A method for determining the retention rate of a dispersed system in a porous medium at pore size

Abstract

The present invention discloses a method for determining the retention rate of a dispersed system in a porous medium at a specific pore size. The method comprises the following steps: 1) filtering the dispersed system through a uniform porous medium model with a range of pore sizes, recording the filtration time and filtration volume, and obtaining the relationship between the filtration volume and filtration time to determine the time required for the porous medium to reach stable retention at a specific pore size; measuring the mass concentration of the filtered solution at the time required for stable retention, and calculating the retention rate of the uniform porous medium at that pore size; 2) fitting the relationship curve between the retention rate obtained in step 1) and the corresponding pore size to obtain a calculation formula for the retention rate and pore size; and 3) weighting the retention rate for each pore throat diameter based on the gas permeability and pore throat size distribution of the reservoir core to be measured by accumulating the weighted sum of the pore throat diameters to obtain the total retention rate of the reservoir core at that gas permeability. The present invention can measure and predict retention rates.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas field development and relates to a method for measuring the retention rate of a dispersed system at pore sizes in a porous medium. Background Art

[0002] With long-term waterflooding in oilfields, reservoir heterogeneity increases further, leading to a rapid increase in water cut in production wells and a significant decrease in waterflooding recovery efficiency. To stabilize oil production and control water cut, profile control agents are often injected into water injection wells. These agents can become trapped or clogged during their migration into the reservoir, reducing the permeability of larger flow channels, diverting subsequent flow, and displacing residual oil in areas of lower permeability. In recent years, various dispersed systems, such as solid-liquid (particulate profile control agents, polymer solutions), liquid-liquid (emulsions), and gas-liquid (foams), have been used for profile control in water injection wells. Polymer solutions are widely used due to their relative uniformity, ease of injection, and excellent mobility. Appropriate retention helps polymers enhance sweep efficiency. However, some retention in low-permeability zones can not only increase polymer loss but also damage the reservoir, reducing permeability or causing blockage, making subsequent injection and displacement difficult. Therefore, before injecting polymer solutions into a specific reservoir, it is often necessary to understand the retention pattern, conditions, and extent of the polymer in the porous medium. Retention is currently widely used in oil fields and laboratories as an indicator of polymer retention in porous media. Retention refers to the mass of polymer retained per unit mass of the porous medium framework, measured in μg / g. Retention can be measured through flow experiments in reservoir cores or sandpack models using the polymer / tracer slug method or the cyclic polymer injection method. Calculating retention based on the mass of the solid particles that make up the porous medium framework provides a general indication of polymer retention, but it does not directly and fully reflect the impact of porous medium properties on retention. Furthermore, the cores or sandpacks used in these retention measurement methods, such as the polymer / tracer slug method or the cyclic polymer injection method, exhibit multi-scale pore structures. This advantage provides retention results that reflect the combined effects of multiple pore sizes, but the disadvantage is that it is difficult to determine the retention effect of a single pore size. Dispersed profile control agents generally exhibit multi-scale and heterogeneous dispersions, and their relationship to pore size determines their retention characteristics, profile control performance, and oil recovery effectiveness. Therefore, developing a method for testing and predicting retention rate under pore size in porous media is of great significance for in-depth understanding of the retention and profile control mechanism of profile control agents, clarifying the migration and plugging properties of profile control agents in porous media, screening, optimizing and developing profile control agent products, and determining reasonable injection methods. Summary of the Invention

[0003] The present invention aims to provide a method for determining the retention rate of a dispersed system in a porous medium at a specific pore size. The method is applicable to evaluating and predicting the migration capacity and displacement properties of polyacrylamide-based flooding systems in oil and gas field development. It can also be used to evaluate and predict the fluid loss performance of polyacrylamide-containing drilling fluids and fracturing fluids in reservoirs.

[0004] The present invention provides a method for determining the retention rate of a dispersed system in a porous medium at different pore sizes, comprising the following steps: 1) filtering the dispersed system through a uniform porous medium model having a series of pore sizes, recording the filtration time and filtration volume, and obtaining a relationship between the filtration volume and filtration time to determine the time required for the porous medium of a certain pore size to reach stable retention; detecting the mass concentration of the filtered solution at the time required for stable retention, and calculating according to Formula I to obtain the retention rate of the uniform porous medium of the pore size;

[0005]

[0006] In Formula I, RC is the retention rate of the uniform porous medium, C 0 is the original concentration, C 1 is the mass concentration of the filtered solution;

[0007] 2) fitting the relationship curve between the retention rate and the corresponding pore diameter obtained in step 1) to obtain the calculation formula of the retention rate and pore diameter;

[0008] 3) Based on the gas permeability and pore throat size distribution of the reservoir core to be tested, the retention rate under each pore throat diameter condition is weighted and accumulated by the proportion of the pore throat diameter, so as to obtain the total retention rate of the reservoir core to be tested under the gas permeability.

[0009] In a specific embodiment of the present invention, when the dispersion system is 14 million to 1000 mg / L partially hydrolyzed polyacrylamide HPAM, the calculation formula obtained in step 2) is as shown in Formula II:

[0010]

[0011] In formula II, RC is the retention rate of the uniform porous medium, D is the pore size, μm.

[0012] In the above method, the driving pressure differential for the profile control agent filtration in step 1) can be 0.2 MPa, and the temperature can be between 20°C and 150°C, specifically 25°C. The temperature can be controlled by placing the filtration device in a constant temperature chamber. The driving pressure differential for the profile control agent filtration achieves the driving effect. The magnitude of the pressure differential affects the filtration rate but has little effect on the filtration mass concentration. Excessive pressure differentials may damage the uniform porous medium, resulting in changes in the filtration mass concentration.

[0013] In the above method, the device for filtering using a uniform pore size porous medium model in step 1) includes a pressure drive system, a temperature control system, a liquid storage container, a uniform pore size porous medium model and a holder;

[0014] The pressure drive system includes a nitrogen cylinder and a pressure reducing valve; the pressure reducing valve is provided on the pipeline connecting the nitrogen cylinder and the liquid storage container; the liquid storage container is connected to the uniform pore porous medium model, and the uniform pore porous medium model is fixed by the clamp; the temperature control system controls the temperature of the environment in which the liquid storage container and the uniform pore porous medium model are located.

[0015] In the present invention, a pressure gauge is provided on the pipeline connecting the liquid storage container and the pressure reducing valve, the bottom of the uniform pore porous medium model is supported by a support net, the pipeline connected to the liquid outlet at the bottom of the uniform pore porous medium model is connected to a measuring cylinder, and a horizontal flow valve is provided on the pipeline connected to the liquid outlet.

[0016] In the above method, the temperature control system is a constant temperature box, and the liquid storage container and the uniform pore size porous medium model are arranged in the constant temperature box.

[0017] In the above method, the uniform pore size porous medium model adopts a polycarbonate membrane.

[0018] In the above method, the pore size of the uniform pore size porous medium model can be 0.1μm~20μm, specifically 5.00, 3.00, 2.00, 1.20, 1.00, 0.80, 0.70, 0.60, 0.45, 0.22, 0.1μm, 0.05μm, 0.01μm or 0.1μm~10μm; the diameter can be 47~48mm, and the membrane thickness can be 9~25μm, specifically 9~10μm.

[0019] In the above method, the number of uniform pore size porous medium models of a series of pore sizes can be 8 to 12, specifically 10, to more comprehensively reflect the size of the porous medium, and the obtained fitting formula is more accurate and reliable.

[0020] The present invention has the following beneficial effects:

[0021] 1. The present invention can perform filtration experiments on a given profile control agent in a series of uniform pore size porous media models (with varying pore sizes) to determine retention rates at different pore sizes. Combined with the pore distribution in the reservoir, the retention rate can be quantified and predicted. The porous media used in the uniform pore size porous media models have a very wide pore size range, enabling simulation of migration and retention characteristics in micron and nanometer pores. The retention rate can be measured at reservoir temperatures (20-150°C).

[0022] 2. For a given dispersed profile control agent, the retention rates at different pore sizes obtained from the filtration experiment of a uniform pore size porous medium, and the resulting fitting curves of retention rate and pore size, can be used as a template for predicting the retention rates of cores with different pore throat distributions. For reservoir models with different pore size distributions, the retention rates can be obtained without repeating the above experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the relationship between the filtration volume and filtration time of 14 million partially hydrolyzed polyacrylamide (HPAM) with a concentration of 1000 mg / L through a series of uniform pore size porous media models (with varying pore sizes) (driving pressure difference is 0.2 MPa);

[0024] Figure 2 This is a graph showing the variation of the retention rate of partially hydrolyzed polyacrylamide (HPAM) with a concentration of 1000 mg / L through a series of uniform pore size porous media models (with varying pore size);

[0025] Figure 3 This is a graph showing the segmented variation of the retention rate of 14 million partially hydrolyzed polyacrylamide (HPAM) with a concentration of 1000 mg / L through a series of uniform pore size porous media models (changing pore size) and the fitting curve. Figure 3 The formula in is the variation of retention rate with pore size after fitting, and R is the square root of the sum of squares of the residuals between the output variable (y) and the independent variable (x); Figure 3 (a) is 0.22≤ D ≤<0.8; (b) 0.8≤ D ≤1.2; (c) 0.2≤ D ≤<3, D The unit is μm.

[0026] Figure 4 This is a frequency diagram of pore throat size distribution in a certain reservoir (gas permeability 522mD);

[0027] Figure 5 This is a frequency diagram of pore throat size distribution in a certain reservoir (gas permeability 63mD);

[0028] Figure 6It is the retention rate of partially hydrolyzed polyacrylamide at a concentration of 1000 mg / L in porous media of reservoirs with different permeabilities;

[0029] Figure 7 It is an experimental device for testing the retention rate of porous media with uniform pore size.

[0030] The various marks in the figure are as follows:

[0031] 1. Nitrogen cylinder; 2. Pressure reducing valve; 3. Pressure gauge; 4. Constant temperature box; 5. Liquid storage container; 6. Clamp; 7. Uniform porous medium model; 8. Support net; 9. Horizontal flow valve; 10. Graduated cylinder. DETAILED DESCRIPTION

[0032] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0033] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0034] The present invention will be further described below in conjunction with specific examples:

[0035] The present invention provides a method for determining the retention rate of a dispersed system in a porous medium at different pore sizes, comprising the following steps: 1) filtering the dispersed system through a uniform porous medium model having a series of pore sizes, recording the filtration time and filtration volume, and obtaining a relationship between the filtration volume and the filtration time to determine the time required for the porous medium of a certain pore size to reach stable retention; detecting the mass concentration of the filtered solution at the time required for stable retention, and calculating according to Formula I to obtain the retention rate of the uniform porous medium of the pore size;

[0036]

[0037] In Formula I, RC is the retention rate of the uniform porous medium, C 0 is the original concentration, C 1 is the mass concentration of the filtered solution;

[0038] like Figure 7 As shown, the device using the uniform pore size porous medium model for filtration includes a pressure drive system, a temperature control system, a liquid storage container 5, a uniform pore size porous medium model 7 and a holder 6;

[0039] The pressure drive system includes a nitrogen cylinder 1 and a pressure reducing valve 2; the pressure reducing valve 2 is provided on the pipeline connecting the nitrogen cylinder 1 and the liquid storage container 5; the liquid storage container 5 is connected to the uniform pore porous medium model 7, and the uniform pore porous medium model 7 is fixed by a clamp 6; the temperature control system controls the temperature of the environment in which the liquid storage container 5 and the uniform pore porous medium model 7 are located; the temperature control system is a constant temperature box 4, and the liquid storage container 5 and the uniform pore porous medium model 7 are placed in the constant temperature box 4;

[0040] 2) fitting the relationship curve between the retention rate and the corresponding pore diameter obtained in step 1) to obtain the calculation formula of the retention rate and pore diameter;

[0041] 3) Based on the gas permeability and pore throat size distribution of the reservoir core to be tested, the retention rate under each pore throat diameter condition is weighted and accumulated by the proportion of the pore throat diameter, so as to obtain the total retention rate of the reservoir core to be tested under the gas permeability.

[0042] Furthermore, the uniform pore size porous medium model uses a polycarbonate filter membrane.

[0043] Furthermore, the pore size of the uniform pore size porous media model can be 0.1μm to 10μm, specifically 5.00, 3.00, 2.00, 1.20, 1.00, 0.80, 0.70, 0.60, 0.45, 0.22, 0.1μm, 0.05μm, and 0.01μm; the diameter can be 47-48mm, and the membrane thickness can be 9-10μm. The pore size of the uniform pore size porous media model depends on the pore throat size distribution range of the reservoir. The choice of pore size depends on the pore throat size distribution of the reservoir. Generally, the lower the permeability, the more uniform pore size porous media are selected, while conversely, more uniform pore size porous media are selected.

[0044] Furthermore, the number of uniform pore size porous media models of a series of pore sizes can be 8 to 12, specifically 10, to more comprehensively reflect the size of the porous media, and the obtained fitting formula is more accurate and reliable.

[0045] Example

[0046] 14 million partially hydrolyzed polyacrylamide (HPAM) with a concentration of 1000 mg / L was passed through a series of uniform pore size porous media models (pore sizes of 3.00, 2.00, 1.20, 1.00, 0.80, 0.70, 0.60, 0.45, 0.22, and 0.1 μm) at a driving pressure difference of 0.2 MPa. The filtration process time was recorded, and the cumulative filtration volume was recorded every 5 seconds. The relationship between filtration volume and filtration time was obtained (e.g. Figure 1As shown in the figure, the time required for a porous medium with a certain pore size to reach stable retention is determined. The filtration volume is observed to change with filtration time. The time when the curve reaches stability is 10 minutes. The mass concentration of the solution after 10 minutes of filtration is detected. C 1. Calculate the aperture ( D ) retention rate of uniform porous media under RC , the retention rate is the original concentration C The ratio of the difference between 0 and the filtered concentration to the original concentration is multiplied by 100%.

[0047] .

[0048] According to the following method, a series of filtration experiments of porous media with uniform pore size were completed to obtain the retention rates at different pore sizes (such as Figure 2 Fitting the relationship curve between retention rate and pore size (as shown in Figure 3 As shown), the retention rate RC The calculation formula of the aperture is as follows.

[0049]

[0050] The calculation process for predicting the retention rate of 14 million 1000 mg / L partially hydrolyzed polyacrylamide solution in a core with a gas permeability of K = 522 mD is as follows. The pore throat diameter of the core with a gas permeability of K = 522 mD and the corresponding distribution frequency of the pore throat diameter are given as follows: Figure 4 As shown in Table 1, the pore throat diameter is calculated D , and then according to Figure 2 Perform segmented fitting, and the fitting results are as follows Figure 3 As shown, the corresponding formula II is obtained.

[0051] Table 1 Calculation results of retention rate in pore throats and retention rate in core (K=522mD)

[0052]

[0053] The retention rate in the pore throats for different pore throat diameters was calculated using Formula II. The retention rate in the pore throats was multiplied by the pore throat distribution frequency and divided by 100 to obtain the percentage of retention rate in the pore throats. The data are shown in Table 1. The retention rate in the core was then calculated to be 25.08% (to two decimal places) by adding the percentages of retention rates in all pore throats.

[0054] On this basis, according to the pore throat size distribution of a certain reservoir (such as Figure 4 and Figure 5As shown in the figure), by weighted accumulation of the proportions of all pore sizes, the retention rate after total retention of the core at that permeability can be obtained. After calculation, the retention rate after filtration of the core with a permeability of 63mD and 522mD is predicted. RP (like Figure 6 shown).

[0055] For gas permeability K=63mD, the pore throat diameter frequency distribution is as follows: Figure 5 As shown in the figure, the calculation process of the retention rate in the pore throat and the retention rate in the core is the same as above, and the retention rate in the core is calculated to be 40.26% (retain 2 decimal places). Figure 6 Based on this, if the pore throat diameter distribution of the core in a certain reservoir is known, the retention situation in the corresponding layer can be calculated. Based on this, the injectivity and profile control performance in the reservoir can be further analyzed.

Claims

1. A method for determining the retention rate of a dispersed system in a porous medium at different pore sizes, comprising the following steps: 1) filtering the dispersed system through a model porous medium having a uniform pore size, recording the filtration time and filtration volume, and obtaining a relationship between the filtration volume and filtration time to determine the time required for the porous medium to reach stable retention at a certain pore size; measuring the mass concentration of the filtered solution at the time required for stable retention, and calculating the retention rate of the uniform porous medium at that pore size according to Formula I; In Formula I, RC is the retention rate of the uniform porous medium, C 0 is the original concentration, C 1 is the mass concentration of the filtered solution; 2) fitting the relationship curve between the retention rate and the corresponding pore diameter obtained in step 1) to obtain the calculation formula of the retention rate and pore diameter; 3) Based on the gas permeability and pore throat size distribution of the reservoir core to be tested, the retention rate under each pore throat diameter condition is weighted and accumulated by the proportion of the pore throat diameter, so as to obtain the total retention rate of the reservoir core to be tested under the gas permeability.

2. The method according to claim 1, characterized in that The driving pressure difference for the filtration of the dispersed system profile control agent in step 1) is 0.2 MPa, and the temperature is 20-150°C.

3. The method according to claim 1 or 2, characterized in that The device for filtering using the uniform pore size porous medium model in step 1) includes a pressure drive system, a temperature control system, a liquid storage container, a uniform pore size porous medium model and a clamp; The pressure drive system includes a nitrogen cylinder and a pressure reducing valve; the pressure reducing valve is provided on the pipeline connecting the nitrogen cylinder and the liquid storage container; the liquid storage container is connected to the uniform pore porous medium model, and the uniform pore porous medium model is fixed by the clamp; the temperature control system controls the temperature of the environment in which the liquid storage container and the uniform pore porous medium model are located.

4. The method according to claim 3, characterized in that The temperature control system is a constant temperature box, and the liquid storage container and the uniform pore size porous medium model are arranged in the constant temperature box.

5. The method according to claim 3, characterized in that The uniform pore size porous medium model adopts a polycarbonate filter membrane.

6. The method according to claim 3, characterized in that The uniform pore size porous medium model has a pore size of 0.1 μm to 20 μm, a diameter of 47 to 48 mm, and a membrane thickness of 9 to 25 μm.

7. The method according to claim 3, characterized in that The number of the uniform pore size porous medium models of the series of pore sizes is 8 to 12.

Images