Physical property time-varying characterization method and system for loose sandstone gas reservoir

Abstract

The invention belongs to the technical field of gas reservoir numerical simulation, and relates to a physical property time-varying characterization method and system for a loose sandstone gas reservoir, and the method comprises the following steps: determining physical property time-varying sensitive parameters of the loose sandstone gas reservoir; constructing a permeability-gas reservoir pressure equation according to the reservoir physical property time-varying sensitive parameters; and based on the permeability-gas reservoir pressure equation, constructing a reservoir physical property time-varying model of the loose sandstone gas reservoir. The system comprises a determination module, a first building module and a second building module. By applying the physical property time-varying characterization method for the loose sandstone gas reservoir, the historical fitting precision can be improved, the residual gas distribution rule can be accurately known, and the gas reservoir recovery ratio can be accurately predicted, so that the accuracy of development prediction is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of gas reservoir numerical simulation, and in particular relates to a method and system for characterizing time-varying physical properties of loose sandstone gas reservoirs. Background Art

[0002] At present, the numerical models used in numerical simulation software for oil and gas reservoirs generally assume that reservoir parameters do not change during the development of oil and gas reservoirs. In other words, reservoir parameters such as permeability are constant during the entire simulation process, which is inconsistent with the actual development process of oil and gas reservoirs.

[0003] As the development of loose sandstone gas reservoirs progresses, the reservoir pressure decreases, the effective stress increases, and the reservoir properties are more likely to change. The initial reservoir physical parameters can no longer reflect the current gas and water flow characteristics. The early processing method was to use segmented numerical simulation to consider the change of physical properties, such as simulating the change of physical properties by modifying the conductivity of different time steps; however, the data at the segment is discontinuous and the number of segments is limited, so the dynamic indicators at the change point often fluctuate, the reservoir parameters cannot be well described, and complex situations are difficult to consider.

[0004] The time-varying numerical simulation technology of reservoir physical properties takes oil and gas reservoir parameters as reference conditions, adjusts reservoir physical properties multiple times, and truly realizes the dynamic and continuous time-varying of physical properties. It is of great significance to reveal the quantitative distribution characteristics of residual gas in the current underground reservoirs and guide the efficient potential of residual gas.

[0005] Therefore, the present invention uses gas reservoir pressure to characterize the change process of reservoir physical properties for the first time, establishes a numerical model that takes into account the change of reservoir permeability with gas reservoir pressure, and realizes the time-varying numerical simulation study of reservoir physical properties. Summary of the invention

[0006] In view of the complex changes in reservoir physical properties, unclear distribution of remaining gas and great difficulty in tapping potential during the development of loose sandstone gas reservoirs, the present invention proposes a time-varying characterization method for reservoir physical properties of loose sandstone gas reservoirs, which can better and more accurately describe the reservoir physical properties and promote the efficient development and sustained stable production of gas fields.

[0007] The technical solution adopted by the present invention is as follows: a method for characterizing the time-varying physical properties of a loose sandstone gas reservoir, the method comprising the following steps: determining the time-varying sensitive parameters of the physical properties of the loose sandstone gas reservoir; constructing a permeability-gas reservoir pressure equation based on the time-varying sensitive parameters of the reservoir physical properties; and constructing a time-varying model of the physical properties of the loose sandstone gas reservoir based on the permeability-gas reservoir pressure equation.

[0008] Furthermore, the determining of time-varying sensitive parameters of reservoir physical properties of loose sandstone gas reservoirs includes: determining time-varying sensitive parameters of reservoir physical properties of loose sandstone gas reservoirs based on time-varying mechanisms of reservoir physical properties, wherein the time-varying sensitive parameters of reservoir physical properties include pressure, and the pressure includes gas reservoir pressure and overburden pressure.

[0009] Furthermore, the construction of the permeability-gas reservoir pressure equation based on the time-varying sensitive parameters of the reservoir physical properties includes: establishing an empirical equation of the permeability of a loose sandstone gas reservoir and the net overburden pressure through an overburden pressure porosity experiment; and establishing a permeability-gas reservoir pressure equation of a loose sandstone gas reservoir based on the empirical equation of the permeability of a loose sandstone gas reservoir and the net overburden pressure.

[0010] Furthermore, the empirical equation of the permeability and net overburden pressure of the loose sandstone gas reservoir is:

[0011] K=2.9006σ eff -0.867 , where K represents the permeability of loose sandstone gas reservoir, σ eff Represents the net overburden pressure.

[0012] Furthermore, the loose sandstone gas reservoir permeability-gas reservoir pressure equation is:

[0013] Among them, ρ r is the total average density of the overlying sediments; g is the gravitational acceleration; D is the vertical height of the overlying rock layer; Φ is the rock porosity; and p is the gas reservoir pressure.

[0014] Furthermore, based on the permeability-gas reservoir pressure equation, constructing a time-varying model of physical properties of a loose sandstone gas reservoir includes: based on the permeability-gas reservoir pressure equation, constructing a gas-water two-phase mathematical model that takes into account the time-varying physical properties; based on the gas-water two-phase mathematical model that takes into account the time-varying physical properties, constructing a fully implicit numerical model that takes into account the time-varying physical properties.

[0015] Furthermore, the construction of a gas-water two-phase mathematical model taking into account the time-varying physical properties based on the permeability-gas reservoir pressure equation includes: substituting the permeability in the permeability-gas reservoir pressure equation into the basic differential equation of gas-water two-phase seepage of the black oil model, replacing the absolute permeability in the basic differential equation of gas-water two-phase seepage, thereby constructing a new gas-water two-phase mathematical model taking into account the dynamic changes of absolute permeability.

[0016] Furthermore, based on the gas-water two-phase mathematical model taking into account the time-varying physical properties, constructing a fully implicit numerical model taking into account the time-varying physical properties includes: discretizing the gas-water two-phase mathematical model taking into account the time-varying physical properties through a finite difference method, and constructing a fully implicit numerical model taking into account the time-varying physical properties.

[0017] In addition, the present invention also proposes a time-varying characterization system for physical properties of loose sandstone gas reservoirs, the system comprising a determination module, a first construction module and a second construction module; wherein the determination module is used to determine the time-varying sensitive parameters of the physical properties of the loose sandstone gas reservoirs; the first construction module is used to construct a permeability-gas reservoir pressure equation based on the time-varying sensitive parameters of the reservoir physical properties; and the second construction module is used to construct a time-varying model of physical properties of loose sandstone gas reservoirs based on the permeability-gas reservoir pressure equation.

[0018] Furthermore, the second construction module is used to construct a time-varying model of physical properties of a loose sandstone gas reservoir based on the permeability-gas reservoir pressure equation, including: the second construction module is used to construct a gas-water two-phase mathematical model that considers the time-varying physical properties based on the permeability-gas reservoir pressure equation; the second construction module is also used to construct a fully implicit numerical model that considers the time-varying physical properties based on the gas-water two-phase mathematical model that considers the time-varying physical properties.

[0019] The present invention targets loose sandstone gas reservoirs, uses gas reservoir pressure to characterize the process of reservoir physical property changes, establishes a numerical model that considers the change of reservoir permeability with gas reservoir pressure, and realizes gas reservoir numerical simulation research that considers time-varying physical properties based on existing commercial numerical simulation software. Using a loose sandstone gas reservoir reservoir physical property time-varying characterization method proposed by the present invention can improve the accuracy of historical matching, accurately understand the distribution law of remaining gas, accurately predict the gas reservoir recovery rate, and thus improve the accuracy of development prediction.

[0020] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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 description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 Schematic diagram of a method for characterizing time-varying physical properties of a loose sandstone gas reservoir in an embodiment of the present invention;

[0023] Figure 2 Schematic diagram of net overburden pressure in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the overburden permeability test results;

[0025] Figure 4 This is the near east-west permeability model section of the TN gas field in the Qaidam Basin;

[0026] Figure 5 This is a plan view of the permeability distribution of four typical sand bodies in the TN gas field in the Qaidam Basin;

[0027] Figure 6 This is a comparison chart of the adjacent permeability of t4-14 and t4-69;

[0028] Figure 7 This is a schematic diagram of the well test results of well t2-5 at different periods;

[0029] Figure 8a This is a schematic diagram of the historical fitting effect of the conventional model of the TN gas field in the Qaidam Basin. Figure 8b This is a schematic diagram of the historical fitting effect of the time-varying model of reservoir physical properties of the loose sandstone gas reservoir in the TN gas field in the Qaidam Basin;

[0030] Fig. 9 The cumulative gas production comparison curves of the conventional model and the time-varying model of reservoir physical properties of loose sandstone gas reservoirs in the Qaidam Basin are shown in Figure 1.

[0031] Fig.10 Schematic diagram of a system for characterizing time-varying physical properties of a loose sandstone gas reservoir in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are 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 are within the scope of protection of the present invention.

[0033] The present invention proposes a method for characterizing the time-varying physical properties of loose sandstone gas reservoirs, which makes the physical properties of loose sandstone gas reservoirs closer to the actual development of gas reservoirs. Figure 1 As shown, the method includes the following steps: determining the time-varying sensitive parameters of the physical properties of the loose sandstone gas reservoir; constructing a permeability-gas reservoir pressure equation according to the time-varying sensitive parameters of the physical properties of the reservoir; and constructing a time-varying model of the physical properties of the loose sandstone gas reservoir based on the permeability-gas reservoir pressure equation.

[0034] Specifically, for loose sandstone, the permeability of the reservoir is not constant as the development proceeds, but it is easy to develop and change. However, in conventional numerical simulations, it is generally believed that the parameters of the reservoir are fixed values, which is inconsistent with the actual development of gas reservoirs. The difficulty in characterizing the time-varying physical properties of the reservoir is to find a sensitive parameter, and to characterize the change of the physical properties of the reservoir by changing the parameter with the development process of the gas reservoir. For different types of gas reservoirs, this sensitive parameter is also different. The present invention determines the time-varying sensitive parameters of the physical properties of the loose sandstone gas reservoir by analyzing the time-varying mechanism of the reservoir physical properties. From the perspective of microscopic mechanism, the core of the loose sandstone is loose, the diagenetic compaction effect is weak, the primary pores between the particles are developed, and the point contact between the particles is mainly. The microscopic characteristics of the rock under this microscope determine that the macroscopic reservoir is very easy to deform under the action of external forces, causing the physical properties of the reservoir to change. From the perspective of macroscopic mechanism, the physical properties of the loose sandstone reservoir are good, mainly high porosity and high permeability, and the high porosity and high permeability reservoir is the stratum basis for the time-varying physical properties. In addition, the change of overburden pressure has a great influence on the porosity and permeability of loose sandstone, especially in the later stage of development of such gas fields, due to the decrease of gas reservoir pressure, the increase of overburden pressure will cause the reservoir permeability to decrease significantly, which will have a certain impact on the gas well production capacity. Therefore, for loose sandstone gas reservoirs, pressure is a sensitive parameter of reservoir physical properties.

[0035] After determining that pressure is a time-varying sensitive parameter of the physical properties of loose sandstone gas reservoirs, the relationship equation between permeability and overburden pressure was obtained through overburden pressure porosity experiment, and then the relationship equation between permeability and gas reservoir pressure was proposed through formula deduction.

[0036] like Figure 2 As shown in the figure, during the development of gas reservoirs, as the formation pressure decreases, the net overburden pressure on the reservoir rocks increases. Since the reservoir rocks of loose sandstone gas reservoirs are loose, the change in net overburden pressure compacts the rocks, causing large deformation of the rocks, resulting in a decrease in the porosity and permeability of the reservoir rocks, and an increase in water saturation. The relative permeability of the two phases changes unfavorably to gas seepage, affecting the production capacity of the gas reservoir. The calculation formula for net overburden pressure is: The calculation formula of overburden pressure is: σ=ρ r gD; where: σ eff is the net overburden pressure, in MPa; σ is the overburden formation pressure, in MPa; p is the reservoir pressure, in MPa; Φ is the porosity of the rock, in f; D is the vertical height of the overburden, in m; ρ r is the total average density of the overlying sediments, in kg / m 3 ; g is the acceleration due to gravity, in m / s 2 .

[0037] Taking the core of loose sandstone gas reservoir as the research object, the AP-608 core automatic analyzer (Coretest, USA) was used to conduct overburden pressure porosity and permeability experiments. By analyzing the experimental data of permeability under different net overburden pressures, the relationship between the permeability of loose sandstone gas reservoir and the net overburden pressure - logarithmic function relationship was determined, and the empirical formula between the permeability and net overburden pressure of loose sandstone gas reservoir was established. The establishment of the relationship between the reservoir permeability and net overburden pressure of loose sandstone gas reservoir is of great significance for the numerical simulation of loose sandstone gas reservoir.

[0038] Figure 3 The figure shows the relationship between the residual change rate of permeability and the overburden pressure. Figure 3 1-2-5, 2-1-5, etc. indicate the core sample numbers. In general, pressure has a great influence on permeability. Permeability decreases with the increase of net overburden pressure. In the low-pressure stage, i.e., the initial stage of the increase of net overburden pressure, the slope of the relationship curve is quite large, and the permeability decreases rapidly with pressure. In the later stage, after about 10MPa, the amplitude of the permeability decrease gradually decreases, and finally tends to be flat. The amplitude of the permeability decrease is related to many factors such as the pore structure and mud content of the rock, and the degree of development of microfractures. In the early stage of the increase of net overburden pressure, the throat and larger pores of the core are first compressed and deformed, causing a significant decrease in the permeability of the reservoir and a large loss of permeability; in the later stage of the increase of net overburden pressure, after the core is compressed to a certain extent, most of the remaining throats are not easy to close, and the small pores are also slightly compressed and deformed, so the permeability loss is sharply reduced.

[0039] From the experimental test results, the relationship between the permeability and the net overburden pressure of the sample is the most accurate when fitted by exponential fitting, and the correlation coefficient is as high as 0.99. Therefore, the exponential relationship can better describe the relationship between the permeability and the net overburden pressure, and the permeability and net overburden pressure equation is established as: K = 2.9006σ eff -0.867 , where K represents the permeability of loose sandstone gas reservoir, σ eff Represents the net overburden pressure. Combining the calculation formula of the net overburden pressure with the calculation formula of the overburden formation pressure, and substituting it into the permeability and net overburden pressure equation, the equation for the change of permeability with gas reservoir pressure can be obtained:

[0040] Specifically, the time-varying mathematical model of reservoir physical properties uses gas reservoir pressure to characterize the time-varying law of permeability parameters, and introduces it into the conventional black oil model to establish a new three-dimensional gas-water two-phase mathematical model. The difference between the two is that the new three-dimensional gas-water two-phase mathematical model can consider the dynamic changes of absolute permeability. The time-varying mathematical model of reservoir physical properties is derived from the transformation of the conventional black oil model so that it can reflect the changes in permeability with gas reservoir pressure. The basic assumptions, auxiliary equations and solution conditions of the new three-dimensional gas-water two-phase mathematical model are the same as those of the traditional black oil model, while the basic differential equations of the gas-water two-phase have changed, as shown in the following equation:

[0041] Basic differential equation of gas phase flow:

[0042] Basic differential equation for water seepage:

[0043] Where K(p) is the absolute permeability of the gas reservoir, in μm 2 ; K rg , K rw are the relative permeabilities of gas and water phases, respectively; B g , B w are the volume coefficients of gas and water phases, respectively; μ g , μ w are the viscosities of the gas and water phases, respectively, in mPa·s; p g , p w are respectively the air and water pressures, in MPa; ρ g , ρ w are the densities of the gas and water phases, respectively, in kg / m 3 ;q vg ,q vw are the volumes of gas and water produced or injected per unit time under standard conditions, in m 3 / s;S g , S w are gas and water phase saturations, respectively;

[0044] In the traditional black oil model, the absolute permeability K is a constant. The permeability K(p) in the permeability-gas reservoir pressure equation is substituted into the basic differential equation of gas phase seepage and the basic differential equation of water phase seepage to replace the absolute permeability K in the traditional black oil model for solution.

[0045] Since the relationship between the permeability, capillary force and saturation of gas reservoirs is nonlinear, the basic differential equations for gas phase seepage and water phase seepage cannot be solved analytically. The unknown quantities in the above basic differential equations for gas phase seepage and water phase seepage are the pressure and saturation of the fluid. When calculating, the differential equations must first be discretized to establish a system of equations, and then solved. The most widely used discretization method at present is the finite difference method, which uses the finite difference method to discretize the previous time-varying mathematical model of physical properties and establish a fully implicit numerical model. The IMPES (Implicit Pressure Explicit Saturation) method has good stability and minimal computational workload. Therefore, the numerical simulation of loose sandstone gas reservoirs first considers using the IMPES method to solve the equations, and uses the difference method to establish a numerical calculation module for calculation.

[0046] Finally, by writing statements and embedding the software, a numerical simulation study of gas reservoirs considering the time-varying physical properties was conducted, and the historical fitting effects of the conventional model and the time-varying model of the physical properties of loose sandstone gas reservoirs were compared. Specifically, the preliminary model was established using the international general commercial numerical simulation software tnavigator, and the permeability-gas reservoir pressure equation was embedded in the schedule module by adding keywords. First, the pressure and saturation of each grid were calculated, and the permeability of each grid was updated according to the time-varying law of permeability. In order to prevent the permeability from being infinitely amplified, the initial permeability can be called in each step to participate in the time-varying calculation instead of the permeability of the previous step. On this basis, the upper limit of the permeability should also be set to prevent the permeability from being greater than the theoretical range. Finally, the calculation results can be viewed using the tnavigator software, and the three-dimensional distribution of data such as gas saturation and pressure, as well as the gas production and pressure curves of the block and single well can be viewed.

[0047] In order to study the impact of the time-varying law of reservoir physical properties on gas reservoir development, the law of permeability changing with gas reservoir pressure was added to commercial software for simulation. In the embodiment of the present invention, a typical work area of ​​loose sandstone in the Qaidam Basin was selected to verify the effect of the present invention. The reservoir of the TN gas field in the Qaidam Basin is shallowly buried (833-1740.7m), the rock is under-compacted, the diagenesis is poor, the degree of cementation is poor, the lithology is loose, the mud content is high, and the heterogeneity is strong. The porosity of the TN gas field has a maximum porosity of 45.45%, a minimum porosity of 6.8%, and an average porosity of 31.68%. Figure 4 and Figure 5 As shown in the figure, the maximum permeability of the TN gas field is 3787mD, the minimum permeability is 1mD, and the average permeability is 19.41mD. The permeability is mainly distributed between 10 and 100mD, accounting for 41.6% of the total number of analyzed samples, followed by 0 to 10mD, accounting for 37.8% of the total number of analyzed samples, and samples greater than 100mD account for 20.6% of the total number.

[0048] Using the existing drilling data, logging data and well test data, statistically compare and analyze the physical property data at different development stages to study the overall change law of reservoir physical properties. In the late development period, the permeability of the TN gas reservoir decreased by an average of 38%, and the gas phase permeability decreased by 55%. Wells with similar distances were selected for inter-well comparison. T4-69 and T4-14 are two adjacent wells, 100m apart. Figure 6 The well logging curves shown show that the permeability of the new well t4-69 is lower than that of the old well t4-14. Figure 7 ), the well test permeability of t2-5 well was 62.1mD in 2014, and the well test permeability in 2018 was 18.3mD, a decrease of 71% compared with 2014. The formation pressure of t2-5 well was 9.9Mpa in 2014, and the formation pressure in 2018 was 7Mpa, a decrease of 29% compared with 2014.

[0049] The conventional model and time-varying model of the loose sandstone gas reservoir in the TN gas field were established, and the historical fitting effects and cumulative gas production of the two models were compared; Figure 8a and Figure 8b As shown in Figure 2, compared with the conventional model, the historical matching effect is better after considering the time-varying reservoir properties, and the accuracy is improved by more than 10%. Fig. 9 The cumulative gas production curves of the conventional model and the case where the permeability is time-varying are shown. For loose sandstone gas reservoirs, the cumulative gas production predicted by the numerical model considering the time-varying physical properties is lower than that of the conventional model. Compared with the conventional model, the cumulative gas production of the model considering the time-varying permeability is reduced by 37%. This is because after considering the time-varying physical properties, the gas reservoir pressure decreases with the progress of mining, the reservoir physical properties deteriorate, and the production decreases. Therefore, by using the time-varying reservoir physical properties, we can accurately understand the distribution law of the remaining gas and accurately predict the gas reservoir recovery rate, thereby improving the accuracy of development prediction.

[0050] In addition, the present invention also proposes a time-varying characterization system for the physical properties of loose sandstone gas reservoirs, such as Fig.10 As shown, the system includes: a determination module, a first construction module and a second construction module; wherein the determination module is used to determine the time-varying sensitive parameters of the physical properties of the loose sandstone gas reservoir; the first construction module is used to construct a permeability-gas reservoir pressure equation according to the time-varying sensitive parameters of the reservoir physical properties; the second construction module is used to construct a time-varying model of the physical properties of the loose sandstone gas reservoir based on the permeability-gas reservoir pressure equation.

[0051] Furthermore, the second construction module is used to construct a time-varying model of physical properties of a loose sandstone gas reservoir based on the permeability-gas reservoir pressure equation, including: the second construction module is used to construct a gas-water two-phase mathematical model that considers the time-varying physical properties based on the permeability-gas reservoir pressure equation; the second construction module is also used to construct a fully implicit numerical model that considers the time-varying physical properties based on the gas-water two-phase mathematical model that considers the time-varying physical properties.

[0052] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for characterizing the time-varying physical properties of loose sandstone gas reservoirs, characterized in that: The method comprises the following steps: Determine the time-varying sensitive parameters of reservoir physical properties in unconsolidated sandstone gas reservoirs; Constructing a permeability-gas reservoir pressure equation according to the time-varying sensitive parameters of the reservoir physical properties; Based on the permeability-gas reservoir pressure equation, a time-varying model of reservoir physical properties of unconsolidated sandstone gas reservoirs is constructed.

2. The method according to claim 1, characterized in that The determination of the time-varying sensitive parameters of the physical properties of the loose sandstone gas reservoir includes: Based on the time-varying mechanism of reservoir physical properties, time-varying sensitive parameters of reservoir physical properties of unconsolidated sandstone gas reservoir are determined. The time-varying sensitive parameters of reservoir physical properties include pressure, and the pressure includes gas reservoir pressure and overburden pressure.

3. The method according to claim 2, characterized in that The construction of the permeability-gas reservoir pressure equation according to the time-varying sensitive parameters of the reservoir physical properties includes: An empirical equation of permeability and net overburden pressure of loose sandstone gas reservoirs was established through overburden pressure porosity test. According to the empirical equation of the loose sandstone gas reservoir permeability and the net overburden pressure, a loose sandstone gas reservoir permeability-gas reservoir pressure equation is established.

4. The method according to claim 3, characterized in that The empirical equation of the permeability and net overburden pressure of the loose sandstone gas reservoir is: X=2.9006σ eff -0.867 , where K represents the permeability of loose sandstone gas reservoir, σ eff Represents the net overburden pressure.

5. The method according to claim 4, characterized in that The loose sandstone gas reservoir permeability-gas reservoir pressure equation is: Among them, ρ r is the total average density of the overlying sediments; g is the gravitational acceleration; D is the vertical height of the overlying rock layer; Φ is the rock porosity; and p is the gas reservoir pressure.

6. The method according to any one of claims 2 to 5, characterized in that: The method of constructing a time-varying model of reservoir physical properties of a loose sandstone gas reservoir based on the permeability-gas reservoir pressure equation includes: Based on the permeability-gas reservoir pressure equation, a gas-water two-phase mathematical model considering the time-varying physical properties is constructed; Based on the gas-water two-phase mathematical model taking into account the time-varying physical properties, a fully implicit numerical model taking into account the time-varying physical properties is constructed.

7. The method according to claim 6, characterized in that The construction of a gas-water two-phase mathematical model taking into account the time-varying physical properties based on the permeability-gas reservoir pressure equation includes: The permeability in the permeability-gas reservoir pressure equation is substituted into the basic differential equation of gas-water two-phase flow of the black oil model to replace the absolute permeability in the basic differential equation of gas-water two-phase flow, thereby constructing a new gas-water two-phase mathematical model that takes into account the dynamic change of absolute permeability.

8. The method according to claim 7, characterized in that The method of constructing a fully implicit numerical model taking into account the time-varying physical properties based on the gas-water two-phase mathematical model taking into account the time-varying physical properties includes: The gas-water two-phase mathematical model considering the time-varying physical properties is discretized by the finite difference method, and a fully implicit numerical model considering the time-varying physical properties is constructed.

9. A time-varying characterization system for physical properties of loose sandstone gas reservoirs, characterized in that: The system comprises: a determination module, a first construction module and a second construction module; wherein, The determination module is used to determine the time-varying sensitive parameters of the physical properties of the loose sandstone gas reservoir; The first construction module is used to construct a permeability-gas reservoir pressure equation according to the time-varying sensitive parameters of the reservoir physical properties; The second construction module is used to construct a time-varying model of reservoir physical properties of a loose sandstone gas reservoir based on the permeability-gas reservoir pressure equation.

10. The system according to claim 9, characterized in that The second construction module is used to construct a time-varying model of reservoir physical properties of a loose sandstone gas reservoir based on the permeability-gas reservoir pressure equation, including: The second construction module is used to construct a gas-water two-phase mathematical model taking into account the time-varying physical properties based on the permeability-gas reservoir pressure equation; The second construction module is also used to construct a fully implicit numerical model that takes into account the time-varying physical properties based on the gas-water two-phase mathematical model that takes into account the time-varying physical properties.

Images