Hydrate-containing porous medium resistivity model construction method considering hydrate heterogeneous distribution
By constructing a resistivity model of a porous medium with heterogeneous hydrate distribution, the problems of low recovery rate and low thermal efficiency in hydrate reservoir mining were solved, and efficient resistivity calculation and accurate simulation of electrothermal mining were realized.
Patent Information
- Application Number
- CN202511434052.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-09
- Publication Date
- 2025-11-28
AI Technical Summary
In existing technologies, the mining of hydrate reservoirs suffers from low recovery rates and low thermal efficiency. In particular, the impact of resistivity changes on electrothermal mining has not been fully studied in depressurization and thermal ignition methods.
A resistivity model for porous media containing hydrates that considers the heterogeneous distribution of hydrates was constructed. Core structure and hydrate occurrence state were obtained by CT scanning. An electrostatic field was applied and the resistivity was calculated. The resistivity change was fitted by a power function to establish a resistivity calculation model for the hydrate decomposition process.
The thermal efficiency of hydrate reservoir mining has been improved. By obtaining the resistivity variation law through simulation calculation, the efficiency and accuracy of electric heating mining have been improved.
Smart Images
Figure CN121027233A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to a hydrate-containing porous medium resistivity model construction method considering hydrate heterogeneity distribution, and belongs to the technical field of hydrate deposit development by electric heating. BACKGROUND
[0002] Natural gas hydrate is regarded as an important alternative energy source to conventional fossil fuels in the future due to its wide distribution and large reserves. In the hydrate deposit exploitation method, the depressurization method as a depletion type of exploitation method leads to low recovery of hydrate deposits; the thermal stimulation method has low thermal efficiency. As a typical in-situ thermal stimulation method, electric heating places electrodes in different wells, uses well-to-well formation resistivity heat dissipation to provide heat supplement for hydrate decomposition under the action of an alternating current electric field, realizes in-situ heat production of the hydrate layer, avoids the problem of large heat loss in the wellbore of the conventional thermal stimulation method, and thus significantly improves the thermal efficiency. The change of resistivity in the hydrate decomposition process has a great influence on electric heating exploitation. The application provides a hydrate-containing porous medium resistivity model construction method considering hydrate heterogeneity distribution, which provides a simple and efficient method for studying the change rule of resistivity in the hydrate decomposition process. SUMMARY
[0003] In view of the above problems, the application aims to provide a hydrate-containing porous medium resistivity model construction method considering hydrate heterogeneity distribution, which comprises the following steps:
[0004] Step S1: simulate a core according to the rock composition of a target hydrate deposit, and obtain the pore throat structure of the core through CT scanning;
[0005] Step S2: generate hydrates in the core by using the gas excess method, and obtain the hydrate occurrence state through CT scanning;
[0006] Step S3: establish a digital core model based on the pore throat structure and the hydrate occurrence state of the core, and apply a static electric field with specific boundary conditions in a numerical simulation software;
[0007] Step S4: change the hydrate saturation degree parameter in the numerical simulation software, obtain the model current by importing the voltage, and calculate the model resistivity;
[0008] Step S5: calculate the critical water saturation degree of hydrates according to the model resistivity and the digital core model;
[0009] Step S6: take the critical water saturation degree as a boundary, and adopt a power form function to fit the ratio resistivity calculation model before and after the critical water saturation degree.
[0010] In step S1, a suitable core is selected based on the target hydrate reservoir strata parameters, and the basic geological parameters of the core are collected by CT scanning, including pore throat structure and rock porosity.
[0011] In step S2, the gas excess method is used to generate hydrates in the core, and then the hydrate occurrence status is collected by CT scanning, including: hydrate saturation, hydrate occurrence location, hydrate particle morphology, and reservoir permeability.
[0012] In step S3, the electrostatic field is applied using plate electrodes along the longest side of the model. The specific boundary conditions of the electrostatic field are: ① The magnitude of the potential at the left boundary is... ② The boundary potential is 0; ③ The remaining boundaries are insulating boundaries, the normal component of the current density is continuous, and the normal derivative of the potential multiplied by the conductivity is 0.
[0013] In step S4, by changing the hydrate saturation parameter in the numerical simulation software, the model current is obtained by importing voltage under different hydrate saturation conditions, and the model resistivity is calculated. The low-frequency electric heating simulation method is referred to in "Fundamentals of Reservoir Seepage in Marine Natural Gas Hydrate Extraction", edited by Wu Nengyou et al.
[0014] In step S5, as the hydrate gradually decomposes, there exists a critical value for water saturation. When the water saturation is below the critical value, some previously unconnected areas begin to connect. During this process, the connectivity of pores and the pore structure change.
[0015] Let the side length of the porous medium model unit be... The average radius of the rock particles that make up the porous medium is The average side length of the hydrate particles in the CT scan is When the water saturation of the model is at a critical value, the geometric condition is satisfied:
[0016] (1)
[0017] When the water saturation of the model is at a critical value, the expressions for the original porosity and water saturation of the model are as follows:
[0018] (2) (3)
[0019] In the formula The void volume of the model, The total volume of the unit cell. This is the critical value for water saturation.
[0020] In step S6, since the distribution morphology of hydrates changes during hydrate decomposition, a new resistivity calculation model is proposed to improve the fitting accuracy of the calculation model. A power-law function is used on both sides of the critical hydrate saturation value to fit the calculated ratio resistivity value of the model. The model formula is as follows:
[0021] (4)
[0022] In the formula, , , All are undetermined coefficients, and their values are related to the pore structure, hydrate location, and particle shape. The model must satisfy the following:
[0023] Since the distribution morphology of hydrates changes during hydrate decomposition, a new resistivity calculation model is proposed to improve the fitting accuracy of the calculation model. A power-law function is used on both sides of the critical hydrate saturation value to fit the calculated ratio resistivity value. The model formula is as follows:
[0024] (5)
[0025] Based on the resistivity values obtained from simulations at different hydrate water saturation levels, the formula for calculating the ratio resistivity of the model was fitted to obtain... , , The values of the undetermined coefficients are determined to complete the construction of the resistivity model.
[0026] The beneficial effects and advantages of this invention are as follows:
[0027] A microscopic numerical simulation method for resistivity of hydrate-bearing three-dimensional porous media was established. Electric field simulations were conducted to calculate the ratio resistivity of hydrate-bearing porous media with heterogeneous hydrate distribution. The influence of hydrate saturation on the resistivity variation of porous media was investigated, and a new model for calculating the resistivity of hydrate reservoirs was established. Combined with in-situ CT experiments, the undetermined coefficients of the ratio resistivity calculation formula during the thermal decomposition of hydrates in the core were solved through simulation calculations. Attached Figure Description
[0028] Figure 1 This is a flowchart of a method for constructing a resistivity model for porous media containing hydrates, based on the heterogeneous distribution of hydrates.
[0029] Figure 2 This is a schematic diagram of applying an electric field to a porous medium model;
[0030] Figure 3 These are voltage field diagrams at different times during the thermal decomposition of hydrates; Detailed Implementation
[0031] The present invention will be further described below with reference to the accompanying drawings, but this does not limit the scope of the invention.
[0032] like Figure 1 As shown, the present invention proposes a method for constructing a resistivity model for hydrate-containing porous media considering the heterogeneous distribution of hydrates, which includes the following steps:
[0033] Step S1: Based on the rock composition of the target hydrate reservoir, a simulated core is prepared, and the pore throat structure of the core is obtained by CT scanning;
[0034] Step S2: Use the gas excess method to generate hydrates in the core and obtain the hydrate occurrence state by CT scanning;
[0035] Step S3: Based on the core pore throat structure and hydrate occurrence state, establish a digital core model and apply an electrostatic field with specific boundary conditions in the numerical simulation software;
[0036] Step S4: Change the hydrate saturation parameter in the numerical simulation software, obtain the model current by importing voltage, and calculate the model resistivity;
[0037] Step S5: Based on the model resistivity and digital core model, calculate the critical water saturation of hydrates;
[0038] Step S6: Using the critical water saturation level as the boundary, a power-law function is used to fit the ratio resistivity calculation model before and after the critical water saturation level.
[0039] In step S1, a suitable core is selected based on the target hydrate reservoir strata parameters, and the basic geological parameters of the core are collected by CT scanning, including pore throat structure and rock porosity.
[0040] In step S2, the gas excess method is used to generate hydrates in the core, and then CT scanning is used to collect the hydrate occurrence state, hydrate saturation, hydrate particle morphology and reservoir permeability.
[0041] In step S3, a digital core model of a porous medium containing hydrates is established based on the core pore throat structure and hydrate occurrence state obtained from CT scans. Then, the digital core model is substituted into an electrostatic field. The three-dimensional porous medium model uses plate-shaped electrodes, and an electric field is applied along the longest side of the model. The electric field satisfies the following boundary conditions: ① The potential at the left boundary is... ② The boundary potential is 0; ③ The remaining boundaries are insulating boundaries, the normal component of the current density is continuous, and the normal derivative of the potential multiplied by the conductivity is 0.
[0042] In step S4, by changing the hydrate saturation parameter in the numerical simulation software, the model current is obtained by importing voltage under different hydrate saturation conditions, and the model resistivity is calculated; the low-frequency electric heating simulation method is referenced from "Fundamentals of Reservoir Seepage in Marine Natural Gas Hydrate Extraction", edited by Wu Nengyou et al.
[0043] In step S5, as the hydrate gradually decomposes, there exists a critical value for water saturation. When the water saturation is below the critical value, some previously unconnected areas begin to connect. During this process, the connectivity of pores and the pore structure change.
[0044] Let the side length of the porous medium model unit be... The average radius of the rock particles that make up the porous medium is The average side length of the hydrate particles in the CT scan is When the water saturation of the model is at a critical value, the geometric condition is satisfied:
[0045] (1)
[0046] When the water saturation of the model is at a critical value, the expressions for the original porosity and water saturation of the model are as follows:
[0047] (2) (3)
[0048] In the formula Where is the radius of the rock particle. The side length of the hydrate particle. The void volume of the model, The total volume of the unit cell. This is the critical value for water saturation.
[0049] In step S6, since the distribution morphology of hydrates changes during hydrate decomposition, a new resistivity calculation model is proposed to improve the fitting accuracy of the calculation model. A power-law function is used on both sides of the critical hydrate saturation value to fit the calculated ratio resistivity value of the model. The model formula is as follows:
[0050] (4)
[0051] In the formula, , , All are undetermined coefficients, and their values are related to the pore structure, hydrate location, and particle shape. The model must satisfy the following:
[0052] Since the distribution morphology of hydrates changes during hydrate decomposition, a new resistivity calculation model is proposed to improve the fitting accuracy of the calculation model. A power-law function is used on both sides of the critical hydrate saturation value to fit the calculated ratio resistivity value. The model formula is as follows:
[0053] (5)
[0054] Based on the geometric relationship between rock particles and hydrate particles in a porous media unit, and according to the definitions of porosity and hydrate saturation, a formula for critical water saturation is established:
[0055] (6)
[0056] In the formula, This represents the volume of the aqueous phase in the unit cell model under critical conditions. This represents the volume of the hydrate phase in the unit cell model under critical conditions.
[0057] In 3D modeling software, a porous medium unit model is established based on the critical conditions, in which hydrate particles are located at the pore center. The volume of the hydrate under the critical conditions is then calculated using the statistical tools within the 3D modeling software.
[0058] Based on the geometric relationship between hydrate particles and rock particles, the critical geometric conditions of porous media units with different hydrate occurrence locations and particle morphologies are determined. Based on the critical geometric conditions, the relationship between the critical water saturation of different porous media and the initial porosity of the rock is derived.
[0059] CT scan data from the thermal decomposition experiment of hydrates were segmented to delineate rock, hydrates, and porous phases. Based on the phase information after data segmentation, the porous phase was extracted to establish a three-dimensional porous medium model. An electric field was applied to the porous medium model, and numerical simulation of the electric field was conducted. The experimental and simulation results were validated and fitted to obtain the desired results. , , The values of the undetermined coefficients are determined, and the fitting calculation formula is used.
[0060] The following specific embodiments further illustrate the content of the present invention:
[0061] Example
[0062] Assuming the target hydrate reservoir's core sample diameter is 6 mm and its length is 7 mm, natural gas hydrates were generated in the core sample under a pressure of 9 MPa using 99.99% pure methane gas and a 5.0% potassium iodide solution. The porous media model was a uniformly distributed array of spherical particles, with 8×4×4 minimum units distributed within a 2000 μm × 1000 μm × 1000 μm computational domain. The ratio of the radius of each rock particle to the side length of the minimum unit was 0.34. The model's original porosity in the absence of hydrates was calculated. It is 34.15%, roughly the same as the core sample.
[0063] It can be observed that when the water saturation is approximately less than 70%, the simulated core pore data is significantly higher than the grain-covered fitted curve. Using experimental data to fit Equation 5, the fitting calculation formula is:
[0064] (1)
[0065] The above embodiments are only used to illustrate the present invention. Any equivalent transformations and improvements made on the basis of the technical solutions of the present invention should not be excluded from the protection scope of the present invention.
Claims
1. A method for constructing a resistivity model for hydrate-containing porous media considering the heterogeneous distribution of hydrates, characterized in that, Includes the following steps: Step S1: Based on the rock composition of the target hydrate reservoir, a simulated core is prepared, and the pore throat structure of the core is obtained by CT scanning; Step S2: Use the gas excess method to generate hydrates in the core and obtain the hydrate occurrence state by CT scanning; Step S3: Based on the core pore throat structure and hydrate occurrence state, establish a digital core model and apply an electrostatic field with specific boundary conditions in the numerical simulation software; Step S4: Change the hydrate saturation parameter in the numerical simulation software, obtain the model current by importing voltage, and calculate the model resistivity; Step S5: Based on the model resistivity and digital core model, calculate the critical water saturation of hydrates; Step S6: Using the critical water saturation level as the boundary, a power-law function is used to fit the ratio resistivity calculation model before and after the critical water saturation level.
2. The method for constructing a resistivity model for hydrate-containing porous media considering heterogeneous distribution of hydrates as described in claim 1, characterized in that, In step S1, a suitable core is selected based on the rock composition of the target hydrate reservoir, and the basic geological parameters of the core are collected by CT scanning, including pore throat structure and rock porosity.
3. The method for constructing a resistivity model for hydrate-containing porous media considering heterogeneous distribution of hydrates as described in claim 1, characterized in that, In step S2, the gas excess method is used to generate hydrates in the core, and then CT scanning is used to collect the hydrate occurrence state, hydrate saturation, hydrate particle morphology and reservoir permeability.
4. The method for constructing a resistivity model for hydrate-containing porous media considering heterogeneous distribution of hydrates as described in claim 1, characterized in that, In step S3, the electrostatic field is applied using plate electrodes along the longest side of the model. The specific boundary conditions of the electrostatic field are: ① The magnitude of the potential at the left boundary is... ② The boundary potential is 0; ③ The remaining boundaries are insulating boundaries, the normal component of the current density is continuous, and the normal derivative of the potential multiplied by the conductivity is 0.
5. The method for constructing a resistivity model for hydrate-containing porous media considering heterogeneous distribution of hydrates as described in claim 1, characterized in that, In step S4, by changing the hydrate saturation parameter in the numerical simulation software, the model current is obtained by importing voltage under different hydrate saturation conditions, and the model resistivity is calculated; the low-frequency electric heating simulation method is referenced from "Fundamentals of Reservoir Seepage in Marine Natural Gas Hydrate Extraction", edited by Wu Nengyou et al.
6. The method for constructing a resistivity model for hydrate-containing porous media considering heterogeneous distribution of hydrates as described in claim 1, characterized in that, In step S5, as the hydrate gradually decomposes, there exists a critical value for water saturation. When the water saturation is below the critical value, some previously unconnected areas begin to connect. During this process, the connectivity of pores and the pore structure change. Let the side length of the porous medium model unit be... The average radius of the rock particles that make up the porous medium is The average side length of the hydrate particles in the CT scan is When the water saturation of the model is at a critical value, the geometric condition is satisfied: When the water saturation of the model is at a critical value, the expressions for the original porosity and water saturation of the model are as follows: In the formula Where is the radius of the rock particle. The side length of the hydrate particle. The void volume of the model, The total volume of the unit cell. This is the critical value for water saturation.
7. The method for constructing a resistivity model for hydrate-containing porous media considering heterogeneous distribution of hydrates as described in claim 1, characterized in that, In step S6, since the distribution morphology of hydrates changes during hydrate decomposition, a new resistivity calculation model is proposed to improve the fitting accuracy of the calculation model. A power-law function is used on both sides of the critical hydrate saturation value to fit the calculated ratio resistivity value of the model. The model formula is as follows: In the formula, , #imgpt16# are both undetermined coefficients, whose values are related to the pore structure, hydrate location, and particle shape. The model must satisfy the following: Based on the resistivity values obtained from simulation calculations under different hydrate water saturation levels, the formula for calculating the ratio resistivity of the model was fitted to obtain the values of the undetermined coefficients #imgpt18#, #imgpt19#, and #imgpt20#, thus completing the construction of the resistivity model.