A method for dividing and evaluating drive units of water flooding effect of low permeability oil reservoir

Abstract

The application discloses a kind of for low permeability reservoir water drive effect driving unit division and evaluation method, it is related to oil and gas field development technical field, and the present scheme is based on streamline model to the injection-production unit is spatially segmented, and face flow ratio (flow-area comprehensive index) and water cut (streamline dynamic water saturation) are defined as two-dimensional evaluation parameters innovatively, and two kinds of indexes are adaptively classified by clustering algorithm;Face flow ratio represents unit area production efficiency, and water cut reflects the dynamic characteristics of water drive front, and the classification threshold of both can be dynamically adjusted according to actual reservoir development needs;Finally, through the arrangement combination of two kinds of indexes, generate multi-scale driving unit type (such as "high speed-high water cut", "medium speed-low water cut" and the like), accurately depict the water drive difference characteristics caused by low permeability reservoir heterogeneity.This method is especially suitable for the low permeability reservoir with high water cut and serious water channeling in the middle and late stages of development, and provides quantitative decision basis for dynamic optimization of injection-production strategy and enhanced recovery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development, in particular to a driving unit division and evaluation method for water drive effect of low-permeability oil reservoirs. BACKGROUND

[0002] Water drive is widely used in oil reservoir development, but oil reservoirs often face problems such as high water content, water channeling and ineffective water injection in the later stage of water drive development, resulting in a decrease in the ultimate recovery of oilfields. Therefore, it is crucial to determine and quantify the oil-water distribution of the reservoir for remaining oil potential tapping, fine development of the oil reservoir and enhanced oil recovery. With low-permeability oil reservoirs gradually becoming the main development subject, it is increasingly important to deepen the understanding of their development characteristics. Low-permeability oil reservoirs generally have the characteristics of strong heterogeneity, making it difficult to identify and classify their geological characteristics. In addition, the special production system during the development of low-permeability oil reservoirs can also lead to more variable oil-water distribution in the formation, so it is particularly necessary to develop methods to characterize the development characteristics of low-permeability oil reservoirs.

[0003] Due to different research objects, current methods for classifying oil reservoirs are mainly based on static geological characteristics or production dynamic parameters. Methods based on static geological characteristics, such as analyzing the sedimentary characteristics of reservoirs through sedimentology and other theories to divide flow units, or classifying reservoirs based on physical parameters such as porosity and permeability, or classifying based on core analysis data and mathematical methods such as clustering; methods based on production dynamic parameters, such as using water cut and recovery degree as indicators for driving unit classification and evaluation, combined with numerical simulation for classification.

[0004] However, the method of dividing flow units by analyzing the sedimentary characteristics of reservoirs through sedimentology and other theories has a weak quantitative degree and is difficult to accurately represent the flow characteristics of the reservoir; the method of classifying reservoirs based on physical parameters such as porosity and permeability is difficult to reflect changes in reservoir properties during production; the method of classifying based on core analysis data and mathematical methods such as clustering has high requirements for data quality. The method of using water cut and recovery degree as indicators for flow unit classification and evaluation has a fine degree that depends on the numerical simulation grid division.

[0005] Therefore, a driving unit division and evaluation method for water drive effect of low-permeability oil reservoirs is proposed to solve the above problems. SUMMARY

[0006] Therefore, the technical problem to be solved by the present application is to provide a driving unit division and evaluation method for water drive effect of low-permeability oil reservoirs.

[0007] To achieve the above object, the present application provides the following technical scheme: a driving unit division and evaluation method for water drive effect of low-permeability oil reservoirs, comprising:

[0008] S1, driving unit division: dividing the flow region surrounded by the flow line to obtain a plurality of unit regions;

[0009] S2, parameter definition and calculation: calculating the face flow ratio and water cut of each unit region after the division in S1;

[0010] S3, driving unit classification: driving unit classification and evaluation: classifying the calculated face flow ratio and water cut in S2 by the clustering method, and evaluating the driving units with different attributes according to the classified unit regions.

[0011] Preferably, the face flow ratio in S2 is defined as the ratio of the flow rate ratio and the area ratio of the unit region; the area ratio is the ratio of the area of the unit region to the area of the entire flow region, and the flow rate ratio is the ratio of the flow rate of the unit region to the flow rate of the entire flow region; the face flow ratio represents the production rate of one unit region.

[0012] Preferably, a unit region is defined as The area of the unit region is defined as The The specific expression of the area ratio is:

[0013]

[0014] In the formula, θ represents the included angle between OA and OB; hθ represents the included angle between the hth flow line on the water injection well side and the main flow line OE; A represents the vertex of the flow line OAE;

[0015] The area ratio is the ratio of the area of the unit region to the area of the entire flow region, and the area ratio is defined as The The specific expression of the area ratio is:

[0016]

[0017] wherein O represents the injection well; E represents the production well; AD represents the vertical distance from the vertex of the shunt line OAE to the main flow line OE; B represents the vertex of the shunt line OBE;

[0018] wherein the flow rate of the unit region is wherein the flow rate of the unit region is The specific expression of Q

[0019]

[0020] wherein q represents the oil flow rate; d represents the ratio of OD to DE;

[0021] wherein

[0022] wherein K represents the permeability; k represents the index of the unit region on the axis to the right of AD; μ0 represents the viscosity of the oil; w represents the length of each segment after the division of DE; G represents the threshold pressure gradient; r represents the distance along the flow line; k ro represents the relative permeability of the oil.

[0023] As preferred, the flow rate of the entire flow region surrounded by OAE is Q max , and the specific expression of Q max

[0024]

[0025] wherein OD represents the distance from D to the injection well; DE represents the distance from D to the production well;

[0026] The flow rate ratio of the unit region is wherein the flow rate of the unit region is The specific expression of Q

[0027]

[0028] wherein α represents the included angle between the outermost flow line and the main flow line on the injection well side; β represents the included angle between the outermost flow line and the main flow line on the production well side.

[0029] As preferred, the surface flow ratio is defined as the ratio of the flow rate ratio of the unit region and the area ratio; according to the definition, The surface flow ratio of Q The specific expression of Q

[0030]

[0031] For the unit region to the right of AD The surface flow ratio of Q The specific expression of Q

[0032] ​

[0033] where yξ represents the angle between the yth flow line on the production well side and the main flow line; and ξ represents the angle of each section after the angle β is evenly divided.

[0034] As preferred, the water cut in S2 is for the unit area If the vertex is MQRN, the average water saturation of the intersection FJ between the flow line and MQRN between OA and OB is The water cut of FJ is S ave , S ave The specific expression is:

[0035]

[0036] where r1 and r2 are the positions of any two adjacent points, S w1 and S w2 are the water saturations of r1 and r2 respectively, a φ is the effective flow area, t is time, k rw represents the relative permeability of water; and μ w represents the viscosity of water.

[0037] As preferred, the water cut of FJ section is the initial water saturation S wi when the water drive front has not reached F point.

[0038] where the water drive front is between F point and J point, the water cut of FJ section S FJ The specific expression is:

[0039]

[0040] where x wf is the position of the water drive front, S wf is the water saturation of the water drive front, S wF is the water saturation of F point; represents the average water saturation between F point and x wf ; S wi represents the initial water saturation; and m represents the length of each section after the angle OD is evenly divided.

[0041] where the water drive front has passed J point, the water cut of FJ section S FJ The specific expression is:

[0042]

[0043] where S wJ represents the water saturation of J point.

[0044] As preferred, the driving unit classification in S3 adopts the k-means clustering method of unsupervised learning algorithm to classify the face flow ratio and water saturation data;

[0045] The face flow ratio data is classified with P1 clustering centers, that is, the face flow ratio data set of all unit regions is divided into P1+1 subsets, and P1+1 driving units classified by the face flow ratio are obtained;

[0046] The water saturation data is classified with P2 clustering centers, that is, the water saturation data set of all unit regions is divided into P2+1 subsets, and P2+1 driving units classified by the water saturation are obtained;

[0047] When the face flow ratio and water saturation are used as classification standards at the same time, (P1+1)(P2+1) driving units are obtained; the classification method of the face flow ratio and water saturation data set can be divided, evaluated and adjusted according to the actual production situation, so as to be more consistent with the development process of the oilfield and the subsequent production needs.

[0048] Compared with the prior art, the present application provides a driving unit division and evaluation method for water drive effect of low-permeability oil reservoirs, which has the following beneficial effects:

[0049] (1) Compared with the method of dividing the flow unit by analyzing the sedimentary characteristics of the reservoir through sedimentology and other theories, the quantitative degree is slightly weak, and it is difficult to accurately represent the flow characteristics of the reservoir. The advantage of the present scheme is that the face flow ratio and water saturation are established based on the streamline method, which respectively represent the flow proportion and water drive degree of the unit, and can distinguish the water drive advantage channel;

[0050] (2) Compared with the method of classifying the reservoir by porosity and permeability and other physical parameters, it is difficult to reflect the change of reservoir properties in the production process. The advantage of the present scheme is that the face flow ratio and water saturation change with the development process, which can dynamically reflect the different unit properties of the water drive reservoir and judge the invalid water drive cycle;

[0051] (3) Compared with the method of classifying based on core analysis data and through clustering and other mathematical methods, the data quality requirement is higher. The advantage of the present scheme is that the overall calculation process of the face flow ratio and water saturation is simple and efficient, and can accurately reflect the physical characteristics of the system without complicated data body analysis, and the classification criteria can be updated dynamically through the water drive of the reservoir. BRIEF DESCRIPTION OF DRAWINGS

[0052] Fig. 1 It is a schematic diagram of the driving unit division and evaluation method for water drive effect of low-permeability oil reservoirs of the present application;

[0053] Fig. 2 It is a schematic diagram of unit region division of the present application;

[0054] Fig. 3 The calculation result diagram of the driving unit of the application is shown. DETAILED DESCRIPTION

[0055] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the application.

[0056] Embodiment, refer to the drawings Figs. 1-3 As shown in the drawings, a driving unit division and evaluation method for water flooding effect of low-permeability oil reservoirs is provided, and the specific implementation process is as follows.

[0057] The nine-point well pattern is used to demonstrate the driving unit change in the water injection process. The whole injection-production unit is a square with a size of 400m*400m, the formation permeability is 5mD-20mD, the porosity is 0.1, the initial oil saturation is 0.7, the starting pressure gradient is set to 0.01MPa / m, the original formation pressure is 20MPa, and the injection well and production well pressures are set to 30MPa and 15MPa respectively.

[0058] Step 1, driving unit division;

[0059] The face flow ratio data is classified with 3 cluster centers to obtain four types of driving units with face flow ratio as the division standard, i.e., low-speed, medium-speed, medium-high-speed and high-speed driving units; the water cut data is classified with 3 cluster centers to obtain four types of driving units with water saturation as the division standard, i.e., low water cut, medium water cut, medium-high water cut and high water cut driving units.

[0060] Step 2, parameter definition and calculation;

[0061] Combined with the face flow ratio and water cut, 16 types of driving units can be obtained, i.e., low-speed-low water cut / medium water cut / medium-high water cut / high water cut, medium-speed-low water cut / medium water cut / medium-high water cut / high water cut, medium-high-speed-low water cut / medium water cut / medium-high water cut / high water cut and high-speed-low water cut / medium water cut / medium-high water cut / high water cut.

[0062] Among them, the face flow ratio is defined as the ratio of the flow rate ratio and the area ratio of the unit area; the area ratio is the ratio of the area of the unit area to the area of the whole flow area, and the flow rate ratio is the ratio of the flow rate of the unit area to the flow rate of the whole flow area; the face flow ratio represents the production rate of a unit area; for a unit area The unit area is defined as The specific expression of the face flow ratio is: The specific expression of the face flow ratio is:

[0063]

[0064] wherein θ represents the included angle between OA and OB; hθ represents the included angle between the hth streamline on the injection well side and the main streamline OE; A represents the vertex of the branch streamline OAE;

[0065] wherein the area ratio is the ratio of the area of the unit region to the area of the entire flow region, and the area ratio is defined as The specific expression of the area ratio is:

[0066]

[0067] wherein O represents the injection well; E represents the production well; AD represents the vertical distance from the vertex of the branch streamline OAE to the main streamline OE; B represents the vertex of the branch streamline OBE;

[0068] wherein the flow rate of the unit region is The specific expression of the flow rate of the unit region is:

[0069]

[0070] wherein q represents the oil flow rate; d represents the ratio of OD and DE;

[0071] wherein

[0072] wherein K represents the permeability; k represents the index of the unit on the axial direction on the right side of AD; μ0 represents the viscosity of the oil; w represents the length of each segment after the equal division of DE; G represents the start-up pressure gradient; r represents the distance along the streamline; k ro represents the relative permeability of the oil;

[0073] The flow rate of the entire flow region surrounded by OAE is Q max The specific expression of Q max

[0074]

[0075] wherein OD represents the distance from D to the injection well; DE represents the distance from D to the production well;

[0076] The flow rate ratio of the unit region is The specific expression of the flow rate ratio of the unit region is:

[0077]

[0078] ​​​​In the formula, α represents the included angle of the outermost streamline and the main streamline at the water injection well side; β represents the included angle of the outermost streamline and the main streamline at the production well side;

[0079] According to the definition, The face flow ratio of the unit region The specific expression is:

[0080]

[0081] For the unit region on the right side of the AD The face flow ratio of the unit region The specific expression is:

[0082]

[0083] In the formula, yξ represents the included angle of the yth streamline at the production well side and the main streamline; ξ represents the included angle of each segment after the average division of β.

[0084] Wherein, the water cut of the unit region If the vertex is MQRN, the average water saturation of the intersection FJ of the streamlines between OA and OB and MQRN is The water cut of the unit region ave The specific expression is: ave The specific expression is:

[0085]

[0086] In the formula, r1 and r2 are the positions of any adjacent two points, S w1 and S w2 are the water saturations of r1 and r2 respectively a φ is the effective flow area, t is time, k rw represents the relative permeability of water; μ w represents the viscosity of water.

[0087] (1) When the water drive front has not reached the F point, the water saturation of the FJ segment is the initial water saturation S wi ;

[0088] (2) When the water drive front is between the F point and the J point, the water saturation of the FJ segment is S FJ The specific expression is:

[0089]

[0090] In the formula, x wf is the position of the water drive front, S wf is the water saturation of the water drive front, S wF is the water saturation of the F point; The average water saturation between F point and x wf S represents the average water saturation between F point and x wi S represents the initial water saturation; m represents the length of each section after OD division;

[0091] (3) Wherein, the water drive front passes through the J point, the water saturation S FJ The specific expression is:

[0092]

[0093] S represents the water saturation at the J point. wJ S represents the water saturation at the J point.

[0094] Step three, driving unit classification evaluation method;

[0095] The face flow ratio data is classified with P1 clustering centers, that is, the face flow ratio data set of all unit areas is divided into P1+1 subsets, obtaining P1+1 driving units classified by face flow ratio;

[0096] The water saturation data is classified with P2 clustering centers, that is, the water saturation data set of all unit areas is divided into P2+1 subsets, obtaining P2+1 driving units classified by water saturation;

[0097] When using face flow ratio and water saturation as classification standards at the same time, (P1+1)(P2+1) driving units are obtained; The classification method of face flow ratio and water saturation data set can be adjusted according to the actual production situation to better meet the development process and subsequent production needs of the oilfield.

[0098] That is, after the above calculation, the driving unit distribution at the 6th month and the 12th month is as shown in Fig. 3 The low-speed-low water unit, medium-speed-medium water unit, medium-high-speed-medium-high water unit and high-speed-high water unit appear at the 6th month, and the proportion of the four units is 74.5%, 7.2%, 14.9% and 3.5% respectively, and the proportion of the four units at the 12th month is 51.3%, 13.9%, 28.7% and 6.2% respectively.

[0099] In summary, according to the above data, the advantages of the present scheme relative to the prior art are as follows:

[0100] (1) Compared with the method of analyzing the sedimentary characteristics of the reservoir by sedimentology and other theories and then dividing the flow unit, the quantitative degree is slightly weak, and it is difficult to accurately represent the flow characteristics of the reservoir. The advantage of the present scheme is based on the streamline method to establish face flow ratio and water saturation, which respectively represent the flow proportion and water drive degree of the unit, and can distinguish the water drive dominant channel;

[0101] (2) Relative to the method of classifying the storage layer by physical parameters such as porosity and permeability, it is difficult to reflect the change of reservoir physical properties in the production process, and the advantage of the scheme is that the face flow ratio and water cut change with the development process, and the different unit properties of the water drive reservoir can be dynamically reflected, and the invalid water drive cycle is judged;

[0102] (3) Relative to the method of classifying based on core analysis data and by clustering and other mathematical methods, the quality requirement of data is higher, and the advantage of the scheme is that the overall calculation process of the face flow ratio and the water cut is simple and efficient, and the physical characteristics of the system can be accurately reflected, without complicated data body analysis, and the classification criteria can be updated through the water drive dynamics of the reservoir.

[0103] The application provides a drive unit division and evaluation method for water drive effect of low-permeability reservoirs, and has the advantages of constructing a reservoir drive feature representation system with clear physical meaning and efficient calculation.

[0104] The application is especially suitable for low-permeability reservoirs with high water cut and serious water channeling in the middle and late development stages, and provides quantitative decision basis for dynamically optimizing injection-production strategies and improving recovery efficiency.

[0105] It should be noted that the term "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or inherent to such a process, method, article or device. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of another identical element in the process, method, article or device including the element.

[0106] Although the embodiments of the application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, replacements and variations of the embodiments can be made without departing from the principles and spirits of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A method for dividing and evaluating drive units for water flooding effect in low permeability reservoirs, characterized by, Comprise: S1, driving unit division: the flow region surrounded by the flow line is segmented to obtain several unit regions; S2, parameter definition and calculation: the face flow ratio and water cut of each unit region segmented in S1 are calculated; The face flow ratio defined in S2 is the ratio of the flow rate ratio and the area ratio of the unit region; the area ratio is the ratio of the area of the unit region to the area of the entire flow region, and the flow rate ratio is the ratio of the flow rate of the unit region to the flow rate of the entire flow region; the face flow ratio represents the production rate of a unit region; the water cut is the flow line dynamic water saturation, reflecting the dynamic characteristics of the water drive front; A unit area is defined as The unit area is defined as O represents the injection well; E represents the production well; AD represents the vertical distance from the top of the shunt line OAE to the main flow line OE; B represents the top of the shunt line OBE; m represents the length of each segment after the OD is evenly divided; and The specific expression is: In the formula, θ represents the included angle between OA and OB; hθ represents the included angle between the hth flow line on the injection well side and the main flow line OE; A represents the vertex of the flow dividing line OAE; Wherein, the area ratio is the ratio of the area of the unit region to the area of the entire flow region, and the area ratio is defined as The specific expression of the area ratio is: The specific expression of the area ratio is: Wherein, the flow of the unit area is It The specific expression is: In the formula, q represents the oil flow rate; d represents the ratio of OD and DE; wherein where K is the permeability; k is the index of the AD right-side unit in the axial direction; μ0 is the viscosity of the oil; w is the length of each section after DE equalization; G is the starting pressure gradient; r is the distance along the flow line; k ro is the relative permeability of the oil; The water content described in S2 for the unit area If its vertex is MQRN, the average water saturation of the intersection FJ between the streamline between OA and OB and MQRN is The water content of the streamline between OA and OB is S ave The S ave The specific expression is: where r1 and r2 are the locations of any two adjacent points, S w1 and S w2 are the water saturations at r1 and r2, respectively, a φ is the effective flow area, t is time, k rw is the relative permeability to water; and μ w is the viscosity of water. S3, driving unit classification and evaluation: the face flow ratio and water cut calculated in S2 are classified by clustering method, and the unit regions after classification are evaluated to have different attributes.

2. The method for dividing and evaluating the drive unit of water flooding effect in low permeability reservoir according to claim 1, characterized in that: The total flow rate of the flow area surrounded by the OAE is Q max The specific expression of Q max is: In the formula, OD represents the distance from D point to the injection well; DE represents the distance from D point to the production well; α represents the included angle between the outermost flow line and the main flow line on the injection well side; β represents the included angle between the outermost flow line and the main flow line on the production well side; The unit area flow rate ratio is The specific expression of the unit area flow rate ratio is The specific expression of the unit area flow rate ratio is 3. The method for dividing and evaluating the drive unit of water flooding effect in low permeability reservoir according to claim 2, characterized in that: The face flow ratio is defined as the ratio of the flow rate ratio and the area ratio of the unit region; according to the definition, the face flow ratio of a unit region is The specific expression is: For the unit region on the right side of AD The specific expression of the surface flow ratio The specific expression is: In the formula, yξ represents the included angle between the yth flow line on the production well side and the main flow line; ξ represents the included angle of each segment after β is evenly divided.

4. The driving unit division and evaluation method for water drive effect of low permeability oil reservoir according to claim 3, characterized in that: The water saturation of the FJ section is the initial water saturation S when the water drive front does not reach the F point wi ; Wherein, when the water drive front is between F point and J point, the water saturation S of FJ section FJ The specific expression is: where x wf is the location of the waterflood front, S wf is the water saturation of the waterflood front, S wF is the water saturation of the F point; is the average water saturation between the F point and x wf ; S wi is the initial water saturation; m is the length of each segment after OD division; Wherein, the water drive front edge crosses the J point, the water saturation S of the FJ section FJ The specific expression is: In the formula, S wJ is expressed as the water saturation at point J.

5. The method for dividing and evaluating the drive unit of water flooding effect in low permeability reservoir according to claim 1, characterized in that: The evaluation method in S3 uses the k-means clustering method of unsupervised learning algorithm to classify the face flow ratio and water cut data, and the classification steps specifically include: S3.1, classify the face flow ratio data with P1 clustering centers, that is, the face flow ratio data set of all unit regions is divided into P1+1 subsets, and P1+1 driving units are obtained according to the face flow ratio as the division standard; S3.2, classify the water cut data with P2 clustering centers, that is, the water saturation data set of all unit regions is divided into P2+1 subsets, and P2+1 driving units are obtained according to the water cut as the division standard; S3.3, when the face flow ratio and water cut are used as the division standard, (P1+1)(P2+1) driving units are obtained; the classification method of the face flow ratio and water cut data set is adjusted according to the actual production situation to better meet the development process of the oilfield and the subsequent production needs.

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