A saturation model construction method considering fracture dip angle and application thereof

Abstract

The application provides a saturation model construction method considering a crack inclination and application, and the method comprises the following steps: 1, in the model establishment process of the porosity index, an equivalent medium theory and a conductivity tensor model of an arbitrary inclination are given; 2, a saturation expression of a matrix pore type reservoir is determined; 3, the porosity attached to the matrix pore system of a fracture-vug type pore system is converted to the matrix pore system; and 4, the matrix water saturation expression of the fracture-vug type reservoir considering the crack inclination is obtained by combining steps 1-3. The saturation model considering the crack inclination obtained by the method can be used in oil and gas evaluation work in the oil industry.

Description

Technical Field

[0001] This invention belongs to the field of oil exploration reservoir evaluation technology, and particularly relates to a method for constructing a saturation model that considers fracture dip angle and its application. Background Technology

[0002] Saturation calculations are crucial in the oil and gas industry, directly impacting various aspects such as oil and gas reserve estimation, fluid distribution analysis, production forecasting, and optimization. In reserve estimation, saturation helps determine the recoverable amount of oil and gas in a reservoir and assess the distribution of different fluids such as oil, gas, and water, which is essential for development planning. During production, changes in saturation reflect the dynamic characteristics of the reservoir, helping to predict extraction effectiveness and optimize production strategies. Particularly in enhanced oil recovery (EOR) technologies, monitoring saturation changes allows for adjustments to water and gas injection methods to improve recovery efficiency. Saturation is also widely used in rock physics research, where data can be used to infer key physical properties of reservoirs, such as porosity and permeability, thus aiding in the construction of accurate reservoir models. Furthermore, saturation plays a vital role in the assessment of heterogeneous reservoirs, helping to identify enriched and depleted areas and optimize development strategies. As production progresses, changes in saturation can effectively monitor water intrusion or contamination issues, providing real-time feedback for reservoir management and ensuring the sustainable and efficient extraction of resources.

[0003] Among saturation calculation methods, the Archie formula is currently the most classic formula for calculating water saturation. For details, see Archie, GE's 1942 paper "The electrical resistivity log as an aid in determining some reservoir characteristics" published in *Translations of the American Institute of Mining and Metallurgical Engineers*. The Archie formula is mainly applicable to reservoirs with well-developed mechanical porosity. In fractured-vuggy reservoirs, due to the influence of pore, vulnerability, and fracture development, the conventional Archie formula exhibits significant errors in saturation calculation, resulting in poor applicability. Current methods for calculating saturation in fractured-vuggy reservoirs are mainly divided into two categories, as detailed below:

[0004] (1) Modeling is performed on the rock electrical parameters in the Archie formula, using variable rock electrical parameters to represent the changes in pores, cavities, and fractures in the reservoir space. Based on this idea, Tian, ​​J., Sima, LQ, Wang, L, published a paper entitled "A novel triple-porosity model for fractured-vuggy reservoirs based on Maxwell-Garnett mixing rule" in the Journal of Petroleum Science and Engineering in 2022, which gave a resistivity model for fractures with arbitrary dip angles; on this basis, combined with the Archie formula, a model for calculating the porosity index was given. This model is only applicable to the calculation of the porosity index and does not involve other parameters of the Archie formula, making it difficult to use as a complete saturation model.

[0005] (2). Based on the Archie formula, a saturation model is established considering the space for fractured and vulcanized reservoirs. Based on this idea, Liao Mingshu constructed a saturation model for fractured reservoirs in his article "Discussion on the Processing Method of Logging Data for Fractured Carbonate Reservoirs" published in the third issue of the Journal of Petroleum Science in 1980. However, the model is only applicable to reservoirs with horizontal fractures and does not consider the development of dissolution pores. Liu Ruilin, Li Ning, and others constructed a saturation model for fractured and vulcanized reservoirs with high-angle and low-angle fractures in their article "Application of the triple porosity model in well-logeffectiveness estimation of the carbonate reservoir in Tarim oilfield" published in the Journal of Petroleum Science and Engineering in 2009. However, the high and low fracture angles are distinguished only by whether they are parallel or perpendicular to the current line: when the fracture is parallel to the current line, it is considered a low angle, and when it is perpendicular to the current line, it is considered a high angle; when the fracture and the current line are at a certain angle, the model does not consider it and is difficult to apply to fractured and vulcanized reservoirs with different fracture angles.

[0006] In summary, there is still a lack of a saturation model that considers the fracture dip angle for the calculation and evaluation of saturation in fractured-vuggy reservoirs. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for constructing a saturation model that considers fracture dip angle, as well as its application. This invention provides a saturation model for fractured-vuggy reservoirs that considers fracture dip angle, for use in oil and gas evaluation in the petroleum industry.

[0008] The present invention adopts the following technical solution:

[0009] A method for constructing a saturation model considering crack dip angle includes:

[0010] Step 1. In the process of establishing the porosity index model, the equivalent medium theory and conductivity tensor model for arbitrary tilt angles are given, as shown in equation (1): ;

[0011] In the formula, The resistivity of fracture-vuggy reservoirs taking into account the fracture dip angle is expressed in Ω·m. , , These are the resistivity of fractures, resistivity of caverns, and resistivity of the matrix, all in Ω·m. , These are the porosity of fractures and the porosity of karst caves, which are attached to the fracture-cavity pore system, respectively, and neither has a unit. , , These are intermediate variables, representing the reservoir resistivity in the horizontal direction, the reservoir resistivity in the vertical direction, and the resistivity of the cavernous reservoir, respectively, all in Ω·m. The angle of the crack;

[0012] Step 2. Determine the saturation expression for matrix porous reservoirs, as shown in equation (2): (2);

[0013] In the formula, The resistivity of the matrix is ​​expressed in Ω·m. This represents the water saturation level of the matrix, without units. The resistivity of formation water is expressed in Ω·m. The term refers to the matrix porosity, which is an integral part of the matrix pore system and has no unit. is the matrix porosity index, dimensionless; n is the saturation index, dimensionless.

[0014] Step 3. Convert the porosity of the matrix pores attached to the slit-type pore system to the matrix pore system of the Archie formula, as shown in equation (3): (3);

[0015] In the formula, The term refers to the matrix porosity, which is an integral part of the matrix pore system and has no unit. The porosity of the matrix, which is part of the fracture-cavity pore system, has no unit. , These are the porosity of fractures and the porosity of karst caves, which are attached to the fracture-cavity pore system, respectively, and neither has a unit.

[0016] Step 4. Combining equations (1), (2), and (3), the expression for the saturation model considering the crack dip angle is: (4);

[0017] In the formula, This represents the water saturation level of the matrix, without units. The resistivity of fracture-vuggy reservoirs taking into account the fracture dip angle is expressed in Ω·m. , , , These are fracture resistivity, cave resistivity, cavernous reservoir resistivity, and formation water resistivity, respectively, all in Ω·m. , , These are the porosity of fractures, the porosity of karst caves, and the matrix porosity of the fracture-cavity system, respectively, all without units. , These are the porosity index and the saturation index, respectively, both of which are dimensionless. This refers to the matrix porosity, which is an integral part of the matrix pore system and has no unit.

[0018] Furthermore, in the numerical solution: under logging conditions, the resistivity of fractured-vuggy reservoirs considering fracture dip angles. Using deep lateral resistivity This indicates that under logging conditions, due to the interconnection of fractures and the filling of mud filtrate within them, the fracture resistivity... resistivity of mud filtrate Replacement; the cave is filled with groundwater, and the cave resistivity Using formation water resistivity Replacement; fracture porosity attached to the fracture-cavity pore system Porosity of karst caves attached to the fissure-cavity pore system Matrix porosity associated with the fracture-pore system Obtained through imaging logging data; matrix porosity index Saturation index It was obtained through rock electric experiments.

[0019] An application of a saturation model that considers fracture dip angle is used to calculate the matrix water saturation in fractured-vuggy reservoirs by combining the above-mentioned expression for matrix water saturation considering fracture dip angle with relevant parameters obtained through conventional logging, imaging logging and rock physics experiments.

[0020] The beneficial effects of this invention are:

[0021] This invention establishes a saturation model that considers fracture dip angle based on core experimental data, conventional logging, and special logging data. For reservoirs with fracture development, as long as the deep and shallow resistivity are obtained from conventional logging, and the porosity of fractures, caverns, and matrix attached to the fracture-cavity pore system is obtained through imaging logging, the saturation can be calculated. This solves the problem that the Archie formula is not applicable to reservoirs with fracture development and improves the accuracy of saturation calculation.

[0022] In the process of establishing the model in this invention, the influence of arbitrary fracture angles is fully considered. The reservoir resistivity in the horizontal direction and the reservoir resistivity in the vertical direction are combined with the fracture angle using the conductivity tensor model. The matrix porosity attached to the fracture-vuggy pore system is converted into the matrix pore system. A saturation model considering the fracture dip angle is established by combining the traditional Archie formula.

[0023] Compared to the former saturation evaluation model that does not consider arbitrary fracture angles, the interpretation results of this invention are more consistent with reality. Through practical application, the accuracy of saturation evaluation in this invention is superior to the traditional Archie formula, effectively solving the problem of interpreting saturation in fractured reservoirs. Since most oilfields in China currently have fractured reservoirs, this method has a wide range of applications. Simultaneously, it solves the problem of inaccurate saturation evaluation in fractured reservoirs, making up for the shortcomings of the traditional Archie formula. Attached Figure Description

[0024] Figure 1 This is a flowchart of the steps of the present invention;

[0025] Figure 2 The figure shows the calculation results of saturation of fractured-vuggy reservoirs with arbitrary dip angles. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] In the process of establishing the porosity index model, the papers "Improved triple porosity model for calculating porosity exponent of fractured-vuggy reservoirs based on Maxwell-Garnett mixing rule and anisotropic conductivity analysis" published by Tian, ​​J., Wang, L., Zhao, R, R in the Journal of Petroleum Science and Engineering in 2022, and "A triple porosity model for petrophysical analysis of naturally fractured reservoirs" published by Aguilera, RF in Petrophysics in 2004, based on equivalent medium theory and conductivity tensor model, give resistivity models of fractured-vuggy reservoirs with arbitrary dip angle fracture development: (1);

[0028] In the formula, The resistivity of fracture-vuggy reservoirs taking into account the fracture dip angle is expressed in Ω·m. , , These are the resistivity of fractures, resistivity of caverns, and resistivity of the matrix, all in Ω·m. , These are the porosity of fractures and the porosity of karst caves, which are attached to the fracture-cavity pore system, respectively, and neither has a unit. , , These are intermediate variables, representing the reservoir resistivity in the horizontal direction, the reservoir resistivity in the vertical direction, and the resistivity of the cavernous reservoir, respectively, all in Ω·m. The angle of the crack.

[0029] The above formula (1) is an intermediate parameter variable model for constructing the porosity index model, based on the papers "Improved triple porosity model for calculating porosity exponent of fractured-vuggy reservoirs based on Maxwell-Garnett mixing rule and anisotropic conductivity analysis" published by Tian, ​​J., Wang, L., Zhao, R, R, et al. in the Journal of Petroleum Science and Engineering in 2022 and "A triple porosity model for petrophysical analysis of naturally fractured reservoirs" published by Aguilera, RF in Petrophysics in 2004. Furthermore, the porosity index model is only a single parameter in the saturation calculation and cannot represent a complete saturation model. Therefore, this invention, based on formula (1), combines the Archie formula saturation expression for matrix reservoirs and considers the conversion between different porosity systems to construct a saturation model that simultaneously considers pores, cavities, fractures, and fracture dip angles.

[0030] A method for constructing a saturation model considering crack dip angle includes:

[0031] According to the Archie formula, the saturation of a matrix-porosity reservoir can be expressed as: (2);

[0032] In the formula, The resistivity of the matrix is ​​expressed in Ω·m. This represents the water saturation level of the matrix, without units. The resistivity of formation water is expressed in Ω·m. The term refers to the matrix porosity, which is an integral part of the matrix pore system and has no unit. is the matrix porosity index, dimensionless, and n is the saturation index, dimensionless.

[0033] The Archie formula applies to matrix-porosity reservoirs, where porosity is an integral part of the matrix pore system. In fracture-vuggy reservoirs, the reservoir space includes matrix pores, caverns, and fractures. When applying the Archie formula, the porosity of the matrix pores, which are integral to the fracture-vuggy pore system, must be considered. Transformation to the Archie formula matrix pore system: (3);

[0034] In the formula, The term refers to the matrix porosity, which is an integral part of the matrix pore system and has no unit. The porosity of the matrix, which is part of the fracture-cavity pore system, has no unit. , These refer to the porosity of cracks and caverns, which are attached to the fissure-cavity pore system, respectively; neither has a unit.

[0035] In formula (1), the resistivity and matrix resistivity of fractured-vuggy reservoirs with fractures of arbitrary dip angles are established. The relationship; in equation (2), the Archie formula represents the water saturation of the matrix. With matrix resistivity The relationship is given in equation (3), which presents the conversion formula from fractured-vuggy reservoir porosity to Archie's matrix porosity. Combining equations (1) and (2), the matrix resistivity of fractured-vuggy reservoirs is used. Substitute matrix resistivity for Archie's formula The water saturation of the matrix can then be obtained. The expression relationship, the conversion of the porosity parameter required in the formula, is given by formula (3).

[0036] In summary, by combining equations (1), (2), and (3), the saturation model expression considering the crack dip angle is as follows: (4);

[0037] In the formula, This represents the water saturation level of the matrix, without units. The resistivity of fracture-vuggy reservoirs taking into account the fracture dip angle is expressed in Ω·m. , , , These are fracture resistivity, cave resistivity, cavernous reservoir resistivity, and formation water resistivity, respectively, all in Ω·m. , , These are the porosity of fractures, the porosity of karst caves, and the matrix porosity of the fracture-cavity system, respectively, all without units. , These are the matrix porosity index and saturation index, respectively, with m and n being dimensionless.

[0038] Equation (4) is the expression for the saturation model considering fracture dip angle, constructed based on the equivalent medium theory and the conductivity tensor model. This equation is linear and implicit, and can be solved numerically. Under logging conditions, the resistivity of fractured-vuggy reservoirs considering fracture dip angle... Using deep lateral resistivity This indicates that under logging conditions, due to the interconnection of fractures and the filling of mud filtrate within them, the fracture resistivity... resistivity of mud filtrate Replacement; the cave is filled with groundwater, and the cave resistivity Using formation water resistivity Replacement; fracture porosity attached to the fracture-cavity pore system Porosity of karst caves attached to the fissure-cavity pore system Matrix porosity associated with the fracture-pore system Obtained through imaging logging data; matrix porosity Saturation index Obtained through rock electric experiments.

[0039] Based on the above formula, the matrix water saturation in fractured-vuggy reservoirs can be calculated by obtaining relevant parameters through conventional logging, imaging logging, and rock physics experiments. Figure 1 As shown.

[0040] Example:

[0041] This invention takes a well in an oil / gas field as an example to evaluate the saturation of a fractured reservoir section. The well's reservoir section is fractured, with fracture dip angles ranging from 5° to 50°. To effectively evaluate saturation, the resistivity of the fractured-vuggy reservoir is evaluated using equation (4) under logging conditions, considering the fracture dip angle. Available deep lateral resistivity This indicates that, due to the continuity of the fracture, it is filled with mud filtrate, and the fracture resistivity... Resistivity of mud filtrate Replacement; the cave is filled with groundwater, and the cave resistivity Available formation water resistivity Replacement; fracture porosity attached to the fracture-cavity pore system Porosity of karst caves attached to the fissure-cavity pore system Matrix porosity associated with the fracture-pore system Obtained through imaging logging data; matrix porosity Saturation index It can be obtained through rock electric experiments.

[0042] like Figure 2 The image shows the interpretation effect of saturation logging using the method of this invention. The first track is an imaging grayscale image, where black clumps represent dissolution pores and black lines represent fractures. This section shows dissolution pores and well-developed inclined fractures, which are marked with white lines. The second track is a black-and-white binary image processed from the imaging logging, where black clump areas represent low-resistivity dissolution pores, black line areas represent fractures, and white areas represent high-resistivity matrix components.

[0043] The third channel is the fracture dip angle channel extracted from imaging, where the left scale of the curve is 0° and the right scale is 90°, and the fracture dip angle curves are distributed between 5° and 50°. The fourth and fifth channels are the fracture porosity and cavern porosity channels calculated from imaging logging, and the curves include fracture porosity POR_FRAC and cavern porosity POR_VUG, without units. The sixth channel is the total porosity channel, and the curves include total porosity POR and core analysis total porosity CPOR, with a high degree of agreement.

[0044] The seventh line represents the saturation line, with curves including the water saturation SW_AR calculated using the Archie formula, the water saturation SW calculated using this invention, and the core water saturation CSW. The figure shows that, under the same calculation conditions, the SW calculated using this invention shows a higher degree of agreement with the core compared to SW_AR. Furthermore, compared to SW_AR calculated using the Archie formula, the SW calculated using this invention exhibits a more significant variation in cavitation and fracture-developed zones, indicating that the SW calculated using this method is more sensitive to pores and has better application results.

[0045] Field application examples show that, compared with existing methods, the present invention provides a saturation model that considers the fracture dip angle under arbitrary fracture dip angle. This model is more reasonable for calculating the water saturation of fracture-vuggy reservoirs, is more sensitive to fracture-vuggy responses, and has a higher agreement with core saturation.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing a saturation model considering crack dip angle, characterized in that... ,include: Step 1. Establish a model for the porosity index and provide the equivalent medium theory and conductivity tensor model for arbitrary inclination angles; Step 2. Determine the saturation expression for matrix-porosity reservoirs; Step 3. Convert the porosity of the matrix pores attached to the slit-type porous system to the Archie formula matrix pore system; Step 3 includes equation (3), as shown below; (3); In the formula, The term refers to the matrix porosity, which is an integral part of the matrix pore system and has no unit. The porosity of the matrix, which is part of the fracture-cavity pore system, has no unit. , These are the porosity of fractures and the porosity of karst caves, which are attached to the fracture-cavity pore system, respectively, and neither has a unit. Step 4. Combining Steps 1-3, give a saturation model that considers the crack dip angle.

2. The method according to claim 1, characterized in that, The equivalent dielectric theory and conductivity tensor model in step 1 are shown in equation (1): ; In the formula, The resistivity of fractured-vuggy reservoirs taking into account the fracture dip angle is expressed in Ω·m. , , These are the resistivity of fractures, resistivity of caverns, and resistivity of the matrix, all in Ω·m. , These are the porosity of fractures and the porosity of karst caves, which are attached to the fracture-cavity pore system, respectively, and neither has a unit. , , These represent reservoir resistivity in the horizontal direction, reservoir resistivity in the vertical direction, and resistivity of cavernous reservoirs, respectively, all in Ω·m. The angle of the crack.

3. The method according to claim 1, characterized in that, The saturation expression for step 2 is shown in equation (2); （2）； In the formula, The resistivity of the matrix is ​​expressed in Ω·m. This represents the water saturation level of the matrix, without units. The resistivity of formation water is expressed in Ω·m. The term refers to the matrix porosity, which is an integral part of the matrix pore system and has no unit. is the matrix porosity index, dimensionless, and n is the saturation index, dimensionless.

4. The method according to claim 1, characterized in that, Step 4, considering the saturation model expression for the crack dip angle, is: （4）； In the formula, This represents the water saturation level of the matrix, without units. The resistivity of fractured-vuggy reservoirs taking into account the fracture dip angle is expressed in Ω·m. , , , These are fracture resistivity, cave resistivity, cavernous reservoir resistivity, and formation water resistivity, respectively, all in Ω·m. , , These are the porosity of fractures, the porosity of karst caves, and the matrix porosity of the fracture-cavity system, respectively, all without units. , These are the porosity index and the saturation index, respectively, both of which are dimensionless. This refers to the matrix porosity, which is an integral part of the matrix pore system and has no unit. The angle of the crack.

5. The method according to claim 1, characterized in that, In numerical solutions: Under logging conditions, the resistivity of fractured-vuggy reservoirs considering fracture dip angle. Using deep lateral resistivity Indicates crack resistivity. resistivity of mud filtrate Alternatives; Cave resistivity Using formation water resistivity Instead, the fracture porosity associated with the fracture-cavity pore system Porosity of karst caves attached to the fissure-cavity pore system and Porosity index obtained from imaging logging data; Saturation index Obtained through rock electric experiments.

6. A method for calculating water saturation using the construction method of the saturation model considering crack dip angle as described in claim 1, characterized in that, By combining relevant parameters obtained through conventional logging, imaging logging, and rock physics experiments, the matrix water saturation in fractured-vuggy reservoirs was obtained.

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