Method for predicting polymer displacement effect
By preparing parallel core models and configuring polymer solutions with different injection schemes, displacement experiments were conducted, and the cumulative resistance coefficient ratio was calculated. This solved the problem of lacking prediction of polymer displacement effect in existing technologies, and improved the efficiency and recovery rate of oil and gas field development.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- PETROCHINA CO LTD
- Filing Date
- 2024-12-31
- Publication Date
- 2026-06-30
Smart Images
Figure CN122304729A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of oil and gas exploration and development technology, and specifically to a method for predicting polymer displacement effects. Background Technology
[0002] With the continued growth of global energy demand and the gradual depletion of oil resources, improving the extraction efficiency of oil, as one of the main energy sources, is of great significance for ensuring energy supply. After years of development, most oilfields have entered the late stage of development characterized by high water cut and high recovery (i.e., the "dual-high development stage"), where waterflood production declines rapidly, remaining oil is scattered, and tapping potential is difficult. Polymer displacement has become a key means to improve oil recovery because it can effectively solve the problem of severe ineffective water circulation in the dual-high development stage.
[0003] However, oil and gas field development involves complex geological formations, often exhibiting significant planar and inter-layer conflicts. When polymer flooding is employed, profile reversal is prone to occur, leading to low utilization of low-permeability layers and high polymer usage. Therefore, to improve the fluid absorption profile as much as possible, control profile reversal, and ultimately enhance oil recovery, it is crucial to predict the effectiveness of polymer flooding before implementing it in the reservoir. This is essential for selecting and optimizing polymer flooding schemes for actual production.
[0004] However, there is currently a lack of methods in the technology to predict the effect of polymer displacement in order to guide actual displacement measures. Summary of the Invention
[0005] The purpose of this invention is to overcome the problem in the prior art of lacking a scheme to predict the polymer displacement effect in order to guide actual displacement measures, and to provide a method for predicting the polymer displacement effect.
[0006] To achieve the above objectives, the present invention provides a method for predicting polymer displacement effects, the prediction method comprising: A first core model and a second core model are prepared, and the first core model and the second core model are connected in parallel to obtain a parallel core model. The permeability of the first core model is greater than that of the second core model. A first polymer solution corresponding to a first polymer displacement scheme and a second polymer solution corresponding to a second polymer displacement scheme are prepared. The first polymer displacement scheme is a single slug injection scheme, and the second polymer displacement scheme is an alternating slug injection scheme. First displacement experiments and second displacement experiments were conducted on the parallel core model based on the first polymer solution and the second polymer solution, respectively. Based on the relevant data from the first displacement experiment, plot the target curve corresponding to the first displacement experiment, and calculate the ratio of the first cumulative resistance coefficient between the second core model and the first core model in the first displacement experiment; based on the relevant data from the second displacement experiment, plot the target curve corresponding to the second displacement experiment, and calculate the ratio of the second cumulative resistance coefficient between the second core model and the first core model in the second displacement experiment. The target curves corresponding to the first and second displacement experiments are compared, and the ratio of the first and second cumulative drag coefficients is compared. Based on the comparison results, the target displacement scheme is determined from the first and second polymer displacement schemes.
[0007] In this embodiment of the application, the preparation of the first core model and the second core model includes: A first core model is prepared based on the permeability of the first formation in the target area reservoir, and a second core model is prepared based on the permeability of the second formation in the target area reservoir, wherein the permeability of the first formation is greater than that of the second formation.
[0008] In the embodiments of this application, the first core model and the second core model have the same shape and size.
[0009] In this embodiment of the application, connecting the first core model and the second core model in parallel includes: Set up one main input pipeline and two branch input pipelines; The inlets of both input branch pipes are connected to the outlet of the main input pipe, and the outlets of the two input branch pipes are connected to the injection end of the first core model and the injection end of the second core model, respectively.
[0010] In the embodiments of this application, the first polymer displacement scheme and the second polymer displacement scheme are polymer displacement schemes pre-designed for the target region reservoir.
[0011] In this embodiment of the application, the first displacement experiment includes water flooding, single polymer flooding and water flooding in sequence, wherein the single polymer flooding is the process of injecting a first polymer solution into a parallel core model; The second displacement experiment includes water flooding, polymer alternating flooding, and water flooding in sequence. The polymer alternating flooding is a process of alternately injecting a second polymer solution into a parallel core model.
[0012] In the embodiments of this application, in the first displacement experiment, Water flooding prior to single polymer flooding includes: Crude oil was injected into the parallel core model, and then water flooding was performed on the parallel core model until the water content in the produced fluid reached the first target value. Water drive following a single polymer flood includes: Water flooding was performed on the parallel core model until the water content in the produced fluid reached a second target value, which was greater than the first target value.
[0013] In this embodiment of the application, in the second displacement experiment, Water drive preceding polymer alternating drive includes: Crude oil was injected into the parallel core model, and then water flooding was performed on the parallel core model until the water content in the produced fluid reached the first target value. Water drive following polymer alternating drive includes: Water flooding was performed on the parallel core model until the water content in the produced fluid reached a second target value, which was greater than the first target value.
[0014] In this embodiment of the application, the first displacement experiment and the second displacement experiment on the parallel core model based on the first polymer solution and the second polymer solution respectively include: Crude oil was injected into the parallel core model, and water flooding was performed on the parallel core model until the water content in the produced fluid reached the first target value. A first predetermined volume of a first polymer solution is injected into the parallel core model; Water drive was performed on the parallel core model until the water content in the produced fluid reached the second target value. Empty the parallel core model, inject crude oil into the parallel core model, and perform water flooding on the parallel core model until the water content in the produced fluid reaches the first target value. A second polymer solution of a second preset volume is alternately injected into the parallel core model; Water flooding was performed on the parallel core model until the water content in the produced fluid reached the second target value.
[0015] In this embodiment of the application, the target curves corresponding to the first displacement experiment include: the diversion rate change curve, the instantaneous drag coefficient change curve, and the instantaneous drag coefficient change rate change curve corresponding to the first core model and the second core model respectively during the first displacement experiment; The target curves corresponding to the second displacement experiment include: the flow rate change curve, the instantaneous drag coefficient change curve, and the drag coefficient change rate change curve corresponding to the first core model and the second core model during the second displacement experiment, respectively.
[0016] In this embodiment, the instantaneous drag coefficients of the first and second core models are calculated based on the following formula: ; in, The instantaneous drag coefficient of the first or second core model; The injection flow rate during water drive is expressed in cm³. 3 / s; The injection flow rate is measured in cm³ for single polymer flooding or alternating polymer flooding. 3 / s; The pressure difference between the injection end and the production end of the first or second core model during water drive, expressed in MPa. The pressure difference between the injection end and the production end of the first or second core model during single polymer flooding or alternating polymer flooding is expressed in MPa.
[0017] In this embodiment, the cumulative drag coefficient of the second core model in the first displacement experiment is calculated based on the following formula: ; in, This represents the cumulative drag coefficient of the second core model; P max This represents the maximum PV number that can be injected into the polymer solution. a and b These are the constants obtained through fitting; The cumulative drag coefficient of the first core model in the first displacement experiment was calculated based on the following formula: ; in, This represents the cumulative drag coefficient of the first core model; c and d The constants obtained from the fitting are denoted as .
[0018] In this embodiment, the ratio of the first cumulative drag coefficient between the second core model and the first core model in the first displacement experiment is calculated based on the following formula: ; in, The ratio of the first cumulative drag coefficient between the second core model and the first core model in the first displacement experiment; P max This represents the maximum PV number that can be injected into the polymer solution. a , b , c and d All of these are constants obtained through fitting.
[0019] In this embodiment, the cumulative drag coefficient of the second core model in the second displacement experiment is calculated based on the following formula: ; in, This represents the cumulative drag coefficient of the second core model; P maxThis represents the maximum PV number that can be injected into the polymer solution. e and f These are the constants obtained through fitting; The cumulative drag coefficient of the first core model in the first displacement experiment was calculated based on the following formula: ; in, This represents the cumulative drag coefficient of the first core model; g and h The constants obtained from the fitting are denoted as .
[0020] In this embodiment, the ratio of the second cumulative drag coefficient between the second core model and the first core model in the second displacement experiment is calculated based on the following formula: ; in, This represents the ratio of the second cumulative drag coefficient between the second core model and the first core model in the second displacement experiment. P max This represents the maximum PV number that can be injected into the polymer solution. e , f , g and h All of these are constants obtained through fitting.
[0021] The above technical solution includes: preparing a first core model and a second core model, and connecting the first core model and the second core model in parallel to obtain a parallel core model, wherein the permeability of the first core model is greater than that of the second core model; preparing a first polymer solution corresponding to a first polymer displacement scheme and a second polymer solution corresponding to a second polymer displacement scheme, wherein the first polymer displacement scheme is a single-slug injection scheme and the second polymer displacement scheme is an alternating slug injection scheme; conducting a first displacement experiment and a second displacement experiment on the parallel core model based on the first polymer solution and the second polymer solution, respectively; and based on the results of the first displacement experiment... Based on relevant data, a target curve corresponding to the first displacement experiment is plotted, and the ratio of the first cumulative resistance coefficient between the second core model and the first core model in the first displacement experiment is calculated. Similarly, based on relevant data from the second displacement experiment, a target curve corresponding to the second displacement experiment is plotted, and the ratio of the second cumulative resistance coefficient between the second core model and the first core model in the second displacement experiment is calculated. The target curves corresponding to the first and second displacement experiments are compared, as are the ratios of the first and second cumulative resistance coefficients. Based on the comparison results, a target displacement scheme is determined from the first and second polymer displacement schemes. The scheme provided in this application embodiment can effectively predict the polymer displacement effect, thereby guiding actual displacement measures. Furthermore, analyzing the improvement effect of the liquid absorption profile based on the ratio of the cumulative resistance coefficient between low-permeability and high-permeability layers enables a more accurate evaluation and prediction of the polymer displacement effect.
[0022] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description
[0023] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. In the drawings: Figure 1 The schematic diagram illustrates a flow chart of a polymer displacement effect prediction method according to an embodiment of this application; Figure 2 The schematic diagram illustrates the flow rate variation curves of a first core model and a second core model according to an embodiment of this application during the first displacement experiment. Figure 3 The illustration schematically shows the instantaneous drag coefficient variation curves of a first core model and a second core model according to an embodiment of this application during a first displacement experiment. Figure 4The illustration shows the instantaneous drag coefficient change rate curves of a first core model and a second core model according to an embodiment of this application during a first displacement experiment. Figure 5 The schematic diagram illustrates the flow rate variation curves of a first core model and a second core model according to an embodiment of this application during a second displacement experiment. Figure 6 The illustration schematically shows the instantaneous drag coefficient variation curves of a first core model and a second core model according to an embodiment of this application during a second displacement experiment. Figure 7 The illustration shows the instantaneous drag coefficient change rate curves of a first core model and a second core model according to an embodiment of this application during a second displacement experiment. Detailed Implementation
[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustration and explanation of the embodiments of this application and are not intended to limit the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.
[0025] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.
[0026] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.
[0027] As described in the background section, with the continuous growth of global energy demand and the gradual depletion of oil resources, improving the extraction efficiency of oil, as one of the main energy sources, is of great significance for ensuring energy supply. After years of development, most oilfields have entered the late stage of development characterized by high water cut and high recovery (i.e., the dual-high development stage), where water-drive production declines rapidly, remaining oil is scattered, and tapping potential is difficult. Polymer displacement has become a key means to improve oil recovery because it can effectively solve the problem of severe ineffective water circulation in the dual-high development stage. However, oil and gas field development systems are complex, often exhibiting prominent planar and inter-layer contradictions. When using polymer displacement, profile reversal is prone to occur, resulting in low utilization of low-permeability layers and large polymer usage. Therefore, in order to improve the fluid absorption profile as much as possible, control profile reversal, and thus improve the recovery rate, it is crucial to predict the effect of polymer displacement before carrying out polymer displacement in the reservoir, which is essential for selecting and optimizing polymer displacement schemes applied in the actual extraction process. However, existing technologies lack methods for predicting polymer displacement effects to guide actual displacement measures, especially methods for predicting the displacement effects of alternating polymer injection.
[0028] To address this, one embodiment of this application provides a method for predicting polymer displacement effects, such as... Figure 1 As shown, the polymer displacement effect prediction method may include the following steps: Step 101: Prepare a first core model and a second core model, and connect the first core model and the second core model in parallel to obtain a parallel core model. The permeability of the first core model is greater than that of the second core model.
[0029] Among them, the first core model and the second core model were artificially manufactured, that is, the first core model and the second core model are artificial cores.
[0030] The permeability of the first core model is greater than that of the second core model; in other words, the first core model is a high-permeability core model, and the second core model is a low-permeability core model. The permeability difference between the first and second core models can be greater than 3.
[0031] More preferably, when preparing the first and second core models, the first core model can be prepared based on the permeability of the first formation in the target area reservoir, and the second core model can be prepared based on the permeability of the second formation in the target area reservoir, where the permeability of the first formation is greater than that of the second formation. The target area is the region where polymer solution will be injected to improve the liquid absorption profile, or the region where polymer displacement will be carried out. The first formation is a high-permeability layer in the target area reservoir, and the second formation is a low-permeability layer in the target area reservoir. That is, the first core model can be prepared based on the permeability of the high-permeability layer in the target area reservoir, so that the permeability of the first core model corresponds to the permeability of the high-permeability layer in the reservoir, and the second core model can be prepared based on the permeability of the low-permeability layer in the target area reservoir, so that the permeability of the second core model corresponds to the permeability of the low-permeability layer in the reservoir.
[0032] In the specific preparation process, the shape and size (i.e., size) of the first core model and the second core model can be the same. For example, if both the first core model and the second core model are cuboids, then the first core model and the second core model have the same length, the same width, and the same thickness.
[0033] In this embodiment, a main input pipeline and two branch input pipelines can be provided. The inlets of the two branch input pipelines are connected to the outlet of the main input pipeline, and the outlets of the two branch input pipelines are connected to the injection end of the first core model and the injection end of the second core model, respectively. Thus, the first core model and the second core model are connected in parallel to obtain a parallel core model.
[0034] Step 102: Configure the first polymer solution corresponding to the first polymer displacement scheme and configure the second polymer solution corresponding to the second polymer displacement scheme. The first polymer displacement scheme is a single slug injection scheme and the second polymer displacement scheme is an alternating slug injection scheme.
[0035] The first and second polymer displacement schemes can be pre-designed polymer displacement schemes for the target reservoir area. In practical applications, when designing a polymer displacement scheme for a target reservoir area, not only are construction details designed, but also the type and concentration of polymer used. When preparing the polymer solution, it can be configured according to the pre-designed polymer type and concentration for the corresponding polymer displacement scheme.
[0036] In practical applications, both the first and second polymer displacement schemes can be single-slug injection schemes, alternating slug injection schemes, or the first polymer displacement scheme can be a single-slug injection scheme and the second polymer displacement scheme can be an alternating slug injection scheme. This application uses a single-slug injection scheme for the first polymer displacement scheme and an alternating slug injection scheme for the second polymer displacement scheme as an example to illustrate the scheme provided in this application.
[0037] A single-slug injection scheme refers to injecting only one type of polymer solution throughout the entire polymer displacement process. Therefore, the first polymer solution corresponding to the first polymer displacement scheme includes one type of polymer solution. An alternating slug injection scheme refers to alternating injection of polymer solutions of different viscosities throughout the entire polymer displacement process. Therefore, the second polymer solution corresponding to the second polymer displacement scheme includes at least two polymer solutions of different viscosities.
[0038] Step 103: Conduct the first displacement experiment and the second displacement experiment on the parallel core model based on the first polymer solution and the second polymer solution, respectively.
[0039] That is, a first displacement experiment is carried out on a parallel core model based on a first polymer solution, and a second displacement experiment is carried out on a parallel core model based on a second polymer solution.
[0040] Specifically, a first polymer solution was used, and a first polymer displacement scheme (single slug injection scheme) was followed to conduct a first displacement experiment on the parallel core model. A second polymer solution was used, and a second polymer displacement scheme (alternating slug injection scheme) was followed to conduct a second displacement experiment on the parallel core model.
[0041] In this embodiment, the first displacement experiment sequentially includes water flooding, single polymer flooding, and water flooding again. The single polymer flooding is the process of injecting a first polymer solution into the parallel core model. The second displacement experiment sequentially includes water flooding, alternating polymer flooding, and water flooding again. The alternating polymer flooding is the process of alternately injecting a second polymer solution into the parallel core model, that is, the process of alternately injecting polymer solutions of different viscosities into the parallel core model.
[0042] In the first displacement experiment, the water flooding process prior to single polymer flooding may include: injecting crude oil into a parallel core model to saturate the model with crude oil, and then water flooding the saturated model until the water cut in the produced fluid reaches a first target value. This simulates the current oil-water characteristics of the target reservoir. The first target value can be set according to the current oil-water characteristics of the target reservoir; for example, it can be 95%. The water flooding process after single polymer flooding may include: water flooding the parallel core model until the water cut in the produced fluid reaches a second target value, which is greater than the first target value. The second target value can be set according to actual needs; for example, it can be 98%.
[0043] Similarly, in the second displacement experiment, the water flooding process prior to polymer alternating flooding may include: injecting crude oil into the parallel core model to saturate it with crude oil, and then water flooding the saturated core model until the water cut in the produced fluid reaches a first target value. The water flooding process following polymer alternating flooding may include: water flooding the parallel core model until the water cut in the produced fluid reaches a second target value, which is greater than the first target value.
[0044] Taking the use of the same parallel core model to conduct the first and second displacement experiments as an example, the process of conducting the first and second displacement experiments on the parallel core model based on the first polymer solution and the second polymer solution respectively may specifically include: Crude oil is injected into the parallel core model to saturate it with crude oil. Water flooding is then performed on the saturated core model until the water cut in the produced fluid reaches a first target value. A first preset volume of a first polymer solution is injected into the parallel core model. Water flooding is then performed on the parallel core model until the water cut in the produced fluid reaches a second target value. The parallel core model is then emptied, and crude oil is injected into it to saturate it with crude oil. Water flooding is then performed on the saturated core model until the water cut in the produced fluid reaches the first target value. A second preset volume of a second polymer solution is alternately injected into the parallel core model. Water flooding is then performed on the parallel core model until the water cut in the produced fluid reaches the second target value. The first preset volume and the second preset volume are equal.
[0045] It is understood that injecting a first preset volume of polymer solution into the parallel core model means injecting the first preset volume of polymer solution into the parallel core model using a single slug injection method. Alternatingly injecting a second preset volume of polymer solution into the parallel core model means injecting the second preset volume of polymer solution into the parallel core model using an alternating injection method. Taking an example where the second polymer solution includes both high-viscosity and low-viscosity polymer solutions, the high-viscosity and low-viscosity polymer solutions are alternately injected into the parallel core model, for a total of the second preset volume. The completion of one alternating injection of a high-viscosity slug and one low-viscosity slug is called one alternating cycle, and the entire injection process typically includes multiple alternating cycles.
[0046] Step 104: Based on the relevant data from the first displacement experiment, plot the target curve corresponding to the first displacement experiment, and calculate the ratio of the first cumulative resistance coefficient between the second core model and the first core model in the first displacement experiment; based on the relevant data from the second displacement experiment, plot the target curve corresponding to the second displacement experiment, and calculate the ratio of the second cumulative resistance coefficient between the second core model and the first core model in the second displacement experiment.
[0047] In this embodiment, the target curves corresponding to the first displacement experiment may include: the flow diversion rate change curve, the instantaneous drag coefficient change curve, and the instantaneous drag coefficient change rate change curve corresponding to the first core model and the second core model respectively during the first displacement experiment. The target curves corresponding to the second displacement experiment may include: the flow diversion rate change curve, the instantaneous drag coefficient change curve, and the drag coefficient change rate change curve corresponding to the first core model and the second core model respectively during the second displacement experiment.
[0048] Among them, the flow split rate change curve is the curve of the flow split rate changing with the fluid injection volume; the instantaneous resistance coefficient change curve is the curve of the instantaneous resistance coefficient changing with the polymer solution injection volume; and the instantaneous resistance coefficient change rate change curve is the curve of the instantaneous resistance coefficient change rate changing with the polymer solution injection volume.
[0049] The split rate can evaluate the distribution of instantaneous liquid uptake. The split rate refers to the percentage of instantaneous liquid uptake of the first core model and the second core model to the total instantaneous liquid uptake. The split rate curve can reflect the improvement effect and change law of the reservoir liquid uptake profile after polymer flooding.
[0050] Regarding the instantaneous drag coefficient variation curve, in this embodiment of the application, the instantaneous drag coefficients of the first core model and the second core model can be calculated based on the following formula (1): (1); In the above formula (1), The instantaneous drag coefficient of the first or second core model; This refers to the injection flow rate during water drive, expressed in cm³. 3 / s; The injection flow rate is measured in cm³ for single polymer flooding or alternating polymer flooding. 3 / s; The pressure difference between the injection end and the production end of the first or second core model during water drive, expressed in MPa. The pressure difference between the injection end and the production end of the first or second core model during single polymer flooding or alternating polymer flooding is expressed in MPa.
[0051] Specifically, when using the above formula (1) to calculate the instantaneous drag coefficient of the first core model during the first displacement experiment, The instantaneous drag coefficient of the first core model. This refers to the injection flow rate during water drive, expressed in cm³. 3 / s; The injection flow rate is for single polymer flooding, in cm³. 3 / s; The pressure difference between the injection end and the production end of the first core model during water drive is expressed in MPa. The pressure difference between the injection end and the production end of the first core model during single polymer flooding is expressed in MPa.
[0052] When using the above formula (1) to calculate the instantaneous drag coefficient of the second core model during the first displacement experiment, The instantaneous drag coefficient of the second core model. This refers to the injection flow rate during water drive, expressed in cm³. 3 / s; The injection flow rate is for single polymer flooding, in cm³. 3 / s; The pressure difference between the injection end and the production end of the second core model during water drive is expressed in MPa. The pressure difference between the injection end and the production end of the second core model during single polymer flooding is expressed in MPa.
[0053] When using the above formula (1) to calculate the instantaneous drag coefficient of the first core model during the second displacement experiment, The instantaneous drag coefficient of the first core model. This refers to the injection flow rate during water drive, expressed in cm³. 3 / s; The injection flow rate during polymer alternating drive is expressed in cm³. 3 / s; The pressure difference between the injection end and the production end of the first core model during water drive is expressed in MPa. The pressure difference between the injection end and the production end of the first core model during polymer alternating drive is expressed in MPa.
[0054] When using the above formula (1) to calculate the instantaneous drag coefficient of the second core model during the second displacement experiment, The instantaneous drag coefficient of the second core model. This refers to the injection flow rate during water drive, expressed in cm³. 3 / s; The injection flow rate during polymer alternating drive is expressed in cm³. 3 / s; The pressure difference between the injection end and the production end of the second core model during water drive is expressed in MPa. The pressure difference between the injection end and the production end of the second core model during polymer alternating drive is expressed in MPa.
[0055] Taking the plotting of the instantaneous drag coefficient variation curves of the first and second core models during the first displacement experiment as an example (specifically, the instantaneous drag coefficient variation curves of the first and second core models during a single polymer flooding process), the specific plotting process may include: First, calculate the instantaneous drag coefficients of the first and second core models during the single polymer flooding process according to the above formula (1). Plot the scatter plots of the instantaneous drag coefficient of the first core model with the polymer solution injection volume and the scatter plots of the instantaneous drag coefficient of the second core model with the polymer solution injection volume in the same coordinate system. Then, fit and regress the scatter plots corresponding to the first and second core models respectively to obtain the instantaneous drag coefficient change curves corresponding to the first and second core models respectively, and obtain the fitting relationship between the two curves respectively. The process of plotting the instantaneous drag coefficient change curves corresponding to the first and second core models in the second displacement experiment (specifically, the instantaneous drag coefficient change curves corresponding to the first and second core models in the polymer alternating flooding process) is similar and will not be described again here.
[0056] Taking the plotting of the instantaneous drag coefficient change rate curves of the first and second core models during the first displacement experiment as an example (specifically, the instantaneous drag coefficient change rate curves of the first and second core models during a single polymer flooding process), the specific plotting process may include: First, differentiate the fitting relationship corresponding to the instantaneous drag coefficient change curve of the first core model to obtain the formula for the instantaneous drag coefficient change rate of the first core model; and differentiate the fitting relationship corresponding to the instantaneous drag coefficient change curve of the second core model to obtain the formula for the instantaneous drag coefficient change rate of the second core model. Then, substitute the instantaneous drag coefficient of the first core model in the first displacement experiment calculated by formula (1) into the formula for the instantaneous drag coefficient change rate of the first core model to obtain multiple scatter points of the instantaneous drag coefficient change rate of the first core model in the first displacement experiment; similarly, substitute the instantaneous drag coefficient of the second core model in the first displacement experiment calculated by formula (1) into the formula for the instantaneous drag coefficient change rate of the second core model to obtain multiple scatter points of the instantaneous drag coefficient change rate of the second core model in the first displacement experiment. Next, scatter plots of the instantaneous drag coefficient change rate as a function of polymer solution injection volume for the first core model and the second core model were plotted in the same coordinate system. Fitting and regression were then performed on the scatter plots for the first and second core models respectively to obtain the instantaneous drag coefficient change rate curves for the first and second core models. The process of plotting the instantaneous drag coefficient change rate curves for the first and second core models during the second displacement experiment (specifically, the instantaneous drag coefficient change rate curves for the first and second core models during polymer alternating displacement) is similar and will not be elaborated here.
[0057] The rate of change of the instantaneous resistance coefficient determines the change in the instantaneous liquid absorption of the first and second core models, while the relative values of the cumulative resistance coefficients of the first and second core models reflect the distribution of the total liquid volume. Therefore, the ratio of the cumulative resistance coefficient of the second core model to that of the first core model can be used to evaluate the improvement of the liquid absorption profile.
[0058] Regarding the first displacement experiment: Based on the empirical formula for the instantaneous drag coefficient derived from the experimental data of single polymer flooding, that is, the fitting relationship corresponding to the curve of instantaneous drag coefficient change, the general formula for the change of instantaneous drag coefficient of single polymer flooding with polymer solution injection volume can be obtained. Among them, the formula corresponding to the second core model can be shown as formula (2) below, and the formula corresponding to the first core model can be shown as formula (3) below: (2); (3); in, This represents the instantaneous drag coefficient of the second core model; The instantaneous drag coefficient of the first core model; x The cumulative injection volume of the polymer solution is expressed in cm³. 3 / s; a , b , c and d All of these are constants obtained through fitting.
[0059] Set the maximum injection PV number to P max That is, the maximum PV number of the polymer solution injection, in [0, P max On the interval and By integrating, the cumulative drag coefficient of the second core model in a single polymer flooding can be obtained, as shown in the following formula (4), and the cumulative drag coefficient of the first core model in a single polymer flooding can be obtained, as shown in the following formula (5): (4); (5); in, This represents the cumulative drag coefficient of the second core model; This represents the cumulative drag coefficient of the first core model.
[0060] Furthermore, the ratio of the first cumulative drag coefficient between the second core model and the first core model in a single polymer flooding process can be calculated based on the following formula (6): (6).
[0061] in, This represents the ratio of the first cumulative drag coefficient between the second core model and the first core model in a single polymer flooding operation. Generally speaking, The smaller the value, the less seepage resistance the polymer solution generates in the low-permeability layer, making it easier for the low-permeability layer to absorb liquid and thus effectively utilize the remaining oil in the low-permeability layer.
[0062] Regarding the second displacement experiment: Based on the empirical formula for the instantaneous drag coefficient derived from the polymer alternating flooding experimental data, i.e., the fitting relationship corresponding to the instantaneous drag coefficient change curve, the general formula for the change of the instantaneous drag coefficient of polymer alternating flooding with the polymer solution injection amount can be obtained. Among them, the formula corresponding to the second core model can be shown as formula (7) below, and the formula corresponding to the first core model can be shown as formula (8) below: (7); (8); in, This represents the instantaneous drag coefficient of the second core model; The instantaneous drag coefficient of the first core model; x The cumulative injection volume of the polymer solution is expressed in cm³. 3 / s; e , f , g and h All of these are constants obtained through fitting.
[0063] Set the maximum injection PV number to P max That is, the maximum PV number of the polymer solution injection, in [0, P max On the interval and By integrating, the cumulative drag coefficient of the second core model in polymer alternating flooding can be obtained, as shown in the following formula (9), and the cumulative drag coefficient of the first core model in polymer alternating flooding can be obtained, as shown in the following formula (10): (9); (10); in, This represents the cumulative drag coefficient of the second core model; This represents the cumulative drag coefficient of the first core model.
[0064] Furthermore, the ratio of the second cumulative drag coefficient between the second core model and the first core model in polymer alternating flooding can be calculated based on the following formula (11): (11); in, This represents the ratio of the second cumulative drag coefficient between the second core model and the first core model in polymer alternating flooding. Generally speaking, The smaller the value, the less seepage resistance the polymer solution generates in the low-permeability layer, making it easier for the low-permeability layer to absorb liquid and thus effectively utilize the remaining oil in the low-permeability layer.
[0065] Step 105: Compare the target curves corresponding to the first and second displacement experiments, and compare the ratio of the first and second cumulative drag coefficients. Based on the comparison results, determine the target displacement scheme from the first and second polymer displacement schemes.
[0066] Specifically, comparing the target curves corresponding to the first displacement experiment and the second displacement experiment can include: comparing the diversion rate change curves corresponding to the first core model and the second core model respectively during the first displacement experiment with the diversion rate change curves corresponding to the first core model and the second core model respectively during the second displacement experiment; comparing the instantaneous drag coefficient change curves corresponding to the first core model and the second core model respectively during the first displacement experiment with the instantaneous drag coefficient change curves corresponding to the first core model and the second core model respectively during the second displacement experiment; and comparing the instantaneous drag coefficient change rate change curves corresponding to the first core model and the second core model respectively during the first displacement experiment with the instantaneous drag coefficient change rate change curves corresponding to the first core model and the second core model respectively during the second displacement experiment.
[0067] It is understandable that the target curve corresponding to the first displacement experiment reflects the improvement effect of the single-slug injection scheme on the fluid absorption profile, i.e., it predicts the effect after implementing the preset single-slug injection scheme in the target reservoir area. The target curve corresponding to the second displacement experiment reflects the improvement effect of the alternating slug injection scheme on the fluid absorption profile, i.e., it predicts the effect after implementing the preset alternating slug injection scheme in the target reservoir area. The magnitude of the cumulative drag coefficient ratio can also reflect the improvement effect on the fluid absorption profile; the smaller the cumulative drag coefficient ratio, the higher the fluid absorption ratio of the low-permeability layer, and the better the improvement effect on the fluid absorption profile. By comparison, the scheme with a better improvement effect on the fluid absorption profile can be selected from the single-slug injection scheme and the alternating slug injection scheme as the target displacement scheme.
[0068] It is understood that the polymer displacement effect prediction method provided in this application includes: preparing a first core model and a second core model, and connecting the first core model and the second core model in parallel to obtain a parallel core model, wherein the permeability of the first core model is greater than the permeability of the second core model; configuring a first polymer solution corresponding to a first polymer displacement scheme and a second polymer solution corresponding to a second polymer displacement scheme, wherein the first polymer displacement scheme is a single slug injection scheme and the second polymer displacement scheme is an alternating slug injection scheme; conducting a first displacement experiment and a second displacement experiment on the parallel core model based on the first polymer solution and the second polymer solution, respectively; and according to the... Based on relevant data from the first displacement experiment, a target curve corresponding to the first displacement experiment is plotted, and the ratio of the first cumulative resistance coefficient between the second core model and the first core model in the first displacement experiment is calculated. Similarly, based on relevant data from the second displacement experiment, a target curve corresponding to the second displacement experiment is plotted, and the ratio of the second cumulative resistance coefficient between the second core model and the first core model in the second displacement experiment is calculated. The target curves corresponding to the first and second displacement experiments are compared, as are the ratios of the first and second cumulative resistance coefficients. Based on the comparison results, a target displacement scheme is determined from the first and second polymer displacement schemes. The scheme provided in this application embodiment can effectively predict the polymer displacement effect, thereby guiding actual displacement measures. Furthermore, analyzing the improvement effect of the liquid absorption profile based on the ratio of the cumulative resistance coefficient between low-permeability and high-permeability layers enables a more accurate evaluation and prediction of the polymer displacement effect.
[0069] The polymer displacement effect prediction method provided in the above embodiments of this application will be described below with specific examples. It should be understood that the following examples are only specific implementation methods and do not imply an undue limitation on the solution of this application.
[0070] The specific implementation plan is as follows: Step 1: Prepare a parallel core model and configure the first polymer solution corresponding to the single slug injection scheme and the second polymer solution corresponding to the alternating slug injection scheme.
[0071] In the parallel core model, the effective permeability of the first core model is 800 × 10⁻⁶. -3 μm 2 The effective permeability of the second core model is 200 × 10⁻⁶. -3 μm 2 The first and second core models are both 0.3m long, 0.045m wide, and 0.045m thick.
[0072] The preparation process of the first polymer solution is as follows: Select a relative molecular mass of 2500 × 10⁻⁶.4 Polyacrylamide was prepared using simulated saline solution with a mineralization of 900 mg / L and stirred for 2 hours to achieve a polyacrylamide mass concentration of 2000 mg / L.
[0073] The second polymer solution includes a low-viscosity polymer solution and a high-viscosity polymer solution. The preparation process for the low-viscosity polymer solution is as follows: A polymer solution with a relative molecular mass of 1200 × 10⁻⁶ is selected. 4 Polyacrylamide was prepared using simulated brine with a mineralization of 900 mg / L and stirred for 2 hours to achieve a polyacrylamide concentration of 1000 mg / L. The preparation process for the high-viscosity polymer solution was as follows: [The following text appears to be unrelated and possibly a separate excerpt:] Take a relative molecular mass of 2500 × 10... 4 Polyacrylamide was prepared using simulated saline solution with a mineralization of 900 mg / L and stirred for 2 hours to achieve a polyacrylamide mass concentration of 2000 mg / L.
[0074] Step 2: Conduct a first displacement experiment on the parallel core model based on the first polymer solution, and a second displacement experiment on the parallel core model based on the second polymer solution.
[0075] The first displacement experiment process was as follows: water flooding was performed until the produced fluid contained 95% water, then 0.56 PV of the first polymer solution was injected, followed by water flooding until the produced fluid contained 98% water.
[0076] The second displacement experiment was conducted as follows: water flooding was performed until the produced fluid contained 95% water, followed by alternating injection of a high-viscosity polymer solution of 0.056 PV and a low-viscosity polymer solution of 0.056 PV, repeated for 5 alternating cycles. Then, water flooding was performed until the produced fluid contained 98% water.
[0077] Step 3: Plot the diversion rate change curves of the first and second core models respectively during the first displacement experiment, as shown below. Figure 2 As shown.
[0078] Plot the instantaneous drag coefficient variation curves of the first and second core models during the first displacement experiment, as follows: Figure 3 As shown.
[0079] Plot the instantaneous drag coefficient change rate curves for the first and second core models during the first displacement experiment, as shown below. Figure 4 As shown.
[0080] Plot the diversion rate change curves of the first and second core models during the second displacement experiment, as shown below. Figure 5 As shown.
[0081] Plot the instantaneous drag coefficient variation curves of the first and second core models during the second displacement experiment, as shown below. Figure 6 As shown.
[0082] Plot the instantaneous drag coefficient change rate curves for the first and second core models during the second displacement experiment, respectively. Figure 7 As shown.
[0083] Figures 2-7 In the model, the high-permeability layer corresponds to the first core model, and the low-permeability layer corresponds to the second core model.
[0084] Depend on Figure 2 It can be seen that after the polymer solution is injected, the liquid uptake of the hypopermeable layer gradually increases, and the liquid uptake profile is improved. In the later stages of polymer solution injection, the liquid uptake of the hypopermeable layer begins to decrease. This process of the liquid uptake of the hypopermeable layer first increasing and then decreasing is called profile reversal.
[0085] Depend on Figure 5 It can be seen that the flow split rate curve of the low-permeability layer rises to a high point and remains there for a relatively long time, before starting to decline during subsequent waterflooding. Figure 2 In comparison, the shunt rate curve shape improved, changing from a "∧" shape to a "∩" shape, indicating a longer effective time for the low-permeability layer. This suggests that the alternating slug injection scheme can effectively suppress or delay the occurrence of profile reversal, and its direct effect is to increase the liquid uptake of the low-permeability layer and improve its mobilization.
[0086] Depend on Figure 3 and Figure 4 It can be seen that during the injection of the polymer solution, the instantaneous resistance coefficient of the high-permeability layer increases logarithmically, while that of the low-permeability layer increases exponentially. The rate of change of the instantaneous resistance coefficient of the high-permeability layer continuously decreases, while that of the low-permeability layer continuously increases. The rate of change of the instantaneous resistance coefficient reflects the speed at which the seepage resistance of that layer increases. In the initial stage of polymer solution injection, the rate of change of the instantaneous resistance coefficient of the high-permeability layer is greater than that of the low-permeability layer, meaning the high-permeability layer exhibits a greater rate of resistance increase. This forces more polymer solution to enter the low-permeability layer to maintain pressure balance, thus adjusting the adsorption profile. When the rate of change of the instantaneous resistance coefficient of the high-permeability layer becomes lower than that of the low-permeability layer, the low-permeability layer begins to exhibit a greater rate of resistance increase. This forces more polymer solution to flow back into the high-permeability layer, i.e., a profile reversal phenomenon occurs. The point where the rates of change of the resistance coefficients of the high-permeability and low-permeability layers are equal (the intersection point) is the moment when profile reversal begins.
[0087] Depend on Figure 6 and Figure 7It can be seen that, using the alternating injection method, the instantaneous resistance coefficient of the high-permeability layer exhibits the same logarithmic increase as the single-slug injection method, while the instantaneous resistance coefficient of the low-permeability layer changes from an exponential increase to a logarithmic increase, indicating that the seepage patterns of the polymer solution in the high- and low-permeability layers show good consistency. Furthermore, the curves showing the rate of change of the instantaneous resistance coefficient in both the high- and low-permeability layers with varying polymer solution injection volume both decrease exponentially, exhibiting the same trend, decreasing numerical differences, and no intersection, indicating that no profile reversal phenomenon occurred.
[0088] Step 4: Calculate the ratio of the first cumulative resistance coefficient between the second core model and the first core model; and calculate the ratio of the second cumulative resistance coefficient between the second core model and the first core model, as shown in Table 1.
[0089] Table 1. Ratio of Cumulative Resistance Coefficient to Enhanced Oil Recovery Value
[0090] The comparison results show that the alternating slug injection scheme has a better effect on improving the fluid absorption profile. Furthermore, it can be observed that the smaller the r or r′ value, the higher the fluid absorption ratio of the low-permeability layer and the greater the recovery rate increase. The r or r′ value has a good correlation with both, indicating that using the r or r′ value to evaluate the improvement of the fluid absorption profile is highly reliable.
[0091] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.
[0092] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.
Claims
1. A method for predicting the effect of polymer flooding, characterized by, The prediction method includes: A first core model and a second core model are prepared, and the first core model and the second core model are connected in parallel to obtain a parallel core model. The permeability of the first core model is greater than that of the second core model. A first polymer solution corresponding to a first polymer displacement scheme and a second polymer solution corresponding to a second polymer displacement scheme are prepared. The first polymer displacement scheme is a single slug injection scheme, and the second polymer displacement scheme is an alternating slug injection scheme. First displacement experiments and second displacement experiments were conducted on the parallel core model based on the first polymer solution and the second polymer solution, respectively. Based on the relevant data from the first displacement experiment, plot the target curve corresponding to the first displacement experiment, and calculate the ratio of the first cumulative resistance coefficient between the second core model and the first core model in the first displacement experiment; based on the relevant data from the second displacement experiment, plot the target curve corresponding to the second displacement experiment, and calculate the ratio of the second cumulative resistance coefficient between the second core model and the first core model in the second displacement experiment. The target curves corresponding to the first and second displacement experiments are compared, and the ratio of the first and second cumulative drag coefficients is compared. Based on the comparison results, the target displacement scheme is determined from the first and second polymer displacement schemes.
2. The polymer displacement effect prediction method according to claim 1, characterized by, The preparation of the first core model and the second core model includes: A first core model is prepared based on the permeability of the first formation in the target area reservoir, and a second core model is prepared based on the permeability of the second formation in the target area reservoir, wherein the permeability of the first formation is greater than that of the second formation.
3. The polymer displacement effect prediction method according to claim 2, characterized by, The first and second core models are identical in shape and size.
4. The polymer displacement effect prediction method according to claim 1, characterized by, The parallel connection of the first core model and the second core model includes: Set up one main input pipeline and two branch input pipelines; The inlets of both input branch pipes are connected to the outlet of the main input pipe, and the outlets of the two input branch pipes are connected to the injection end of the first core model and the injection end of the second core model, respectively.
5. The polymer displacement effect prediction method according to claim 2, characterized by, The first polymer displacement scheme and the second polymer displacement scheme are polymer displacement schemes pre-designed for the target area reservoir.
6. The method for predicting polymer displacement effect according to claim 1, characterized in that, The first displacement experiment includes water flooding, single polymer flooding and water flooding in sequence, wherein the single polymer flooding is the process of injecting a first polymer solution into a parallel core model; The second displacement experiment includes water flooding, polymer alternating flooding, and water flooding in sequence. The polymer alternating flooding is a process of alternately injecting a second polymer solution into a parallel core model.
7. The polymer displacement efficiency prediction method of claim 6, wherein, In the first displacement experiment, Water flooding prior to single polymer flooding includes: Crude oil was injected into the parallel core model, and then water flooding was performed on the parallel core model until the water content in the produced fluid reached the first target value. Water drive following a single polymer flood includes: Water flooding was performed on the parallel core model until the water content in the produced fluid reached a second target value, which was greater than the first target value.
8. The polymer displacement efficiency prediction method of claim 6, wherein, In the second displacement experiment, Water drive preceding polymer alternating drive includes: Crude oil was injected into the parallel core model, and then water flooding was performed on the parallel core model until the water content in the produced fluid reached the first target value. Water drive following polymer alternating drive includes: Water flooding was performed on the parallel core model until the water content in the produced fluid reached a second target value, which was greater than the first target value.
9. The polymer displacement efficiency prediction method of claim 6, wherein, The first displacement experiment and the second displacement experiment were carried out on the parallel core model based on the first polymer solution and the second polymer solution, respectively, including: Crude oil was injected into the parallel core model, and water flooding was performed on the parallel core model until the water content in the produced fluid reached the first target value. A first predetermined volume of a first polymer solution is injected into the parallel core model; Water drive was performed on the parallel core model until the water content in the produced fluid reached the second target value. Empty the parallel core model, inject crude oil into the parallel core model, and perform water flooding on the parallel core model until the water content in the produced fluid reaches the first target value. A second polymer solution of a second preset volume is alternately injected into the parallel core model; Water flooding was performed on the parallel core model until the water content in the produced fluid reached the second target value.
10. The method for predicting polymer displacement effect according to claim 6, characterized in that, The target curves corresponding to the first displacement experiment include: the flow rate change curve, the instantaneous drag coefficient change curve, and the instantaneous drag coefficient change rate change curve corresponding to the first core model and the second core model respectively during the first displacement experiment; The target curves corresponding to the second displacement experiment include: the flow rate change curve, the instantaneous drag coefficient change curve, and the drag coefficient change rate change curve corresponding to the first core model and the second core model during the second displacement experiment, respectively.
11. The method for predicting polymer displacement effects according to claim 10, characterized in that, The instantaneous drag coefficients of the first and second core models are calculated based on the following formula: ； in, The instantaneous drag coefficient of the first or second core model; This refers to the injection flow rate during water drive, expressed in cm³. 3 / s; The injection flow rate is measured in cm³ for single polymer flooding or alternating polymer flooding. 3 / s; The pressure difference between the injection end and the production end of the first or second core model during water drive, expressed in MPa. The pressure difference between the injection end and the production end of the first or second core model during single polymer flooding or alternating polymer flooding is expressed in MPa.
12. The method for predicting polymer displacement effects according to claim 6, characterized in that, The cumulative drag coefficient of the second core model in the first displacement experiment was calculated based on the following formula: ； in, This represents the cumulative drag coefficient of the second core model; P max This represents the maximum PV number that can be injected into the polymer solution. a and b These are the constants obtained through fitting; The cumulative drag coefficient of the first core model in the first displacement experiment was calculated based on the following formula: ； in, This represents the cumulative drag coefficient of the first core model; c and d The constants obtained from the fitting are denoted as .
13. The method for predicting polymer displacement effects according to claim 12, characterized in that, The ratio of the first cumulative drag coefficient between the second core model and the first core model in the first displacement experiment was calculated based on the following formula: ； in, The ratio of the first cumulative drag coefficient between the second core model and the first core model in the first displacement experiment; P max This represents the maximum PV number that can be injected into the polymer solution. a , b , c and d All of these are constants obtained through fitting.
14. The method for predicting polymer displacement effect according to claim 6, characterized in that, The cumulative drag coefficient of the second core model in the second displacement experiment was calculated based on the following formula: ； in, This represents the cumulative drag coefficient of the second core model; P max This represents the maximum PV number that can be injected into the polymer solution. e and f These are the constants obtained through fitting; The cumulative drag coefficient of the first core model in the first displacement experiment was calculated based on the following formula: ； in, This represents the cumulative drag coefficient of the first core model; g and h The constants obtained from the fitting are denoted as .
15. The method for predicting polymer displacement effects according to claim 14, characterized in that, The ratio of the second cumulative drag coefficient between the second core model and the first core model in the second displacement experiment was calculated based on the following formula: ； in, The ratio of the second cumulative drag coefficient between the second core model and the first core model in the second displacement experiment; P max This represents the maximum PV number that can be injected into the polymer solution. e , f , g and h All of these are constants obtained through fitting.