Method and device for obtaining shear wave velocity curve of thin carbonate reservoir

Abstract

The invention discloses a carbonate rock thin reservoir shear wave velocity curve obtaining method, and the method comprises the steps: building a first Poisson's ratio model related to lithology based on shale content data; according to the first Poisson's ratio model and the porosity data, establishing a second Poisson's ratio model related to the lithology and the physical property; according to the second Poisson's ratio model and the oil saturation data, establishing a target Poisson's ratio model related to the lithology, the physical property and the fluid; and obtaining a shear wave velocity curve according to the target Poisson's ratio model. According to the method, the shear wave data is obtained based on the target Poisson's ratio model for the carbonate rock thin reservoir, so that the pre-stack parameter-longitudinal and transverse wave velocity ratio can better identify the oil-containing reservoir and the water-containing reservoir, and the risk of pre-stack inversion prediction of oil and gas is reduced. The method is high in pertinence, sensitive to oil gas and good in timeliness, and has important practical significance in research areas of complex carbonate rock thin reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum exploration and development, and in particular to a method and device for obtaining a shear wave velocity curve of a thin carbonate reservoir. Background Art

[0002] As the difficulty of oil and gas energy exploration and development increases, the accuracy of seismic pre-stack inversion prediction of reservoir fluids has become a difficult and key point in reservoir prediction, and shear wave data is a key parameter that restricts the accuracy of pre-stack inversion prediction of reservoir fluids. At present, mature shear wave logging curve prediction methods are mainly research methods developed for clastic rocks. With the gradual deepening of exploration and development, the proportion of exploration and development of carbonate oil reservoirs is increasing. Therefore, oil and gas prediction methods for thin carbonate reservoirs are more urgent. Using the current mature shear wave logging curve prediction methods, such as shear wave data estimated based on multivariate pore rock physics theoretical models, the pre-stack elastic parameters have weak ability to identify oil, gas and water. Therefore, it is urgent to establish a shear wave estimation method for thin carbonate reservoirs.

[0003] In recent years, theoretical research in rock physics, exemplified by Gassmann, has rapidly advanced. The current results of rock physics techniques provide a variety of sensitive elastic parameters for reservoir identification and oil and gas analysis, effectively guiding reservoir identification and prediction. The Gassmann equation derives a formula for the elastic modulus of porous rocks saturated with fluid. It uses skeletal properties to calculate the effect of fluid on P-wave velocity and density. By calculating the bulk modulus of pores saturated with fluid, the known bulk moduli of the solid matrix, rock skeleton, and pore fluid are used to derive the bulk modulus. This provides a foundation for the relationship between the elastic properties and physical properties of sedimentary rocks. However, while shear waves based on conventional multivariate pore structure estimation can effectively identify thin carbonate reservoirs, the high overlap of oil-bearing and water-bearing reservoirs presents significant risks in predicting oil and gas reserves.

[0004] Therefore, it is important to provide a shear wave estimation method that has high estimation accuracy and good pertinence, and can effectively identify fluids (oil and natural gas). Summary of the Invention

[0005] The present invention aims to provide a method and device for obtaining a shear wave velocity curve of a thin carbonate reservoir to solve the above-mentioned problem.

[0006] To achieve the above object, the present invention provides a method for obtaining a shear wave velocity curve of a thin carbonate reservoir, the method comprising:

[0007] Based on the mud content data, the first Poisson's ratio model related to lithology was established;

[0008] Based on the first Poisson's ratio model and porosity data, a second Poisson's ratio model related to lithology and physical properties is established;

[0009] Based on the second Poisson's ratio model and oil saturation data, a target Poisson's ratio model related to lithology, physical properties and fluid is established;

[0010] According to the target Poisson's ratio model, the shear wave velocity curve is obtained.

[0011] Optionally, the formula of the first Poisson's ratio model is:

[0012] Poisson'Ratio*100_VSH=A*VSH+D

[0013] Wherein, Poisson'Ratio*100_VSH is the Poisson's ratio related to lithology; A and D are empirical parameters; VSH is the shale content.

[0014] Optionally, the formula of the second Poisson's ratio model is:

[0015] Poisson'Ratio*100_VSH POR=A*VSH+D+C*POR

[0016] Where Poisson'Ratio*100_VSH POR is the Poisson's ratio related to lithology and physical properties; C is an empirical parameter; POR = porosity.

[0017] Optionally, the formula of the target Poisson's ratio model is:

[0018] Poisson'Ratio*100_VSH POR SO=A*VSH+C*POR+D+B*SO

[0019] Poisson'Ratio*100_VSH POR SO is the Poisson's ratio related to lithology, physical properties and fluid; B is an empirical parameter; SO is oil saturation.

[0020] Optionally, obtain a shear wave velocity curve based on the target Poisson's ratio model, including:

[0021] According to the target Poisson's ratio model, the P-wave and S-wave velocity ratio curves are obtained;

[0022] Determine the shear wave velocity curve based on the longitudinal and shear wave velocity ratio curve.

[0023] Optionally, based on the target Poisson's ratio model, the P-wave velocity ratio curve can be obtained using the following formula:

[0024] VP / VS=SQRT((1-Poisson'Ratio) / (0.5-Poisson'Ratio))

[0025] Where VP / VS is the ratio of longitudinal and transverse wave velocities; SQRT is the square root function.

[0026] Optionally, the shear wave velocity curve is determined according to the longitudinal and shear wave velocity ratio curve using the following formula:

[0027] DTSM=DTCO*(VP / VS)

[0028] Among them, DTSM is the shear wave velocity; DTCO is the longitudinal wave velocity.

[0029] Optionally, before obtaining the shear wave velocity curve according to the target Poisson's ratio model, the following steps are further included:

[0030] Determine whether the empirical parameters in the target Poisson's ratio model are reasonable. If so, obtain the shear wave velocity curve based on the target Poisson's ratio model.

[0031] If it is unreasonable, the first Poisson's ratio model is re-established and the cycle is repeated until the empirical parameters in the target Poisson's ratio model are reasonable.

[0032] The present invention also provides a device for obtaining a shear wave velocity curve of a thin carbonate reservoir, the device comprising:

[0033] A first model obtaining unit is used to establish a first Poisson's ratio model related to lithology based on mud content data;

[0034] A second model obtaining unit is used to establish a second Poisson's ratio model related to lithology and physical properties based on the first Poisson's ratio model and porosity data;

[0035] a target model acquisition unit, for establishing a target Poisson's ratio model related to lithology, physical properties and fluid according to the second Poisson's ratio model and oil saturation data;

[0036] The velocity acquisition unit is used to obtain a shear wave velocity curve according to a target Poisson's ratio model.

[0037] Optionally, based on the target Poisson's ratio model, obtain the shear wave velocity, including:

[0038] According to the target Poisson's ratio model, the P-wave and S-wave velocity ratio curves are obtained;

[0039] Determine the shear wave velocity curve based on the longitudinal and shear wave velocity ratio curve.

[0040] Technical effects and advantages of the present invention:

[0041] The present invention provides a method for obtaining a shear wave velocity curve of a thin carbonate reservoir. The method comprises: establishing a first Poisson's ratio model related to lithology based on mud content data; establishing a second Poisson's ratio model related to lithology and physical properties based on the first Poisson's ratio model and porosity data; establishing a target Poisson's ratio model related to lithology, physical properties and fluid based on the second Poisson's ratio model and oil saturation data; and obtaining a shear wave velocity curve based on the target Poisson's ratio model.

[0042] This method targets thin carbonate reservoirs. By acquiring shear wave data based on a targeted Poisson's ratio model, the prestack parameter—the P-wave velocity ratio—can effectively identify oil-bearing and water-bearing reservoirs, thereby reducing the risk of prestack inversion prediction of oil and gas. The method is highly targeted, sensitive to oil and gas, and highly timely, making it of great practical significance in complex research areas with thin carbonate reservoirs.

[0043] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The flow chart of the method for obtaining shear wave velocity curves of thin carbonate reservoirs is provided;

[0045] Figure 2 This is an analysis diagram of the intersection of shear waves estimated by conventional method and shear waves estimated by this scheme method. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings provided by the present invention. Moreover, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for understanding and reading by those familiar with this technology, and are not used to limit the conditions for implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose that can be achieved by the present invention. At the same time, terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0048] To address the shortcomings of the existing technology, the present invention discloses a shear wave curve estimation model established for the prediction of thin carbonate reservoirs. This method of estimating shear waves is to first establish a Poisson's ratio model (the Poisson's ratio model takes into account lithology, physical properties and fluid properties at the same time), and then calculate the shear wave velocity. This is superior to the traditional method of directly estimating shear waves from longitudinal waves.

[0049] The present invention starts with estimating the Poisson's ratio model (i.e., the first Poisson's ratio model), establishes a Poisson's ratio model related to lithology, physical properties, and fluids, and finally uses the target Poisson's ratio model to estimate the shear wave data curve. This technology can effectively identify oil and gas in the study area of ​​thin carbonate reservoirs and can better distinguish between oil, gas, and water layers. The present invention first standardizes the measured data, and optimizes the three basic parameters such as mud content, porosity, and oil saturation to carry out shear wave estimation. Combined with the results of test oil production, the pre-stack sensitive parameters of oil and gas are optimized, and the threshold values ​​of the sensitive parameters of oil, gas, and water are divided.

[0050] The key to the present invention is to establish a Poisson's ratio model. The specific implementation process is as follows: first, a Poisson's ratio model related to lithology based on shale content VSH is established. On this basis, a Poisson's ratio model related to porosity POR and lithology and physical properties is established. Finally, based on the first two steps, a Poisson's ratio model related to oil saturation SO and lithology, physical properties and fluid is established.

[0051] In order to better understand this solution, the following Figure 1 A detailed introduction to the method of obtaining shear wave velocity curves of thin carbonate reservoirs:

[0052] A method for obtaining a shear wave velocity curve of a thin carbonate reservoir, the method comprising:

[0053] 1. Based on the mud content data, the first Poisson's ratio model related to lithology is established.

[0054] Specifically: The Poisson's ratio formula for classic lithology (VSH) replacement calculation is:

[0055] Poisson'Ratio*100_VSH=A*VSH+D

[0056] Where Poisson'Ratio*100_VSH is the Poisson's ratio related to lithology, and A and D are empirical parameters.

[0057] Among them, according to the lithology developed in the actual study area, a Poisson's ratio estimation based on lithology is carried out, and the values ​​of the empirical parameters A and D are determined according to the standard value range of the Poisson's ratio of mudstone and limestone.

[0058] 2. Based on the first Poisson's ratio model and porosity data, a second Poisson's ratio model related to lithology and physical properties is established.

[0059] Specifically, the effective porosity is replaced by the water layer using the porosity (POR) curve:

[0060] Poisson'Ratio*100_VSH POR=A*VSH+D+C*POR

[0061] Where Poisson'Ratio*100_VSHPOR is the Poisson's ratio related to lithology and physical properties; C is an empirical parameter.

[0062] Among them, on the basis of the Poisson's ratio estimated based on lithology, the Poisson's ratio estimation of porous limestone and dense limestone based on porosity POR is carried out, and the value of parameter C is determined according to the standard value range of Poisson's ratio of dense limestone and porous limestone.

[0063] 3. Based on the second Poisson's ratio model and oil saturation data, establish a target Poisson's ratio model related to lithology, physical properties and fluid.

[0064] Specifically, the oil saturation curve is used as the basis for fluid property (oil and gas) replacement:

[0065] Poisson'Ratio*100=A*VSH+C*POR+D+B*SO

[0066] Where Poisson'Ratio is the Poisson's ratio that is ultimately related to lithology, physical properties, and fluid; B is an empirical parameter.

[0067] Among them, on the basis of the Poisson's ratio estimated based on lithology and physical properties, the Poisson's ratio of fluids including oil, gas and water based on oil saturation SO is estimated, and the value of parameter B is determined according to the standard value range of Poisson's ratio of oil, water and gas layers.

[0068] According to the above, the calculation formula of the Poisson's ratio model of reliable fluid displacement can be obtained:

[0069] Poisson'Ratio*100=A*VSH+B*SO+C*POR+D

[0070] Where: Poisson'Ratio is Poisson's ratio; VSH is the shale content; SO is the oil saturation; POR is the porosity; VSH, SO, POR∈(0~100) are in %; Poisson'Ratio∈(0~0.5).

[0071] In addition, it is necessary to verify the rationality of the parameters in the target Poisson's ratio model. The reasonable results are as follows:

[0072] The Poisson's ratio of gas, oil, water, dry layer, and shale (dense limestone, dense igneous rock) should reach the standard range: 0.05-0.15-0.20-0.25-0.375-0.45;

[0073] The D constant value is the empirical value measured in various blocks around the world;

[0074] A∈(0~0.125); B∈(-0.2~0); C∈(-0.05~0).

[0075] 4. Obtain the shear wave velocity curve based on the target Poisson's ratio model.

[0076] Specifically, according to the target Poisson's ratio model, the longitudinal and shear wave velocity ratios are obtained; and according to the longitudinal and shear wave velocity ratios, the shear wave velocity curve is determined.

[0077] The formula for obtaining the ratio of the longitudinal and transverse wave velocity curves is:

[0078] VP / VS=SQRT((1-Poisson'Ratio) / (0.5-Poisson'Ratio))

[0079] Where VP / VS is the ratio of longitudinal and transverse wave velocities; SQRT is the square root function; and Poisson'Ratio is the target Poisson's ratio curve.

[0080] The formula for obtaining the shear wave velocity curve is:

[0081] DTSM=DTCO*(VP / VS)

[0082] Where DTSM is the shear wave velocity curve; DTCO is the longitudinal wave velocity curve.

[0083] In addition, shear wave velocity can be used in prestack inversion to obtain reliable elastic parameters (Poisson's ratio, Young's modulus, etc. used for rock brittleness and TOC calculation).

[0084] In order to better illustrate the present invention, examples are provided below.

[0085] The present invention provides parameter determination for establishing a Poisson's ratio model for the T-13 well. The specific operation is as follows: a Poisson's ratio model is established for the T-13 well based on three curves: mud content VSH, porosity POR, and oil saturation SO; the value ranges of parameters A, B, C, and D are determined; the P-wave velocity ratio Vp / Vs is calculated based on the Poisson's ratio; and finally, the S-wave velocity is calculated in combination with the P-wave velocity.

[0086] Specifically, first, based on the mud content VSH and the distribution characteristics of the Poisson's ratio curve of mudstone and limestone, which ranges from 0.375 to ≤0.45, A=0.05 and D=32 were determined. Then, based on the porosity POR and the distribution characteristics of the Poisson's ratio curve of porous limestone and tight limestone, which ranges from ≤0.25 to 0.325, C=-0.3 was determined. Then, based on the oil saturation SO and the distribution characteristics of the Poisson's ratio curve of gas, oil, water, and dry layers, which ranges from 0.05 to 0.15 to 0.20 to 0.25 to 0.375, B=-0.2 was determined.

[0087] Through continuous testing, the Poisson's ratio model formula was finally determined to be:

[0088] Poisson'Ratio*100=0.05*VSH-0.2*SO-0.3*POR+32

[0089] Where, Poisson'Ratio is Poisson's ratio, VSH is shale content, SO is oil saturation, and POR is porosity.

[0090] Then VP / VS=SQRT((1-Poisson'Ratio) / (0.5-Poisson'Ratio)), calculate the longitudinal and transverse wave velocity ratio curve (VP / VS), and finally combine the longitudinal wave velocity curve according to

[0091] DTSM=DTCO*(VP / VS) to obtain the shear wave velocity curve.

[0092] VP / VS - ratio of longitudinal and shear wave velocities, DTSM - shear wave velocity, DTCO - longitudinal wave velocity.

[0093] Among them, the estimated Vp / Vs value distribution range in the logging curve of the KT-II layer of the target layer of T-13 well is: 1.5-1.63 for oil layers, 1.7-1.87 for water layers, 1.94-2 for tight limestone, and 1.96-2.14 for mudstone.

[0094] Figure 2The intersection analysis of shear waves estimated by conventional methods and this method shows that the prestack parameter Vp / Vs estimated by this method (right) is significantly more discriminating between oil, gas, and water. The Vp / Vs-wave impedance-lithology-oil, gas, and water-dry layer intersection diagram shows that a Vp / Vs value of 1.9 is the threshold for porous limestone and tight limestone, while 1.7 is the threshold for oil, gas, and water layers.

[0095] The present invention also provides a device for obtaining a shear wave velocity curve of a thin carbonate reservoir, the device comprising: a first model obtaining unit, for establishing a first Poisson's ratio model related to lithology based on mud content data; a second model obtaining unit, for establishing a second Poisson's ratio model related to lithology and physical properties based on the first Poisson's ratio model and porosity data; a target model obtaining unit, for establishing a target Poisson's ratio model related to lithology, physical properties and fluid based on the second Poisson's ratio model and oil saturation data; and a velocity obtaining unit, for obtaining a shear wave velocity curve based on the target Poisson's ratio model.

[0096] Since the content protected by this device is similar to that protected by the above method, no further explanation will be given here. Please refer to the discussion in the method section for details.

[0097] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for obtaining a shear wave velocity curve of a thin carbonate reservoir, characterized in that: The method comprises: Based on the mud content data, the first Poisson's ratio model related to lithology was established; Based on the first Poisson's ratio model and porosity data, a second Poisson's ratio model related to lithology and physical properties is established; Based on the second Poisson's ratio model and oil saturation data, a target Poisson's ratio model related to lithology, physical properties and fluid is established; According to the target Poisson's ratio model, the shear wave velocity curve is obtained.

2. The method according to claim 1, characterized in that The formula of the first Poisson's ratio model is: Poisson'Ratio*100_VSH=A*VSH+D Wherein, Poisson'Ratio*100_VSH is the Poisson's ratio related to lithology; A and D are empirical parameters; VSH is the shale content.

3. The method according to claim 1, characterized in that The formula of the second Poisson's ratio model is: Poisson'Ratio*100_VSH POR=A*VSH+D+C*POR Where Poisson'Ratio*100_VSH POR is the Poisson's ratio related to lithology and physical properties; C is an empirical parameter; POR = porosity.

4. The method according to claim 1, wherein The formula of the target Poisson's ratio model is: Poisson'Ratio*100_VSH POR SO=A*VSH+C*POR+D+B*SO Poisson'Ratio*100_VSH POR SO is the Poisson's ratio related to lithology, physical properties and fluid; B is an empirical parameter; SO is oil saturation.

5. The method according to claim 1, wherein According to the target Poisson's ratio model, the shear wave velocity curve is obtained, including: According to the target Poisson's ratio model, the P-wave and S-wave velocity ratio curves are obtained; Determine the shear wave velocity curve based on the longitudinal and shear wave velocity ratio curve.

6. The method according to claim 5, characterized in that According to the target Poisson's ratio model, the P-wave velocity ratio curve is obtained by the following formula: VP / VS=SQRT((1-Poisson'Ratio) / (0.5-Poisson'Ratio)) Where VP / VS is the ratio of longitudinal and transverse wave velocities; SQRT is the square root function.

7. The method according to claim 5, characterized in that According to the longitudinal and shear wave velocity ratio curve, the shear wave velocity curve is determined by the following formula: DTSM=DTCO*(VP / VS) Among them, DTSM is the shear wave velocity; DTCO is the longitudinal wave velocity.

8. The method according to claim 1, characterized in that Before obtaining the shear wave velocity curve according to the target Poisson's ratio model, the following steps are also included: Determine whether the empirical parameters in the target Poisson's ratio model are reasonable. If so, obtain the shear wave velocity curve based on the target Poisson's ratio model. If it is unreasonable, the first Poisson's ratio model is re-established and the cycle is repeated until the empirical parameters in the target Poisson's ratio model are reasonable.

9. A device for obtaining shear wave velocity curves of thin carbonate reservoirs, characterized in that: The device comprises: A first model obtaining unit is used to establish a first Poisson's ratio model related to lithology based on mud content data; A second model obtaining unit is used to establish a second Poisson's ratio model related to lithology and physical properties based on the first Poisson's ratio model and porosity data; a target model acquisition unit, for establishing a target Poisson's ratio model related to lithology, physical properties and fluid according to the second Poisson's ratio model and oil saturation data; The velocity acquisition unit is used to obtain a shear wave velocity curve according to a target Poisson's ratio model.

10. The device according to claim 9, characterized in that According to the target Poisson's ratio model, the shear wave velocity is obtained, including: According to the target Poisson's ratio model, the P-wave and S-wave velocity ratio curves are obtained; Determine the shear wave velocity curve based on the longitudinal and shear wave velocity ratio curve.

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