CN-117352072-B - Method and system for calculating molecular weight distribution of wide molecular polymer

CN117352072BCN 117352072 BCN117352072 BCN 117352072BCN-117352072-B

Abstract

A method for calculating a broad molecular weight distribution of a polymer includes obtaining a pore radius distribution of a target reservoir and calculating a median pore radius, determining an average molecular weight of the polymer to be evaluated based on the median pore radius, determining at least one first function for estimating the molecular weight distribution of the polymer 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 a sweep factor and a polymer recovery improvement amplitude of the first function based on the comparison result, and determining an optimal polymer molecular weight distribution based on the polymer recovery improvement amplitude of the first function. The invention realizes the purpose of improving the recovery ratio of crude oil to the maximum extent.

Inventors

JI BINGYU
YANG SHU
HE YINGFU
XU GUANLI
LIAO HAIYING
ZHOU YUANLONG
FANG XIN
MA TAO

Assignees

中国石油化工股份有限公司
中国石油化工股份有限公司石油勘探开发研究院

Dates

Publication Date: 20260512
Application Date: 20220627

Claims (8)

1. A method for calculating a broad molecular polymer molecular weight distribution, comprising: acquiring pore radius distribution of a target reservoir and calculating a pore radius median value; determining the average molecular weight of the polymer to be evaluated according to the median pore radius; Determining the type of a first function according to the median pore radius and the average molecular weight of the polymer, and setting different function parameters for the current function to form at least one first function for estimating the molecular weight distribution of the polymer; Comparing the polymer pore radius distribution function with the first function, so as to calculate the sweep coefficient of the first function and the polymer recovery ratio improvement amplitude according to the comparison result; Determining an optimal polymer molecular weight distribution based on the magnitude of the polymer recovery enhancement of the first function, wherein, In the step of comparing the polymer pore radius distribution function with the first function, comprising: the first step, setting the selection times and marking the real-time times as zero; a second step of randomly extracting a data point from the polymer pore radius distribution function and marking the data point as a first pore, and randomly extracting a data point from the first function and marking the data point as a first polymer molecular weight measurement point; third, determining a radius of gyration of the first polymer molecular weight measurement point, based on which, in combination with the first pores, a diagnosis is made as to whether a polymer having a currently selected molecular weight can pass through the selected pores; Fourth, repeating the second and third steps continuously, counting the number of times that the measuring point passes through the corresponding hole according to the diagnosis result corresponding to each selection until the real-time number of times is larger than the selection number of times, and entering a fifth step; And fifthly, calculating the sweep coefficient according to all statistical results.
2. The method of claim 1, wherein the type of the first function comprises an overall distribution function, a uniform distribution function, and a constant function.
3. The method according to claim 1, wherein, in the fourth step, When the current polymer molecular weight measurement point passes through the current first pore, calculating the viscosity parameter corresponding to the current first polymer molecular weight, and And adding one to the real-time times, and returning to the second step.
4. The method of claim 3, wherein the step of, Carrying out ratio operation on the counted measuring point passing times and the selected times to obtain polymer accessible pore proportion aiming at the currently estimated polymer molecular weight distribution data, thereby obtaining the sweep coefficient; and according to the viscosity parameters of each first polymer measuring point, combining the sweep coefficient, and calculating the recovery ratio improvement amplitude of the corresponding polymer which can enter the target reservoir under the condition of corresponding polymer molecular weight distribution data.
5. The method according to claim 1, wherein, in the fourth step, And when the current polymer molecular weight distribution measuring point cannot pass through the current first pore, adding one to the real-time number, and returning to the second step to reselect the first pore and the first polymer molecular weight measuring point which are different from the extracted data points.
6. The method according to any one of claims 1 to 5, wherein when there are a plurality of first functions, the recovery ratio improvement amplitude 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 ratio improvement amplitude is determined as the optimal polymer molecular weight distribution.
7. The method according to any one of claims 1 to 5, wherein in the step of determining the average molecular weight of the polymer to be evaluated based on the median pore radius, the method comprises: the average molecular weight of the polymer is determined according to the requirement that no oil layer blockage occurs when the ratio of the median pore radius to the mean square radius of gyration of the polymer molecules to be evaluated in the aqueous solution is greater than 5.
8. A system for calculating a broad molecular polymer molecular weight distribution, wherein the system is for performing the method of any one of claims 1-7, the system comprising: a reservoir characteristics generation module configured to obtain a pore radius distribution of a target reservoir and calculate a pore radius median; A polymer characterization module configured to determine an 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 a molecular weight distribution of the polymer 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 a sweep factor and a polymer recovery enhancement magnitude of the first function based on the comparison; a molecular weight distribution characterization preference module configured to determine an optimal polymer molecular weight distribution based on the magnitude of polymer recovery enhancement of the first function.

Description

Method and system for calculating molecular weight distribution of wide molecular polymer Technical Field The invention relates to the technical field of oilfield development, in particular to a method and a system for calculating molecular weight distribution of a wide molecular polymer. Background Chemical flooding is an important technical measure for improving the final recovery ratio of a water injection oil field, and is also one of the main succession technologies for secondary development of the old oil field. In recent years, with the successful application of chemical flooding technology in Daqing, liaohe, victory and other oil fields, chemical flooding theory and technology are becoming deeper and more complete, and the implementation blocks are gradually changed from common high-permeability, low-temperature and thin-oil reservoirs with better reservoir physical properties to reservoirs with high temperature, low permeability, strong heterogeneity and complex oil properties. The chemical technology provides important technical guarantee for stable yield and benefit development of crude oil in China. The adaptability of the chemical flooding system and different types of oil reservoirs is the key of the successful application of chemical flooding, and particularly, the compatibility relation between the molecular size/molecular weight of the polymer and the pore throat size of the rock not only determines whether the polymer can be successfully injected, but also relates to the oil displacement efficiency of the polymer. If a learner indicates that an oil layer with the permeability below 300mD is suitable for medium-relative molecular weight and common strand polymer mass concentration injection, and an oil layer with the permeability above 900mD is suitable for high-relative molecular weight and high polymer mass concentration injection. In addition, the scholars point out that oil layer blockage does not occur when the mean square radius of gyration of the core pore radius and the polymer molecules in the aqueous solution is larger than 5, and the molecular weight can be optimized according to the method. But the pore radius of the reservoir is non-uniform and distributed according to a certain rule. The polymer injected has too large molecules, and some pores are not accessible, which affects the sweep efficiency and the final recovery ratio, while if the molecules are too small, the viscosity is lower and the fluidity ratio is not controlled in place, which affects the polymer flooding effect. Meanwhile, it has been pointed out by the scholars that the high molecular polymer is a mixture composed of homologous molecules with different sizes, has polydisperse property, and the size of the proportion of the molecules with different molecular weights is described by the molecular weight distribution. The broad molecular polymer is prepared by mixing polymers with different molecular weights according to a certain proportion, so as to increase the distribution width of the molecular weight. Mine tests also show that better oil displacement effect can be obtained by adopting the broad molecular polymer. The prior art has little research on a method for determining the molecular weight distribution of a wide molecular polymer, the most main method is still to determine the molecular weight distribution according to the conditions that the ratio of the median value of the pore radius of a core to the mean square radius of a polymer molecule is larger than 5 and the like, and the method is combined with an indoor physical simulation method, and the method needs to carry out a large amount of indoor physical simulation evaluation, has huge workload, can only carry out experiments on a partially compounded polymer system, and is difficult to obtain the optimal wide molecular polymer. This is also one of the reasons that wide molecular weight polymers are limited in their popularization and application. Accordingly, there is a need in the art to provide a molecular weight distribution characterization scheme for broad molecular weight polymers that addresses one or more of the above-described problems. Disclosure of Invention In order to solve the technical problems, the embodiment of the invention provides a method for calculating a wide molecular polymer molecular weight distribution, which comprises the steps of obtaining a pore radius distribution of a target reservoir and calculating a pore radius median value, determining the average molecular weight of a polymer to be evaluated according to the pore radius median value, determining at least one first function for estimating the molecular weight distribution of the polymer according to the pore radius median value and the average molecular weight of the polymer, comparing the polymer pore radius distribution function with the first function, calculating the sweep coefficient and the polymer recovery ratio improvement amplitude of the first functi