A method and apparatus for determining compacted sandstone water film thickness

Abstract

A method and device for determining the water film thickness of compacted sandstone, the method comprising: performing nuclear magnetic resonance testing on a sample saturated with simulated formation water to obtain a pore size distribution curve; performing a centrifugal experiment on the sample saturated with simulated formation water, and combining the pore size distribution curve to determine an optimal centrifugal force; and under the action of the optimal centrifugal force, combining the pore size distribution curve to determine the water film thickness of the sandstone at different pore sizes according to a water film thickness calculation model.

Description

Technical Field

[0001] This article relates to the field of oil and gas field development technology, and in particular to a method and apparatus for determining the thickness of water film in tight sandstone. Background Technology

[0002] In the development of tight sandstone gas, the challenge of extremely low recovery rates remains. Even with large-scale horizontal drilling and high-intensity hydraulic fracturing, recovery rates hover only between 5% and 10%. The key to this predicament lies in the unique properties of tight sandstone reservoirs. Their pore structure exhibits nanoscale pore size, strong heterogeneity, and a complex pore network, resulting in the presence of a large amount of bound water. This bound water significantly hinders the flow of natural gas, severely limiting the improvement of recovery rates.

[0003] Therefore, how to develop a method that can accurately quantify the thickness and content of water film in dense sandstone is an urgent problem to be solved. Summary of the Invention

[0004] This application provides a method and apparatus for determining the thickness of a water film in dense sandstone. The method is based on obtaining pore size distribution characteristics through nuclear magnetic resonance testing. On this basis, van der Waals forces, electrostatic forces, and structural forces are calculated using DLVO theory, taking into account the forces acting on water molecules in the pore space, thus determining the water film thickness more accurately.

[0005] In a first aspect, this application provides a method for determining the thickness of a water film in tight sandstone, the method comprising:

[0006] Nuclear magnetic resonance (NMR) tests were performed on samples of saturated simulated formation water to obtain pore size distribution curves.

[0007] Centrifugation experiments were conducted on samples of saturated simulated formation water, and the optimal centrifugal force was determined based on the pore size distribution curve.

[0008] Under the optimal centrifugal force, the sandstone water film thickness under different pore sizes is determined according to the water film thickness calculation model.

[0009] Secondly, embodiments of the present invention also provide an apparatus for determining the thickness of a water film in dense sandstone, the apparatus comprising: a memory and a processor; the memory is used to store a program for determining the thickness of a water film in dense sandstone, and the processor is used to read and execute the program for determining the thickness of a water film in dense sandstone, and to execute the method described in any of the above embodiments.

[0010] Thirdly, embodiments of the present invention also provide a computer-readable storage medium storing a data processing program, wherein the data processing program is executed by a processor using any one of the above embodiments to determine the thickness of a water film in dense sandstone.

[0011] Compared with related technologies, this application provides a method and apparatus for determining the thickness of a water film in dense sandstone. The method includes: performing nuclear magnetic resonance (NMR) testing on a sample of saturated simulated formation water to obtain a pore size distribution curve; performing a centrifugation experiment on the sample of saturated simulated formation water and determining the optimal centrifugal force based on the pore size distribution curve; and determining the sandstone water film thickness under different pore sizes under the optimal centrifugal force, based on the pore size distribution curve and a water film thickness calculation model. This application utilizes NMR testing to determine the pore distribution characteristics, and on this basis, calculates van der Waals forces, electrostatic forces, and structural forces based on DLVO theory, considering the forces acting on water molecules in the pore space, and comprehensively determines the water film thickness.

[0012] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the solutions described in the description and the accompanying drawings. Attached Figure Description

[0013] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0014] Figure 1 This is a flowchart illustrating the method for determining the thickness of a water film in dense sandstone according to an embodiment of this application.

[0015] Figure 2 This is a schematic diagram of a device for determining the thickness of a water film in dense sandstone according to an embodiment of this application;

[0016] Figure 3 This is a schematic diagram of nuclear magnetic resonance analysis of the pore structure of dense sandstone in some exemplary embodiments;

[0017] Figure 4 Centrifugation curves are shown in some exemplary embodiments;

[0018] Figure 5 Here are some exemplary embodiments of water film thickness diagrams;

[0019] Figure 6 This is a schematic diagram of a capillary bundle model in some exemplary embodiments. Detailed Implementation

[0020] This application describes several embodiments, but these descriptions are exemplary and not restrictive, and it will be apparent to those skilled in the art that many more embodiments and implementations are possible within the scope of the embodiments described herein. Although many possible combinations of features are shown in the drawings and discussed in the detailed description, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with, or may replace, any feature or element of any other embodiment.

[0021] This application includes and contemplates combinations of features and elements known to those skilled in the art. The embodiments, features, and elements disclosed in this application may also be combined with any conventional features or elements to form a unique inventive scheme as defined by the claims. Any feature or element of any embodiment may also be combined with features or elements from other inventive schemes to form another unique inventive scheme as defined by the claims. Therefore, it should be understood that any feature shown and / or discussed in this application may be implemented individually or in any suitable combination. Therefore, the embodiments are not limited except by the limitations imposed by the appended claims and their equivalents. Furthermore, various modifications and changes may be made within the scope of the appended claims.

[0022] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation of the claims. Moreover, the claims concerning the method and / or process should not be limited to the steps performed in the written order, and those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0023] Accurate determination of the thickness and content of water films in tight sandstone provides crucial data for reservoir evaluation. On one hand, the presence of water films affects the physical properties of the reservoir; for example, by accurately measuring permeability, the reservoir's seepage capacity can be more accurately assessed. On the other hand, accurate determination of the thickness and content of water films in tight sandstone helps to accurately determine the distribution of fluids in the reservoir, clarify the ratio of bound water to mobile fluids, and thus more accurately assess the reservoir's potential productivity, providing an important basis for the formulation of subsequent exploitation plans.

[0024] During their research on water films in dense sandstone, the inventors discovered that:

[0025] In terms of models for bound water, both traditional capillary water-bound models and water film water-bound models have significant shortcomings. The capillary water-bound model assumes that bound water exists only in small pores, which is inconsistent with reality; while the water film water-bound model considers the existence of a water film, its definition, thickness, and distribution are unclear. Early researchers believed that the water film thickness was relatively uniform, ranging from 0.05 to 1 μm. However, with the application of advanced technologies such as molecular dynamics simulations in the petroleum industry, it has been found that the water film thickness is much thinner and highly heterogeneous, approximately 0.7 nm. By solving the molecular force balance equations, the water film thickness is shown at the molecular scale, correcting the traditional understanding. It is now believed that the water film thickness is not uniform.

[0026] Nuclear magnetic resonance (NMR) technology is widely used in quantitative research. NMR obtains T2 spectra by measuring the relaxation time of atomic nuclei, which is then converted into pore size distribution curves (PSD) to analyze the relationship between pore structure and water film. The principle is that the relaxation time of fluids with different pore sizes is different. However, previous studies using NMR technology to quantify water films have shortcomings. They did not fully consider the influence of different pore environments on the water film, such as the different adsorption capacities of pore surfaces with different mineral compositions for water films; nor did they explore in depth the influence of the interaction between the water film and factors such as the charge distribution on the pore surface and the concentration of fluid ions on the quantitative results, resulting in less accurate quantitative results.

[0027] In measuring the thickness and content of water films in dense sandstone, existing techniques utilize mercury intrusion porosimetry (MIP) to obtain information on pore size and distribution by observing the entry of mercury into the pores under different pressures. However, this method has limitations in measuring water films, as it cannot directly measure water film thickness and content. Scanning electron microscopy (SEM) can observe the microstructure of pores, but it is difficult to accurately quantify water film parameters.

[0028] Based on the above analysis, the inventors discovered:

[0029] Based on NMR technology and DLVO theory, an innovative method and system for quantitative calculation of water film parameters has been constructed. By accurately quantifying water film thickness and content, the shortcomings of traditional research methods are effectively overcome, significantly improving the understanding of tight sandstone reservoirs and providing key technical support and reliable decision-making basis for reservoir evaluation and production capacity prediction in oil and gas exploration and development.

[0030] Definitions:

[0031] (1) Dense sandstone;

[0032] Dense sandstone: a special type of sandstone, composed of relatively dense clastic rocks, mainly including siltstone, fine sandstone and some medium to coarse sandstone; dense sandstone generally has a porosity of 7% to 12% and an air permeability of less than 1.0 mD, and the pore radius of sandstone is generally less than 0.5 μm.

[0033] (2) Water film;

[0034] Water film: refers to a layered structure formed in macropores due to electrochemical forces. It has uneven thickness and may contain several water molecules. It has a significant impact on reservoir physical properties and gas flow mechanisms, such as reducing gas permeability and altering gas flow patterns.

[0035] (3) Binding water;

[0036] Bound water: mainly composed of capillary bound water (existing in small pores and macropores confined by small pores) and layered water films in macropores. Its occurrence state has a significant impact on the flow of natural gas in the nanoscale pore network and is a key consideration for reservoir evaluation, production prediction, and exploitation.

[0037] (4) Pore structure;

[0038] Pore ​​structure refers to the type, size, distribution, and interconnections of pores and throats within a rock. A rock's pore system consists of two parts: pores and throats. Pores are the expanded parts of the system, while throats are the small parts connecting the pores. Pores are the basic storage spaces for fluids within rocks, while throats are important channels controlling fluid seepage. When fluids flow through the complex pore systems of nature, they pass through a series of alternating pores and throats.

[0039] (5) DLVO theory;

[0040] DLVO theory: A theory used to calculate the adsorption thickness of water film on the pore wall surface. It comprehensively considers the van der Waals force, electrostatic force and structural force on water molecules on the pore wall surface, and plays a key role in determining the thickness of water film.

[0041] (6) Capillary bundle model;

[0042] Capillary bundle model: A model that assumes the pores are in the shape of capillaries and is used to calculate the water film content. Based on this model, the content of water film in the pore structure of the target sample is determined by the relationship between the specific surface area of ​​the pores and the pore radius.

[0043] This invention provides a method for determining the thickness of a water film in dense sandstone, such as... Figure 1 As shown, the method includes steps S1-S3:

[0044] S1: Nuclear magnetic resonance testing was performed on a sample of saturated simulated formation water to obtain the pore size distribution curve;

[0045] S2: Centrifuge the sample of saturated simulated formation water and determine the optimal centrifugal force based on the pore size distribution curve.

[0046] S3: Under the optimal centrifugal force, the sandstone water film thickness under different pore sizes is determined according to the water film thickness calculation model.

[0047] In one exemplary embodiment, step S1 involves performing nuclear magnetic resonance (NMR) testing on a sample of saturated simulated formation water to obtain a pore size distribution curve, including:

[0048] The sample of saturated simulated formation water was subjected to nuclear magnetic resonance (NMR) testing, and the T2 spectrum obtained under saturated water conditions was converted into a pore size distribution curve (PSD).

[0049] The conversion formula for obtaining the pore size distribution curve from the T2 spectral data is: T2 = mr n ;

[0050] In the above conversion formula, T2 is the T2 spectrum data, r is the porosity radius, and m and n are conversion coefficients, which are constants.

[0051] In one exemplary embodiment, in step S2, a centrifugation experiment is performed on a sample of saturated simulated formation water at different rotation speeds, and the optimal centrifugal force is selected based on the NMR PSD (pore size distribution curve) of the sample at each rotation speed; the optimal centrifugal force is the centrifugal force that displaces the movable fluid within the pore structure.

[0052] In one exemplary embodiment, the van der Waals forces experienced by water molecules on the pore wall surface are calculated using the following formula:

[0053]

[0054] Among them, Π m (h) represents the van der Waals force, which is the magnitude of the van der Waals force exerted on the pore wall surface by water molecules in the wet film system, in MPa; A is the Hamaker constant, in J; and h is the water film thickness, in m, which is the distance parameter between the water film and the solid surface considered when calculating the van der Waals force.

[0055] In one exemplary embodiment, the electrostatic force on the pore wall surface of water molecules is calculated using the following formula:

[0056]

[0057] Among them, Π e (h) represents the electrostatic force, which is the magnitude of the electrostatic force experienced by water molecules on the pore wall surface, measured in MPa; ε r ε0 is the static relative permittivity of water, which is dimensionless; ε0 is the vacuum permittivity; k B is Boltzmann constant; T is the reservoir temperature where the gas and water are located, in K; e is the electron charge; Z is the ion valence, dimensionless.

[0058] In one exemplary embodiment, the structural forces exerted on the pore wall surface by water molecules are calculated using the following formula:

[0059]

[0060] Among them, Π s (h) represents the structural force, which is the magnitude of the structural force experienced by water molecules on the pore wall surface. It is the attractive or repulsive force between two surfaces caused by the overlap of boundary layers with structural changes; k is the structural force strength coefficient.

[0061] In one exemplary embodiment, in step S3, under the action of the optimal centrifugal force, the sandstone water film thickness under different pore sizes is determined by combining the pore size distribution curve and the water film thickness calculation model.

[0062] The water film thickness calculation model is based on the Derjaguin-Landau-Verwey-Overbee theory (DLVO theory for short), and the water film thickness calculation model is as follows:

[0063]

[0064] In the above formula, ΔP is the optimal centrifugal force, MPa; Π m (h) represents the van der Waals force experienced by water molecules on the pore wall surface, Π e (h) represents electrostatic force, Π s (h) represents the structural force; r is the pore radius, h is the water film thickness, and σ is the structural force. gw It is the interfacial tension between air and water.

[0065] In this embodiment, under the optimal centrifugal force, the sandstone water film thickness under different pore sizes is determined by combining the pore size distribution curve and the water film thickness calculation model. Based on the capillary bundle model, the saturation of the bound water film is calculated using the water film thickness.

[0066] In one exemplary embodiment, calculating the saturation of the bound water film based on the water film thickness using a capillary bundle model includes:

[0067] S41. Determine the pore volume corresponding to different pore radii based on the pore size distribution curve and the pore size distribution curve after the optimal centrifugal force.

[0068] S42. Calculate the surface area corresponding to a pore radius based on the pore volume corresponding to different pore radii.

[0069] S43. Determine the water film volume corresponding to the pore radius based on the surface area and water film thickness corresponding to the pore radius;

[0070] S44. Determine the saturation of the bound water film based on the water film volume corresponding to different pore radii and the pore volume of the sample.

[0071] In step S41, the pore volume corresponding to different pore radii is determined based on the pore size distribution curve and the pore size distribution curve after the optimal centrifugal force. The process is as follows:

[0072] S411. Determine the first porosity component corresponding to different pore radii based on the pore size distribution curve;

[0073] S412. Determine the second porosity component corresponding to different pore radii based on the pore size distribution curve after the optimal centrifugal force is applied.

[0074] S413. Calculate the pore volume corresponding to different pore radii using the pore volume formula based on the sample volume, the first porosity component, and the second porosity component.

[0075] The formula for pore volume is:

[0076]

[0077] Among them, V li V is the pore volume with pore radius i; V is the sample volume. It is the first porosity component, that is, the porosity component (%) with pore radius i; It is the second porosity component, that is, the porosity component with pore radius i after the optimal centrifugal force (%).

[0078] In step S42, the surface area corresponding to the pore radius is calculated based on the volume corresponding to different pore radii;

[0079] Specifically, the surface area corresponding to a given pore radius is calculated based on the volume corresponding to different pore radii and the pore radius itself, combined with the pore surface area formula. The pore surface area formula is as follows:

[0080]

[0081] Among them, S li It is the pore surface area (cm²) of pores with pore radius i. 2 );r i It is the pore radius, V li Let i be the pore volume with pore radius i.

[0082] S43. Determine the water film volume corresponding to the pore radius based on the surface area and water film thickness corresponding to the pore radius;

[0083] In this step, V fi It is the volume of the water film in a movable fluid pore with pore radius i;

[0084] Among them, V fi =S li ×h i ;

[0085] In the above formula, V fi h is the volume of the water film in a movable fluid pore with pore radius i; i S is the thickness of the water film in a movable fluid pore with pore radius i; li It is the pore surface area with pore radius i.

[0086] S44. Determine the saturation of the bound water film based on the water film volume corresponding to the different pore radii and the sample pore volume.

[0087] In this step, the saturation of the bound water film is determined based on the water film volume corresponding to different pore radii and the sample pore volume, including:

[0088] The formula for calculating the saturation of bound water film is as follows:

[0089]

[0090] Among them, S f It is the saturation of the bound water film; V f It is the total volume of the bound water film; V p It is the pore volume of the sample; r c It is the smallest pore radius that can overcome the capillary force of the fluid inside the pore under optimal centrifugal force. It is porosity (%); V fi V is the volume of the water film in a movable fluid pore with pore radius i; V is the sample volume.

[0091] The method for determining the thickness of water film in dense sandstone implemented in this embodiment has the following technical effects:

[0092] I. By converting T2 spectra to PSD using nuclear magnetic resonance (NMR) technology, the pore distribution characteristics can be obtained. Based on this, van der Waals forces, electrostatic forces, and structural forces are calculated using DLVO theory. Taking into account the forces acting on water molecules within the pore space, the water film thickness and content are determined. Compared to traditional techniques, this method significantly improves the accuracy of water film quantification.

[0093] Second, accurate data on water film thickness and content help to accurately assess reservoirs, including determining reservoir permeability and fluid distribution, thereby more accurately predicting production capacity and providing important reference for formulating reasonable exploitation plans, which is of great significance for improving oil and gas extraction efficiency.

[0094] Secondly, embodiments of the present invention also provide a device for determining the thickness of a water film in dense sandstone, such as... Figure 2 As shown, the device includes a memory 200 and a processor 210; the memory is used to store a program for determining the thickness of a water film in dense sandstone, and the processor is used to read and execute the program for determining the thickness of a water film in dense sandstone, and to execute the method described in any of the above embodiments.

[0095] Thirdly, embodiments of the present invention also provide a computer-readable storage medium storing a data processing program, wherein the data processing program is executed by a processor using any one of the above embodiments to determine the thickness of a water film in dense sandstone.

[0096] Example 1

[0097] Taking a study block as an example, the process of quantitatively determining the thickness of the water film in tight sandstone is as follows:

[0098] Step 1. Perform nuclear magnetic resonance (NMR) tests on a sample of saturated simulated formation water to obtain the pore size distribution curve.

[0099] In this step, the saturated simulated formation water sample is subjected to nuclear magnetic resonance (NMR) testing, and the pore size distribution curve (PSD) is determined based on the T2 spectrum data obtained under saturated water conditions.

[0100] like Figure 3 Nuclear magnetic resonance analysis of the pore structure of dense sandstone shows... Figure 3 The left figure in the figure is a schematic diagram of T2 spectrum data. The horizontal axis is T2 data and the vertical axis is porosity component. Figure 3 The right figure in the figure shows the pore size distribution curve, with the horizontal axis representing the pore radius data and the vertical axis representing the porosity component.

[0101] Step 2. Perform centrifugation experiments on saturated simulated formation water samples and determine the optimal centrifugal force based on the pore size distribution curve.

[0102] In this step, samples of saturated simulated formation water were centrifuged at 2000, 3500, 5000, 7500, 10000, 12500, and 15000 rpm. Based on the changes in NMR PSD amplitude and bound water saturation at each speed, 8.53 MPa (15000 rpm) was selected as the optimal centrifugal force. Figure 4 The figure shown is a centrifugal curve. Figure 4 The left figure shows the pore radius on the horizontal axis and the porosity component on the vertical axis. Figure 4 The right figure shows the bound water saturation curves under different centrifugal forces. The horizontal axis represents the rotational speed, and the vertical axis represents the bound water saturation. Figure 4 As shown in the right figure, the optimal centrifugal force is determined to be the minimum bound water saturation, which is 8.53 MPa at 15000 rpm.

[0103] Step 3. Calculate the van der Waals forces acting on water molecules at the pore wall surface:

[0104]

[0105] Step 4. Calculate the electrostatic force on the pore wall surface of the water molecules:

[0106]

[0107] Step 5. Calculate the structural forces acting on water molecules at the pore wall surface:

[0108]

[0109] Step 6. Calculate the water film thickness under different pore sizes under optimal centrifugal force;

[0110]

[0111] This step calculates the water film thickness as follows: Figure 5 As shown.

[0112] Step 7. Based on the capillary bundle model, calculate the water film content by using the relationship between pore specific surface area and pore radius.

[0113] like Figure 6 The figure shows a capillary bundle model, which simplifies pores into capillary bundles, where the radius of the capillary bundle is the radius of the pore, and the length of the capillary bundle is the length of the pore.

[0114] Step 71. Calculate the pore surface area of ​​the water film. The calculation formula is as follows:

[0115]

[0116] Among them, S li It is the surface area (cm²) of the water film pores with pore radius i. 2 );r i It is the radius of the pores in the water film; V li It is the volume (cm³) of the water film pores with pore radius i. 3 V is the sample volume (cm³). 3 );φ i It is the porosity component (%) of the water film with pore radius i; φ ci It is the porosity component (%) of the water film with radius i after centrifugation.

[0117] Step 72. Calculate the water film volume. The volume of the water film with radius i in the pores is calculated using the surface area of ​​the large pores and the water film thickness. The calculation formula is as follows:

[0118] V fi =S li ×h i

[0119] Among them, V fi It is the volume (cm³) of the water film in the pore with pore radius i. 3 );h i It is the thickness of the water film inside the pore with pore radius i.

[0120] Step 73. The formula for calculating the saturation of the bound water film is as follows:

[0121]

[0122] Among them, S f It is the saturation of the bound water film (%); V f It is the total volume of the bound water film (cm²) 3 );V p The pore volume of the sample (cm³) 3 );r c It is the minimum pore radius (μm) that can overcome the capillary force of the fluid inside the pore under optimal centrifugal force; φ is the porosity (%).

[0123] The calculations show that, under the optimal centrifugal force of 8.53 MPa, the water film thickness ranges from 0.10 to 3.72 nm for different pore radii. Specifically, a pore radius of 11.72 nm corresponds to a water film thickness of 0.7 nm, which is close to the result of molecular dynamics simulation (0.4 nm). Therefore, this demonstrates that the method for calculating water film thickness is both accurate and convenient.

[0124] This example demonstrates the precise quantification of water film thickness and content in tight sandstone based on NMR technology and DLVO theory. NMR technology converts T2 spectra into PSD pore size distribution curves to obtain pore distribution characteristics. Based on this, van der Waals forces, electrostatic forces, and structural forces are calculated using DLVO theory. Considering the forces acting on water molecules within the pore space, the water film thickness and content are comprehensively determined. Compared to traditional techniques, this method significantly improves the accuracy of water film quantification, establishing a complete and systematic quantitative calculation system and providing a more scientific and comprehensive approach for related research.

[0125] Meanwhile, accurate data on water film thickness and content help to accurately assess reservoirs, including determining reservoir permeability and fluid distribution, thereby more accurately predicting production capacity and providing important reference for formulating reasonable exploitation plans, which is of great significance for improving oil and gas extraction efficiency.

[0126] It will be understood by those skilled in the art that all or some of the steps, systems, or apparatuses disclosed above, and their functional modules / units, can be implemented as software, firmware, hardware, or suitable combinations thereof. In hardware implementations, the division between functional modules / units mentioned above does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed collaboratively by several physical components. Some or all components may be implemented as software executed by a processor, such as a digital signal processor or microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit (ASIC). Such software may be distributed on a computer-readable medium, which may include computer storage media (or non-transitory media) and communication media (or transient media). As is known to those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. Furthermore, it is well known to those skilled in the art that communication media typically contain computer-readable instructions, data structures, program modules, or other data in modulated data signals such as carrier waves or other transmission mechanisms, and may include any information delivery medium.

Claims

1. A method for determining the thickness of a water film in dense sandstone, characterized in that, The method includes: Nuclear magnetic resonance (NMR) tests were performed on samples of saturated simulated formation water to obtain pore size distribution curves. Centrifugation experiments were conducted on samples of saturated simulated formation water, and the optimal centrifugal force was determined based on the pore size distribution curve. Under the optimal centrifugal force, the sandstone water film thickness under different pore sizes is determined according to the water film thickness calculation model.

2. The method for determining the thickness of a water film in dense sandstone according to claim 1, characterized in that, After determining the sandstone water film thickness under different pore sizes based on the water film thickness calculation model under the optimal centrifugal force, the method further includes: Based on the capillary bundle model, the saturation of the bound water film is calculated using the sandstone water film thickness under different pore sizes.

3. The method for determining the thickness of a water film in dense sandstone according to claim 2, characterized in that, The nuclear magnetic resonance (NMR) test of the saturated simulated formation water sample to obtain the pore size distribution curve includes: Nuclear magnetic resonance (NMR) tests were performed on samples of saturated simulated formation water to obtain T2 spectral data under saturated water conditions. The aperture distribution curve is obtained using the conversion formula based on the T2 spectrum data; The conversion formula is: T2=mr n ; In the above conversion formula, T2 is the T2 spectrum data, r is the porosity radius, and m and n are conversion coefficients, which are constants.

4. The method for determining the thickness of a water film in dense sandstone according to claim 3, characterized in that, The determination of sandstone water film thickness under different pore sizes under the optimal centrifugal force, based on the water film thickness calculation model, includes: The van der Waals force, electrostatic force, and structural force experienced by water molecules on the pore wall surface were determined respectively. Under the optimal centrifugal force, the sandstone water film thickness under different pore sizes is determined using a water film thickness calculation model based on the van der Waals force, the electrostatic force, and the structural force.

5. The method for determining the thickness of a water film in dense sandstone according to claim 4, characterized in that, The water film thickness calculation model is as follows: In the above formula, ΔP is the optimal centrifugal force, and Π m (h) represents van der Waals force, Π e (h) represents electrostatic force, Π s (h) represents the structural force, r represents the pore radius, h represents the water film thickness, and σ gw This refers to the interfacial tension between air and water.

6. The method for determining the thickness of a water film in dense sandstone according to claim 5, characterized in that, The van der Waals force is: Among them, Π m (h) represents the van der Waals force, A is the Hamark constant, and h is the thickness of the water film. The electrostatic force is: Among them, Π e (h) represents the electrostatic force, ε r ε is the static relative permittivity of water, ε0 is the vacuum permittivity, and k is the static relative permittivity of water. B Where is Boltzmann constant, T is reservoir temperature, e is electron charge, and Z is ion valence. The structural force is: Among them, Π s (h) represents the structural force, and k represents the structural force strength coefficient.

7. The method for determining the thickness of a water film in dense sandstone according to claim 5, characterized in that, The calculation of the bound water film saturation based on the capillary bundle model and the water film thickness includes: The pore volume corresponding to different pore radii is determined based on the pore size distribution curve and the pore size distribution curve after the application of optimal centrifugal force. Calculate the surface area corresponding to a pore radius based on the pore volume corresponding to different pore radii; The volume of the water film corresponding to the pore radius is determined based on the surface area and water film thickness corresponding to the pore radius. The saturation of the bound water film is determined by the water film volume corresponding to different pore radii and the pore volume of the sample.

8. The method for determining the thickness of a water film in dense sandstone according to claim 7, characterized in that, The step of determining the pore volume corresponding to different pore radii based on the pore size distribution curve and the pore size distribution curve after optimal centrifugal force includes: The first porosity component corresponding to different pore radii is determined based on the pore size distribution curve. The second porosity component corresponding to different pore radii is determined based on the pore size distribution curve after the optimal centrifugal force is applied. Based on the sample volume, the first porosity component, and the second porosity component, the pore volume corresponding to different pore radii is calculated using the pore volume formula. The formula for pore volume is: Among them, V li V is the pore volume with pore radius i; V is the sample volume. It is the first porosity component; It is the second porosity component.

9. The method for determining the thickness of a water film in dense sandstone according to claim 7, characterized in that, The calculation of the surface area corresponding to a pore radius based on the pore volume corresponding to different pore radii includes: The surface area corresponding to a given pore radius is calculated by combining the pore volume corresponding to different pore radii with the pore surface area formula. The formula for the pore surface area is: Among them, S li It is the pore surface area with pore radius i, r i It is the pore radius, V li Let i be the pore volume with pore radius i.

10. The method for determining the thickness of a water film in dense sandstone according to claim 7, characterized in that, The determination of the bound water film saturation based on the water film volume corresponding to different pore radii and in conjunction with the sample pore volume includes: The volume of water film corresponding to different pore radii is determined based on the pore surface area and water film thickness corresponding to different pore radii. The saturation of the bound water film is determined by combining the water film volume corresponding to different pore radii with the pore volume of the sample. The saturation degree of the bound water film is: In the above formula, S f It is the saturation of the bound water film, V f It is the total volume of the bound water film, V p It is the sample pore volume; r c V is the minimum pore radius centrifuged by the optimal centrifugal force, and V is the sample volume. It is the porosity of the sample, V fi h is the volume of the water film with pore radius i. i It is the thickness of the water film with pore radius i; Among them, V fi =S li ×h i .

11. An apparatus for determining the thickness of a water film in dense sandstone, characterized in that, The apparatus includes a memory and a processor; the memory is used to store a program for determining the thickness of a water film in tight sandstone, and the processor is used to read and execute the program for determining the thickness of a water film in tight sandstone, and to execute the method according to any one of claims 1-10.

12. A computer-readable storage medium storing a data processing program, the data processing program being executed by a processor according to any one of claims 1-10, the method for determining the thickness of a water film in dense sandstone.

Images