Driving unit division and evaluation method for water drive effect of low-permeability reservoir

Abstract

The invention discloses a driving unit division and evaluation method for the water drive effect of a low-permeability reservoir, and relates to the technical field of oil and gas field development. The method comprises the following steps: innovatively defining a surface flow ratio (flow-area comprehensive index) and water content (streamline dynamic water saturation) as two-dimensional evaluation parameters, and carrying out adaptive classification on the two types of indexes through a clustering algorithm; the surface flow ratio represents the unit area extraction efficiency, the water content reflects the dynamic characteristics of the water drive front, and the classification thresholds of the two can be dynamically adjusted according to the actual oil reservoir development requirements; and finally, through permutation and combination of the two types of indexes, multi-scale driving unit types (such as high speed-high water content, medium speed-low water content and the like) are generated, and water drive difference characteristics caused by heterogeneity of the low-permeability reservoir are accurately described. The method is particularly suitable for developing low-permeability reservoirs with high water content and serious water channeling in the middle and later periods, and a quantitative decision basis is provided for dynamically optimizing an injection-production strategy and improving the recovery ratio.

Description

Technical Field

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

[0002] Water flooding is widely used in reservoir development. However, in the later stages of water flooding, reservoirs often face problems such as high water cut, water breakthrough, and ineffective water injection, resulting in reduced ultimate oil recovery. Therefore, clarifying and quantifying the oil and water distribution in the reservoir is crucial for tapping the potential of remaining oil, achieving refined reservoir development, and improving oil recovery. As low-permeability reservoirs gradually become the main development targets, a deeper understanding of their development characteristics is becoming increasingly important. Low-permeability reservoirs are generally characterized by strong heterogeneity, making the identification and classification of geological features difficult. Furthermore, the special production regimes during the exploitation of low-permeability reservoirs can lead to more variable oil and water distribution in the formation. Therefore, it is particularly necessary to develop methods to characterize the development characteristics of low-permeability reservoirs.

[0003] Due to different research objects, the 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 theories such as sedimentology and then dividing flow units, or classifying reservoirs through physical parameters such as porosity and permeability, or classifying based on core analysis data and through mathematical methods such as clustering; methods based on production dynamic parameters, such as using water content and recovery degree as indicators for driving unit classification and evaluation, combined with numerical simulation for classification.

[0004] However, methods that analyze reservoir sedimentary characteristics through theories such as sedimentology and then classify flow units have a weaker degree of quantification and are unable to accurately characterize reservoir flow characteristics. Methods that classify reservoirs based on physical parameters such as porosity and permeability cannot accurately reflect changes in reservoir physical properties during production. Methods that classify based on core analysis data and mathematical methods such as clustering require high data quality. Methods that use water content and recovery level as flow unit classification evaluation indicators require a high level of precision depending on the numerical simulation grid division.

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

[0006] In light of this, the present invention addresses the technical problem of proposing a method for classifying and evaluating drive units for waterflooding in low-permeability reservoirs. Based on streamline calculations, the present invention defines surface flow ratio and water content as flow unit classification and evaluation indicators during waterflooding, and applies a clustering approach to classify drive units. The specific division boundaries of these two evaluation indicators can be adjusted based on the specific development conditions of different reservoirs. By permuting and combining the units classified by surface flow ratio and water content, a series of drive unit types reflecting the reservoir's waterflooding state can be obtained.

[0007] To achieve the above-mentioned object, the present invention provides the following technical solution: a method for dividing and evaluating driving units for water flooding effect in low-permeability oil reservoirs, comprising:

[0008] S1, driving unit division: divide the flow area surrounded by streamlines into several unit areas;

[0009] S2, parameter definition and calculation: calculate the surface flow ratio and water content of each unit area after segmentation in S1;

[0010] S3, driving unit classification: driving unit classification evaluation: the surface flow ratio and water content calculated in S2 are classified into intervals through the clustering method, and driving units with different attributes are evaluated according to the classified unit areas.

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

[0012] As an example, a unit area is defined as The unit area is defined as That The specific expression is:

[0013]

[0014] Where θ is the angle between OA and OB; hθ is the angle between the hth streamline on the injection well side and the main flow line OE; A is the vertex of the diversion line OAE;

[0015] The area ratio is the ratio of the area of the unit area to the area of the entire flow area. The area ratio is defined as That The specific expression is:

[0016]

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

[0018] The flow rate in the unit area is That The specific expression is:

[0019]

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

[0021] in,

[0022] Where K is the permeability; k is the axial index of the unit on the right side of AD; μ0 is the viscosity of the oil; w is the length of each segment after DE is evenly divided; G is the starting pressure gradient; r is the distance along the streamline; k ro Expressed as relative permeability of oil.

[0023] As a preference, the flow rate of the entire flow area surrounded by the OAE is Q max , its Q max The specific expression is:

[0024]

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

[0026] The unit area flow ratio is That The specific expression is:

[0027]

[0028] Where α is the angle between the outermost streamline and the main flow line on the injection well side; β is the angle between the outermost streamline and the main flow line on the production well side.

[0029] Preferably, the surface flow ratio is defined as the ratio of the flow rate ratio and the area ratio of the unit area; according to the definition, Surface flow ratio The specific expression is:

[0030]

[0031] For the unit area on the right side of AD Its surface flow ratio The specific expression is:

[0032]

[0033] Where yξ is the angle between the yth streamline on the production well side and the main flow line; ξ is the angle between each segment after β is evenly divided.

[0034] As a preference, the water content described in S2 is for the unit area If its vertex is MQRN, the average water saturation of the intersection FJ of the streamline between OA and OB and MQRN is The average water saturation between any two points on a streamline is S ave , its S ave The specific expression is:

[0035]

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

[0037] As a preference, when the water flooding front does not reach point F, the water saturation of the FJ section is the initial water saturation S wi ;

[0038] Among them, when the water flooding front is between points F and J, the water saturation S of the FJ section is FJ The specific expression is:

[0039]

[0040] Where x wf is the position of the water drive front, S wf is the water saturation at the water flooding front, S wF is the water saturation at point F; Represented as point F and x wf The average water saturation between wi It is represented by the initial water saturation; m is represented by the length of each segment after OD is evenly divided;

[0041] Among them, after the water flooding front passes point J, the water saturation S FJ The specific expression is:

[0042]

[0043] Where S wJ Expressed as water saturation at point J.

[0044] Preferably, the driving unit classification described in S3 uses the k-means clustering method of the unsupervised learning algorithm to classify the surface flow ratio and water content data;

[0045] The surface flow ratio data are classified into P1 cluster centers, that is, the surface flow ratio data sets of all unit areas are divided into P1+1 subsets, and P1+1 types of driving units based on the surface flow ratio are obtained;

[0046] The water content data is classified into P2 cluster centers, that is, the water saturation data set of all unit areas is divided into P2+1 subsets, and P2+1 driving units based on water content are obtained;

[0047] When both the surface flow ratio and water content are used as the classification criteria, (P1+1)(P2+1) types of driving units are obtained. The classification method of the surface flow ratio and water content dataset can be adjusted based on the actual production situation to better meet the development process and subsequent production needs of the oilfield.

[0048] Compared with the prior art, the present invention provides a method for dividing and evaluating driving units for water flooding effects in low-permeability reservoirs, which has the following beneficial effects:

[0049] (1) Compared with the method of dividing flow units by analyzing the sedimentary characteristics of the reservoir through sedimentology and other theories, the degree of quantification is slightly weaker and it is difficult to accurately characterize the flow characteristics of the reservoir. The advantage of this scheme is that it establishes the surface flow ratio and water content based on the streamline method, which respectively represent the flow proportion and water flooding degree of the unit, and can identify the dominant water flooding channel;

[0050] (2) Compared with the method of classifying reservoirs by physical parameters such as porosity and permeability, which is difficult to reflect the changes in reservoir physical properties during the production process, the advantage of this scheme is that the surface flow ratio and water content change with the development process, which can dynamically reflect the different unit properties of the water flooding reservoir and determine the ineffective water flooding cycle;

[0051] (3) Compared with the method based on core analysis data and classification through mathematical methods such as clustering, which has high requirements on data quality, the advantage of this scheme is that the overall calculation process of surface flow ratio and water content is concise and efficient, and can accurately reflect the physical characteristics of the system without the need for tedious data body analysis, and the classification criteria can be updated according to the water drive state of the reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of a driving unit division and evaluation method for water flooding effect in low permeability oil reservoirs according to the present invention;

[0053] Figure 2 This is a schematic diagram of the unit area division of the present invention;

[0054] Figure 3 This is a schematic diagram of the calculation results of the drive unit of the present invention. DETAILED DESCRIPTION

[0055] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0056] For example, see the attached Figure 1-3 As shown in FIG, a driving unit division and evaluation method for water flooding effect in low permeability reservoirs is described, and the specific implementation process is as follows;

[0057] The nine-point well network method was used to demonstrate the changes in the driving unit during the water injection process. The entire injection and production unit was a 400m×400m square, with a formation permeability of 5mD~20mD, a porosity of 0.1, an initial oil saturation of 0.7, a starting pressure gradient set to 0.01MPa / m, an original formation pressure of 20MPa, and injection well and production well pressures set to 30MPa and 15MPa, respectively.

[0058] Step 1: driving unit division;

[0059] The surface flow ratio data were classified into three cluster centers, and four types of driving units were obtained based on the surface flow ratio, namely low speed, medium speed, medium-high speed, and high speed driving units; the water content data were classified into three cluster centers, and four types of driving units were obtained based on the water saturation, namely low water content, medium water content, medium-high water content, and high water content driving units.

[0060] Step 2: Parameter definition and calculation;

[0061] Combining the surface flow ratio and water content, a total of 16 drive units can be obtained, including low speed-low water content / medium water content / medium-high water content / high water content, medium speed-low water content / medium water content / medium-high water content / high water content, medium-high speed-low water content / medium water content / medium-high water content / high water content, and high speed-low water content / medium water content / medium-high water content / high water content.

[0062] The surface 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 entire flow area, and the flow ratio is the ratio of the flow rate of the unit area to the flow rate of the entire flow area; the surface flow ratio represents the production rate of a unit area; for a unit area The unit area is defined as That The specific expression is:

[0063]

[0064] Where θ is the angle between OA and OB; hθ is the angle between the hth streamline on the injection well side and the main flow line OE; A is the vertex of the diversion line OAE;

[0065] The area ratio is the ratio of the area of the unit area to the area of the entire flow area. The area ratio is defined as That The specific expression is:

[0066]

[0067] Where, O represents the injection well; E represents the production well; AD represents the vertical distance from the vertex of the diversion line OAE to the main flow line OE; B represents the vertex of the diversion line OBE;

[0068] The flow rate in the unit area is That The specific expression is:

[0069]

[0070] Where q represents the oil flow rate; d represents the ratio of OD to DE;

[0071] in,

[0072] Where K is the permeability; k is the axial index of the unit on the right side of AD; μ0 is the viscosity of the oil; w is the length of each segment after DE is evenly divided; G is the starting pressure gradient; r is the distance along the streamline; k ro Expressed as relative permeability of oil;

[0073] The flow rate of the entire flow area surrounded by the OAE is Q max , its Q max The specific expression is:

[0074]

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

[0076] The unit area flow ratio is That The specific expression is:

[0077]

[0078] Where α is the angle between the outermost streamline and the main flow line on the injection well side; β is the angle between the outermost streamline and the main flow line on the production well side;

[0079] By definition, Surface flow ratio The specific expression is:

[0080]

[0081] For the unit area on the right side of AD Its surface flow ratio The specific expression is:

[0082]

[0083] Where yξ is the angle between the yth streamline on the production well side and the main flow line; ξ is the angle between each segment after β is evenly divided.

[0084] Among them, the water content for the unit area If its vertex is MQRN, the average water saturation of the intersection FJ of the streamline between OA and OB and MQRN is The average water saturation between any two points on a streamline is S ave , its S ave The specific expression is:

[0085]

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

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

[0088] (2) When the water flooding front is between points F and J, the water saturation S FJ The specific expression is:

[0089]

[0090] Where x wf is the position of the water drive front, S wf is the water saturation at the water flooding front, S wF is the water saturation at point F; Represented as point F and x wf The average water saturation between wi It is represented by the initial water saturation; m is represented by the length of each segment after OD is evenly divided;

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

[0092]

[0093] Where S wJ Expressed as water saturation at point J.

[0094] Step 3: Driver unit classification and evaluation method;

[0095] The surface flow ratio data are classified into P1 cluster centers, that is, the surface flow ratio data sets of all unit areas are divided into P1+1 subsets, and P1+1 types of driving units based on the surface flow ratio are obtained;

[0096] The water content data is classified into P2 cluster centers, that is, the water saturation data set of all unit areas is divided into P2+1 subsets, and P2+1 driving units based on water content are obtained;

[0097] When both the surface flow ratio and water cut are used as the classification criteria, (P1+1)(P2+1) types of driving units are obtained. The classification method of the surface flow ratio and water cut datasets can be adjusted according to the actual production situation to better meet the development process of the oilfield and subsequent production needs.

[0098] That is, after the above calculation, the distribution of drive units at 6 months and 12 months of production is as follows: Figure 3 As shown, at the 6th month, low-speed-low water content unit, medium-speed-medium water content unit, medium-high-speed-medium-high water content unit and high-speed-high water content unit appeared, and the proportions of these four units were 74.5%, 7.2%, 14.9% and 3.5%, respectively. At the 12th month, the proportions of these four units were 51.3%, 13.9%, 28.7% and 6.2%, respectively.

[0099] In summary, based on the above data, it can be concluded that this solution has the following advantages over existing technologies:

[0100] (1) Compared with the method of dividing flow units by analyzing the sedimentary characteristics of the reservoir through sedimentology and other theories, the degree of quantification is slightly weaker and it is difficult to accurately characterize the flow characteristics of the reservoir. The advantage of this scheme is that it establishes the surface flow ratio and water content based on the streamline method, which respectively represent the flow proportion and water flooding degree of the unit, and can identify the dominant water flooding channel;

[0101] (2) Compared with the method of classifying reservoirs by physical parameters such as porosity and permeability, which is difficult to reflect the changes in reservoir physical properties during the production process, the advantage of this scheme is that the surface flow ratio and water content change with the development process, which can dynamically reflect the different unit properties of the water flooding reservoir and determine the ineffective water flooding cycle;

[0102] (3) Compared with the method based on core analysis data and classification through mathematical methods such as clustering, which has high requirements on data quality, the advantage of this scheme is that the overall calculation process of surface flow ratio and water content is concise and efficient, and can accurately reflect the physical characteristics of the system without the need for tedious data body analysis, and the classification criteria can be updated according to the water drive state of the reservoir.

[0103] The present invention proposes a driving unit division and evaluation method for the water flooding effect of low-permeability reservoirs. It has the function of constructing a reservoir driving characteristic characterization system with clear physical meaning and efficient calculation. The scheme spatially segments the injection and production units based on the streamline model, innovatively defines the surface flow ratio (flow-area comprehensive index) and water content (streamline dynamic water saturation) as two-dimensional evaluation parameters, and adaptively classifies the two types of indicators through a clustering algorithm. Specifically, the surface flow ratio characterizes the regional recovery efficiency of the unit, and the water content reflects the dynamic characteristics of the water flooding front. The classification thresholds of the two can be dynamically adjusted according to the actual needs of reservoir development. Finally, through the permutation and combination of the two types of indicators, multi-scale driving unit types (such as "high speed-high water content" and "medium speed-low water content") are generated to accurately characterize the differential characteristics of water flooding caused by the heterogeneity of low-permeability reservoirs.

[0104] This solution is particularly suitable for low-permeability reservoirs with high water content and severe water breakthrough in the middle and late stages of development, providing a quantitative decision-making basis for dynamically optimizing injection-production strategies and improving recovery rates.

[0105] It should be noted that the term "comprises" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article, or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0106] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for dividing and evaluating driving units for water flooding effect in low permeability reservoirs, characterized in that: include: S1, driving unit division: divide the flow area surrounded by streamlines into several unit areas; S2, parameter definition and calculation: calculate the surface flow ratio and water content of each unit area after segmentation in S1; S3, driving unit classification evaluation: The surface flow ratio and water content calculated in S2 are classified into intervals using a clustering method, and driving units with different attributes are evaluated based on the classified unit areas.

2. The method for dividing and evaluating driving units for water flooding effect in low permeability reservoirs according to claim 1, characterized in that: The surface flow ratio described in S2 is defined as the ratio of the flow 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 entire flow area, and the flow ratio is the ratio of the flow of the unit area to the flow of the entire flow area; the surface flow ratio represents the production rate of a unit area.

3. The method for dividing and evaluating driving units for water flooding effect in low permeability reservoirs according to claim 2, characterized in that: Define a unit area as The unit area is defined as That The specific expression is: Where θ is the angle between OA and OB; hθ is the angle between the hth streamline on the injection well side and the main flow line OE; A is the vertex of the diversion line OAE; The area ratio is the ratio of the area of the unit area to the area of the entire flow area. The area ratio is defined as That The specific expression is: Where, O represents the injection well; E represents the production well; AD represents the vertical distance from the vertex of the diversion line OAE to the main flow line OE; B represents the vertex of the diversion line OBE; The flow rate in the unit area is That The specific expression is: Where q represents the oil flow rate; d represents the ratio of OD to DE; in, Where K is the permeability; k is the axial index of the unit on the right side of AD; μ0 is the viscosity of the oil; w is the length of each segment after DE is evenly divided; G is the starting pressure gradient; r is the distance along the streamline; k ro Expressed as relative permeability to oil.

4. The method for dividing and evaluating driving units for water flooding effect in low permeability reservoirs according to claim 3, characterized in that: The flow rate of the entire flow area surrounded by the OAE is Q max , its Q max The specific expression is: Where OD represents the distance from point D to the injection well; DE represents the distance from point D to the production well; The unit area flow ratio is That The specific expression is: Where α is the angle between the outermost streamline and the main flow line on the injection well side; β is the angle between the outermost streamline and the main flow line on the production well side.

5. The method for dividing and evaluating driving units for water flooding effect in low permeability reservoirs according to claim 4, characterized in that: The surface flow ratio is defined as the ratio of the flow rate ratio and the area ratio of the unit area; according to the definition, the surface flow ratio of a unit area is The specific expression is: For the unit area on the right side of AD Its surface flow ratio The specific expression is: Where yξ is the angle between the yth streamline on the production well side and the main flow line; ξ is the angle between each segment after β is evenly divided.

6. The method for dividing and evaluating driving units for water flooding effect in low permeability reservoirs according to claim 5, characterized in that: The water content described in S2 is for the unit area If its vertex is MQRN, the average water saturation of the intersection FJ of the streamline between OA and OB and MQRN is The average water saturation between any two points on a streamline is S ave , its S ave The specific expression is: In the formula, 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, and a φ is the effective flow area, t is the time, k rw Expressed as the relative permeability of water; μ w Expressed as the viscosity of water.

7. The method for dividing and evaluating driving units for water flooding effect in low permeability reservoirs according to claim 6, characterized in that: When the water flooding front does not reach point F, the water saturation of the FJ section is the initial water saturation S wi ; Among them, when the water flooding front is between points F and J, the water saturation S of the FJ section is FJ The specific expression is: Where x wf is the position of the water drive front, S wf is the water saturation at the water flooding front, S wF is the water saturation at point F; Represented as point F and x wf The average water saturation between wi It is represented by the initial water saturation; m is represented by the length of each segment after OD is evenly divided; Among them, after the water flooding front passes point J, the water saturation S FJ The specific expression is: Where S wJ Expressed as water saturation at point J.

8. The method for dividing and evaluating driving units for water flooding effect in low permeability reservoirs according to claim 1, characterized in that: The evaluation method described in S3 uses the k-means clustering method of the unsupervised learning algorithm to classify the surface flow ratio and water content data. The classification steps include: S3.1, the surface flow ratio data are classified into P1 cluster centers, that is, the surface flow ratio data set of all unit areas is divided into P1+1 subsets, and P1+1 types of driving units based on the surface flow ratio are obtained; S3.2, the water content data is classified into P2 cluster centers, that is, the water saturation data set of all unit areas is divided into P2+1 subsets, and P2+1 driving units based on water content are obtained; S3.3, when using the surface flow ratio and water content as the classification criteria, (P1+1)(P2+1) types of drive units are obtained; The classification method of the surface flow ratio and water cut data set can be divided, evaluated and adjusted according to actual production conditions to better meet the development process and subsequent production needs of the oil field.

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