A method, apparatus and system for determining the thickness of water film in sandstone.

Abstract

This invention provides a method, apparatus, and system for determining the thickness of a water film in sandstone. The method involves obtaining a T2 NMR spectrum curve from a sandstone sample, and then determining the corresponding capillary radius distribution curve based on the T2 NMR spectrum curve and a pre-defined pore structure. The number of capillaries in the sandstone sample is determined based on the pore volume and capillary radius distribution curve. The bound water saturation is established by centrifuging the sandstone sample, and the bound water volume is determined. The water film thickness is then determined based on the bound water volume, the number of capillaries, and the capillary radius distribution curve. This invention enables a quantitative description of the sandstone water film thickness. The determined water film thickness can be effectively applied to the analysis of movable water in gas reservoirs and the evaluation of reservoir gas production capacity, providing technical support for subsequent analysis of movable water in gas reservoirs and the evaluation of reservoir gas production capacity.

Description

Technical Field

[0001] This invention relates to a method, apparatus, and system for determining the thickness of a water film in sandstone. Background Technology

[0002] The thickness of the water film determines the saturation of bound water in the reservoir and the gas phase permeability of the reservoir. Accurately and quickly obtaining the water film thickness is crucial for the analysis of movable water in gas reservoirs and the evaluation of gas production capacity. Currently, the water film thickness is mainly obtained through synchrotron radiation experiments, X-ray scanning experiments, and nano-CT experiments. The water film thickness is determined by observing rock samples saturated with water. Summary of the Invention

[0003] The inventors of this invention have discovered that existing methods for determining sandstone water film thickness are mainly used for observing the water film and qualitatively describing its thickness, but cannot quantitatively describe the sandstone water film thickness. Therefore, the test results are difficult to effectively apply to the analysis of movable water in gas reservoirs and the evaluation of reservoir gas production capacity. In view of the above problems, this invention provides a method, apparatus, and system for determining sandstone water film thickness to solve or partially solve these problems. The technical solution proposed by this invention is as follows:

[0004] In a first aspect, embodiments of the present invention provide a method for determining the thickness of a sandstone water film, comprising:

[0005] Determine the pore volume of the sandstone sample to be tested;

[0006] Nuclear magnetic resonance T2 spectrum curves of the sandstone sample after saturation with formation water;

[0007] The capillary radius distribution curve of the sandstone sample to be tested is determined based on the pre-set pore structure and the nuclear magnetic resonance T2 spectrum curve.

[0008] The number of capillaries in the sandstone sample to be tested is determined based on the pore volume and the capillary radius distribution curve of the sandstone sample to be tested.

[0009] After saturating the formation water, the sandstone sample to be tested was centrifuged until the water in the sandstone sample was in a bound water state, and the volume of bound water was determined.

[0010] The water film thickness of the sandstone sample to be tested is determined based on the bound water volume, the number of capillary bundles, and the capillary bundle radius distribution curve.

[0011] In one or more embodiments, the centrifugation of the sandstone sample after saturation with formation water until the water in the sandstone sample is in a bound water state, and the determination of the bound water volume, includes:

[0012] After the sandstone sample was saturated with formation water, it was centrifuged until the water in the sandstone sample was in a bound water state.

[0013] Obtain the first mass of the sandstone sample to be tested and the third mass of the sandstone sample after centrifugation;

[0014] The volume of bound water in the sandstone sample to be tested is determined using the following formula 1 based on the first and third masses of the sample:

[0015]

[0016] Where V is the volume of bound water, m3 is the third mass, m1 is the first mass, and ρ is the density of formation water.

[0017] In one or more embodiments, determining the water film thickness of the sandstone sample based on the bound water volume, the number of capillary bundles, and the capillary bundle radius distribution curve includes:

[0018] The capillary bundle ratio of the sandstone sample to be tested was determined based on the nuclear magnetic resonance T2 spectrum curve.

[0019] The capillary bundle radius is determined based on the capillary bundle radius distribution curve.

[0020] The water film thickness of the sandstone sample to be tested is determined by the following formula 2 based on the bound water volume, capillary radius, capillary ratio, and number of capillary bundles.

[0021]

[0022] Where d is the water film thickness, m3 is the third mass, m1 is the first mass, N is the number of capillary bundles, ρ is the formation water density, L is the core length, and σ i Let r be the proportion of the capillary bundle at the i-th node. i Let be the capillary radius of the i-th node, and n be the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

[0023] In one or more embodiments, determining the number of capillaries in the sandstone sample to be tested based on the pore volume and the capillary radius distribution curve of the sandstone sample to be tested includes:

[0024] The capillary radius and capillary ratio are determined based on the capillary radius distribution curve of the sandstone sample to be tested.

[0025] The number of capillaries in the sandstone sample to be tested is determined using the following formula 3 based on the pore volume, the capillary bundle ratio, and the capillary bundle radius:

[0026]

[0027] Where N is the number of capillary bundles, V P Where L is the pore volume, L is the core length, and σ is the pore volume.i Let r be the proportion of the capillary bundle at the i-th node. i Let be the capillary radius of the i-th node, and n be the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

[0028] In one or more embodiments, the pre-set pore structure of the sandstone sample to be tested includes multiple capillary bundles with different capillary radii.

[0029] The step of determining the capillary radius distribution curve of the sandstone sample based on the pre-set pore structure and the nuclear magnetic resonance T2 spectrum curve includes:

[0030] Based on the nuclear magnetic resonance T2 spectrum curve, the capillary radius corresponding to each transverse relaxation time is determined using the following formula 4, thus obtaining the capillary radius distribution curve of the sandstone sample to be tested:

[0031] r i =0.02T 2i , formula 4;

[0032] Where, r i Let T be the capillary bundle radius of the i-th node. 2i Let be the lateral relaxation time of the i-th node.

[0033] In one or more embodiments, the capillary bundle ratio is obtained in the following manner:

[0034] Based on the nuclear magnetic resonance T2 spectrum curve, the capillary bundle ratio corresponding to each capillary bundle radius of the sandstone sample to be tested is determined by the following formula 5:

[0035]

[0036] Where, σ i Let β be the proportion of capillary bundles at the i-th node. i Let β be the signal amplitude of the nuclear magnetic resonance curve at the i-th node. j Let be the signal amplitude of the NMR curve at the j-th node, and n be the number of nodes in the NMR T2 spectrum curve.

[0037] In one or more embodiments, the pore volume is determined in the following manner:

[0038] Obtain the first mass of the sandstone sample to be tested and the second mass of the sandstone sample after saturation with formation water;

[0039] The pore volume is determined based on the first mass and the second mass using the following formula 6:

[0040]

[0041] Among them, V PLet m be the pore volume, m2 be the second mass, m1 be the first mass, and ρ be the formation water density.

[0042] In a second aspect, embodiments of the present invention provide a device for determining the thickness of a sandstone water film, comprising:

[0043] The pore volume determination module is used to determine the pore volume of the sandstone sample to be tested.

[0044] The nuclear magnetic resonance T2 spectrum curve determination module is used to determine the nuclear magnetic resonance T2 spectrum curve of the sandstone sample to be tested after saturation with formation water.

[0045] The capillary radius distribution curve determination module is used to determine the capillary radius distribution curve of the sandstone sample to be tested based on the pre-set pore structure of the sandstone sample and the nuclear magnetic resonance T2 spectrum curve.

[0046] The capillary bundle number determination module is used to determine the number of capillary bundles in the sandstone sample to be tested based on the pore volume and the capillary bundle radius distribution curve of the sandstone sample to be tested.

[0047] The bound water volume determination module is used to centrifuge the sandstone sample to be tested after it has been saturated with formation water until the water in the sandstone sample is in a bound water state, and to determine the bound water volume.

[0048] The water film thickness determination module is used to determine the water film thickness of the sandstone sample to be tested based on the bound water volume, the number of capillary bundles, and the capillary bundle radius distribution curve.

[0049] Thirdly, embodiments of the present invention provide a sandstone water film thickness determination system, comprising:

[0050] The nuclear magnetic resonance T2 spectrum curve determination device is used to perform nuclear magnetic resonance testing on sandstone samples after they are saturated with formation water, and to obtain the nuclear magnetic resonance T2 spectrum curve of the sandstone samples after they are saturated with formation water.

[0051] Centrifuge device is used to centrifuge sandstone samples saturated with formation water until the water in the sandstone samples is in a bound water state.

[0052] The terminal device is used to determine the capillary radius distribution curve of the sandstone sample to be tested based on the pre-set pore structure and the nuclear magnetic resonance T2 spectrum curve; to determine the number of capillaries in the sandstone sample to be tested based on the pore volume and the capillary radius distribution curve; and to determine the water film thickness of the sandstone sample to be tested based on the bound water volume, the number of capillaries, and the capillary radius distribution curve.

[0053] In one or more embodiments, the sandstone water film thickness determination system further includes: a mass determination device for determining a first mass of the sandstone sample to be tested, a second mass of the sandstone sample to be tested after saturation with formation water, and a third mass of the sandstone sample to be tested after centrifugation to a bound water state.

[0054] Fourthly, embodiments of the present invention provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the sandstone water film thickness determination method as described above.

[0055] Fifthly, embodiments of the present invention provide an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the sandstone water film thickness determination method as described above.

[0056] Based on the above technical solution, the beneficial effects of the present invention compared with the prior art are as follows:

[0057] The method for determining sandstone water film thickness provided in this invention involves determining the pore volume of the sandstone sample to be tested and the T2 spectrum curve of the sandstone sample after saturation with formation water. Then, based on the T2 spectrum curve and a pre-defined pore structure, the corresponding capillary radius distribution curve is determined. The number of capillaries in the sandstone sample is determined based on the pore volume and capillary radius distribution curves. The bound water saturation is established by centrifuging the sandstone sample to determine the bound water volume. The water film thickness is then determined based on the bound water volume, the number of capillaries, and the capillary radius distribution curves. This invention enables a quantitative description of sandstone water film thickness. The determined water film thickness can be effectively applied to the analysis of movable water in gas reservoirs and the evaluation of reservoir gas production capacity, providing technical support for subsequent analysis of movable water in gas reservoirs and the evaluation of reservoir gas production capacity. Attached Figure Description

[0058] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0059] Figure 1 This is a flowchart illustrating the method for determining the thickness of a sandstone water film provided in an embodiment of the present invention;

[0060] Figure 2 This is a schematic diagram of the nuclear magnetic resonance T2 spectrum curve provided in an embodiment of the present invention;

[0061] Figure 3 This is a schematic diagram of the capillary bundle radius distribution curve provided in an embodiment of the present invention;

[0062] Figure 4 This is a schematic diagram of the sandstone water film thickness determination device provided in an embodiment of the present invention;

[0063] Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0065] It should be noted that, unless otherwise specified, the various features in the embodiments of this invention can be combined with each other, all of which are within the protection scope of this invention. Furthermore, although functional modules are divided in the device schematic diagram and a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than the module division in the device or the order in the flowchart. Moreover, the terms "first," "second," and "third" used in this invention do not limit the data or execution order, but only distinguish identical or similar items with essentially the same function and effect.

[0066] Currently, water film thickness is mainly obtained through synchrotron radiation experiments, X-ray scanning experiments, and nano-CT experiments. Water film thickness is determined by observing water-saturated rock samples. These experimental methods for determining water film thickness have three problems: ① The testing process is complex; existing methods typically require simultaneous NMR, high-speed centrifugation, and adsorption experiments, and multiple NMR tests are often necessary; ② The test rock samples are small, often on the order of millimeters or even smaller, resulting in insufficient representativeness; ③ They are mainly used for observing water films and qualitatively describing water film thickness, and the test results are difficult to effectively apply to the analysis of movable water in gas reservoirs and the evaluation of reservoir gas production capacity. Therefore, this invention provides a method for determining sandstone water film thickness, such as... Figure 1 As shown, it includes:

[0067] S101. Determine the pore volume of the sandstone sample to be tested;

[0068] In step S101 above, the dry weight of the sandstone sample to be tested is first obtained, and then the sandstone sample to be tested is subjected to vacuum saturation with formation water to obtain the sandstone sample to be tested after saturation with formation water. The mass of the sandstone sample to be tested after saturation with formation water is obtained, and the pore volume is determined based on the dry weight of the sandstone sample to be tested, the mass of the sandstone sample to be tested after saturation with formation water, and the density of formation water.

[0069] S102. Determine the nuclear magnetic resonance T2 spectrum curve of the sandstone sample to be tested after saturation with formation water;

[0070] In step S102 above, nuclear magnetic resonance (NMR) testing is performed on the sandstone sample saturated with formation water to obtain the NMR T2 spectrum curve, as shown below. Figure 2 As shown.

[0071] S103. Determine the capillary radius distribution curve of the sandstone sample to be tested based on the pre-set pore structure and the nuclear magnetic resonance T2 spectrum curve.

[0072] In step S103 above, in this embodiment of the invention, it is assumed that the pore structure of the sandstone sample to be tested is composed of microcapillary bundles of different radii. Based on the determined transverse relaxation time of each node in the nuclear magnetic resonance T2 spectrum curve, the corresponding capillary bundle radius is determined, and the corresponding capillary bundle radius distribution curve is obtained, as shown below. Figure 3 As shown.

[0073] S104. Determine the number of capillaries in the sandstone sample to be tested based on the pore volume and the capillary radius distribution curve of the sandstone sample to be tested.

[0074] In step S104 above, the capillary radius distribution curve of the sandstone sample to be tested can be used to determine the capillary radius and capillary ratio of each node. By using the capillary radius and capillary ratio of all nodes, the relationship between pore volume and capillary quantity can be established, thereby determining the capillary mass based on the pore volume, capillary radius and capillary ratio.

[0075] S105. Centrifuge the sandstone sample to be tested after it is saturated with formation water until the water in the sandstone sample is in a bound water state, and determine the volume of bound water.

[0076] In step S105 above, the sandstone sample to be tested, after being saturated with formation water, is centrifuged at a preset centrifugation speed and for a preset centrifugation time to ensure that the water in the sandstone sample is in a bound water state. The preset centrifugation speed and preset centrifugation time can be set according to actual needs to centrifuge the sandstone sample after it has been saturated with formation water until the water in the sandstone sample is in a bound water state. As a specific implementation, the preset centrifugation speed is 12000 r / min, and the preset centrifugation time is 30–45 min. Those skilled in the art can also refer to the specific descriptions in the prior art for the specific implementation of centrifuging the sandstone sample to the bound water state.

[0077] S106. Determine the water film thickness of the sandstone sample to be tested based on the bound water volume, the number of capillary bundles, and the capillary bundle radius distribution curve.

[0078] The method for determining sandstone water film thickness provided in this invention relates to core experimental analysis techniques. It involves obtaining the T2 spectrum curve of the nuclear magnetic resonance (NMR) test on the sandstone sample, establishing the relationship between capillary radius and transverse relaxation time, and determining the corresponding capillary radius distribution curve based on a pre-defined pore structure. The number of capillaries in the sandstone sample is determined based on the pore volume and capillary radius distribution curve. The bound water saturation is established by centrifuging the sandstone sample, and the bound water volume is determined. The water film thickness is then determined based on the bound water volume, the number of capillaries, and the capillary radius distribution curve. This invention provides quantitative confirmation of water film thickness, which can be effectively applied to the analysis of movable water in gas reservoirs and the evaluation of reservoir gas production capacity, overcoming the limitations of existing methods in sandstone water film thickness testing. Furthermore, this method can be performed in a laboratory, is easy to operate, and the test results can support basic research on the evaluation of low-permeability / tight sandstone gas reservoir production capacity and enhanced oil recovery. This invention only requires nuclear magnetic resonance (NMR) testing and centrifugation of the sandstone sample to be tested, eliminating the need for synchrotron radiation experiments, X-ray scanning experiments, nano-CT experiments, and adsorption experiments, thus simplifying the testing process. Furthermore, multiple sandstone cores can be tested simultaneously, resulting in high testing efficiency. The sample specifications in this invention are a core diameter of 2.5 cm and a length of 2–3 cm, which is significantly larger than the millimeter-sized rock fragments or even smaller thin sections used in existing testing methods. Moreover, the method for determining the water film thickness in sandstone provided by this invention can be applied not only to sandstone but also to other rocks, such as carbonate rocks.

[0079] In one embodiment, the centrifugation of the sandstone sample after saturation with formation water in step S105 until the water in the sandstone sample is in a bound water state, and the determination of the bound water volume, includes:

[0080] S1051. Centrifuge the sandstone sample to be tested after it is saturated with formation water until the water in the sandstone sample is in a bound water state.

[0081] S1052. Obtain the first mass of the sandstone sample to be tested and the third mass of the sandstone sample after centrifugation.

[0082] In step S1052 above, the sandstone sample to be tested is weighed to obtain the dry weight of the sandstone sample to be tested, which is the first mass; the sandstone sample to be tested after centrifugation is weighed to obtain the mass of the sandstone sample to be tested after centrifugation, which is the third mass.

[0083] S1053. The volume of bound water in the sandstone sample to be tested is determined according to the first and third masses of the sandstone sample using the following formula 1:

[0084]

[0085] Where V is the volume of bound water, mL; m3 is the third mass, g; m1 is the first mass, g; and ρ is the density of formation water, g / cm³. 3 ;

[0086] In step S1053 above, the mass of bound water is obtained by subtracting the dry weight of the sandstone sample to be tested (i.e., the first mass) from the third mass of the centrifuged sandstone sample; the volume of bound water is obtained by dividing the mass of bound water by the density of bound water (i.e., the density of formation water).

[0087] In one embodiment, the step S106 above, which involves determining the water film thickness of the sandstone sample based on the bound water volume, the number of capillary bundles, and the capillary bundle radius distribution curve, specifically includes:

[0088] S1061. Determine the capillary bundle ratio of the sandstone sample to be tested based on the nuclear magnetic resonance T2 spectrum curve.

[0089] In step S1061 above, based on the nuclear magnetic resonance T2 spectrum curve as shown... Figure 2 As shown, the proportion of capillary bundles corresponding to each node is determined.

[0090] S1062. Determine the capillary bundle radius based on the capillary bundle radius distribution curve;

[0091] In step S1062 above, based on the capillary bundle radius distribution curve as shown... Figure 3 As shown, the capillary bundle half of each node is determined.

[0092] The volume of bound water and the thickness of the water film satisfy the following relationship:

[0093]

[0094] S1063. The water film thickness of the sandstone sample to be tested is determined by the following formula 2 based on the bound water volume, capillary radius, capillary ratio, and number of capillary bundles of the sandstone sample to be tested.

[0095]

[0096] Where d is the water film thickness (nm); m3 is the third mass (g); m1 is the first mass (g); N is the number of capillary bundles; and ρ is the formation water density (g / cm³). 3 L is the core length, in cm; σ i Let r be the proportion of the capillary bundle at the i-th node. i denoted as the capillary radius of the i-th node, in μm; n is the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

[0097] In step S1063 above, the bound water volume obtained in step S105, the capillary bundle ratio corresponding to each node obtained in step S1061, and the capillary bundle radius of each node obtained in step S1061 are substituted into formula 2 above to obtain the water film thickness. The number of nodes n in the NMR T2 spectrum curve is determined according to the equipment parameters of the NMR device. As a specific embodiment, the NMR device used in this embodiment of the invention has 64 nodes in its NMR T2 spectrum curve.

[0098] In one embodiment, the step S104 above, which involves determining the number of capillaries in the sandstone sample based on the pore volume and the capillary radius distribution curve of the sandstone sample to be tested, specifically includes:

[0099] S1041. Determine the capillary radius and capillary ratio based on the capillary radius distribution curve of the sandstone sample to be tested.

[0100] In step S1041 above, based on the capillary bundle radius distribution curve as shown... Figure 3 As shown, the capillary bundle radius of each node and the capillary bundle ratio corresponding to each node are determined.

[0101] S1042. The number of capillaries in the sandstone sample to be tested is determined according to the pore volume, capillary bundle ratio, and capillary bundle radius using the following formula 3:

[0102]

[0103] Where N is the number of capillary bundles; V P The pore volume is in cm³. 3 ρ is the density of formation water, g / cm³ 3 L is the core length, in cm; σ i Let r be the proportion of the capillary bundle at the i-th node. i is the capillary radius of the i-th node, in μm; n is the number of nodes in the nuclear magnetic resonance T2 spectrum curve;

[0104] In step S1042 above, the pore volume obtained in step S101 above, the capillary bundle radius of each node obtained in step S1041 above, and the capillary bundle ratio corresponding to each node are substituted into formula 3 to obtain the number of capillary bundles.

[0105] In one embodiment, the pre-set pore structure of the sandstone sample to be tested includes multiple capillary bundles with different capillary radii.

[0106] The step S103 above, which involves determining the capillary radius distribution curve of the sandstone sample based on the pre-defined pore structure and the nuclear magnetic resonance T2 spectrum curve, specifically includes:

[0107] Based on the nuclear magnetic resonance T2 spectrum curve, the capillary radius corresponding to each transverse relaxation time is determined using the following formula 4, thus obtaining the capillary radius distribution curve of the sandstone sample to be tested:

[0108] r i =0.02T 2i , formula 4;

[0109] Where, r i T is the capillary bundle radius of the i-th node, in μm; 2i Let be the lateral relaxation time of the i-th node, in milliseconds.

[0110] In this embodiment of the invention, it is assumed that the pores of the sandstone sample to be tested are composed of microscopic capillary bundles of different radii. Therefore, the pre-set pore structure includes multiple capillary bundles with different capillary bundle radii. The capillary bundle radius is obtained based on the nuclear magnetic resonance T2 spectrum curve. Specifically, the corresponding capillary bundle radius is determined according to Formula 4 based on the transverse relaxation time corresponding to each node in the nuclear magnetic resonance T2 spectrum curve. Based on the capillary bundle radii of all nodes, the capillary bundle radius distribution curve of the sandstone sample to be tested is obtained, as shown below. Figure 3 As shown, the amplitude value corresponding to each capillary bundle radius in the capillary bundle radius distribution curve is determined based on the NMR signal amplitude corresponding to the transverse relaxation time of that capillary bundle radius in the NMR T2 spectrum curve. For example... Figure 3 As shown, the amplitude value corresponding to each capillary bundle radius is the signal amplitude of the nuclear magnetic resonance curve corresponding to the transverse relaxation time of that capillary bundle radius.

[0111] In one embodiment, the capillary bundle ratio is obtained in the following manner:

[0112] Based on the nuclear magnetic resonance T2 spectrum curve, the capillary bundle ratio corresponding to each capillary bundle radius of the sandstone sample to be tested is determined by the following formula 5:

[0113]

[0114] Where, σ i Let β be the proportion of capillary bundles at the i-th node. i Let β be the signal amplitude of the nuclear magnetic resonance curve at the i-th node. j Let be the amplitude of the nuclear magnetic resonance curve at the j-th node, and n be the number of nodes in the T2 spectrum curve.

[0115] In one embodiment, the pore volume in step S101 above is determined in the following manner:

[0116] S1011. Obtain the first mass of the sandstone sample to be tested and the second mass of the sandstone sample to be tested after saturation with formation water;

[0117] In step S1011 above, the sandstone sample to be tested is weighed to obtain its dry weight, i.e., the first mass; the sandstone sample to be tested after saturation with formation water is weighed to obtain its mass after saturation with formation water, i.e., the second mass. After weighing the sandstone sample to be tested, the sample is evacuated for a preset time, and then saturated with formation water. According to GB / T29172-2012 "Core Analysis Methods", the sandstone sample to be tested should be saturated with a liquid of known density, filtered, low viscosity, and low vapor pressure. In this embodiment of the invention, simulated formation water is used to saturate the sandstone sample to be tested. This allows for the simultaneous processing of many samples, direct determination of pore volume, simple experimental operation, and high experimental efficiency.

[0118] S1012. Determine the pore volume based on the first mass and the second mass using the following formula 6:

[0119]

[0120] Among them, V P The pore volume is mL (cm³). 3 m2 is the second mass, in grams; m1 is the first mass, in grams; ρ is the density of formation water, in grams per cubic centimeter. 3 .

[0121] In step S1012 above, the formation water mass is obtained by subtracting the dry weight (i.e., the first mass) of the sandstone sample after it has been saturated with formation water from the second mass of the sandstone sample. The pore volume is obtained by dividing the formation water mass by the formation water density.

[0122] The pore volume, or capillary volume, of the sandstone sample to be tested satisfies the following relationship:

[0123]

[0124] Formula 3.1 for the number of capillary bundles is derived from Formula 6.1:

[0125]

[0126] Where N is the number of capillary bundles, dimensionless; V P The pore volume is in cm³. 3 m2 is the second mass, in grams; m1 is the first mass, in grams; ρ is the density of formation water, in grams per cubic centimeter. 3 L is the core length, in cm; σ i Let r be the proportion of the capillary bundle at the i-th node. i denoted as the capillary radius of the i-th node, in μm; n is the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

[0127] The experimental rock sample specifications, nuclear magnetic resonance parameters, and centrifugation experimental parameters in this embodiment of the invention are unified, meeting the requirements of standardized testing; moreover, the experimental principle is clear, and the calculation formula is concise. The experimental equipment is mostly conventional, the operation process is simple, and the experimental efficiency is high, which can meet the requirements of large-scale core water film testing and provide basic data for gas reservoir development scheme design.

[0128] As a specific embodiment, eight groups of sandstone samples were selected for water film thickness testing according to the sandstone water film thickness determination method provided in this embodiment of the invention. The sandstone specifications were: diameter 2.5cm, deviation not exceeding 0.1cm; length 3cm, deviation not exceeding 0.2cm. The tests were conducted according to steps S101-S106 above, and the water film thickness measurement results were determined, as shown in Table 1.

[0129]

[0130]

[0131] Table 1

[0132] As shown in Table 1, the water film thickness of the eight core samples ranged from 10 to 48 nm, with an average of 25 nm, which is comparable to the water film thickness determined by the semi-permeable septum method and scanning electron microscopy. However, the water film thickness determination method provided by this invention only requires nuclear magnetic resonance testing and centrifugation of the rock sample to be tested, making the experimental operation simple; moreover, it can test up to six core samples at a time, resulting in high efficiency.

[0133] Based on the same inventive concept, embodiments of the present invention provide a device for determining the thickness of a sandstone water film, such as... Figure 4 As shown, it includes:

[0134] The pore volume determination module 201 is used to determine the pore volume of the sandstone sample to be tested.

[0135] The nuclear magnetic resonance T2 spectrum curve determination module 202 is used to determine the nuclear magnetic resonance T2 spectrum curve of the sandstone sample to be tested after saturation with formation water.

[0136] The capillary radius distribution curve determination module 203 is used to determine the capillary radius distribution curve of the sandstone sample to be tested based on the pre-set pore structure of the sandstone sample to be tested and the nuclear magnetic resonance T2 spectrum curve.

[0137] The capillary bundle number determination module 204 is used to determine the number of capillary bundles in the sandstone sample to be tested based on the pore volume and the capillary bundle radius distribution curve of the sandstone sample to be tested.

[0138] The bound water volume determination module 205 is used to centrifuge the sandstone sample to be tested after it is saturated with formation water until the water in the sandstone sample is in a bound water state, and to determine the bound water volume.

[0139] The water film thickness determination module 206 is used to determine the water film thickness of the sandstone sample to be tested based on the bound water volume, the number of capillary bundles, and the capillary bundle radius distribution curve.

[0140] Based on the same inventive concept, embodiments of the present invention also provide a sandstone water film thickness determination system, comprising:

[0141] The nuclear magnetic resonance T2 spectrum curve determination device is used to perform nuclear magnetic resonance testing on sandstone samples after they are saturated with formation water, and to obtain the nuclear magnetic resonance T2 spectrum curve of the sandstone samples after they are saturated with formation water.

[0142] Centrifuge device is used to centrifuge sandstone samples saturated with formation water until the water in the sandstone samples is in a bound water state.

[0143] The terminal device is used to determine the capillary radius distribution curve of the sandstone sample to be tested based on the pre-set pore structure and the nuclear magnetic resonance T2 spectrum curve; to determine the number of capillaries in the sandstone sample to be tested based on the pore volume and the capillary radius distribution curve; and to determine the water film thickness of the sandstone sample to be tested based on the bound water volume, the number of capillaries, and the capillary radius distribution curve.

[0144] As a specific embodiment, the nuclear magnetic resonance T2 spectrum curve determination device in this invention is a nuclear magnetic resonance spectrometer, the centrifugation device is a high-speed centrifuge, and the terminal device is a computer or other device with computing capabilities.

[0145] In one embodiment, the sandstone water film thickness determination system further includes: a mass determination device for determining the first mass of the sandstone sample to be tested, the second mass of the sandstone sample to be tested after saturation with formation water, and the third mass of the sandstone sample to be tested after centrifugation to a bound water state. The mass determination device, used to determine the mass of the sandstone sample to be tested in different states, can be a balance or a mass meter, or other instruments with mass measurement functions.

[0146] The specific implementation of the sandstone water film thickness determination system provided in this embodiment of the invention can be found in the detailed description of the sandstone water film thickness determination method, which will not be repeated here.

[0147] This invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method for determining the thickness of a sandstone water film as described above.

[0148] This invention also provides an electronic device 300, such as... Figure 5As shown, it includes a memory 302, a processor 301, and a computer program stored in the memory 302 and executable on the processor 301. When the processor 301 executes the program, it implements the sandstone water film thickness determination method as described above.

[0149] The device or equipment embodiments described above are merely illustrative. The unit modules described as separate components may or may not be physically separate. The components shown as module units may or may not be physical units; that is, they may be located in one place or distributed across multiple network module units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0150] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented using software plus a general-purpose hardware platform, or of course, using hardware. Based on this understanding, the above technical solutions, in essence or the parts that contribute to the related technology, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; under the concept of the present invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the present invention as described above, which are not provided in detail for the sake of brevity; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for determining the thickness of a water film in sandstone, characterized in that, include: Determine the pore volume of the sandstone sample to be tested; Nuclear magnetic resonance T2 spectrum curves of the sandstone sample after saturation with formation water; The capillary radius distribution curve of the sandstone sample to be tested is determined based on the pre-set pore structure and the nuclear magnetic resonance T2 spectrum curve. The number of capillaries in the sandstone sample to be tested is determined based on the pore volume and the capillary radius distribution curve of the sandstone sample to be tested. After the sandstone sample was saturated with formation water, it was centrifuged until the water in the sandstone sample was in a bound water state. Obtain the first mass of the sandstone sample to be tested and the third mass of the sandstone sample after centrifugation; The volume of bound water in the sandstone sample to be tested is determined using the following formula 1 based on the first and third masses of the sample: , Formula 1; in, To bind the water volume, As the third quality, For the first quality, Density of formation water; The capillary bundle ratio of the sandstone sample to be tested was determined based on the nuclear magnetic resonance T2 spectrum curve. The capillary bundle radius is determined based on the capillary bundle radius distribution curve. The water film thickness of the sandstone sample to be tested is determined using the following formula 2 based on the bound water volume, capillary radius, capillary ratio, and number of capillary bundles: , Formula 2; in, For water film thickness, As the third quality, For the first quality, For the number of capillary bundles, The density of the formation water, The length of the core sample. Let i be the proportion of the capillary bundle at the i-th node. Let be the radius of the capillary bundle at the i-th node. This represents the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

2. The method for determining the thickness of sandstone water film according to claim 1, characterized in that, The step of determining the number of capillaries in the sandstone sample to be tested based on the pore volume and the capillary radius distribution curve of the sandstone sample to be tested includes: The capillary radius and capillary ratio are determined based on the capillary radius distribution curve of the sandstone sample to be tested. The number of capillaries in the sandstone sample to be tested is determined using the following formula 3 based on the pore volume, the capillary bundle ratio, and the capillary bundle radius: , Formula 3; in, For the number of capillary bundles, For pore volume, The length of the core sample. Let i be the proportion of the capillary bundle at the i-th node. Let be the radius of the capillary bundle at the i-th node. This represents the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

3. The method for determining the thickness of sandstone water film according to claim 1, characterized in that, The pre-set pore structure of the sandstone sample to be tested includes multiple capillary bundles with different capillary radii. The step of determining the capillary radius distribution curve of the sandstone sample based on the pre-set pore structure and the nuclear magnetic resonance T2 spectrum curve includes: Based on the nuclear magnetic resonance T2 spectrum curve, the capillary radius corresponding to each transverse relaxation time is determined using the following formula 4, thus obtaining the capillary radius distribution curve of the sandstone sample to be tested: , Official 4; in, Let be the radius of the capillary bundle at the i-th node. Let be the lateral relaxation time of the i-th node.

4. The method for determining the thickness of sandstone water film according to claim 1, characterized in that, The capillary bundle ratio was obtained in the following manner: Based on the nuclear magnetic resonance T2 spectrum curve, the capillary bundle ratio corresponding to each capillary bundle radius of the sandstone sample to be tested is determined by the following formula 5: , Official 5; in, Let i be the proportion of the capillary bundle at the i-th node. Let be the signal amplitude of the nuclear magnetic resonance curve at the i-th node. Let J be the signal amplitude of the NMR curve at the j-th node. This represents the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

5. The method for determining the thickness of sandstone water film according to claim 1, characterized in that, The pore volume is determined in the following manner: Obtain the first mass of the sandstone sample to be tested and the second mass of the sandstone sample after saturation with formation water; The pore volume is determined based on the first mass and the second mass using the following formula 6: , Formula 6; in, For pore volume, For the second mass, For the first quality, This represents the density of formation water.

6. A device for determining the thickness of a sandstone water film, characterized in that, include: The pore volume determination module is used to determine the pore volume of the sandstone sample to be tested. The nuclear magnetic resonance T2 spectrum curve determination module is used to determine the nuclear magnetic resonance T2 spectrum curve of the sandstone sample to be tested after saturation with formation water. The capillary radius distribution curve determination module is used to determine the capillary radius distribution curve of the sandstone sample to be tested based on the pre-set pore structure of the sandstone sample and the nuclear magnetic resonance T2 spectrum curve. The capillary bundle number determination module is used to determine the number of capillary bundles in the sandstone sample to be tested based on the pore volume and the capillary bundle radius distribution curve of the sandstone sample to be tested. The bound water volume determination module is used to centrifuge a sandstone sample after it has been saturated with formation water until the water in the sandstone sample is in a bound water state; to obtain the first mass and the third mass of the sandstone sample after centrifugation; and to determine the bound water volume of the sandstone sample based on the first mass and the third mass using the following formula 1: , Formula 1; in, To bind the water volume, As the third quality, For the first quality, Density of formation water; The water film thickness determination module is used to determine the capillary bundle ratio of the sandstone sample to be tested based on the nuclear magnetic resonance T2 spectrum curve; determine the capillary bundle radius based on the capillary bundle radius distribution curve; and determine the water film thickness of the sandstone sample to be tested using the following formula 2 based on the bound water volume, capillary bundle radius, capillary bundle ratio, and number of capillary bundles: , Formula 2; in, For water film thickness, As the third quality, For the first quality, For the number of capillary bundles, The density of the formation water, The length of the core sample. Let i be the proportion of the capillary bundle at the i-th node. Let be the radius of the capillary bundle at the i-th node. This represents the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

7. A system for determining the thickness of a sandstone water film, characterized in that, include: The nuclear magnetic resonance T2 spectrum curve determination device is used to perform nuclear magnetic resonance testing on sandstone samples after they are saturated with formation water, and to obtain the nuclear magnetic resonance T2 spectrum curve of the sandstone samples after they are saturated with formation water. Centrifuge device is used to centrifuge sandstone samples saturated with formation water until the water in the sandstone samples is in a bound water state. Obtain the first mass of the sandstone sample to be tested and the third mass of the sandstone sample after centrifugation; The volume of bound water in the sandstone sample to be tested is determined using the following formula 1 based on the first and third masses of the sample: , Formula 1; in, To bind the water volume, As the third quality, For the first quality, Density of formation water; The terminal device is used to determine the capillary radius distribution curve of the sandstone sample to be tested based on the pre-set pore structure and the nuclear magnetic resonance T2 spectrum curve; determine the number of capillaries in the sandstone sample to be tested based on the pore volume and the capillary radius distribution curve; determine the capillary ratio of the sandstone sample to be tested based on the nuclear magnetic resonance T2 spectrum curve; determine the capillary radius based on the capillary radius distribution curve; and determine the water film thickness of the sandstone sample to be tested using the following formula 2 based on the bound water volume, the capillary radius, the capillary ratio, and the number of capillaries: , Formula 2; in, For water film thickness, As the third quality, For the first quality, For the number of capillary bundles, The density of the formation water, The length of the core sample. Let i be the proportion of the capillary bundle at the i-th node. Let be the radius of the capillary bundle at the i-th node. This represents the number of nodes in the nuclear magnetic resonance T2 spectrum curve.

8. The sandstone water film thickness determination system according to claim 7, characterized in that, Also includes: A mass determination device is used to determine the first mass of a sandstone sample to be tested, the second mass of a sandstone sample to be tested after saturation with formation water, and the third mass of a sandstone sample to be tested after centrifugation to a bound water state.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method for determining the thickness of sandstone water film as described in any one of claims 1-5.

10. An electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the method for determining the thickness of sandstone water film as described in any one of claims 1-5.

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