Method and device for estimating hydrate saturation based on generalized weight equation coupled by dual occurrence modes

Abstract

The invention discloses a method for estimating hydrate saturation based on a generalized weight equation coupled by dual occurrence modes. The method comprises the following steps: determining initial hydrate saturation of a reservoir, occurrence modes of hydrates, porosity of the reservoir and shale content of the reservoir; a generalized weight equation (GWE) is deduced on the basis of a Wyllie time average equation and a Wood equation, the influence of pore filling type and skeleton supporting type hydrates on stratum elastic response characteristics is considered on the basis, a generalized weight equation coupled with a dual-occurrence mode is further proposed, and a dual-occurrence-form hydrate reservoir rock physical model is constructed; a target function is constructed by taking longitudinal wave impedance as a constraint, hydrate saturation inversion is performed based on the target function by using a grid search method, a reservoir hydrate saturation value is estimated, the method is applied to hydrate saturation quantitative prediction of an actual hydrate stratum, and hydrate reservoir modeling precision and quantitative description capability are effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of geophysical exploration technology, and in particular to a method, a device and an electronic device 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 and low temperature conditions. They are widely distributed in sediments of terrestrial permafrost zones and deepwater basins at the continental margin (Kvenvolden, 1993) and are the most promising alternative energy resources in the future (Boswell and Collett, 2011). On the other hand, hydrates are very easy to decompose when the temperature and pressure conditions of the formation change, which in turn induces submarine geological disasters (Archer et al., 2009) and aggravates global warming (Sultan et al., 2004). Accurate prediction of hydrate content and distribution is not only the basis for quantitative evaluation of hydrate resource potential and response to climate and environmental hazards, but also an important prerequisite for understanding the hydrate accumulation mechanism and guiding the successful exploitation of hydrates. Hydrate saturation can be estimated using the 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), but the elastic coupling effect between hydrate saturation and occurrence morphology directly affects the accuracy of hydrate reservoir characterization. Therefore, a deep understanding of the impact of hydrates on the acoustic properties of formations is the key to quantitative characterization of hydrate reservoirs.

[0003] The rock physics model establishes a quantitative relationship between hydrate saturation and 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 fill the pore space) and skeleton support (hydrates support skeleton particles) are the two most common types of hydrate occurrence, many rock physics models for these two types of hydrate reservoirs have been proposed by predecessors. Early simple and practical empirical models, such as the Wyllie time-averaged equation, the Wood equation, and the three-phase weighted equation, are often 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 the microscopic distribution pattern, and a large amount of measured data is needed to calibrate the model parameters (Liu Xinxin 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 improved Biot-Gassmann theory (Lee et al., 2004) and the simplified three-phase equation (Lee et al., 2008), have also been successfully applied to convert velocity information into hydrate saturation (Terry and Knapp et al., 2018; Pan et al., 2022). However, these models involve many model parameters and are mostly established based on the assumption of a single occurrence form, making it difficult to accurately describe hydrate formations with coexistence of multiple occurrence forms. Therefore, it is necessary to establish a simple and practical rock physics theory that couples multiple occurrence forms of hydrates. 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 solution:

[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 of the reservoir, the occurrence mode of hydrate, the reservoir porosity, and the reservoir mud content;

[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 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: using Hill average 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;

[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 form coupling, wherein:

[0018] The generalized weight equation based on the coupling of dual occurrence forms 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 , h , 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, which reflects the consolidation degree of the hydrate formation. The smaller J is, the better the consolidation degree of the formation is. Further, step S21 also includes the calculation of the longitudinal wave impedance of the rock matrix: solid minerals and skeleton-supported hydrates are combined 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 rock matrix bulk modulus and shear modulus are calculated using the Hill average:

[0025]

[0026] In the formula, 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 hydrates, respectively; f sd 、f c and f h,ms are the volume fractions of quartz, clay and framework-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] In the formula, ρ sd , c and ρ h are the densities of quartz, clay and hydrate, respectively.

[0030] The rock matrix longitudinal wave impedance expression 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, and its 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 P-wave velocities of rock matrix, hydrate and water, respectively;

[0035] The three-phase time average equation is rewritten as: Further simplified to: In the formula, ρ b is the bulk density of saturated rock, ρ m , 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: determine 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 building unit: building a rock physics model of hydrate reservoir 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, hydrate saturation inversion is performed based on the objective function to estimate the reservoir hydrate saturation value.

[0048] Furthermore, the rock physics model construction unit constructs a dual-occurrence hydrate reservoir rock physics model including: a rock matrix calculation unit: using Hill average to calculate the rock matrix bulk modulus and shear modulus 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 form coupling.

[0050] Furthermore, the saturated rock calculation unit uses a generalized weight equation based on dual occurrence form 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 coupling of dual occurrence forms 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 , h , 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, which reflects the consolidation degree of the hydrate formation. The smaller J is, the better the consolidation degree of the formation is. Furthermore, the rock matrix calculation unit also includes a rock matrix longitudinal wave impedance calculation unit: solid minerals and skeleton-supported hydrates are combined to form a rock matrix, which together play a stress support role. When the volume fractions and elastic moduli of various mineral components are known, the rock matrix bulk modulus and shear modulus are calculated using Hill average:

[0058]

[0059] In the formula, 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 hydrates, respectively; f sd 、f c and f h,ms are the volume fractions of quartz, clay and framework-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] In the formula, ρ sd , c and ρ h are the densities of quartz, clay and hydrate, respectively.

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

[0064]

[0065] Furthermore, the saturated rock calculation unit also includes a derivation unit 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 and applied to the natural gas hydrate formation, and 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 P-wave velocities of rock matrix, hydrate and water, respectively;

[0068] The three-phase time average equation is rewritten as: Further simplified to: In the formula, ρ b is the bulk density of saturated rock, ρ m , 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, and 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 reservoir is achieved.

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

[0077] The present invention derives a generalized weight equation based on the Wyllie time-averaged equation and the Wood equation. On this basis, 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 coupled dual occurrence modes is further proposed. The method is further combined with the grid search method to develop a hydrate saturation prediction method constrained by longitudinal wave impedance, and is applied to the quantitative prediction of hydrate saturation in actual hydrate formations, effectively improving the modeling accuracy and quantitative characterization capability of hydrate reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0079] Figure 2 A flowchart showing the specific details of the method for estimating hydrate saturation based on the generalized weight equation for dual occurrence mode coupling provided in accordance with 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 specific details of the method for constructing a rock physics model of a hydrate reservoir with dual occurrence forms according to an embodiment of the present invention;

[0082] Figure 5 A structural diagram of a device for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes according to an embodiment of the present invention;

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

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

[0085] Figure 8 This is a comparison effect 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. Fig. 9 The present invention is a structural diagram of an electronic device provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0086] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme 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 described embodiments 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 creative work should fall within the scope of protection of the present invention.

[0087] It should be noted that the terms "first", "second", etc. in the specification 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 data 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 that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0088] Figure 1 The flowchart of the method for estimating hydrate saturation based on the generalized weight equation of dual occurrence mode coupling provided in accordance with an embodiment of the present invention is shown for the convenience of description, and the details are as follows:

[0089] A method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes includes:

[0090] Step S1: determining the initial hydrate saturation of the reservoir, the occurrence mode of hydrate, the reservoir porosity, and the reservoir mud content;

[0091] The occurrence mode of the hydrate is a dual occurrence mode, which takes into account two microscopic occurrence forms: pore filling and skeleton support;

[0092] Step S2: constructing a rock physics model of a dual-occurrence hydrate reservoir;

[0093] Step S3: construct an objective function with longitudinal wave impedance as a constraint, the objective function is:

[0094]

[0095] Where: and is the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; ε is the given minimum error;

[0096] Step S4: using a grid search method to perform hydrate saturation inversion based on the objective function to estimate the reservoir hydrate saturation value.

[0097] Figure 2 The following is a flowchart of the detailed implementation of the method for estimating hydrate saturation based on the generalized weight equation for dual occurrence mode coupling according to an embodiment of the present invention. For ease of description, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0098] Determine the initial hydrate saturation of the reservoir, the occurrence pattern of hydrates, the reservoir porosity, and the reservoir mud content;

[0099] Conduct reservoir rock physics modeling; the rock physics model is a dual-occurrence hydrate reservoir rock physics model;

[0100] Based on the constructed dual-occurrence hydrate reservoir rock physics model, the hydrate saturation inversion is performed based on the objective function using the grid search method to estimate the reservoir hydrate saturation value. Specifically:

[0101] The predicted value of P-wave impedance is calculated based on the constructed rock physics model of the dual-occurrence hydrate reservoir, and the error value is calculated between it and the measured value of P-wave impedance. The error value calculation meets 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 iterative inversion is performed again until the cutoff condition is met.

[0102] 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 in 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:

[0103]

[0104] Where: and are the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; ε is the given minimum error.

[0105] Figure 3 This is a flow chart of a method for constructing a dual-occurrence hydrate reservoir rock physics model according to an embodiment of the present invention. For ease of description, only the parts related to the embodiment of the present invention are shown, which are described in detail as follows:

[0106] The construction of dual-occurrence hydrate reservoir rock physics model includes:

[0107] Step S21: using Hill average 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;

[0108] 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.

[0109] Figure 4 The following is a flowchart of the detailed implementation of the method for constructing a dual-occurrence hydrate reservoir rock physical model according to an embodiment of the present invention. For ease of description, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0110] Determine the rock matrix composition, including solid minerals and skeleton-supported hydrates, where solid minerals include quartz, calcite, and clay.

[0111] The bulk modulus and shear modulus of the rock matrix composed of solid minerals and skeleton-supported hydrates are calculated using Hill average as follows:

[0112] It is assumed that solid minerals and skeleton-supported hydrates combine to form a rock matrix, which together play a stress support 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 the Hill average (Hill, 1952):

[0113]

[0114] In the formula, 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 hydrates, respectively; f sd 、f c and f h,ms are the volume fractions of quartz, clay and framework-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, shale 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 calculation results of formulas (1) and (2) are the solid mineral matrix modulus.

[0115] Calculation of rock matrix longitudinal wave impedance:

[0116] Using the rock physics volume model, the rock matrix density can be expressed as:

[0117] ρ ma =f sd ρ sd +f c ρ c +f h,ms ρ h

[0118] In the formula, ρ sd , c and ρ h are the densities of quartz, clay and hydrate, respectively.

[0119] The rock matrix longitudinal wave impedance expression is as follows:

[0120]

[0121] 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 form coupling.

[0122] Calculation of longitudinal wave impedance of saturated rock:

[0123] 1) Combining Wyllie time-averaged equation and Wood equation to derive generalized weight equation

[0124] Timur expanded the two-phase Wyllie time-averaged equation describing 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 similarity between the elastic properties of hydrates and ice, Pearson et al. applied the three-phase time-averaged equation to hydrate-containing formations, and its expression is:

[0125]

[0126] 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 When =0, the above equation becomes the Wyllie time-averaged equation.

[0127] Rewriting the time-averaged equation:

[0128]

[0129] The formula can be simplified to:

[0130]

[0131] In the formula, 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 , h and ρ w are the densities of rock matrix, hydrate and water, respectively.

[0132] When there is a high mud content in the sediment and the cementation degree is poor, the calculation results of the time-averaged equation are inconsistent with the actual measurement results. Therefore, Lee et al. proposed a three-phase Wood equation applicable to the gas hydrate layer based on the two-phase Wood equation, and its expression is:

[0133]

[0134] Where V P,Wis the longitudinal wave velocity calculated by Wood's formula.

[0135] Similarly, Wood's equation is rewritten as:

[0136]

[0137] Comparing the rewritten forms of the time-averaged equation and the Wood equation, we introduced the consolidation coefficient J (1≤J≤2) and further derived the generalized weight equation, which is:

[0138]

[0139] When J approaches 1, the weight of the time-averaged equation is relatively large, and it is applicable to low-porosity, well-cemented hydrate-bearing formations. When J = 1, the formula is a three-phase time-averaged equation. When J approaches 2, the weight of the Wood equation is relatively large, and it is applicable to high-porosity, unconsolidated hydrate-bearing formations. When J = 2, the formula is a three-phase Wood equation.

[0140] 2) Pore-filling and skeleton-supported hydrates are introduced, and a generalized weight equation for the coupling of dual occurrence forms is further proposed, as follows:

[0141]

[0142] In the formula, 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 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 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, reflecting the consolidation degree of the 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 .

[0143] Figure 5 This is a structural diagram of a device for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes according to an embodiment of the present invention. For ease of description, only the parts related to the embodiment of the present invention are shown, which are described in detail as follows:

[0144] A device for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes, comprising:

[0145] Initial assignment unit: determine the initial hydrate saturation, hydrate occurrence mode, reservoir porosity, and reservoir mud content of the reservoir;

[0146] The occurrence mode of the hydrate is a dual occurrence mode, which takes into account two microscopic occurrence forms: pore filling and skeleton support;

[0147] Rock physics model building unit: building a rock physics model of hydrate reservoir with dual occurrence forms;

[0148] Objective function setting unit: construct an objective function with longitudinal wave impedance as a constraint, and the objective function is:

[0149]

[0150] Where: and is the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; ε is the given minimum error;

[0151] Reservoir hydrate saturation inversion unit: using a grid search method, hydrate saturation inversion is performed based on the objective function to estimate the reservoir hydrate saturation value.

[0152] Figure 6 This is a structural diagram of a rock physics model unit for constructing a dual-occurrence hydrate reservoir according to an embodiment of the present invention. For ease of description, only the parts related to the embodiment of the present invention are shown, which are described in detail as follows:

[0153] The rock physics model building unit builds a dual-occurrence hydrate reservoir rock physics model including:

[0154] Rock matrix calculation unit: uses Hill average 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, clay;

[0155] 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 form coupling.

[0156] Figure 7 This is a comparison effect diagram of the hydrate saturation calculated under pore filling, skeleton support and dual occurrence forms and the hydrate saturation calculated by resistivity according to an embodiment of the present invention. For ease of description, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0157] Figure 7 Comparison of predicted and actual values ​​of hydrate saturation under different occurrence forms in Well GC955H. (a) Actual value of P-wave impedance (black solid line), predicted value of P-wave impedance under dual occurrence form (grey solid line), and P-wave impedance of hydrate-free formation (grey dashed line); (b) The black solid line is the actual hydrate saturation, the grey solid line is the hydrate saturation when the skeleton support percentage is 38%; the black dashed line is the pore-filling hydrate saturation; the grey dashed line is the skeleton-supported hydrate saturation.

[0158] The sandstone hydrate reservoir in the 415-439 mbsf depth section of the GC955H well in the Gulf of Mexico, USA, was used as the target layer for studying hydrate saturation. Based on the above modeling process, the skeleton support morphology percentage fms was given as 38%, and the empirical coefficient J was 1.49. The grid search method was used to invert the hydrate saturation of the GC955H well with the longitudinal wave impedance as a constraint.

[0159] Figure 7 The hydrate saturation calculated under pore-filling, skeleton-supported and dual-occurrence forms was compared with the hydrate saturation calculated by resistivity. As can be seen from the figure, the hydrate saturation values ​​predicted based on single pore-filling and single skeleton-supported forms are not much different, and the prediction results can be regarded as considering the uncertainty of the pore-filling and skeleton-supported forms. The estimated value of hydrate saturation of pore-filling hydrate is slightly higher than the reference value; the hydrate saturation of skeleton-supported hydrate is slightly lower than the reference value; and the hydrate saturation predicted by considering dual-occurrence forms is between the hydrate saturations predicted by the two single-occurrence forms, and the overall saturation change trend is consistent, which is consistent with the actual saturation. Skeleton-supported hydrates account for about 38% of the total hydrates, reflecting that the study layer is mainly a pore-filling hydrate layer.

[0160] Figure 8This is a comparison effect 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 according to an embodiment of the present invention. For ease of description, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0161] Figure 8 Comparison between the predicted and actual results of hydrate saturation under different models for Well GC955H. The black solid line is the actual hydrate saturation; the gray solid line is the hydrate saturation predicted by the generalized weight equation; the black dashed line is the hydrate saturation predicted by the Wyllie time-averaged equation; and the gray dashed line is the hydrate saturation predicted by the Wood equation.

[0162] Figure 8 The comparison between the hydrate saturation predicted by the Wyllie time-averaged equation, the Wood equation and the generalized weight equation and the actual saturation is shown in Figure 2. The results show that the saturation calculated by the time-averaged equation and the Wood equation is far from the actual saturation. The formation P-wave impedance predicted by the time-averaged equation is too high and the hydrate saturation is too low, while the formation P-wave impedance predicted by the Wood equation is too low and the hydrate saturation is too high. The main reason is that the time-averaged equation is suitable for describing the velocity of well-consolidated formations, while the Wood equation is mainly used to describe the velocity of unconsolidated formations. Compared with the traditional empirical formula, the saturation estimated by the generalized weight equation considering the coupling of dual occurrence modes is in better agreement with the actual saturation.

[0163] 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 there are 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 with acoustic data as a constraint, and in the future, electrical characteristics can be combined to further improve the prediction accuracy of hydrate saturation.

[0164] Fig. 9 A structural diagram of an electronic device provided by an embodiment of the present invention, such as Fig. 9As shown, the device includes: a memory 21 for storing a computer program; 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. Among them, the processor 22 may include one or more processing cores, such as a 4-core processor, an 8-core processor, etc. The processor 22 may be implemented in at least one hardware form of a digital signal processor (DSP), a field-programmable gate array (FPGA), and 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 an awake state, also known as a central processing unit (CPU); the coprocessor is a low-power processor for processing data in a standby state. In some embodiments, the processor 22 may be integrated with a graphics processing unit (GPU), and the GPU is responsible for rendering and drawing the content to be displayed on the display screen. In some embodiments, the processor 22 may also include an artificial intelligence (AI) processor, which is used to process computing operations related to machine learning.

[0165] The memory 21 may include one or more computer-readable storage media, which may be non-transitory. The memory 21 may also include a high-speed random access memory, and a non-volatile memory, such as one or more disk storage devices, flash memory storage devices. In this embodiment, the memory 21 is at least used to store 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 coupled with dual occurrence modes 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 the data involved in the method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes, etc.

[0166] In some embodiments, the electronic device may further include a display screen 23 , an input / output interface 24 , a communication interface 25 , a power source 26 , and a communication bus 27 .

[0167] Those skilled in the art will understand that Fig. 9 The structure shown in the figure does not constitute a limitation on the electronic device, and may include more or fewer components than shown in the figure.

[0168] 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.

[0169] For an introduction to an electronic device 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.

[0170] Furthermore, the present invention also provides a computer-readable storage medium having a computer program stored thereon, and 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.

[0171] 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 such an understanding, the technical solution of the present invention is essentially 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 to execute all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk and other media that can store program code.

[0172] 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.

[0173] 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 embodiments can be referenced 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, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the present invention.

[0174] 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 such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

Claims

1. A method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes, characterized in that: Step S1: determining the initial hydrate saturation of the reservoir, the occurrence mode of hydrate, the reservoir porosity, and the reservoir mud content; The occurrence mode of the hydrate is a dual occurrence mode, which takes into account two microscopic occurrence forms: pore filling and skeleton support; Step S2: constructing a rock physics model of a dual-occurrence hydrate reservoir; Step S3: construct an objective function with longitudinal wave impedance as a constraint, the objective function is: Where: and is the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; 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.

2. The method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes according to claim 1, characterized in that: The step S2 of constructing the dual-occurrence morphology hydrate reservoir rock physics model includes: Step S21: using Hill average 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; 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.

3. The method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes according to claim 2, characterized in that: 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 form coupling, wherein: The generalized weight equation based on the coupling of dual occurrence forms 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 , h , 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 framework-supported morphology, and hydrate saturation, 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 is.

4. The method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes according to claim 3, characterized in that: The step S21 also includes the calculation of rock matrix longitudinal wave impedance: solid minerals and skeleton-supported hydrates are combined to form a rock matrix, which together play a stress support role. When the volume fractions and elastic moduli of various mineral components are known, the rock matrix bulk modulus and shear modulus are calculated using Hill average: In the formula, 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 hydrates, respectively; f sd 、f c and f h,ms are the volume fractions of quartz, clay and framework-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; Using the rock physics volume model, the rock matrix density can be expressed as: r ma =f sd r sd +f c r c +f h,ms r h In the formula, ρ sd , c and ρ h are the densities of quartz, clay and hydrate, respectively. The rock matrix longitudinal wave impedance expression is as follows: The 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, and its expression is: 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 P-wave velocities of rock matrix, hydrate and water, respectively; The three-phase time average equation is rewritten as: Further simplified to: In the formula, ρ b is the bulk density of saturated rock, ρ m , h and ρ w are the densities of rock matrix, hydrate, and water, respectively; Furthermore, the three-phase Wood equation applied to the gas hydrate formation is expressed as: Where V P,W is the longitudinal wave velocity calculated by Wood’s formula; 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:

5. A device for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes, characterized in that: Initial assignment unit: determine 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 building unit: building a rock physics model of hydrate reservoir with dual occurrence forms; Objective function setting unit: construct an objective function with longitudinal wave impedance as a constraint, and the objective function is: Where: and is the actual value of longitudinal wave impedance and the predicted value of longitudinal wave impedance; ε is the given minimum error; Reservoir hydrate saturation inversion unit: using a grid search method, hydrate saturation inversion is performed based on the objective function to estimate the reservoir hydrate saturation value.

6. The device for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes according to claim 5, characterized in that: The rock physics model building unit constructs a dual-occurrence hydrate reservoir rock physics model including: Rock matrix calculation unit: uses Hill average 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, clay; 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 form coupling.

7. The method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes according to claim 6, characterized in that: The saturated rock calculation unit uses a generalized weight equation based on dual occurrence form 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 coupling of dual occurrence forms 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 , h , 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 framework-supported morphology, and hydrate saturation, 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 is.

8. The method for estimating hydrate saturation based on the generalized weight equation coupled with dual occurrence modes according to claim 7, characterized in that: The rock matrix calculation unit also includes a rock matrix longitudinal wave impedance calculation unit: solid minerals and skeleton-supported hydrates combine to form a rock matrix, which together play a stress support role. When the volume fractions and elastic moduli of various mineral components are known, the rock matrix bulk modulus and shear modulus are calculated using Hill average: In the formula, 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 hydrates, respectively; f sd 、f c and f h,ms are the volume fractions of quartz, clay and framework-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; Using the rock physics volume model, the rock matrix density can be expressed as: r ma =f sd r sd +f c r c +f h,ms r h In the formula, ρ sd , c and ρ h are the densities of quartz, clay and hydrate, respectively. The rock matrix longitudinal wave impedance expression is as follows: 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 the consolidated formation is expanded into a three-phase time-averaged equation and applied to the natural gas hydrate formation. Its expression is: 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 P-wave velocities of rock matrix, hydrate and water, respectively; The three-phase time average equation is rewritten as: Further simplified to: In the formula, ρ b is the bulk density of saturated rock, ρ m , h and ρ w are the densities of rock matrix, hydrate, and water, respectively; Furthermore, the three-phase Wood equation applied to the gas hydrate formation is expressed as: Where V P,W is the longitudinal wave velocity calculated by Wood’s formula; 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:

9. An electronic device, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the steps of the method for estimating hydrate saturation based on a generalized weight equation coupled with dual occurrence modes as described in any one of claims 1 to 4 when executing the computer program.

10. 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 described in any one of claims 1 to 4.

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