Saturation model building method based on rock physical classification and application

Abstract

The invention discloses a saturation model building method and application based on rock physical classification, and belongs to the technical field of dynamic saturation field modeling of oil well logging, three-dimensional geological modeling and oil and gas reservoir numerical simulation. S2, PG classification is carried out; s3, establishing a relation between the PG and the RRT to realize PG division; s4, determining an oil-water interface; s5, determining a free water interface; and S6, establishing a saturation model based on the height of the oil-gas column and calculating the water saturation, and solving the problems that the saturation modeling technology in the prior art is unreliable in saturation when being used for complex gas reservoir logging calculation, and the obtained dynamic saturation field of the oil-gas reservoir is poor in matching property with production characteristics. The method can be used for supporting three-dimensional saturation geological modeling and establishing a digital-analog saturation dynamic field, and can better reflect the characteristics of oil and gas reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of dynamic saturation field modeling of oil well logging, three-dimensional geological modeling and oil and gas reservoir numerical simulation, and in particular to a saturation model establishment method and application based on rock physics classification. Background Art

[0002] Saturation evaluation is the core of quantitative evaluation of oil and gas reservoirs, and is also one of the key parameter models to be built in 3D geological modeling and numerical simulation. Although some other logging technologies such as nuclear magnetic resonance logging, pulsed neutron saturation logging, and PSSL full energy spectrum saturation logging can also provide information on reservoir saturation, the saturation evaluation based on resistivity is still the most commonly used in logging interpretation.

[0003] Oil and gas saturation interpretation models are divided into four categories:

[0004] Category 1: Classic Archie formula.

[0005] The second category: saturation interpretation models that take into account the influence of mud, such as the Simon degree; the WS model that takes into account the cation exchange capacity of clay; the double water (DW) conductivity model that considers that the conductivity of muddy sandstone is a parallel combination of clay water and free water; and the saturation interpretation model based on the effective medium theory.

[0006] The third category: Saturation interpretation models that consider the influence of skeleton and multiple pores, such as Fraser, Givens, Crane, fracture-porosity reservoir saturation model and other models.

[0007] The fourth category: general saturation interpretation model based on network conductivity under heterogeneous conditions. Starting from the theory of heterogeneous anisotropic strata and their network conductivity, Li Ning and other researchers adopted a complex series and parallel conductivity form through complete mathematical derivation, making important improvements to the traditional parallel conductivity model.

[0008] One of the uses of saturation calculation is to carry out single well saturation evaluation. Another important use is to establish a three-dimensional saturation geological model and a dynamic saturation field of oil and gas reservoir digital model in the preparation of development plans. Well logging engineers need to provide relevant models and parameters for saturation modeling. The current conventional practice is that well logging engineers calculate saturation based on the saturation model selected from the above four types of models, and then input the saturation parameter curve to the modeling engineer to establish a three-dimensional saturation geological model, which is then output to the oil and gas reservoir engineer after coarsening to form a saturation field.

[0009] However, the current saturation modeling technology has the following two main defects:

[0010] ① In practical applications, the underlying assumption of the current saturation model is that the lithology, physical properties, pore structure, etc. remain basically unchanged. However, most gas reservoirs have complex reservoir types, large changes in physical properties, complex pore structures, and complex gas-water distribution. As a result, most gas reservoirs do not meet this assumption, making the saturation calculated by well logging in complex gas reservoirs unreliable.

[0011] ② Saturation is closely related to lithology, physical properties, reservoir type, pore structure, and oil and gas column height. The existing saturation modeling technology cannot fully establish a saturation model related to the above parameters, resulting in poor matching between the dynamic saturation field of the oil and gas reservoir and the production characteristics.

[0012] As a result, the existing saturation modeling model cannot accurately reflect the actual characteristics of oil and gas wells. Summary of the invention

[0013] The purpose of the present invention is to provide a method and application for establishing a saturation model based on rock physical classification, which solves the problems that the saturation calculated by logging using the saturation modeling technology in the prior art for complex gas reservoirs is unreliable, and the dynamic saturation field of the obtained oil and gas reservoirs has a poor match with the production characteristics.

[0014] The present invention is achieved through the following technical solutions:

[0015] A method for establishing a saturation model based on rock physics classification comprises the following steps:

[0016] S1. RRT classification: The classification of RRT is determined based on the lithology of rock thin sections, combined with the core description of lithology, reservoir type, and porosity-permeability relationship characteristics;

[0017] S2, PG classification: Combine the mercury injection curve and its pore throat size characteristics to classify, and classify the same displacement pressure, pore throat distribution characteristics, pore throat size, and pore throat sorting into one category;

[0018] S3. Establish the connection between PG and RRT to realize the division of PG: According to the distribution areas of different types of RRT and PG on the core pore-permeability intersection diagram, the classification standard of PG is established on the basis of RRT classification, and the division standard is established according to the porosity and permeability distribution areas;

[0019] S4. Determination of the oil-water interface;

[0020] S5. Determination of free water interface;

[0021] S6. Establish a saturation model based on the oil and gas column height and calculate the water saturation.

[0022] Furthermore, in step S1, the lithology of a certain depth point is determined based on the rock thin section, and then the lithology of the rock thin section is combined with the lithology described by the core to determine the lithology of a certain section, and then the RRT classification is determined for the same type of lithology section combined with the reservoir type and porosity-permeability relationship characteristics.

[0023] Furthermore, in step S1, RRT classification can be divided into five categories: RRT1, RRT2, RRT3, RRT4, and RRT5:

[0024] Among them, in the RRT1 type, the lithology of the thin sections includes spherulite-bone granular limestone, spherulite-bone granular mudstone, and bone granular mudstone-mudstone. The lithology is complex, but the core lithology is mainly grain limestone. The reservoir type is a pore-type reservoir with medium-to-high porosity and high permeability.

[0025] RRT2 is mudstone with well-developed dissolution pores, medium-high porosity and medium permeability.

[0026] RRT3 is mudstone, which is a porous reservoir with medium-high porosity and low permeability.

[0027] In the RRT4 type, the lithology is mainly granular marl-pelite limestone, porous reservoir, low-medium porosity and low permeability;

[0028] In the RRT5 type, the lithology is mudstone and granular limestone, but it is not a reservoir.

[0029] Furthermore, in step S2, the mercury injection curve and its pore throat size characteristics are combined to classify them into PG1, PG2, PG3, PG4, and PG5.

[0030] Among them, PG1 is: medium pore throat sorting, narrow pore throat size distribution, pore throats are mainly distributed in 1-10 microns, and the displacement pressure of PG1 is higher than that of PG2;

[0031] PG2 category: moderate pore throat sorting, wide distribution of pore throat size, pore throats mainly distributed in 0.5-10 μm;

[0032] PG3 category: pore throats are well sorted, and the pore throat size is less than 1 micron;

[0033] PG4: Poor pore throat sorting, wide pore throat size distribution, pore throats are mainly distributed in 0.02-2 microns;

[0034] PG5: It is a non-reservoir layer with poor pore throat sorting, fine skewness, and high displacement pressure. The pore throats are mainly distributed in the range of 0.04-0.2 μm.

[0035] Furthermore, in step S2, the PG3 class is further divided into two classes, PG3-1 and PG3-2, according to the difference in pore throat size;

[0036] Among them, PG3-1: the pore throat size distribution is narrow, and the pore throat is mainly distributed in 0.4-1 micron;

[0037] PG3-2: The pore throat size distribution is wide, and the pore throat is mainly distributed in 0.2-0.4 microns.

[0038] Furthermore, in step s3, the classification standard of PG is established based on the RRT classification, and the classification standard is established according to the porosity and permeability distribution area:

[0039] Within RRT1, when the permeability is greater than 65 mD, RRT1 belongs to the PG1 category; when the permeability is less than 65 mD, RRT1 belongs to the PG2 category;

[0040] RRT2 all belong to PG2 category;

[0041] In RRT3, when the porosity is greater than 22%, it belongs to PG3-1; when the porosity is less than 22%, it belongs to PG3-2;

[0042] In RRT4, when the porosity is >11%, it belongs to PG3-2; when the porosity is 8-11%, it belongs to PG4;

[0043] RRT5: RRT5 belongs to the dense layer and is classified as PG5.

[0044] Furthermore, in step S4, the oil-water interface is an interface with a water saturation of 100%. The 100% water saturation interface can be determined by the oil and gas content of the core, or by conventional saturation interpretation models such as the Archie formula and the double water model.

[0045] Furthermore, in step s5, the free water interface is below the interface with a water saturation of 100%. The threshold pressure of the capillary force curve is first determined, and then the threshold pressure P of the oil-water system under reservoir conditions is calculated according to formula (1). ow ,

[0046]

[0047] P ow -Threshold pressure of oil-water system under reservoir conditions; σ ow -Interfacial tension between oil and water phases under reservoir conditions; θ ow - oil-water wetting angle under reservoir conditions; σ Hg -Surface tension of mercury-air; θ Hg - mercury-air wetting angle; P hg - Mercury intrusion curve threshold pressure;

[0048] Obtain the threshold pressure P of the oil-water system under reservoir conditions ow Then, the height h between the 100% water-containing surface and the free water surface is calculated according to formula (2):

[0049]

[0050] In the formula, ρ w - Density of water, ρ o - density of the oil,

[0051] Free water level (FWL) = Depth above sea level of 100% oil-water interface - h.

[0052] Furthermore, in step S6, a saturation model based on the oil and gas column height is established, and the water saturation Sw_J satisfies the following equations (3) and (4):

[0053]

[0054] Sw_J-a*J b (4);

[0055] Where, Sw_J is water saturation; a is empirical coefficient 1; b is empirical coefficient 2; H is the height from the free water level (FWL), ft.

[0056] Furthermore, the coefficients a and b are determined by continuously adjusting a and b so that the water saturation Sw_J calculated by formula (4) and the saturation Sw_Log calculated by conventional saturation interpretation models such as the conventional Alch formula and the double water model can achieve good correlation.

[0057] An application of the aforementioned method for establishing a saturation model based on rock physical classification is used in a method for establishing three-dimensional saturation geological modeling and a digital model saturation dynamic field.

[0058] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0059] 1. In the present invention, the saturation established fully considers factors such as lithology, physical properties, reservoir type, pore structure, and oil and gas column height. The core of the invention is that the saturation model is based on the RRT (rock classification based on reservoir characteristics) classification. RRT is a rock unit that describes the characteristics of the reservoir and has a clear macroscopic geological meaning. On the basis of the RRT model, PG classification (rock physics classification) is performed according to the characteristics of the mercury injection curve and the distribution characteristics of the pore throat size, and then the relationship between PG and RRT is established, and then the saturation model based on the oil and gas column height of different PG is established to calculate the saturation. The method for establishing the saturation model provided by the present invention is not only focused on improving the saturation calculation from the saturation model itself, but also takes into account the geological factors that affect the saturation, such as lithology, physical properties, reservoir type, pore structure, oil and gas column height, etc. The results provide new data for the establishment of three-dimensional geological modeling and dynamic saturation field of oil and gas reservoirs. The calculated saturation can better reflect the saturation distribution characteristics of the oil and gas reservoir, and the dynamic saturation field of the oil and gas reservoir is better matched with the production characteristics.

[0060] 2. In the present invention, an important use is to support the establishment of three-dimensional saturation geological modeling and digital model saturation dynamic field. The technical advantage is mainly reflected in the fact that the saturation calculation is established by classification. The classification fully considers the influencing factors such as lithology, physical properties, reservoir type, pore structure, oil and gas column height, etc., and can better reflect the characteristics of oil and gas reservoirs. The first level of classification is RRT classification. In addition to considering lithology, RRT classification also fully combines the structure, structure, reservoir type, pore-permeability relationship, etc. of the rock. The second level is PG classification based on RRT classification. PG classification fully considers the pore structure. The third level is to establish a corresponding relationship between RRT and PG. The final saturation calculation is based on the PG classification calculation. The saturation models of different PGs use the saturation model that considers the oil and gas column height.

[0061] 3. In the present invention, this method is generally applicable to all oil and gas reservoirs, and has a better application effect on oil and gas reservoirs with obvious oil-gas-water transition zones. The application effect of the method is limited by the richness of the data. Rich coring data, analytical and testing data can establish a more refined RRT and PG classification scheme, and rich test data can accurately determine the height of the oil and gas column.

[0062] Fourth, in the present invention, the existing technology is improved mainly from four aspects: First, RRT classification is significantly improved compared with the conventional lithology-based classification. RRT classification not only considers lithology, but also considers rock structure, structure, reservoir type, pore-permeability characteristics, etc., which can more accurately describe the characteristics of oil and gas reservoirs; second, it does not only focus on improving the saturation calculation from the saturation model itself, but fully considers the geological factors that affect the saturation, and reflects these factors through rock classification, improving the calculation method of saturation; third, the final saturation calculation is based on PG classification, and PG classification fully considers the pore structure characteristics of rocks; fourth, linking RRT classification with PG classification, first, solves the problem of difficulty in identification based on pore structure classification logging, and second, solves the geological problems such as the same RRT but different pore structure, or different RRT but the same PG. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is the thin-section lithology frequency histogram of RRT1 in Example 1.

[0064] Figure 2 It is the porosity-permeability relationship diagram of RRT1 in Example 1.

[0065] Figure 3 It is the thin-section lithology frequency histogram of RRT2 in Example 1.

[0066] Figure 4 This is the porosity-permeability relationship diagram of RRT2 in Example 1.

[0067] Figure 5 It is the thin-section lithology frequency histogram of RRT3 in Example 1.

[0068] Figure 6 This is the porosity-permeability relationship diagram of RRT3 in Example 1.

[0069] Figure 7 It is the thin-section lithology frequency histogram of RRT4 in Example 1.

[0070] Figure 8 This is the porosity-permeability relationship diagram of RRT4 in Example 1.

[0071] Fig. 9 These are core photographs of RRT1, RRT2, RRT3, and RRT4 in Example 1. In the figure, A, B, C, and D are core photographs of RRT1, RRT2, RRT3, and RRT4, respectively.

[0072] Fig.10 It is the porosity-permeability relationship diagram of different RRTs in Example 1.

[0073] Fig.11It is the mercury injection curve and pore throat size distribution diagram of PG1 in Example 1.

[0074] Fig.12 It is the mercury injection curve and pore throat size distribution diagram of PG2 in Example 1.

[0075] Fig.13 It is the mercury injection curve and pore throat size distribution diagram of PG3 in Example 1.

[0076] Fig.14 It is the mercury injection curve and pore throat size distribution diagram of PG4 in Example 1.

[0077] Fig.15 It is the mercury injection curve and pore throat size distribution diagram of PG5 in Example 1.

[0078] Fig.16 It is the mercury injection curve and pore throat size distribution diagram of PG6 in Example 1.

[0079] Fig.17 It is the distribution diagram of RRT and PG of Thamma IV layer in Example 1 on the porosity-permeability intersection diagram.

[0080] Fig.18 It is the comprehensive logging curve and oil-water interface diagram of a well in Example 1.

[0081] Fig.19 It is a diagram of the comprehensive logging curve and saturation calculation results of a well in Example 1.

[0082] Fig. 20 This is a flowchart for constructing a saturation model in Example 1.

[0083] Fig.21 It is a correlation verification diagram between water saturation Sw_J and saturation Sw_Log calculated by conventional saturation interpretation models such as the conventional Alzi formula and double water model. DETAILED DESCRIPTION

[0084] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0085] The following will describe the implementation methods of the present invention in detail with reference to the drawings, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0086] Example 1

[0087] To facilitate the public to understand the present invention, this embodiment uses this method in the preparation of the Belbazem development plan in the United Arab Emirates, and takes the Thamma IV layer as an example to further illustrate this plan, which involves the technical field of dynamic saturation field modeling of oil well logging, three-dimensional geological modeling and numerical simulation of oil and gas reservoirs.

[0088] In this embodiment, the saturation model establishment method process refers to Fig. 20 , specifically including the following steps:

[0089] Step 1: RRT classification, i.e. rock classification based on reservoir characteristics

[0090] RRT classification first determines the lithology at a certain depth based on rock thin sections, but the lithology of thin sections or plug samples does not represent the macroscopic lithology. Then the lithology of rock thin sections is combined with the lithology described by the core to determine the lithology of a certain section (macroscopic lithology of the well section). Then, for the same type of lithology section (macroscopic lithology of the well section), the RRT classification is determined in combination with the reservoir type and the porosity-permeability relationship characteristics. RRT classification belongs to the rock classification based on the characteristics of oil and gas reservoirs. The same RRT well sections not only have the same macroscopic lithology, but also the same reservoir type, good consistency in porosity-permeability relationship, and different RRTs also have the same lithology.

[0091] RRT classification, i.e. rock classification based on reservoir characteristics, breaks through the traditional lithology-based classification scheme and improves the traditional rock classification based on thin sections.

[0092] In this example, the Thamma IV layer of the Belbazem oilfield is divided into five types of RRT, and the classification results are shown in Table 1.

[0093] First, the lithology of a certain depth point is determined based on the rock thin section, and the structure and texture of the rock are analyzed, such as the 1st and 2nd columns in Table 1. Then the lithology of the rock thin section is combined with the lithology described by the core to determine the lithology of a certain section (macro-lithology of the well section), such as the 3rd column in Table 1. Then, for the same type of lithology section (macro-lithology of the well section), the classification of RRT is determined in combination with the reservoir type and the porosity-permeability relationship characteristics, such as the 6th column in Table 1. Considering that RRT describes the characteristics of the reservoir, RRT5 is classified as a non-reservoir layer despite its lithology of mudstone and granular limestone.

[0094] Table 1: RRT classification of Thamma IV layer in Belbazem oilfield

[0095]

[0096] As shown in Table 1, the lithology of RRT1: RRT1 thin sections includes spherulite-bone granular limestone, spherulite-bone granular mudstone, and bone granular mudstone-mudstone. The lithology is complex, but the core lithology is mainly granular limestone. The reservoir type is a vuggy reservoir with medium-to-high porosity and high permeability.

[0097] The lithology of RRT2 and RRT3 is mainly mudstone, but RRT2 has well-developed dissolution pores, medium-high porosity and medium permeability. RRT3 is a porous reservoir with medium-high porosity and low permeability. Although the two have the same lithology, there are differences in reservoir type and physical properties, so they are divided into two categories.

[0098] RRT4: The lithology is mainly granular marl-grained limestone, porous reservoir, low-medium porosity and low permeability.

[0099] RRT5: Although its lithology is mudstone and granular limestone, it is not a reservoir, so it is classified as one.

[0100] Through the statistics of thin-section lithology in the same RRT section, it is not difficult to find that the thin-section lithology of the same RRT is not exactly the same, but generally a certain type of lithology is dominant.

[0101] In this embodiment, the different RRT lithology and porosity-permeability relationship diagrams of the Thamma IV layer in the Belbazem oilfield are shown in the attached Figure 1-8 , attached Fig. 9 There are four types of core photos of this layer, among which A, B, C, and D are core photos of RRT1, RRT2, RRT3, and RRT4 types respectively. Fig.10 It is the porosity-permeability relationship diagram of different RRT obtained based on the results.

[0102] Step 2: PG (Petrophysical group) classification

[0103] Combining the mercury injection curve and its pore throat size characteristics, the pores with the same displacement pressure, pore throat distribution characteristics, pore throat size and pore throat sorting are classified into one category.

[0104] In this embodiment, PG is classified into five categories, namely PG1, PG2, PG3, PG4 and PG5.

[0105] PG1: The pore throat sorting is moderate, the pore throat size distribution is narrow, and the pore throats are mainly distributed in 1-10 microns. The displacement pressure of PG1 is higher than that of PG2.

[0106] PG2: The pore throat sorting is moderate, the pore throat size distribution is wide, and the pore throat is mainly distributed in 0.5-10 microns;

[0107] The pore throats of PG3-1 and PG3-2 are well sorted, and the pore throat size is generally less than 1 micron. The obvious difference between them is the difference in pore throat size, among which:

[0108] PG3-1: The pore throat size distribution is narrow, and the pore throats are mainly distributed in the range of 0.4-1 μm;

[0109] PG3-2: The pore throat size distribution is wide, and the pore throat is mainly distributed in 0.2-0.4 microns;

[0110] PG4: Poor pore throat sorting, wide pore throat size distribution, pore throats are mainly distributed in 0.02-2 microns;

[0111] PG5: It is a non-reservoir layer with poor pore throat sorting, fine skewness, and high displacement pressure. The pore throats are mainly distributed in the range of 0.04-0.2 μm.

[0112] In this embodiment, the mercury injection curves and pore throat size distribution diagrams of PG1, PG2, PG3-1, PG3-2, PG4, and PG5 are shown in the attached figure. Figure 11-16 .

[0113] Step 3: Connect PG to RRT and establish the relationship between PG and RRT

[0114] According to the distribution areas of different types of RRT and PG on the core pore-permeability intersection diagram, the classification standard of PG is established on the basis of RRT classification, and the classification standard is established according to the porosity and permeability distribution areas.

[0115] PG is determined based on the mercury injection curve. The same RRT may have different PGs, and different RRTs may have the same PG. PG and RRT do not necessarily have a one-to-one correspondence, which requires the establishment of a connection between PG and RRT. Establishing the relationship between PG and RRT solves the problem that conventional logging is difficult to effectively divide pore structures.

[0116] According to the distribution characteristics of different PGs in different types of RRT on the porosity-permeability cross-plot, the PG classification standard based on the RRT classification is established according to the porosity and permeability distribution area. In this embodiment, the distribution of Thamma IV layer RRT and PG on the porosity-permeability cross-plot is shown in Fig.17 .

[0117] In RRT1, when the permeability is greater than 65mD, RRT1 belongs to PG1. When the permeability is less than 65mD, RRT1 belongs to PG2.

[0118] RRT2 all belong to PG2 category.

[0119] In RRT3, when the porosity is greater than 22%, it belongs to PG3-1; when the porosity is less than 22%, it belongs to PG3-2.

[0120] In RRT4, when the porosity is greater than 11%, it belongs to PG3-2; when the porosity is between 8-11%, it belongs to PG4.

[0121] RRT5: RRT5 belongs to the dense layer and uses PG5.

[0122] The specific criteria established are shown in Table 2.

[0123] Table 2: Criteria for the relationship between RRT and PG in Belbazem oilfield

[0124]

[0125] Step 4: Determination of the oil-water interface

[0126] The oil-water contact (OWC) is an interface with 100% water saturation, not the oil-water interface of the test. The 100% water saturation interface can be determined by the hydrocarbon content of the core, or by conventional saturation interpretation models such as the Archie formula and the double water model.

[0127] In this embodiment, reference Fig.18 , the elevation depth of 100% oil-water contact in Well A is -2530.75m, and the oil-water contact of Thamma IV in Belbazem oil field is determined to be -2530.75m. Depth from elevation (TVDSS) = core elevation - well vertical depth.

[0128] Step 5: Determination of the Free Water Surface (FWL)

[0129] The free water interface is below the interface with a water saturation of 100%. First, the threshold pressure of the capillary force curve is determined. Second, the capillary force data is converted into the capillary pressure of the oil-water system under reservoir conditions. The capillary force data is converted into the capillary pressure of the oil-water system under reservoir conditions. The formula is as follows:

[0130]

[0131] P ow -Threshold pressure of oil-water system under reservoir conditions;

[0132] σ ow -Interfacial tension between oil and water phases under reservoir conditions;

[0133] θ ow - Oil-water wetting angle under reservoir conditions;

[0134] σ Hg - Mercury-air surface tension;

[0135] θ Hg - Mercury-air wetting angle;

[0136] P hg -Hg intrusion curve threshold pressure.

[0137] Finally, the height h between the 100% water-containing surface and the free water surface is determined according to the following formula:

[0138]

[0139] Free water level (FWL) = 100% oil-water interface altitude depth - h

[0140] In this embodiment, the free water interface is located below the interface with a water saturation of 100%. The threshold pressure of the capillary force curve is determined first. The PG type at the oil-water interface of Well A belongs to PG3-1, and the threshold pressure of PG3-1 is 10 Psi. According to formula (1), the threshold pressure of the oil-water system under reservoir conditions is calculated to be 0.96 psi.

[0141] According to formula (2), the height between the 100% water-containing surface and the free water surface is calculated to be 338 m. The free water level (FWL) altitude is -2534.13 m.

[0142] Step 6: Establish a saturation model for different PGs based on the oil and gas column height and calculate the saturation of the well

[0143] A saturation model based on the height of the oil and gas column is established, and the saturation formulas are shown in equations (3) and (4). The saturation calculation model is related to porosity, permeability and the height of the oil and gas column. The physical properties are relatively good, with a high gas saturation. At the low point of the structure, the corresponding gas saturation is also low. The model can well reflect the vertical distribution characteristics of the gas saturation of the oil and gas reservoir. The water saturation can be calculated according to equation (4).

[0144]

[0145] Sw_J a*J b Formula (4);

[0146] o-Surface tension, dyne / cm 2 ;

[0147] θ - wetting angle;

[0148] K-permeability, mD;

[0149] Φ-porosity, decimal;

[0150] H - height from free water level (FWL), ft;

[0151] Δρ-density difference between two phases, g / cm3 ;

[0152] Sw_J-water saturation;

[0153] a-empirical coefficient 1;

[0154] b-empirical coefficient 2.

[0155] Method for determining empirical coefficients a and b: Continuously adjust a and b so that the water saturation Sw_J calculated by formula (4) and the saturation Sw_Log calculated by conventional saturation interpretation models such as the conventional Alzi formula and the double water model can achieve good correlation. Fig.21 .

[0156] In this embodiment, the saturation calculation parameters of different PGs are shown in Table 3.

[0157] Table 3

[0158] PG Classification a b PG1 0.3467 -0.508 PG2 0.2747 -0.596 PG3-1 0.2075 -0.745 PG3-2 0.1765 -0.65 PG4 0.2222 -0.622 PG5 0.2613 -0.9

[0159] In this embodiment, the comprehensive logging curve and saturation calculation results of Well A are referenced Fig.19 . From the above, it can be seen that the method for establishing a saturation model based on rock physical classification in the present invention is reliable. This method can support the establishment of three-dimensional saturation geological modeling and digital model saturation dynamic field. The technical advantage is mainly reflected in the fact that the saturation calculation is established by classification. The classification fully considers the influencing factors such as lithology, physical properties, reservoir type, pore structure, oil and gas column height, etc., and can better reflect the characteristics of oil and gas reservoirs.

[0160] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for establishing a saturation model based on rock physics classification, characterized in that: The steps include: S1. RRT classification: The classification of RRT is determined based on the lithology of rock thin sections, combined with the core description of lithology, reservoir type, and porosity-permeability relationship characteristics; S2, PG classification: Combine the mercury injection curve and its pore throat size characteristics to classify, and classify the same displacement pressure, pore throat distribution characteristics, pore throat size, and pore throat sorting into one category; S3. Establish the connection between PG and RRT to realize the division of PG: According to the distribution areas of different types of RRT and PG on the core pore-permeability intersection diagram, the classification standard of PG is established on the basis of RRT classification, and the division standard is established according to the porosity and permeability distribution areas; S4. Determination of the oil-water interface; S5. Determination of free water interface; S6. Establish a saturation model based on the oil and gas column height and calculate the water saturation.

2. The method for establishing a saturation model based on rock physical classification according to claim 1, characterized in that: In step S1, the lithology of a certain depth point is determined based on the rock thin section, and then the lithology of the rock thin section is combined with the lithology described by the core to determine the lithology of a certain section. Then, for the same type of lithology section, the RRT classification is determined in combination with the reservoir type and the porosity-permeability relationship characteristics.

3. The method for establishing a saturation model based on rock physical classification according to claim 2, characterized in that: In step S1, RRT classification can be divided into five categories: RRT1, RRT2, RRT3, RRT4, and RRT5: Among them, in the RRT1 type, the lithology of the thin sections includes spherulite-bone granular limestone, spherulite-bone granular mudstone, and bone granular mudstone-mudstone. The lithology is complex, but the core lithology is mainly grain limestone. The reservoir type is a pore-type reservoir with medium-to-high porosity and high permeability. RRT2 is mudstone with well-developed dissolution pores, medium-high porosity and medium permeability. RRT3 is mudstone, which is a porous reservoir with medium-high porosity and low permeability. In the RRT4 type, the lithology is mainly granular marl-pelite limestone, porous reservoir, low-medium porosity and low permeability; In the RRT5 type, the lithology is mudstone and granular limestone, but it is not a reservoir.

4. The method for establishing a saturation model based on rock physical classification according to claim 1, characterized in that: In step S2, the mercury injection curve and its pore throat size characteristics are combined to classify them into PG1, PG2, PG3, PG4, and PG5. Among them, PG1 is: medium pore throat sorting, narrow pore throat size distribution, pore throats are mainly distributed in 1-10 microns, and the displacement pressure of PG1 is higher than that of PG2; PG2 category: moderate pore throat sorting, wide distribution of pore throat size, pore throats mainly distributed in 0.5-10 μm; PG3 category: pore throats are well sorted, and the pore throat size is less than 1 micron; PG4: Poor pore throat sorting, wide pore throat size distribution, pore throats are mainly distributed in 0.02-2 microns; PG5: It is a non-reservoir layer with poor pore throat sorting, fine skewness, and high displacement pressure. The pore throats are mainly distributed in the range of 0.04-0.2 μm.

5. The method for establishing a saturation model based on rock physical classification according to claim 4, characterized in that: In step S2, the PG3 class is further divided into two classes, PG3-1 and PG3-2, according to the difference in pore throat size; Among them, PG3-1: the pore throat size distribution is narrow, and the pore throat is mainly distributed in 0.4-1 micron; PG3-2: The pore throat size distribution is wide, and the pore throat is mainly distributed in 0.2-0.4 microns.

6. The method for establishing a saturation model based on rock physical classification according to claim 1, characterized in that: In step S3, the classification standard of PG is established based on the RRT classification, and the classification standard is established according to the porosity and permeability distribution area: Within RRT1, when the permeability is greater than 65 mD, RRT1 belongs to the PG1 category; when the permeability is less than 65 mD, RRT1 belongs to the PG2 category; RRT2 all belong to PG2 category; In RRT3, when the porosity is greater than 22%, it belongs to PG3-1; when the porosity is less than 22%, it belongs to PG3-2; In RRT4, when the porosity is >11%, it belongs to PG3-2; when the porosity is 8-11%, it belongs to PG4; RRT5: RRT5 belongs to the dense layer and is classified as PG5.

7. The method for establishing a saturation model based on rock physical classification according to claim 1, characterized in that: In step S4, the oil-water interface is an interface with a water saturation of 100%. The 100% water saturation interface can be determined by the oil and gas content of the core, or by conventional saturation interpretation models such as the Archie formula and the double water model.

8. The method for establishing a saturation model based on rock physical classification according to claim 1, characterized in that: In step S5, the free water interface is below the interface with a water saturation of 100%. The threshold pressure of the capillary force curve is first determined, and then the threshold pressure P of the oil-water system under reservoir conditions is calculated according to formula (1). ow , P ow -Threshold pressure of oil-water system under reservoir conditions; σ ow -Interfacial tension between oil and water phases under reservoir conditions; θ ow - oil-water wetting angle under reservoir conditions; σ Hg -Surface tension of mercury-air; θ Hg - mercury-air wetting angle; P hg - mercury injection curve threshold pressure; obtain the threshold pressure P of the oil-water system under reservoir conditions ow Then, the height h between the 100% water-containing surface and the free water surface is calculated according to formula (2): In the formula, ρ w - Density of water, ρ o - density of the oil; Free water interface FWL = 100% oil-water interface altitude depth - h.

9. The method for establishing a saturation model based on rock physical classification according to claim 8, characterized in that: In step S6, a saturation model based on the oil and gas column height is established, and the water saturation Sw_J satisfies the following equations (3) and (4): Sw_J=a*J b (4); Where, Sw_J is water saturation; a is empirical coefficient 1; b is empirical coefficient 2; H is the height from the free water interface FWL, ft.

10. The method for establishing a saturation model based on rock physical classification according to claim 9, characterized in that: The coefficients a and b are determined by continuously adjusting a and b so that the water saturation Sw_J calculated by formula (4) and the saturation Sw_Log calculated by conventional saturation interpretation models such as the conventional Archie formula and the double water model can achieve good correlation.

11. An application of the method for establishing a saturation model based on rock physical classification according to claim 1, characterized in that: Used in three-dimensional saturation geological modeling and the establishment of digital model saturation dynamic field.

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