Research Method for Fluid Distribution at Sub - millimeter Scale in Complex - Structure Large Models

Abstract

A research method for fluid distribution at sub - millimeter scale in large models of complex structures, belonging to the field of oil and gas fields, includes: Step 1: Extraction of geological simulation of complex - structure reservoirs and fabrication of large models at meter - scale for indoor simulation experiments; Step 2: Design of experimental fluid injection parameters based on the similarity principle; Step 3: Steps of indoor simulation experiments; Step 4: Obtaining the original CT values of experimental media; Step 5: Determining the CT values of cores near each layer and physical property barriers in the complex - structure model; Step 6: Three - dimensional oil - water distribution and quantitative description at each part of the model at different development stages; Step 7: Analysis of three - dimensional oil - water distribution at the physical property barrier part; Step 8: Evaluation of the effectiveness of remaining oil production near the barrier at different development stages. This research method for fluid distribution at sub - millimeter scale in large models of complex structures has important guiding significance for the design of development plans for complex - structure parts of oil fields.

Description

Technical Field:

[0001] The present invention belongs to the field of oil and gas fields, and particularly relates to a research method for fluid distribution at sub-millimeter scale in a large model of complex structures. Background Art:

[0002] Residual oil refers to the crude oil that cannot be produced from the oil reservoir by different development methods under the current oilfield development technology level, and is the core object of research in the field of enhanced oil recovery in the world at present.

[0003] Currently, the research on residual oil mainly uses numerical simulation methods and logging interpretation methods macroscopically, and the distribution law of residual oil between oil reservoirs and wells can be obtained. The scale range of the results is from meters to dozens of meters, and the analysis results have problems of extremely difficult verification and poor effect on complex structural parts of the oil reservoir. At the same time, worldwide, the research on residual oil uses industrial CT detection and nuclear magnetic fluid detection methods to obtain quantitative data of residual oil at the micron level of pore scale, and computer algorithms such as digital cores can obtain the distribution law of fluids in pores. However, there is a problem that the similarity between the simulation experiment detection method and the actual oil reservoir development process cannot be achieved, and due to the too small size of the detection samples in this type of microscopic detection method, even if a large number of detection samples are increased at high cost, it is difficult to obtain an understanding that conforms to the fluid distribution law in the actual oil reservoir structure. Summary of the Invention:

[0004] The purpose of the present invention is to provide a SBS modified asphalt anti-freezing and pulling-out device technology applicable to PHC pile foundations, mainly solving the problems that the microscopic quantification method of residual oil pores cannot effectively reflect the distribution law of residual oil in the oil reservoir structure, and the accuracy size of the residual oil interpretation results of logging and numerical simulation macroscopic methods is too large to effectively guide the optimization of the residual oil development plan for each structural part of the complex structural oil reservoir.

[0005] Based on the above purpose, the technical solution adopted by the present invention is: a research method for fluid distribution at sub-millimeter scale in a large model of complex structures, and the research method is as follows:

[0006] Based on the above purpose, the technical solution adopted by the present invention is: a research method for fluid distribution at sub-millimeter scale in a large model of complex structures, and the research method is as follows:

[0007] (1) Extraction for geological simulation of complex-structured reservoirs and fabrication of large-scale models at the meter scale for indoor simulation experiments; To ensure that the indoor water flooding experiments carried out using large-scale models at the meter scale in this project can truly reproduce the physical essence of the flow phenomenon of oil and water in the oil reservoir under the same well pattern conditions, and to ensure that the physical essence of the model experiment process is the same as that of the flow phenomenon in the reservoir formation, so as to achieve the similarity of fluid mechanics; Maintaining geometric similarity is the most basic requirement for fabricating a fluid mechanics experimental model. During the model fabrication process, ensure that the scale ratios of all corresponding linear lengths of the model and the simulated formation prototype are consistent. The length, width, and height scale ratios Kl are all 0.04. Fabricate the model at this scale ratio in the laboratory and conduct simulated flow experiments.

[0008]

[0009] In the formula: l'—represents the model length; l—represents the formation length;

[0010] (2) Similarity principle for designing experimental fluid injection parameters; On the premise of ensuring the geometric similarity of the model, to ensure the similarity of the seepage process of fluid micro-elements during the fluid flow process in the model and the oil reservoir, it is required that the time required for the fluid to pass through the corresponding paths in the two must be in a certain proportion. The time scale ratio is calculated as follows:

[0011]

[0012] In the formula: t’—represents the model time;

[0013] t—represents the formation time;

[0014] v’—represents the model velocity;

[0015] v—represents the formation velocity;

[0016] Among them, based on geometric similarity and kinematic similarity, the l 、 v Scale ratios of kinematic quantities are as follows:

[0017] Acceleration scale ratio:

[0018] Volume flow rate scale ratio:

[0019] Kinematic viscosity scale ratio:

[0020] Angular velocity scale ratio:

[0021] In the formula: a’—represents the model acceleration;

[0022] a—represents the formation acceleration;

[0023] ω’—represents the model angular velocity;

[0024] ω—represents the angular velocity of the formation.

[0025] The length ratio and velocity ratio of the model and the oil layer are determined by calculation, and then the ratio of the kinematic quantities of the model and the oil layer is calculated to ensure the similarity of the fluid seepage process in the model and the oil layer.

[0026] (3) Indoor simulation experiment steps: using a large heterogeneous model to carry out water-to-oil flooding experiments, water flooding at different stages until the water content reaches 98% and then ending the experiment, and performing CT scanning to obtain the distribution map of the remaining oil in each layer;

[0027] (4) Obtaining the original CT value of the experimental medium; in order to determine and calculate the changes in fluid saturation in the test model at different experimental stages, CT detection of different components was carried out before the experiment, and CT value testing and calibration were performed;

[0028] (5) Determination of the CT values ​​of the cores near each layer and physical barrier of the complex structural model; the computer calculates the X-ray absorption coefficient of each voxel (relative to the volume of the tissue "block" corresponding to each pixel), that is, the attenuation coefficient (μ value), which is the digital basis for imaging. w ) is 1, bone (μ B ) is 2.0, air (μ A ) is 0.0013 (≥0) [1] The X-ray absorption capacity of each voxel obtained by converting the μ value, that is, the unified unit for expressing the tissue density in the CT image, is a relative value called the CT value, which stipulates that the attenuation coefficient (μ) of the measured substance M ) and water as the ratio, and the attenuation coefficients of bone and air are used as the upper and lower limits for division, thereby calculating the CT value.

[0029]

[0030] Where: α is the graduation factor. Now the CT value is generally expressed in Hounsfield units (Hu), so α is 1000;

[0031] Using the CT value calculation method, the commonly used oil saturation calculation formula is as follows:

[0032]

[0033] Where: H two-phase ——Core CT value at a certain time during water flooding,

[0034] H oil ― CT value of crude oil,

[0035] H a,r―Average CT value of dry core before saturation with formation water,

[0036] H air ―CT value of air,

[0037] H w,r ―Average CT value of wet core after saturation with formation water,

[0038] H water ―CT value of formation water

[0039] Since it is a core model with a complex multi-layer structure, during the detection process, each part has different fluid distribution laws in a single detection process. Therefore, it is necessary to calculate the fluid distribution of each part separately. The present invention designs an oil saturation calculation and statistical formula according to the volume weight of each part as follows, and conducts the calculation and analysis of the oil saturation of each part's pixel points and the oil saturation of the model.

[0040]

[0041]

[0042] where:S ori —Oil saturation of the part, [%, i = 1~x×y×z]

[0043] V—Volume value of the part, [cm 3

[0044] W Vi～n —Volume weight of the part, [%, i = 1~13]

[0045] x,y,z—Analysis part x,y,z scan pixel number;

[0046] (6) Three-dimensional oil-water distribution and quantitative description of each part of the model at different development stages; Detect the three-dimensional model at different development stages, and calculate the sub-millimeter scale quantitative data of the remaining oil distribution inside the core at different water flooding stages based on the large-scale medical CT detection data;

[0047] (7) Analysis of three-dimensional oil-water distribution in the physical property interlayer part; Analyze the remaining oil distribution law at different water flooding stages near the physical property interlayer for the remaining oil distribution data obtained by calculating the large-scale medical CT detection results of the physical oil displacement experiment model, and evaluate the remaining oil production law at the millimeter scale;

[0048] (8) Evaluation of the remaining oil production effect near the interlayer at different development stages; Conduct physical simulation of oil displacement by methods such as pressure increase, changing the liquid flow direction, and straight-flat combination in sequence for the model after conventional water flooding of the basic well pattern of the meter-scale three-dimensional complex model, and conduct scanning analysis of the remaining oil distribution to evaluate the effect of various measures. ​

[0049] In the step (3), the experimental steps are as follows:

[0050] 1) A high-displacement vacuum pump evacuates and saturates water at the outlet end of the core, and then a displacement pump is used to inject water saturated with KI into the model until the injection and production fluid volumes are equal. Record the saturated water volume, calculate the porosity, and conduct CT scan tests.

[0051] 2) Saturate the core with oil, and displace water with oil at an injection rate of 2.40 ml / min until only oil comes out at the outlet end of the model; record the oil injection volume, water production volume, oil production volume, and inlet end pressure at regular intervals.

[0052] 3) End the water flooding process when the real-time water cut at the outlet end reaches 98%. Summarize the oil production of each well and calculate the recovery factor.

[0053] 4) Conduct CT tests to analyze the remaining oil distribution in each layer.

[0054] 5) Change the oil displacement scheme and continue the displacement. Repeat steps 3) and 4) until the experiment ends.

[0055] After adopting the above technical solution, the present invention has the following advantages:

[0056] 1. Compared with the traditional resistivity saturation measurement method, the present invention improves the accuracy of remaining oil description by several orders of magnitude, and the test analysis accuracy of the detection results for complex sandstone models can reach 0.25 mm.

[0057] 2. The present method uses a complex structure model with a meter-scale size to carry out fluid displacement experiments, ensuring the similarity between the model simulation experiment and the oil reservoir development process. At the same time, the method is reliable in obtaining sub-millimeter scale fluid distribution quantification data and does not damage the detected model structure.

[0058] 3. Based on the analysis of sub-millimeter scale fluid distribution data, the present method can analyze the fluid distribution state in different structural parts at different development stages and provide quantitative data on oil-water fluid distribution. The test results are highly similar to the oil reservoir development and can be used to guide the design and selection of the next development plan for the oilfield.

[0059] 4. The present invention establishes a quantitative test and analysis method for sub-millimeter scale fluid distribution in complex structure models.

[0060] 5. For the model after conventional water flooding in the basic well pattern, the present method successively conducts physical simulations of oil displacement by methods such as pressure increase, changing the liquid flow direction, and straight-flat combination. The scanning analysis results of the remaining oil distribution show that the oil increment effect is the best in the straight-flat combination stage. Description of the Drawings:

[0061] Figure 1 Flow chart of the experimental detection method for sub-millimeter scale fluid distribution of the present invention.

[0062] Figure 2 Schematic diagram of the comparison of the designed model size after actual reservoir extraction;

[0063] Figure 3 3D development display diagram of the indoor complex pore model;

[0064] Figure 4 Schematic diagram of the original data of X-ray detection of core samples;

[0065] Figure 5 2D diagram of fluid distribution converted from X-ray scan data of core samples;

[0066] Figure 6 3D diagram of fluid distribution at sub-millimeter scale;

[0067] Figure 7 Curves of recovery factor, injection pressure and water cut at different displacement stages of the model;

[0068] Figure 8 Example of fluid distribution at different development stages of reservoir layer 1 of the model;

[0069] Figure 9 Example of a schematic diagram of fluid distribution at the saturated oil and straight-flat combined stage at the bottom barrier part. Specific implementation method:

[0070] Referring to the figures, a research method for fluid distribution at sub-millimeter scale in a large model with complex structure is as follows:

[0071] (1) Extraction of geological simulation of complex-structured reservoirs and production of large models at meter scale for indoor simulation experiments; To ensure that the indoor water flooding experiment using the large model at meter scale in this project can truly reproduce the physical essence of the oil-water flow phenomenon in the reservoir under the same well pattern conditions, ensure that the physical essence of the model experiment process is the same as that of the flow phenomenon in the reservoir formation, and achieve the similarity of fluid mechanics; Maintaining geometric similarity is the most basic requirement for the production of fluid mechanics experimental models. During the model production process, ensure that the scale ratios of all corresponding linear lengths of the model and the simulated formation prototype are consistent, and the length, width, and height scale ratios Kl are all 0.04. The indoor model production parameters and the actual reservoir thickness parameters are shown in Table 1. Make the model at this scale ratio in the laboratory and carry out simulated flow experiments.

[0072]

[0073] In the formula: l'—represents the model length; l—represents the formation length;

[0074] (2) Design similarity principle of experimental fluid injection parameters; on the premise of ensuring model geometric similarity, to ensure the similarity of the seepage process of fluid micro-elements during the fluid flow process in the model and the oil reservoir, it is required that the time required for the fluid to pass through the corresponding paths in the two must be in a certain proportion. The time scale is calculated as follows:

[0075]

[0076] In the formula: t’—represents the model time;

[0077] t—represents the formation time;

[0078] v’—represents the model velocity;

[0079] v—represents the formation velocity;

[0080] Among them, based on geometric similarity and kinematic similarity, the scales of kinematic quantities such as k l 、k v are as follows:

[0081]

[0082] Acceleration scale:

[0083] Volume flow rate scale:

[0084] Kinematic viscosity scale:

[0085] Angular velocity scale:

[0086] In the formula: a’—represents the model acceleration;

[0087] a—represents the formation acceleration;

[0088] ω’—represents the model angular velocity;

[0089] ω—represents the formation angular velocity.

[0090] By calculating, the length scale and velocity scale of the model and the oil reservoir are determined, and then the scales of kinematic quantities of the model and the oil reservoir are calculated, ensuring the similarity of the fluid seepage process in the model and the oil reservoir;

[0091] (3) Indoor simulation experiment steps, use a large heterogeneous model to carry out water flooding experiment, and end the experiment when the water cut reaches 98% at different stages. Conduct CT scans to obtain the remaining oil distribution maps of each layer;

[0092] (4) Obtaining the original CT value of the experimental medium; in order to determine and calculate the changes in fluid saturation in the test model at different experimental stages, CT detection of different components was carried out before the experiment, and CT value testing and calibration were performed;

[0093] (5) Determination of the CT values ​​of the cores near each layer and physical barrier of the complex structural model; the computer calculates the X-ray absorption coefficient of each voxel (relative to the volume of the tissue "block" corresponding to each pixel), that is, the attenuation coefficient (μ value), which is the digital basis for imaging. w ) is 1, bone (μ B ) is 2.0, air (μ A ) is 0.0013 (≥0) [1] The X-ray absorption capacity of each voxel obtained by converting the μ value, that is, the unified unit for expressing the tissue density in the CT image, is a relative value called the CT value, which stipulates that the attenuation coefficient (μ) of the measured substance M ) and water as the ratio, and the attenuation coefficients of bone and air as the upper and lower limits for division, thereby calculating the CT value.

[0094]

[0095] Where: α is the graduation factor. Now the CT value is generally expressed in Hounsfield units (Hu), so α is 1000;

[0096] Using the CT value calculation method, the commonly used oil saturation calculation formula is as follows:

[0097]

[0098] Where: H two-phase ——Core CT value at a certain time during water flooding,

[0099] H oil ―CT value of crude oil,

[0100] H a,r - Average CT value of dry core before saturation with formation water,

[0101] H air ―CT value of air,

[0102] H w,r - Average CT value of wet core after saturation with formation water,

[0103] H water ―CT value of formation water

[0104] Since the core model has a complex multi-layer structure, different parts have different fluid distribution laws during a single detection process. Therefore, it is necessary to calculate the fluid distribution of each part separately. The present invention designs an oil saturation calculation and statistical formula according to the volume weight of each part as follows, and conducts the calculation and analysis of the oil saturation of each part's pixel points and the oil saturation of the model.

[0105]

[0106]

[0107] where:S ori — Oil saturation of the part, [%, i = 1~x×y×z]

[0108] V— Volume value of the part, [cm 3

[0109] W Vi～n — Volume weight of the part, [%, i = 1~13]

[0110] x,y,z— Analysis part x,y,z scan pixel number;

[0111] The volume weights of each part of the model are shown in the following table.

[0112] Table 2 Calculated volume values of different permeability parts of the model

[0113]

[0114]

[0115] (6) Three-dimensional oil-water distribution and quantitative description of each part of the model at different development stages; Detect the three-dimensional model at different development stages, and calculate the sub-millimeter scale quantitative data of the remaining oil distribution inside the core based on the large medical CT detection data;

[0116] (7) Analysis of three-dimensional oil-water distribution in the physical property barrier part; Analyze the remaining oil distribution law in the vicinity of the physical property barrier at different water flooding stages based on the remaining oil distribution data obtained by calculating the large medical CT detection results of the physical oil displacement experiment model, and evaluate the remaining oil production law at the millimeter scale;

[0117] (8) Evaluation of the remaining oil production effect near the barrier at different development stages; Conduct oil displacement physical simulations such as pressure increase, changing the fluid flow direction, and straight-flat combination on the model after the conventional water flooding of the basic well pattern of the meter-scale three-dimensional complex model, and conduct remaining oil distribution scanning analysis to evaluate the effects of various measures.

[0118] The experimental steps in step (3) are as follows:​

[0119] 1) The high - displacement vacuum pump evacuates the saturated water at the core outlet end, and then uses a displacement pump to inject water saturated with KI into the model until the injection and production fluid volumes are equal. Record the saturated water volume, calculate the porosity, and conduct CT scan tests.

[0120] 2) Saturate the core with oil, and under the condition of an injection rate of 2.40 ml / min, drive water with oil until only oil comes out at the model outlet end; record the oil injection volume, water production volume, oil production volume, and inlet - end pressure at the inlet end at regular intervals.

[0121] 3) End the water - flooding process when the real - time water cut at the outlet end reaches 98%. Summarize the oil production of each well and calculate the recovery factor.

[0122] 4) Conduct CT tests to analyze the remaining oil distribution in each layer.

[0123] 5) Change the oil - displacement plan and continue the displacement. Repeat steps 3) and 4) until the experiment ends.

[0124] The object of the present invention is to study a method for identifying and quantifying the millimeter - scale oil - water distribution in a heterogeneous complex three - dimensional model with physical property barriers, which is used to solve the problem that in the current oilfield development and tertiary oil recovery processes, there is a lack of a test method that can ensure the similarity of the oil reservoir structure, well layout with the oil reservoir and the actual oilfield, and at the same time can visually obtain the millimeter - scale quantitative analysis of the oil - water distribution and the remaining oil distribution. This method can solve the technical defects of the kilometer - scale remaining oil distribution method in the actual engineering field and the research method of the remaining oil distribution in the core pore nano - micron scale. The method for studying the three - dimensional remaining oil distribution near the physical property barriers at different development stages of the multi - layer heterogeneous model provided by the present invention is based on the physical model oil - displacement experiment samples containing physical property barriers with a meter - scale size, uses medical CT detection to obtain fluid distribution data at different development stages, and quantitatively analyzes the formation mechanism and production situation of the remaining oil in each part of the barrier and the model from the millimeter scale, providing a reliable and effective method for studying the formation and distribution evolution of the actual remaining oil in the oil reservoir during the oilfield development process.

[0125] The technical problems to be solved by the present invention mainly focus on two aspects:

[0126] (1) Highly similar simulation of the fluid displacement experiment process in the indoor model and the fluid seepage process in the actual complex structure parts of the oil reservoir

[0127] Based on the similarity criterion, this method designs the model structure to effectively represent the oil reservoir geological structure and inter - layer differences, and uses indoor detection and fluid distribution calculation methods to give an understanding of the sub - millimeter - scale remaining oil distribution in the complex structure parts, ensuring the similarity of the experimental detection process, the actual oil reservoir structure of the oilfield, and the fluid flow process in the actual oilfield development process of the research results.

[0128] (2) Sub - millimeter scale quantification and analysis of fluid distribution in the interlayer part of complex structure models

[0129] During the fluid distribution detection process, ensure testing at the sub - millimeter scale, accurately distinguish the fluid distribution in different structural parts of the model, distinguish the changes in fluids at different development stages, and be able to perform quantitative analysis of oil saturation.

[0130] Combined with Figure 1 As shown, to solve the above two problems, the technical solutions adopted in the present invention are specifically as follows:

[0131] First, extract and prepare experimental complex three - dimensional pore model parameters according to actual oil reservoir information;

[0132] During the indoor production of large - size models, the similarity with the actual oil reservoir structure is maintained. During the model design process, the principle of the proportional physical model in seepage mechanics is followed, and the flow phenomena are reproduced or pre - rehearsed in the laboratory at a certain scale (generally a reduced scale). According to the typical heterogeneous reservoir distribution characteristics of the actual block, design indoor experimental simulations to study the composition and structural dimensions of the artificial model oil reservoir.

[0133] Secondly, to ensure the similarity between the simulation process and the actual oil reservoir, carry out the calculation of similarity experimental parameters and the design of experimental steps

[0134] During the experimental design, under the condition of meeting geometric similarity, use fluids and media similar to those in the oil reservoir, and control the simulation pressure between 0.1 - 0.3 MPa. In line with the adoption of the normal model, on the premise of ensuring the geometric similarity of the model, to ensure the similarity of the fluid micro - mass seepage process during the fluid flow process in the model and the oil reservoir, it is required that the time required for the fluid to pass through the corresponding paths in the two must be in a certain proportion, and the time scale calculation is as follows.

[0135]

[0136] Among them, based on geometric similarity and kinematic similarity, k l 、k v The scales of kinematic quantities are as follows:

[0137] On the premise of ensuring the geometric similarity of the model, to ensure the similarity of the fluid micro - mass seepage process during the fluid flow process in the model and the oil reservoir, it is required that the time required for the fluid to pass through the corresponding paths in the two must be in a certain proportion, and the time scale calculation is as follows.

[0138] Based on the volume flow rate scale, calculate the injection velocity of the model experiment, and the formula is as follows:

[0139]

[0140] Finally, calculate and analyze the scanning results

[0141] (1) Analysis of fluid experiment results

[0142] In order to study the remaining oil changes in different water flooding stages and evaluate the effects of different development measures under water flooding limit conditions, indoor oil displacement experiments were carried out. The model was saturated with KI water, the porosity and the original oil saturation of the model were calculated, and oil displacement experiments with different development methods were carried out. The liquid production, water production and water cut at the outlet of the model were measured, the recovery rate was calculated, and the oil displacement effects of different development methods were analyzed.

[0143] (2) Analysis of fluid distribution and quantification results at sub - millimeter scale

[0144] 1) Gray scale calibration of core skeleton, water and oil, as shown in Table 1;

[0145] Table 1 CT value calibration of each component in indoor oil displacement experiment

[0146]

[0147] 2) Detection of fluid distribution in the model at different development stages, and result examples are as Figure 5 ;

[0148] In order to study the distribution change law of remaining oil inside the core during the physical oil displacement experiment under simulated reservoir conditions based on the test conditions of large - scale medical CT, the core at different water flooding stages was scanned and tested by large - scale medical CT to obtain the model detection data at different development stages.

[0149] 3) Reconstruct the two - dimensional images of oil and water in the pores, such as Figure 6 ;

[0150] In order to analyze the distribution change of remaining oil at each stage of the medical CT test model, using the large - scale medical CT test data, combined with the CT value calculation formula, calculate the CT values of fluids at each part of the model, and use image processing software to form a fluid distribution comparison chart to analyze and compare the oil saturation of the analyzed parts.

[0151] 4) Using the image analysis software and the calculation results of CT detection data, construct a three - dimensional fluid distribution model of the model to analyze the influence of the change of fluids at each part of the model with different development methods.

[0152] Result processing and analysis:

[0153] Through the coordinated work of the above steps, it is possible to obtain the sub - millimeter scale distribution images and quantification data of fluids in a complex three - dimensional model at the meter scale, which can effectively guide the identification of the remaining oil distribution in complex structural oil layers and can carry out the evaluation and analysis of the fluid utilization ability of each part of the complex structural oil layer by different development methods.

[0154] (1) Analyze the experimental simulation results and compare them with the development effects of the actual development well groups in the oil layer;

[0155] (2) Analyze the influence law of sub-millimeter scale remaining oil in different development stages;

[0156] (3) Analyze the difference in production effect and influencing factors of remaining oil in different parts during the development process;

[0157] (4) Compare the changes and proportions of remaining oil types in different structural parts.

[0158] Example 1:

[0159] 1. Extraction design and production of model parameters

[0160] First, according to the actual reservoir parameters, design the indoor simulation experiment model data. Following the geometric similarity criterion, the final size of the model is 60.0 cm in length, 20.8 cm in height, and 30 cm in width, including two interlayers with a thickness of 4 mm and a net weight of 82.6 kg and 81.5 kg. The basic well pattern is set according to the five-spot method, with the central water well (W 1 and W 2 ) and 6 oil wells (O 1 、O 2 、O 3 、O 4 、O 5 and O 6 ). To study the remaining oil distribution in different displacement stages and analyze the influence of parameters such as interlayers and permeability on the oil saturation distribution, 8 horizontal layers were extracted for comparison. Each analysis layer was compared layer by layer from top to bottom. At the same time, a horizontal front view and a right side view were introduced in the comparative analysis of the oil saturation change for comparison. The data of each layer are shown in Table 2, and the development diagrams of each analysis layer are shown in Appendix Figure 2 , and the three-dimensional development schematic diagram is shown in Appendix Figure 3 .

[0161] Table 2 Parameters of each layer and each simulated part of the complex heterogeneous model

[0162]

[0163] 2. Steps of the oil displacement experiment plan in the example

[0164] Carry out the water flooding experiment using a large heterogeneous model. End the experiment when the water cut reaches 98% at different stages, and perform CT scans to obtain the remaining oil distribution maps of each layer.

[0165] Design the indoor experiment injection rate according to the similarity criterion at a rate of 2.16 m per day for every meter of oil reservoir thickness in the simulated block. According to the volume flow ratio scale calculation, the single-well injection rate of the ordinary water flooding stage of the two injection wells in the indoor model is 2.40 ml / min (unit: ml / min) to carry out the indoor water flooding simulation experiment. The simulation experiments and fluid detection steps of different development methods are as follows:

[0166] 1) Ordinary water flooding stage: W 1 and W 2 Water flooding, injection rate of 2.40 ml / min per well, O 1 -O 6 Wells produce oil. Ordinary water flooding is carried out, and the model is flooded with ordinary water until the water cut reaches 98%. After water flooding, CT scanning is carried out for evaluation.

[0167] 2) First pressure increase water flooding experiment stage:

[0168] W 1 and W 2 Water flooding injection wells. The injection rate of the first pressure increase of well A in the model is 3.04 ml / min. CT scanning is carried out to obtain the remaining oil distribution map of each layer;

[0169] 3) Second pressure increase water flooding experiment stage:

[0170] W 1 and W 2 Water flooding injection. The injection rate of the second pressure increase is 3.60 ml / min per well. The water flooding ends when the water cut reaches 98% in this stage. CT scanning is carried out to obtain the remaining oil distribution map of each layer.

[0171] 4) Experiment stage of changing the fluid flow direction:

[0172] W 1 and W 2 Wells are closed, O 2 and O 5 Wells are adjusted to injection wells for water injection. The injection rate per well is adjusted to 3.60 ml / min, O 1 、O 3 、O 4 and O 6 Wells produce oil. The water flooding ends when the water cut reaches 98% in this stage. CT scanning is carried out to obtain the remaining oil distribution map of each layer.

[0173] 5) Straight-horizontal combined oil displacement experiment stage:

[0174] W 1 and W 2 Wells are closed, O 2 and O 5 are used as injection wells for water injection. The injection rate per well is 3.60 ml / min. Horizontal wells P 1 and P 2 produce oil. The water flooding ends when the water cut reaches 98% in this stage. CT scanning is carried out to obtain the remaining oil distribution map of each layer. A horizontal wellbore is drilled 2.5 cm from the top of the model after the fluid flow direction of water flooding is reversed, and production is put into operation in the straight-horizontal combined stage.

[0175] 3. Analysis of physical oil displacement experiment results

[0176] The experimental model parameters are shown in Table 3, the indoor water flooding experimental scheme, injection conditions and results are shown in Table 4, and the experimental characteristic curves are shown in the appendix Figure 8 。

[0177] Table 3 Model parameters

[0178]

[0179] Table 4 Experimental scheme and results

[0180]

[0181] It can be seen from the experimental results that the oil production increase effect of the pressure-increasing water flooding experiment carried out after the water cut reaches 98% is relatively low. Only 6.32% of oil is increased by two pressure increases in this stage; in the stage of changing the injection-production relationship after pressure-increasing water flooding, 7.85% of oil is increased after a new liquid flow channel is formed in the model. Finally, the combined development of vertical well + horizontal well has a relatively high oil production increase effect, and the incremental stage recovery factor reaches 16.82%. The cumulative recovery factor of Model A is 41.36%.

[0182] 1. Analysis of fluid distribution and quantification results at different development stages of the sub-micron scale three-dimensional model

[0183] (1) Fluid distribution in different parts

[0184] From the results of the remaining oil distribution at the millimeter scale in each analysis part of the model at different development stages of improving the water flooding development effect, it can be seen that the barrier layer has an impact on the change of oil saturation in the nearby structural parts. The barrier layer has an obvious impact on the remaining oil production in parts 1, 2, 3, 5 and 6 in each water flooding development measure, while the impact on parts 7 and 8 is relatively small. A specific example is the oil saturation distribution map of model layer 1 at each stage, see the appendix Figure 9 。

[0185] (2) Quantitative analysis of oil saturation in different parts

[0186] Model A carried out a comparison of water flooding, primary pressure-increasing water flooding, secondary pressure-increasing water flooding, changing the liquid flow direction and combined vertical-horizontal water flooding development methods in sequence. According to the indoor oil displacement experimental data, the oil saturation decreased by 10.36% in the basic water flooding stage and 16.82% in the combined vertical-horizontal stage during each displacement stage of the model, which are the best in terms of development effect among each displacement method. Followed by the liquid flow diversion stage, where the oil saturation decreased by 7.85%.

[0187] Table 5 Oil saturation data of each part of the model at different displacement stages

[0188]

[0189]

[0190] From the millimeter-scale oil saturation quantification data tables 7, 8 of CT detection and Figure 1 It can be seen that during each displacement stage, the oil saturation of each layer decreases significantly during water flooding, straight-line horizontal combined flooding, and fluid diversion stages; through the CT detection data, the changes in oil saturation at different permeability levels and near the barrier layers during different displacement stages can be further analyzed. The overall trend of oil saturation of each layer during different water flooding stages is downward, but the oil saturation at individual locations increases abnormally during different water flooding stages. Among them, the right part of analysis location 1 is 7.52% higher than the original oil saturation after water flooding; the oil content at the right part of analysis location 5 increases by 1.14%.

[0191] (3) Using two-dimensional and three-dimensional fluid distribution images, compare and analyze the fluid distribution results at the sub-micron scale, evaluate the influence of different development methods on the oil saturation of different structural parts of the complex model, and give effective methods for remaining oil in different parts to guide the design of development plans in oilfield mines. The quantitative diagram of fluid distribution at the barrier layer part of the model is shown in the attached figure.

[0192] In the present invention, medical CT is used for the first time to perform non-destructive detection on the fluid displacement experiment of a complex structure model with a meter-scale size. In the detection and analysis of remaining oil in a large model with a meter-scale size, the spatial resolution of the test accuracy of the model reaches 0.2 mm, overcoming the problems existing in the current methods for evaluating and studying remaining oil. Under the conditions of geometric similarity and kinematic quantity similarity where the oil layer structure and well pattern arrangement are completely similar to the oil layer, the consistency between the simulation experiment process and the oilfield development process is ensured. The obtained quantitative results of fluid distribution can effectively study and analyze the production law of oil saturation in different parts of the complex structure by different development methods, providing a favorable support for the design of oilfield development plans.

[0193] In summary, the specific implementation steps of the present invention include: extraction of geological simulation of complex structure reservoirs and production of a large model with a meter-scale size for indoor simulation experiments; design of experimental parameters based on the similarity principle; determination of oil saturation of cores near each layer and physical barrier layers of the complex structure model; three-dimensional oil-water distribution and quantitative description of different parts of the model at different development stages; analysis of the production law of remaining oil near the barrier layer based on the analysis of the production law of remaining oil in different parts of the model, and evaluation of the production effect of remaining oil near the barrier layer at different development stages. The research method for the three-dimensional distribution of remaining oil near the physical barrier layer at different development stages of the multi-layer heterogeneous model provided by the present invention is based on physical model oil displacement experiment samples with a meter-scale size containing physical barrier layers, uses medical CT detection to obtain fluid distribution data at different development stages, and quantitatively analyzes the formation mechanism and production situation of remaining oil in the barrier layer and different parts of the model from the millimeter scale, providing a reliable and effective method for studying the formation and distribution evolution of actual remaining oil in oilfield development processes.

[0194] In view of the deficiencies in the description methods of remaining oil at the pore nano- and micro-size levels and the research methods of remaining oil in oilfields at the macroscopic meter scale, the model size and experimental parameters are designed based on similarity criteria. Using the prepared physical model at the meter scale, ensuring that the model structure can effectively represent the reservoir geological structure and interlayer differences, indoor displacement experiments with different development methods are carried out. Using a medical CT detection system, fluid distribution data in the model at different development stages are obtained. A calculation formula for the oil saturation of each part of a single inspection complex structure model is designed, and the remaining oil distribution results at the sub-millimeter level are given. Thus, it is ensured that the remaining oil distribution data obtained by this method are under the condition of taking into account the similarity with the actual oil layer structure of the oilfield and the fluid flow process in the actual oilfield development process. A three-dimensional oil-water distribution and quantitative test analysis method for complex structure models at the sub-millimeter scale is established, which has important guiding significance for the development plan design of complex structure parts in oilfields.

Claims

1. A research method for sub - millimeter - scale fluid distribution in complex - structure large models, Characterized in that: The steps of its research method are as follows: Step 1: Extraction of complex - structure reservoir geological simulation and production of a large model at the meter - scale for indoor simulation experiments; To ensure that the indoor water - flooding experiment using the large model at the meter - scale in this project can truly reproduce the physical essence of the oil - water flow phenomenon in the oil layer under the same well - pattern conditions, ensure that the physical essence of the model experiment process is the same as that of the flow phenomenon in the reservoir formation, and achieve the similarity of fluid mechanics; Maintaining geometric similarity is the most basic requirement for the production of fluid - mechanics experimental models. During the model production process, ensure that the scale ratios of all corresponding linear lengths of the model and the simulated formation prototype are consistent. The length, width, and height scale ratios Kl are all 0.

04. Make the model at this scale ratio reduction in the laboratory and carry out simulated flow experiments; In the formula: l'—represents the model length; l—represents the formation length; Step 2: The design similarity principle of experimental fluid injection parameters; On the premise of ensuring the geometric similarity of the model, to ensure the similarity of the fluid - micro - mass seepage process during the fluid flow process in the model and the oil layer, it is required that the time required for the fluid to pass through the corresponding paths in the two must be in a certain proportion. The calculation of its time scale ratio is as follows: In the formula: t’—represents the model time; t—represents the formation time; v’—represents the model velocity; v—represents the formation velocity; Among them, the scales of kinematic quantities of k l and k v are as follows: Acceleration scale ratio: Volume flow ratio scale: Kinematic viscosity scale ratio: Angular velocity scale ratio: In the formula: a’—represents the model acceleration; a—represents the formation acceleration; ω’—represents the model angular velocity; ω—represents the formation angular velocity; Determine the length scale ratio and velocity scale ratio of the model and the oil layer through calculation, and then calculate the scale ratios of the kinematic quantities of the model and the oil layer, ensuring the similarity of the fluid seepage process in the model and the oil layer; Step 3: Indoor simulation experiment steps, use a large heterogeneous model to carry out water - flooding experiments, end the experiment when the water cut reaches 98% at different stages, conduct CT scans, and obtain the remaining - oil distribution maps of each layer; Step 4: Obtaining the original CT values of the experimental medium; To measure and calculate the fluid - saturation changes in the test model at different experimental stages, conduct CT detections on different components before the experiment starts, and carry out CT - value tests and calibrations; Step 5: Determination of the CT values of the cores near each layer and physical property barriers of the complex structure model; the computer calculates the X-ray absorption coefficient of each voxel (the volume of the tissue "block" corresponding to each pixel) from the information scanned by X-rays in multiple directions, that is, the attenuation coefficient (μ value), which is the digital basis of imaging; the attenuation coefficient of water (μ w ) is known to be 1, and that of bone (μ B ) is 2.0, and that of air (μ A ) is 0.0013 (≥0) [1] ; the X-ray absorption ability used to represent each voxel obtained by converting the μ value, that is, the unified unit expressing the tissue density in the CT image, is a relative value called the CT value. It is stipulated that the attenuation coefficient of the measured substance (μ M ) is calculated as the ratio with the attenuation coefficient of water, and is graduated with the attenuation coefficients of bone and air as the upper and lower limits respectively, and thus the CT value is calculated. In the formula: α―scaling factor. Currently, the CT value generally uses the Hounsfield unit (Hu), so α is 1000; Using the CT - value calculation method, the commonly used oil - saturation calculation formula is as follows currently, Where: H two-phase - CT value of core at a certain moment of water flooding oil displacement, H oil - CT value of crude oil, H a,r ―Average CT value of dry core before saturated with formation water, H air - CT value of air H w,r ―Average CT value of wet core after saturation with formation water H water - CT value of formation water Since it is a core model with a complex multi - layer structure, during the detection process, each part has different fluid - distribution laws during a single detection. Therefore, it is necessary to calculate the fluid distribution of each part separately. The present invention designs an oil - saturation calculation and statistical formula based on the volume weights of each part as follows, and conducts the calculation and analysis of the oil - saturation of each part's pixel points and the oil - saturation of the model; where: S ori — oil saturation of the part, [%,i = 1~x×y×z] V - Part volume value, [cm 3 ​ W Vi～n — Part volume weight, [%, i = 1 to 13] x,y,z—Analysis part x,y,z scan pixel number; Step 6: Three - dimensional oil - water distribution and quantitative description of each part of the model at different development stages; Detect the three - dimensional model at different development stages, and calculate the sub - millimeter - scale quantitative data of the remaining - oil distribution inside the core at different water - flooding stages based on the large - scale medical CT detection data; Step 7: Analysis of the three-dimensional oil-water distribution in the physical property barrier zone; for the remaining oil distribution data obtained by calculating the results of the large-scale medical CT detection of the physical oil displacement experiment model, analyze the remaining oil distribution law in different water flooding stages near the physical property barrier, and evaluate the remaining oil production law at the millimeter scale; Step 8: Evaluation of the remaining oil production effect near the barrier in different development stages; conduct physical oil displacement simulations of methods such as pressure increase, changing the liquid flow direction, and straight-horizontal combination in sequence on the model after the conventional water flooding of the basic well pattern of the meter-scale three-dimensional complex model, and perform remaining oil distribution scanning analysis to evaluate the effects of various measures.

2. A research method for sub-millimeter scale fluid distribution in a large complex structure model according to claim 1, characterized in that: the experimental steps in step 3 are as follows: 1) A high-displacement vacuum pump evacuates and saturates water at the outlet end of the core, and then uses a displacement pump to inject KI-containing water to saturate the model until the injection and production fluid volumes are equal. Record the saturated water volume, calculate the porosity, and perform CT scanning tests; 2) Saturate the core with oil, and displace water with oil at an injection rate of 2.40 ml / min until only oil comes out at the outlet end of the model; Record the oil injection volume, water production volume, oil production volume, and inlet end pressure at the inlet end at regular intervals; 3) End the water flooding process when the real-time water cut at the outlet end reaches 98%. Summarize the oil production of each well and calculate the recovery factor; 4) Conduct CT tests to analyze the remaining oil distribution in each layer; 5) Change the oil displacement plan and continue the displacement, repeating steps 3) and 4) until the experiment ends.

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