Polymer flooding injection concentration determination method based on oil phase fluidity control

Abstract

The invention relates to a polymer flooding injection concentration determination method based on oil phase fluidity control. The method comprises the following steps: determining the minimum effective viscosity of an underground polymer solution required to meet fluidity control requirements based on an oil phase fluidity control criterion; estimating the front edge concentration of the polymer slug when the polymer slug migrates to the front edge in the stratum; the current ground injection concentration is subjected to stratum shear loss verification and compensation, and the shaft bottom zero shear viscosity is obtained; determining the ground zero shear viscosity of the ground injection liquid; the corresponding polymer concentration is reversely solved, and the minimum ground injection concentration is obtained; and updating the ground injection concentration and the permeability decrease coefficient, and carrying out iterative calculation until the difference between the minimum ground injection concentrations obtained by two adjacent iterations is smaller than a preset tolerance. By matching the polymer fluidity with the oil phase fluidity, microscopic fingering is inhibited, and the oil displacement efficiency is improved; the closed loop iteration is coupled with a multi-loss mechanism, parameter self-consistency is ensured, the concentration design precision is improved, and a more scientific engineering basis is provided for polymer flooding in the high water cut period.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, and in particular to a method for determining the injection concentration of polymer flooding based on oil phase mobility control. Background Technology

[0002] In the later stages of oilfield development, as formation water cut increases, the effectiveness of conventional water injection gradually diminishes, leading to a bottleneck in enhanced oil recovery. Polymer flooding, a mature chemical flooding technology, increases the viscosity of the displacing fluid and improves the water-oil mobility ratio by adding high-molecular-weight polymers (such as partially hydrolyzed polyacrylamide HPAM) to the injected water. This expands the sweep range and suppresses water surge and viscous propulsion phenomena. This technology has become an important means to further enhance oil recovery in high water-cut oilfields.

[0003] In polymer flooding design, the determination of the injection concentration directly affects the technical effectiveness and economic benefits. Too low a concentration makes it impossible to effectively control mobility, easily leading to instability in the displacement process and fingering; too high a concentration significantly increases costs and may damage the formation or cause polymer degradation due to excessive injection pressure. Therefore, scientifically determining the minimum necessary polymer injection concentration while ensuring displacement effectiveness is crucial for optimizing polymer flooding design and implementation.

[0004] Currently, the concentration determination criterion commonly used in polymer flooding design is the "total mobility control criterion." This criterion requires that the mobility of the polymer solution not exceed the minimum total mobility of the oil-water two-phase flow at its front edge, and its expression is generally as follows:

[0005] ,

[0006] Where K is the absolute penetration rate, k rw k ro These represent the relative permeability of the aqueous and oil phases, in μ. w μ o The viscosity of water and crude oil, respectively, in μ. p R represents the effective viscosity of the polymer solution. k This represents the permeability reduction coefficient caused by polymer adsorption. This criterion aims to maintain the stability of the macroscopic displacement front by controlling the overall migration velocity of the polymer slug to not exceed the velocity of the upstream oil-water mixing zone.

[0007] The “total mobility control criterion” has obvious shortcomings: (1) It takes controlling the mobility of the polymer slug to be no greater than the total mobility of the oil-water mixing zone at its leading edge as the standard. However, in areas with high water saturation, the water phase mobility dominates the total mobility. Although this criterion can ensure that the polymer slug does not advance ahead of the oil-water mixing zone on a macroscopic scale, it cannot constrain the viscous fingering of the remaining crude oil on a microscopic scale, resulting in the crude oil being bypassed and the displacement efficiency being reduced; (2) This criterion relaxes the restrictions on polymers because it includes the water phase mobility. The minimum injection concentration designed accordingly may not be the optimal value for achieving stable displacement, which may easily lead to excessively high polymer usage and insufficient targeting, or conversely, insufficient concentration may lead to crossflow, both of which affect the technical and economic effects; (3) When calculating key parameters such as formation shear, the actual degradation process of the polymer solution in the oil-dominated flow environment is not fully considered, resulting in a deviation in the prediction of viscosity loss, which affects the accuracy of calculating the surface injection parameters from the underground demand.

[0008] In general, in regions with high water saturation, the total oil-water mobility is primarily dominated by the aqueous phase mobility. Even if the overall polymer mobility satisfies the aforementioned inequality, its local mobility within the oil-bearing pores may still be significantly higher than that of the crude oil itself. This leads to viscous fingering of the polymer solution into the crude oil within the micro-channels, causing the crude oil to be bypassed and unable to be effectively displaced, thus reducing micro-level oil displacement efficiency and affecting the final recovery rate. In other words, while the above criteria can constrain the overall polymer propulsion, they cannot effectively limit the polymer's propulsion speed relative to the crude oil at the pore scale, making it difficult to achieve truly protective displacement of the oil phase. Summary of the Invention

[0009] To address the technical problem of insufficient micro-finding control in existing polymer flooding technologies, this invention provides a method for determining polymer flooding injection concentration based on oil phase mobility control. The technical solution is as follows:

[0010] This invention provides a method for determining the injection concentration of polymer flooding based on oil phase mobility control. The method includes: determining the minimum effective viscosity of the underground polymer solution required to meet mobility control requirements based on the permeability decrease coefficient and base reservoir parameters, using oil phase mobility control criteria; estimating the leading-edge concentration of the polymer slug when it migrates to the leading edge in the formation based on the surface injection concentration, the base reservoir parameters, and polymer system parameters; and verifying and compensating for formation shear loss based on the minimum effective viscosity, the base reservoir parameters, the polymer system parameters, and engineering operation parameters to determine the usable concentration. The bottom-hole zero-shear viscosity is determined; based on the bottom-hole zero-shear viscosity and the engineering operation parameters, the surface injection fluid should possess a surface zero-shear viscosity; based on the surface zero-shear viscosity and the polymer system parameters, the corresponding polymer concentration is calculated to obtain the minimum surface injection concentration; the minimum surface injection concentration obtained in this iteration is used as the surface injection concentration for the next iteration, and the permeability reduction coefficient is updated based on the newly estimated leading edge concentration. The above steps are repeated for the next iteration calculation until the difference between the minimum surface injection concentrations obtained in two adjacent iterations is less than the preset tolerance, and the final minimum surface injection concentration is output.

[0011] The beneficial effects of the technical solution provided by the embodiments of the present invention include at least the following: by directly matching and controlling the polymer solution mobility with the crude oil mobility under the current reservoir water saturation, a method for determining the injection concentration of polymer flooding based on oil phase mobility control is constructed. This method fundamentally suppresses the micro-finding and flow-around phenomena of polymer in oil-bearing pores, realizes a more stable displacement front, and thus improves the micro-displacement efficiency. At the same time, by constructing a closed-loop iterative algorithm, the system couples multiple loss mechanisms such as adsorption, formation shear, and borehole shear, ensuring the self-consistency between polymer concentration, front concentration, and viscosity requirements, significantly improving the calculation accuracy of the minimum injection concentration and the system reliability of the scheme, providing a more scientific and practical design basis for polymer flooding in high water-cut reservoirs, and possessing both theoretical innovation and engineering practical value. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a flowchart of a polymer flooding injection concentration determination method based on oil phase mobility control provided by an embodiment of the present invention;

[0014] Figure 2This is a schematic diagram of the relative permeability curves of oil and water provided in an embodiment of the present invention;

[0015] Figure 3 This is a comparison chart of the required front polymer solution viscosity under different reservoir water saturation levels provided in the embodiments of the present invention;

[0016] Figure 4 This is a comparison chart of the required front polymer solution concentrations under different reservoir water saturation levels provided in the embodiments of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0018] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0019] In the embodiments of this invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the distinction between them, they convey the same meaning. Similarly, the terms "of," "corresponding (relevant)," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the distinction between them, they convey the same meaning.

[0020] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0021] To facilitate understanding of this invention, the parameters involved will be briefly described first. The parameters in this invention include known parameters and unknown parameters, wherein the known parameters include basic reservoir parameters, polymer system parameters, and engineering operation parameters.

[0022] Basic reservoir parameters refer to a series of parameters that describe the geological and fluid properties of a target reservoir. These include: absolute permeability K, porosity, etc. Rock density ρ rock Crude oil viscosity μ o Injected water viscosity μ w Oil-water relative permeability curve, current water saturation S w Current oil saturation These parameters are the basic inputs for polymer drive scheme design.

[0023] Polymer system parameters refer to a series of parameters characterizing the physicochemical properties of the polymer solution used. These include: maximum adsorption capacity (a), adsorption equilibrium coefficient (b), and infinite shear viscosity (μ). ∞ Characteristic shear rate Parameters such as the power-law exponent p, zero-shear viscosity function, viscosity-concentration standard curve or fitting formula of polymer solution, etc., reflect the migration and deformation behavior of polymers in the formation.

[0024] Engineering operating parameters refer to parameters related to the injection process and wellbore conditions, including: oil-phase Darcy velocity v. o Formation geometric factor β, characterizing pore structure complexity, and borehole shear viscosity retention rate η. perf These parameters are used to correct for the shear degradation loss of the polymer during the injection process.

[0025] The unknown parameters are some parameters that are solved throughout the process, including: the permeability reduction coefficient R. k Minimum effective viscosity μ eff,req Ground injection concentration C p,inj Leading edge concentration C p,front Bottom-hole zero shear viscosity μ0 (C) p,inj Ground zero shear viscosity μ surface Minimum ground injection concentration .

[0026] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0027] Please see Figure 1 This invention provides a method for determining the injection concentration of polymer flooding based on oil phase mobility control. The processing flow of this method may include steps S1 to S6.

[0028] Step S1: Based on the permeability reduction coefficient and basic reservoir parameters, determine the minimum effective viscosity of the underground polymer solution required to meet the flow control requirements according to the oil phase flow control criterion.

[0029] Optionally, the base reservoir parameters include crude oil viscosity μ. o Current water saturation S w And the oil-water relative permeability curve. Step S1 includes: (1.1) According to the oil-water relative permeability curve, the curve is as follows: Figure 2As shown, calculate the relative permeability of the oil phase and the relative permeability of the water phase corresponding to the current water saturation; (1.2) Based on the initial preset or updated permeability reduction coefficient, the relative permeability of the oil phase, the relative permeability of the water phase, and the viscosity of the crude oil, determine the minimum effective viscosity based on the oil phase mobility control criterion. In the first iteration calculation (i.e., the first execution of steps S1~S6), the minimum effective viscosity can be calculated directly based on the initial preset permeability reduction coefficient R. k For example, it can be 1, and in subsequent iterations, the updated penetration rate decrease coefficient will be used for iterative correction.

[0030] This step, based on the oil phase mobility control criterion, directly matches the polymer mobility with the crude oil mobility under the current reservoir conditions, thereby establishing the minimum effective subsurface viscosity required for stable displacement. Compared to traditional methods, this criterion more strictly constrains the local fingering of polymers into crude oil, providing a more precise physical basis for subsequent concentration design and helping to improve micro-displacement efficiency.

[0031] Optionally, the formula for calculating the minimum effective viscosity is:

[0032] ,

[0033] In the formula, S w k represents the current water saturation of the target reservoir. ro (S w ) and k rw (S w ) represents the relative permeability of the oil phase and the relative permeability of the water phase at the current water saturation level, in μ. o R represents the viscosity of crude oil. k This represents the penetration rate reduction coefficient.

[0034] In this embodiment, the oil phase mobility control criterion proposed in this invention is: the polymer solution mobility is less than or equal to the current reservoir water saturation S. w The following crude oil flow rate:

[0035] ,

[0036] Right now:

[0037] ,

[0038] The formula for calculating the minimum effective viscosity can be obtained by simplification.

[0039] Step S2: Based on the surface injection concentration, basic reservoir parameters, and polymer system parameters, estimate the leading edge concentration of the polymer slug when it migrates to the leading edge in the formation.

[0040] Optionally, the basic reservoir parameters include rock density and porosity, and the polymer system parameters include maximum adsorption capacity and adsorption equilibrium coefficient. These parameters are known. Step S2 includes: (2.1) Based on the initial preset or updated surface injection concentration, maximum adsorption capacity, adsorption equilibrium coefficient, rock density, and porosity, establishing a set of equations between the surface injection concentration, the front concentration, and the polymer loss caused by adsorption, based on the principle of mass balance; (2.2) Solving the set of equations to obtain the front concentration.

[0041] The ground injection concentration in step 2.1 can be set with an initial preset value based on experience. The initial calculation is performed, and subsequent calculations use the updated value.

[0042] This step estimates the actual effective concentration at the displacement front by establishing a set of mass balance equations, considering the adsorption and retention effects of the polymer in the formation. This process connects the surface injection concentration with the actual underground polymer concentration involved in flow control, and is a key step in correcting adsorption losses and ensuring the self-consistency of the concentration design, thus improving the practicality and reliability of the scheme.

[0043] Alternatively, the above system of equations can be:

[0044] ,

[0045] In the formula, C p,inj To inject concentration into the ground, C p,front ρ represents the leading edge concentration. rock For rock density, Here, ρ is porosity, a is the maximum adsorption capacity, and b is the adsorption equilibrium coefficient; these parameters are all known. PV is the pore volume. This represents the average adsorption amount. M represents the average polymer concentration. rock For rock quality, these parameters can be considered as intermediate values. The purpose of the entire equation system is to determine the ground injection concentration C. p,inj To calculate the leading edge concentration C p,front Its function is to establish the correlation between the target viscosity underground and the polymer concentration at a specific location in the stratum, which is a key link connecting macroscopic design and microscopic consumption.

[0046] Step S3: Based on the minimum effective viscosity, basic reservoir parameters, polymer system parameters, and engineering operation parameters, verify and compensate for formation shear loss at the current surface injection concentration to determine the available bottom hole zero shear viscosity.

[0047] Optionally, step S3 includes steps 3.1 to 3.4.

[0048] Step 3.1: Calculate the formation equivalent shear rate based on the basic reservoir parameters and engineering operation parameters.

[0049] Optionally, the basic reservoir parameters include absolute permeability, porosity, current oil saturation, and oil-water relative permeability curves; the engineering operation parameters include the oil-phase Darcy velocity and formation geometry factors characterizing pore structure complexity; the formula for calculating the formation equivalent shear rate is:

[0050] ,

[0051] In the formula, β is a formation geometry factor characterizing the complexity of the pore structure, and its value ranges from 2 to 4. o Let K be the Darcy velocity of the oil phase and K be the absolute permeability. Porosity Given the current oil saturation, This represents the relative permeability of the oil phase corresponding to the current oil saturation. This step proposes an equivalent shear rate calculation formula based on the oil phase flow environment. This formula uses the oil phase Darcy velocity and the relative permeability of the oil phase as core parameters, more realistically reflecting the shear history experienced by the polymer in oil-bearing pores. Compared to traditional formulas based on aqueous phase or average conditions, this method significantly improves the accuracy of viscosity loss prediction, making the compensation calculation closer to the actual seepage environment.

[0052] Step 3.2: Based on the minimum effective viscosity, the formation equivalent shear rate, and the polymer system parameters, the zero-shear viscosity required to meet the minimum effective viscosity requirement is calculated using the shear-thinning model, thus obtaining the required zero-shear viscosity.

[0053] Optionally, the polymer system parameters include infinite shear viscosity, characteristic shear rate, and power-law exponent; the formula for calculating the required zero shear viscosity is:

[0054] ,

[0055] In the formula, μ eff,req Minimum effective viscosity μ ∞ For infinite shear viscosity, Here, p represents the characteristic shear rate, and p is the power-law exponent. This step utilizes a shear-thinning model to inversely calculate the required zero-shear viscosity at the wellbore based on the formation shear rate and the required minimum effective viscosity. This process achieves the inverse calculation from subsurface viscosity requirements to wellbore conditions, providing crucial input for subsequent compensation of near-wellbore shear losses and ensuring that the polymer still meets flowability control requirements underground.

[0056] Step 3.3: Obtain the actual zero-shear viscosity based on the current ground injection concentration and the zero-shear viscosity function in the polymer system parameters. In this step, it is only necessary to adjust the ground injection concentration... Substitute into the zero shear viscosity function The actual zero-shear viscosity can be obtained from this, and can be denoted as: .

[0057] Step 3.4: Determine the actual zero-shear viscosity Is it higher than the required zero shear viscosity? If so, then the actual zero shear viscosity will be... As the bottom-hole zero-shear viscosity If not, the injection concentration at the surface is adjusted, and the new actual zero-shear viscosity is recalculated until the judgment condition is met. This step verifies whether the current injection concentration meets the viscosity requirements after formation shear by comparing the actual zero-shear viscosity with the required zero-shear viscosity. If not, the injection concentration needs to be adjusted and recalculated until the actual viscosity is not lower than the required value. This mechanism ensures that the polymer still has sufficient viscosity in the formation to maintain stable displacement, improving the robustness of the scheme.

[0058] Step S4: Determine the surface zero-shear viscosity that the injection fluid should possess based on the bottom hole zero-shear viscosity and engineering operation parameters.

[0059] Optionally, engineering operating parameters include borehole shear viscosity retention rate; the formula for calculating ground zero shear viscosity is:

[0060] ,

[0061] In the formula, μ0(C p,inj η is the bottom-hole zero-shear viscosity. perf The borehole shear viscosity retention rate ranges from 0.5 to 0.8. This step further considers the viscosity loss caused by borehole shear, converting the bottomhole zero-shear viscosity to the surface zero-shear viscosity requirement using the borehole shear viscosity retention rate. This compensation mechanism ensures that the polymer viscosity is maintained throughout the entire process from the wellhead to the formation, allowing the surface injection concentration to accurately reflect the subsurface displacement demand.

[0062] Step S5: Based on the ground zero-shear viscosity and polymer system parameters, calculate the corresponding polymer concentration to obtain the minimum injection concentration at ground level.

[0063] Optionally, the polymer system parameters include a viscosity-concentration standard curve or fitting formula for the polymer solution, the expression of which is:

[0064] ,

[0065] In the formula, μ w The viscosity of the injected water is given by A1, A2, A3, and s, which are fitting coefficients. C is the viscosity of the injected water. sep This is the electrolyte concentration correction factor. In step S5, it is only necessary to set the value in the above formula as follows: The ground zero-shear viscosity calculated in step S4 The minimum polymer concentration C that satisfies the viscosity requirement obtained by solving the inverse equation. p This is the minimum injection concentration at ground level. This step utilizes the viscosity-concentration relationship curve or fitting formula of the polymer solution to back-calculate the ground zero-shear viscosity requirement into the corresponding polymer concentration, i.e., the minimum injection concentration at ground level. This process achieves the final conversion from physical requirements to engineering parameters, providing clear and actionable concentration indicators for on-site injection.

[0066] Step S6: Substitute the minimum injection concentration obtained in this iteration into the injection concentration for the next iteration in step S2. Update the permeability reduction coefficient based on the newly estimated leading edge concentration and recalculate the minimum effective viscosity in step S1. Repeat the above steps for the next iteration until the difference between the minimum injection concentrations obtained in two adjacent iterations is less than the preset tolerance. Output the final minimum injection concentration. Re-executing steps S1 and S2 is to update the permeability reduction coefficient and the minimum effective viscosity; re-executing steps S3 to S5 is to calculate the new minimum injection concentration. After obtaining each new minimum injection concentration, compare it with the result obtained in the previous calculation. If its change is less than the preset tolerance, the minimum injection concentration obtained in this calculation can be output as the final minimum injection concentration.

[0067] This step employs an iterative mechanism, using the minimum injection concentration obtained in the previous step as new input to recalculate the frontal concentration, permeability reduction coefficient, and minimum effective viscosity. It then repeats the viscosity compensation and concentration back-calculation process until the concentration converges. This closed-loop iteration ensures the self-consistency of multiple mechanisms, including adsorption, shearing, and permeability reduction, throughout the entire process, significantly improving the system accuracy and reliability of the final concentration results.

[0068] To verify the effectiveness of this invention, calculations were performed using a real-world case. In this case, the oil phase mobility at the current reservoir's actual water saturation (0.5) was used as the upper limit of control. Through iterative calculations, effects such as adsorption, formation shear, and borehole shear were comprehensively corrected, resulting in a minimum surface injection concentration of 1179 mg / L, corresponding to an effective subsurface viscosity of 28.269 mPa·s. Compared to the traditional method based on the minimum sum of oil and water mobility (whose design point water saturation of 0.3368 often does not exist in actual reservoirs), this invention, although requiring a higher concentration (the traditional method only requires 292 mg / L), significantly enhances the control capability of oil phase mobility, effectively suppressing oil phase fingering during displacement and improving sweep efficiency. This method closely aligns with the actual development of reservoirs in the medium-to-high water cut stage, possesses clear technical feasibility within the maximum feasible polymer concentration range, and has a complete and reliable calculation process. It provides a design approach for polymer flooding in the medium-to-high water cut stage that is closer to production practice, combining theoretical innovation with engineering practical value.

[0069] Figure 3 This paper presents the relationship between the viscosity of the front-end polymer solution calculated using the method of this invention and the conventional method, respectively, and the change with reservoir water saturation. It can be seen that as water saturation increases, the polymer viscosity required by the method of this invention increases significantly, especially at high water saturation levels, reflecting the high viscosity requirement needed to maintain effective displacement under conditions of low residual oil saturation. In contrast, the viscosity calculated by the conventional method increases slowly across the entire water saturation range, remaining below 10 mPa·s even at high water saturation, which does not conform to the requirements of actual displacement kinetics. The results of this invention clearly show that, near the residual oil state, the required front-end viscosity can exceed 100 mPa·s, which is more in line with the field practice understanding that "the less oil, the higher the required viscosity."

[0070] Figure 4 The curves showing the change in front polymer solution concentration with water saturation calculated by the method of this invention and the conventional method are presented. As water saturation increases, the polymer concentration calculated by the method of this invention shows a significant upward trend, falling within the 1000-2500 mg / L range commonly used in oilfields such as Daqing, which aligns well with field design experience. In contrast, the concentration obtained by the conventional method is consistently below 500 mg / L, showing a significant discrepancy from actual field application data and making it difficult to guide field injection. The concentration-saturation relationship provided by this invention is more closely aligned with the design requirements of polymer flooding in medium-to-high water-cut reservoirs, demonstrating good field applicability and promising prospects for widespread application.

[0071] In summary, the method for determining the minimum injection concentration of polymer flooding based on oil phase mobility control provided by this invention has achieved significant innovations in criteria, models, and processes, and can bring the following significant benefits compared with the prior art.

[0072] (1) The criteria are more stringent, the displacement is more stable, and the microscopic oil displacement efficiency is higher. This invention breaks through the traditional idea of ​​"total oil-water mobility control" and proposes for the first time the "oil phase mobility control" criterion with crude oil mobility as the direct constraint object, requiring that the polymer mobility should never be higher than the oil phase mobility at the current oil saturation. This criterion effectively inhibits the viscous fingering and flow around the polymer in the oil-bearing pores from a physical mechanism perspective, making the displacement front more uniform and stable at both the macroscopic and microscopic levels, significantly improving the microscopic oil washing efficiency, and laying a solid foundation for ultimately improving the recovery rate.

[0073] (2) The physical model is closer to the actual seepage environment, and the design basis is more scientific. Targeting the critical loss factor of formation shear, this invention innovatively proposes an equivalent shear rate calculation formula based on the oil phase Darcy velocity and the relative permeability of the oil phase. This formula directly correlates the shear environment with the flow state of crude oil (the current water injection development state of the reservoir). Compared with traditional formulas based on aqueous phase or average conditions, it can more realistically reflect the shear history experienced by the polymer in the target displacement region (oil-bearing pores), thus making the viscosity loss compensation calculation more accurate and reliable.

[0074] (3) The design process is complete, and the accuracy and reliability of the results are significantly improved. This invention constructs a closed-loop iterative algorithm that calculates the surface injection concentration from the underground viscosity requirement. The system couples key loss mechanisms such as adsorption retention, formation shear, and borehole shear, and achieves full-process self-consistency between polymer concentration, front-end concentration, permeability reduction coefficient, and viscosity requirement through double-loop iteration. This method overcomes the bias of traditional single-step calculation or empirical formulas, making the determination of the minimum injection concentration more rigorous in theory and more instructive for field applications.

[0075] (4) Balancing technological advancement with engineering practicality, this method offers significant economic benefits. Although the minimum injection concentration calculated by this method is typically higher than that of traditional methods due to stricter control standards (approximately 68.2% higher in the examples), potentially increasing chemical costs in the short term, the substantial improvement in displacement stability and sweep efficiency it brings enables more effective utilization of remaining oil resources and is expected to significantly improve oil recovery. From the perspective of the entire life cycle benefits of the oilfield, this technology possesses outstanding input-output advantages and has significant promotional value and application prospects.

[0076] The above embodiments can be implemented, in whole or in part, by software, hardware (such as circuits), firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more sets of available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive.

[0077] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0078] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0079] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0080] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0081] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the devices, apparatuses, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0082] In the several embodiments provided by this invention, it should be understood that the disclosed devices, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another device, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0083] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0084] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0085] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0086] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for determining the injection concentration of polymer flooding based on oil phase mobility control, characterized in that, The method includes: Based on the permeability reduction coefficient and basic reservoir parameters, the minimum effective viscosity of the underground polymer solution required to meet the mobility control requirements is determined according to the oil phase mobility control criterion. Based on the surface injection concentration, the basic reservoir parameters, and the polymer system parameters, the leading edge concentration of the polymer slug when it migrates to the leading edge in the formation is estimated. Based on the minimum effective viscosity, the basic reservoir parameters, the polymer system parameters, and the engineering operation parameters, the current surface injection concentration is used to verify and compensate for formation shear loss in order to determine the available bottom hole zero shear viscosity. Based on the bottom hole zero-shear viscosity and the engineering operation parameters, determine the surface injection fluid's required surface zero-shear viscosity. Based on the ground zero-shear viscosity and the polymer system parameters, the corresponding polymer concentration is calculated in reverse to obtain the minimum injection concentration at ground level; The minimum injection concentration obtained in this iteration is used as the injection concentration for the next iteration. The permeability reduction coefficient is updated based on the newly estimated leading edge concentration. The above steps are repeated for the next iteration calculation until the difference between the minimum injection concentrations obtained in two adjacent iterations is less than the preset tolerance. The final minimum injection concentration is then output.

2. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 1, characterized in that, The basic reservoir parameters include crude oil viscosity, current water saturation, and oil-water relative permeability curves; Based on the permeability decrease coefficient and basic reservoir parameters, the minimum effective viscosity of the subsurface polymer solution required to meet the mobility control requirements is determined according to the oil phase mobility control criterion, including: Based on the oil-water relative permeability curve, calculate the relative permeability of the oil phase and the relative permeability of the water phase corresponding to the current water saturation. The minimum effective viscosity is determined based on the initial or updated permeability reduction coefficient, the relative permeability of the oil phase, the relative permeability of the water phase, and the viscosity of the crude oil, according to the oil phase mobility control criterion.

3. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 2, characterized in that, The formula for calculating the minimum effective viscosity is as follows: ， In the formula, S w k represents the current water saturation of the target reservoir. ro (S w ) and k rw (S w ) represents the relative permeability of the oil phase and the relative permeability of the water phase corresponding to the current water saturation, in μ. o R represents the viscosity of the crude oil. k The permeability reduction coefficient is denoted as .

4. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 1, characterized in that, The basic reservoir parameters include rock density and porosity, and the polymer system parameters include maximum adsorption capacity and adsorption equilibrium coefficient. Based on the surface injection concentration, the base reservoir parameters, and the polymer system parameters, the leading edge concentration of the polymer slug as it migrates to the leading edge in the formation is estimated, including: Based on the initial or updated ground injection concentration, the maximum adsorption capacity, the adsorption balance coefficient, the rock density, and the porosity, a set of equations is established between the ground injection concentration, the front concentration, and the amount of polymer loss caused by adsorption, based on the principle of mass balance. Solve the system of equations to obtain the leading edge concentration.

5. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 4, characterized in that, The system of equations is as follows: ， In the formula, C p,inj For the ground injection concentration, C p,front The leading edge concentration, ρ rock The density of the rock is... Where is the porosity, a is the maximum adsorption capacity, b is the adsorption equilibrium coefficient, and PV is the pore volume. This represents the average adsorption amount. M represents the average polymer concentration. rock For rock mass.

6. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 1, characterized in that, Based on the minimum effective viscosity, the basic reservoir parameters, the polymer system parameters, and engineering operation parameters, the current surface injection concentration is used to verify and compensate for formation shear loss in order to determine the usable bottomhole zero-shear viscosity, including: Calculate the formation equivalent shear rate based on the basic reservoir parameters and the engineering operation parameters; Based on the minimum effective viscosity, the formation equivalent shear rate, and the polymer system parameters, the zero-shear viscosity required to meet the minimum effective viscosity requirement is calculated using the shear thinning model, thus obtaining the required zero-shear viscosity. The actual zero-shear viscosity is obtained based on the current ground injection concentration and the zero-shear viscosity function in the polymer system parameters; Determine whether the actual zero-shear viscosity is higher than the required zero-shear viscosity: If so, the actual zero-shear viscosity is taken as the bottom-hole zero-shear viscosity; If not, adjust the ground injection concentration until the judgment condition is met.

7. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 6, characterized in that, The basic reservoir parameters include absolute permeability, porosity, current oil saturation, and oil-water relative permeability curves. The engineering operation parameters include oil-phase Darcy velocity and formation geometry factors characterizing pore structure complexity. The formula for calculating the equivalent shear rate of the formation is as follows: ， In the formula, β is the formation geometry factor characterizing the complexity of the pore structure, and v o Let K be the Darcy velocity of the oil phase and K be the absolute permeability. The porosity is... The current oil saturation, This represents the relative permeability of the oil phase corresponding to the current oil saturation.

8. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 7, characterized in that, The polymer system parameters include infinite shear viscosity, characteristic shear rate, and power-law exponent. The formula for calculating the required zero-shear viscosity is as follows: ， In the formula, μ eff,req The minimum effective viscosity μ ∞ For the infinite shear viscosity, Let p be the characteristic shear rate, and p be the power law exponent.

9. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 1, characterized in that, The engineering operation parameters include borehole shear viscosity retention rate; The formula for calculating the zero-shear viscosity of the ground is: ， In the formula, μ0(C p,inj ) represents the bottom-hole zero-shear viscosity, η perf The shear viscosity retention rate of the borehole.

10. The method for determining polymer flooding injection concentration based on oil phase mobility control according to claim 1, characterized in that, The polymer system parameters include the viscosity-concentration standard curve or fitting formula of the polymer solution, the expression of which is: ， In the formula, μ w The viscosity of the injected water is given by A1, A2, A3, and s, which are fitting coefficients. C is the viscosity of the injected water. sep Electrolyte concentration correction factor; In the step of calculating the minimum injection concentration at ground level by inversely determining the corresponding polymer concentration based on the ground zero-shear viscosity and the polymer system parameters, let the above formula... The minimum polymer concentration C that satisfies the viscosity requirement at zero shear viscosity of the ground surface is obtained by inverse equation solving. p This is the minimum injection concentration at ground level.

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