Device and method for making sand filling model for crude oil displacement experiment

Abstract

A device and method for making a sand-filled model for crude oil displacement experiments. It mainly solves the problems of large permeability deviation, poor experimental repeatability, and easy particle migration of the sand-filled model used in the displacement experiment. It is characterized by: drying and screening the obtained rock sand, selecting rock sand of suitable particle size; filling the rock sand according to the estimated single filling amount and pressing pressure, and measuring the air permeability after filling; repeatedly filling to obtain several groups of data; fitting the data to obtain the linear relationship between the comprehensive evaluation coefficient and the model air permeability, and the linear relationship between the single filling amount and the total filling amount, establishing a set of equations for the two linear relationships, and obtaining the target parameters, filling the sand according to the obtained parameters, and obtaining the target permeability model. The device and method for making a sand-filled model for crude oil displacement experiments effectively solve the problem of particle migration of fluids during the displacement process, and can quickly fill models with required permeability in batches.

Description

Technical Field

[0001] The invention relates to the field of oil fields, in particular to a device and method for making a sand-filling model for a crude oil displacement experiment. Background Art

[0002] The cores used in the indoor simulation experiment of crude oil displacement usually include natural cores, artificial cores and sand filling. Natural cores can only be obtained by drilling coring wells with special drill bits and drilling tools. The cost is very expensive and cannot be used in large quantities for daily experiments; the structure of artificial cores is too ideal to truly simulate the flow law of fluids in the formation and the interaction between fluids and rocks under displacement conditions. The rock sand used in the sand filling model is the real rock sand in the formation, and through compaction, it is filled into a core model with a permeability similar to that of the formation core. In comparison, this model can better simulate the displacement process of fluids in the formation. At present, the permeability deviation of the sand filling model is large and cannot meet the actual needs. It can occasionally be filled to the required permeability, but the success rate is low and the repeatability of the model experiment is extremely poor. Summary of the invention

[0003] In order to overcome the shortcomings of the sand-filling model used in the existing displacement experiment, such as large permeability deviation, poor experimental repeatability, and easy generation of particle migration, the present invention provides a device and method for making a sand-filling model for a crude oil displacement experiment. The device and method for making a sand-filling model for a crude oil displacement experiment effectively solve the problem of particle migration of the fluid during the displacement process, and can quickly fill models with required permeability in batches. This method greatly improves the success rate of sand-filling work for models with different permeabilities, thereby providing a strong guarantee for the success of indoor physical simulation experiments of crude oil displacement.

[0004] The technical solution of the present invention is: a device for making a sand filling model for a crude oil displacement experiment, comprising a sand filling pipe and a pressure rod, the lower end of the pressure rod is placed in the sand filling pipe, the pressure rod is connected to a hydraulic pump, the hydraulic pump is controlled by a controller, and the controller is provided with a pressure control table for adjusting the pressure of the hydraulic pump.

[0005] A vibrator is arranged outside the sand filling pipe.

[0006] A method for manufacturing a sand filling model device using the crude oil displacement experiment comprises the following steps:

[0007] (1) Drying and screening the obtained rock sand to select rock sand with suitable particle size;

[0008] (2) Rock sand is loaded according to the estimated single loading volume and pressing pressure, and the air permeability is measured after loading is completed;

[0009] (3) Compare the air permeability measured in step (2) with the permeability of the target sand filling model, adjust the single filling amount, pressing pressure and single pressing times, and repeat the filling until the difference between the air permeability and the target permeability is no more than ±10%, and record each group of data, including single filling amount, pressing pressure, single pressing times, total sand filling amount and air permeability;

[0010] (4) According to the grey correlation method, the main controlling factors affecting the air permeability of the model are determined as follows: pressing pressure, single loading volume, and total loading volume;

[0011] (5) The grey correlation method was used to analyze a large amount of experimental data to obtain the correlation between each main control factor and air permeability, and the key factors affecting the model permeability were obtained based on the correlation. The weights of the above factors in the model permeability were obtained by combining the experimental data with the hierarchical analysis method: the total filling volume was 0.459, the pressing pressure was 0.295, and the single filling volume was 0.246. By optimizing the main control factors and quantifying the main control factors of permeability, the formula for the comprehensive evaluation coefficient E of the sand filling model was obtained.

[0012] E = pressing pressure × 0.295 + maximum weight of sand filling / single filling amount × 0.246 + total filling amount × 0.459 ①

[0013] The maximum weight of sand filling = volume of sand filling pipe × density of rock sand;

[0014] (6) Based on the data obtained in step (3), the total loading amount formula is obtained:

[0015] Total loading volume = A × single loading volume + B ②

[0016] Linear regression calculation is performed to obtain the values ​​of A and B. Combining formulas ① and ②, the suppression parameters are calculated, and filling is performed according to the parameters to produce a sand filling model with the target permeability.

[0017] In the step (2), when filling the rock sand, a screen is installed in the sand filling pipe, the diameter of the screen is the same as the inner diameter of the sand filling pipe, and the aperture of the screen hole is smaller than the minimum sand particle size.

[0018] The present invention has the following beneficial effects: due to the adoption of the above scheme, the method for making the sand-filled model for crude oil displacement experiment realizes the use of machines instead of manual operation, saves a lot of physical labor, avoids the influence of human operation errors on system errors, and provides an accurate and reliable solution for controlling the permeability of the model; and the operation process is simple and convenient, and the single filling time is shortened from more than two hours to less than 20 minutes, which effectively improves the experimental efficiency and provides a strong guarantee for subsequent indoor physical simulation experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1It is a schematic diagram of the structure of the present invention;

[0020] Figure 2 It is the relationship diagram between comprehensive evaluation coefficient and air permeability;

[0021] Figure 3 It is the relationship diagram between the single sand filling volume and the total filling volume;

[0022] Figure 4 It is the relationship diagram between the injected PV number and the model pressure difference.

[0023] In the figure, 1-controller, 2-pressure control meter, 3-hydraulic pump, 4-pressurizing rod, 5-vibrator, 6-sand filling pipe, 7-balance, 8-bracket. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings:

[0025] Depend on Figure 1 As shown, a device for making a sand-filled model for crude oil displacement experiment includes a sand-filled tube 6 and a pressure rod 4. The pressure rod is used to press rock sand, and its size is slightly smaller than the inner diameter of the model tube. The lower end of the pressure rod 4 is placed in the sand-filled tube 6. The pressure rod 4 is connected to a hydraulic pump 3, which provides pressure for the model, and the working range is 0-21MPa. The hydraulic pump 3 is controlled by a controller 1, and the controller 1 controls the pump in and out, the motor switch, etc. The controller 1 is provided with a pressure control table 2, which can control the pressure of the hydraulic pump, and can immediately disconnect the hydraulic pump 3 for pressure relief when the required pressure is reached, so as to ensure that the pressure of each pressing is consistent. A vibrator 5 is provided on the outside of the sand-filled tube 6, and the vibrator 5 is used to vibrate the model to make the rock sand more compact and uniform during the filling process. The device also includes a balance, which is used to accurately weigh the single sand filling amount.

[0026] A method for manufacturing a sand filling model device using the crude oil displacement experiment comprises the following steps:

[0027] (1) Select rock sand. The preferred rock sand is formation rock sand. If formation rock sand is not available, artificial quartz sand can be used instead. If formation sand is mixed with crude oil, the rock sand needs to be pre-washed. The rock sand should be dried for at least 4 hours before the experiment to ensure that there is no bound water in the rock sand. At the same time, the sand filling pipe and the front and rear plugs are placed in an oven for drying to ensure that the experiment is carried out under dry conditions.

[0028] After drying, the rock sand is sieved with a standard sieve and classified into 50-80 mesh, 80-100 mesh, 100-120 mesh, 120-140 mesh, 140-160 mesh, 160-180 mesh, 180-200 mesh and above 200 mesh. According to the actual formation conditions, the proportions of various types are prepared and the experiment is carried out after sufficient mixing. Before the experiment, more rock sand should be prepared, at least 10 times the amount of sand filling in a single tube.

[0029] Select rock sand according to the particle size of the formation core. If there is no distribution data of the particle size of the formation core, use rock sand of a single particle size. For the specific particle size selection, according to a large amount of experimental data, if the permeability is above 2000mD, it is recommended to use 50-100 mesh rock sand, if the permeability is within the range of 1000-2000mD, it is recommended to use 100-160 mesh rock sand, if the permeability is below 1000mD, it is recommended to use rock sand above 160 mesh. The first sand filling is also mainly based on trial and error to establish reference data for subsequent filling.

[0030] Before the experiment, connect and seal one end of the sand filling pipe with the plug, connect the other end with the matching clamp of the sand filling device and put it into the sand filling slot, connect the vibrator to the sand filling pipe body and tighten it with bolts.

[0031] (2) After all the connection work is ready, start weighing the rock sand. According to the permeability requirements, estimate a weight for filling. The single filling amount should not be too large. For example, if filling sand with a size of 2.5*30cm and a permeability of 1500mD, the single filling amount should be between 15-30 grams. After pre-setting the filling amount, ensure that the filling amount is consistent each time, and the error is controlled within the range of 0.01g. During the filling process, ensure that the vibrator is in working condition.

[0032] According to the formation permeability, first estimate an initial pressure. The pressure selection follows the principle of low first and high later, which is convenient for later adjustment. Adjust the gear of the hydraulic pump. Use low gear for low pressure and high gear for high pressure. Select according to the actual situation. For the first filling, select low pressure operation and adjust the warning line of the pressure control gauge to the required pressure. Use the same pressure for each filling. After weighing the rated sand filling volume each time, pour it evenly into the sand filling tube and manually operate the control button of the controller to press. For the first sand filling, the single pressing number is preferably once. Try to ensure that the sand body covers the marked line inside the sand filling tube after the last filling volume is pressed. Measure the air permeability after the filling is completed.

[0033] After filling, calculate the total filling amount. When the pressure, number of single fillings and rock sand particle size are the same, the permeability is sensitive to the total filling amount. It is particularly important to control the total filling amount, especially the last filling amount. Each operation must be carried out strictly in accordance with the standards. The pressing pressure, single filling amount, number of single pressings, etc. must be kept the same.

[0034] (3) Compare the air permeability measured in step (2) with the permeability of the target sand filling model. If the air permeability after filling is significantly different from the target permeability, the number of single compressions of the second sand filling is increased to 2 times, and no more than 3 times. The specific number is estimated based on the actual difference. According to the results of previous experiments, the permeability will decrease by about 300-500mD for each increase in the number of single compressions. If it is a loose formation with a formation permeability of more than 1500mD, it is recommended that the single compression be 1 time. If the formation permeability is between 500-1500mD, it is recommended that the single compression be 2 times. If the formation permeability is below 500, it is recommended that the single compression be 3 times.

[0035] Adjust the single loading volume, pressing pressure and single pressing times, and repeat the loading. Measure the air permeability after each loading until the difference between the air permeability and the target permeability is no more than ±10%. Record each set of data, including single loading volume, pressing pressure, single pressing times, total loading volume and air permeability.

[0036] (4) According to the grey correlation method, the main controlling factors affecting the air permeability of the model are determined as follows: pressing pressure, single loading volume, and total loading volume;

[0037] In the actual sand filling process, it is difficult to achieve the required permeability model in one filling. There are many factors that affect the permeability of the sand filling model. The difficulty of quantifying these factors is different. Some are the main influencing factors, and some factors are difficult to quantify. For the main control factors that can be quantified, through the experience accumulation of a large number of model fillings, the gray correlation analysis is performed on each influencing factor, and the factors with the largest correlation with the model permeability are determined as the main influencing factors. For the factors between two systems or multiple systems and another system, the size of the correlation that changes with different objects or time and space is called the correlation degree. It describes the similarity or development trend between the two factors. The change trend is consistent. If the degree of synchronous change is high, the correlation degree is high. Therefore, when using the gray correlation analysis method to analyze data, we must first determine the reference series and the comparison series, calculate the correlation degree, and compare their similarities by comparing the size of the correlation degree. The correlation degree between the model permeability and the influencing factors is shown in Table 1.

[0038] Table 1 Correlation between model permeability and influencing factors in descending order

[0039] Serial number factor Relevance 1 Pressure limit 0.9163 2 Total filling volume 0.9215 3 Single filling volume 0.9124 4 Compaction times 0.8807 5 Gear 0.8985

[0040] According to the correlation between each influencing factor and the model permeability, it can be determined that the factors of the model permeability are ranked as follows: pressing pressure > total loading > single loading > single pressing times > gear position. Through the analysis of the grey correlation theory, the parameters with a correlation greater than 0.9 are: pressing pressure, total loading, single loading, while the correlation of single pressing times and gear position is less than 0.9. Therefore, it can be determined that the main controlling factors affecting the model permeability are: upper limit of pressure, total loading, and single loading.

[0041] (5) The weights of the above factors in the model permeability are obtained by using the analytic hierarchy process and combining the experimental data for error elimination (see Table 2), and then the comprehensive evaluation coefficient E of the main controlling factors is obtained.

[0042] Table 2 Correlation and weight coefficients among various influencing factors

[0043] factor Relevance Weight coefficient Total filling volume 0.9215 0.459 Suppression pressure 0.9163 0.295 Single filling volume 0.9124 0.246

[0044] As shown in Table 2, the weights of the above factors in the model permeability are: through the hierarchical analysis method, the total filling volume, upper pressure limit, and single filling volume are assigned 3, 2, and 3 respectively according to the experimental importance using the Saaty scaling method, so that the weights of each factor are 0.5, 0.33, and 0.17 respectively. The coefficients are substituted into the comprehensive evaluation coefficient E of the sand filling model, and the single filling volume and total filling volume are calculated. The calculated results deviate from the actual data. According to the inverse calculation results, 0.5, 0.33, and 0.17 are adjusted several times, and the final weights are determined to be 0.459, 0.295, and 0.246, so that the error is within a reasonable range. The formula for the comprehensive evaluation coefficient E of the sand filling model is obtained:

[0045] E = pressing pressure × pressure weight + maximum weight of sand filling / single loading volume × single weight + total loading volume × total loading weight, that is

[0046] E = pressing pressure × 0.295 + maximum weight of sand filling / single filling amount × 0.246 + total filling amount × 0.459 ①

[0047] The maximum weight of sand filling = volume of sand filling pipe × density of rock sand;

[0048] For example, if the diameter of the sand filling pipe is 2.5 cm, the length is 30 cm, the volume is 147 ml, and the density of sandstone is between 2.5-2.7, and 2.7 is the maximum density, then the total weight is 147×2.7=397 g, rounded to 400 g, that is, the maximum weight of sand filling in a 30 cm sand filling pipe is 400 g.

[0049] (6) Based on the data obtained in step (3), it is found that there is a certain mathematical relationship between the total loading volume and the single loading volume of the same formation rock sand. The regression curves show a linear negative correlation between the two, and the total loading volume formula is obtained:

[0050] Total loading volume = A × single loading volume + B ②

[0051] Linear similarity calculation is performed to obtain the values ​​of A and B. The single filling volume and the total filling volume are calculated by combining formulas ① and ② as well as the filling pressure. When filling, the preferred number of single pressing is 1. If the air permeability is far from the target, the number of single pressing can be increased to 2 times, that is, a sand filling model with the target permeability can be produced. Example

[0052] The rock sand used in this case is the formation rock sand of a certain oil field in Suizhong, CNOOC. The filling target is an air permeability of 3000mD, and the size of the sand filling model is 2.5×30cm. The rock sand is fully dried at 80℃ for 24h and the rock sand is screened by standard. The rock sand particle size is matched according to the formation rock sand particle size ratio. The initial pressing pressure is set to 8MPa, the single filling amount is 15g, and the single pressing number is 2 times. After pressing, the final sand filling amount is 280.16g, and the model air permeability is 550mD. Because the air permeability is far from the target, the second pressing pressure is reduced to 7MPa, the single pressing number is 2 times, the single filling amount is 20g, the final sand filling amount is 268.71g, and the model air permeability is 2000mD. The result is still far from the target. The third sand filling pressure remained unchanged, the number of single pressings was changed to 1, the single filling amount was changed to 30g, the final sand filling amount was 250.96g, and the model air permeability was 4200mD, which was greater than the target permeability. The fourth sand filling pressure remained unchanged, the number of single pressings was 1, the single filling amount was 25g, the final sand filling amount was 259.87g, and the model air permeability was 3300mD, which was still a gap from the target. The fifth sand filling pressure remained unchanged, the number of single pressings was 1, the single filling amount was 22g, the final sand filling amount was 265g, and the model air permeability was 2600mD, which was closer to the target.

[0053] According to the comprehensive judgment formula E = pressing pressure × 0.295 + 400 / single loading volume × 0.246 + total loading volume × 0.459, the main control factors of the experiment are substituted and the comprehensive evaluation coefficients of each experiment in Table 3 are obtained.

[0054] Table 3 Comprehensive evaluation coefficient of sand filling model and model permeability data table

[0055] With the comprehensive evaluation coefficient as the horizontal axis and the filling permeability as the vertical axis, the relationship curve between the two is obtained (such as Figure 2). According to the relationship curve between the comprehensive evaluation coefficient and the model permeability, the comprehensive evaluation coefficient formula of the main control parameters under different given permeabilities can be regressed into:

[0056] K = -218.66E + 30597.73 (where K is the packing permeability),

[0057] Our target permeability is K=3000mD. According to the above formula, E=126.21.

[0058] At the same time, through multiple experiments, it was found that there is a certain mathematical relationship between the total loading volume and the single loading volume of the same formation rock sand, and the regression curves have a linear negative correlation (such as Figure 3 ):

[0059] Total loading amount = -1.926 × single loading amount + 308.081,

[0060] When the comprehensive evaluation coefficient of the predetermined permeability is obtained, according to the formula

[0061] E = pressing pressure × 0.295 + 400 / single filling volume × 0.246 + total filling volume × 0.459

[0062] Total filling volume = -1.926 × single filling volume + 308.081, which can quantitatively obtain the specific values ​​of the three main control parameters (i.e., compression pressure, single filling volume, and total filling volume), guide the model sand filling process, and more accurately fill the target permeability.

[0063] At this point, we can confirm the parameters one by one, namely: the pressing pressure is 7MPa, the number of single pressing times is 1 time, the single filling amount is 24.38g, and the total filling amount is 261.16g. According to the parameters, three fillings were carried out respectively, and the total filling amounts of the three times were 261.25g, 261.2g, and 261.33g respectively. The three air permeabilities were 3050mD, 3070mD, and 3030mD respectively. From the experimental results, the experimental repeatability is high and the error is within the allowable range.

[0064] At present, some sand-filled models are prone to particle migration: when the fluid passes through the compacted rock sand, due to viscosity and pressure, it will interact with the fine particles in the rock sand. When the viscosity and pressure are too high, the fluid will carry the particles, that is, the particles will migrate, affecting the permeability of the entire model. The degree of migration is greatly affected by the fluid viscosity and displacement pressure. For example, in the polymer displacement process, since the viscosity of the polymer is much greater than that of water or even oil, it is inevitable to carry sand, which is easy to block the model and cause the experiment to fail. In order to prevent particle migration, some researchers use epoxy resin to artificially cement the rock particles, but after the cementing material is mixed into the sand-filled model, the permeability of the model is changed, which will inevitably produce large deviations. The problems of low success rate and poor repeatability have not been effectively solved in the industry for a long time.

[0065] In view of this situation, the present invention adopts a method of installing a screen in the sand filling pipe during the sand filling process to solve the problem. During the experiment, it is decided whether to install a screen according to the actual situation: if it is necessary to simulate the sand production of the formation at the same time, there is no need to install a screen, or only a small amount of screen is added; if the sand filling is seriously speed-sensitive, that is, the degree of particle migration is relatively intense, a screen can be installed during the filling process. If the sand filling model is used for thin oil displacement and particle migration is prone to occur, a screen is installed in the middle of the model; if the sand filling model is used for ordinary heavy oil displacement, two screens are installed in the model with the same screen spacing; if the sand filling model is used for higher viscosity heavy oil, three screens can be installed as needed, and so on. The number of screens is related to the viscosity of the crude oil and the displacement pressure, and the distance between the screens is consistent. The size of the screen is the same as the inner diameter of the sand filling pipe, and the screen aperture is smaller than the minimum rock sand particle size. The number and position of the added screens are determined according to the actual degree of migration.

[0066] Implementation Case 2

[0067] According to the method described in Example 1, two 2.5×30cm sand-filled models were prepared, each with a permeability of about 1500mD. One of them was without a screen, and the other was equipped with a screen. Both models were evacuated at room temperature, saturated with water, and injected with water at flow rates of 3.0mL / min, 6.0mL / min, and 9.0mL / min, respectively. The pressure curves were then recorded. The experimental results are shown in Figure 1. Figure 4 From the results, when the flow rate is 3.0mL / min and 6.0mL / min, both of them show good Darcy seepage characteristics. When the flow rate increases to 9.0mL / min, the pressure difference of the model with screen is still relatively stable, while the model without screen has obvious particle migration. It can be seen that the screen plays a significant role in reducing the velocity sensitivity of the sand filling model.

Claims

1. A method for making a sand filling model for crude oil displacement experiment, characterized in that The following steps are involved: (1) Drying and screening the obtained rock sand to select rock sand with suitable particle size; (2) Rock sand is loaded according to the estimated single loading volume and pressing pressure, and the air permeability is measured after loading is completed; (3) Compare the air permeability measured in step (2) with the permeability of the target sand filling model, adjust the single filling amount, pressing pressure and single pressing times, and repeat the filling until the difference between the air permeability and the target permeability is no more than ±10%, and record each group of data, including single filling amount, pressing pressure, single pressing times, total sand filling amount and air permeability; (4) According to the grey correlation method, the main controlling factors affecting the air permeability of the model are determined as follows: pressing pressure, single loading volume, and total loading volume; (5) The grey correlation method was used to analyze a large amount of experimental data to obtain the correlation between each main control factor and air permeability, and the key factors affecting the model permeability were obtained based on the correlation. The weights of the above factors in the model permeability were obtained by combining the experimental data with the analytic hierarchy process: the total filling volume was 0.459, the pressing pressure was 0.295, and the single filling volume was 0.

246. By optimizing the main control factors and quantifying the main control factors of permeability, the formula for the comprehensive evaluation coefficient E of the sand filling model was obtained: E = pressing pressure × 0.295 + maximum weight of sand filling / single filling amount × 0.246 + total filling amount × 0.459 ① The maximum weight of sand filling = volume of sand filling pipe × density of rock sand; With the comprehensive evaluation coefficient as the horizontal coordinate and the filling permeability as the vertical coordinate, the relationship curve between the two is obtained; according to the relationship curve between the comprehensive evaluation coefficient and the model permeability, the comprehensive evaluation coefficient formula of the main control parameters under different given permeabilities is regressed: K = -218.66E + 30597.73 Where K is the packing permeability; (6) Based on the data obtained in step (3), the total loading amount formula is obtained: Total loading volume = A × single loading volume + B ② Linear regression calculation is performed to obtain the values ​​of A and B. Combining formulas ① and ②, the suppression parameters are calculated, and filling is performed according to the parameters to produce a sand filling model with the target permeability.

2. The method for making a sand-filling model for crude oil displacement experiment according to claim 1, characterized in that: In the step (2), when filling the rock sand, a screen is installed in the sand filling pipe, the diameter of the screen is the same as the inner diameter of the sand filling pipe, and the aperture of the screen hole is smaller than the minimum sand particle size.

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