Method and device for predicting hydrate saturation based on microscopic occurrence morphology

Abstract

The present invention discloses a method and device for predicting hydrate saturation based on microscopic occurrence forms, the method comprising: determining the proportion of multiple microscopic occurrence forms of hydrate according to the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actually measured P-wave and S-wave velocities; using the hydrate saturation interpreted by logging as the initial value, and combining the proportion, cyclically determining the P-wave and S-wave velocity error value of each cycle: obtaining the P-wave and S-wave velocities calculated for the current cycle according to the hydrate saturation value of the current cycle and the pre-established unified contact cementation model; determining the error between the P-wave and S-wave velocities calculated for the current cycle and the actually measured P-wave and S-wave velocities; when the cycle end condition is not met, giving the hydrate saturation value of the next cycle; when the condition is met, comparing the P-wave and S-wave velocity error values ​​of each cycle to obtain the predicted hydrate saturation value. The present invention can improve the accuracy of predicting natural gas hydrate saturation, and has scientific guiding significance for oil and natural gas exploitation.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum geophysical exploration, and in particular to a method and a device for predicting hydrate saturation based on microscopic occurrence forms. Background Art

[0002] This section is intended to provide a background or context to the embodiments of the invention recited in the claims. No admission is made that the description herein is prior art by inclusion in this section.

[0003] In recent years, gas hydrates have attracted increasing attention due to their potential as an alternative resource and their impact on climate and the environment. Therefore, it is important to accurately predict the saturation of gas hydrates from geophysical measurements. However, current methods for predicting gas hydrate saturation have low accuracy. Summary of the invention

[0004] The embodiment of the present invention provides a method for predicting hydrate saturation based on microscopic occurrence morphology, so as to improve the accuracy of predicting hydrate saturation. The method includes:

[0005] Interpret the hydrate saturation and the actual measured P- and S-wave velocities based on resistivity or NMR logging to determine the proportion of various microscopic occurrence forms of hydrates;

[0006] The hydrate saturation interpreted by well logging is used as the initial value of hydrate saturation prediction, and the proportion of multiple microscopic occurrence forms of hydrate is used to distribute the hydrate saturation of different occurrence forms. The P-wave and S-wave velocity error values ​​corresponding to each cycle are determined cyclically. The following operations are performed in each cycle:

[0007] The P- and S-wave velocities calculated for the current cycle are obtained according to the hydrate saturation value of the current cycle and the percentages of the various occurrence forms determined, as well as the pre-established unified contact cementation model; the unified contact cementation model is established by improving the cementation model based on the introduction of the regularized contact cementation radius and adopting the Hashin-Shtrikman boundary condition constraint;

[0008] Determine the error between the P-wave and S-wave velocities calculated in the current cycle and the actually measured P-wave and S-wave velocities, and obtain the P-wave and S-wave velocity error value corresponding to the current cycle; when the preset cycle end condition is not met, give the hydrate saturation value of the next cycle;

[0009] When the preset cycle end condition is met, the P-wave and S-wave velocity error values ​​corresponding to each cycle are compared, and the hydrate saturation value corresponding to the minimum P-wave and S-wave velocity error value is taken as the optimal hydrate saturation value.

[0010] The embodiment of the present invention further provides a device for predicting hydrate saturation based on microscopic occurrence forms, so as to improve the accuracy of predicting hydrate saturation. The device comprises:

[0011] A determination unit is used to determine the proportion of various microscopic occurrence forms of hydrates based on the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actual measured P- and S-wave velocities;

[0012] The processing unit is used to use the hydrate saturation interpreted by the well logging as the predicted initial value of the hydrate saturation, and to distribute the hydrate saturations of different occurrence forms by using the proportions of the various microscopic occurrence forms of the hydrate, and to cyclically determine the P-wave and S-wave velocity error values ​​corresponding to each cycle. The following operations are performed in each cycle:

[0013] The P- and S-wave velocities calculated for the current cycle are obtained according to the hydrate saturation value of the current cycle and the percentages of the various occurrence forms determined, as well as the pre-established unified contact cementation model; the unified contact cementation model is established by improving the cementation model based on the introduction of the regularized contact cementation radius and adopting the Hashin-Shtrikman boundary condition constraint;

[0014] Determine the error between the P-wave and S-wave velocities calculated in the current cycle and the actually measured P-wave and S-wave velocities, and obtain the P-wave and S-wave velocity error value corresponding to the current cycle; when the preset cycle end condition is not met, give the hydrate saturation value of the next cycle;

[0015] The prediction unit is used to compare the P-wave and S-wave velocity error values ​​corresponding to each cycle when the preset cycle end condition is met, and take the hydrate saturation value corresponding to the minimum P-wave and S-wave velocity error value as the predicted hydrate saturation value.

[0016] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above-mentioned method for predicting hydrate saturation based on microscopic occurrence morphology when executing the computer program.

[0017] An embodiment of the present invention further provides a computer-readable storage medium, which stores a computer program for executing the above-mentioned method for predicting hydrate saturation based on microscopic occurrence morphology.

[0018] In an embodiment of the present invention, a scheme for predicting hydrate saturation based on microscopic occurrence forms is as follows: determining the ratio of multiple microscopic occurrence forms of hydrate according to the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actually measured P- and S-wave velocities; using the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging as the initial value of the hydrate saturation to be predicted, and using the determined ratio of multiple microscopic occurrence forms of hydrate to allocate hydrate saturations of different occurrence forms, cyclically determining the P- and S-wave velocity error values ​​corresponding to each cycle, and performing the following operations in each cycle: obtaining the P- and S-wave velocity values ​​calculated for the current cycle according to the hydrate saturation value of the current cycle and the determined percentages of multiple occurrence forms, as well as a pre-established unified contact cementation model; degree; the unified contact cementation model is established by improving the cementation model based on the introduced regularized contact cementation radius and adopting the Hashin-Shtrikman boundary condition constraint; the error between the P-wave and S-wave velocities calculated in the current cycle and the actually measured P-wave and S-wave velocities is determined to obtain the P-wave and S-wave velocity error value corresponding to the current cycle; when the preset cycle end condition is not met, the hydrate saturation value of the next cycle is given; when the preset cycle end condition is met, the P-wave and S-wave velocity error values ​​corresponding to each cycle are compared, and the hydrate saturation value corresponding to the minimum P-wave and S-wave velocity error value is taken as the optimal hydrate saturation value, which can improve the accuracy of predicting natural gas hydrate saturation and has scientific guiding significance for oil and natural gas extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0020] Figure 1 It is a schematic flow chart of a method for predicting hydrate saturation based on microscopic occurrence forms in an embodiment of the present invention;

[0021] Figure 2 It is a schematic diagram of the principle of predicting hydrate saturation based on microscopic occurrence morphology in an embodiment of the present invention;

[0022] Figure 3A A schematic diagram showing a comparison between the longitudinal wave velocity calculated by the method for predicting hydrate saturation based on microscopic occurrence morphology in an embodiment of the present invention and the existing method;

[0023] Figure 3B A schematic diagram showing a comparison between the shear wave velocity calculated by the method for predicting hydrate saturation based on microscopic occurrence morphology in an embodiment of the present invention and the existing method;

[0024] Figure 4A is a cross-plot of P-wave velocity and hydrate saturation in an embodiment of the present invention;

[0025] Figure 4B is a cross-plot of shear wave velocity and hydrate saturation in an embodiment of the present invention;

[0026] Figure 5 A schematic diagram of the saturation evaluation results of the NGHP-01-16A well using the method for predicting hydrate saturation based on microscopic occurrence morphology in the method of the embodiment of the present invention;

[0027] Figure 6 It is a schematic diagram of the structure of the device for predicting hydrate saturation based on microscopic occurrence morphology in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0029] Before introducing the solution provided by the embodiment of the present invention, the inventor first introduces the technical problem discovered by the inventor and the idea of ​​proposing the solution provided by the embodiment of the present invention to solve the technical problem. The inventor discovered the following technical problem:

[0030] The presence of natural gas hydrates generally increases the P- and S-wave velocities of the reservoir. However, the increase in P- and S-wave velocities is not only related to the hydrate saturation but also to the microscopic occurrence form of the hydrate. According to the interaction between hydrate particles and solid particles, some scholars have summarized six microscopic occurrence forms of hydrates: contact cementation, particle encapsulation, skeleton support, pore filling, matrix-inclusion and nodule / fracture filling. Different microscopic occurrence forms have different effects on the P- and S-wave velocities, which in turn affect the prediction accuracy of hydrate saturation. Therefore, a better understanding of the occurrence form of hydrates is very important for simulating the elastic response of hydrate reservoirs and predicting hydrate saturation.

[0031] The microscopic occurrence form of hydrates can usually be obtained by the following methods: 1. Laboratory observation, that is, using a pressure core analysis system to directly observe the occurrence form of hydrate samples taken from pressure cores. This method is relatively expensive, the cores are easily disturbed by mechanics, and the number of samples is small, making it difficult to effectively cover the entire well section; 2. Resistivity imaging logging, which can distinguish between hydrates filled in pores and those filled in vertical or semi-vertical fractures, but cannot identify nodules and vein-like hydrates and hydrates filled in fractures with small angles; 3. Conventional crossplots of P- and S-wave velocities and hydrate saturation, which can better identify the main occurrence form of hydrates. Comparing these three methods, the crossplots of P- and S-wave velocities and hydrate saturation can be constructed based on different rock physics models, so they are currently the most widely used.

[0032] At present, the commonly used rock physics models of natural gas hydrate reservoirs, such as cementation model, effective medium model, SCA-DEM model, simplified three-phase equation, etc., respectively describe the relationship between P-wave and S-wave velocity and hydrate saturation under different microscopic occurrence forms. For example, the cementation model can be used to describe contact cementation and particle-encapsulated hydrates; the effective medium model can be used to describe skeleton-supported and particle-encapsulated hydrates; the SCA-DEM model can characterize cementation and matrix-inclusion hydrates. All of the above models can only describe two hydrate occurrence forms at most, that is, they are not applicable to hydrate reservoirs with more complex microscopic forms. In addition, firstly, the shear wave velocities predicted by the conventional cementation model and effective medium model are often too high. In the actual prediction of hydrate saturation, it is usually assumed that hydrates are in a single occurrence form. Such an assumption based on a single form will bring a large error to the prediction results, resulting in low accuracy of the final predicted hydrate saturation, and the two models cannot be unified; secondly, the experimental observation pressure coring results show that hydrates usually appear in the reservoir in a variety of microscopic occurrence forms, but the existing rock physics models are not applicable to hydrates in a variety of occurrence forms.

[0033] Considering the above technical problems, the inventor proposed a scheme for predicting hydrate saturation based on microscopic occurrence morphology. The scheme proposed a new regularized contact cementation radius to improve the conventional cementation model, and proposed a unified contact cementation model by using the Hashin-Shtrikman upper and lower boundary constraints and introducing the sliding friction coefficient and the regularized hydrate cementation layer thickness. The model effectively integrates the cementation model and the effective medium model, so that the newly invented unified contact cementation model can simultaneously characterize four hydrate microscopic morphologies. Based on the model, a longitudinal and transverse wave velocity-hydrate saturation intersection diagram is constructed, and the percentages of various hydrate microscopic occurrence morphologies are statistically calculated in combination with the superimposed measurement data, and the longitudinal and transverse wave velocities are used to predict the hydrate saturation. This method not only improves the prediction accuracy of hydrate saturation, but also reveals the actual complex microscopic occurrence morphology of hydrates. The scheme for predicting hydrate saturation based on microscopic occurrence morphology is introduced in detail below.

[0034] Figure 1 FIG. 1 is a flow chart of a method for predicting hydrate saturation based on microscopic occurrence forms in an embodiment of the present invention. Figure 1 As shown, the method comprises the following steps:

[0035] Step 101: determining the proportions of various microscopic occurrence forms of hydrates based on the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actually measured P- and S-wave velocities;

[0036] Step 102: The hydrate saturation interpreted by the well logging is used as the predicted initial value of the hydrate saturation, and the proportions of the various microscopic occurrence forms of the hydrate are used to distribute the hydrate saturations of the different occurrence forms, and the P-wave and S-wave velocity error values ​​corresponding to each cycle are determined cyclically. The following operations are performed in each cycle:

[0037] Step 1021: according to the hydrate saturation value of the current cycle and the percentages of the determined multiple occurrence forms, and the pre-established unified contact cementation model, the P- and S-wave velocities calculated for the current cycle are obtained; the unified contact cementation model is established by improving the cementation model based on the introduced regularized contact cementation radius and adopting the Hashin-Shtrikman boundary condition constraint;

[0038] Step 1022: Determine the error between the P-wave and S-wave velocities calculated in the current cycle and the P-wave and S-wave velocities actually measured, and obtain the P-wave and S-wave velocity error value corresponding to the current cycle; when the preset cycle end condition is not met, give the hydrate saturation value of the next cycle;

[0039] Step 103: When the preset cycle end condition is met, the P-wave and S-wave velocity error values ​​corresponding to each cycle are compared, and the hydrate saturation value corresponding to the minimum P-wave and S-wave velocity error value is used as the predicted hydrate saturation value.

[0040] The method for predicting hydrate saturation based on microscopic occurrence morphology provided in an embodiment of the present invention may further include: applying the predicted hydrate saturation value to oil and gas drilling, such as performing reserve calculations, well site deployment, and perforation scheme design.

[0041] In specific implementation, the proportion of microscopic occurrence forms can be a percentage or a ratio.

[0042] In specific implementation, the proportion of each microscopic occurrence form of hydrate is determined based on the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actually measured P- and S-wave velocities, which can include: determining the proportion of multiple microscopic occurrence forms of hydrate based on the positions of the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actually measured P- and S-wave velocities projected on the velocity-water saturation cross-plot constructed based on the rock physics model.

[0043] In one embodiment, Figure 2 As shown in the figure, according to the hydrate saturation value of the current cycle and the percentage of multiple occurrence forms determined, as well as the pre-established unified contact cementation model, the P- and S-wave velocities calculated for the current cycle are obtained, which may include:

[0044] According to the hydrate saturation value of the current cycle and the percentage of various occurrence forms determined, the rock matrix modulus, fluid modulus and dry rock skeleton modulus based on the pre-established unified contact cementation model are obtained;

[0045] According to the rock matrix modulus, fluid modulus and dry rock skeleton modulus, the saturated rock modulus of the current cycle is obtained;

[0046] According to the saturated rock modulus of the current period, the P- and S-wave velocities calculated in the current period are obtained.

[0047] In specific implementation, the following formulas (3) and (4) can be used to implement: the step of obtaining the hydrate matrix modulus according to the hydrate saturation value of the current cycle; the following formula (13) can be used to implement: the step of obtaining the hydrate fluid modulus according to the hydrate saturation value of the current cycle; the following formulas (7)-(10) can be used to implement: the step of obtaining the dry rock skeleton modulus based on the pre-established unified contact cementation model according to the hydrate saturation value of the current cycle; the following formulas (11)-(13) can be used to implement: the step of obtaining the saturated rock modulus of the current cycle according to the hydrate matrix modulus, the fluid modulus and the dry rock skeleton modulus; the following formulas (14)-(15) can be used to implement: the step of obtaining the P- and S-wave velocities calculated for the current cycle according to the saturated rock modulus of the current cycle.

[0048] In specific implementation, the above implementation method of obtaining the P- and S-wave velocities calculated in the current period is conducive to further improving the accuracy of predicting hydrate saturation.

[0049] In one embodiment, when the porosity (φ) of the reservoir to be measured is lower than the critical porosity (φ c ), the unified contact bonding model includes:

[0050]

[0051]

[0052] When the porosity (φ) of the reservoir to be measured is higher than the critical porosity (φ c ), the unified contact bonding model includes:

[0053]

[0054]

[0055] Among them, K dry is the effective dry rock bulk modulus, μ dry is the effective dry rock bulk shear modulus.

[0056] In specific implementation, the implementation of the unified contact cementation model is conducive to further improving the accuracy of predicting hydrate saturation. The unified contact cementation model may include (5)-(10).

[0057] In one embodiment, determining the proportions of various microscopic occurrence forms of hydrates based on the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actually measured P- and S-wave velocities may include:

[0058] According to a pre-established rock physics model, a cross-plot of P-wave and S-wave velocities and hydrate saturation is constructed; the rock physics model is obtained according to a unified contact cementation model;

[0059] According to the cross-plot, the proportions of various microscopic occurrence forms of hydrates are determined.

[0060] In specific implementation, the above-mentioned implementation method of determining the proportion of each microscopic occurrence form of hydrate is conducive to further improving the accuracy of predicting hydrate saturation.

[0061] In one embodiment, the rock physics model is:

[0062] K sat =K dry +λ 2 K fl [φ e +(λ-φ e )Kfl / K ma ] -1 ;

[0063] μ sat =μ dry ;

[0064] Among them, the Biot coefficient λ=1-K dry / K ma , effective porosity φ e =φ(1-S hms -S hc ), K fl is the bulk modulus of the fluid, S hc , S hpf and S hms are the saturations of cemented, pore-filling and skeleton-supported hydrates, respectively, K h and K w are the bulk moduli of hydrate and water, respectively.

[0065] In specific implementation, the implementation method of the above-mentioned rock physics model is conducive to further improving the accuracy of predicting hydrate saturation.

[0066] In order to facilitate understanding of how to implement the present invention, the following Figures 2 to 5 , an overall introduction is given to the natural gas hydrate saturation prediction scheme of the embodiment of the present invention.

[0067] The inventors consider that the shear wave velocity predicted by the conventional cementation model and the effective medium model is too high, and the two cannot be integrated together. In the actual prediction of hydrate saturation, it is usually assumed that hydrates are in a single occurrence form. Such an assumption based on a single form will bring great errors to the prediction results. Secondly, the experimental observation pressure coring results show that hydrates usually appear in reservoirs in a variety of microscopic occurrence forms, but the existing rock physics model cannot be applied to hydrates in a variety of occurrence forms. Therefore, the main core of the natural gas hydrate saturation prediction scheme in the embodiment of the present invention proposed by the inventor has two aspects: first, a generalized regularized contact cementation radius is proposed and the cementation model is improved, and a unified contact cementation model is proposed in combination with the Hashin-Shtrikman upper and lower boundaries (Hashin and Shtrikman, 1963) constraints; second, a longitudinal and shear wave velocity-hydrate saturation intersection diagram is constructed based on the proposed rock physics model, and the percentages of various occurrence forms are statistically calculated using superimposed measurement data, and finally substituted into a unified contact cementation model to calculate the hydrate saturation. For example, if the determined occurrence form percentage is: contact cementation: skeleton support: pore filling = 1:2:1, and the hydrate saturation is 0.4, then the cementation hydrate saturation is 0.4×0.25=0.1, the skeleton support hydrate saturation is 0.5×0.4=0.2, and the pore filling hydrate saturation is 0.25×0.4=0.1. Then the cementation hydrate saturation S is needed in formulas (1)-(2). hc = 0.1, formulas (3)-(4) require the use of the framework-supported hydrate saturation S hms = 0.2, formula (13) requires the use of pore-filling hydrate saturation S hpf =0.1. Since S h =S hc +S hms +S hpf , the specific calculation can be done by iterative solution of hydrate saturation. That is, the hydrate saturation is allocated using the determined occurrence form percentage (ratio), and then substituted into formulas (1)-(13) for calculation. The above ratios are statistically derived and will not change in the future. The only thing that changes during the prediction process is the hydrate saturation.

[0068] The present invention is implemented by the following technical solution, and the specific steps include:

[0069] 1. First, we introduce the steps to pre-build various models.

[0070] (1) Derive the generalized contact bonding radius of contact bonding and particle wrapping morphology.

[0071] 1.1) The generalized regularized radius β of the contact bonding morphology is

[0072]

[0073] 1.2) The generalized regularized radius β of the particle encapsulation morphology is

[0074]

[0075] In the formula is the initial regularized contact radius, μ ma and σ ma are the shear modulus and Poisson’s ratio of the matrix, P eff is the effective pressure. ξ=h / R is the normalized hydrate layer thickness, h and R are the cementation layer thickness and particle radius, respectively. k is the coordination number, S hc and φ c They are cementation (contact cementation and particle encapsulation, contact cementation and particle encapsulation are collectively referred to as cementation morphology, which are two manifestations of cementation morphology), hydrate saturation and critical porosity.

[0076] (2) Assuming that the hydrate is in a skeleton-supported form, the bulk modulus of the skeleton matrix (K ma ) and shear modulus (μ ma ) can be calculated by Hill average:

[0077]

[0078]

[0079] Where φ h =φS hms is the pore volume occupied by the skeleton-supported hydrate, S hms K is the saturation of the skeleton-supported hydrate. h and K s is the bulk modulus of the hydrate and solid phase, μ h and μ s is the shear modulus of the hydrate and solid phases.

[0080] (3) By introducing the sliding friction coefficient to improve the cementation model, the rock bulk modulus (K) at the critical porosity is calculated using the following formula: ect ) and shear modulus (μ ect ).

[0081]

[0082]

[0083] Where τ is the sliding friction coefficient, S N and S T are the normal and tangential stiffnesses respectively.

[0084] (4) The bulk modulus and shear modulus at any porosity are obtained by the Hashin-Shtrikman boundary condition. c ), effective dry rock volume (K dry ) and shear (μ dry ) modulus is calculated by the modified Hashin-Shtrikman lower bound as:

[0085]

[0086]

[0087] For porosity (φ) higher than the critical porosity (φ c ), the effective bulk and shear moduli are calculated by the modified Hashin-Shtrikman upper bound as:

[0088]

[0089]

[0090] (5) The bulk modulus (K) of saturated rock is calculated using the Gassmann equation (Gassmann, 1951). sat ) and shear modulus (μ sat ):

[0091] K sat =K dry +λ 2 K fl [φ e +(λ-φ e )K fl / K ma ] -1 (11)

[0092] and

[0093] μ sat =μ dry (12)

[0094] Where Biot coefficient λ = 1-K dry / K ma Among them, the effective porosity φ e =φ(1-S hms -S hc ). fl is the bulk modulus of the fluid. When hydrates fill the pores, the hydrates are regarded as part of the fluid, and the fluid modulus can be calculated using the Reuss average:

[0095]

[0096] S hc , S hpf and S hms is the saturation of cemented, pore-filling and skeleton-supported hydrates, K h and K w are the bulk moduli of hydrate and water, respectively.

[0097] (6) Calculate the longitudinal wave (V) based on the bulk modulus and shear modulus of fluid-saturated rock p cal ) and shear waves (V s cal )speed.

[0098]

[0099]

[0100] In the formula, ρ b is the bulk density of saturated rock, which can be calculated using the rock physics bulk modulus.

[0101] Second, the detailed steps of calculating hydrate saturation using the above-mentioned pre-established model, such as the above-mentioned formulas (1)-(15), are introduced.

[0102] (7) Using the formulas in steps (1) to (6), a cross-plot of P-wave velocity and S-wave velocity versus hydrate saturation is constructed (e.g. Figure 4A and Figure 4B As shown) and superimposed the measured data, and then used the least squares fitting method to fit the cubic polynomials between the longitudinal and transverse wave velocities and the hydrate saturation in the case of 50% particle encapsulation and 50% skeleton support and 50% skeleton support and 50% pore filling hydrates, respectively. Assume that the measured data points fall under the curve of the case of 50% particle encapsulation and 50% skeleton support and on the curve of the case of 50% skeleton support and 50% pore filling, it is regarded as skeleton-supported hydrate; the measured data fall on the curve of the case of 50% particle encapsulation and 50% skeleton support, it is regarded as particle-encapsulated hydrate; the measured data fall under the curve of the case of 50% skeleton support and 50% pore filling, it is regarded as pore-filling hydrate. Then, according to the number of measured data points falling into the corresponding interval, the ratio of particle encapsulation, skeleton support and pore filling hydrate is statistically determined as N. gc :N ms :N pf , parameter N gc ,N ms ,N pf are the number of particle-encapsulated, skeleton-supported, and pore-filled hydrate forms corresponding to the measured data points. Thus, the percentage of particle-encapsulated hydrate can be determined as: The percentage of skeleton-supported hydrate is: The percentage of pore filling hydrate is:

[0103] (8) Compare the P-wave and S-wave velocities calculated by forward modeling with the P-wave and S-wave velocities actually measured, and calculate the error between them:

[0104]

[0105] In the formula, is the measured longitudinal wave velocity, V s obs is the measured shear wave velocity; W p , W s is the weighting factor, W p +W s =1.

[0106] When it comes to specific implementation, Figure 2 The objective function OF in can be the above formula (16).

[0107] (9) A nonlinear global optimization algorithm is used to modify the given initial hydrate saturation to obtain new P- and S-wave velocities. The above (4)-(7) are repeated to calculate the corresponding errors, compare the errors, and finally obtain the optimal hydrate saturation (predicted hydrate saturation value) and the P- and S-wave velocities corresponding to the optimal hydrate saturation.

[0108] In a specific implementation, the loop end condition may be: the number of loops reaches a preset number of times or the loop calculation time reaches a preset duration.

[0109] Next, attach Figures 2 to 5 Supplementary description is given in the description.

[0110] Figure 2 It is a flow chart of the principle of hydrate saturation prediction related to the occurrence form constructed based on the unified contact cementation model.

[0111] Figure 3A and Figure 3B The unified contact bonding model proposed by the method of the present invention is compared with the conventional bonding model and the effective medium model. Figure 3A and Figure 3BIt can be seen that the longitudinal wave velocity calculated by the unified contact cementation model is consistent with the longitudinal wave velocity calculated by the effective medium model, while the calculated shear wave velocity is lower than that of the effective medium model; the longitudinal wave velocity calculated by the unified contact cementation model is in good agreement when the hydrate saturation is lower than 65%, while the longitudinal wave velocity calculated when the hydrate saturation is higher than 65% is higher than that of the conventional cementation model; the calculated shear wave velocities are lower than those of the conventional cementation model. This also shows that the unified contact cementation model of the present invention can effectively overcome the problem of high shear wave velocity predicted by the conventional contact cementation model and the effective medium model. In addition, the unified contact cementation model provided in the embodiment of the present invention can better characterize the velocity evolution characteristics of hydrates. That is Figure 3A and Figure 3B The longitudinal and transverse wave velocities calculated in the method provided in the embodiment of the present invention are compared with the conventional bonding model and the effective medium model, and the feasibility of the model is verified by using experimental data.

[0112] Figure 4A and Figure 4B The well logging data of NGHP-01-16A well were constructed using the unified contact cementation model to diagnose the P-wave and S-wave velocity-hydrate saturation. Figure 4A and Figure 4B The velocity and hydrate saturation curves of 50% particle encapsulation and 50% skeleton support and 50% skeleton support and 50% pore filling are fitted at the same time. It can be found from the figure that hydrates present a variety of hydrate occurrence forms. The application of statistical methods can estimate that the percentage of the three occurrence forms of particle encapsulation, skeleton support and pore filling is 1:15:4. That is, Figure 4A and Figure 4B The hydrate occurrence form of the NGHP-01-16A well was diagnosed by using the P-wave and S-wave velocity-hydrate saturation crossplot.

[0113] Figure 5 This is the result of hydrate saturation prediction for NGHP-01-16A well using the unified contact cementation model. The solid line is the predicted speed, and the dotted line is the measured speed. The fourth column shows the hydrate saturation calculated using the unified contact cementation model and the hydrate saturation from resistivity logging interpretation and chloride ion content analysis. It can be seen that the hydrate saturation predicted by the unified contact cementation model proposed in the present invention is generally consistent with the results of resistivity interpretation and chloride ion content analysis, and the difference with the resistivity prediction result mainly comes from the different vertical resolutions of resistivity and acoustic logging instruments. That is, Figure 5 The saturation evaluation results of the NGHP-01-16A well using the method of the present invention, the dotted line is the actual measured velocity, the solid line is the predicted velocity, wherein the third column is the porosity calculated by density, and the fourth column is the hydrate saturation evaluated by the method of the present invention and the hydrate saturation calculated by resistivity and chloride ion content.

[0114] In summary, the natural gas hydrate saturation prediction scheme provided by the embodiment of the present invention has the following characteristics:

[0115] 1. The present invention improves the cementation model based on the generalized regularized contact cementation radius, breaking through the limitation of the classical cementation theory being independent of pressure; overcomes the problem of high predicted shear wave velocity by introducing the sliding friction coefficient and the regularized cementation layer thickness; couples the effective medium model and the cementation model, so that four hydrate reservoirs with different microscopic occurrence forms can be simultaneously characterized.

[0116] 2. The method for predicting hydrate saturation that depends on the hydrate occurrence form of the present invention takes into account the complex occurrence form characteristics of hydrates, which can effectively reduce the influence of the occurrence form on the longitudinal and transverse wave velocities, thereby improving the accuracy of hydrate saturation prediction and effectively avoiding the defect that conventional models are only applicable to specific hydrate forms.

[0117] The present invention constructs a cross-plot of P-wave velocity and S-wave velocity-hydrate saturation based on a unified contact cementation model, determines the percentages of various occurrence forms, and then uses the Gassmann equation and the newly invented unified contact cementation model to establish the relationship between the parameters based on the P-wave velocity, porosity, shale content and other parameters of the rock, and then uses a nonlinear inversion algorithm to predict hydrate saturation. The key is to unify the construction of a rock physics model and a new method for predicting hydrate saturation related to occurrence forms.

[0118] The present invention also provides a device for predicting hydrate saturation based on microscopic occurrence forms, as described in the following embodiments. Since the principle of the device to solve the problem is similar to the method for predicting hydrate saturation based on microscopic occurrence forms, the implementation of the device can refer to the implementation of the method for predicting hydrate saturation based on microscopic occurrence forms, and the repeated parts will not be repeated.

[0119] Figure 6 FIG. 1 is a schematic diagram of the structure of a device for predicting hydrate saturation based on microscopic occurrence forms in an embodiment of the present invention. Figure 6 As shown, the device comprises:

[0120] Determination unit 02, for determining the proportion of various microscopic occurrence forms of hydrates based on the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actually measured P- and S-wave velocities;

[0121] The processing unit 04 is used to use the hydrate saturation interpreted by the well logging as the predicted initial value of the hydrate saturation, and to use the determined ratios of multiple microscopic occurrence forms of hydrate to distribute the hydrate saturations of different occurrence forms, and to cyclically determine the P-wave and S-wave velocity error values ​​corresponding to each cycle. Each cycle performs the following operations:

[0122] The P- and S-wave velocities calculated for the current cycle are obtained according to the hydrate saturation value of the current cycle and the percentages of the various occurrence forms determined, as well as the pre-established unified contact cementation model; the unified contact cementation model is established by improving the cementation model based on the introduction of the regularized contact cementation radius and adopting the Hashin-Shtrikman boundary condition constraint;

[0123] Determine the error between the P-wave and S-wave velocities calculated in the current cycle and the actually measured P-wave and S-wave velocities, and obtain the P-wave and S-wave velocity error value corresponding to the current cycle; when the preset cycle end condition is not met, give the hydrate saturation value of the next cycle;

[0124] The prediction unit 06 is used to compare the P-wave and S-wave velocity error values ​​corresponding to each cycle when the preset cycle end condition is met, and use the hydrate saturation value corresponding to the minimum P-wave and S-wave velocity error value as the predicted hydrate saturation value.

[0125] In one embodiment, according to the hydrate saturation value of the current period and the percentages of the multiple occurrence forms determined, and the pre-established unified contact cementation model, the P- and S-wave velocities calculated for the current period are obtained, which may include:

[0126] According to the hydrate saturation value of the current cycle and the percentage of various occurrence forms determined, the rock matrix modulus, fluid modulus and dry rock skeleton modulus based on the pre-established unified contact cementation model are obtained;

[0127] According to the rock matrix modulus, fluid modulus and dry rock skeleton modulus, the saturated rock modulus of the current cycle is obtained;

[0128] According to the saturated rock modulus of the current period, the P- and S-wave velocities calculated in the current period are obtained.

[0129] In one embodiment, the determining unit may be specifically configured to:

[0130] According to a pre-established rock physics model, a cross-plot of P-wave and S-wave velocities and hydrate saturation is constructed; the rock physics model is obtained according to a unified contact cementation model;

[0131] According to the cross-plot, the proportions of various microscopic occurrence forms of hydrates are determined.

[0132] In order to facilitate the understanding of the prediction scheme provided by the embodiment of the present invention, the inventor's ideas are introduced again: the current experimental observation pressure coring results show that hydrates usually appear in reservoirs in a variety of microscopic occurrence forms, but the existing rock physics model is not applicable to hydrates in a variety of occurrence forms. In the actual prediction of hydrate saturation, hydrate saturation can only be predicted based on a single occurrence form. In addition, the shear wave velocity predicted by the classical cementation model and the effective medium model is often too high, and these two particle effective medium models cannot be combined together. According to the newly invented unified contact cementation model, the shear wave velocity prediction accuracy is adjusted by introducing the sliding friction coefficient and the regularized hydrate layer thickness; in addition, it can also effectively identify the occurrence form of hydrates and determine the percentage of multiple forms, as well as quantitatively predict hydrate saturation; finally, the invented new model can also perform shear wave velocity prediction, characterize cementation and compaction effects, and conduct logging evaluation. The newly invented hydrate saturation prediction method effectively reduces the uncertainty of the hydrate saturation prediction results caused by multiple hydrate occurrence forms.

[0133] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above-mentioned method for predicting hydrate saturation based on microscopic occurrence morphology when executing the computer program.

[0134] An embodiment of the present invention further provides a computer-readable storage medium, which stores a computer program for executing the above-mentioned method for predicting hydrate saturation based on microscopic occurrence morphology.

[0135] In the embodiment of the present invention, the scheme for predicting hydrate saturation based on microscopic occurrence forms comprises: determining the proportion of various microscopic occurrence forms of hydrate according to the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actually measured P- and S-wave velocities; using the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging as the initial value of hydrate saturation, and combining the determined proportion of various microscopic occurrence forms of hydrate, cyclically determining the P- and S-wave velocity error value corresponding to each cycle, and performing the following operations in each cycle: obtaining the P- and S-wave velocities calculated for the current cycle according to the hydrate saturation value of the current cycle and the pre-established unified contact cementation model; the unified contact cementation model is based on the introduction of The regularized contact cementation radius is used to improve the cementation model and is established with the Hashin-Shtrikman boundary condition constraint; the error between the P-wave and S-wave velocities calculated in the current cycle and the actually measured P-wave and S-wave velocities is determined to obtain the P-wave and S-wave velocity error value corresponding to the current cycle; when the preset cycle end condition is not met, the hydrate saturation value of the next cycle is given; when the preset cycle end condition is met, the P-wave and S-wave velocity error values ​​corresponding to each cycle are compared, and the hydrate saturation value corresponding to the minimum P-wave and S-wave velocity error value is used as the predicted hydrate saturation value, which can improve the accuracy of predicting natural gas hydrate saturation and has scientific guiding significance for oil and natural gas extraction.

[0136] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0137] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0138] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0139] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0140] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for predicting hydrate saturation based on microscopic occurrence morphology, characterized in that: include: Determine the proportion of various microscopic occurrence forms of hydrates based on the hydrate saturation interpreted by resistivity or NMR logging and the actual measured P- and S-wave velocities; The hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging is used as the initial value of the hydrate saturation to be predicted, and the proportions of various microscopic occurrence forms of hydrates are used to distribute the hydrate saturations of different occurrence forms. The P-wave and S-wave velocity error values ​​corresponding to each cycle are determined cyclically. The following operations are performed in each cycle: The P- and S-wave velocities calculated for the current cycle are obtained according to the hydrate saturation value of the current cycle and the percentages of the various occurrence forms determined, as well as the pre-established unified contact cementation model; the unified contact cementation model is established by improving the cementation model based on the introduction of the regularized contact cementation radius and adopting the Hashin-Shtrikman boundary condition constraint; Determine the error between the P-wave and S-wave velocities calculated in the current cycle and the actually measured P-wave and S-wave velocities, and obtain the P-wave and S-wave velocity error value corresponding to the current cycle; when the preset cycle end condition is not met, give the hydrate saturation value of the next cycle; When the preset cycle end condition is met, the P-wave and S-wave velocity error values ​​corresponding to each cycle are compared, and the hydrate saturation value corresponding to the minimum P-wave and S-wave velocity error value is used as the predicted hydrate saturation value; When the porosity (φ) of the reservoir to be tested is lower than the critical porosity (φ c ), the unified contact bonding model includes: When the porosity (φ) of the reservoir to be measured is higher than the critical porosity (φ c ), the unified contact bonding model includes: Among them, K dry is the effective dry rock bulk modulus, μ dry is the effective dry rock bulk shear modulus, K ma The bulk modulus of the skeleton is the matrix, K ect and μ ect is the rock bulk modulus and shear modulus under critical porosity, φ is the porosity of the reservoir to be measured, φ c is the critical porosity.

2. The method for predicting hydrate saturation based on microscopic occurrence morphology according to claim 1, characterized in that: According to the hydrate saturation value of the current cycle and the percentage of various occurrence forms determined, as well as the pre-established unified contact cementation model, the P- and S-wave velocities calculated for the current cycle are obtained, including: According to the hydrate saturation value of the current cycle and the percentage of various occurrence forms determined, the rock matrix modulus, fluid modulus and dry rock skeleton modulus based on the pre-established unified contact cementation model are obtained; According to the rock matrix modulus, fluid modulus and dry rock skeleton modulus, the saturated rock modulus of the current cycle is obtained; According to the saturated rock modulus of the current period, the P- and S-wave velocities calculated in the current period are obtained.

3. The method for predicting hydrate saturation based on microscopic occurrence form according to claim 1, characterized in that: Based on the hydrate saturation interpreted by resistivity or NMR logging and the actual measured P- and S-wave velocities, the proportions of various microscopic occurrence forms of hydrate are determined, including: According to a pre-established rock physics model, a cross-plot of P-wave and S-wave velocities and hydrate saturation is constructed; the rock physics model is obtained according to a unified contact cementation model; According to the cross-plot, the proportions of various microscopic occurrence forms of hydrates are determined.

4. The method for predicting hydrate saturation based on microscopic occurrence form according to claim 3, characterized in that: The rock physics model is: K sat =K dry +λ 2 K fl [f e +(λ-φ e )K fl / K ma ] -1 ; m sat =μ dry ; Among them, the Biot coefficient λ=1-K dry / K ma , effective porosity φ e =φ(1-S hms -S hc ), K fl is the bulk modulus of the fluid, S hc , S hpf and S hms is the saturation of cemented, pore-filling and skeleton-supported hydrates, K h and K w are the bulk moduli of hydrate and water, respectively.

5. A device for predicting hydrate saturation based on microscopic occurrence morphology, characterized in that: include: A determination unit is used to determine the proportion of various microscopic occurrence forms of hydrates based on the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging and the actual measured P- and S-wave velocities; The processing unit is used to use the hydrate saturation interpreted by resistivity or nuclear magnetic resonance logging as the initial value of hydrate saturation, and to allocate the hydrate saturation of different occurrence forms by using the ratio of multiple microscopic occurrence forms of hydrate determined. Each cycle performs the following operations: The P- and S-wave velocities calculated for the current cycle are obtained according to the hydrate saturation value of the current cycle and the percentages of the various occurrence forms determined, as well as the pre-established unified contact cementation model; the unified contact cementation model is established by improving the cementation model based on the introduction of the regularized contact cementation radius and adopting the Hashin-Shtrikman boundary condition constraint; Determine the error between the P-wave and S-wave velocities calculated in the current cycle and the actually measured P-wave and S-wave velocities, and obtain the P-wave and S-wave velocity error value corresponding to the current cycle; when the preset cycle end condition is not met, give the hydrate saturation value of the next cycle; A prediction unit, for comparing the P-wave and S-wave velocity error values ​​corresponding to each cycle when a preset cycle end condition is met, and taking the hydrate saturation value corresponding to the minimum P-wave and S-wave velocity error value as the predicted hydrate saturation value; When the porosity (φ) of the reservoir to be tested is lower than the critical porosity (φ c ), the unified contact bonding model includes: When the porosity (φ) of the reservoir to be measured is higher than the critical porosity (φ c ), the unified contact bonding model includes: Among them, K dry is the effective dry rock bulk modulus, μ dry is the effective dry rock bulk shear modulus, K ma The bulk modulus of the skeleton is the matrix, K ect and μ ect is the rock bulk modulus and shear modulus under critical porosity, φ is the porosity of the reservoir to be measured, φ c is the critical porosity.

6. The device for predicting hydrate saturation based on microscopic occurrence forms according to claim 5, characterized in that: According to the hydrate saturation value of the current cycle and the percentage of various occurrence forms determined, as well as the pre-established unified contact cementation model, the P- and S-wave velocities calculated for the current cycle are obtained, including: According to the hydrate saturation value of the current cycle and the percentage of various occurrence forms determined, the rock matrix modulus, fluid modulus and dry rock skeleton modulus based on the pre-established unified contact cementation model are obtained; According to the rock matrix modulus, fluid modulus and dry rock skeleton modulus, the saturated rock modulus of the current cycle is obtained; According to the saturated rock modulus of the current period, the P- and S-wave velocities calculated in the current period are obtained.

7. The device for predicting hydrate saturation based on microscopic occurrence forms according to claim 5, characterized in that: The determining unit is specifically used for: According to a pre-established rock physics model, a cross-plot of P-wave and S-wave velocities and hydrate saturation is constructed; the rock physics model is obtained according to a unified contact cementation model; According to the cross-plot, the proportions of various microscopic occurrence forms of hydrates are determined.

8. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 4 is implemented.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program for executing the method according to any one of claims 1 to 4.

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