A method and system for determining a reasonable lower limit of water drive for horizontal well development in an ultra-low permeability reservoir

Abstract

The application discloses a method and system for determining a reasonable water drive lower limit of horizontal well development in an ultra-low permeability reservoir, and belongs to the field of oilfield development. By obtaining the throat radius, the direct factor of restricting the fluid flow capacity, the reservoir percolation capacity can be better reflected; the higher the proportion of the number of fractures in the non-safe range, the greater the risk of water breakthrough in the fractured reservoir, and the less favorable the water injection development effect; the proportion of the water breakthrough oil production well can determine the adaptability of water injection development; according to the obtained yield, water injection development can be adopted when the yield is greater than 1; according to the average throat radius membership function, the number of fractures in the non-safe range membership function, the water breakthrough oil production well proportion membership function and the economic benefit membership function, the reservoir evaluation coefficient is obtained; when the reservoir evaluation coefficient is greater than the set value, the reservoir is suitable for horizontal well water injection development; when the reservoir evaluation coefficient is less than the set value, the reservoir is not suitable for horizontal well water injection development, and the horizontal well development mode of the ultra-low permeability reservoir can be determined.

Description

Technical Field

[0001] This invention belongs to the field of oilfield development technology and relates to a method and system for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs. Background Technology

[0002] As oilfield development deepens, production capacity construction is gradually shifting towards ultra-low permeability reservoirs with lower porosity and permeability. Currently, the main development methods for these reservoirs include long horizontal wells with pre-replenishment quasi-natural energy development and short horizontal wells with water injection for replenishment. When using pre-replenishment quasi-natural energy development, the development results vary due to differences in reservoir properties between development blocks, with significant differences in initial production. Furthermore, in blocks with good initial production, formation energy cannot be replenished in a timely manner, exhibiting rapid formation energy decay, resulting in low pressure levels, rapid production decline, difficulty in stabilizing production, and low EUR per well. Water injection development, if an effective displacement system is successfully established, can replenish formation energy to a certain extent, maintain overall pressure at a good level, thereby extending the stable production cycle of horizontal wells, improving the final recovery rate, and increasing economic benefits. However, some oil reservoirs are dense, with small throat radii and well-developed fractures, making it impossible to establish an effective displacement system. This results in a high-speed seepage channel between the water injection well and the horizontal well, leading to a long water injection effectiveness cycle, ineffective water injection, or even water breakthrough in the horizontal well, creating the risk of sudden water flooding. This not only fails to improve the recovery rate but also causes a significant decline in the production level of the horizontal well, which is counterproductive.

[0003] The remaining reserves of ultra-low permeability oil reservoirs are enormous and represent the main replacement resources for the next stage of oilfield development. Currently, there is no universally applicable standard for determining development methods. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of inaccurate applicability judgment for water injection development of ultra-low permeability reservoirs in the prior art, and to provide a method and system for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention proposes a method for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs, comprising the following steps:

[0007] Obtain the average throat radius, the percentage of fractures in the unsafe zone, the percentage of wells that have reached water and produced oil, and the profitability;

[0008] Determine the membership function of the average laryngeal radius based on the average laryngeal radius;

[0009] The membership function for the proportion of cracks in the unsafe area is determined based on the proportion of cracks in the unsafe area.

[0010] The membership function for the proportion of wells that have reached water production is determined based on the proportion of wells that have reached water production.

[0011] Determine the membership function of economic benefits based on the rate of return;

[0012] Based on the membership functions of average throat radius, number of fractures in unsafe areas, water-bearing wells, and economic benefits, reservoir evaluation coefficients are obtained to determine the development mode of horizontal wells in ultra-low permeability reservoirs.

[0013] Preferably, the method for obtaining the average larynx radius is as follows:

[0014]

[0015] Where k is the rock sample permeability, in mD; The average throat radius is expressed in μm.

[0016] Preferably, the method for obtaining the proportion of cracks outside the safe range is as follows:

[0017] The expression for the angle θ between the line connecting the fracture monitoring points of the injection well and the horizontal well and the direction of the maximum principal stress is as follows:

[0018]

[0019] Where A is the percentage of fractures within the unsafe range, α is the direction of the maximum principal stress in the formation (horizontal well azimuth is perpendicular to the maximum principal stress), β is the angle between the line connecting the injection well and the furthest target point of the horizontal well and the direction of the maximum principal stress, and n 总 Let n be the number of natural cracks, and n(α-β<θ<α+β) be the number of natural cracks outside the safe range.

[0020]

[0021] Where L1 is the well spacing × 0.5; L2 is the row spacing; and L3 is the distance from the fracture monitoring point to the end point of the horizontal well.

[0022] Preferably, the method for obtaining the proportion of wells that produce water is as follows:

[0023]

[0024] Where C represents the percentage of wells that have reached water and are producing oil, and W... 水 W represents the number of wells that produce water. 总 This represents the total number of oil wells.

[0025]

[0026] Where m is the increase in water content, and V i V represents the water cut of the oil well in the i-th month of production.i+1 The water cut of the oil well in the (i+1)th month of production;

[0027]

[0028] Wherein, ΔS is the rate of change in salt content in the produced fluid of the oil well when the injected water is clear water; S fw i S represents the salinity of the oil well in the i-th month of production, expressed in mg / L. fw i+1 The salinity of the oil well in the (i+1)th month of production, expressed in mg / L;

[0029] When the water cut increase m>75% and the injected water is clear water, and the salt content change rate ΔS in the produced fluid of the oil well is>30%, the number of oil wells that have encountered injected water is determined as the number of water-bearing oil wells W. 水 .

[0030] Preferably, the method for obtaining the rate of return is as follows:

[0031]

[0032] Where K is the rate of return, Q is the economic benefit coefficient per ton of oil, n is the proportion of oil and water wells in different well patterns, and C w The total cost of a single water well is given, and Δc represents the cumulative increase in oil production per well during the evaluation period compared to water injection development based on natural energy development.

[0033] Δc=C1-C2

[0034] C1 represents the cumulative oil production of a single well with supporting water injection wells in water injection development; C2 represents the cumulative oil production of a single well without supporting water injection wells in natural energy development.

[0035] Preferably, the method for determining the membership function U1 of the average laryngeal radius based on the average laryngeal radius is as follows:

[0036]

[0037] The method for determining the membership function U2 based on the proportion of cracks within the unsafe range is as follows:

[0038]

[0039] The method for determining the membership function U3 of the proportion of water-bearing oil wells based on the proportion of water-bearing oil wells is as follows:

[0040]

[0041] The method for determining the economic benefit membership function U4 based on the rate of return is as follows:

[0042]

[0043] in, Let A be the average throat radius, C be the percentage of fractures in the unsafe area, K be the percentage of wells that have reached water and are producing oil, and K be the rate of return.

[0044] Preferably, the method for obtaining the reservoir evaluation coefficient F(U) based on the membership function of average throat radius, the membership function of the proportion of fractures in the unsafe range, the membership function of the proportion of wells that have reached water and are producing oil, and the membership function of economic benefits is as follows:

[0045] F(U)=U4(k1×U1+k2×U2+k3×U3)

[0046] Where k1 is the first weight, k2 is the second weight, and k3 is the third weight. When F(U)>0.3, the reservoir is suitable for horizontal well water injection development; when F(U)<0.3, the reservoir is not suitable for horizontal well water injection development.

[0047] This invention proposes a system for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs, comprising:

[0048] The parameter acquisition module is used to acquire the average throat radius, the proportion of fractures in the unsafe range, the proportion of wells that have reached water and the rate of return.

[0049] The first membership function acquisition module is used to determine the average throat radius membership function based on the average throat radius.

[0050] The second membership function acquisition module is used to determine the membership function of the proportion of cracks in the unsafe range based on the proportion of cracks in the unsafe range.

[0051] The third membership function acquisition module is used to determine the membership function of the proportion of water-bearing oil wells based on the proportion of water-bearing oil wells.

[0052] The fourth membership function acquisition module is used to determine the economic benefit membership function based on the rate of return.

[0053] The reservoir evaluation coefficient acquisition module is used to obtain reservoir evaluation coefficients based on the membership functions of average throat radius, the proportion of fractures in the unsafe range, the proportion of water-bearing wells, and economic benefits, and to determine the development mode of horizontal wells in ultra-low permeability reservoirs.

[0054] A computer device includes a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of a method for determining a reasonable lower limit for water drive in the development of horizontal wells in ultra-low permeability reservoirs.

[0055] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of a method for determining a reasonable lower limit for water drive in the development of horizontal wells in ultra-low permeability reservoirs.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] This invention proposes a method for determining the reasonable lower limit of waterflooding for horizontal well development in ultra-low permeability reservoirs. By obtaining the throat radius, a direct factor restricting fluid flow capacity, it effectively reflects the reservoir's permeability. A higher proportion of fractures within the unsafe range indicates a greater risk of water breakthrough due to fractures, making water injection development less effective. The proportion of wells that produce water determines the suitability for water injection development. Based on the obtained rate of return, water injection development can be adopted when the rate of return is greater than 1. Reservoir evaluation coefficients are obtained based on the membership functions of average throat radius, the proportion of fractures within the unsafe range, the proportion of wells that produce water, and economic benefit. A reservoir evaluation coefficient greater than a set value indicates that the reservoir is suitable for horizontal well water injection development; a reservoir evaluation coefficient less than a set value indicates that the reservoir is not suitable for horizontal well water injection development, thus determining the appropriate horizontal well development method for ultra-low permeability reservoirs. Therefore, the method proposed in this invention solves the problem of inaccurate suitability assessment for water injection development in ultra-low permeability reservoirs in existing technologies.

[0058] This invention proposes a system for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs. By dividing the system into a parameter acquisition module, a first membership function acquisition module, a second membership function acquisition module, a third membership function acquisition module, a fourth membership function acquisition module, and a reservoir evaluation coefficient acquisition module, the modular approach makes each module independent of the others, facilitating unified management of each module. Attached Figure Description

[0059] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 The flowchart illustrates the method for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs according to this invention.

[0061] Figure 2 This is a scatter plot showing the different permeabilities and pore throat radii of the present invention.

[0062] Figure 3 This diagram illustrates the proportion of pore space controlled by throats of different sizes at different permeabilities, as presented in this invention.

[0063] Figure 4 This is a schematic diagram illustrating the calculation of the lower limit used in this invention.

[0064] Figure 5 This is the nuclear magnetic resonance spectrum of Y34-3 in this invention.

[0065] Figure 6 This is the nuclear magnetic resonance spectrum of Z211-5 of the present invention.

[0066] Figure 7 This is a schematic diagram of the crack in the unsafe zone of the present invention.

[0067] Figure 8 This is a graph showing the relationship between the proportion of cracks in the unsafe zone of region Y34 and the water content in this invention.

[0068] Figure 9 This is a production capacity curve of a single well with a depth of 100 meters for different types according to the present invention.

[0069] Figure 10 This is a schematic diagram illustrating the increased production effect of water injection development according to the present invention.

[0070] Figure 11 This invention provides a system diagram for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs. Detailed Implementation

[0071] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0072] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0073] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0074] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0075] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0076] The present invention will now be described in further detail with reference to the accompanying drawings:

[0077] This invention proposes a method for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs, such as... Figure 1 As shown, it includes the following steps:

[0078] S1. Obtain the average throat radius, the percentage of fractures in the unsafe range, the percentage of wells that produce water, and the profitability.

[0079] The method for obtaining the average larynx radius is as follows:

[0080]

[0081] Where k is the rock sample permeability, in mD; The average throat radius is expressed in μm.

[0082] The method for obtaining the percentage of cracks outside the safe range is as follows:

[0083] The expression for the angle θ between the line connecting the fracture monitoring points of the injection well and the horizontal well and the direction of the maximum principal stress is as follows:

[0084]

[0085] Where A is the percentage of fractures within the unsafe range, α is the direction of the maximum principal stress in the formation (horizontal well azimuth is perpendicular to the maximum principal stress), β is the angle between the line connecting the injection well and the furthest target point of the horizontal well and the direction of the maximum principal stress, and n 总 Let n be the number of natural cracks, and n(α-β<θ<α+β) be the number of natural cracks outside the safe range.

[0086]

[0087] Where L1 is the well spacing × 0.5; L2 is the row spacing; and L3 is the distance from the fracture monitoring point to the end point of the horizontal well.

[0088] The method for obtaining the percentage of wells that produce water is as follows:

[0089]

[0090] Where C represents the percentage of wells that have reached water and are producing oil, and W... 水 W represents the number of wells that produce water. 总 This represents the total number of oil wells.

[0091]

[0092] Where m is the increase in water content, and V i V represents the water cut of the oil well in the i-th month of production. i+1 The water cut of the oil well in the (i+1)th month of production;

[0093]

[0094] Wherein, ΔS is the rate of change in salt content in the produced fluid of the oil well when the injected water is clear water; S fw i S represents the salinity of the oil well in the i-th month of production, expressed in mg / L. fw i+1 The salinity of the oil well in the (i+1)th month of production, expressed in mg / L;

[0095] When the water cut increase m>75% and the injected water is clear water, and the salt content change rate ΔS in the produced fluid of the oil well is>30%, the number of oil wells that have encountered injected water is determined as the number of water-bearing oil wells W. 水 .

[0096] The methods for obtaining the rate of return are as follows:

[0097]

[0098] Where K is the rate of return, Q is the economic benefit coefficient per ton of oil, n is the proportion of oil and water wells in different well patterns, and C w The total cost of a single water well is given, and Δc represents the increase in cumulative oil production per well during the evaluation period compared to natural energy development.

[0099] Δc=C1-C2

[0100] C1 represents the cumulative oil production of a single well with supporting water injection wells in water injection development; C2 represents the cumulative oil production of a single well without supporting water injection wells in natural energy development.

[0101] S2. Determine the membership function of the average throat radius based on the average throat radius;

[0102] The method for determining the membership function U1 of the average laryngeal radius based on the average laryngeal radius is as follows:

[0103]

[0104] S3. Determine the membership function of the proportion of cracks in the unsafe area based on the proportion of cracks in the unsafe area;

[0105] The method for determining the membership function U2 based on the proportion of cracks within the unsafe range is as follows:

[0106]

[0107] S4. Determine the membership function of the proportion of water-bearing oil wells based on the proportion of water-bearing oil wells;

[0108] The method for determining the membership function U3 of the proportion of water-bearing oil wells based on the proportion of water-bearing oil wells is as follows:

[0109]

[0110] S5. Determine the membership function of economic benefits based on the rate of return;

[0111] The method for determining the economic benefit membership function U4 based on the rate of return is as follows:

[0112]

[0113] in, Let A be the average throat radius, C be the percentage of fractures in the unsafe area, K be the percentage of wells that have reached water and are producing oil, and K be the rate of return.

[0114] S6. Based on the membership functions of average throat radius, number of fractures in the unsafe range, water-bearing wells, and economic benefits, obtain the reservoir evaluation coefficients and determine the development mode of horizontal wells in ultra-low permeability reservoirs.

[0115] The method for obtaining the reservoir evaluation coefficient F(U) based on the membership functions of average throat radius, the proportion of fractures in the unsafe range, the proportion of wells that have reached water and are producing oil, and economic benefits is as follows:

[0116] F(U)=U4(k1×U1+k2×U2+k3×U3)

[0117] Where k1 is the first weight, k2 is the second weight, and k3 is the third weight. When F(U)>0.3, the reservoir is suitable for horizontal well water injection development; when F(U)<0.3, the reservoir is not suitable for horizontal well water injection development.

[0118] This invention proposes a method for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs, the specific steps of which are as follows:

[0119] Step 1: Determine the effectiveness of water injection development based on the throat radius.

[0120] The size of the throat radius is a direct factor restricting fluid flow capacity and can reflect the reservoir's permeability.

[0121] (1) Penetration rate

[0122] In ultra-low permeability reservoirs, submicron-sized throats occupy a certain proportion of the reservoir space. When the permeability reaches a certain limit, the proportion of large throat pore space available for fluid movement begins to increase significantly. Based on field practice, permeability and throat radius show a positive correlation. The linear regression equation between the average throat radius and permeability is obtained as follows:

[0123]

[0124] Where k is the rock sample permeability, in mD; The average throat radius is expressed in μm. Lithological permeability k is related to the average throat radius. There is a certain correlation; lithological permeability k data is relatively easy to obtain. Based on this equation, the throat radius of the rock sample can be determined. Therefore, the average throat radius of the reservoir can be calculated based on the readily available gas permeability k data.

[0125] like Figure 2 and Figure 3 As shown, for reservoirs with rock sample permeability k between 0.1 and 0.3 mD, when the permeability k reaches above 0.18 mD, the percentage of movable fluid controlled by throats larger than 1 μm begins to increase significantly, and the space that can be driven by water also increases accordingly. The evaluation throat radius corresponding to 0.18 mD is 0.15 μm.

[0126] (2) Fluid distribution boundary

[0127] The throat radius is the boundary between movable and immovable fluids. For example... Figure 5 As shown, in nuclear magnetic resonance (NMR) experiments, the relaxation time T2 reflects the environment of hydrogen protons inside the sample, i.e., the internal structure of the pores. The position of the peak in the T2 spectrum reflects the size of the pores, and the area of ​​the peak reflects the pore volume. Through NMR displacement experiments under constant and gradually increasing displacement pressures, the pore throat kinetic characteristics under different displacement methods were analyzed. The cutoff time of relaxation time T2 is the dividing line between movable and immovable fluids; pore throats with a value greater than this are considered movable fluids, and those with a value less than this are considered immovable fluids.

[0128] like Figure 6 As shown, the throat radius corresponding to the T2 cutoff time was obtained by nuclear magnetic resonance experiment as 0.15 μm. This throat radius can be regarded as the dividing line between movable fluid and immovable fluid. When the throat radius is less than 0.15 μm, the injected water cannot flow in it, and thus the water-driven oil effect cannot be achieved. Therefore, the water-driven limit can be set at 0.15 μm.

[0129] Based on the actual production conditions on site and the results of indoor experiments, the reasonable water drive limit for the throat radius of ultra-low permeability reservoirs is determined to be 0.15 μm.

[0130] Step 2: Determine the ease of water drive effectiveness based on the degree of coupling of natural fractures.

[0131] The injected medium will preferentially migrate along channels with low resistance and high permeability (such as fractures). If there are too many high-permeability channels, the injected medium will not be able to displace the crude oil. The throat radius determines whether the reservoir is suitable for water injection development, while natural fractures determine the effectiveness of water injection development.

[0132] Studies of fractures using methods such as fracture monitoring and imaging logging have revealed a strong correlation between the direction of artificial fractures and the direction of in-situ stress. During formation fracturing, the artificial fractures produced are often extensions of natural fractures or extensions of the principal stress direction of the formation. Figure 7 As shown, to improve the fracturing effect, the horizontal well orientation is selected perpendicular to the direction of the maximum principal stress α. A certain well spacing L1 and row spacing L2 can ensure that the artificial fractures will not connect the production wells and injection wells when extending along the principal stress, thus preventing water flooding. Secondly, the orientation of natural fractures is also important. When the angle between the orientation of natural fractures and the geostress is too large and there are many natural fractures, even if the reservoir has good compressibility, good fluid properties, and uniform pore throat distribution, it can still cause sudden water breakthrough in the wells, affecting the single-well EUR and reducing the reservoir development effect.

[0133] Therefore, the degree and direction of natural crack development are key factors affecting water injection development. The more natural cracks develop, the higher the proportion of cracks in the unsafe range, the greater the risk of water seepage due to cracks, and the less effective the water injection development will be.

[0134] The expression for the angle θ between the line connecting the fracture monitoring points of the injection well and the horizontal well and the direction of the maximum principal stress is as follows:

[0135]

[0136] Where L1 is the well spacing × 0.5, m; L2 is the row spacing, m; and L3 is the distance from the fracture monitoring point to the end point of the horizontal well.

[0137]

[0138] Where α is the direction of the maximum principal stress in the formation, the horizontal well azimuth is perpendicular to the maximum principal stress, and the wellbore direction is also α; β is the angle between the line connecting the farthest target point of the injection well and the horizontal well and the direction of the maximum principal stress, and n 总 Let n be the number of natural cracks, n(α-β<θ<α+β) be the number of natural cracks outside the safe range, and A be the percentage of cracks outside the safe range.

[0139] like Figure 8 As shown, by statistically analyzing the number of rapid fractures in zones Y34, H220, and Z211, it was found that when the proportion of fractures (A value) in the unsafe range is greater than 55%, the proportion of wells that reach water increases significantly.

[0140] Step 3: Evaluate the adaptability of water injection development based on the dynamic characteristics of oil wells.

[0141] Fracturing oil and water wells can improve reservoir properties and extend the length of natural fractures, but it carries the risk of directly connecting injection wells and production wells. After preliminary assessment of the feasibility of formation water injection in steps 1 and 2, a small-group test is conducted, with W production wells. 总 The adaptability of water injection development can be further evaluated through monitoring the dynamic characteristics of oil wells.

[0142] When the water cut increase m > 75% and the salinity change rate ΔS > 30%, the oil well can be considered to have injected water, the quantity of which is W. 水 When the proportion of wells producing water (C) is greater than 60%, the adaptability of water injection development is poor.

[0143]

[0144] Where m is the increase in water content, and V i V represents the water cut of the oil well in the i-th month of production. i+1 The water cut of the oil well in the (i+1)th month of production.

[0145]

[0146] Where ΔS is the rate of change in salt content in the produced fluid of the oil well when the injected water is clean water; S fw i The salinity of the oil well in the i-th month of production, in mg / L; S fw i+1 The salinity of the oil well in the (i+1)th month of production, in mg / L.

[0147] The water cut increase m and the salt content change rate ΔS in the produced fluid of the oil well when the injected water is clear water are the conditions for determining whether it is a water injection well.

[0148]

[0149] Where C represents the percentage of wells that have reached water and are producing oil, and W... 水 W represents the number of wells that produce water.总 This represents the total number of oil wells.

[0150] Step 4: Calculate economic benefits

[0151] Water injection development aims to increase economic benefits. If the effectiveness of water injection development is low, then this development method loses its meaning. Reasonable water injection during oil well development can improve the stable production of oil wells, transforming them into stable production types, ultimately achieving higher cumulative oil production per well and thus better economic benefits.

[0152] The wells implemented in Zone Z211 can be categorized into three types: stable-type (with water injection development), declining-type (without water injection development), and natural energy development (without water injection development). Among these, the stable-type wells with declining production show the best results, while natural energy development exhibits a faster decline, with the single-well productivity per 100 meters after 16 months being lower than that of the declining-type wells developed with water injection. During the evaluation period, the stable-type wells showed a higher cumulative oil production increase compared to natural energy development, with the increased production yielding a greater return than the investment in water injection wells, resulting in better economic benefits and making water injection development a viable option. Conversely, the declining-type wells showed less effective production increases with water injection, with the increased production yielding a lesser return than the investment in water injection wells, making them less economically viable than natural energy development. Figure 9 As shown.

[0153] Δc=C1-C2

[0154] C1 represents water injection development, with the cumulative oil production of a single well equipped with water injection wells; C2 represents natural energy development, with the cumulative oil production of a single well without water injection wells; Δc represents the increase in cumulative oil production per well during the evaluation period compared to natural energy development, such as... Figure 10 As shown, under the natural energy development model, the cumulative oil production of a single well changes over time.

[0155] When the rate of return K is greater than 1, water injection development can be adopted:

[0156]

[0157] Where Q is the economic benefit coefficient per ton of oil, n is the proportion of oil and water wells in different well patterns, and C w The total cost for a single well.

[0158] Step 5: Determine the composite index

[0159] (1) Define the membership function

[0160] Average throat radius of ultra-low permeability reservoirs The larger the value, the shorter the effective development cycle and the better the implementation results of horizontal well water injection. The membership function U1 for the average throat radius is determined as follows:

[0161]

[0162] The higher the proportion (A) of fractures within the unsafe zone in ultra-low permeability reservoirs, the higher the risk of water breakthrough in the production wells. The membership function U2 for determining the proportion of fractures within the unsafe zone is as follows:

[0163]

[0164] The higher the proportion (C) of water-bearing wells in ultra-low permeability reservoirs, the lower the average well production in the block, and the worse the development effect. The membership function U3 for determining the proportion of water-bearing wells is as follows:

[0165]

[0166] When the economic benefit K of an ultra-low permeability reservoir is greater than 1, water injection development is economically feasible. The membership function U4 for determining the economic benefit is as follows:

[0167]

[0168] (2) Establish an evaluation model

[0169] A multi-level mathematical evaluation model is established using fuzzy hierarchical analysis, comprising four indicators: average throat radius membership function U1, the proportion of fractures within the unsafe range membership function U2, the proportion of wells producing water through water membership function U3, and economic benefit membership function U4. Economic benefit is the decisive factor. Reservoir evaluation coefficient F(U):

[0170] F(U)=U4(k1×U1+k2×U2+k3×U3)

[0171] Wherein, k1 is the first weight, k2 is the second weight, and k3 is the third weight. The relative importance of each parameter is compared pairwise. When assigning values ​​to the proportional scale, a scale of 0 to 4 is used for evaluation, that is, extremely important 3 to 4, very important 2 to 3, slightly important 1 to 2, slightly unimportant 1 / 2 to 1, unimportant 1 / 2 to 1 / 3, and extremely unimportant less than or equal to 1 / 3. Finally, the eigenvector method is used to obtain the ranking weight value from the judgment matrix.

[0172] When the reservoir evaluation coefficient F(U) > 0.3, the reservoir is suitable for horizontal well water injection development;

[0173] When the reservoir evaluation coefficient F(U) < 0.3, the reservoir is not suitable for horizontal well water injection development.

[0174] After obtaining parameters such as pore throat radius, natural fractures, dynamic water breakthrough characteristics, and economic benefits of the block, this method can quickly and accurately determine the development mode of horizontal wells in ultra-low permeability reservoirs, effectively increase the EUR of a single well, and improve the development effect.

[0175] Using this method, the development effect of two oil fields was successfully verified. Both oil fields adopted horizontal well water injection development. The first oil field had a U value greater than 0.3, and the water injection development effect was good; the second oil field had a U value less than 0.3, and the water injection development effect was not ideal.

[0176] This invention proposes a system for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs, such as... Figure 11 As shown, it includes: a parameter acquisition module, a first membership function acquisition module, a second membership function acquisition module, a third membership function acquisition module, a fourth membership function acquisition module, and a reservoir evaluation coefficient acquisition module;

[0177] The parameter acquisition module is used to obtain the average throat radius, the proportion of fractures in the non-safe range, the proportion of wells that have reached water and the rate of return.

[0178] The first membership function acquisition module is used to determine the average throat radius membership function based on the average throat radius;

[0179] The second membership function acquisition module is used to determine the membership function of the proportion of cracks in the unsafe range based on the proportion of cracks in the unsafe range.

[0180] The third membership function acquisition module is used to determine the membership function of the proportion of water-bearing oil wells based on the proportion of water-bearing oil wells.

[0181] The fourth membership function acquisition module is used to determine the economic benefit membership function based on the rate of return.

[0182] The reservoir evaluation coefficient acquisition module is used to obtain reservoir evaluation coefficients based on the membership functions of average throat radius, the proportion of fractures in the unsafe range, the proportion of wells that produce water, and economic benefits, and to determine the development mode of horizontal wells in ultra-low permeability reservoirs.

[0183] An embodiment of the present invention provides a terminal device comprising: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps in the various method embodiments described above. Alternatively, when the processor executes the computer program, it implements the functions of each module / unit in the various device embodiments described above.

[0184] The computer program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present invention.

[0185] The terminal device may be a desktop computer, laptop, handheld computer, or cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0186] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0187] The memory can be used to store the computer program and / or module. The processor implements various functions of the terminal device by running or executing the computer program and / or module stored in the memory and calling the data stored in the memory.

[0188] If the modules / units integrated into the terminal device are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0189] This invention proposes a method and system for determining the reasonable lower limit of waterflooding for horizontal well development in ultra-low permeability reservoirs. Based on the collection of reservoir characteristics and development status of the target reservoir, and according to the reservoir characteristics of ultra-low permeability reservoirs, easily obtainable and highly reliable data are selected as evaluation parameters. An evaluation system is established based on existing experimental conclusions and actual production data to determine the reasonable water injection limit for horizontal well development in ultra-low permeability reservoirs, thus providing technical reserves for the efficient development of such reservoirs. After obtaining parameters such as pore throat radius, natural fractures, dynamic water breakthrough characteristics, and economic benefits of the block, this method can quickly and accurately determine the development mode of horizontal wells in ultra-low permeability reservoirs, effectively increasing the EUR (Effective Water Injection) of a single well and improving development efficiency. It effectively optimizes development technology policies before oilfield production, providing a strong basis for efficient oilfield development.

[0190] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the reasonable lower limit of waterflooding for horizontal well development in ultra-low permeability reservoirs, characterized in that, Includes the following steps: Obtain the average throat radius, the percentage of fractures in the unsafe zone, the percentage of wells that have reached water and produced oil, and the profitability; Determine the membership function of the average laryngeal radius based on the average laryngeal radius; The membership function for the proportion of cracks in the unsafe area is determined based on the proportion of cracks in the unsafe area. The membership function for the proportion of wells that have reached water production is determined based on the proportion of wells that have reached water production. Determine the membership function of economic benefits based on the rate of return; Based on the membership functions of average throat radius, number of fractures in unsafe areas, water-bearing wells, and economic benefits, reservoir evaluation coefficients are obtained to determine the development mode of horizontal wells in ultra-low permeability reservoirs. The method for obtaining the average larynx radius is as follows: in, The rock sample permeability is expressed in mD. This represents the average throat radius, in μm. The method for obtaining the percentage of cracks outside the safe range is as follows: The angle between the line connecting the fracture monitoring points of the injection well and the horizontal well and the direction of the maximum principal stress. The expression is as follows: in, This represents the percentage of cracks outside the safe zone. The direction of the maximum principal stress in the formation is indicated by the orientation of the horizontal well, which is perpendicular to the maximum principal stress. The angle between the line connecting the furthest target point of the injection well and the horizontal well and the direction of the maximum principal stress. This represents the number of natural cracks. This refers to the number of natural cracks outside the safe range; in, It is the well spacing × 0.5; This refers to the row spacing; This is the distance from the fracture monitoring point to the endpoint of the horizontal well.

2. The method for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs according to claim 1, characterized in that, The method for obtaining the percentage of wells that produce water is as follows: in, The percentage of wells that produce water. The number of wells that produce water. This represents the total number of oil wells. in, The increase in water content, For the production of oil wells Moisture content over months For the production of oil wells Moisture content over one month; in, The rate of change in salt content in the produced fluid of an oil well when the injected water is clear water; For the production of oil wells Salt content over a month, expressed in mg / L; For the production of oil wells Salt content over a month, expressed in mg / L; When the water content increases >75%, and the injected water is clean water, the rate of change in salt content in the produced fluid of the oil well When the water injection rate is greater than 30%, the number of wells that have encountered water is determined as the number of wells that have encountered water. .

3. The method for determining the reasonable lower limit of waterflooding for horizontal well development in ultra-low permeability reservoirs according to claim 1, characterized in that, The methods for obtaining the rate of return are as follows: in, For the rate of return, The economic benefit coefficient per ton of oil. The ratio of oil wells to water wells in different well patterns. For the total cost of a single well, To increase the cumulative oil production per well during the evaluation period compared to water injection development during natural energy development; in, Cumulative oil production of a single well with supporting water injection wells for water injection development; Cumulative oil production of a single well without supporting water injection wells for natural energy development.

4. The method for determining the reasonable lower limit of waterflooding for horizontal well development in ultra-low permeability reservoirs according to claim 1, characterized in that, Determine the membership function of the average laryngeal radius based on the average laryngeal radius. The method is as follows: Determine the membership function of the proportion of cracks in the unsafe area based on the proportion of cracks in the unsafe area. The method is as follows: Determine the membership function of the proportion of water-bearing oil wells based on the proportion of water-bearing oil wells. The method is as follows: Determine the membership function of economic benefits based on the rate of return. The method is as follows: in, This represents the average throat radius. This represents the percentage of cracks outside the safe zone. The percentage of wells that produce water. This represents the rate of return.

5. The method for determining the reasonable lower limit of water drive for horizontal well development in ultra-low permeability reservoirs according to claim 1, characterized in that, Reservoir evaluation coefficients are obtained based on the membership functions of average throat radius, the proportion of fractures in the unsafe zone, the proportion of wells that have reached water and are producing oil, and economic benefits. The method is as follows: in, As the first weight, As the second weight, As the third weight, when When the value is >0.3, the reservoir is suitable for horizontal well water injection development; when When the value is less than 0.3, the reservoir is not suitable for horizontal well water injection development.

6. A system for determining the reasonable lower limit of waterflooding for horizontal well development in ultra-low permeability reservoirs, characterized in that, The method for determining the reasonable water drive lower limit for horizontal well development in ultra-low permeability reservoirs, as described in any one of claims 1 to 5, includes: The parameter acquisition module is used to acquire the average throat radius, the proportion of fractures in the unsafe range, the proportion of wells that have reached water and the rate of return. The first membership function acquisition module is used to determine the average throat radius membership function based on the average throat radius. The second membership function acquisition module is used to determine the membership function of the proportion of cracks in the unsafe range based on the proportion of cracks in the unsafe range. The third membership function acquisition module is used to determine the membership function of the proportion of water-bearing oil wells based on the proportion of water-bearing oil wells. The fourth membership function acquisition module is used to determine the economic benefit membership function based on the rate of return. The reservoir evaluation coefficient acquisition module is used to obtain reservoir evaluation coefficients based on the membership functions of average throat radius, the proportion of fractures in the unsafe range, the proportion of water-bearing wells, and economic benefits, and to determine the development mode of horizontal wells in ultra-low permeability reservoirs.

7. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes a computer program, it implements the steps of the method for determining the reasonable lower limit of water drive for the development of horizontal wells in ultra-low permeability reservoirs as described in any one of claims 1 to 5.

8. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for determining the reasonable water drive lower limit for the development of horizontal wells in ultra-low permeability reservoirs as described in any one of claims 1 to 5.

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