Evaluation method for gas-water two-phase micro seepage in compact low-permeability gas reservoir

Abstract

This invention discloses a method for evaluating the microscopic seepage of gas and water two-phase flow in tight, low-permeability gas reservoirs. The method includes: obtaining the basic characteristics of the pore-throat structure of multiple reservoir types; creating a corresponding pore-throat structure schematic diagram for each reservoir type based on its basic characteristics; establishing a corresponding pore-throat structure model for each reservoir type based on its schematic diagram; conducting saturated water experiments, gas-driven water experiments, and water-driven gas experiments sequentially on the pore-throat structure model for each reservoir type; and establishing a porous media model based on multiple experimental results to obtain the flow rate per unit time and flow resistance of the pore-throat size. This invention can realistically and intuitively describe the specific transport mechanism of gas and water two-phase fluids in complex pore-throat structures and the final distribution state of gas and water after transport. It solves the current problem of the disconnect between theoretical and experimental research in microscopic seepage, and the inability of microscopic model gas-water two-phase research to explore the deeper gas-water seepage mechanism in tight, low-permeability gas reservoirs.

Description

Technical Field

[0001] This invention belongs to the technical field of gas injection enhanced oil recovery simulation methods, specifically relating to a method for evaluating the two-phase micro-permeability flow of gas and water in tight, low-permeability gas reservoirs. Background Technology

[0002] Extensive exploration and development practices and research findings indicate that the complex seepage characteristics of tight sandstone gas reservoirs are a major factor affecting gas well productivity and development, while the microscopic pore-throat structure of the reservoir rock is key to influencing oil and gas accumulation and seepage capacity. In recent years, research on the pore-throat structure and gas-water seepage characteristics of tight sandstone reservoirs has been a focus of attention for many scholars. Scholars such as Gao Wanglai believe that the seepage characteristics of fluids in tight sandstone reservoirs are controlled by multiple factors, including physical properties, pore-throat structure, and water saturation. When analyzing the reservoir seepage mechanism, the influence of pore-throat structure and fluid on its effects should be comprehensively considered. Scholars such as Xu Guosheng believe that the seepage characteristics of tight sandstone reservoirs are controlled by multiple factors, including physical properties, pore-throat structure, and reservoir water saturation, with pore-throat structure and diverse pore-throat types significantly affecting reservoir permeability. Subsequently, scholars such as Fu Xiaoyan applied a real sandstone microscopic model to study the seepage characteristics of low-permeability oil layers, proposing that the heterogeneity and wettability characteristics of the reservoir pore-throat structure are the main factors affecting seepage characteristics. However, overall, current microscopic model studies of gas and water two-phase flow only describe experimental phenomena and do not effectively combine the differences in pore-throat structure to analyze its seepage characteristics. These studies have failed to integrate the study of complex pore-throat structure in reservoirs with actual microscopic displacement models. They also fail to realistically and intuitively describe the specific transport mechanisms of gas and water two-phase fluids in complex pore-throat structures, as well as the final distribution state of gas and water after transport.

[0003] Therefore, there is a particular need for an evaluation method that can accurately and intuitively describe the specific transport mechanism of gas and water two-phase fluids in complex pore throat structures, as well as the final distribution state of gas and water after transport. Summary of the Invention

[0004] The purpose of this invention is to propose a method for evaluating the microscopic seepage of gas and water two-phase flow in tight, low-permeability gas reservoirs that can realistically and intuitively describe the specific migration mechanism of gas and water two-phase fluids in complex pore throat structures and the final distribution state of gas and water after migration.

[0005] This invention provides a method for evaluating the microscopic seepage of gas and water two-phase flow in tight, low-permeability gas reservoirs, comprising: obtaining the basic characteristics of the pore-throat structure of multiple types of reservoirs based on rock samples; for each type of reservoir, creating a corresponding pore-throat structure schematic diagram based on its basic characteristics; for each type of reservoir, establishing a corresponding pore-throat structure model based on its corresponding pore-throat structure schematic diagram; sequentially performing saturated water experiments, gas-driven water experiments, and water-driven gas experiments on the pore-throat structure model corresponding to each type of reservoir, and establishing a porous media model based on the multiple experimental results corresponding to multiple types of reservoirs; and obtaining the flow rate per unit time and flow resistance of the pore-throat size based on the porous media model.

[0006] Optionally, the basic characteristics of the pore-throat structure of multiple reservoir types are obtained according to the following steps: Obtain the experimental results of conventional mercury injection testing of the rock samples to determine the displacement pressure, median saturation pressure, and bound water saturation; based on the displacement pressure, median saturation pressure, and bound water saturation, determine the distribution frequency of different pore-throat radii of rock samples with different permeability and the percentage of pore volume controlled by different pore-throat radii of rock samples with different permeability; perform nuclear magnetic resonance (NMR) experiments on the rock samples to obtain NMR T2 spectra after centrifugation at different speeds; combining the porosity, permeability, distribution frequency of different pore-throat radii of rock samples with different permeability, percentage of pore volume controlled by different pore-throat radii of rock samples with different permeability, and NMR T2 spectra of the rock samples, classify the reservoirs of the rock samples and determine the basic characteristics of the pore-throat structure of each type of reservoir.

[0007] Optionally, the basic characteristics of the pore throat structure include the core throat and pore size. Determining the basic characteristics of the pore throat structure for each type of reservoir includes: obtaining the capillary radius distribution based on mercury intrusion porosimetry data; obtaining the average core throat radius of each type of reservoir based on the capillary radius distribution; and measuring the average pore radius of each type of reservoir based on thin section data analysis.

[0008] Optionally, the step of establishing a corresponding pore-throat structure model for each type of reservoir based on its corresponding pore-throat structure schematic diagram includes: based on the pore-throat structure schematic diagram corresponding to each type of reservoir, using a photochemical etching process to photolithographically print the basic features of the pore-throat structure onto a planar glass, and then subjecting the photolithographically printed planar glass to high-temperature firing to obtain the pore-throat structure model corresponding to the reservoir.

[0009] Optionally, based on multiple experimental results corresponding to multiple types of reservoirs, a porous medium model is established, including: based on multiple experimental results of pore throat structure models corresponding to multiple types of reservoirs, and according to the basic characteristics of the pore throat structure and the core saturation determined according to the resonance T2 spectrum, an abstract gas-water distribution model is derived; and a porous medium model is established based on the gas-water distribution model.

[0010] Optionally, the porous media model includes a total flow rate model and a total flow resistance model for all micro-pores and throats. The step of establishing the porous media model based on the gas-water distribution model includes: establishing a mathematical model of the total flow resistance and a mathematical model of the total flow pressure difference in a single micro-pore and throat based on the gas-water distribution model; and establishing a total flow rate model and a total flow resistance model for all micro-pores and throats based on the mathematical models of the total flow resistance and the total flow pressure difference in a single micro-pore and throat, respectively.

[0011] Optionally, the total flow rate model in all microscopic pore throats is:

[0012]

[0013] in, For flow rate; This represents the total flow resistance. This refers to the injection end pressure; The pressure at the production end is denoted by n; the number of throats is denoted by m; and the number of pores is denoted by m. For interfacial tension; The viscosity of water; For gas viscosity; The length of the capillary tube; Where is the pore radius; The radius of the throat; Water saturation; denoted as the number of discrete segments of the discontinuous gas phase; i represents the i-th segment of the discontinuous gas phase. To approximate the air-water contact angle in the throat; To keep away from the air-water contact angle in the throat.

[0014] Optionally, a mathematical model of the total flow resistance in the single micro-throat can be established based on the Hagen-Poiseuille equation.

[0015] Optionally, the total flow resistance model in all the micro-holes and throats is:

[0016] in, This represents the total flow resistance. For interfacial tension; The viscosity of water; For gas viscosity; For flow rate; The length of the capillary tube; Where is the pore radius; The radius of the throat; Water saturation; denoted as the number of discrete segments of the discontinuous gas phase; i represents the i-th segment of the discontinuous gas phase. To approximate the air-water contact angle in the throat; To keep away from the air-water contact angle in the throat.

[0017] The beneficial effects of this invention are as follows: The microscopic seepage evaluation method for gas-water two-phase flow in tight, low-permeability gas reservoirs is combined with the study of complex pore-throat structures in the reservoirs to obtain pore-throat structure models corresponding to each type of reservoir. Saturated water experiments, gas-driven water experiments, and water-driven gas experiments are conducted sequentially on the pore-throat structure models corresponding to each type of reservoir. Based on the results of multiple experiments, a porous medium model of the microscopic gas-water distribution law is established to evaluate the unit time flow rate and flow resistance of different pore-throat sizes. The gas-water seepage mechanism in tight, low-permeability gas reservoirs and its impact on development are explored. This method can realistically and intuitively describe the specific migration mechanism of gas and water two-phase fluids in complex pore-throat structures and the final distribution state of gas and water after migration. It solves the problem that current microscopic seepage research is disconnected from theoretical and experimental research, and that the study of gas-water two-phase flow in microscopic models is only a simple description of experiments and experimental phenomena, which cannot explore the in-depth study of the gas-water seepage mechanism in tight, low-permeability gas reservoirs.

[0018] The present invention has other features and advantages that will be apparent from or will be set forth in detail in the accompanying drawings and following detailed description, which together serve to explain the particular principles of the invention. Attached Figure Description

[0019] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0020] Figure 1 A flowchart of a method for evaluating the two-phase micro-permeability flow of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention is shown.

[0021] Figure 2 A porosity component data diagram is shown for a method for evaluating the two-phase micro-permeability of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention.

[0022] Figure 3 The diagram illustrates the pore throat volume controlled by the throat radius in a method for evaluating the microscopic seepage of gas-water two-phase flow in a tight, low-permeability gas reservoir according to an embodiment of the present invention.

[0023] Figure 4 A schematic diagram of the reservoir pore throat structure is shown in a method for evaluating the two-phase micro-permeability of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention.

[0024] Figure 5 A reservoir-corridor pore throat structure model is shown as an example of a method for evaluating the two-phase micro-permeability of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention.

[0025] Figure 6 The experimental results of the pore throat structure model corresponding to the reservoir are shown in a method for evaluating the two-phase micro-permeability of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention.

[0026] Figure 7 An abstract model of gas-water two-phase flow in the pore throat is shown as an evaluation method for gas-water two-phase micro-flow in a tight, low-permeability gas reservoir according to an embodiment of the present invention.

[0027] Figure 8 The diagram illustrates a discontinuous gas phase discretization of an abstract model of gas-water two-phase flow in a pore throat, according to an embodiment of the present invention, for evaluating the gas-water two-phase micro-flow in a tight, low-permeability gas reservoir.

[0028] Figure 9 A diagram illustrating the specific configuration relationship between pore throats in a tight, low-permeability gas reservoir using a gas-water two-phase micro-permeability evaluation method according to an embodiment of the present invention is shown.

[0029] Figure 10 The diagram shows a comparison of the flow resistance of the gas phase and the gas-water two-phase flow under different throat radii in a microscopic seepage evaluation method for a tight, low-permeability gas reservoir according to an embodiment of the present invention.

[0030] Figure 11 The diagram illustrates a comparison of flow resistance and instantaneous velocity in the gas-water two-phase flow of a tight, low-permeability gas reservoir according to an embodiment of the present invention, showing a method for evaluating gas-water two-phase micro-flow at different throat radii. Detailed Implementation

[0031] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0032] This invention provides a method for evaluating the microscopic seepage of gas and water in tight, low-permeability gas reservoirs, comprising: obtaining the basic characteristics of the pore-throat structure of multiple types of reservoirs based on rock samples; creating a corresponding pore-throat structure schematic diagram for each type of reservoir based on its basic characteristics; establishing a corresponding pore-throat structure model for each type of reservoir based on its corresponding pore-throat structure schematic diagram; sequentially conducting saturated water experiments, gas-driven water experiments, and water-driven gas experiments on the pore-throat structure model corresponding to each type of reservoir, and establishing a porous media model based on the multiple experimental results corresponding to multiple types of reservoirs; and obtaining the flow rate per unit time and flow resistance of the pore-throat size based on the porous media model.

[0033] Specifically, the pore-throat structure of core samples from the study area was evaluated. Based on the characteristics of mercury intrusion porosimetry (MIP) curves for porosity Φ, permeability K, displacement pressure, and median pressure, combined with NMR experiments, reservoir parameters were classified into four categories. The basic characteristics of the pore-throat structure for each category were summarized, and schematic diagrams of the pore-throat structure for each category were created. These diagrams were then precisely photolithographically printed onto flat glass, and high-temperature firing was used to fabricate corresponding pore-throat structure models for each category. Three experiments were conducted on each pore-throat structure model: saturated water, gas-driven water (simulated reservoir formation), and water-driven gas (simulated development). Based on the experimental results of all pore-throat structure models, a gas-water distribution model was abstracted, and a porous medium model describing the microscopic gas-water distribution was established. Using this porous medium model, the flow rate per unit time and flow resistance for different pore-throat sizes were calculated.

[0034] According to an exemplary implementation, the microscopic seepage evaluation method for gas-water two-phase flow in tight, low-permeability gas reservoirs combines the research results of complex pore-throat structures and microscopic visualization displacement models to establish a porous medium model of microscopic gas-water distribution patterns. It evaluates the flow rate per unit time and flow resistance for different pore-throat sizes, explores the gas-water seepage mechanism in tight, low-permeability gas reservoirs and its impact on development, and can realistically and intuitively describe the specific migration mechanism of gas and water two-phase fluids in complex pore-throat structures, as well as the final distribution state of gas and water after migration. This solves the current problem of the disconnect between theoretical and experimental research in microscopic seepage, where microscopic model gas-water two-phase research is merely a simple description of experiments and phenomena, failing to uncover the deeper mechanisms of gas-water seepage in tight, low-permeability gas reservoirs.

[0035] As an optional approach, the basic characteristics of the pore-throat structure of multiple reservoir types are obtained according to the following steps: Obtain the experimental results of conventional mercury injection testing of rock samples to determine the displacement pressure, median saturation pressure, and bound water saturation; based on the displacement pressure, median saturation pressure, and bound water saturation, determine the distribution frequency of different pore-throat radii for rock samples with different permeability and the percentage of pore volume controlled by different pore-throat radii for rock samples with different permeability; perform nuclear magnetic resonance (NMR) experiments on the rock samples to obtain NMR T2 spectra after centrifugation at different speeds; combining the porosity, permeability, distribution frequency of different pore-throat radii for rock samples with different permeability, percentage of pore volume controlled by different pore-throat radii for rock samples with different permeability, and NMR T2 spectra of the rock samples, classify the rock samples into reservoir types and determine the basic characteristics of the pore-throat structure for each type of reservoir.

[0036] Specifically, firstly, based on conventional mercury intrusion porosimetry (MIP) experimental data, the experimental results of conventional MIP sample testing were compiled and calculated to determine the distribution frequency of different pore throat radii in rock samples with different permeabilities. Based on the distribution frequency of different pore throat radii in rock samples with different permeabilities, the percentage of pore volume controlled by different pore throat radii in different permeabilities was determined. Nuclear magnetic resonance (NMR) T2 spectra measured after centrifugation at different speeds (or after displacement) were obtained, and the water saturation of the core under different conditions was calculated to evaluate the mobile water saturation and bound water saturation of rock samples with different permeabilities. Combining the porosity Φ and permeability K of the rock samples, the distribution frequency of different pore throat radii in rock samples with different permeabilities obtained from conventional MIP experimental data, and the percentage of pore volume controlled by different pore throat radii in rock samples with different permeabilities, and combining the NMR T2 spectra, the reservoir parameters were classified into four categories.

[0037] As an optional approach, the basic characteristics of pore throat structure include core throat and pore size. Determining the basic characteristics of pore throat structure for each type of reservoir includes: obtaining capillary radius distribution based on mercury intrusion porosimetry data; obtaining the average core throat radius of each type of reservoir based on capillary radius distribution; and measuring the average pore radius of each type of reservoir based on thin section data analysis.

[0038] Specifically, the average throat radius of the reservoir core is obtained from the capillary radius distribution obtained from the mercury intrusion porosimetry data; the average pore radius can be measured from the analysis of the collected thin section data.

[0039] As an optional approach, for each type of reservoir, a corresponding pore-throat structure model is established based on its corresponding pore-throat structure schematic diagram. This includes: based on the pore-throat structure schematic diagram corresponding to each type of reservoir, using photochemical etching process, photolithographically imprinting the basic features of the pore-throat structure onto a planar glass, and then firing the photolithographically imprinted planar glass at high temperature to obtain the pore-throat structure model corresponding to the reservoir.

[0040] Specifically, four types of pore-throat structures are established based on the four types of pore-throat structures. The specific operational steps are as follows: A schematic diagram of the pore-throat structure is drawn based on the parameters of each type; a photochemical etching process is used to precisely etch the structure onto a flat glass surface, followed by high-temperature firing. The flow mesh combination and morphological distribution of the microscopic model conform to the drawn schematic diagram of the pore-throat structure. The standard model size is 40mm × 40mm, and the pore cross-section is elliptical. The wettability of the pore-throat surface after high-temperature firing exhibits strong hydrophilicity; however, it can also be made neutral or hydrophilic depending on the surface treatment of the throat.

[0041] As an optional approach, based on multiple experimental results corresponding to various reservoir types, a porous media model is established, including: based on multiple experimental results of pore throat structure models corresponding to various reservoir types, an abstract gas-water distribution model is derived according to the basic characteristics of the pore throat structure and the core saturation determined by the resonance T2 spectrum; and a porous media model is established based on the gas-water distribution model.

[0042] Specifically, based on the pore-throat structure size, reservoir core saturation, and all experimental results, a gas-water distribution model was abstracted. The pore-throat structure size was determined from a schematic diagram, and the core saturation for different reservoir types was determined from T2 spectra.

[0043] As an optional approach, the porous media model includes a total flow rate model and a total flow resistance model for all micropores and throats. Based on a gas-water distribution model, the porous media model is established by: establishing a mathematical model of the total flow resistance and the total flow pressure difference for a single micropore and throat based on the gas-water distribution model; and establishing a total flow rate model and a total flow resistance model for all micropores and throats based on the mathematical models of the total flow resistance and the total flow pressure difference for a single micropore and throat, respectively.

[0044] As an alternative, a mathematical model of the total flow resistance in a single micro-hole throat is established based on the Hagen-Poiseuille equation.

[0045] Specifically, the model considers the influence of capillary forces in each phase and the Hagen-Poiseuille equation, studies the unit-time flow rate and capillary resistance in different types of reservoirs, and evaluates the permeability of high water-cut tight reservoirs.

[0046] (1) Establish a model of air-water flow resistance mechanism in porous media

[0047] Total flow resistance in a single micro-orifice throat:

[0048]

[0049] in, The total flow resistance is expressed in Pa.

[0050] The viscosity of water is Pa·s.

[0051] Pa.s; Let be the length of the capillary tube, in meters (m).

[0052] For flow velocity, m 3 / s; Where is the pore radius, in meters;

[0053] Where is the radius of the throat, in meters;

[0054] f is the water saturation level; t is the fraction of the discontinuous gas phase discretization, an integer.

[0055] For the i-th part of the discontinuous gas phase, an integer;

[0056] Interfacial tension, N / m;

[0057] To approximate the air-water contact angle in the throat;

[0058] To keep away from the air-water contact angle in the throat.

[0059] Total flow pressure difference in a single micro-hole throat:

[0060]

[0061] in, The total flow resistance is expressed in Pa. The injection pressure is in Pa. The pressure at the production end is Pa.

[0062] As an optional approach, the total flow rate model for all microscopic orifices and throats is as follows:

[0063]

[0064] in, For flow rate; This represents the total flow resistance. This refers to the injection end pressure; The pressure at the production end is denoted by n; the number of throats is denoted by m; and the number of pores is denoted by m. For interfacial tension; The viscosity of water; For gas viscosity; The length of the capillary tube; Where is the pore radius; The radius of the throat; Water saturation; denoted as the number of discrete segments of the discontinuous gas phase; i represents the i-th segment of the discontinuous gas phase. To approximate the air-water contact angle in the throat; To keep away from the air-water contact angle in the throat.

[0065] As an alternative, the total flow resistance model for all micro-holes and throats is as follows:

[0066]

[0067] in, This represents the total flow resistance. For interfacial tension; The viscosity of water; For gas viscosity; For flow rate; The length of the capillary tube; Where is the pore radius; The radius of the throat; Water saturation; denoted as the number of discrete segments of the discontinuous gas phase; i represents the i-th segment of the discontinuous gas phase. To approximate the air-water contact angle in the throat; To keep away from the air-water contact angle in the throat.

[0068] Specifically, a pore throat distribution configuration diagram conforming to the characteristics of gas reservoirs is established, and pore throat flow resistance formulas for different configuration relationships are established. Based on the mathematical model of the total flow resistance in a single micro pore throat and the mathematical model of the total flow pressure difference, a porous media seepage model considering the micro gas-water distribution law of different pore throat distribution configuration relationships is established.

[0069] Assuming a core-associated flow unit has n throats and m pores, the total flow rate in the microscopic pore throats is:

[0070]

[0071] Where n is the number of throats, an integer; and m is the number of pores, an integer.

[0072] Establish the total flow resistance:

[0073]

[0074] Example 1

[0075] Figure 1 A flowchart of a method for evaluating the two-phase micro-permeability flow of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention is shown. Figure 2 A porosity component data diagram is shown for a method for evaluating the two-phase micro-permeability of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention. Figure 3 The diagram illustrates the pore throat volume controlled by the throat radius in a method for evaluating the microscopic seepage of gas-water two-phase flow in a tight, low-permeability gas reservoir according to an embodiment of the present invention. Figure 4 A schematic diagram of the reservoir pore throat structure is shown in a method for evaluating the two-phase micro-permeability of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention. Figure 5 A reservoir-corridor pore throat structure model is shown as an example of a method for evaluating the two-phase micro-permeability of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention. Figure 6 The experimental results of the pore throat structure model corresponding to the reservoir are shown in a method for evaluating the two-phase micro-permeability of gas and water in a tight, low-permeability gas reservoir according to an embodiment of the present invention. Figure 7 An abstract model of gas-water two-phase flow in the pore throat is shown as an evaluation method for gas-water two-phase micro-flow in a tight, low-permeability gas reservoir according to an embodiment of the present invention. Figure 8The diagram illustrates a discontinuous gas phase discretization of an abstract model of gas-water two-phase flow in a pore throat, according to an embodiment of the present invention, for evaluating the gas-water two-phase micro-flow in a tight, low-permeability gas reservoir. Figure 9 A diagram illustrating the specific configuration relationship between pore throats in a tight, low-permeability gas reservoir using a gas-water two-phase micro-permeability evaluation method according to an embodiment of the present invention is shown. Figure 10 The diagram shows a comparison of the flow resistance of the gas phase and the gas-water two-phase flow under different throat radii in a microscopic seepage evaluation method for a tight, low-permeability gas reservoir according to an embodiment of the present invention. Figure 11 The diagram illustrates a comparison of flow resistance and instantaneous velocity in the gas-water two-phase flow of a tight, low-permeability gas reservoir according to an embodiment of the present invention, showing a method for evaluating gas-water two-phase micro-flow at different throat radii.

[0076] Combination Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 and Figure 11 As shown, the method for evaluating the two-phase micro-permeability flow of gas and water in this tight, low-permeability gas reservoir includes:

[0077] Step 1: Based on rock samples, obtain the basic characteristics of the pore-throat structure of various reservoirs;

[0078] The basic characteristics of the pore-throat structure of various reservoir types are obtained according to the following steps: Obtaining experimental results from conventional mercury injection testing of rock samples to determine the displacement pressure, median saturation pressure, and bound water saturation; Based on the displacement pressure, median saturation pressure, and bound water saturation, determining the distribution frequency of different pore-throat radii for rock samples with different permeability and the percentage of pore volume controlled by different pore-throat radii for rock samples with different permeability; Performing nuclear magnetic resonance (NMR) experiments on rock samples to obtain NMR T2 spectra after centrifugation at different speeds; Combining the porosity, permeability, distribution frequency of different pore-throat radii for rock samples with different permeability, percentage of pore volume controlled by different pore-throat radii for rock samples with different permeability, and NMR T2 spectra of the rock samples, the reservoirs of the rock samples are classified, and the basic characteristics of the pore-throat structure of each type of reservoir are determined.

[0079] Among them, the basic characteristics of pore throat structure include core throat and pore size. Determining the basic characteristics of pore throat structure for each type of reservoir includes: obtaining capillary radius distribution based on mercury intrusion porosimetry data; obtaining the average core throat radius of each type of reservoir based on capillary radius distribution; and measuring the average pore radius of each type of reservoir based on thin section data analysis.

[0080] Step 2: For each type of reservoir, create a corresponding schematic diagram of the pore-throat structure based on its basic characteristics.

[0081] Step 3: For each type of reservoir, establish the corresponding pore-throat structure model based on the corresponding pore-throat structure diagram;

[0082] Specifically, for each type of reservoir, the establishment of a corresponding pore-throat structure model based on its corresponding pore-throat structure schematic diagram includes: based on the pore-throat structure schematic diagram corresponding to each type of reservoir, using photochemical etching process to photolithographically print the basic features of the pore-throat structure onto a planar glass, and then firing the photolithographically printed planar glass at high temperature to obtain the pore-throat structure model corresponding to the reservoir.

[0083] Step 4: Conduct saturated water experiments, gas-driven water experiments, and water-driven gas experiments on the pore throat structure model corresponding to each type of reservoir in sequence, and establish a porous media model based on the experimental results corresponding to multiple types of reservoirs.

[0084] Among them, based on multiple experimental results corresponding to multiple types of reservoirs, a porous medium model is established, including: based on multiple experimental results of pore throat structure models corresponding to multiple types of reservoirs, an abstract gas-water distribution model is derived according to the basic characteristics of the pore throat structure and the core saturation determined by the resonance T2 spectrum; and a porous medium model is established based on the gas-water distribution model.

[0085] The porous media model includes the total flow rate model and total flow resistance model in all micropore throats. Based on the gas-water distribution model, the porous media model is established as follows: based on the gas-water distribution model of each experiment, the mathematical model of total flow resistance and total flow pressure difference in a single micropore throat is established; based on the mathematical model of total flow resistance and total flow pressure difference in a single micropore throat, the total flow rate model and total flow resistance model in all micropore throats are established respectively.

[0086] The total flow rate model for all microscopic pores and throats is as follows:

[0087]

[0088] in, For flow rate; This represents the total flow resistance. This refers to the injection end pressure; The pressure at the production end is denoted by n; the number of throats is denoted by m; and the number of pores is denoted by m. For interfacial tension; The viscosity of water; For gas viscosity; The length of the capillary tube; Where is the pore radius; The radius of the throat; Water saturation; denoted as the number of discrete segments of the discontinuous gas phase; i represents the i-th segment of the discontinuous gas phase. To approximate the air-water contact angle in the throat; To keep away from the air-water contact angle in the throat.

[0089] Among them, a mathematical model of the total flow resistance in a single micro-hole throat is established based on the Hagen-Poiseuille equation.

[0090] The model for the total flow resistance in all micro-holes and throats is as follows:

[0091]

[0092] in, This represents the total flow resistance. For interfacial tension; The viscosity of water; For gas viscosity; For flow rate; The length of the capillary tube; Where is the pore radius; The radius of the throat; Water saturation; denoted as the number of discrete segments of the discontinuous gas phase; i represents the i-th segment of the discontinuous gas phase. To approximate the air-water contact angle in the throat; To keep away from the air-water contact angle in the throat.

[0093] Step 5: Based on the porous media model, obtain the flow rate per unit time and flow resistance for the pore throat size.

[0094] Taking the two-phase micro-flow of gas and water in the tight, low-permeability gas reservoir of JS as an example.

[0095] (1) Create a schematic diagram of the pore throat structure of the four types of reservoirs.

[0096] First, based on conventional mercury intrusion porosimetry experimental data, the experimental results of conventional mercury intrusion porosimetry sample testing were organized and calculated to determine the distribution frequency of different pore throat radii in rock samples with different permeability. Based on the distribution frequency of different pore throat radii in rock samples with different permeability, the percentage of pore volume controlled by different pore throat radii in rock samples with different permeability was determined.

[0097] Based on the characteristics of the mercury intrusion pressure curves (IOPs) of rock samples with different porosity Φ, permeability K, displacement pressure, median pressure, and pore volume percentage controlled by different pore throat radii for rock samples with different permeability, and combined with nuclear magnetic resonance experiments, reservoir parameters are classified.

[0098] The average throat radius of each type of reservoir core can be obtained from the capillary radius distribution obtained from mercury injection data, such as... Figure 2 and Figure 3 As shown; the average radius of the pore size can be measured based on the analysis of the collected thin section data.

[0099] Based on the above analysis, the basic characteristics of the pore throat (radius) structure of four types of reservoirs in JS tight low-permeability gas reservoirs can be summarized as follows:

[0100] Class I reservoir: average throat size 0.368 μm, average pore size 50 μm;

[0101] Class II reservoir: Average throat size 0.261 μm, average pore size 30 μm;

[0102] Class III reservoir: average throat size 0.142 μm, average pore size 15 μm;

[0103] Class IV reservoir: average throat size 0.085 μm, average pore size 10 μm;

[0104] A schematic diagram of the pore-throat structure of four types of reservoirs was also prepared, see [link / reference]. Figure 4 As shown, Figure a represents a type I mesopore fine throat, Figure b represents a type II mesopore extra-fine throat, Figure c represents a type III mesopore extra-fine throat, and Figure d represents a type IV small pore extra-fine to micro throat.

[0105] (2) Based on the four types of pore-throat structures, the pores are precisely photolithographically etched onto a flat glass surface and then fired at high temperature to fabricate the structure. Specific steps: A schematic diagram of the pore-throat structure is drawn based on the parameters of each type of pore-throat structure; a photochemical etching process is used to precisely photolithographically etch the pores onto a flat glass surface, followed by high-temperature firing to obtain the pore-throat structure model corresponding to the reservoir. The flow grid combination and morphological distribution of the pore-throat structure model corresponding to the reservoir conform to the drawn schematic diagram of the pore-throat structure, such as... Figure 5 As shown. The standard model is 40mm × 40mm in size, and the cross-section of the channel is elliptical. The wettability of the throat surface is strong hydrophilic after high-temperature firing, but it can also be made neutral or hydrophilic depending on the throat surface treatment.

[0106] The experiment was divided into three processes: saturated water experiment, gas-driven water (simulated reservoir formation) experiment, and water-driven gas experiment (simulated development).

[0107] In the initial stage of water-driven gas displacement: Under capillary force, water preferentially enters smaller channels at a faster speed. However, the smaller channels have a smaller volume, and the gas is quickly displaced. Meanwhile, the seepage velocity in larger channels is slower, and the faster water penetration of the smaller channels causes some gas in the larger channels to be trapped, forming closed gas. In the middle and later stages of water-driven gas displacement: The water velocity increases, and under the action of hydrodynamics, it preferentially enters the larger channels. The faster water penetration of the larger channels causes some gas in the smaller channels to be trapped, such as... Figure 6 As shown.

[0108] (3) Based on the experimental results, a gas-water distribution model was abstracted. The pore-throat structure size was determined based on the schematic diagram of the pore-throat structure. The reservoir core saturation was determined based on the T2 spectrum. Combining the pore-throat structure size and the reservoir core saturation, a gas-water distribution model was abstracted.

[0109] Taking the initial stage of water-driven gas discharge in the JS2 Class III reservoir as an example, a porous media model describing the microscopic gas-water distribution is established. The model considers the influence of capillary forces in each phase and the Hagen-Poiseuille equation, studies the flow rate and flow resistance per unit time, and evaluates the gas-water permeability in the microscopic pore throats of high water-cut tight reservoirs. The abstract model is shown below. Figure 7 .

[0110] 1) Establish a model of the air-water flow resistance mechanism in porous media.

[0111] First, consider the effect of capillary force in porous media:

[0112] for Figure 2 Capillary force on the left side of the discontinuous gas phase for:

[0113]

[0114] Capillary force on the right side of the discontinuous gas phase for:

[0115]

[0116] Poor capillary force for:

[0117]

[0118] Furthermore, considering the influence of viscous flow dynamics of gas in the pore throat, according to the Hagen-Poiseuille equation,

[0119]

[0120] Therefore, the gas flow resistance is:

[0121]

[0122] Furthermore, considering the heterogeneity of the pore throat, the gas phase mesh is discretized, and the discontinuous gas phase is discretized into t equal parts. The discretization diagram is shown below. Figure 8 .

[0123]

[0124] Furthermore, the pore length is l, and the length of the discontinuous gas phase within the pore is... ,therefore,

[0125] The above formula simplifies to:

[0126]

[0127] The flow resistance of the water phase in the pores, according to the Hagen-Poiseuille equation,

[0128]

[0129] The flow resistance of the water phase in the throat, according to the Hagen-Poiseuille equation,

[0130]

[0131] The flow resistance of the aqueous phase in the pore throat,

[0132]

[0133] Therefore, the total flow resistance in the microscopic throat is:

[0134]

[0135] Total flow pressure difference in the micro-pore throat:

[0136]

[0137] 2) Establish a pore throat distribution configuration diagram that conforms to the characteristics of gas reservoirs, establish pore throat flow resistance formulas for different configuration relationships, and establish a porous media seepage model that considers the microscopic gas-water distribution law of different pore throat distribution configuration relationships.

[0138] Based on the gas-water distribution analysis results of the Shaximiao reservoir, the relationships of the three pore-throat configurations in the Shaximiao reservoir are abstracted, such as... Figure 9 As shown, the radius values ​​of the five throats in Figure a are all greater than 0.28 μm; the radius values ​​of the four throats in Figure b are between 0.03 and 0.28 μm; and the radius values ​​of the three throats in Figure c are all less than 0.03 μm. The average pore radius of the three figures is approximately 30 μm.

[0139] Assuming one pore connects to n throats and there are m pores, the total flow rate in the microscopic pore throats is:

[0140]

[0141] Establish the total flow resistance:

[0142]

[0143] 3) Based on the experimental test parameters, calculate the flow rate per unit time and flow resistance for different orifice throat sizes. Evaluate the microscopic gas-water distribution pattern.

[0144] Table 1. Basic parameters of JS reservoir cores of three types.

[0145]

[0146] Calculation results show that, under the same production pressure differential of 10 MPa and the same capillary length of 30 µm, the throat radius has a significant impact on flow resistance and instantaneous flow velocity. The logarithm of the throat radius and flow resistance exhibits a power-law decreasing relationship. The seepage resistance of gas-water two-phase flow is much greater than the pore resistance of gas-phase flow at the same pore size. As the throat radius decreases from 10 µm to 4 µm, the gas-water two-phase flow resistance increases from 5.42 MPa to 131 MPa; while the gas-phase flow resistance increases from 0.22 MPa to 8.6 MPa. The throat radius of the three types of reservoirs is even smaller, averaging 0.261 µm, yet the flow resistance increases to 1E6 MPa. Such dense, fine pores and throats generate enormous resistance to gas flow. Therefore, even after more than 20 years of production, the affected area of ​​development wells deployed in the three types of JS gas reservoirs is only about 300 m. For gas reservoirs geologically identified as superimposed sedimentary channels in deltaic plains, exhibiting a blanket-like or wide-band distribution, some areas remain undeveloped. Furthermore, the high water saturation of these reservoirs significantly increases seepage resistance due to the gas-water two-phase flow. Therefore, improving the recovery rate of these gas reservoirs still focuses on deploying new well sites, densifying the well network, and conducting large-scale reservoir stimulation to utilize most of the gas remaining in the reservoir. Particularly for Type III reservoirs, it is recommended to adopt a horizontal well multi-stage fracturing and proppant injection development method to improve flow space and increase gas recovery.

[0147] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for evaluating the two-phase micro-permeability flow of gas and water in tight, low-permeability gas reservoirs, characterized in that, include: Based on rock samples, the basic characteristics of pore-throat structure of various reservoirs were obtained; For each type of reservoir, a corresponding schematic diagram of the pore-throat structure is created based on the basic characteristics of its pore-throat structure. For each type of reservoir, a corresponding pore-throat structure model is established based on its corresponding pore-throat structure diagram. For each type of reservoir, saturated water experiments, gas-driven water experiments, and water-driven gas experiments were conducted sequentially on the pore throat structure model. Based on the experimental results of multiple types of reservoirs, a porous media model was established. Based on the porous media model, the flow rate per unit time and flow resistance of the pore throat size are obtained; The basic characteristics of pore-throat structures of various reservoir types are obtained by following these steps: Obtain the experimental results of conventional mercury intrusion porosimetry of the rock sample to determine the displacement pressure, median saturation pressure, and bound water saturation. Based on the displacement pressure, median saturation pressure, and bound water saturation, the distribution frequency of different pore throat radii of rock samples with different permeability and the percentage of pore volume controlled by different pore throat radii of rock samples with different permeability are determined. Nuclear magnetic resonance experiments were performed on the rock samples to obtain the nuclear magnetic resonance T2 spectra after centrifugation at different speeds; By combining the porosity, permeability, distribution frequency of different pore throat radii of rock samples with different permeability, percentage of pore volume controlled by different pore throat radii of rock samples with different permeability, and nuclear magnetic resonance T2 spectrum, the reservoirs of the rock samples are classified, and the basic characteristics of the pore throat structure of each type of reservoir are determined. The basic characteristics of the pore throat structure include the core throat and pore size. Determining the basic characteristics of the pore throat structure for each type of reservoir includes: obtaining the capillary radius distribution based on mercury intrusion porosimetry data; obtaining the average core throat radius of each type of reservoir based on the capillary radius distribution; and measuring the average pore radius of each type of reservoir based on thin section data analysis.

2. The method for evaluating the two-phase micro-permeability flow of gas and water in tight, low-permeability gas reservoirs according to claim 1, characterized in that, The step of establishing a corresponding pore-throat structure model for each type of reservoir based on its corresponding pore-throat structure diagram includes: Based on the schematic diagram of the pore throat structure corresponding to each type of reservoir, the basic features of the pore throat structure are photolithographically etched onto a planar glass using a photochemical etching process. The photolithographically etched planar glass is then subjected to high-temperature firing to obtain the pore throat structure model corresponding to the reservoir.

3. The method for evaluating the two-phase micro-permeability flow of gas and water in tight, low-permeability gas reservoirs according to claim 2, characterized in that, The establishment of a porous media model based on multiple experimental results corresponding to multiple types of reservoirs includes: Based on multiple experimental results of pore-throat structure models corresponding to various reservoir types, the core saturation was determined according to the basic characteristics of the pore-throat structure and the nuclear magnetic resonance T2 spectrum, and a gas-water distribution model was abstracted. Based on the aforementioned gas-water distribution model, a porous media model is established.

4. The method for evaluating the two-phase micro-permeability flow of gas and water in tight, low-permeability gas reservoirs according to claim 3, characterized in that, The porous media model includes a total flow rate model and a total flow resistance model in all microscopic pore throats. The establishment of the porous media model based on the gas-water distribution model includes: Based on the aforementioned gas-water distribution model, a mathematical model of the total flow resistance and the total flow pressure difference in a single microscopic pore throat are established. Based on the mathematical models of total flow resistance and total flow pressure difference in each individual micro-hole throat, a total flow rate model and a total flow resistance model are established for all micro-hole throats.

5. The method for evaluating the two-phase micro-permeability flow of gas and water in tight, low-permeability gas reservoirs according to claim 4, characterized in that, The total flow rate model for all microscopic pore throats is as follows: in, For flow rate; This represents the total flow resistance. This refers to the injection end pressure; The pressure at the production end is denoted by n; the number of throats is denoted by m; and the number of pores is denoted by m. For interfacial tension; The viscosity of water; Gas viscosity; The length of the capillary tube; Where is the pore radius; The radius of the throat; Water saturation; denoted as the number of discrete segments of the discontinuous gas phase; i represents the i-th segment of the discontinuous gas phase. To approximate the air-water contact angle in the throat; To keep away from the air-water contact angle in the throat.

6. The method for evaluating the two-phase micro-permeability flow of gas and water in tight, low-permeability gas reservoirs according to claim 5, characterized in that, A mathematical model of the total flow resistance in the single micro-hole throat is established based on the Hagen-Poiseuille equation.

7. The method for evaluating the two-phase micro-permeability flow of gas and water in tight, low-permeability gas reservoirs according to claim 6, characterized in that, The model for the total flow resistance in all micro-holes and throats is as follows: in, This represents the total flow resistance. For interfacial tension; The viscosity of water; Gas viscosity; For flow rate; The length of the capillary tube; Where is the pore radius; The radius of the throat; Water saturation; denoted as the number of discrete segments of the discontinuous gas phase; i represents the i-th segment of the discontinuous gas phase. To approximate the air-water contact angle in the throat; To keep away from the air-water contact angle in the throat.

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