Shale hydrophilicity evaluation method based on drop stopping method

Abstract

The invention discloses a shale hydrophilicity evaluation method based on a drop stopping method. The shale hydrophilicity evaluation method comprises the following steps: (1) preparing a shale sample; (2) collecting dynamic images of water drops on the surface of the shale sample at different moments based on a drop stopping method; (3) measuring contact angles of water drops on the surface of the shale sample at different moments by adopting a contact angle measuring instrument; (4) calculating volumes of water drops on the surface of the shale sample at different moments based on an image analysis method; and (5) drawing a change curve of the contact angle of the water drop on the surface of the shale sample at different moments and a change curve of the actual volume of the water drop, and evaluating the hydrophilicity of the shale. According to the method, the hydrophilicity of the fresh shale sample can be simply and quickly evaluated, and the defects that the wettability of the shale sample with extremely low porosity and permeability cannot be evaluated by a traditional Amott method and a traditional USBM method based on a flow experiment, the adaptability is poor, and even evaluation cannot be carried out are overcome.

Description

Technical Field

[0001] The present invention belongs to the field of shale oil development, and particularly relates to a method for evaluating shale hydrophilicity based on the sessile drop method. Background Art

[0002] Wettability is the result of the interaction between rock minerals and reservoir fluids. Like porosity and permeability, wettability is one of the important physical properties of porous media. Especially for shale reservoirs, due to their extremely low porosity and permeability, the capillary pressure is very high. Wettability is a key factor in the magnitude of capillary force, which not only determines the magnitude of capillary force but also its direction. It determines whether capillary force is the driving force or resistance for fluid flow.

[0003] Conventional wettability evaluation of sandstone reservoirs uses the imbibition displacement method based on displacement flow experiments to evaluate the in-situ wettability of reservoirs. Due to the extremely poor fluid flow ability of shale reservoirs, under conventional pressure differences and time scales, no measurable flow can occur in shale, and the imbibition displacement method is not suitable for evaluating the wettability of shale reservoirs, and even unable to evaluate the wettability of shale reservoirs.

[0004] The traditional contact angle method for wettability testing has the advantages of being fast, simple, and visual. However, it requires the test sample to have a smooth and uniform surface. Generally, quartz and calcite slices are used to simulate hydrophilic and oleophilic reservoirs respectively. Shale is a very dense porous medium, with a smooth cross-section along the bedding direction and a relatively single mineral composition. Therefore, when using the sessile drop method to measure the water droplet contact angle, on the one hand, due to the wettability of the shale surface, the water droplet forms a relatively stable contact angle on the shale surface; on the other hand, due to the influence of the wettability of the shale pore structure, the water droplet will undergo an imbibition effect, and the water droplet will gradually imbibe into the shale porous medium, and the volume of the water droplet will continuously shrink. Both of the above effects are controlled by wettability. Therefore, the wettability of shale can be evaluated by analyzing the relatively stable contact angle and the change in water droplet volume, so as to realize the hydrophilicity evaluation of the wettability of the shale surface and pore structure.

[0005] Chinese invention patent CN 112378818 B discloses a method and device for evaluating the wettability of a shale reservoir. The method includes: obtaining a captured image corresponding to a sample to be tested; the sample to be tested includes a shale reservoir and a target fluid on the surface of the shale reservoir; the captured image is used to show the contact angle between the shale reservoir and the target fluid; calculating a contact angle wettability parameter of the sample to be tested by using the contact angle; measuring the spontaneous imbibition mass of the target fluid inhaled by the shale reservoir; determining a spontaneous imbibition wettability parameter of the sample to be tested according to the spontaneous imbibition mass; obtaining a nuclear magnetic resonance spectrum corresponding to the sample to be tested to determine the nuclear magnetic resonance mass of the target fluid inhaled by the shale reservoir; obtaining a nuclear magnetic wettability parameter of the sample to be tested through the nuclear magnetic resonance mass; and evaluating the wettability of the shale reservoir by integrating the contact angle wettability parameter, the imbibition wettability parameter, and the nuclear magnetic wettability parameter.

[0006] Chinese invention patent application CN 111175169 A discloses a method for evaluating the wettability of a rock. The evaluation method is to place a rock sample in a closed container containing a saturated salt solution, and the saturated salt solution forms a constant humidity atmosphere in the closed container. The rock sample continuously absorbs moisture in the air within a certain period of time until it reaches a constant weight. Finally, the wettability of the rock can be quantitatively evaluated by obtaining a constant humidity change curve and calculating the constant weight duration, the constant humidity rate, and the moisture content. The present invention conducts an equilibrium humidity recovery test on the rock sample to quantitatively evaluate the wettability of the rock from three dimensions of the accurately obtained measured values of the constant weight duration, the constant humidity rate, and the moisture content.

[0007] Chinese invention patent application CN 111553047 A discloses a method for obtaining wettability evaluation parameters and a terminal device. The method for obtaining wettability evaluation parameters includes: obtaining spontaneous imbibition experimental data obtained from a spontaneous imbibition experiment on a target sample; and determining a wettability evaluation parameter of the target sample by using a Debye model according to the spontaneous imbibition experimental data.

[0008] However, the above-mentioned method for evaluating the hydrophilicity of shale still has the following deficiencies: (1) When evaluating wettability by combining the contact angle with spontaneous imbibition, when the spontaneous imbibition amount is measured online by nuclear magnetic resonance, the problem of oil-water signal recognition accuracy must be solved, which is difficult, complex to operate, and due to the small droplet volume, it is difficult to ensure the measurement accuracy of the imbibition amount by nuclear magnetic resonance; (2) When using the spontaneous imbibition method for hydrophilicity evaluation, the core samples used have been pretreated by cleaning and drying, and it is impossible to realize the in-situ wettability evaluation of shale, and it will also affect the pore structure of shale; (3) When using the shale sample equilibrium humidity recovery experiment for shale hydrophilicity evaluation, the experimental conditions are demanding, the operation is complex, the experimental period is long, and it is difficult to ensure humidity balance inside the core of shale with extremely low pore porosity and permeability. Summary of the Invention

[0009] Purpose of the invention: In view of the shortcomings of the above-mentioned prior art, the present invention discloses a shale hydrophilicity evaluation method based on the sessile drop method, which has the advantages of simple operation, rapid testing and visualization. The present invention can simply and quickly evaluate the hydrophilicity of fresh shale samples, overcoming the shortcomings of the traditional Amott method and USBM method based on flow experiments that cannot evaluate the wettability of shale samples with extremely low porosity and permeability, have poor adaptability or even cannot be evaluated.

[0010] Technical solution: Shale hydrophilicity evaluation method based on sessile drop method, including:

[0011] Step (1), preparation of shale samples;

[0012] Step (2), collecting dynamic images of water droplets on the surface of shale samples at different times based on the sessile drop method;

[0013] Step (3), using a contact angle measuring instrument to measure the contact angle of a water drop on the surface of the shale sample at different times;

[0014] Step (4), based on the image analysis method, calculate the volume of water droplets on the surface of the shale sample at different times;

[0015] Step (5), draw the change curve of the contact angle of the water drop on the shale sample surface at different times and the change curve of the actual volume of the water drop to evaluate the hydrophilicity of the shale.

[0016] Further, step (1) includes the following steps:

[0017] (11) From the full-diameter shale core sampled from the drilling site, split the full-diameter shale slices of a certain thickness along the bedding direction, wrap them with plastic wrap, place them in a cold production device, and store them in cold storage;

[0018] (12) Under liquid nitrogen freezing conditions, cutting the full-diameter shale slices obtained in step (11) into regular block-shaped or columnar shale slices;

[0019] (13) Smooth the upper and lower surfaces of the shale slice obtained in step (12) to prepare a shale sample to be tested.

[0020] Furthermore, the thickness of the full-diameter shale slice in step (11) is 0.5 to 1.5 cm.

[0021] Furthermore, in step (13), an argon ion polisher is used to smooth the upper and lower surfaces of the shale slice obtained in step (12), and the upper and lower surfaces of the shale slice are bombarded with argon ion beams to obtain a flat surface.

[0022] ​​​​Further, step (2) includes the following steps:

[0023] (21), immersing the shale sample obtained in step (1) in depolarized neutral kerosene;

[0024] (22) Drop a water drop on the upper surface of the shale sample, and use a high-speed camera to collect dynamic images of the water drop on the upper surface of the shale sample.

[0025] Furthermore, in step (22), a water droplet with a volume of 3-8 microliters is dropped on the upper surface of the shale sample using a micro-injector to minimize the effect of gravity on the shape of the water droplet.

[0026] Furthermore, a high-speed camera was used to collect dynamic images of water drops on the upper surface of the shale sample for at least 600 seconds, of which

[0027] In the first 60 seconds, the image sampling frequency is once every 1 to 10 seconds;

[0028] After 60 seconds, the image sampling frequency is once every 20 to 60 seconds.

[0029] Furthermore, in step (3), the contact angle measurement software provided by the contact angle measuring instrument is used to fit the water droplet on the surface of the shale sample into a spherical shape, thereby determining the contact angle θ of the water droplet on the surface of the shale sample at different times 水 size.

[0030] Further, step (4) includes the following steps:

[0031] (41), converting all the dynamic images obtained in step (2) into binary grayscale images in sequence, and then obtaining the height and radius of the droplet at different times, both in pixels;

[0032] (42) Calculate the volume of the water drop image on the binary grayscale image at time ts. The specific formula is as follows:

[0033] Of which:

[0034] is the volume of the water drop image on the binary grayscale image at time ts, in pixels;

[0035] h is the height of the water drop image on the binary grayscale image at time ts, in pixels;

[0036] R is the radius of the water drop image on the binary grayscale image at time ts, in pixels;

[0037] (43) The actual volume of the water droplet on the surface of the shale sample at time ts is calculated as follows:​​​

[0038] Wherein:

[0039] V t is the actual volume of the water droplet on the surface of the shale sample at time ts;

[0040] is the volume of the water droplet image on the binarized grayscale image at time ts, with the unit of pixel;

[0041] V 0 is the actual volume of the water droplet at the initial time;

[0042] is the volume of the water droplet image on the binarized grayscale image at the initial time, with the unit of pixel.

[0043] Further, step (5) includes:

[0044] (51) Plot the change curve of the contact angle θ of the water droplet on the surface of the shale sample at different times, and select the contact angle at the relatively stable time as the equilibrium contact angle of the water droplet on the upper surface of the shale sample 水 If the upper surface of the shale sample is highly hydrophilic and there is no stable state for the water droplet on the upper surface of the shale sample and it keeps decreasing, then take the initial contact angle of the water droplet on the surface of the shale sample as the equilibrium contact angle Wherein: The larger the equilibrium contact angle

[0045] , the poorer the hydrophilicity of the shale sample surface; the smaller the equilibrium contact angle , the better the hydrophilicity of the shale sample surface;

[0046] (52) Plot the change curve of the actual volume of the water droplet at different times, and obtain the slope of the change curve of the actual volume of the water droplet. Wherein:

[0047] The larger the absolute value of the slope of the change curve of the actual volume of the water droplet, the better the hydrophilicity of the shale sample surface; the smaller the absolute value of the slope of the change curve of the actual volume of the water droplet, the poorer the hydrophilicity of the shale sample surface.

[0048] The present invention can visually and quantitatively evaluate the hydrophilicity of fresh shale samples, overcome the influence of sample pretreatment on the hydrophilicity of shale in the prior art for shale hydrophilicity testing, clarify the problem of how to determine the value of the contact angle of the water droplet on the shale surface when the contact angle changes dynamically, and the large error in the water absorption amount analyzed by nuclear magnetic resonance due to the small amount of water after the liquid droplet is imbibed by dense shale. The existing testing methods are complex in operation and long in testing time. Compared with the prior art, the present invention has the following advantages:

[0049] ​The present invention evaluates the hydrophilicity of shale by using a contact angle measuring instrument through the sessile drop method, collects dynamic images of water droplets on the shale surface at different times, and evaluates the hydrophilicity of the shale surface by measuring or calculating the contact angle of the water droplets on the shale surface and the change of the water droplet volume over time.

[0050] The present invention fully considers the complex wettability of the pore structure on the surface and inside of the shale, which leads to the dynamic changes of the contact angle and volume of water droplets on its surface, and characterizes the hydrophilicity of the shale surface through the changes of the dynamic contact angle and the water droplet volume.

[0051] Wettability is one of the key factors in the imbibition displacement oil displacement mechanism of shale reservoirs. This method overcomes the inadaptability of the spontaneous imbibition displacement method for evaluating the wettability of shale due to the poor fluidity of the fluid in the shale reservoir within the conventional pressure difference and time scale. The testing method has the advantages of simplicity, rapidity and visualization, and is a reliable testing means for evaluating the hydrophilicity of shale. Brief Description of the Drawings

[0052] Figure 1 It is a flow chart of the method for evaluating the hydrophilicity of shale based on the sessile drop method disclosed by the present invention.

[0053] Figure 2 It is a schematic diagram showing the changes of the contact angle and volume of a water droplet on the surface of a shale specimen over time during the sessile drop method test of the present invention.

[0054] Figure 3 It is a schematic diagram showing the change of the volume of a water droplet in a specific embodiment of the present invention.

[0055] Figure 4 It is a curve graph showing the change of the contact angle of a water droplet on the surface of a shale specimen over time in a specific embodiment of the invention.

[0056] Figure 5 It is a curve graph showing the change of the volume of a water droplet on the surface of a shale specimen over time in a specific embodiment of the invention. Detailed Embodiments:

[0057] The following is a detailed description of the specific embodiments of the present invention.

[0058] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0059] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0060] As Figure 1 shown, the shale hydrophilicity evaluation method based on the sessile drop method includes:

[0061] Step (1), preparation of shale specimens;

[0062] (11), From the full-diameter shale core taken from the drilling site in a sealed manner, split out a certain thickness of full-diameter shale slices along the bedding direction, wrap them with plastic wrap and place them in a cold production device for refrigerated storage;

[0063] (12), Under the condition of liquid nitrogen freezing, cut the full-diameter shale slices obtained in step (11) into regular block-shaped or columnar shale slices;

[0064] (13), Smooth the upper and lower surfaces of the shale slices obtained in step (12),

[0065] to make the shale specimens to be tested;

[0066] Step (2), collect the dynamic images of water droplets on the surface of the shale specimen at different times based on the sessile drop method, Figure 2 This is a schematic diagram of the change of the contact angle and volume of water droplets with time on the surface of the shale specimen during the sessile drop method test of the present invention. As Figure 2 shown, step (2) includes:

[0067] (21), Immerse the shale specimen obtained in step (1) in depolarized neutral kerosene;

[0068] (22), Drop a water droplet on the upper surface of the shale specimen, and at the same time start to collect the dynamic images of the water droplet on the upper surface of the shale specimen by using a high-speed camera;

[0069] Step (3), measure the contact angle size of the water droplet on the surface of the shale specimen at different times by using a contact angle measuring instrument;

[0070] Step (4), calculate the volume of the water droplet on the surface of the shale specimen at different times based on the image analysis method;

[0071] (41), Convert all the dynamic images obtained in step (2) into binary grayscale images in sequence, and then obtain the height and radius of the liquid droplet at different times, and their units are all pixels;

[0072] (42) Calculate the volume of the water droplet image on the binarized grayscale image at time \(t_s\). The specific formula is as follows:

[0073] Where:

[0074] is the volume of the water droplet image on the binarized grayscale image at time \(t_s\), with the unit of pixel;

[0075] \(h\) is the height of the water droplet image on the binarized grayscale image at time \(t_s\), with the unit of pixel;

[0076] \(R\) is the radius of the water droplet image on the binarized grayscale image at time \(t_s\), with the unit of pixel;

[0077] (43) Calculate the actual volume of the water droplet on the surface of the shale specimen at time \(t_s\). The calculation formula is as follows:

[0078] Where:

[0079] \(V\) t is the actual volume of the water droplet on the surface of the shale specimen at time \(t_s\);

[0080] is the volume of the water droplet image on the binarized grayscale image at time \(t_s\), with the unit of pixel;

[0081] \(V\) 0 is the actual volume of the water droplet at the initial time;

[0082] is the volume of the water droplet image on the binarized grayscale image at the initial time, with the unit of pixel.

[0083] Step (5): Plot the change curves of the contact angles of water droplets on the surface of the shale specimen at different times and the change curves of the actual volumes of water droplets, and evaluate the hydrophilicity of the shale:

[0084] (51) Plot the change curve of the contact angle \(\theta\) 水 of water droplets on the surface of the shale specimen at different times, and select the contact angle at the relatively stable time as the equilibrium contact angle of the water droplet on the upper surface of the shale specimen If the hydrophilicity of the upper surface of the shale specimen is very strong and there is no stable state on the upper surface of the shale specimen and the contact angle keeps decreasing, then take the initial contact angle of the water droplet on the surface of the shale specimen as the equilibrium contact angle Where:

[0085] The equilibrium contact angle The larger the equilibrium contact angle, the poorer the hydrophilicity of the surface of the shale specimen; the equilibrium contact angle The smaller the equilibrium contact angle, the better the hydrophilicity of the surface of the shale specimen;

[0086] (52) Plot the change curve of the actual volume of the water droplet at different times, and obtain the slope of the change curve of the actual volume of the water droplet, where:

[0087] The larger the absolute value of the slope of the change curve of the actual volume of the water droplet, the better the hydrophilicity of the shale specimen surface; the smaller the absolute value of the slope of the change curve of the actual volume of the water droplet, the worse the hydrophilicity of the shale specimen surface.

[0088] Furthermore, in step (11), the thickness of the full-diameter shale slice is 0.5 - 1.5 cm.

[0089] Furthermore, in step (13), an argon ion polishing machine (IB-09010CP type ion cross-section polishing instrument) is used to smooth the upper and lower surfaces of the shale slice obtained in step (12), and the upper and lower surfaces of the shale slice are bombarded with an argon ion beam to obtain a flat surface:

[0090] Furthermore, in step (22), a microsyringe is used to drop a water droplet with a volume of 3 - 8 μL on the upper surface of the shale specimen to minimize the influence of gravity on the shape of the water droplet.

[0091] Furthermore, a high-speed camera is used to collect the dynamic images of the water droplet on the upper surface of the shale specimen for at least 600 seconds, where

[0092] Within the first 60 seconds, the picture sampling frequency is 1 time every 1 - 10 seconds;

[0093] After 60 seconds, the picture sampling frequency is 1 time every 20 - 60 seconds. That is, the image acquisition density is large at the initial moment, and the acquisition time interval is shorter. When the image change tends to be stable, the image acquisition time interval is longer.

[0094] The present invention provides a simple, fast and visual shale hydrophilicity evaluation method based on the sessile drop method, which is of great significance for deepening the understanding of the wettability of shale reservoirs and evaluating the potential of shale oil imbibition displacement development.

[0095] Example 1

[0096] The shale hydrophilicity evaluation method based on the sessile drop method includes:

[0097] Step (1), preparation of the shale specimen;

[0098] Step (2), collecting the dynamic images of the water droplet on the shale specimen surface at different times based on the sessile drop method;

[0099] Step (3), measuring the contact angle of the water droplet on the shale specimen surface at different times by using a contact angle measuring instrument;

[0100] Step (4), based on the image analysis method, calculate the volume of water droplets on the surface of the shale sample at different times;

[0101] Step (5), draw the change curve of the contact angle of the water drop on the shale sample surface at different times and the change curve of the actual volume of the water drop to evaluate the hydrophilicity of the shale.

[0102] Further, step (1) includes the following steps:

[0103] (11) From the full-diameter shale core sampled from the on-site sealed core of Well A in Shengli Oilfield, full-diameter shale slices of a certain thickness are split along the bedding direction, wrapped with plastic wrap, placed in a cold production device, and stored in cold storage;

[0104] (12) Under liquid nitrogen freezing conditions, cutting the full-diameter shale slices obtained in step (11) into regular block-shaped shale slices;

[0105] (13) Smooth the upper and lower surfaces of the shale slice obtained in step (12) to prepare a shale sample to be tested.

[0106] Furthermore, the thickness of the full-diameter shale slice in step (11) is 1 cm.

[0107] Furthermore, in step (13), an argon ion polisher is used to smooth the upper and lower surfaces of the shale slice obtained in step (12), and the upper and lower surfaces of the shale slice are bombarded with argon ion beams to obtain a flat surface.

[0108] Further, step (2) includes the following steps:

[0109] (21), immersing the shale sample obtained in step (1) in depolarized neutral kerosene;

[0110] (22) Drop a water drop on the upper surface of the shale sample, and use a high-speed camera to collect dynamic images of the water drop on the upper surface of the shale sample;

[0111] Furthermore, in step (22), a water droplet with a volume of 5 microliters is dropped on the upper surface of the shale sample using a micro-injector to minimize the effect of gravity on the shape of the water droplet.

[0112] Furthermore, a high-speed camera was used to collect dynamic images of water drops on the upper surface of the shale sample for a total of 700 seconds, of which

[0113] In the first 60 seconds, the image sampling frequency is once every 5 seconds;

[0114] After 60 seconds, the image sampling frequency is once every 20 seconds.

[0115] ​​​​​Furthermore, in step (3), the contact angle measurement software provided by the contact angle measuring instrument is used to fit the water drop on the surface of the shale sample into a spherical shape, thereby determining the contact angle θ of the water drop on the surface of the shale sample at different times. 水 The specific process is as follows: Figure 3 As shown.

[0116] Further, step (4) includes the following steps:

[0117] (41), converting all the dynamic images obtained in step (2) into binary grayscale images in sequence, and then obtaining the height and radius of the droplet at different times, both in pixels;

[0118] (42) Calculate the volume of the water drop image on the binary grayscale image at time ts. The specific formula is as follows:

[0119] Of which:

[0120] is the volume of the water drop image on the binary grayscale image at time ts, in pixels;

[0121] h is the height of the water drop image on the binary grayscale image at time ts, in pixels;

[0122] R is the radius of the water drop image on the binary grayscale image at time ts, in pixels;

[0123] (43) The actual volume of the water droplet on the surface of the shale sample at time ts is calculated as follows:

[0124] Of which:

[0125] V t is the actual volume of water droplets on the surface of the shale sample at time ts;

[0126] is the volume of the water drop image on the binary grayscale image at time ts, in pixels;

[0127] V 0 is the actual volume of the water droplet at the beginning;

[0128] is the volume of the water drop image on the binary grayscale image at the initial time, in pixels.

[0129] Further, step (5) includes:

[0130] (51) Plot the contact angle θ of water drop on the shale sample surface at different times 水 's change curve (specifically as Figure 4 ​​​​​As shown in the figure, the contact angle at a relatively stable time is selected as the equilibrium contact angle of the water droplet on the upper surface of the shale sample. If the upper surface of the shale sample is highly hydrophilic and there is no stable state when the water droplet is on the upper surface of the shale sample and it keeps decreasing, then the initial contact angle of the water droplet on the surface of the shale sample is taken as the equilibrium contact angle. Wherein:

[0131] Equilibrium contact angle The larger the equilibrium contact angle, the worse the hydrophilicity of the surface of the shale sample; the equilibrium contact angle The smaller the equilibrium contact angle, the better the hydrophilicity of the surface of the shale sample.

[0132] (52) Draw the change curve of the actual volume of the water droplet at different times (specifically as shown in Figure 5 the figure), and obtain the slope of the change curve of the actual volume of the water droplet. Wherein:

[0133] The larger the absolute value of the slope of the change curve of the actual volume of the water droplet, the better the hydrophilicity of the surface of the shale sample; the smaller the absolute value of the slope of the change curve of the actual volume of the water droplet, the worse the hydrophilicity of the surface of the shale sample.

[0134] Example 2

[0135] The shale hydrophilicity evaluation method based on the sessile drop method includes:

[0136] Step (1), preparation of the shale sample;

[0137] Step (2), collecting dynamic images of the water droplet on the surface of the shale sample at different times based on the sessile drop method;

[0138] Step (3), measuring the contact angle size of the water droplet on the surface of the shale sample at different times by using a contact angle measuring instrument;

[0139] Step (4), calculating the volume of the water droplet on the surface of the shale sample at different times based on the image analysis method;

[0140] Step (5), drawing the change curve of the contact angle of the water droplet on the surface of the shale sample and the change curve of the actual volume of the water droplet at different times to evaluate the shale hydrophilicity.

[0141] Furthermore, step (1) includes the following steps:

[0142] (11) From the whole-diameter shale core taken from the closed coring of Well B at the Shengli Oilfield, split out a certain thickness of whole-diameter shale slices along the bedding direction, wrap them with plastic wrap and place them in a cold production device for cold storage;

[0143] (12) Under the condition of liquid nitrogen freezing, cut the whole-diameter shale slices obtained in step (11) into regular block-shaped shale slices;

[0144] (13) Smooth the upper and lower surfaces of the shale slice obtained in step (12) to prepare a shale sample to be tested.

[0145] Furthermore, the thickness of the full-diameter shale slice in step (11) is 0.5 cm.

[0146] Furthermore, in step (13), an argon ion polisher is used to smooth the upper and lower surfaces of the shale slice obtained in step (12), and the upper and lower surfaces of the shale slice are bombarded with argon ion beams to obtain a flat surface.

[0147] Further, step (2) includes the following steps:

[0148] (21), immersing the shale sample obtained in step (1) in depolarized neutral kerosene;

[0149] (22) Drop a water drop on the upper surface of the shale sample, and use a high-speed camera to collect dynamic images of the water drop on the upper surface of the shale sample;

[0150] Furthermore, in step (22), a water droplet with a volume of 3 microliters is dropped on the upper surface of the shale sample using a micro-injector to minimize the effect of gravity on the shape of the water droplet.

[0151] Furthermore, a high-speed camera was used to collect dynamic images of water drops on the upper surface of the shale sample for a total of 1000 seconds, of which

[0152] In the first 60 seconds, the image sampling frequency is once every 1 second;

[0153] After 60 seconds, the image sampling frequency is once every 40 seconds.

[0154] Furthermore, in step (3), the contact angle measurement software provided by the contact angle measuring instrument is used to fit the water droplet on the surface of the shale sample into a spherical shape, thereby determining the contact angle θ of the water droplet on the surface of the shale sample at different times 水 Size

[0155] Further, step (4) includes the following steps:

[0156] (41), converting all the dynamic images obtained in step (2) into binary grayscale images in sequence, and then obtaining the height and radius of the droplet at different times, both in pixels;

[0157] (42) Calculate the volume of the water drop image on the binary grayscale image at time ts. The specific formula is as follows:

[0158] Of which: ​​

[0159] At time ts, it is the volume of the water droplet image on the binarized grayscale image, with the unit of pixel;

[0160] h is the height of the water droplet image on the binarized grayscale image at time ts, with the unit of pixel;

[0161] R is the radius of the water droplet image on the binarized grayscale image at time ts, with the unit of pixel;

[0162] (43) Calculate the actual volume of the water droplet on the surface of the shale sample at time ts, and its calculation formula is as follows:

[0163] Where:

[0164] V t Is the actual volume of the water droplet on the surface of the shale sample at time ts;

[0165] Is the volume of the water droplet image on the binarized grayscale image at time ts, with the unit of pixel;

[0166] V 0 Is the actual volume of the water droplet at the initial time;

[0167] Is the volume of the water droplet image on the binarized grayscale image at the initial time, with the unit of pixel.

[0168] Furthermore, step (5) includes:

[0169] (51) Draw the change curve of the contact angle θ 水 Of the water droplet on the surface of the shale sample at different times, and select the contact angle at the relatively stable time as the equilibrium contact angle of the water droplet on the upper surface of the shale sample If the upper surface of the shale sample is very hydrophilic and there is no stable state on the upper surface of the shale sample for the water droplet and it has been decreasing, then take the initial contact angle of the water droplet on the surface of the shale sample as the equilibrium contact angle Where:

[0170] Equilibrium contact angle The larger it is, the worse the hydrophilicity of the surface of the shale sample; the equilibrium contact angle The smaller it is, the better the hydrophilicity of the surface of the shale sample;

[0171] (52) Draw the change curve of the actual volume of the water droplet at different times, and obtain the slope of the change curve of the actual volume of the water droplet, where:

[0172] The larger the absolute value of the slope of the change curve of the actual volume of the water droplet, the better the hydrophilicity of the surface of the shale sample; the smaller the absolute value of the slope of the change curve of the actual volume of the water droplet, the worse the hydrophilicity of the surface of the shale sample.

[0173] Example 3

[0174] Shale hydrophilicity evaluation method based on sessile drop method, including:

[0175] Step (1), preparation of shale samples;

[0176] Step (2), collecting dynamic images of water droplets on the surface of shale samples at different times based on the sessile drop method;

[0177] Step (3), using a contact angle measuring instrument to measure the contact angle of a water drop on the surface of the shale sample at different times;

[0178] Step (4), based on the image analysis method, calculate the volume of water droplets on the surface of the shale sample at different times;

[0179] Step (5), draw the change curve of the contact angle of the water drop on the shale sample surface at different times and the change curve of the actual volume of the water drop to evaluate the hydrophilicity of the shale.

[0180] Further, step (1) includes the following steps:

[0181] (11) From the full-diameter shale core sampled from the closed core at the drilling site C of Shengli Oilfield, full-diameter shale slices of a certain thickness are split along the bedding direction, wrapped with plastic wrap, placed in a cold production device, and stored in cold storage;

[0182] (12) Under liquid nitrogen freezing conditions, cutting the full-diameter shale slices obtained in step (11) into regular block-shaped shale slices;

[0183] (13) Smooth the upper and lower surfaces of the shale slice obtained in step (12) to prepare a shale sample to be tested.

[0184] Furthermore, the thickness of the full-diameter shale slice in step (11) is 1.5 cm.

[0185] Furthermore, in step (13), an argon ion polisher is used to smooth the upper and lower surfaces of the shale slice obtained in step (12), and the upper and lower surfaces of the shale slice are bombarded with argon ion beams to obtain a flat surface.

[0186] Further, step (2) includes the following steps:

[0187] (21), immersing the shale sample obtained in step (1) in depolarized neutral kerosene;

[0188] (22) Drop a water drop on the upper surface of the shale sample, and use a high-speed camera to collect dynamic images of the water drop on the upper surface of the shale sample;

[0189] ​​​​Furthermore, in step (22), a water droplet with a volume of 8 microliters is dropped on the upper surface of the shale sample using a micro-injector to minimize the effect of gravity on the shape of the water droplet.

[0190] Furthermore, a high-speed camera was used to collect dynamic images of water drops on the upper surface of the shale sample for a total of 600 seconds, of which

[0191] In the first 60 seconds, the image sampling frequency is once every 10 seconds;

[0192] After 60 seconds, the image sampling frequency is once every 60 seconds.

[0193] Furthermore, in step (3), the contact angle measurement software provided by the contact angle measuring instrument is used to fit the water droplet on the surface of the shale sample into a spherical shape, thereby determining the contact angle θ of the water droplet on the surface of the shale sample at different times 水 Size

[0194] Further, step (4) includes the following steps:

[0195] (41), converting all the dynamic images obtained in step (2) into binary grayscale images in sequence, and then obtaining the height and radius of the droplet at different times, both in pixels;

[0196] (42) Calculate the volume of the water drop image on the binary grayscale image at time ts. The specific formula is as follows:

[0197] Of which:

[0198] is the volume of the water drop image on the binary grayscale image at time ts, in pixels;

[0199] h is the height of the water drop image on the binary grayscale image at time ts, in pixels;

[0200] R is the radius of the water drop image on the binary grayscale image at time ts, in pixels;

[0201] (43) The actual volume of the water droplet on the surface of the shale sample at time ts is calculated as follows:

[0202] Of which:

[0203] V t is the actual volume of water droplets on the surface of the shale sample at time ts;

[0204] is the volume of the water drop image on the binary grayscale image at time ts, in pixels;

[0205] ​​​V 0 is the actual volume of the water droplet at the initial time;

[0206] is the volume of the water droplet image on the binary grayscale image at the initial time, with the unit of pixel.

[0207] Further, step (5) includes:

[0208] (51) Plot the change curve of the contact angle θ of the water droplet on the surface of the shale specimen at different times, and select the contact angle at the relatively stable time as the equilibrium contact angle of the water droplet on the upper surface of the shale specimen 水 If the upper surface of the shale specimen is very hydrophilic and there is no stable state on the upper surface of the shale specimen for the water droplet and it keeps decreasing, then take the initial contact angle of the water droplet on the surface of the shale specimen as the equilibrium contact angle where:

[0209] The larger the equilibrium contact angle , the worse the hydrophilicity of the surface of the shale specimen; the smaller the equilibrium contact angle , the better the hydrophilicity of the surface of the shale specimen;

[0210] (52) Plot the change curve of the actual volume of the water droplet at different times, and obtain the slope of the change curve of the actual volume of the water droplet, where:

[0211] The larger the absolute value of the slope of the change curve of the actual volume of the water droplet, the better the hydrophilicity of the surface of the shale specimen; the smaller the absolute value of the slope of the change curve of the actual volume of the water droplet, the worse the hydrophilicity of the surface of the shale specimen.

[0212] Finally, it should be noted that: The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.​

Claims

1. A shale hydrophilicity evaluation method based on the sessile drop method, characterized in that: include: Step (1), preparation of shale samples; Step (2), collecting dynamic images of water droplets on the surface of the shale sample at different times based on the sessile drop method; Step (3), using a contact angle measuring instrument to measure the contact angle of a water drop on the surface of the shale sample at different times; Step (4), calculating the volume of water droplets on the surface of the shale sample at different times based on an image analysis method; Step (5), drawing the change curve of the contact angle of the water drop on the surface of the shale sample at different times and the change curve of the actual volume of the water drop, and evaluating the hydrophilicity of the shale.

2. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 1, characterized in that: Step (1) comprises the following steps: (11) From the full-diameter shale core sampled from the drilling site, a full-diameter shale slice of a certain thickness is split along the bedding direction, wrapped with plastic wrap, and placed in a cold production device for refrigerated storage; (12) under liquid nitrogen freezing conditions, cutting the full-diameter shale slices obtained in step (11) into regular block-shaped or columnar shale slices; (13) Smooth the upper and lower surfaces of the shale slice obtained in step (12) to prepare a shale sample to be tested.

3. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 2, characterized in that: The thickness of the full-diameter shale slice in step (11) is 0.5 to 1.5 cm.

4. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 2, characterized in that: In step (13), an argon ion polisher is used to smooth the upper and lower surfaces of the shale slice obtained in step (12), and the upper and lower surfaces of the shale slice are bombarded with an argon ion beam to obtain a flat surface.

5. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 1, characterized in that: Step (2) comprises the following steps: (21) immersing the shale sample obtained in step (1) in depolarized neutral kerosene; (22) Drop a water drop on the upper surface of the shale sample, and use a high-speed camera to collect dynamic images of the water drop on the upper surface of the shale sample.

6. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 5, characterized in that: In step (22), a water droplet with a volume of 3-8 μl is dropped on the upper surface of the shale sample using a micro-injector.

7. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 5, characterized in that: In step (22), a high-speed camera is used to collect dynamic images of water droplets on the upper surface of the shale sample for at least 600 seconds, wherein: In the first 60 seconds, the image sampling frequency is once every 1 to 10 seconds; After 60 seconds, the image sampling frequency is once every 20 to 60 seconds.

8. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 1, characterized in that: In step (3), the contact angle measurement software provided by the contact angle measuring instrument is used to fit the water drop on the surface of the shale sample into a spherical shape, thereby determining the contact angle θ of the water drop on the surface of the shale sample at different times. 水 size.

9. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 1, characterized in that: Step (4) comprises the following steps: (41), converting all the dynamic images obtained in step (2) into binary grayscale images in sequence, and then obtaining the height and radius of the droplet at different times, both in pixels; (42) Calculate the volume of the water drop image on the binary grayscale image at time ts. The specific formula is as follows: in: is the volume of the water drop image on the binary grayscale image at time ts, in pixels; h is the height of the water drop image on the binary grayscale image at time ts, in pixels; R is the radius of the water drop image on the binary grayscale image at time ts, in pixels; (43) The actual volume of the water droplet on the surface of the shale sample at time ts is calculated as follows: in: V t is the actual volume of the water drop on the surface of the shale sample at time ts; is the volume of the water drop image on the binary grayscale image at time ts, in pixels; V0 is the actual volume of the water droplet at the initial time; is the volume of the water drop image on the binary grayscale image at the initial time, in pixels.

10. The shale hydrophilicity evaluation method based on the sessile drop method according to claim 1, characterized in that: Step (5) comprises: (51) Plot the contact angle θ of a water drop on the shale sample surface at different times 水 The contact angle at a relatively stable state is selected as the equilibrium contact angle of the water drop on the surface of the shale sample. If the upper surface of the shale sample is very hydrophilic, there is no stable state when the water drop on the upper surface of the shale sample, and it keeps getting smaller, then the initial contact angle of the water drop on the surface of the shale sample is taken as the equilibrium contact angle. in: Equilibrium contact angle The larger the value, the worse the hydrophilicity of the shale sample surface; the equilibrium contact angle The smaller it is, the better the hydrophilicity of the shale sample surface is; (52) Draw the change curve of the actual volume of the water drop at different times, and obtain the slope of the change curve of the actual volume of the water drop, where: The larger the absolute value of the slope of the water droplet actual volume change curve, the better the hydrophilicity of the shale sample surface; the smaller the absolute value of the slope of the water droplet actual volume change curve, the worse the hydrophilicity of the shale sample surface.

Images