Microscopic oil displacement energy conversion analysis method

Abstract

The invention relates to the technical field of oil exploitation, in particular to a microscopic oil displacement energy conversion analysis method. The method comprises the following steps: making a pore throat channel pattern into a glass microscopic model by using a wet etching method, performing a microfluidic displacement experiment by using the model, and recording result images of each displacement stage; identifying and acquiring a contact angle value distribution condition by utilizing an experimental result image in each displacement stage, and metering shape parameter values such as contour perimeter and the like of each remaining oil region; according to the contact angle identification and measurement result, the pore radius value corresponding to each remaining oil distribution area is obtained, the average radius is calculated, and the average capillary pressure is obtained and used for representing the microcosmic remaining oil starting pressure; and according to a definition formula of work, combining the contact angle value, the perimeter of the contour of the remaining oil area and the average capillary pressure to obtain the magnitude of work required for using the remaining oil at the corresponding position. The method provided by the invention effectively guides the actual water injection development of the oil field in the high-water-cut period, and realizes the improvement of the recovery degree of the remaining oil in the high-water-cut period.

Description

Technical Field

[0001] This invention relates to the technical field of oil extraction, and in particular to a microscopic method for analyzing the energy conversion of oil displacement. Background Technology

[0002] In the early stages of oilfield development, water injection has a significant effect on replenishing bottom energy and increasing oil production during the water drive phase. However, as water injection oil production measures are advanced, most of the injected water flows cross along the dominant channels, leading to a gradual increase in the injection-production ratio. Currently, most inland oilfields at home and abroad have entered the medium-high water cut stage, or even the ultra-high water cut stage.

[0003] Currently, many inland oilfields both domestically and internationally have entered the medium-high water-cut or ultra-high water-cut stages, but their overall recovery rate is low, around 30%. After entering the high water-cut stage, the distribution of remaining oil changes significantly compared to the previous stage, and the stress state of the remaining oil also changes accordingly. The dominant force shifts from the original displacement pressure to the viscous shear force between water and oil, directly affecting the remaining oil's occurrence state and start-up conditions. Entering the ultra-high water-cut stage, the driving force of the microscopic remaining oil changes, shifting from the original displacement pressure to microscopic viscous shear force becoming the dominant force.

[0004] As oilfield water injection development enters the ultra-high water-cut stage, the occurrence and distribution of remaining oil change significantly. Some extraction theories from the low-to-medium water-cut stage are no longer applicable to the actual situation in the ultra-high water-cut stage. Therefore, the rational classification of remaining oil in the ultra-high water-cut stage becomes the foundation and key to subsequent research. This transformation is crucial for the stress analysis of the microstructure of remaining oil and directly relates to the determination of the conditions for its activation.

[0005] Entering the ultra-high water-cut stage significantly increases the difficulty of oilfield development, and the stress state of the remaining oil changes markedly. In the early stages of development, the remaining oil in the reservoir is mainly driven by water-drive energy, while microscopic forces have little impact. As the oilfield development progresses, the microscopic forces acting on the remaining oil play a crucial role. Traditional methods for assessing the stress on the remaining oil rely on the subjective judgment of technicians based on the patterns of injection pressure changes, and are difficult to accurately analyze complex oilfield development processes. Currently, the theoretical foundation and technical support for the development of ultra-high water-cut oilfields by researchers both domestically and internationally are not mature enough, and there is relatively little research on the distribution, occurrence state, start-up conditions, deformation, and decomposition of remaining oil in the ultra-high water-cut stage.

[0006] In the context of existing oilfield development in my country, research on the microscopic stress analysis, existence forms, and deformation modes of residual oil during the ultra-high water-cut stage is of great significance. Based on the microscopic stress state of residual oil during the ultra-high water-cut stage, a clearer understanding of the flow mechanism of residual oil at this stage can be achieved, analyzing the relationship between residual oil flow and pore water flow velocity, as well as the intrinsic connection between pore water flow velocity and injection pressure. This provides effective guidance for actual water injection development in ultra-high water-cut oilfields. Oilfield water injection development is a complex process of replacing crude oil from the capillary channels of formation rocks. In the early stages of water injection development, it is mainly carried out in the form of pressurized displacement, where the effect of microscopic forces is relatively small. However, in the later stages, the reservoir saturation ratio changes significantly, and the oil saturation drops sharply. Displacement-based development is no longer feasible in the main oil-producing areas, and the effect of microscopic forces becomes significant. In the early stages, residual oil mainly existed in continuous sheet-like forms, while in the high water-cut stage, residual oil mainly exists in the form of oil droplets and oil films. The theories from the initial development phase are no longer applicable. A re-understanding of the fluid distribution and characteristics within the reservoir pore structure, as well as the microscopic stress state of the residual oil, is necessary to gain a deeper understanding of the intrinsic mechanism of waterflooding and to take appropriate practical measures to ensure efficient waterflooding development. In the ultra-high water-cut stage, residual oil often exists in a more discrete state. Generally, the residual oil in the reservoir pores is mainly affected by a combination of forces, including capillary force, gravity, buoyancy, hysteresis, displacement pressure, frictional resistance with the rock, and additional resistance. Therefore, to address these shortcomings, a microscopic energy conversion analysis method for oil displacement is proposed. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] This invention provides a microscopic oil displacement energy conversion analysis method to overcome the shortcomings of the existing technology for the development of ultra-high water-cut oilfields, which lacks a mature theoretical foundation and technical support. There is relatively little research on the distribution, occurrence state, start-up conditions, deformation and decomposition of residual oil in ultra-high water-cut periods, resulting in the difficulty of studying oil displacement energy conversion from a microscopic perspective.

[0009] (II) Technical Solution

[0010] To address the above problems, this invention provides a method for analyzing the energy conversion of microscopic oil displacement, comprising:

[0011] Step S1: The pore throat channel pattern is fabricated into a glass micro-model using a wet etching method, and the model is used to conduct microfluidic displacement experiments. During the experiment, the results images of each displacement stage are recorded.

[0012] Step S2: Using the experimental result images of each displacement stage obtained in step S1, identify and obtain the distribution of contact angle values, and measure the shape parameter values ​​such as the perimeter of each remaining oil area.

[0013] Step S3: Based on the contact angle identification and measurement results obtained in step S2, obtain the pore radius values ​​corresponding to each residual oil distribution area, statistically analyze the numerical distribution and calculate the average radius, obtain the average capillary pressure based on the capillary force formula, and use it as a characteristic parameter to characterize the micro residual oil starting pressure.

[0014] Step S4: Based on the definition of work, combined with the contact angle value and the perimeter of the remaining oil area obtained in step S2, and the average capillary pressure obtained in step S3, calculate the amount of work required to mobilize the remaining oil at the corresponding position.

[0015] Preferably, in step S1, the microfluidic displacement experiment involves four displacement stages, including model saturated oil, pre-treatment water displacement, oil displacement system displacement, and post-treatment water displacement.

[0016] Preferably, the operation process and image acquisition process of each displacement stage are as follows:

[0017] Model saturation with oil: Using a micro displacement constant flow pump and a matching syringe, a constant injection rate is set to saturate the micro model with oil. The operation is stopped when the model is full of simulated oil, and the image of the model saturated with oil is taken and recorded.

[0018] Pre-measure water displacement: The simulated water is stained with a water-soluble dye and impurities are filtered out. A quantitative amount of stained simulated water is taken and water is injected at a fixed rate to displace it. The operation is stopped when the water flow range in the model does not change, i.e. the model shows a high water content. The oil-water distribution is observed and the results of the pre-measure water displacement are recorded by taking pictures.

[0019] Oil displacement system: Prepare an oil displacement system of the required concentration, take a quantitative amount of the system and inject it into the specified slug size at a fixed rate, observe the microscopic phenomena such as reduced interfacial tension, changed wettability or emulsification of the oil displacement system, as well as the fluid state such as the distribution position of oil and water, the ratio of oil and water area and the change of the morphology of the remaining oil, and take pictures to record the displacement results of the system.

[0020] Post-treatment water displacement: This step is the same as the pre-treatment water displacement operation. Observe its effect on the recovery of remaining oil and the oil-water distribution, and take pictures to record the post-treatment water displacement results.

[0021] Preferably, during the displacement process of the oil displacement system, the fixed velocity range is 0.1 μL / min to 1.0 μL / min, and the slug size ranges from 0.1 PV to 1.0 PV.

[0022] Preferably, in step S2, the method for processing the numerical distribution of the contact angle is an automatic measurement method for the microscopic three-phase contact angle based on digital image processing. The recognition of the microscopic experimental image is based on the detection of pixels, and the rock edge is extracted using the Canny edge detection method. The constituent elements of the contact angle include the contact point being the intersection of pixels with three different gray values: oil, water, and rock.

[0023] Preferably, the calculation method used in the automatic measurement method of microscopic three-phase contact angle is the adaptive binarization method. The rock, oil and water are separated and extracted by the adaptive binarization method, the contact angle vertex is identified by the neighborhood detection method, and the three-phase interface is fitted by the least squares idea. The contact angle is calculated according to the relative position of the three points, and the contact angle is batch statistically analyzed by contact angle vertex.

[0024] Preferably, the method for determining the contact angle is as follows: by expanding the monitoring window, taking the set of pixels at the rock edge as the detection target, and using a "5×5" detection window to detect the image matrix, if it is found that oil, water, and rock pixels are adjacent in position in eight directions around a certain rock edge pixel and the oil and water pixels are all in contact, then the rock edge pixel is considered a contact point; if there are multiple adjacent pixels within the "5×5" detection window, the average position of multiple contact points is taken as the contact point. This ensures the accuracy of the contact point and also filters out too many useless contact points.

[0025] Preferably, in step S3, the method for calculating the residual oil starting pressure is to sort the throats in the region where the residual oil is located according to their radius (e.g., r1 > r2 > r3 > ...). Then, the residual oil starting condition only needs to satisfy the fluid flow between the throats with radii of r1 and r2 in the pore body. Therefore, the fluid intrusion resistance of these two throats is taken as the microscopic residual oil starting pressure, and the minimum starting pressure is the highest capillary resistance corresponding to the throats with radii of r1 and r2.

[0026] Preferably, in step S4, the specific calculation method for the work required by the remaining oil is as follows:

[0027] S401. Taking the clustered residual oil in a certain area as an example, the energy required to utilize the residual oil in this area can be calculated using formula (1):

[0028] W c1 =P c1 ·l c1 (1)

[0029] Among them, W c1 -- The amount of work required to utilize the clustered residual oil in a certain area;

[0030] P c2-- The starting pressure value required to utilize the clustered residual oil in a certain area;

[0031] l c3 -- The perimeter of the contact contour between the clustered residual oil in a certain area and the channel wall;

[0032] n — Clustered residual oil markers in a certain area (n = 1, 2, 3, ...);

[0033] S402. The energy required to utilize all the remaining clustered oil in the mobilization model can be calculated using formula (2):

[0034] W c =W c1 +W c2 +W c3 +…+W cn =P c1 ·l c1 +P c2 ·l c2 +…P cn ·l cn (2)

[0035] Among them, W cn -- The amount of work required to utilize the remaining oil clusters in each area;

[0036] P cn -- The starting pressure value required to utilize the remaining oil clusters in each area;

[0037] l cn --Circumference of the contact profile between the clustered residual oil in each area and the channel wall;

[0038] n -- Clustered residual oil markers for each region (n = 1, 2, 3, ...);

[0039] S403. The energy required to utilize all remaining oil in the model can be calculated using formula (3):

[0040] W = W c +W k +W z +W d +W m (3)

[0041] Where W — the work required to utilize all types of microscopic residual oil;

[0042] W c —The amount of work required to utilize all the remaining clustered oil;

[0043] W k -- The amount of work required to utilize all the remaining porous oil;

[0044] W ZThe amount of work required to utilize all remaining oil in the column;

[0045] W d —The amount of work required to utilize all remaining droplets of oil;

[0046] W m —The amount of work required to utilize all remaining film-like oil;

[0047] S504. Based on the above numerical calculation results, the curve of the remaining oil kinetic work change with the displacement stage can be plotted to further analyze the energy conversion law.

[0048] (III) Beneficial Effects

[0049] The microscopic oil displacement energy conversion analysis method provided by this invention utilizes computer graphics and computer vision methods and means to form a microscopic residual oil visualization dynamic analysis system. It can perform dynamic analysis of microscopic residual oil from a visualization perspective, effectively guiding the actual water injection development of oilfields in the high water cut period. By adjusting the development, it can increase the recoverable reserves of residual oil in the high water cut period. By studying the stress analysis of microscopic discontinuous residual oil in the high water cut period, it can determine the location of recoverable residual oil or the minimum mobilization conditions of movable residual oil, effectively improving the recovery degree of residual oil in the high water cut period, thereby improving the economic benefits of oilfield development, which is of great significance to increasing oilfield production. Attached Figure Description

[0050] Figure 1 This is a flowchart of the microscopic oil displacement energy conversion analysis method according to an embodiment of the present invention;

[0051] Figure 2 The figures shown are the results of the microscopic displacement experiment in the embodiment of the present invention, where a is a schematic diagram of the saturated oil stage, b is a schematic diagram of water displacement before the measures are taken, c is a schematic diagram of the oil displacement system, and d is a schematic diagram of water displacement after the measures are taken.

[0052] Figure 3 The image shows the result of three-dimensional contact angle marking without angle according to an embodiment of the present invention, where a is an overall view of the contact angle recognition result and b is a magnified partial view of the contact angle recognition result;

[0053] Figure 4 This is a microscopic residual oil starting pressure field diagram of an embodiment of the present invention;

[0054] Figure 5 This is a diagram showing the microscopic residual oil start-up calculation results of an embodiment of the present invention;

[0055] Figure 6 This is a graph showing the change in energy required to utilize the remaining oil in each displacement stage of an embodiment of the present invention. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Figure 1 This is a flowchart of the microscopic oil displacement energy conversion analysis method according to an embodiment of the present invention, as shown below. Figure 1 As shown, this invention provides a method for analyzing the energy conversion of microscopic oil displacement, specifically including:

[0058] Step S1: The pore throat channel pattern is fabricated into a glass micro-model using a wet etching method, and the model is used to conduct microfluidic displacement experiments. During the experiment, the results images of each displacement stage are recorded.

[0059] Step S2: Using the experimental result images of each displacement stage obtained in step S1, identify and obtain the distribution of contact angle values, and measure the shape parameter values ​​such as the perimeter of each remaining oil area.

[0060] Step S3: Based on the contact angle identification and measurement results obtained in step S2, obtain the pore radius values ​​corresponding to each residual oil distribution area, statistically analyze the numerical distribution and calculate the average radius, obtain the average capillary pressure based on the capillary force formula, and use it as a characteristic parameter to characterize the micro residual oil starting pressure.

[0061] Step S4: Based on the definition of work, combined with the contact angle value and the perimeter of the remaining oil area obtained in step S2, and the average capillary pressure obtained in step S3, calculate the amount of work required to mobilize the remaining oil at the corresponding position.

[0062] In this method, in step S1, a pore throat channel pattern is designed and formed according to the experimental objective. A microscopic glass model for the experiment is fabricated using a wet etching method, and the model is used to conduct a microfluidic displacement experiment. During the experiment, the result images of each displacement stage are recorded. The microfluidic displacement experiment involves four displacement stages, including model saturation with oil, pre-treatment water injection displacement, oil displacement system displacement, and post-treatment water injection displacement. The specific image processing procedure for each displacement stage is as follows:

[0063] Model saturation with oil: Using a micro displacement constant flow pump and a matching syringe, a constant injection rate is set to saturate the micro model with oil. The operation is stopped when the model is full of simulated oil, and the image of the model saturated with oil is taken and recorded.

[0064] Pre-measure water displacement: The simulated water is stained with a water-soluble dye and impurities are filtered out. A quantitative amount of stained simulated water is taken and water is injected at a fixed rate to displace it. The operation is stopped when the water flow range in the model does not change, i.e. the model shows a high water content. The oil-water distribution is observed and the results of the pre-measure water displacement are recorded by taking pictures.

[0065] Oil displacement system: Prepare an oil displacement system of the required concentration, take a quantitative amount of the system and inject it into the specified slug size at a fixed rate, observe the microscopic phenomena such as reduced interfacial tension, changed wettability or emulsification of the oil displacement system, as well as the fluid state such as the distribution position of oil and water, the ratio of oil and water area and the change of the morphology of the remaining oil, and take pictures to record the displacement results of the system.

[0066] Post-treatment water displacement: This step is the same as the pre-treatment water displacement operation. Observe its effect on the recovery of remaining oil and the oil-water distribution, and take pictures to record the post-treatment water displacement results.

[0067] In practical applications, during the displacement process of the oil displacement system, the fixed velocity range is 0.1 μL / min to 1.0 μL / min, and the slug size ranges from 0.1 PV to 1.0 PV.

[0068] In this method, in step S2, the method for processing the numerical distribution of the contact angle is based on a microscopic three-phase contact angle automatic measurement method established by digital image processing. The detection of the microscopic experimental image is based on pixel detection, and the rock edge is extracted using the Canny edge detection method. The constituent elements of the contact angle include the contact point being the intersection of pixels with three different gray values: oil, water, and rock.

[0069] In practical applications, the automatic measurement method for microscopic three-phase contact angles uses an adaptive binarization method. The adaptive binarization method is used to separate and extract rock, oil and water, and the contact angle vertices are identified by the neighborhood detection method. The three-phase interface is fitted using the least squares approach. The contact angle is calculated based on the relative positions of the three points, and the contact angles are batch statistically analyzed using the contact angle vertices as units.

[0070] It is important to note that the specific method for determining the contact angle is as follows: by expanding the monitoring window and using the set of pixels at the rock edge as the detection target, the image matrix is ​​detected using a "5×5" detection window. If it is found that oil, water, and rock pixels are adjacent in position in eight directions around a certain rock edge pixel and the oil and water pixels are all in contact, then the rock edge pixel is considered a contact point. If there are multiple adjacent pixels within the "5×5" detection window, the average position of the multiple contact points is taken as the contact point. This ensures the accuracy of the contact point and also filters out too many useless contact points.

[0071] In this method, in step S3, the calculation method for the residual oil starting pressure is to sort the throats in the region where the residual oil is located according to their radius (e.g., r1 > r2 > r3 > ...). Then, the residual oil starting condition only needs to satisfy the fluid flow between the throats with radii of r1 and r2 in the pore body. Therefore, the fluid intrusion resistance of these two throats is taken as the microscopic residual oil starting pressure, and the minimum starting pressure is the highest capillary resistance corresponding to the throats with radii of r1 and r2.

[0072] In step S3, the formula for calculating capillary force is as follows:

[0073]

[0074] Among them, P c σ is the capillary force, Pa; σ is the interfacial tension, mN / m; r is the capillary radius, m.

[0075] In practical applications, in step S4, work is a measure of changing the form of energy. Therefore, the value of work done can be used as a numerical representation of the energy conversion between water and oil. The definition of work is W = F·1·cosθ, where W is work, i; F is force, N; and l is distance, m.

[0076] In this method, the specific calculation method for the work required by the remaining oil in step S4 is as follows:

[0077] S401. Taking the clustered residual oil in a certain area as an example, the energy required to utilize the residual oil in this area can be calculated using formula (1):

[0078] W c1 =P c1 ·l c1 (1)

[0079] Among them, W c1 -- The amount of work required to utilize the clustered residual oil in a certain area;

[0080] P c2 -- The starting pressure value required to utilize the clustered residual oil in a certain area;

[0081] l c3 -- The perimeter of the contact contour between the clustered residual oil in a certain area and the channel wall;

[0082] n -- Clustered residual oil markers in a certain area (n = 1, 2, 3, ...);

[0083] S402. The energy required to utilize all the remaining clustered oil in the mobilization model can be calculated using formula (2):

[0084] W c =W c1 +W c2 +W c3+…+W cn =P c1 ·l c1 +P c2 ·l c2 +…P cn ·l cn (2)

[0085] Among them, W cn -- The amount of work required to utilize the remaining oil clusters in each area;

[0086] P cn -- The starting pressure value required to utilize the remaining oil clusters in each area;

[0087] l cn --Circumference of the contact profile between the clustered residual oil in each area and the channel wall;

[0088] n -- Clustered residual oil markers for each region (n = 1, 2, 3, ...);

[0089] S403. The energy required to utilize all remaining oil in the model can be calculated using formula (3):

[0090] W = W c +W k +W z +W d +W m (3)

[0091] Where W — the work required to utilize all types of microscopic residual oil;

[0092] W c — The amount of work required to utilize all remaining clustered oil;

[0093] W k -- The amount of work required to utilize all the remaining porous oil;

[0094] W z The amount of work required to utilize all remaining oil in the column;

[0095] W d The amount of work required to utilize all remaining droplets of oil;

[0096] W m —The amount of work required to utilize all remaining film-like oil;

[0097] S504. Based on the above numerical calculation results, the curve of the remaining oil kinetic work change with the displacement stage can be plotted to further analyze the energy conversion law.

[0098] This invention provides a microscopic oil displacement energy conversion analysis method. Utilizing computer graphics and computer vision methods, it forms a visualized dynamic analysis system for microscopic residual oil. This system enables dynamic analysis of microscopic residual oil from a visual perspective, effectively guiding actual water injection development in oilfields during high water cut periods. By adjusting development methods, it increases the recoverable reserves of residual oil during high water cut periods. Through stress analysis of the discontinuous microscopic residual oil during high water cut periods, it identifies the location of recoverable residual oil or the minimum mobilization conditions for movable residual oil, effectively improving the recovery rate of residual oil during high water cut periods, thereby enhancing the economic benefits of oilfield development and having significant implications for increasing oilfield production. The working principle of this microscopic oil displacement energy conversion analysis method is described in detail below:

[0099] Step 1: The pore throat channel pattern is fabricated into a glass micro-model using a wet etching method, and the model is used to conduct microfluidic displacement experiments. During the experiment, the results images of each displacement stage are recorded.

[0100] In this embodiment, as Figure 2 As shown, the specific image processing procedure for each displacement stage is as follows:

[0101] Model saturated oil: such as Figure 2 As shown in a, a micro-displacement constant flow pump and a matching syringe are used to saturate the micro-model with oil at a constant injection rate. The operation is stopped when the model is full of simulated oil, and the image of the model saturated with oil is recorded by taking a picture.

[0102] Pre-treatment water displacement: such as Figure 2 As shown in b, the simulated water was stained with a water-soluble dye and impurities were filtered out. A quantitative amount of stained simulated water was taken and a fixed rate of water was injected to displace the water. The water flow range in the model changed very little, that is, the model showed a high water content. The operation was stopped when the oil-water distribution was observed and the water displacement result before the measure was recorded by taking pictures.

[0103] Oil displacement systems: such as Figure 2 As shown in c, prepare an oil displacement system with the required concentration, take a quantitative amount of the system and inject it into the specified sluice block size at a fixed rate, observe the microscopic phenomena of the oil displacement system and the oil-water distribution state, and take pictures to record the displacement results of the system.

[0104] Post-treatment water displacement: such as Figure 2 As shown in d, this step is consistent with the water displacement operation before the measure. Observe its effect on the mobilization of the remaining oil and the oil-water distribution state, and take pictures to record the water displacement result image after the measure.

[0105] Step 2: Using the experimental results images of each displacement stage, identify and obtain the distribution of contact angle values, and measure the shape parameters such as the perimeter of each remaining oil area.

[0106] In this embodiment, an adaptive binarization method is used to separate and extract rock, oil, and water. A neighborhood detection method is employed to identify contact angle vertices, and a least-squares approach is used to fit the three-phase interface. The contact angles are calculated based on the relative positions of the three points, and batch statistics are performed on the contact angles at each contact angle vertex. The accuracy and effectiveness of this method are verified by manual measurement results, the wettability of the microfluidic model, and the characteristics of the capillary pressure curves.

[0107] In practical applications, an automatic measurement method for microscopic three-phase contact angles is established based on digital image processing. Image detection is based on pixel-level detection, using the Canny edge detection method to extract rock edges. Among the elements constituting the contact angle, the contact point is the intersection of pixels with three different grayscale values: oil, water, and rock. However, contact angle identification based on this approach encounters the following problems: image boundaries are not properly identified, and there are too few oil and water pixels around the contact point, resulting in contact angles that are useless for microscopic analysis of residual oil stress or are difficult to utilize. Therefore, the algorithm is improved to ensure that the contact angles identified are usable. The main operation is to expand the monitoring window, using the rock edge pixel set as the detection target, and utilizing a "5×5" detection window to detect the image matrix. If it is found that oil, water, and rock pixels are adjacent in position and oil and water pixels are in contact with each other in 8 directions around a rock edge pixel, then the rock edge pixel is considered a contact point. If there are multiple adjacent pixels in the "5×5" detection window, the average position of multiple contact points is taken as the contact point. This can ensure the accuracy of the contact point and filter out too many useless contact points.

[0108] In this embodiment, the automatic measurement method for microscopic three-phase contact angle is developed into a software system, such as... Figure 3 of Figure 3 a and Figure 3 As shown in b, this software is used to complete... Figure 2 of Figure 2 a to Figure 2 The angles of each oil-water contact surface in step d are identified and numerically calculated. Table 1 shows the numerical calculation results of the contact angles. As shown in Table 1, the variation law of the contact angle in each displacement stage is analyzed, and the characteristic values ​​of the contact angle in each displacement stage are obtained by statistical processing.

[0109] Table 1. Calculation results of contact angle numerical values

[0110] Value / ° Pre-treatment water displacement / % Oil displacement system displacement / % Post-treatment water displacement / % 0-75° (hydrophilic) 34.83 36.17 40.52 75-105° (neutral) 15.26 14.81 14.03 105-180° (Oleophilic) 49.90 49.02 45.45 average value 100.01° 98.39° 94.75°

[0111] Step S3: Based on the contact angle identification and measurement results obtained in step S2, obtain the pore radius values ​​corresponding to each residual oil distribution area, statistically analyze the numerical distribution and calculate the average radius, obtain the average capillary pressure based on the capillary force formula, and use it as a characteristic parameter to characterize the microscopic residual oil starting pressure.

[0112] In this embodiment, by analyzing the contact angle data characteristics under different displacement stages, different residual oil types, and different pore throat environments, the dynamic trends of the number, mean, and standard deviation of contact angles under each condition are clarified, further revealing the dynamic changes in the microscopic oil-water contact relationship at each stage of waterflooding. Considering the distribution characteristics of contact angle and pore throat radius, a model for calculating the average capillary pressure curve is established. The microscopic contact angle data is incorporated into the overall dynamic law of the microfluidic oil-water system, combined with the Brooks-Corey capillary pressure calculation model, to verify the accuracy of the calculation model.

[0113] In practical applications, residual oil startup only requires fluid to flow between the two larger throats of the pore body. Therefore, the fluid intrusion resistance of these two throats is taken as the microscopic residual oil startup pressure, and the minimum startup pressure is the highest capillary resistance corresponding to the two larger throats.

[0114] In this embodiment, as Figure 4 and Figure 5 As shown, different types of residual oil in different regions are identified. Based on the contact angle measurement results, the pore throat radius of the residual oil distribution area is measured and statistically analyzed, and the average radius is calculated. Based on the obtained parameter data, the average capillary pressure is obtained using the capillary force formula. This average capillary pressure is used as a characteristic parameter to characterize the microscopic residual oil starting pressure, thereby realizing a dynamic description of the change of starting pressure of various types of residual oil with saturation.

[0115] Step S4: Based on the definition of work, combined with the contact angle value and the perimeter of the remaining oil area obtained in step S2, and the average capillary pressure obtained in step S3, calculate the amount of work required to mobilize the remaining oil at the corresponding position.

[0116] In this embodiment, based on the definition of work, the work done is used as a numerical representation of the energy conversion between water and oil. The work done can be quantified by obtaining parameters such as the starting pressure at a certain location and the corresponding residual oil profile circumference. The total work done by each type of residual oil can be represented by the sum of the work done by all parts of that type of residual oil. The calculation method for the total work done by all residual oils is similar. This method provides an important reference for the selection of measures and the adjustment of implementation parameters during the displacement process.

[0117] In practical applications, such as Figure 6As shown, work is a measure of changing the form of energy, so the work done can be used as a numerical representation of the energy conversion between water and oil. According to the definition formula of work W=F·l·cosθ, and the starting pressure value has a corresponding relationship with the remaining oil module, the work done can be quantified by obtaining the starting pressure at a certain position and the corresponding remaining oil profile perimeter. Taking the clustered remaining oil in a certain area as an example, the energy required to mobilize the remaining oil in this area can be calculated by formula (1), while the energy required to mobilize all clustered remaining oil or all remaining oil in the model is calculated by formula (2) and formula (3) respectively. The curve of the work done by the remaining oil mobilization with the displacement stage can be plotted to analyze the energy conversion law in depth.

[0118] Compared with traditional methods for studying the conditions for residual oil utilization, this embodiment can accurately obtain the angles formed at each oil-water contact point; it can reasonably characterize the starting pressure of each residual oil region based on the capillary pressure calculation formula, and measure the shape parameters of the residual oil through image recognition operation to calculate the work done by the residual oil at each stage to represent the energy change law, aiming to expand the understanding of the starting conditions for residual oil and the energy conversion law of oil and water.

[0119] In practical applications, this embodiment, based on a detailed study of the microstructure and physical properties of the target reservoir, fully utilizes microscopic experimental methods and image processing techniques. Through simulation experiments and data analysis, it identifies and obtains contact angles and various residual oil shape parameters based on experimental image results. It completes operational steps such as effectively measuring start-up pressure and rationally characterizing oil displacement energy, clarifying the energy conversion laws during the displacement process, and providing strong support and effective reference for scheme design and measure adjustment. Its beneficial effects include:

[0120] (1) As a force analysis of micro-discontinuous residual oil during the high water cut period, the location of recoverable residual oil or the minimum mobilization conditions of movable residual oil can be further studied, so as to further improve the recovery degree of residual oil during the high water cut period.

[0121] (2) By using computer graphics and computer vision methods and means to form a microscopic residual oil visualization dynamic analysis system, it is possible to perform dynamic analysis of microscopic residual oil from a visualization perspective. This system can effectively guide the actual water injection development of oilfields in the high water-cut period, make further development adjustments, increase the recoverable reserves of residual oil in the high water-cut period, and thus improve the economic benefits of oilfield development. This is of great significance to the increase of oilfield production.

[0122] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for analyzing the energy conversion of microscopic oil displacement, characterized in that, include: Step S1: The pore throat channel pattern is fabricated into a glass micro-model using a wet etching method, and the model is used to conduct microfluidic displacement experiments. During the experiment, the results images of each displacement stage are recorded. Step S2: Using the experimental result images of each displacement stage obtained in step S1, identify and obtain the distribution of contact angle values, and measure the shape parameter values ​​such as the perimeter of each remaining oil area. Step S3: Based on the contact angle identification and measurement results obtained in step S2, obtain the pore radius values ​​corresponding to each residual oil distribution area, statistically analyze the numerical distribution and calculate the average radius, obtain the average capillary pressure based on the capillary force formula, and use it as a characteristic parameter to characterize the micro residual oil starting pressure. Step S4: Based on the definition of work, combined with the contact angle value and the perimeter of the remaining oil area obtained in step S2, and the average capillary pressure obtained in step S3, calculate the amount of work required to mobilize the remaining oil at the corresponding position.

2. The microscopic oil displacement energy conversion analysis method according to claim 1, characterized in that, In step S1, the microfluidic displacement experiment involves four displacement stages, including model saturated oil, pre-treatment water injection displacement, oil displacement system displacement, and post-treatment water injection displacement.

3. The microscopic oil displacement energy conversion analysis method according to claim 2, characterized in that, The specific procedures for each displacement stage and the acquisition of the resulting images are as follows: Model saturation with oil: Using a micro displacement constant flow pump and a matching syringe, a constant injection rate is set to saturate the micro model with oil. The operation is stopped when the model is full of simulated oil, and the image of the model saturated with oil is taken and recorded. Pre-measure water displacement: The simulated water is stained with a water-soluble dye and impurities are filtered out. A quantitative amount of stained simulated water is taken and water is injected at a fixed rate to displace it. The operation is stopped when the water flow range in the model does not change, i.e. the model shows a high water content. The oil-water distribution is observed and the results of the pre-measure water displacement are recorded by taking pictures. Oil displacement system: Prepare an oil displacement system of the required concentration, take a quantitative amount of the system and inject it into the specified slug size at a fixed rate, observe the microscopic phenomena such as reduced interfacial tension, changed wettability or emulsification of the oil displacement system, as well as the fluid state such as the distribution position of oil and water, the ratio of oil and water area and the change of the morphology of the remaining oil, and take pictures to record the displacement results of the system. Post-treatment water displacement: This step is the same as the pre-treatment water displacement operation. Observe its effect on the recovery of remaining oil and the oil-water distribution, and take pictures to record the post-treatment water displacement results.

4. The microscopic oil displacement energy conversion analysis method according to claim 3, characterized in that, During the displacement process of the oil displacement system, the fixed velocity range is 0.1 μL / min to 1.0 μL / min, and the slug size ranges from 0.1 PV to 1.0 PV.

5. The microscopic oil displacement energy conversion analysis method according to claim 1, characterized in that, In step S2, the method for processing the numerical distribution of the contact angle is based on an automatic measurement method for the microscopic three-phase contact angle established by digital image processing. The identification of the microscopic experimental image is based on the detection of pixels, and the Canny edge detection method is used to extract the rock edge. The constituent elements of the contact angle include the contact point being the intersection of pixels with three different gray values: oil, water, and rock.

6. The microscopic oil displacement energy conversion analysis method according to claim 5, characterized in that, The automatic measurement method for microscopic three-phase contact angle uses an adaptive binarization method. The adaptive binarization method is used to separate and extract rock, oil and water, and the contact angle vertex is identified by the neighborhood detection method. The three-phase interface is fitted using the least squares idea. The contact angle is calculated based on the relative position of the three points, and the contact angle is batch statistically analyzed in units of the contact angle vertex.

7. The microscopic oil displacement energy conversion analysis method according to claim 6, characterized in that, The specific method for determining the contact angle is as follows: by expanding the monitoring window and taking the set of pixels at the rock edge as the detection target, the image matrix is ​​detected using a "5×5" detection window. If it is found that oil, water, and rock pixels are adjacent in position in eight directions around a certain rock edge pixel and the oil and water pixels are in contact, then the rock edge pixel is considered a contact point. If there are multiple adjacent pixels within the "5×5" detection window, the average position of the multiple contact points is taken as the contact point. This ensures the accuracy of the contact point and also filters out too many useless contact points.

8. The microscopic oil displacement energy conversion analysis method according to claim 1, characterized in that, In step S3, the method for calculating the residual oil starting pressure is to sort the throats in the region where the residual oil is located according to their radius (e.g., r1 > r2 > r3 > ...). The residual oil starting condition only needs to satisfy the fluid flow between the throats with radii of r1 and r2 in the pore body. Therefore, the fluid intrusion resistance of these two throats is taken as the microscopic residual oil starting pressure, and the minimum starting pressure is the highest capillary resistance corresponding to the throats with radii of r1 and r2.

9. The microscopic oil displacement energy conversion analysis method according to claim 1, characterized in that, In step S4, the specific calculation method for the work required by the remaining oil is as follows: S401. Taking the clustered residual oil in a certain area as an example, the energy required to utilize the residual oil in this area can be calculated using formula (1): W c1 =P c1 ·l c1 (1) Among them, W c1 —The amount of work required to utilize the clustered residual oil in a certain area; P c2 —The starting pressure value required to utilize the clustered residual oil in a certain area; l c3 —The perimeter of the contact contour between the clustered residual oil in a certain area and the channel wall; n——A cluster of remaining oil markers in a certain area (n=1,2,3,…); S402. The energy required to utilize all the remaining clustered oil in the mobilization model can be calculated using formula (2): W c =q c1 +W c2 +W c3 +…+W cn =P c1 ·l c1 +P c2 ·l c2 +…P cn ·l cn (2) Among them, W cn —The amount of work required to utilize the remaining oil clusters in each region; P cn —The starting pressure required to utilize the remaining oil clusters in each area; l cn —The perimeter of the contact contour between the clustered residual oil in each area and the channel wall; n——The cluster of remaining oil in each region (n=1,2,3,…); S403. The energy required to utilize all remaining oil in the model can be calculated using formula (3): W=W c +W k +W z +W d +W m (3) Where W is the work required to utilize all types of microscopic residual oil. W c —The amount of work required to utilize all the remaining clustered oil; W k —The amount of work required to utilize all the remaining porous oil; W z —The amount of work required to utilize all remaining oil in the column; W d —The amount of work required to utilize all remaining droplets of oil; W m —The amount of work required to utilize all remaining film-like oil; S504. Based on the above numerical calculation results, the curve of the remaining oil kinetic work change with the displacement stage can be plotted to further analyze the energy conversion law.

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