A method and system for calculating the molecular weight distribution of a broad molecular polymer

Abstract

The application discloses a method for calculating wide molecular polymer molecular weight distribution, comprising the following steps: obtaining the pore radius distribution of a target reservoir and calculating the pore radius median; determining the average molecular weight of a polymer to be evaluated according to the pore radius median; determining at least one first function for estimating the polymer molecular weight distribution according to the pore radius median and the average molecular weight of the polymer, and comparing the polymer pore radius distribution function with the first function, so as to calculate the sweep efficiency and the polymer recovery improvement range of the first function according to the comparison result; and determining the optimal polymer molecular weight distribution according to the polymer recovery improvement range of the first function. The application realizes the purpose of improving the crude oil recovery with the maximum range.

Description

Technical Field

[0001] This invention relates to the field of oilfield development technology, and in particular to a method and system for calculating the molecular weight distribution of broad molecular weight polymers. Background Technology

[0002] Chemical flooding is a crucial technology for enhancing ultimate recovery in water-injected oilfields and a major replacement technology for the secondary development of older oilfields. In recent years, with the successful application of chemical flooding technology in oilfields such as Daqing, Liaohe, and Shengli, the theory and technology of chemical flooding have become increasingly sophisticated and refined. The implementation blocks have gradually shifted from ordinary high-permeability, low-temperature, and light-oil reservoirs with relatively good reservoir properties to reservoirs with high temperature, low permeability, strong heterogeneity, and complex oil properties. Overall, chemical flooding technology provides an important technical guarantee for the stable production and efficient development of crude oil in my country.

[0003] The adaptability of chemical flooding systems to different types of reservoirs is crucial for the successful application of chemical flooding. In particular, the compatibility between polymer molecular size / molecular weight and rock pore throat size not only determines the smooth injection of polymers but also their oil displacement efficiency. For example, some scholars have pointed out that reservoirs with permeability below 300 mD are suitable for injection of medium relative molecular weight polymers with ordinary polymer mass concentrations; reservoirs with permeability above 900 mD are suitable for injection of high relative molecular weight polymers with high polymer mass concentrations. Furthermore, other scholars have indicated that when the ratio of the median core pore radius to the mean square radius of gyration of polymer molecules in aqueous solution is greater than 5, reservoir blockage will not occur, and this can be used for molecular weight optimization.

[0004] However, reservoir pore radii are non-uniform and distributed according to certain rules. If the injected polymer molecules are too large, a considerable portion of the pores will be inaccessible, affecting the sweep efficiency and final recovery rate; conversely, if the molecules are too small, the viscosity will be lower at the same concentration, and the mobility ratio will not be properly controlled, which will also affect the polymer flooding effect.

[0005] Meanwhile, some scholars have pointed out that polymers are mixtures composed of homologous molecules of different sizes, exhibiting polydispersity characteristics. The proportion of molecules with different molecular weights is described by molecular weight distribution. Broad molecular weight polymers are created by mixing polymers of different molecular weights in a certain proportion, thereby increasing the width of the molecular weight distribution. Field trials have also shown that using broad molecular weight polymers can achieve better oil displacement effects.

[0006] There is limited research on methods for determining the molecular weight distribution of broad molecular weight polymers. The most common method still relies on conditions such as a ratio of permeability or median core pore radius to the polymer's mean square radius of gyration greater than 5, combined with indoor physical simulations. This method requires extensive indoor physical simulation evaluation, resulting in a huge workload, and can only be applied to some blended polymer systems, making it difficult to obtain the optimal broad molecular weight polymer. This is one of the reasons for the limited widespread application of broad molecular weight polymers.

[0007] Therefore, the existing technology needs to provide a scheme for calculating the molecular weight distribution characteristics of wide molecular weight polymers in order to solve one or more of the above-mentioned technical problems. Summary of the Invention

[0008] To address the aforementioned technical problems, embodiments of the present invention provide a method for calculating the molecular weight distribution of a wide-molecule polymer, comprising: obtaining the pore radius distribution of a target reservoir and calculating the median pore radius; determining the average molecular weight of the polymer to be evaluated based on the median pore radius; determining at least one first function for estimating the polymer molecular weight distribution based on the median pore radius and the average molecular weight of the polymer, and comparing the polymer pore radius distribution function with the first function, thereby calculating the sweep efficiency coefficient and the polymer recovery rate improvement based on the comparison result; and determining the optimal polymer molecular weight distribution based on the polymer recovery rate improvement based on the first function.

[0009] Preferably, the type of the first function is determined based on the median pore radius and the average molecular weight of the polymer, and different function parameters are set for the current function to form at least one first function.

[0010] Preferably, the type of the first function includes a global distribution function, a uniform distribution function, and a constant function.

[0011] Preferably, the step of comparing the polymer pore radius distribution function with the first function includes: First, setting the number of selections and marking the real-time number as zero; Second, randomly selecting a data point from the polymer pore radius distribution function and recording it as the first pore, and randomly selecting a data point from the first function and recording it as the first polymer molecular weight measurement point; Third, determining the gyrometry radius of the first polymer molecular weight measurement point, and based on this, combined with the first pore, diagnosing whether a polymer with the currently selected molecular weight can pass through the selected pore; Fourth, continuously repeating the second and third steps above, and counting the number of times the measurement point passes through the corresponding pore according to the diagnostic result corresponding to each selection, until the real-time number is greater than the number of selections, thus proceeding to the fifth step; Fifth, calculating the sweep efficiency based on all statistical results.

[0012] Preferably, in the fourth step, when the current polymer molecular weight measurement point can pass through the current first pore, the viscosity parameter corresponding to the current first polymer molecular weight is calculated; and the real-time count is incremented by one before returning to the second step.

[0013] Preferably, the ratio of the number of times the measured points are passed to the number of times they are selected is calculated to obtain the proportion of accessible pores of the polymer for the currently estimated polymer molecular weight distribution data, thereby obtaining the sweep efficiency coefficient; based on the viscosity parameter of each first polymer measured point and in combination with the sweep efficiency coefficient, the recovery rate improvement of the corresponding polymer that can enter the target reservoir under the corresponding polymer molecular weight distribution data is calculated.

[0014] Preferably, in the fourth step, when the current polymer molecular weight distribution measurement point cannot pass through the current first pore, the real-time count is incremented by one and the process returns to the second step to reselect the first pore and the first polymer molecular weight measurement point that are different from the data points that have been extracted.

[0015] Preferably, when there are multiple first functions, the recovery rate improvement of the polymer molecular weight distribution data corresponding to each first function is calculated, and the polymer molecular weight distribution data that matches the maximum recovery rate improvement is determined as the optimal polymer molecular weight distribution.

[0016] Preferably, the step of determining the average molecular weight of the polymer to be evaluated based on the median pore radius includes: determining the average molecular weight of the polymer based on the requirement that oil layer blockage will not occur when the ratio of the median pore radius to the mean square radius of gyration of the polymer molecule in the aqueous solution is greater than 5.

[0017] On the other hand, a system for calculating the molecular weight distribution of a wide-molecule polymer is provided. The system includes: a reservoir feature generation module configured to acquire the pore radius distribution of a target reservoir and calculate the median pore radius; a polymer feature generation module configured to determine the average molecular weight of the polymer to be evaluated based on the median pore radius; a feature comparison module configured to determine at least one first function for estimating the polymer molecular weight distribution based on the median pore radius and the average polymer molecular weight, and to compare the polymer pore radius distribution function with the first function, thereby calculating the sweep efficiency coefficient and the polymer recovery enhancement rate based on the comparison result; and a molecular weight distribution feature optimization module configured to determine the optimal polymer molecular weight distribution based on the polymer recovery enhancement rate of the first function.

[0018] Compared with the prior art, one or more embodiments of the above solutions may have the following advantages or beneficial effects:

[0019] This invention proposes a method and system for calculating the molecular weight distribution of broad-molecule polymers. The method and system first determine the average molecular weight of the polymer suitable for the work area based on the median pore radius of the actual reservoir. Second, based on the average molecular weight of the polymer and the reservoir pore radius distribution function, a polymer molecular weight distribution function is generated. Then, considering the polymer bridging effect, the proportion of polymer-accessible pore volume and the proportion of inaccessible pore volume are calculated, thereby obtaining the polymer flooding recovery rate under this distribution function. Finally, by comparing the enhanced oil recovery values ​​of different polymer distribution functions, the polymer molecular weight distribution that maximizes the enhanced oil recovery rate is determined. This invention mainly addresses the shortcomings of polymer molecular weight optimization in polymer flooding by utilizing the actual reservoir pore radius distribution function to obtain the optimal polymer molecular weight distribution that matches it. This reduces the workload of laboratory screening while maximizing the enhanced oil recovery rate and economic benefits of polymer flooding, thereby achieving the goal of maximizing crude oil recovery. Furthermore, starting from the actual pore distribution of the reservoir, it does not rely on laboratory experimental evaluation, reducing the experimental workload while maximizing the enhanced oil recovery rate of polymers, providing excellent guidance for actual oilfields.

[0020] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0022] Figure 1 This is a step diagram of a method for calculating the molecular weight distribution of a broad molecular weight polymer according to an embodiment of this application.

[0023] Figure 2 This is a schematic diagram of the specific process in the method for calculating the molecular weight distribution of wide molecular polymers according to an embodiment of this application.

[0024] Figure 3 This is an example diagram illustrating the actual pore radius distribution characteristics in a method for calculating the molecular weight distribution of wide-molecule polymers according to an embodiment of this application.

[0025] Figure 4 This is an example diagram comparing the effective viscosity under different polymer molecular weight distribution conditions in the method for calculating the molecular weight distribution of broad molecular weight polymers according to embodiments of this application.

[0026] Figure 5This is an example diagram comparing the sweep efficiency under different polymer molecular weight distribution conditions in the method for calculating the molecular weight distribution of wide-molecule polymers according to embodiments of this application.

[0027] Figure 6 This is an example diagram showing the improvement in recovery rate under different polymer molecular weight distribution conditions in the method for calculating the molecular weight distribution of broad polymers according to embodiments of this application.

[0028] Figure 7 This is a block diagram of a system for calculating sand spreading rate according to an embodiment of this application. Detailed Implementation

[0029] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, so that the process of how the present invention uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that, as long as there is no conflict, the various embodiments and features in the various embodiments of the present invention can be combined with each other, and the resulting technical solutions are all within the protection scope of the present invention.

[0030] Furthermore, the steps illustrated in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Also, although a logical order is shown in the flowcharts, in some cases the steps shown or described may be performed in a different order than that shown here.

[0031] Chemical flooding is a crucial technology for enhancing ultimate recovery in water-injected oilfields and a major replacement technology for the secondary development of older oilfields. In recent years, with the successful application of chemical flooding technology in oilfields such as Daqing, Liaohe, and Shengli, the theory and technology of chemical flooding have become increasingly sophisticated and refined. The implementation blocks have gradually shifted from ordinary high-permeability, low-temperature, and light-oil reservoirs with relatively good reservoir properties to reservoirs with high temperature, low permeability, strong heterogeneity, and complex oil properties. Overall, chemical flooding technology provides an important technical guarantee for the stable production and efficient development of crude oil in my country.

[0032] The adaptability of chemical flooding systems to different types of reservoirs is crucial for the successful application of chemical flooding. In particular, the compatibility between polymer molecular size / molecular weight and rock pore throat size not only determines the smooth injection of polymers but also their oil displacement efficiency. For example, some scholars have pointed out that reservoirs with permeability below 300 mD are suitable for injection of medium relative molecular weight polymers with ordinary polymer mass concentrations; reservoirs with permeability above 900 mD are suitable for injection of high relative molecular weight polymers with high polymer mass concentrations. Furthermore, other scholars have indicated that when the ratio of the median core pore radius to the mean square radius of gyration of polymer molecules in aqueous solution is greater than 5, reservoir blockage will not occur, and this can be used for molecular weight optimization.

[0033] However, reservoir pore radii are non-uniform and distributed according to certain rules. If the injected polymer molecules are too large, a considerable portion of the pores will be inaccessible, affecting the sweep efficiency and final recovery rate; conversely, if the molecules are too small, the viscosity will be lower at the same concentration, and the mobility ratio will not be properly controlled, which will also affect the polymer flooding effect.

[0034] Meanwhile, some scholars have pointed out that polymers are mixtures composed of homologous molecules of different sizes, exhibiting polydispersity characteristics. The proportion of molecules with different molecular weights is described by molecular weight distribution. Broad molecular weight polymers are created by mixing polymers of different molecular weights in a certain proportion, thereby increasing the width of the molecular weight distribution. Field trials have also shown that using broad molecular weight polymers can achieve better oil displacement effects.

[0035] There is limited research on methods for determining the molecular weight distribution of broad molecular weight polymers. The most common method still relies on conditions such as a ratio of permeability or median core pore radius to the polymer's mean square radius of gyration greater than 5, combined with indoor physical simulations. This method requires extensive indoor physical simulation evaluation, resulting in a huge workload, and can only be applied to some blended polymer systems, making it difficult to obtain the optimal broad molecular weight polymer. This is one of the reasons for the limited widespread application of broad molecular weight polymers.

[0036] Therefore, to address one or more of the aforementioned technical problems, this application of the present invention proposes a method and system for calculating the molecular weight distribution of broad molecular weight polymers. This method and system utilize stochastic simulation to calculate the proportion of pore volume into which polymers can enter by comparing the actual reservoir pore radius distribution function with the assumed polymer molecular weight distribution function, thereby obtaining the polymer flooding recovery rate and ultimately achieving the polymer molecular weight distribution that maximizes the recovery rate. Compared to single-molecular-weight polymer flooding, the optimized broad molecular weight polymer flooding of this invention provides a greater increase in recovery rate, and compared to conventional polymer molecular weight optimization methods, it requires less workload and is less costly.

[0037] Figure 1 This is a step diagram illustrating a method for calculating the molecular weight distribution of a broad-molecule polymer according to an embodiment of this application. Refer to the following... Figure 1 The steps of the method for calculating the molecular weight distribution of wide molecular weight polymers (hereinafter referred to as the "molecular weight distribution calculation method") described in the embodiments of the present invention will be explained.

[0038] like Figure 1As shown, step S110 obtains the pore radius distribution of the target reservoir and calculates the median pore radius. The target reservoir mentioned in step S11 refers to the reservoir oilfield where the wide molecular weight polymer to be studied is intended for application. Then, step S120 determines the average molecular weight of the polymer to be evaluated that matches the current target reservoir based on the median pore radius obtained in step S110. Next, step S130 determines at least one first function for estimating the polymer molecular weight distribution based on the median pore radius of the target reservoir and the average molecular weight of the polymer obtained from steps S110 and S120, respectively, and compares the polymer pore radius distribution function with the first function to calculate the sweep efficiency and polymer recovery enhancement rate matched with the corresponding first function based on the comparison results. Finally, step S140 determines the optimal (polymer) molecular weight distribution of the wide molecular weight polymer to be evaluated based on the polymer flooding recovery rate of the (corresponding) first function.

[0039] Thus, this invention, taking into account the characteristics of the pore radius distribution of actual oil reservoirs, obtains a polymer molecular weight distribution that is compatible with the actual oil reservoir, thereby achieving the goal of maximizing the recovery rate of crude oil.

[0040] Figure 2 This is a schematic flowchart illustrating the method for calculating the molecular weight distribution of broad-molecule polymers according to an embodiment of this application. See below for reference. Figure 2 The specific process of the molecular weight distribution calculation method described in the embodiments of the present invention will be explained.

[0041] like Figure 2 As shown, in step S110, the actual pore radius distribution characteristics of the oilfield area under study are first obtained using mercury intrusion porosimetry or other methods. This process converts the actual pore radius distribution characteristics into a pore radius distribution function specific to the target reservoir. In this embodiment of the invention, fitting methods or other methods can be used to convert the actual pore radius distribution characteristics into the corresponding pore radius distribution function.

[0042] Figure 3 This is an example diagram illustrating the actual pore radius distribution characteristics in a method for calculating the molecular weight distribution of wide-molecule polymers according to an embodiment of this application. Figure 3 This example illustrates the actual pore radius distribution characteristics, where the horizontal axis represents pore size data and the vertical axis represents the distribution probability.

[0043] In addition, step S110 will calculate the median pore radius of the current target reservoir based on the currently obtained actual pore radius distribution data.

[0044] Then, after determining the median pore radius, the process proceeds to step S120. In step S120, the average molecular weight of the polymer under study is determined based on the requirement that oil layer blockage will not occur when the ratio of the currently calculated median pore radius to the mean square radius of gyration of the polymer molecule to be evaluated in the aqueous solution is greater than 5.

[0045] Furthermore, based on the requirement that oil reservoir blockage will not occur when the ratio of the currently calculated median pore radius to the mean square radius of gyration of the polymer molecules under evaluation in aqueous solution is greater than 5, and considering the relationship between the molecular weight distribution of the polymer under study and its mean square radius of gyration, the average molecular weight of the polymer suitable for the oilfield area under study is determined. Generally, the radius of gyration of a polymer is related to its molecular weight distribution; under a certain concentration, the larger the molecular weight, the larger the radius of gyration. The radius of gyration of the corresponding polymer can be obtained using the formula for calculating the radius of gyration. Alternatively, the radius of gyration of the polymer under evaluation can also be directly determined by laboratory experiments, such as using light scattering or ultracentrifugation.

[0046] Next, proceed to step S130. In step S130, firstly, based on the median pore radius calculated in step S110 and the average molecular weight of the polymer obtained in step S120, at least one first function for estimating the molecular weight distribution of the polymer is determined.

[0047] In the process of generating one or more first functions, step S130 first determines the type of the current first function based on the median pore radius and the average molecular weight of the polymer, and then sets different function parameters for the currently set first function, thereby forming one or more first functions. Multiple first functions are formed by different function types and by configuring different function parameters for each set function type.

[0048] Furthermore, in this embodiment of the invention, the first function can be configured with the following function types: normal distribution function, uniform distribution function, and constant function.

[0049] After generating one or more first functions, step S130 compares the target reservoir pore radius distribution function formed in step S110 with the one or more first functions generated above, and calculates the sweep efficiency coefficient and the corresponding polymer recovery rate improvement for each first function based on the comparison results.

[0050] In practical applications, if a first function is generated, the target reservoir pore radius distribution function is directly compared with the first function, and the sweep efficiency and polymer recovery improvement of the current first function are calculated based on the comparison results. Alternatively, if multiple first functions are generated, the target reservoir pore radius distribution function is compared with each of the individual first functions, and the sweep efficiency and polymer recovery improvement of the corresponding first function are calculated based on the comparison results. In this embodiment of the invention, regardless of the number of first functions generated, the comparison process between the pore radius distribution function and each first function is similar. Therefore, this invention only uses the comparison process between the pore radius distribution function and a single first function as an example to illustrate this process.

[0051] refer to Figure 2 The first step is to set the selection (total) number of times, and mark the real-time number of times (NT, the sequence number of the total number of times) as zero, and mark the pass number parameter (NS) as zero.

[0052] The second step is to randomly select a data point from the current polymer pore radius distribution function. The currently selected (extracted) pore radius data point is recorded as the first pore; and a data point y is randomly selected from the current first function, and the currently selected (extracted) polymer molecular weight data point is recorded as the first polymer molecular weight measurement point. After completing the random selection of the data point, proceed to the third step.

[0053] The third step involves determining the radius of gyration corresponding to the molecular weight of the polymer under study, based on the relationship between the molecular weight and the mean square radius of gyration of the polymer at the first molecular weight measurement point. Then, based on the radius of gyration of the first polymer measurement point obtained at the moment, and in conjunction with the first pore size mentioned above, a diagnosis is made as to whether a polymer with the currently selected molecular weight can pass through the selected pore size.

[0054] Specifically, if the ratio of the porosity value corresponding to the first pore point to the radius of gyration corresponding to the first polymer measuring point is greater than or equal to 5, that is... This determines that a polymer with the current molecular weight can pass through the currently selected first pore (point). Additionally, if the ratio of the pore value corresponding to the first pore point to the radius of gyration corresponding to the first polymer measurement point is less than 5, i.e. If this is determined, the polymer with the current molecular weight cannot pass through the currently selected first pore (point). Therefore, after completing the function comparison task performed for the current real-time count, the process proceeds to the fourth step.

[0055] The fourth step is to continuously repeat the second and third steps above, and count the number of times the selected polymer molecular weight measurement point can pass through the corresponding pore based on the diagnostic results of each selection (extraction) (i.e., count the number of times it passes through the parameter), until the real-time number is greater than the total number of selections, then proceed to the fifth step.

[0056] In the fourth step, when the current polymer molecular weight measurement point can pass through the current first pore, the passage count parameter is incremented by one. Simultaneously, the viscosity parameter corresponding to the current first polymer molecular weight is calculated. After completing the viscosity parameter calculation, the current real-time count is incremented by one, and the process returns to the second step. This allows for the selection of a new first pore point different from the previously extracted data points, and a new first polymer molecular weight measurement point different from the previously extracted data points is also selected. When calculating the viscosity of the current first polymer molecular weight measurement point, the relationship between the molecular weight distribution and viscosity of the polymer under study is used to determine the viscosity parameter corresponding to the current first polymer molecular weight data.

[0057] Furthermore, the viscosity of a polymer is closely related to its molecular weight. Under certain concentration conditions, the larger the molecular weight of the polymer, the greater its viscosity. The viscosity calculation formula is as follows: .in, The value represents viscosity, and M represents the molecular weight of the first polymer.

[0058] Figure 4 This is an example diagram comparing the effective viscosity under different polymer molecular weight distribution conditions in the method for calculating the molecular weight distribution of broad molecular weight polymers according to embodiments of this application. Figure 4 The diagram shows the effective viscosity distribution of polymers under different polymer molecular weight distribution conditions formed by different polymer molecular weight distribution function types and different function parameters.

[0059] In addition, when the current polymer molecular weight distribution measurement point cannot pass through the current first pore, the current real-time count is incremented by one and the process returns to the second step, thereby reselecting a first pore point different from the previously extracted data point, and at the same time reselecting a first polymer molecular weight measurement point different from the previously extracted data point.

[0060] The fifth step involves calculating the sweep efficiency and polymer recovery rate improvement corresponding to the current first function based on all statistical results. In this fifth step, the sweep efficiency and polymer recovery rate improvement corresponding to the current first function are calculated based on the diagnostic results obtained from each comparison task.

[0061] Specifically, the ratio of the statistically recorded number of times the measurement points were passed (i.e., the NS value obtained from the comparison of all measurement points) to the total number of selections is calculated to obtain the proportion of accessible pores of the polymer for the currently estimated polymer molecular weight distribution data (the first function used to estimate the current polymer molecular weight distribution characteristics). The corresponding proportion of inaccessible pores is then calculated, and the current polymer accessible proportion is used as the corresponding sweep efficiency. The polymer accessible and inaccessible pore proportions corresponding to the current first function are calculated using the following expressions:

[0062] (1)

[0063] (2)

[0064] in, This represents the number of successful comparisons after all (number of) measurement points have been compared. Indicates the total number of selections. Indicates the proportion of polymer-accessible pores. Indicates the proportion of inaccessible pores.

[0065] Figure 5 This is an example diagram comparing the sweep efficiency under different polymer molecular weight distribution conditions in the method for calculating the molecular weight distribution of wide-molecule polymers according to embodiments of this application. Figure 5 The distribution of sweep efficiency coefficients is shown under different polymer molecular weight distribution conditions formed by different polymer molecular weight distribution function types and different function parameters.

[0066] Then, based on the viscosity parameters of each first polymer measurement point and combined with the aforementioned sweep efficiency coefficient, the recovery rate improvement is calculated based on the polymer molecular weight distribution data conditions, representing the potential for the polymer to enter the target reservoir's sweepable range (pore volume). This is equivalent to calculating the recovery rate improvement corresponding to the polymer molecular weight distribution data configured in the current first function. The current recovery rate improvement is calculated using the following expression:

[0067] (3)

[0068] (4)

[0069] in, Viscosity corresponding to the current molecular weight data of the first polymer This represents the recovery rate of the entire pore volume (the working space of the target reservoir). This indicates the extent to which the polymer can enter the pore volume within the reachable range, thus increasing the oil recovery rate (polymer displacement efficiency).

[0070] Figure 6This is an example diagram showing the improvement in recovery rate under different polymer molecular weight distribution conditions in the method for calculating the molecular weight distribution of broad polymers according to embodiments of this application. Figure 6 The diagram shows the distribution of recovery rate improvement under different polymer molecular weight distribution conditions formed by different polymer molecular weight distribution function types and different function parameters.

[0071] Thus, after obtaining the recovery rate improvement data corresponding to the polymer molecular weight distribution data conditions that match the current first function, the process proceeds to step S140.

[0072] Step S140 determines the optimal polymer molecular weight distribution based on the polymer recovery rate improvement magnitude corresponding to several first functions. In step S140, when multiple first functions exist, the recovery rate improvement magnitude of the polymer molecular weight distribution data corresponding to each first function is calculated, and the polymer molecular weight distribution data matching the maximum recovery rate improvement magnitude is determined as the current optimal polymer molecular weight distribution. Alternatively, when generating a first function, the recovery rate improvement magnitude of the polymer molecular weight distribution data corresponding to the current first function is directly used as the current optimal polymer molecular weight distribution.

[0073] The polymer molecular weight distribution calculation method described in this invention is applied to the enhanced oil recovery stage of an oil reservoir block in a certain region. Taking Block B of Oilfield A as an example, the reservoir permeability of this block is 800 mD, and the water cut of waterflooding has reached 90%. Polymer flooding is planned to further enhance the oil recovery, and therefore, a wide molecular weight polymer selection process is conducted:

[0074] (1) Determine the pore diameter distribution in the work area using mercury intrusion porosimetry (see Figure 1 ), and the median pore radius was calculated to be 80. m;

[0075] (2) Determine the average molecular weight of the polymer:

[0076] Based on the requirement that oil layer blockage will not occur when the ratio of the median pore radius to the mean square gyroscope radius of polymer molecules in aqueous solution is greater than 5, and the relationship between polymer molecular weight and mean square gyroscope radius, the average molecular weight of the polymer suitable for this work area is determined to be 10 million.

[0077] (3) Assume that the molecular weight distribution of the polymer is normally distributed, and set NT=0 and NS=0;

[0078] (4) Randomly select a value from the pore diameter distribution function. 120 The number of selections is NT←NT+1; a value of 8 million is randomly selected from the polymer molecular weight distribution function.

[0079] (5) Calculate the radius of gyration of the selected molecular weight 800 based on the relationship between the polymer molecular weight and its radius of gyration. ;

[0080] (6) Due to It is assumed that the polymer with this molecular weight can pass through the pores selected in step (4), at which point NS←NS+1, and the viscosity of this molecular weight is obtained according to the relationship between polymer molecular weight and viscosity, see [reference]. Figure 2 ;

[0081] (7) Proceed to step (4) and repeat steps (4)-(6) until the maximum number of calculations is reached (generally set to 1000 times); if the calculated polymer gyroscope radius is greater than one-fifth of the pore radius, step (6) is not performed and step (4) is directly entered.

[0082] (8) Calculate the accessible porosity of the polymer, i.e., calculate the sweep efficiency of the polymer, see [reference needed]. Figure 3 .

[0083] (9) Calculate the enhanced oil recovery margin of broad molecular weight polymers under this distribution condition, see [reference needed]. Figure 4 .

[0084] On the other hand, based on the above-mentioned polymer molecular weight distribution calculation method, this embodiment of the invention also provides a system for calculating the molecular weight distribution of wide molecular polymers (hereinafter referred to as "molecular weight distribution calculation system"). Figure 7 This is a block diagram of a system for calculating sand-spreading rate according to an embodiment of this application. Figure 7 As shown, the polymer molecular weight distribution calculation system of this invention includes: a reservoir feature generation module 71, a polymer feature generation module 72, a feature comparison module 73, and a molecular weight distribution feature optimization module 74.

[0085] Specifically, the reservoir feature generation module 71, according to the method embodiment of step S110 above, is configured to obtain the pore radius distribution of the target reservoir and calculate the median pore radius; the polymer feature generation module 72, according to the method embodiment of step S120 above, is configured to determine the average molecular weight of the polymer to be evaluated based on the median pore radius; the feature comparison module 73, according to the method embodiment of step S130 above, is configured to determine at least one first function for estimating the polymer molecular weight distribution based on the median pore radius and the average molecular weight of the polymer, and compare the polymer pore radius distribution function with at least one first function, thereby calculating the sweep efficiency and polymer recovery rate improvement of the first function based on the comparison result; the molecular weight distribution feature optimization module 74, according to the method embodiment of step S140 above, is configured to determine the optimal polymer molecular weight distribution based on the polymer recovery rate improvement of the current first function.

[0086] This invention discloses a method and system for calculating the molecular weight distribution of broad-molecule polymers. The method and system first determine the average molecular weight of the polymer suitable for the work area based on the median pore radius of the actual reservoir. Second, based on the average molecular weight of the polymer and the reservoir pore radius distribution function, a polymer molecular weight distribution function is generated. Then, considering the polymer bridging effect, the proportion of polymer-accessible pore volume and the proportion of inaccessible pore volume are calculated, thereby obtaining the polymer flooding recovery rate under this distribution function. Finally, by comparing the enhanced oil recovery values ​​of different polymer distribution functions, the polymer molecular weight distribution that maximizes the enhanced oil recovery rate is determined. This invention mainly addresses the shortcomings of polymer molecular weight optimization in polymer flooding by utilizing the actual reservoir pore radius distribution function to obtain the optimal polymer molecular weight distribution that matches it. This reduces the workload of laboratory screening while maximizing the enhanced oil recovery rate and economic benefits of polymer flooding, thereby achieving the goal of maximizing crude oil recovery. Furthermore, starting from the actual pore distribution of the reservoir, it does not rely on laboratory experimental evaluation, reducing the experimental workload while maximizing the enhanced oil recovery rate of polymers, providing excellent guidance for actual oilfields.

[0087] The above description is merely a preferred 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.

[0088] It should be understood that the embodiments disclosed herein are not limited to the specific structures, processing steps, or materials disclosed herein, but should be extended to equivalent substitutions of these features as understood by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0089] The phrase "an embodiment" or "an embodiment" used in this specification means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Therefore, the phrase "an embodiment" or "an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0090] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection of this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for calculating the molecular weight distribution of broad molecular weight polymers, characterized in that, include: Obtain the pore radius distribution of the target reservoir and calculate the median pore radius; The average molecular weight of the polymer to be evaluated is determined based on the median pore radius. Based on the median pore radius and the average molecular weight of the polymer, the type of the first function is determined, and different function parameters are set for the current function to form at least one first function for estimating the molecular weight distribution of the polymer. The polymer pore radius distribution function is compared with the first function, and the sweep efficiency and polymer recovery rate improvement are calculated based on the comparison results. Based on the increase in polymer recovery rate according to the first function, the optimal polymer molecular weight distribution is determined, wherein... The step of comparing the polymer pore radius distribution function with the first function includes: The first step is to set the number of selections and mark the real-time count as zero; The second step is to randomly select a data point from the polymer pore radius distribution function and record it as the first pore, and randomly select a data point from the first function and record it as the first polymer molecular weight measurement point. The third step is to determine the radius of gyration of the first polymer molecular weight measurement point. Based on this, and in conjunction with the first pore, a diagnosis is made as to whether a polymer with the currently selected molecular weight can pass through the selected pore. The fourth step is to continuously repeat the second and third steps above, and count the number of times the measuring point passes through the corresponding aperture based on the diagnostic result of each selection, until the real-time count is greater than the number of selections, and then proceed to the fifth step. The fifth step is to calculate the ripple coefficient based on all statistical results.

2. The method according to claim 1, characterized in that, The first function can be of the following types: global distribution function, uniform distribution function, and constant function.

3. The method according to claim 1, characterized in that, In the fourth step, Calculate the viscosity parameter corresponding to the current polymer molecular weight when the current polymer molecular weight measurement point can pass through the current first pore; and Increment the real-time count by one and return to the second step.

4. The method according to claim 3, characterized in that, The ratio of the number of times the measured points were passed to the number of times they were selected was calculated to obtain the proportion of accessible pores of the polymer for the currently estimated polymer molecular weight distribution data, thereby obtaining the sweep efficiency. Based on the viscosity parameters of each first polymer measuring point and the sweep efficiency, the recovery rate improvement of the corresponding polymer that can enter the target reservoir under the corresponding polymer molecular weight distribution data is calculated.

5. The method according to claim 1, characterized in that, In the fourth step, If the current polymer molecular weight distribution measurement point cannot pass through the current first pore, the real-time count is incremented by one and the process returns to the second step to reselect the first pore and the first polymer molecular weight measurement point that are different from the data points that have been extracted.

6. The method according to any one of claims 1 to 5, characterized in that, When multiple first functions exist, the recovery rate improvement of the polymer molecular weight distribution data corresponding to each first function is calculated, and the polymer molecular weight distribution data that matches the maximum recovery rate improvement is determined as the optimal polymer molecular weight distribution.

7. The method according to any one of claims 1 to 5, characterized in that, The step of determining the average molecular weight of the polymer to be evaluated based on the median pore radius includes: The average molecular weight of the polymer is determined based on the requirement that no oil layer blockage will occur when the ratio of the median pore radius to the mean square gyroscope radius of the polymer molecule being evaluated in aqueous solution is greater than 5.

8. A system for calculating the molecular weight distribution of broad molecular weight polymers, characterized in that, The system is used to perform the method as described in any one of claims 1-7, the system comprising: A reservoir feature generation module is configured to obtain the pore radius distribution of the target reservoir and calculate the median pore radius. A polymer feature generation module is configured to determine the average molecular weight of the polymer to be evaluated based on the median pore radius. The feature comparison module is configured to determine at least one first function for estimating the polymer molecular weight distribution based on the median pore radius and the average molecular weight of the polymer, and compare the polymer pore radius distribution function with the first function, thereby calculating the sweep efficiency of the first function and the increase in polymer recovery rate based on the comparison result. The molecular weight distribution feature optimization module is configured to determine the optimal polymer molecular weight distribution based on the increase in polymer recovery rate of the first function.

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