A method for evaluating enhanced oil recovery under carbon dioxide flooding development mode

Abstract

The present invention belongs to the technical field of oilfield development, and specifically relates to a method for evaluating enhanced oil recovery under a carbon dioxide drive development mode. The method comprises the following steps: optimizing key parameters that have a great influence on enhanced oil recovery under carbon dioxide drive; establishing a characterization function of the optimized key parameters; and constructing a calculation model for oil recovery under a carbon dioxide drive development mode. Starting from the perspective of seepage mechanics and reservoir engineering, the present invention establishes a basic model for evaluating enhanced oil recovery under a carbon dioxide drive development mode that can characterize reservoir properties, seepage characteristics, and development characteristics, and forms a quantitative evaluation reservoir engineering method for enhanced oil recovery under carbon dioxide drive in low permeability reservoirs, which fills the gap in theoretical models and evaluation methods for evaluating enhanced oil recovery under carbon dioxide drive, and has important practical significance for the evaluation results of enhanced oil recovery and the prediction of development effects under a quantitative carbon dioxide drive development mode.

Description

Technical Field

[0001] The invention belongs to the technical field of oil field development, and in particular relates to a method for evaluating enhanced oil recovery in a carbon dioxide flooding development mode. Background Art

[0002] The proven reserves of low-permeability oil reservoirs in my country account for 60% of the total remaining oil resources, and have great development potential. However, low-permeability oil reservoirs generally have geological fluid characteristics such as poor reservoir properties, low porosity, low permeability, severe heterogeneity, and low oil saturation, which leads to poor water drive development effects, usually showing development characteristics such as rapid production decline, rapid formation pressure drop, and low water drive recovery rate.

[0003] Carbon dioxide flooding has the mechanism of increasing oil recovery by expanding crude oil volume, reducing crude oil viscosity, improving oil-water mobility ratio, and reducing interfacial tension, which can better meet the requirements of injectivity and oil recovery efficiency of low permeability reservoirs in my country. my country began to pay attention to the theory and technology of carbon dioxide flooding in the early 1960s. Since the 1980s, Xinjiang, North China, Shengli, Jiangsu, Jilin and other oil fields have successively carried out indoor experiments and field tests on carbon dioxide flooding in low permeability reservoirs. Although certain results have been achieved, the theoretical research on carbon dioxide flooding reservoir engineering is still incomplete.

[0004] At present, the research on CO2 flooding recovery prediction and potential evaluation is mainly carried out with the help of indoor physical experiments, reservoir numerical simulation, curve regression analysis and BP neural network. From the perspective of reservoir engineering, there is no set of prediction models and evaluation methods specifically for CO2 flooding to enhance recovery. Summary of the invention

[0005] The main purpose of the present invention is to provide an evaluation method for improving oil recovery under a carbon dioxide flooding development mode, so as to solve the problem that there is currently no set of reservoir engineering theoretical models and evaluation methods specifically for improving oil recovery under carbon dioxide flooding. This method has important practical significance for quantifying the evaluation results of improving oil recovery and the prediction of development effects under the carbon dioxide flooding development mode.

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

[0007] The present invention provides a method for evaluating enhanced oil recovery in a carbon dioxide flooding development mode, which comprises the following steps:

[0008] Step 1. Optimizing key parameters that have a great impact on CO2 flooding and enhanced oil recovery;

[0009] Step 2. Establishing a characterization function of the key parameters obtained by optimization;

[0010] Step 3. Construct a calculation model for the recovery factor under the carbon dioxide flooding development mode.

[0011] Furthermore, in step 1, the key parameters preferably obtained include vertical heterogeneity coefficient, average reservoir permeability, mobility ratio, well pattern density, formation pressure, minimum miscibility pressure, and ratio of injection volume to total pore volume.

[0012] Furthermore, the characterization function of the vertical heterogeneity correction is:

[0013] (1-0.98V k 1.2444 ) (1)

[0014] Among them, V k is the vertical heterogeneity coefficient, f.

[0015] Furthermore, the characterization function of the coordinated parameter correction of permeability and mobility ratio is:

[0016]

[0017] Where, k is the average reservoir permeability, mD; M is the mobility ratio, f.

[0018] Furthermore, the characterization function of the well pattern influencing factor is:

[0019]

[0020] Where n is the well pattern density, wells / km 2 ; k is the average reservoir permeability, mD; M is the mobility ratio, f.

[0021] Furthermore, the characterization function of the correction of formation pressure effect is:

[0022]

[0023] Where, P is the formation pressure, MPa; P MMP is the minimum miscible pressure, MPa.

[0024] Furthermore, the characterization function of the correction of the effect of injection volume on recovery factor is:

[0025] f(PV)=0.3872×(PV) 3 -1.2521×(PV) 2 +1.763×PV+0.0136 (5)

[0026] Where PV is the ratio of the injected volume to the total pore volume, f.

[0027] Furthermore, in step 3, the calculation model of the recovery factor under the carbon dioxide flooding development mode is constructed as follows:

[0028]

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention optimizes key parameters that have a great impact on improving oil recovery, establishes a characterization function of the main controlling factors that affect improving oil recovery, and finally constructs a basic model for improving oil recovery evaluation under a carbon dioxide flooding development mode. From the perspective of seepage mechanics and reservoir engineering, a basic model for improving oil recovery evaluation under a carbon dioxide flooding development mode that can characterize reservoir properties, seepage characteristics, and development characteristics is established, forming a quantitative evaluation reservoir engineering method for improving oil recovery under carbon dioxide flooding in low permeability reservoirs, filling the gap in theoretical models and evaluation methods for evaluating oil recovery under carbon dioxide flooding, and having important practical significance for the evaluation results of improving oil recovery and the prediction of development effects under a quantitative carbon dioxide flooding development mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0032] Figure 1 This is a flow chart of a method for evaluating enhanced oil recovery in a carbon dioxide flooding development mode according to a specific embodiment of the present invention;

[0033] Figure 2 This is a comparison chart of the actual recovery rate of carbon dioxide flooding in the M1 block of a certain oil field described in a specific embodiment of the present invention and the recovery rate calculated by the evaluation model. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0036] 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 in conjunction with specific embodiments.

[0037] Example 1

[0038] like Figure 1 As shown, the method for evaluating enhanced oil recovery in the carbon dioxide flooding development mode comprises the following steps:

[0039] Step 1. Optimize key parameters that have a great impact on CO2 flooding to enhance oil recovery, including vertical heterogeneity coefficient, average reservoir permeability, mobility ratio, well pattern density, formation pressure, minimum miscibility pressure, and the ratio of injection volume to total pore volume.

[0040] Step 2. Establish the characterization function of the key parameters obtained by optimization:

[0041] The characterization function for the correction of vertical heterogeneity is:

[0042] (1-0.98V k 1.2444 ) (1)

[0043] Among them, V k is the vertical heterogeneity coefficient, f.

[0044] The characterization function of the coordinated parameter correction of permeability and mobility ratio is:

[0045]

[0046] Where, k is the average reservoir permeability, mD; M is the mobility ratio, f.

[0047] The characterization function of the well pattern influencing factor is:

[0048]

[0049] Where n is the well pattern density, wells / km 2 ; k is the average reservoir permeability, mD; M is the mobility ratio, f.

[0050] The characterization function of the correction of formation pressure effect is:

[0051]

[0052] Where, P is the formation pressure, MPa; P MMP is the minimum miscible pressure, MPa.

[0053] The characterization function of the correction of the effect of injection volume on recovery factor is:

[0054] f(PV)=0.3872×(PV) 3 -1.2521×(PV) 2 +1.763×PV+0.0136 (5)

[0055] Where PV is the ratio of the injected volume to the total pore volume, f.

[0056] Step 3. Construct a calculation model for the recovery factor under the carbon dioxide flooding development mode:

[0057]

[0058] This example compares and analyzes the existing enhanced oil recovery evaluation methods under the carbon dioxide drive development mode, selects 7 key parameters that have a great impact on enhanced oil recovery, and establishes 5 characterization functions of the main controlling factors that affect enhanced oil recovery. On the basis of clarifying the 7 key parameters and the characterization functions of the 5 main controlling factors, a basic model for enhanced oil recovery evaluation under the carbon dioxide drive development mode is constructed. This embodiment fills the deficiencies in the existing theoretical models and evaluation methods for enhanced oil recovery evaluation in the carbon dioxide drive development mode, and has important practical significance for quantifying the enhanced oil recovery evaluation results and development effect prediction under the carbon dioxide drive development mode.

[0059] Example 2

[0060] The method described in Example 1 was used to evaluate the enhanced oil recovery in the M1 block of the oil field under the carbon dioxide flooding development mode:

[0061] The average reservoir permeability of the M1 block is 5mD, the average porosity is 0.2, the vertical heterogeneity coefficient is 0.2, the mobility ratio is 34, the original formation pressure is 35MPa, and the experimental measurement of the minimum miscible pressure of carbon dioxide flooding in this area is 32MPa. The M1 area has been injected with gas since the end of 2011, using a five-point well pattern development method, continuously injecting carbon dioxide, with an average well spacing of 250m and a well pattern density of 16 wells / km 2 By the end of 2019, a total of 0.28 PV of carbon dioxide gas had been injected.

[0062] The comparison between the actual recovery rate of the block and the recovery rate calculated by the evaluation model of the present invention is as follows: Figure 2 As shown. Figure 2 It can be seen that the theoretically calculated recovery factor and the actual recovery factor have little difference in value, the degree of agreement is high, and the reliability is strong.

[0063] 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 equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for evaluating enhanced oil recovery in a carbon dioxide flooding development mode, characterized in that: Step 1. Key parameters that have a great impact on CO2 flooding EOR; Step 2. Establishing a characterization function of the obtained key parameters; Step 3. Construct a calculation model for the recovery factor under the carbon dioxide flooding development mode; In step 1, the key parameters obtained include vertical heterogeneity coefficient, average reservoir permeability, mobility ratio, well pattern density, formation pressure, minimum miscibility pressure, and the ratio of injection volume to total pore volume; The characterization function for the correction of vertical heterogeneity is: (1-0.98V k 1.2444 ) (1)； Among them, V k is the vertical heterogeneity coefficient; The characterization function of the coordinated parameter correction of permeability and mobility ratio is: Where, k is the average permeability of the reservoir, in mD, millidarcy; M is the mobility ratio; The characterization function of the well pattern influencing factor is: Where n is the well pattern density, in units of wells / km 2 , one mouth per square kilometer; k is the average reservoir permeability, in mD, millidarcy; M is the mobility ratio; The characterization function of the correction of formation pressure effect is: Where, P is the formation pressure, in MPa; P MMP is the minimum miscible pressure, in MPa.

2. The evaluation method according to claim 1, characterized in that: The characterization function of the correction of the effect of injection volume on recovery factor is: f(PV)=0.3872×(PV) 3 -1.2521×(PV) 2 +1.763×PV+0.0136 (5) Where PV is the ratio of the injected volume to the total pore volume.

3. The evaluation method according to any one of claims 1 to 2, characterized in that: In step 3, the calculation model of the recovery factor under the carbon dioxide flooding development mode is constructed as follows:

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