assigned values ​​of 0, 1, 5, 11, and 17 respectively;

[0038] 4) Based on the data from steps 2) and 3), various parameters such as core water saturation, natural gamma, deep induction resistivity, acoustic wave time difference, compensated neutron, compensated density and oil and gas display assignment are multivariately analyzed in Excel in the office software.

[0039] After data analysis, the following water saturation calculation formula is established;

[0040] Sw=-111.8573-0.3461AC-0.1971ILD+94.8098DEN+0.9392CNL+0.3316GR-3.1020YQ Wherein: Sw is water saturation, AC is acoustic time difference, ILD is deep induction resistivity, DEN is compensated density, CNL is compensated neutron, GR is natural gamma, and YQ is oil and gas display assignment.

[0041] 5) Based on the data from step 4), the oil saturation value of the tight sandstone reservoir is calculated according to the formula So=100-Sw; wherein,

[0042] So is the oil saturation and Sw is the water saturation.

[0043] For the closed coring experiment analysis data, the corresponding core experiment analysis oil saturation values ​​are counted according to the oil and gas display levels such as fluorescence / no display, oil traces, oil spots, and oil immersion. The average oil saturation of the oil trace core is taken as the base value, and the multiple of the average oil saturation of the oil spot and oil immersion cores to the oil trace core is calculated.

[0044] The present invention is described below with a specific example:

[0045] a. Obtain historical data, including logging, mud logging, core and experimental analysis of the closed coring sections of the three wells.

[0046] b. Correct the oil saturation (So) and water saturation (Sw) obtained from the core test to So+Sw=100.

[0047] Papers related to the correction of oil and water saturation in sealed cores can be downloaded from CNKI and the correction can be performed according to the methods described therein, such as "Saturation Correction Method for Oil-Based Mud Sealed Coring" (Well Logging Technology, 2014.08).

[0048] c. The corresponding core experimental analysis oil saturation values ​​were counted according to the oil and gas display levels such as fluorescence / no display, oil trace, oil spot, and oil immersion. The average oil saturation of the oil trace core was taken as the base value, and the multiples of the average oil saturation of the oil spot and oil immersion core to the oil trace core were calculated. The results are shown in Table 1. According to the oil content level classification standard of porous oil-bearing cuttings in the "Oil and Gas Well Geological Logging Specifications", the specific standards are shown in Table 2. The maximum value of 5% of the oil-bearing cuttings in the oil trace cuttings was taken as the base value, and the multiples of the median proportion of oil-bearing cuttings such as oil spot, oil immersion, and oil-rich to the oil trace cuttings were calculated. After comprehensive comparative analysis, as shown in Table 3, the oil and gas display levels such as fluorescence / no display, oil trace, oil class, oil immersion, and oil-rich were assigned values ​​of 0, 1, 5, 11, and 17 respectively;

[0049] Table 1 Oil saturation statistics of closed coring section experimental analysis

[0050] category average value(%) multiple Number of samples (pieces) Oil immersion 54.5 10.1 34 Oil spots 28.8 5.3 97 Oil stains 5.4 1 24 Fluorescence 0 0 0

[0051] Table 2 Statistical table of oil content classification of porous oil-bearing rock fragments

[0052]

[0053] d. Draw the comprehensive logging interpretation diagram of the coring section of three wells, XX37P40, XX162 and XX168, on the resform software, draw the coring lithology profile and coring position of each well, and perform core homing in combination with the core lithology description and natural gamma logging curve. Read the natural gamma, deep induction resistivity, acoustic time difference, compensated neutron and compensated density logging values ​​corresponding to the well depth of the core sample, see Table 3.

[0054] Table 3 Statistics of logging parameters of the closed coring section of wells XX37P40, XX168 and XX162

[0055]

[0056]

[0057]

[0058]

[0059] e. Perform multiple regression data analysis on various parameters such as core water saturation, natural gamma, deep induction resistivity, acoustic time difference, compensated neutron, compensated density and oil and gas display assignment in Excel in the office software to establish a water saturation calculation formula; the formula is:

[0060] Sw=-111.8573-0.3461AC-0.1971ILD+94.8098DEN+0.9392CNL+0.3316GR-3.1020YQwherein: Sw is water saturation, AC is acoustic time difference, ILD is deep induction resistivity, DEN is compensated density, CNL is compensated neutron, GR is natural gamma, and YQ is oil and gas display assignment.

[0061] f. Based on the logging data of the target layer, assign the oil and gas display level on the logging data body, and use the water saturation calculation formula in step e to calculate the water saturation of the target layer in the study area.

[0062] g. Use the water saturation value calculated in step f to calculate the oil saturation value of the target layer in the study area according to the formula So=100-Sw.

[0063] h. According to steps e and f, the established water saturation calculation formula is used to interpret the core sections of three wells, XX37P40, XX162, and XX168. The results are as follows: Figure 2 , 3, as shown in Figures 4 and 5. From the three comprehensive logging interpretation diagrams, the confidence of the logging interpretation results of the water saturation calculation formula established this time is relatively high, and is within the core experimental analysis data. However, in some places, the oil saturation logging interpretation results are lower or higher than the core experimental analysis values. For example, XX37P40 is higher than the core experimental analysis value in 2 places and lower than it in 2 places. Well XX162 is lower than it in 1 place and well XX168 is lower than it in 2 places. According to the comprehensive research results of the rock electrical parameters and formation water resistivity of the Red River Oilfield and their values ​​(a=1.0288, b=1.0345, m=1.8580, n=2.4661, the formation water resistivity range Rw=0.03~0.08Ω·m, the meaning of the characters refers to the description in the background technology), the Archie formula logging interpretation was carried out on the core sections of the three wells XX37P40, XX162 and XX168, and the results are as follows Figure 2 , 3 , 4. From the comparison between the oil saturation values ​​interpreted by the well logging and the core experimental analysis values, it can be seen that the water saturation well logging interpretation formula established this time has higher accuracy than the Archie formula, and the method is direct, simple and fast.

[0064] The present invention establishes a simplified logging interpretation method related to oil saturation calculation based on parameters in closed core, well logging, and logging data: water saturation, oil saturation, natural gamma, acoustic time difference, compensated neutron and compensated density, and oil and gas display level. It greatly reduces the cost of sample experimental analysis of cores and their rock electrical parameters and formation water resistivity, eliminates the uncertainty factors when taking values ​​of various parameters, and the method is direct, simple, and reliable. According to logging and logging data, through this water saturation calculation formula, the type of oil layer can be quickly and accurately determined, the dynamic and static data of the oil field can be better matched, the geological understanding can be improved, and the data foundation for increasing reserves and building production in tight sandstone reservoirs can be consolidated.

Claims

1. A method for well logging interpretation of oil saturation in tight sandstone reservoirs, characterized in that: The steps include: 1) Collect well logging data, mud logging data and core test analysis data, and determine the target layer; 2) Return the sealed core to its original position; calibrate the oil saturation and water saturation of the core experimental test; obtain the logging value of the core sample corresponding to the well depth based on the above logging data; 3) Assign values ​​according to the oil and gas display levels based on core test analysis data; 4) Based on the data from steps 2) and 3), multiple regression data analysis is performed on the core water saturation and the corresponding logging values ​​and oil and gas display values ​​to establish a water saturation calculation formula; 5) Calculate the water saturation based on the logging data and the water saturation calculation formula; 6) Combined with the correction in step 2), the oil saturation value of the tight sandstone reservoir is calculated based on the water saturation.

2. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 1, characterized in that: The logging data include natural gamma, deep induction resistivity, acoustic time difference, compensated neutron and compensated density.

3. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 1, characterized in that: In the step 2), the oil saturation and water saturation of the core test are corrected to So+Sw=100; wherein So is the oil saturation and Sw is the water saturation; in the step 6), the oil saturation value of the tight sandstone reservoir is calculated according to the formula So=100-Sw.

4. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 2, characterized in that: In the steps 2) and 4), if the deep induction resistivity is not tested during drilling, the logging value is replaced by the deep lateral resistivity or the array induction resistivity.

5. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 1, characterized in that: In the step 4), various parameters including core water saturation, natural gamma, deep induction resistivity, acoustic wave time difference, compensated neutron, compensated density and oil and gas display assignment are subjected to multivariate regression data analysis in Excel in the office software.

6. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 5, characterized in that: In the step 4), the water saturation calculation formula is: Sw=b+k1AC+k2ILD+k3DEN+k4CNL+k5GR+k6YQ, where b is a constant term, k1~k6 are regression coefficients, Sw is water saturation, AC is acoustic time difference, ILD is deep induction resistivity, DEN is compensated density, CNL is compensated neutron, GR is natural gamma, and YQ is oil and gas display value.

7. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 6, characterized in that: In the water saturation calculation formula, b=-111.8573, k1=-0.3461, k2=-0.1971, k3=94.8098, k4=0.9392, k5=0.3316, k6=-3.1020.

8. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 1, characterized in that: The oil and gas display levels in step 3) include fluorescence / no display, oil traces, oil spots, and oil immersion.

9. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 1, characterized in that: In the step 3), the method of assigning values ​​according to the oil and gas display level includes: According to the oil and gas display level, the corresponding oil saturation values ​​in the core experimental analysis data are counted, and the average oil saturation of the oil-trace core is taken as the base value, and the multiples of the average oil saturation of the oil-spot and oil-immersed cores to the oil-trace core are calculated; referring to the oil content grade classification standard of porous oil-bearing cuttings in the industry standard, the maximum value of the proportion of oil-bearing cuttings in oil-trace cuttings is set as the base value, and the multiples of the median proportion of the two types of oil-bearing cuttings and oil-immersed cuttings to the oil-trace cuttings are calculated.

10. The method for logging interpretation of oil saturation in tight sandstone reservoirs according to claim 9, characterized in that: The four oil and gas display levels of fluorescence / no display, oil stains, oil spots, and oil immersion are assigned values, which are Y1=0, Y2=1, Y3=5, Y4=11, and Y5=17 respectively.

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