Method and device for estimating hydrate saturation based on coupling of double-permeability model

Abstract

The application discloses a method for estimating hydrate saturation based on a generalized weight equation coupled with a double occurrence mode, which comprises the following steps: determining the initial hydrate saturation of a reservoir, the occurrence mode of the hydrate, the porosity of the reservoir and the shale content of the reservoir; deriving a generalized weight equation (GWE) based on a Wyllie time average equation and a Wood equation; on the basis of the GWE, further proposing a generalized weight equation coupled with a double occurrence mode, and constructing a rock physical model of a hydrate reservoir with a double occurrence mode; and constructing a target function with the longitudinal wave impedance as a constraint, inverting the hydrate saturation based on the target function by using a grid search method, estimating the hydrate saturation value of the reservoir, and applying the method to the quantitative prediction of the hydrate saturation of an actual hydrate formation, so that the modeling accuracy and the quantitative description capability of the hydrate reservoir are effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of geophysical exploration technology, and in particular to a method, device and electronic equipment for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes. Background Art

[0002] Natural gas hydrates are ice-like crystalline compounds formed by natural gas and water under high-pressure, low-temperature conditions. They are widely distributed in sediments of terrestrial permafrost zones and deepwater basins along continental margins (Kvenvolden, 1993) and represent one of the most promising future alternative energy resources (Boswell and Collett, 2011). However, hydrates are highly susceptible to decomposition under changing formation temperature and pressure conditions, potentially triggering submarine geological hazards (Archer et al., 2009) and exacerbating global warming (Sultan et al., 2004). Accurate prediction of hydrate content and distribution is not only fundamental for quantitatively evaluating hydrate resource potential and addressing climate and environmental hazards, but also crucial for understanding hydrate accumulation mechanisms and guiding successful hydrate recovery. Hydrate saturation can be estimated using seismic elastic characteristics of hydrate reservoirs (Lee et al., 2008; Best et al., 2013; Wang et al., 2016; Pan et al., 2019; Liu et al., 2020). However, the elastic coupling effect between hydrate saturation and occurrence morphology directly impacts the accuracy of hydrate reservoir characterization. Therefore, a deep understanding of the impact of hydrates on formation acoustic properties is the key to quantitative characterization of hydrate reservoirs.

[0003] Rock physics models establish a quantitative relationship between hydrate saturation, microscopic occurrence morphology, and elastic response characteristics, laying a theoretical foundation for describing seismic elastic response characteristics and estimating hydrate saturation. Since pore-filling (hydrates filling the pore space) and skeleton-supported (hydrates supporting skeleton particles) are the two most common types of hydrate occurrence, numerous rock physics models have been proposed for these two types of hydrate reservoirs. Early, simple and practical empirical models, such as the Wyllie time-averaged equation, the Wood equation, and the three-phase weighted equation, were frequently used to describe the relationship between the elastic response of hydrate reservoirs and hydrate saturation. However, these models lack physical meaning and do not consider microscopic distribution patterns, requiring extensive field data to calibrate model parameters (Liu et al., 2018). For example, considering the microscopic distribution pattern of hydrates, some theoretical models, such as the contact model (Dvorkin et al., 1999; Helgerud et al., 1999), the SCA-DEM model (Chand et al., 2006), the modified Biot-Gassmann theory (Lee et al., 2004), and the simplified three-phase equation (Lee et al., 2008), have been successfully applied to convert velocity information into hydrate saturation (Terry and Knapp et al., 2018; Pan et al., 2022). However, these models involve numerous model parameters and are mostly based on the assumption of a single occurrence form, making it difficult to accurately describe hydrate formations with multiple occurrence forms. Therefore, it is necessary to develop a simple, practical rock physics theory that couples multiple hydrate occurrence forms. Summary of the Invention

[0004] The object of the present invention is to provide a method, device and electronic device for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes, so as to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, a method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes is provided, comprising:

[0007] Step S1: determining the initial hydrate saturation, hydrate occurrence pattern, reservoir porosity, and reservoir mud content of the reservoir;

[0008] The occurrence mode of the hydrate is a dual occurrence mode, which takes into account two microscopic occurrence forms: pore filling and skeleton support;

[0009] Step S2: constructing a rock physics model of a dual-occurrence hydrate reservoir;

[0010] Step S3: Construct an objective function with the longitudinal wave impedance as a constraint. The objective function is:

[0011]

[0012] Where: and is the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; ε is the given minimum error;

[0013] Step S4: using a grid search method to perform hydrate saturation inversion based on the objective function to estimate the reservoir hydrate saturation value.

[0014] Furthermore, in step S2, constructing a dual-occurrence morphology hydrate reservoir rock physics model includes:

[0015] Step S21: Calculating the bulk modulus and shear modulus of the rock matrix composed of solid minerals and skeleton-supported hydrates using Hill average, wherein the solid minerals include quartz, calcite, and clay;

[0016] Step S22: Calculate the bulk modulus and shear modulus of saturated rock composed of rock matrix, water, and pore-filling hydrate using a generalized weight equation based on dual occurrence morphology coupling.

[0017] Furthermore, in step S22, the bulk modulus and shear modulus of saturated rock composed of rock matrix, water and pore-filling hydrate are calculated using a generalized weight equation based on dual occurrence morphology coupling, where:

[0018] The generalized weight equation based on the dual occurrence morphology coupling is:

[0019]

[0020] Where: Z P,w , Z P,h , Z P,ma and Z P are the longitudinal wave impedances of water, hydrate, rock matrix and saturated rock, respectively; ρ w , ρ h , ρ ma and ρ b are the densities of water, hydrate, rock matrix and saturated rock, respectively,

[0021] ρ b =(1-φ)(1-V sh )ρ sd +(1-φ)V sh ρ c +φS h ρ h +φ(1-S h )ρ w ;

[0022] φe is the effective porosity, φ e =φ-φS h f ms ; Among them: φ, f ms and S h are porosity, percentage of framework-supported morphology, and hydrate saturation, respectively;

[0023] S hpfe is the pore-filling hydrate saturation, S hpfe =S h (1-f ms ) / [1-S h +S h (1-f ms )];S we is the normalized water saturation, S we =(1-S h ) / [1-S h +S h (1-f ms )];

[0024] J is the consolidation coefficient of the hydrate formation, reflecting the degree of consolidation of the hydrate formation. The smaller J is, the better the degree of consolidation of the formation. Furthermore, step S21 also includes the calculation of the longitudinal wave impedance of the rock matrix: solid minerals and skeleton-supported hydrates combine to form the rock matrix, which together play a stress support role. When the volume fractions and elastic moduli of various mineral components are known, the Hill average is used to calculate the rock matrix bulk modulus and shear modulus:

[0025]

[0026] Where K sd , K c , K h,ms and μ sd 、μ c 、μ h,ms are the bulk modulus and shear modulus of quartz, clay and skeleton-supported hydrate, respectively; f sd 、f c and f h,ms are the volume fractions of quartz, clay and skeleton-supported hydrates, respectively, where f sd =(1-φ)(1-V sh ) / (1-φ+f ms S h φ), f c =(1-φ)V sh / (1-φ+f ms S h φ), f h,ms =f ms S hφ / (1-φ+f ms S h φ), φ, V sh 、f ms and S h They are porosity, shale content, percentage of skeletal support morphology, and hydrate saturation;

[0027] Using the rock physics volume model, the rock matrix density can be expressed as:

[0028] ρ ma =f sd ρ sd +f c ρ c +f h,ms ρ h

[0029] Where, ρ sd , ρ c and ρ h are the densities of quartz, clay, and hydrate, respectively.

[0030] The expression of rock matrix longitudinal wave impedance is as follows:

[0031]

[0032] Furthermore, step S22 also includes the derivation of the generalized weight equation: the two-phase Wyllie time-averaged equation describing the relationship between porosity and velocity in the consolidated formation is expanded into a three-phase time-averaged equation, which is applied to the natural gas hydrate formation. The expression is:

[0033]

[0034] Where V P,T is the P-wave velocity of hydrate-bearing formations calculated using the Wyllie equation; V P,m 、V P,h and V P,w are the longitudinal wave velocities of rock matrix, hydrate and water, respectively;

[0035] Rewrite the three-phase time-averaged equation: Further simplified to: Where, ρ b is the bulk density of saturated rock, ρ m , ρ h and ρ w are the densities of rock matrix, hydrate and water respectively; further, the three-phase Wood equation applied to natural gas hydrate formation is expressed as:

[0036]

[0037] Where V P,W is the longitudinal wave velocity calculated by Wood’s formula;

[0038] The three-phase Wood equation is simplified as follows: By comparing the simplified three-phase time-averaged equation with the simplified three-phase Wood equation, the consolidation coefficient J is introduced, 1≤J≤2, and the generalized weight equation is derived. The generalized weight equation is:

[0039]

[0040] In a second aspect, a device for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes is provided, comprising:

[0041] Initial assignment unit: determines the initial hydrate saturation, hydrate occurrence mode, reservoir porosity, and reservoir mud content of the reservoir;

[0042] The occurrence mode of the hydrate is a dual occurrence mode, which takes into account two microscopic occurrence forms: pore filling and skeleton support;

[0043] Rock physics model construction unit: constructs a rock physics model of hydrate reservoirs with dual occurrence forms;

[0044] Objective function setting unit: construct an objective function with longitudinal wave impedance as a constraint, and the objective function is:

[0045]

[0046] Where: and is the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; ε is the given minimum error;

[0047] Reservoir hydrate saturation inversion unit: using a grid search method, performing hydrate saturation inversion based on the objective function, and estimating the reservoir hydrate saturation value.

[0048] Furthermore, the rock physics model construction unit constructs a rock physics model of a dual-occurrence hydrate reservoir, including: a rock matrix calculation unit: using Hill averaging to calculate the bulk modulus and shear modulus of the rock matrix composed of solid minerals and skeleton-supported hydrates, wherein the solid minerals include quartz, calcite, and clay;

[0049] Saturated rock calculation unit: The bulk modulus and shear modulus of saturated rock composed of rock matrix, water and pore-filling hydrate are calculated using a generalized weight equation based on dual occurrence morphology coupling.

[0050] Furthermore, the saturated rock calculation unit uses a generalized weight equation based on dual occurrence morphology coupling to calculate the bulk modulus and shear modulus of saturated rock composed of rock matrix, water, and pore-filling hydrate, where:

[0051] The generalized weight equation based on the dual occurrence morphology coupling is:

[0052]

[0053] Where: Z P,w , Z P,h , Z P,ma and Z P are the longitudinal wave impedances of water, hydrate, rock matrix and saturated rock, respectively; ρ w , ρ h , ρ ma and ρ b are the densities of water, hydrate, rock matrix and saturated rock, respectively,

[0054] ρ b =(1-φ)(1-V sh )ρ sd +(1-φ)V sh ρ c +φS h ρ h +φ(1-S h )ρ w ;

[0055] φ e is the effective porosity, φ e =φ-φS h f ms ; Among them: φ, f ms and S h are porosity, percentage of framework-supported morphology, and hydrate saturation, respectively;

[0056] S hpfe is the pore-filling hydrate saturation, S hpfe =S h (1-f ms ) / [1-S h +S h (1-f ms )];S we is the normalized water saturation, S we =(1-S h ) / [1-S h +S h (1-f ms )];

[0057] J is the consolidation coefficient of the hydrate formation, reflecting the degree of consolidation of the hydrate formation. The smaller J is, the better the degree of consolidation of the formation. Furthermore, the rock matrix calculation unit also includes a rock matrix longitudinal wave impedance calculation unit: solid minerals and skeleton-supported hydrates combine to form the rock matrix, which together play a stress support role. When the volume fraction and elastic modulus of various mineral components are known, the Hill average is used to calculate the rock matrix bulk modulus and shear modulus:

[0058]

[0059] Where K sd , K c , K h,ms and μ sd 、μ c 、μ h,ms are the bulk modulus and shear modulus of quartz, clay and skeleton-supported hydrate, respectively; f sd 、f c and f h,ms are the volume fractions of quartz, clay and skeleton-supported hydrates, respectively, where f sd =(1-φ)(1-V sh ) / (1-φ+f ms S h φ), f c =(1-φ)V sh / (1-φ+f ms S h φ), f h,ms =f ms S h φ / (1-φ+f ms S h φ), φ, V sh 、f ms and S h They are porosity, shale content, percentage of skeletal support morphology, and hydrate saturation;

[0060] Using the rock physics volume model, the rock matrix density can be expressed as:

[0061] ρ ma =f sd ρ sd +f c ρ c +f h,ms ρ h

[0062] Where, ρ sd , ρ c and ρ h are the densities of quartz, clay, and hydrate, respectively.

[0063] The expression of rock matrix longitudinal wave impedance is as follows:

[0064]

[0065] Furthermore, the saturated rock calculation unit also includes a derivation unit for the generalized weight equation: the two-phase Wyllie time-averaged equation describing the relationship between porosity and velocity in consolidated formations is expanded into a three-phase time-averaged equation and applied to natural gas hydrate formations. Its expression is:

[0066]

[0067] Where V P,T is the P-wave velocity of hydrate-bearing formations calculated using the Wyllie equation; V P,m 、V P,h and V P,w are the longitudinal wave velocities of rock matrix, hydrate and water, respectively;

[0068] Rewrite the three-phase time-averaged equation: Further simplified to: Where, ρ b is the bulk density of saturated rock, ρ m , ρ h and ρ w are the densities of rock matrix, hydrate and water respectively; further, the three-phase Wood equation applied to natural gas hydrate formation is expressed as:

[0069]

[0070] Where V P,W is the longitudinal wave velocity calculated by Wood’s formula;

[0071] The three-phase Wood equation is simplified as follows: By comparing the simplified three-phase time-averaged equation with the simplified three-phase Wood equation, the consolidation coefficient J is introduced, 1≤J≤2, and the generalized weight equation is derived. The generalized weight equation is:

[0072]

[0073] In a third aspect, an electronic device is provided, comprising: a memory for storing a computer program; and a processor for implementing the steps of a method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes when executing the computer program.

[0074] In a fourth aspect, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of a method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes are implemented.

[0075] By adopting the above technical solution, the quantitative prediction of the hydrate saturation of the natural gas hydrate-containing reservoir is achieved.

[0076] Compared with the prior art, the present invention has the following beneficial effects:

[0077] Based on the Wyllie time-averaged equation and the Wood equation, this paper derives a generalized weight equation. Based on this, the influence of pore-filling and skeleton-supported hydrates on the elastic response characteristics of the formation is considered, and a generalized weight equation for the coupled dual occurrence mode is further proposed. In combination with the grid search method, a hydrate saturation prediction method based on longitudinal wave impedance as a constraint is developed, and applied to the quantitative prediction of hydrate saturation in actual hydrate formations, effectively improving the accuracy of hydrate reservoir modeling and the quantitative characterization capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 A flowchart of a method for estimating hydrate saturation using a generalized weight equation based on dual occurrence mode coupling according to an embodiment of the present invention;

[0079] Figure 2 A flowchart illustrating the detailed implementation of a method for estimating hydrate saturation using a generalized weight equation based on dual occurrence mode coupling according to an embodiment of the present invention;

[0080] Figure 3 A flowchart of a method for constructing a rock physics model of a hydrate reservoir with dual occurrence forms according to an embodiment of the present invention;

[0081] Figure 4 A flowchart showing the detailed implementation of the method for constructing a rock physics model for a hydrate reservoir with dual occurrence forms according to an embodiment of the present invention;

[0082] Figure 5 This is a structural diagram of a device for estimating hydrate saturation using a generalized weight equation based on dual occurrence mode coupling according to an embodiment of the present invention;

[0083] Figure 6 A structural diagram of a rock physics model unit for a dual-occurrence hydrate reservoir according to an embodiment of the present invention;

[0084] Figure 7 This is a comparison diagram of the hydrate saturation calculated under pore filling, skeleton support and dual occurrence modes and the hydrate saturation calculated by resistivity according to an embodiment of the present invention;

[0085] Figure 8 This is a comparison diagram of the hydrate saturation predicted based on the Wyllie time-averaged equation, the Wood equation, and the generalized weight equation and the actual saturation provided in an embodiment of the present invention.

[0086] Figure 9 The figure is a structural diagram of an electronic device provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0087] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0088] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0089] Figure 1 This is a flowchart illustrating a method for estimating hydrate saturation using a generalized weighted equation based on dual occurrence mode coupling according to an embodiment of the present invention. For ease of description, only the portion relevant to the embodiment of the present invention is shown, which is described in detail below:

[0090] A method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence models includes:

[0091] Step S1: determining the initial hydrate saturation, hydrate occurrence pattern, reservoir porosity, and reservoir mud content of the reservoir;

[0092] The occurrence mode of the hydrate is a dual occurrence mode, which takes into account two microscopic occurrence forms: pore filling and skeleton support;

[0093] Step S2: constructing a rock physics model of a dual-occurrence hydrate reservoir;

[0094] Step S3: Construct an objective function with the longitudinal wave impedance as a constraint. The objective function is:

[0095]

[0096] Where: and is the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; ε is the given minimum error;

[0097] Step S4: using a grid search method to perform hydrate saturation inversion based on the objective function to estimate the reservoir hydrate saturation value.

[0098] Figure 2 This is a flowchart illustrating the detailed implementation of a method for estimating hydrate saturation using a generalized weighted equation based on dual occurrence mode coupling according to an embodiment of the present invention. For ease of description, only the portion relevant to the embodiment of the present invention is shown, which is described in detail below:

[0099] Determine the initial hydrate saturation, hydrate occurrence pattern, reservoir porosity, and reservoir mud content of the reservoir;

[0100] Conduct reservoir rock physics modeling; the rock physics model is a dual-occurrence hydrate reservoir rock physics model;

[0101] Based on the constructed dual-occurrence morphology hydrate reservoir rock physics model, the grid search method is used to perform hydrate saturation inversion based on the objective function to estimate the reservoir hydrate saturation value. Specifically:

[0102] Based on the constructed dual-occurrence morphology hydrate reservoir rock physics model, the predicted value of P-wave impedance is calculated, and the error value is calculated between it and the measured value of P-wave impedance. The error value calculation satisfies the cutoff condition. If the current error value is less than the cutoff given error value, the natural gas hydrate saturation is output; if the current error value is greater than the cutoff given error value, the hydrate saturation is updated and the iterative inversion is performed again until the cutoff condition is met.

[0103] Furthermore, the rock physics model of the coupled dual occurrence mode and the grid search method constructed above are used to obtain the hydrate saturation corresponding to the minimum of the objective function constructed by the inversion of the single occurrence form and the dual occurrence form, and the hydrate saturation accuracy predicted by the generalized weight equation, Wyllie time-averaged equation and Wood equation coupled with the dual occurrence mode is compared. The model constructed by the present invention considers hydrates of two microscopic occurrence forms, pore filling and skeleton support. When the single pore filling or skeleton support form is inverted, f msare 0 and 1 respectively; when the Wyllie time-averaged equation and the Wood equation are inverted, J is 1 and 2 respectively. The objective function (J) is defined as the error between the measured data and the forward simulation response of the rock physics model, that is:

[0104]

[0105] Where: and are the actual value and predicted value of longitudinal wave impedance; ε is the given minimum error.

[0106] Figure 3 This is a flowchart of a method for constructing a rock physics model for a dual-occurrence hydrate reservoir according to an embodiment of the present invention. For ease of description, only the portion relevant to the embodiment of the present invention is shown, which is described in detail as follows:

[0107] The construction of dual-occurrence hydrate reservoir rock physics model includes:

[0108] Step S21: Calculating the bulk modulus and shear modulus of the rock matrix composed of solid minerals and skeleton-supported hydrates using Hill average, wherein the solid minerals include quartz, calcite, and clay;

[0109] Step S22: Calculate the bulk modulus and shear modulus of saturated rock composed of rock matrix, water, and pore-filling hydrate using a generalized weight equation based on dual occurrence morphology coupling.

[0110] Figure 4 This is a flowchart of the detailed implementation of the method for constructing a dual-occurrence morphology hydrate reservoir rock physics model according to an embodiment of the present invention. For ease of description, only the parts relevant to the embodiment of the present invention are shown, which are detailed as follows:

[0111] Determine the rock matrix composition, including solid minerals and skeleton-supported hydrates, where solid minerals include quartz, calcite, and clay.

[0112] The bulk modulus and shear modulus of the rock matrix composed of solid minerals and skeleton-supported hydrates are calculated using Hill averaging as follows:

[0113] Assuming that solid minerals and skeleton-supported hydrates combine to form the rock matrix, they together play a stress-supporting role. When the volume fractions and elastic moduli of various mineral components are known, the rock matrix bulk modulus and shear modulus can be calculated using Hill averaging (Hill, 1952):

[0114]

[0115] Where K sd , K c, K h,ms and μ sd 、μ c 、μ h,ms are the bulk modulus and shear modulus of quartz, clay and skeleton-supported hydrate, respectively; f sd 、f c and f h,ms are the volume fractions of quartz, clay and skeleton-supported hydrates, respectively, where f sd =(1-φ)(1-V sh ) / (1-φ+f ms S h φ), f c =(1-φ)V sh / (1-φ+f ms S h φ), f h,ms =f ms S h φ / (1-φ+f ms S h φ), φ, V sh 、f ms and S h are porosity, mud content, percentage of skeleton-supported morphology, and hydrate saturation. It is worth noting that when there is no skeleton-supported hydrate f ms When =0, the results calculated by formulas (1) and (2) are the solid mineral matrix modulus.

[0116] Calculation of rock matrix longitudinal wave impedance:

[0117] Using the rock physics volume model, the rock matrix density can be expressed as:

[0118] ρ ma =f sd ρ sd +f c ρ c +f h,ms ρ h

[0119] Where, ρ sd , ρ c and ρ h are the densities of quartz, clay, and hydrate, respectively.

[0120] The expression of rock matrix longitudinal wave impedance is as follows:

[0121]

[0122] The bulk modulus and shear modulus of saturated rock composed of rock matrix, water and pore-filling hydrate are calculated using a generalized weight equation based on dual occurrence morphology coupling.

[0123] Calculation of longitudinal wave impedance of saturated rock:

[0124] 1) Combining the Wyllie time-averaged equation and the Wood equation to derive the generalized weight equation

[0125] Timur expanded the two-phase Wyllie time-averaged equation, which describes the relationship between porosity and velocity in consolidated formations, into a three-phase time-averaged equation, and used it to describe the elastic response characteristics of frozen formations. Considering the similarities between the elastic properties of hydrates and ice, Pearson et al. applied the three-phase time-averaged equation to hydrate-bearing formations, and the expression is:

[0126]

[0127] Where V P,T is the P-wave velocity of hydrate-bearing formations calculated using the Wyllie equation; V P,m 、V P,h and V P,w are the longitudinal wave velocities of rock matrix, hydrate and water respectively; when S h =0, the above equation becomes the Wyllie time-averaged equation.

[0128] Rewrite the time-averaged equation as:

[0129]

[0130] The formula can be simplified to:

[0131]

[0132] Where, ρ b is the volume density of the formation, which can be expressed as ρ b =(1-φ)ρ m +φS h ρ h +φ(1-S h )ρ w ρ m , ρ h and ρ w are the densities of rock matrix, hydrate and water, respectively.

[0133] When the sediment contains a high mud content and poor cementation, the results calculated by the time-averaged equation are inconsistent with the actual measurement results. Therefore, Lee et al. proposed a three-phase Wood equation applicable to gas hydrate layers based on the two-phase Wood equation. Its expression is:

[0134]

[0135] Where V P,Wis the P-wave velocity calculated by Wood equation.

[0136] Similarly, the Wood equation is rewritten as:

[0137]

[0138] Comparing the time-averaged equation and the rewritten form of the Wood equation, we introduce the consolidation coefficient J (1≤J≤2), and further derive the generalized weight equation, which is:

[0139]

[0140] When J tends to 1, the time-averaged equation has a larger weight, which is suitable for low porosity and well-cemented hydrate-bearing formation. When J = 1, the formula is the three-phase time-averaged equation. When J tends to 2, the Wood equation has a larger weight, which is suitable for high porosity and unconsolidated hydrate-bearing formation. When J = 2, the formula is the three-phase Wood equation.

[0141] 2) Introducing pore filling and skeleton supporting hydrates, we further propose a generalized weight equation coupled with double occurrence forms, which is as follows:

[0142]

[0143] In the formula, Z P,w , Z P,h , Z P,ma , and Z P are the P-wave impedances of water, hydrate, rock matrix, and saturated rock, respectively; ρ w and ρ b are the densities of water and saturated rock, respectively; φ e is the effective porosity, φ e = φ-φS h f ms ; S hpfe is the saturation of pore filling hydrate, S hpfe = S h (1-f ms ) / [1-S h +S h (1-f ms )]; S we is the normalized water saturation, S we =(1-S h ) / [1-S h +S h (1-f ms )]; J is the consolidation coefficient of hydrate formation, reflecting the consolidation degree of hydrate formation. The smaller J is, the better the consolidation degree of the formation is; ρ b is the bulk density of saturated rock, ρb =(1-φ)(1-V sh )ρ sd +(1-φ)V sh ρ c +φS h ρ h +φ(1-S h )ρ w .

[0144] Figure 5 This is a diagram of the structure of an apparatus for estimating hydrate saturation using a generalized weighted equation based on dual occurrence mode coupling according to an embodiment of the present invention. For ease of description, only the portion relevant to the embodiment of the present invention is shown, which is described in detail below:

[0145] A device for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes, comprising:

[0146] Initial assignment unit: determines the initial hydrate saturation, hydrate occurrence mode, reservoir porosity, and reservoir mud content of the reservoir;

[0147] The occurrence mode of the hydrate is a dual occurrence mode, which takes into account two microscopic occurrence forms: pore filling and skeleton support;

[0148] Rock physics model construction unit: constructs a rock physics model of hydrate reservoirs with dual occurrence forms;

[0149] Objective function setting unit: construct an objective function with longitudinal wave impedance as a constraint, and the objective function is:

[0150]

[0151] Where: and is the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; ε is the given minimum error;

[0152] Reservoir hydrate saturation inversion unit: using a grid search method, performing hydrate saturation inversion based on the objective function, and estimating the reservoir hydrate saturation value.

[0153] Figure 6 This is a diagram of the unit structure of a rock physics model for a dual-occurrence hydrate reservoir according to an embodiment of the present invention. For ease of description, only the parts relevant to the embodiment of the present invention are shown, which are detailed as follows:

[0154] The rock physics model construction unit builds a dual-occurrence hydrate reservoir rock physics model including:

[0155] Rock matrix calculation unit: uses Hill averaging to calculate the bulk modulus and shear modulus of the rock matrix composed of solid minerals and skeleton-supported hydrates. The solid minerals include quartz, calcite, and clay.

[0156] Saturated rock calculation unit: The bulk modulus and shear modulus of saturated rock composed of rock matrix, water and pore-filling hydrate are calculated using a generalized weight equation based on dual occurrence morphology coupling.

[0157] Figure 7 This figure compares the hydrate saturation calculated under pore-filling, skeleton-supported, and dual-occurrence conditions with the hydrate saturation calculated by resistivity according to an embodiment of the present invention. For ease of description, only the portion relevant to the embodiment of the present invention is shown, which is detailed below:

[0158] Figure 7 Comparison of predicted and actual hydrate saturations for Well GC955H under different occurrence patterns. (a) Actual P-wave impedance (black solid line), predicted P-wave impedance under dual occurrence pattern (gray solid line), and P-wave impedance for hydrate-free formations (gray dashed line). (b) The black solid line represents the actual hydrate saturation, while the gray solid line represents the hydrate saturation at a 38% skeleton support percentage. The black dashed line represents the pore-filling hydrate saturation, while the gray dashed line represents the skeleton-supported hydrate saturation.

[0159] The sandstone hydrate reservoir at depths of 415 to 439 mbsf in the GC955H well in the Gulf of Mexico, USA, was selected as the target layer for hydrate saturation analysis. Based on the aforementioned modeling process, the hydrate saturation of the GC955H well was inverted using a grid search method with P-wave impedance as the constraint, given a skeletal support morphology percentage (fms) of 38% and an empirical coefficient (J) of 1.49.

[0160] Figure 7 The hydrate saturations calculated for pore-filling, skeleton-supported, and dual-occurrence morphologies were compared with those calculated using resistivity. As shown in the figure, the hydrate saturations predicted based on the single pore-filling and skeleton-supported morphologies are similar, and the predictions can be considered as considering the uncertainty of the pore-filling and skeleton-supported morphology models. The estimated hydrate saturation for the pore-filling model is slightly higher than the reference value; the hydrate saturation for the skeleton-supported model is slightly lower than the reference value; and the hydrate saturation predicted for the dual-occurrence morphology falls between the hydrate saturations predicted for the two single-occurrence morphologies. Overall, the saturation trends are consistent and agree well with the actual saturations. Skeleton-supported hydrates account for approximately 38% of the total hydrate content, reflecting that the study interval is primarily composed of pore-filling hydrate layers.

[0161] Figure 8This figure compares the predicted hydrate saturation using the Wyllie time-averaged equation, the Wood equation, and the generalized weighted equation with the actual hydrate saturation according to an embodiment of the present invention. For ease of description, only the portion relevant to the embodiment of the present invention is shown, which is detailed below:

[0162] Figure 8 Comparison of predicted and actual hydrate saturation results for Well GC955H under different models. The black solid line represents the actual hydrate saturation; the gray solid line represents the hydrate saturation predicted by the generalized weighted equation; the black dashed line represents the hydrate saturation predicted by the Wyllie time-averaged equation; and the gray dashed line represents the hydrate saturation predicted by the Wood equation.

[0163] Figure 8 This paper compares the hydrate saturations predicted by the Wyllie time-averaged equation, the Wood equation, and the generalized weighted equation with the actual saturations. The results show that the saturations calculated using the time-averaged equation and the Wood equation differ significantly from the actual saturations. The time-averaged equation predicts an overly high P-wave impedance and undervalues ​​the hydrate saturation, while the Wood equation predicts a lower P-wave impedance and overvalues ​​the hydrate saturation. This is primarily due to the fact that the time-averaged equation is suitable for describing the velocity of well-consolidated formations, while the Wood equation primarily describes the velocity of unconsolidated formations. Compared to traditional empirical formulas, the saturation estimated by the generalized weighted equation, which considers dual-occurrence mode coupling, agrees better with the actual saturation.

[0164] The present invention designs a dual-occurrence-morphology coupled rock physics modeling of hydrate reservoirs and a method for inverting hydrate saturation based on a generalized weight equation. This method can not only improve the prediction accuracy of hydrate saturation, but also lay a theoretical foundation for describing seismic elastic response characteristics and estimating hydrate saturation. This method overcomes the limitations of traditional rock physics models based on the assumption that hydrates have a single occurrence morphology, and the presence of different rock physics free parameters (such as critical porosity, aspect ratio, cementation index, etc.) in the inversion process. The present invention provides a practical method for elastic response characteristic analysis and quantitative interpretation of hydrate reservoirs. The rock physics modeling strategy of the present invention can also be used to invert the microscopic occurrence morphology of hydrates, and can also solve the problem of coexistence of hydrates and free gas by introducing free gas. The present invention estimates hydrate saturation using acoustic data as a constraint, and in the future it can be combined with electrical characteristics to further improve the prediction accuracy of hydrate saturation.

[0165] Figure 9 A structural diagram of an electronic device provided by an embodiment of the present invention, such as Figure 9As shown, the device includes: a memory 21 for storing a computer program; and a processor 22 for implementing the steps of the method for estimating hydrate saturation based on a generalized weight equation for dual-occurrence mode coupling when executing the computer program. The processor 22 may include one or more processing cores, such as a quad-core processor or an octal-core processor. The processor 22 may be implemented in at least one hardware form: a digital signal processor (DSP), a field-programmable gate array (FPGA), or a programmable logic array (PLA). The processor 22 may also include a main processor and a coprocessor. The main processor is a processor for processing data in the awake state, also known as a central processing unit (CPU); the coprocessor is a low-power processor for processing data in the standby state. In some embodiments, the processor 22 may be integrated with a graphics processing unit (GPU), which is responsible for rendering and drawing content required to be displayed on the display screen. In some embodiments, the processor 22 may also include an artificial intelligence (AI) processor for processing computational operations related to machine learning.

[0166] The memory 21 may include one or more computer-readable storage media, which may be non-transitory. The memory 21 may also include high-speed random access memory, and non-volatile memory, such as one or more disk storage devices, flash memory storage devices. In this embodiment, the memory 21 is used to store at least the following computer program 211, wherein, after the computer program is loaded and executed by the processor 22, it can implement the relevant steps of the method for estimating hydrate saturation based on the generalized weight equation of dual occurrence mode coupling disclosed in any of the aforementioned embodiments. In addition, the resources stored in the memory 21 may also include an operating system 212 and data 213, etc., and the storage method may be temporary storage or permanent storage. Among them, the operating system 212 may include Windows, Unix, Linux, etc. The data 213 may include but is not limited to data involved in the method for estimating hydrate saturation based on the generalized weight equation of dual occurrence mode coupling, etc.

[0167] In some embodiments, the electronic device may further include a display screen 23 , an input / output interface 24 , a communication interface 25 , a power supply 26 , and a communication bus 27 .

[0168] Those skilled in the art will understand that Figure 9 The structure shown in the figure does not constitute a limitation of the electronic device, and may include more or fewer components than shown in the figure.

[0169] The processor 22 calls the instructions stored in the memory 21 to implement the steps of the method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes provided in any of the above embodiments.

[0170] For an introduction to an electronic device provided by the present invention, please refer to the above method embodiment, and the present invention will not be repeated here. It has the same beneficial effects as the steps of the above method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes.

[0171] Furthermore, the present invention also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by the processor 22, the steps of the method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes as described above are implemented.

[0172] It is understandable that if the method in the above embodiment is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium and executes all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0173] For an introduction to a computer-readable storage medium provided by the present invention, please refer to the above method embodiment, which will not be described in detail herein. It has the same beneficial effects as the steps of the above method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes.

[0174] The above is a detailed introduction to the method, device, equipment and medium for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes provided by the present invention. The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the present invention.

[0175] It should also be noted that, in this specification, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

Claims

1. A method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes, characterized by: Step S1: determining the initial hydrate saturation, hydrate occurrence mode, reservoir porosity, and reservoir mud content of the reservoir; the hydrate occurrence mode is a dual occurrence mode, which considers two microscopic occurrence forms: pore filling and skeleton support; Step S2: constructing a dual-occurrence-mode hydrate reservoir rock physics model; Step S3: Construct an objective function with the longitudinal wave impedance as a constraint. The objective function is: Where: and are the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance respectively; ε is the given minimum error; Step S4: using a grid search method to perform hydrate saturation inversion based on the objective function to estimate the reservoir hydrate saturation value; The step S2 of constructing the dual occurrence mode hydrate reservoir rock physics model includes: Step S21: Calculating the bulk modulus and shear modulus of the rock matrix composed of solid minerals and skeleton-supported hydrates using Hill average, wherein the solid minerals include quartz, calcite, and clay; Step S22: Calculating the bulk modulus and shear modulus of saturated rock composed of rock matrix, water, and pore-filling hydrate using a generalized weight equation based on dual occurrence mode coupling; In step S22, the bulk modulus and shear modulus of saturated rock composed of rock matrix, water and pore-filling hydrate are calculated using a generalized weight equation based on dual occurrence mode coupling, wherein: The generalized weight equation based on the dual-existence mode coupling is: Where: Z P,w , Z P,h , Z P,ma and Z P are the longitudinal wave impedances of water, hydrate, rock matrix and saturated rock, respectively; ρ w , ρ h , ρ ma and ρ b are the densities of water, hydrate, rock matrix and saturated rock, respectively, r b =(1-φ)(1-V) sh )r sd +(1-φ)V sh r c +φS h r h +φ(1-S h )r w ; φ e is the effective porosity, φ e =φ-φS h f ms ; Among them: φ, f ms and S h are porosity, percentage of skeleton support morphology and hydrate saturation respectively; V sh is the mud content; ρ sd , ρ c are the densities of quartz and clay, respectively; S hpfe is the pore-filling hydrate saturation, S hpfe =S h (1-f ms ) / [1-S h +S h (1-f ms )];S we is the normalized water saturation, S we =(1-S h ) / [1-S h +S h (1-f ms )]; J is the consolidation coefficient of the hydrate formation, which reflects the consolidation degree of the hydrate formation. The smaller J is, the better the consolidation degree of the formation.

2. A device for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes, characterized by: Initial assignment unit: determines the initial hydrate saturation, hydrate occurrence mode, reservoir porosity, and reservoir mud content of the reservoir; The occurrence mode of the hydrate is a dual occurrence mode, which takes into account two microscopic occurrence forms: pore filling and skeleton support; Rock physics model construction unit: constructs a rock physics model of hydrate reservoir with dual occurrence mode; Objective function setting unit: construct an objective function with longitudinal wave impedance as a constraint, and the objective function is: Where: and are the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance respectively; ε is the given minimum error; Reservoir hydrate saturation inversion unit: using a grid search method to perform hydrate saturation inversion based on the objective function to estimate the reservoir hydrate saturation value; The rock physics model construction unit constructs a dual occurrence mode hydrate reservoir rock physics model including: Rock matrix calculation unit: uses Hill averaging to calculate the bulk modulus and shear modulus of the rock matrix composed of solid minerals and skeleton-supported hydrates. The solid minerals include quartz, calcite, and clay. Saturated rock calculation unit: uses a generalized weight equation based on dual occurrence mode coupling to calculate the bulk modulus and shear modulus of saturated rock composed of rock matrix, water and pore-filling hydrate; The saturated rock calculation unit uses a generalized weight equation based on dual occurrence mode coupling to calculate the bulk modulus and shear modulus of saturated rock composed of rock matrix, water and pore-filling hydrate, where: The generalized weight equation based on the dual-existence mode coupling is: Where: Z P,w , Z P,h , Z P,ma and Z P are the longitudinal wave impedances of water, hydrate, rock matrix and saturated rock, respectively; ρ w , ρ h , ρ ma and ρ b are the densities of water, hydrate, rock matrix and saturated rock, respectively, r b =(1-φ)(1-V) sh )r sd +(1-φ)V sh r c +φS h r h +φ(1-S h )r w ; φ e is the effective porosity, φ e =φ-φS h f ms ; Among them: φ, f ms and S h are porosity, percentage of skeleton support morphology and hydrate saturation respectively; V sh is the mud content; ρ sd , ρ c are the densities of quartz and clay, respectively; S hpfe is the pore-filling hydrate saturation, S hpfe =S h (1-f ms ) / [1-S h +S h (1-f ms )];S we is the normalized water saturation, S we =(1-S h ) / [1-S h +S h (1-f ms )]; J is the consolidation coefficient of the hydrate formation, which reflects the consolidation degree of the hydrate formation. The smaller J is, the better the consolidation degree of the formation.

3. An electronic device, characterized in that: include: memory for storing computer programs; A processor is configured to implement the steps of the method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes as claimed in claim 1 when executing the computer program.

4. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes as claimed in claim 1.

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