A concentration optimization method for heterogeneous chemical flooding systems

Abstract

The present invention relates to the technical field of oilfield development, and in particular to a concentration optimization method applicable to heterogeneous chemical flooding systems. The method comprises the following steps: establishing a displacement agent-polymer composite system displacement phase / crude oil viscosity ratio-fluid flow diversion coefficient-concentration relationship chart; determining the optimal ratio of the displacement agent and its polymer according to target reservoir conditions, preparing displacement agent-polymer composite systems of different concentrations according to this ratio, and measuring the viscosity of each composite system; calculating the viscosity ratio of the displacement agent-polymer composite to crude oil of different concentrations; and obtaining the fluid flow diversion coefficient based on the obtained viscosity ratio and the established chart, while taking into account the viscosity ratio limit of the composite system, and determining the minimum use concentration of the displacement agent-polymer composite system. The method of the present invention can quickly and effectively achieve the optimization of the minimum concentration of the viscoelastic particle displacement agent and the polymer composite system.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield development, and in particular to a concentration optimization method applicable to a heterogeneous chemical flooding system. Background Art

[0002] Polymer flooding is an effective technology for enhancing oil recovery, but due to the severe heterogeneity of continental sedimentary reservoirs, a significant amount of remaining movable oil remains unused or poorly utilized after polymer flooding. Further significant increases in oil recovery using water flooding and single chemical flooding technologies are becoming increasingly difficult. Heterogeneous chemical flooding is a new chemical flooding system developed in recent years, offering enhanced sweep and displacement efficiency. It provides an effective approach for significantly increasing oil recovery in post-polymer flooding reservoirs and in reservoirs with high water content, high recovery rates, and strong heterogeneity. This has far-reaching strategic significance for maintaining stable production in mature oilfields.

[0003] The design of a heterogeneous chemical flooding system is the core and foundation of heterogeneous chemical flooding applications. The entanglement of viscoelastic particulate flooding agents with polymers can strengthen the network structure and improve the system's viscoelasticity, thereby further enhancing the heterogeneous chemical flooding system's ability to expand its sweep.

[0004] The applicant previously studied a method for optimizing the ratio of oil-displacing agents to polymers in heterogeneous chemical flooding systems (patent application number: CN201910812301.7). However, in the current optimization of heterogeneous chemical flooding formulations, there is a lack of effective and rapid methods for optimizing the concentration of viscoelastic particle-polymer composite systems. Therefore, it is necessary to study methods for optimizing the concentration of viscoelastic particle-polymer composite systems to provide technical guidance for the design of heterogeneous chemical flooding systems. Summary of the Invention

[0005] The main purpose of the present invention is to provide a concentration optimization method suitable for heterogeneous chemical flooding systems. The method of the present invention can quickly and effectively achieve the optimal minimum concentration of the viscoelastic particle flooding agent and polymer composite system, providing strong technical support for the design of heterogeneous chemical flooding systems.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a concentration optimization method applicable to a heterogeneous chemical flooding system, which comprises the following steps:

[0008] Step 1: Conduct a physical simulation test of flow separation between high and low permeability layers to establish a relationship chart between displacement phase / crude oil viscosity ratio, flow diversion coefficient, and concentration for the oil displacement agent-polymer composite system;

[0009] Step 2: Determine the optimal ratio of the oil displacement agent and the polymer according to the target reservoir conditions, prepare oil displacement agent-polymer composite systems of different concentrations according to the ratio, and measure the viscosity of each composite system;

[0010] Step 3, calculating the viscosity ratio of the oil displacement agent-polymer composite to the crude oil at different concentrations;

[0011] Step 4: Based on the viscosity ratio obtained in step 3 and the chart established in step 1, the flow diversion coefficient is obtained, while taking into account the viscosity ratio limit of the composite system to determine the minimum use concentration of the oil displacement agent-polymer composite system.

[0012] Furthermore, the step 1 specifically includes the following steps:

[0013] ① Prepare oil-displacing agent-polymer composite systems with different concentrations and a certain ratio of oil-displacing agent to polymer, and measure the viscosity of each composite system;

[0014] ② Calculate the underground viscosity of the oil displacement agent-polymer composite system;

[0015] ③ Determine the underground crude oil viscosity of the target reservoir;

[0016] ④Calculate the viscosity ratio of the oil displacement agent-polymer composite system to the crude oil;

[0017] ⑤ Using a split flow physical simulation test, record the liquid production of high and low permeability pipes injected with different concentrations of oil displacement agent-polymer composite system, and calculate the corresponding liquid flow diversion coefficient;

[0018] ⑥ Based on the results of ④ and ⑤, by plotting the oil displacement agent-polymer composite system / crude oil viscosity ratio, the corresponding concentration and the flow diversion coefficient, a relationship chart of the displacement phase / crude oil viscosity ratio-flow diversion coefficient-concentration of the oil displacement agent-polymer composite system was established.

[0019] Furthermore, the viscosity of the underground crude oil in the target oil reservoir is in the range of 40-150 mPa·s.

[0020] Furthermore, in step ①, the ratio of the oil-displacing agent to the polymer is 1-20:1-10.

[0021] Furthermore, in step ①, the mass concentration of the oil displacement agent-polymer composite system is in the range of 0.1%-0.5%.

[0022] Furthermore, in step 2, the mass concentration of the oil-displacing agent-polymer composite system is in the range of 0.15% to 0.3%.

[0023] Furthermore, the minimum concentration of the oil-displacing agent-polymer composite system used in step 4 should satisfy the corresponding flow diversion coefficient ≤ 1, and the viscosity ratio of the composite system to the crude oil at this concentration should be ≥ 0.2.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The method of the present invention utilizes an established displacement phase / crude oil viscosity ratio-fluid flow diversion coefficient-concentration relationship chart of the oil-displacing agent and polymer composite system to quickly and effectively achieve the optimization of the minimum concentration of the viscoelastic particle oil-displacing agent and polymer composite system.

[0026] The method of the present invention is simple, practical and easy to operate, and provides reliable technical support for the design of heterogeneous chemical flooding systems that achieve optimal flooding effects while maintaining economy under different reservoir conditions, thereby ensuring the implementation of heterogeneous chemical flooding in mining fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a concentration optimization method for a viscoelastic particle flooding agent and polymer composite system in a heterogeneous chemical flooding system according to a specific embodiment of the present invention;

[0028] Figure 2 This is a graph showing the relationship between displacement phase / crude oil viscosity ratio, flow diversion coefficient, and concentration of a viscoelastic particle oil-displacing agent and polymer composite system in a specific embodiment of the present invention;

[0029] Figure 3 In a specific embodiment of the present invention, the concentration of the viscoelastic particle displacement agent and polymer composite system is 0.24% in a heterogeneous chemical flooding system with a high permeability of 3000×10 -3 μm 2 , low permeability 1000×10 -3 μm 2 The flow rate distribution curve in the parallel double-tube sand filling model;

[0030] Figure 4 In a specific embodiment of the present invention, the concentration of the viscoelastic particle displacement agent and polymer composite system is 0.24% in a heterogeneous chemical flooding system with a high permeability of 3000×10 -3 μm 2 , low permeability 1000×10 -3 μm 2 Enhanced oil recovery curve in the parallel double-tube sand filling model. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and "include" are used in this specification, they indicate the presence of features, steps, operations and combinations thereof.

[0033] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0034] The viscoelastic particle oil displacement agent used in this embodiment was independently developed by Shengli Oilfield (US9080096B2), and the polymer is partially hydrolyzed polyacrylamide. The viscoelastic particle oil displacement agent and polymer used in the present invention are not limited to the above components.

[0035] Example 1

[0036] like Figure 1 As shown, the concentration optimization method applicable to the heterogeneous chemical flooding system comprises the following steps:

[0037] Step 1: Conduct physical simulation tests on the flow rate of high and low permeability layers, and establish a relationship chart of displacement phase / crude oil viscosity ratio-fluid flow diversion coefficient-concentration for the oil displacement agent-polymer composite system.

[0038] The specific steps include:

[0039] ① Prepare oil-displacing agent-polymer composite systems with different concentrations and a certain ratio of oil-displacing agent to polymer, and measure the viscosity of each composite system;

[0040] ② Calculate the underground viscosity of the oil displacement agent-polymer composite system;

[0041] ③ Determine the underground crude oil viscosity of the target reservoir;

[0042] ④Calculate the viscosity ratio of the oil displacement agent-polymer composite system to the crude oil;

[0043] ⑤ Using a split flow physical simulation test, record the liquid production of high and low permeability pipes injected with different concentrations of oil displacement agent-polymer composite system, and calculate the corresponding liquid flow diversion coefficient;

[0044] ⑥ Based on the results of ④ and ⑤, by plotting the oil displacement agent-polymer composite system / crude oil viscosity ratio, the corresponding concentration and the flow diversion coefficient, a relationship chart of the displacement phase / crude oil viscosity ratio-flow diversion coefficient-concentration of the oil displacement agent-polymer composite system was established.

[0045] Step 2: Determine the optimal ratio of the oil displacement agent and the polymer according to the target reservoir conditions, prepare oil displacement agent-polymer composite systems of different concentrations according to the ratio, and measure the viscosity of each composite system;

[0046] Step 3, calculating the viscosity ratio of the oil displacement agent-polymer composite to the crude oil at different concentrations;

[0047] Step 4: Based on the viscosity ratio obtained in step 3 and the chart established in step 1, the flow diversion coefficient is obtained, while taking into account the viscosity ratio limit of the composite system, and determining the minimum use concentration of the oil-displacing agent-polymer composite system; the minimum use concentration of the oil-displacing agent-polymer composite system should satisfy its corresponding flow diversion coefficient ≤ 1, and at this concentration, the viscosity ratio of the composite system to the crude oil is ≥ 0.2.

[0048] The aforementioned oil-displacing agent is a viscoelastic particle oil-displacing agent. The method for determining the appropriate viscoelastic particle oil-displacing agent for the target reservoir is described in the patent "Efficient Selection Method for Viscoelastic Particle Oil-Displacing Agents Adapting to Different Reservoir Requirements" (ZL201910165770.4). The method for determining the optimal ratio of the viscoelastic particle oil-displacing agent to the polymer is described in the patent application "A Method for Optimizing the Ratio of a Heterogeneous Chemical Flooding System."

[0049] Example 2

[0050] like Figure 1 As shown, the concentration optimization method applicable to the heterogeneous chemical flooding system comprises the following steps:

[0051] Step 1: Conduct physical simulation tests on the flow rate of high and low permeability layers, and establish a relationship chart of displacement phase / crude oil viscosity ratio-fluid flow diversion coefficient-concentration for the oil displacement agent-polymer composite system.

[0052] The specific steps include:

[0053] ① preparing oil-displacing agent-polymer composite systems with different concentrations of a certain ratio of oil-displacing agent to polymer, and measuring the viscosity of each composite system; the ratio of oil-displacing agent to polymer is 1-20:1-10; the mass concentration range of the oil-displacing agent-polymer composite system is 0.1%-0.5%;

[0054] ② Calculate the underground viscosity of the oil displacement agent-polymer composite system;

[0055] ③ Determine the underground crude oil viscosity of the target oil reservoir; the underground crude oil viscosity of the target oil reservoir is in the range of 40-150 mPa·s;

[0056] ④Calculate the viscosity ratio of the oil displacement agent-polymer composite system to the crude oil;

[0057] ⑤ Using a split flow physical simulation test, record the liquid production of high and low permeability pipes injected with different concentrations of oil displacement agent-polymer composite system, and calculate the corresponding liquid flow diversion coefficient;

[0058] ⑥ Based on the results of ④ and ⑤, by plotting the oil displacement agent-polymer composite system / crude oil viscosity ratio, the corresponding concentration and the flow diversion coefficient, a relationship chart of the displacement phase / crude oil viscosity ratio-flow diversion coefficient-concentration of the oil displacement agent-polymer composite system was established.

[0059] Step 2: Determine the optimal ratio of the oil-displacing agent and the polymer based on the target reservoir conditions, prepare oil-displacing agent-polymer composite systems of different concentrations according to the ratio, and measure the viscosity of each composite system; the mass concentration range of the oil-displacing agent-polymer composite system is 0.15%-0.3%;

[0060] Step 3, calculating the viscosity ratio of the oil displacement agent-polymer composite to the crude oil at different concentrations;

[0061] Step 4: Based on the viscosity ratio obtained in step 3 and the chart established in step 1, the flow diversion coefficient is obtained, while taking into account the viscosity ratio limit of the composite system, and determining the minimum use concentration of the oil-displacing agent-polymer composite system; the minimum use concentration of the oil-displacing agent-polymer composite system should satisfy its corresponding flow diversion coefficient ≤ 1, and at this concentration, the viscosity ratio of the composite system to the crude oil is ≥ 0.2.

[0062] The aforementioned oil-displacing agent is a viscoelastic particle oil-displacing agent. The method for determining the appropriate viscoelastic particle oil-displacing agent for the target reservoir is described in the patent "Efficient Selection Method for Viscoelastic Particle Oil-Displacing Agents Adapting to Different Reservoir Requirements" (ZL201910165770.4). The method for determining the optimal ratio of the viscoelastic particle oil-displacing agent to the polymer is described in the patent application "A Method for Optimizing the Ratio of a Heterogeneous Chemical Flooding System."

[0063] Example 3

[0064] Take Hekouchengdong Ng5 22 Reservoir conditions (average reservoir pore throat radius of 25 μm, average displacement pressure gradient of 0.043 MPa / m, underground crude oil viscosity of 150 mPa·s), the concentration optimization method applicable to the heterogeneous chemical flooding system comprises the following steps:

[0065] Step 1: Based on the physical simulation test of the flow rate of high and low permeability layers, a displacement phase / crude oil viscosity ratio-fluid diversion coefficient-concentration relationship chart of the viscoelastic particle displacement agent and polymer composite system is established;

[0066] The specific method is:

[0067] ① Prepare a series of composite system solutions with a certain ratio of viscoelastic particle displacement agent and polymer and different total concentrations, and measure the viscosity μ of each composite system solution. i The ratio of viscoelastic particle displacement agent to polymer in the composite system was 1:1, and the composite system concentrations were 0.15%, 0.2%, 0.22%, 0.25%, 0.3%, and 0.35%, respectively; the corresponding viscosities were 11.4mPa·s, 21.7mPa·s, 26.6mPa·s, 34.9mPa·s, 52.6mPa·s, and 73.5mPa·s, respectively.

[0068] ②Calculate the underground viscosity μ of the composite system w =μ i ×Viscosity retention rate: The viscosity retention rate of the Shengli Oilfield flooding system underground is generally 50%.

[0069] ③ Determine the underground crude oil viscosity μ of the target reservoir o ;

[0070] ④Calculate the viscosity ratio of the composite system to crude oil N=μ w / μ o ;

[0071] ⑤ Using the flow rate splitting physical simulation test, record the liquid production of high and low permeability pipes injected with different concentrations of viscoelastic particle displacement agent-polymer composite solution, and calculate the corresponding liquid flow diversion coefficient Q i , Q i =H i / L i ; Hi is the minimum value of the high permeability pipe flow rate, L i It is the highest value of the low permeability pipe flow rate;

[0072] ⑥ Based on the results of ④ and ⑤, by plotting the composite system / crude oil viscosity ratio, the corresponding concentration and the flow diversion coefficient, a relationship chart of the viscoelastic particle displacement agent and polymer composite system / crude oil viscosity ratio-flow diversion coefficient-concentration is established, as shown in the figure: Figure 2 shown.

[0073] Step 2: Targeting Hekou Chengdong Ng5 22 Reservoir conditions (average pore throat radius 25 μm, average displacement pressure gradient 0.043 MPa / m, underground crude oil viscosity 150 mPa·s) were met. A viscoelastic particle displacement agent with a diameter of 300-900 μm, suitable for the reservoir, was used to prepare composite system solutions with an optimal ratio of 1:1 between the viscoelastic particle displacement agent and the polymer. The total concentrations were 0.2%, 0.22%, 0.24%, 0.26%, and 0.28%, respectively. The corresponding viscosities were measured to be 39.6 mPa·s, 45.7 mPa·s, 59.6 mPa·s, 64.4 mPa·s, and 77.7 mPa·s.

[0074] Step 3: Calculate the viscosity ratios of the viscoelastic particle displacement agent-polymer composite system to crude oil at different concentrations of 0.2%, 0.22%, 0.24%, 0.26%, and 0.28%, which are 0.13, 0.15, 0.2, 0.21, and 0.26, respectively.

[0075] Step 4, based on Figure 2 The flow diversion coefficients obtained at various concentrations were 1.4, 1.06, 0.81, 0.67, and 0.5. The smaller the value, the greater the heterogeneous adjustment capability of the viscoelastic particle displacement agent / polymer composite system. When the flow diversion coefficient is ≤1, the composite system can divert flow in both high and low permeability zones, while also meeting the viscosity ratio requirement of the composite system to crude oil of ≥0.2. After comprehensive consideration, the minimum concentration of the viscoelastic particle displacement agent / polymer composite system was determined to be 0.24%.

[0076] At high permeability 3000×10 -3 μm 2 , low permeability 1000×10 -3 μm 2 The corresponding physical simulation test was carried out to verify the heterogeneous chemical flooding system by injecting viscoelastic particle flooding agent and polymer composite system with a concentration of 0.24% into the parallel double-tube sand filling model.

[0077] The results of the flow rate curve of the heterogeneous chemical flooding system in the physical simulation test are shown in Figure 3 , the results of enhanced oil recovery are shown in Figure 4 .Depend on Figure 3 It can be seen that during the injection of the heterogeneous chemical flooding system slug, the low permeability model's fractional flow rate exceeded that of the high permeability model, indicating that the system can effectively activate the low permeability layer and exhibit good heterogeneous adjustment capabilities. In addition, due to the discontinuous migration of the viscoelastic particle flooding agent, the fractional flow rate fluctuates. This fractional flow adjustment is still effective in the subsequent water flooding stage, and the heterogeneous chemical flooding after water flooding has an enhanced oil recovery of 28.3% ( Figure 4 The results of the physical simulation tests are consistent with the optimization results based on the relationship chart of the viscoelastic particle displacement agent and polymer composite system / crude oil viscosity ratio-fluid flow diversion coefficient-concentration.

[0078] Through a large number of experiments, it can be seen that the present invention can effectively and quickly determine the minimum usage concentration of the viscoelastic particle flooding agent and polymer composite system in the heterogeneous chemical flooding system according to the needs of different oil reservoirs, realize the efficiency and economy of the optimized design of the heterogeneous chemical flooding system, and ensure the application effect of the heterogeneous chemical flooding mine.

[0079] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A concentration optimization method applicable to a heterogeneous chemical flooding system, characterized in that: The following steps are involved: Step 1: Conduct a physical simulation test of flow separation between high and low permeability layers to establish a relationship chart between displacement phase / crude oil viscosity ratio, flow diversion coefficient, and concentration for the oil displacement agent-polymer composite system; Step 2: Determine the optimal ratio of the oil displacement agent and the polymer according to the target reservoir conditions, prepare oil displacement agent-polymer composite systems of different concentrations according to the ratio, and measure the viscosity of each composite system; Step 3, calculating the viscosity ratio of the oil displacement agent-polymer composite to the crude oil at different concentrations; Step 4, based on the viscosity ratio obtained in step 3 and the plate established in step 1, obtain the flow diversion coefficient, while taking into account the viscosity ratio limit of the composite system, and determine the minimum concentration of the oil displacement agent-polymer composite system; The minimum concentration of the oil displacement agent-polymer composite system used in step 4 should satisfy the corresponding flow diversion coefficient ≤ 1, and the viscosity ratio of the composite system to the crude oil at this minimum concentration should be ≥ 0.

2.

2. The concentration optimization method applicable to a heterogeneous chemical flooding system according to claim 1, characterized in that: The step 1 specifically includes the following steps: ① Prepare oil-displacing agent-polymer composite systems with different concentrations and a certain ratio of oil-displacing agent to polymer, and measure the viscosity of each composite system; ② Calculate the underground viscosity of the oil displacement agent-polymer composite system; ③ Determine the underground crude oil viscosity of the target reservoir; ④Calculate the viscosity ratio of the oil displacement agent-polymer composite system to the crude oil; ⑤ Using a split flow physical simulation test, record the liquid production of high and low permeability pipes injected with different concentrations of oil displacement agent-polymer composite system, and calculate the corresponding liquid flow diversion coefficient; ⑥ Based on the results of ④ and ⑤, by plotting the oil displacement agent-polymer composite system / crude oil viscosity ratio, the corresponding concentration and the flow diversion coefficient, a relationship chart of the displacement phase / crude oil viscosity ratio-flow diversion coefficient-concentration of the oil displacement agent-polymer composite system was established.

3. The concentration optimization method applicable to a heterogeneous chemical flooding system according to claim 1, characterized in that: The mass concentration range of the oil displacement agent-polymer composite system in step 2 is 0.15%-0.3%.

4. The concentration optimization method applicable to a heterogeneous chemical flooding system according to claim 2, characterized in that: The viscosity of the underground crude oil in the target reservoir ranges from 40 to 150 mPa·s.

5. The concentration optimization method applicable to a heterogeneous chemical flooding system according to claim 2, characterized in that: In step ①, the ratio of the oil-displacing agent to the polymer is 1-20:1-10.

6. The concentration optimization method applicable to a heterogeneous chemical flooding system according to claim 2, characterized in that: The mass concentration range of the oil displacement agent-polymer composite system in step ① is 0.1%-0.5%.

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