Method for evaluating water injection development effect of low-grade oil reservoir

Abstract

The application provides a low-grade oil reservoir water injection development effect evaluation method, comprising the following steps: S1, collecting core scale limit oil displacement efficiency data; S2, collecting well pattern controlled reserve degree data; S3, calculating sweep efficiency of the low-grade water drive oil reservoir; S4, correcting the sweep efficiency according to the changes of reservoir physical property parameters caused by near-well pollution and reservoir energy decline; and S5, calculating the reference recovery rate and evaluating the development effect. The application can effectively avoid collecting and arranging a large number of cumbersome production dynamic data, fully utilize the flow characteristics and dynamic physical property parameter evolution of the low-grade oil reservoir, accurately evaluate the development effect of the low-grade oil reservoir, and be beneficial to efficient development of the low-grade oil reservoir.

Description

A method for evaluating the effectiveness of water injection development in low-grade oil reservoirs Technical Field

[0001] This invention belongs to the field of oil and gas field development engineering, and specifically relates to a method for evaluating the effect of water injection development in low-grade oil reservoirs. Background Technology

[0002] Low-grade oil reservoirs are characterized by low reserves, low recovery rates, and low production rates, and are often developed using waterflooding. Currently, the main methods for evaluating the development effectiveness of conventional waterflooded reservoirs include: (1) industry standard method, (2) development curve evaluation method, and (3) recovery rate prediction evaluation method. These methods combine industry standards, field production data, or historical production data to evaluate the development of conventional waterflooded reservoirs, but none of these evaluation methods can achieve true objectivity and accuracy.

[0003] Current conventional waterflood reservoir development evaluation methods have the following problems: industry standards select a wide variety of indicators, which are difficult to operate and are greatly affected by human factors; when drawing development curves, different analysts may obtain contradictory evaluation results due to different focuses of factors, resulting in poor generalizability; the recovery rate prediction and evaluation steps are cumbersome and it is difficult to take into account the fluid flow characteristics of low-grade reservoirs.

[0004] Compared with conventional waterflooding, waterflooding development of low-grade reservoirs has poor well pattern adaptability, low level of perfection, and large differences in the effectiveness of water injection. Therefore, current evaluation methods are difficult to be comprehensive and accurate. Summary of the Invention

[0005] This application provides a method for evaluating the development effect of water injection in low-grade oil reservoirs. It can effectively avoid collecting and sorting out a large amount of cumbersome production dynamic data, make full use of the flow characteristics and dynamic physical property parameter evolution of low-grade oil reservoirs, and accurately evaluate the development effect of low-grade oil reservoirs, which is conducive to the efficient development of low-grade oil reservoirs.

[0006] This application provides a method for evaluating the effectiveness of water injection development in low-grade oil reservoirs, including:

[0007] S1, collect core-scale data on ultimate displacement efficiency;

[0008] S2, collects data on the degree of well network control of reserves;

[0009] S3, calculate the sweep efficiency of low-grade water-drive reservoirs;

[0010] S4, The sweep efficiency is corrected based on the changes in reservoir physical parameters caused by near-wellbore contamination and reservoir energy decline;

[0011] S5, calculate the reference recovery rate and evaluate the development effect.

[0012] Step S1 includes: using representative cores from the target block of the low-grade oil reservoir, collecting and organizing waterflooding experimental data of such cores, and obtaining the ultimate oil displacement efficiency at the core scale.

[0013] Step S1 includes:

[0014] S1.1, Place the core into the core holder, evacuate the vacuum, and fully saturate the core with simulated oil. Record the mass m of the saturated oil phase. ini ;

[0015] S1.2, inject formation water into one side of the core holder, injecting water at a uniform rate of 50 times the core pore volume;

[0016] S1.3, records the volume V of water injected into the core at different times t. w The mass m of the simulated oil displaced from the core out Combined with pore volume V φ Calculate the cumulative displacement pore volume ratio N corresponding to time t. PV With oil displacement efficiency ED,

[0017] N PV =V w / V φ (1)

[0018] ED = m out / m ini (2)

[0019] S1.4, using the collected cumulative displacement pore volume multiple N PV Plot the relationship curve between the oil displacement efficiency (ED) data and the oil displacement efficiency data.

[0020] S1.5, based on N PV The relationship curve between ED and the limiting oil displacement efficiency is determined by analyzing the changing trend of the curves.

[0021] Step S1.5 includes: [The text abruptly ends here, so the translation stops.] PV The relationship between the displacement efficiency ED and the cumulative displacement pore volume ratio shows that the displacement efficiency increases with the increase of the cumulative displacement pore volume ratio N, until it reaches a limiting stable value, that is, the displacement efficiency ED no longer increases with the cumulative displacement pore volume ratio N. PV As the number of cores increases, the oil displacement efficiency at this point becomes the limiting oil displacement efficiency R at the core scale. 理想 .

[0022] Step S2 includes: dividing the target block into development units, collecting the well network controlled reserves and geological reserves of each development unit, and calculating the degree of well network controlled reserves.

[0023] Step S2 includes:

[0024] S2.1, reservoirs that meet the first preset condition in terms of reservoir properties, are located in the same hydrodynamic system, belong to the same set of development layers and are contiguous in the region, and whose production time meets the second preset condition are classified as a development unit.

[0025] S2.2, Collect the geological reserves Ω of each development unit. i Ω of well network controlled reserves within each unit 井网，i Calculate the well network control reserve level B for each unit. 井网，i The calculation method is as follows

[0026] B 井网，i =Ω 井网，i / Ω i (3).

[0027] Step S3 includes: based on the collection of production pressure, injection pressure, start-up pressure gradient, and well spacing of low-grade oil reservoirs, calculating the water drive sweep efficiency by trial calculation of the maximum sweep angle of water drive.

[0028] Step S3 includes:

[0029] S3.1, Combine the oil and water well layout method to statistically analyze the location information of oil and water wells in the target block, and calculate the average oil and water well spacing d;

[0030] S3.2, Collect the starting pressure gradient test data of the low-grade oil reservoir core of the target block to obtain the starting pressure gradient λ of the reservoir fluid flow;

[0031] S3.3, Combine the production dynamic data of oil and water wells to obtain the bottom hole pressure p of the water injection well. i Production well bottom pressure p w ;

[0032] S3.4, Combining core porosity and permeability test data with formation fluid property data, the reservoir permeability k and formation fluid mixed viscosity μ are obtained, where the mixed viscosity μ is calculated as follows:

[0033]

[0034] Where: μ o Oil phase viscosity, mPa·s; μ w The viscosity of the aqueous phase is mPa·s; S iw S represents the instantaneous water saturation. iwc To constrain water saturation, S ior Residual oil saturation;

[0035] S3.5, using a trial-and-error method, calculate the maximum value α of the water drive sweep angle α that conforms to the following formula. max :

[0036]

[0037] The parameters and their units in the formula are as follows: k is the formation permeability, 10 -3 μm 2 μ is the viscosity of the formation mixed fluid, mPa·s; λ is the starting pressure gradient, MPa / m; p i The bottom pressure of the injection well is 0.1 MPa; p w The oil well pressure is 0.1 MPa.

[0038] S3.6, Calculate the sweep coefficient B 波及 The calculation formula is:

[0039] B 波及 =2α max / π (6).

[0040] Step S4 includes:

[0041] S4.1 Collect stress sensitivity test data of target blocks of low-grade oil reservoirs, analyze the permeability change law when reservoir energy decreases, and correct the current permeability of the reservoir with reference to the current reservoir energy level in the block.

[0042] S4.2, Considering near-wellbore contamination, collect the additional pressure drop Δp caused by near-wellbore contamination. s ;

[0043] S4.3, considering stress sensitivity and near-wellbore contamination to correct for the sweep efficiency, the calculation method is the same as in step S3 initially, and α is calculated in step 3.5. max When the discriminant formula is changed to:

[0044]

[0045] Using the corrected α max The calculated sweep efficiency is denoted as EV. eff ;

[0046] S4.4, Calculate the correction coefficient B considering the dynamic evolution of physical properties. 演变

[0047] B 演变 =EV eff / B 波及 (8).

[0048] 10. The evaluation method for the water injection development effect of low - grade reservoirs according to claim 1 or 2, characterized in that step S5 includes:

[0049] S5.1, calculate the reference recovery rate R 参考 , and the calculation method is:

[0050] R 参考 = R 理想 ×B 井网 ×B 波及 ×B 演变 (9)

[0051] S5.2, combine the current production degree of the target block and compare it with the reference recovery rate calculated in step S5.1 to make an evaluation result. When the production degree of the target low - grade reservoir is lower than 60% of the reference recovery rate, the development effect of the target reservoir is L1. When the production degree of the target low - grade reservoir is between 60% and 80% of the reference recovery rate, the development effect of the target reservoir is L2. When the production degree of the target low - grade reservoir is higher than 80% of the reference recovery rate, the development effect of the target reservoir is L3, where L1 < L2 < L3, and the larger the value of the development effect, the better the development effect.

[0052] The evaluation method for the water injection development effect of low - grade reservoirs in the embodiments of the present application has the following beneficial effects:

[0053] 1. It avoids the staff from collecting and sorting out a large amount of production dynamic data such as liquid production and oil production, overcomes the strong dependence on on - site production dynamic data in most current reservoir development effect evaluations, greatly improves the work efficiency of the staff, and saves the time for data sorting and valuable computing and storage resources;

[0054] 2. It makes full use of various test data of the cores of low - grade reservoirs in the current on - site exploration and development stage. The workload of collecting and sorting out such data is relatively small, and it can fully reflect the geological and fluid seepage characteristics of low - grade reservoirs. Starting from the microscopic structure of the reservoir, it fully considers various factors affecting the water - flooding development effect during the development process, especially considering the dynamic evolution mechanism of reservoir physical properties during the reservoir development process, and efficiently and accurately evaluates the water injection development effect of low - grade reservoirs, making up for the shortcoming of mainly static evaluations in most current evaluation methods. The present invention provides a basis for formulating reasonable development plans and treatment measures for low - grade reservoirs, which is beneficial to the efficient development of low - grade reservoirs. Brief Description of the Drawings

[0055] Figure 1 is a schematic flow chart of the evaluation method for the water injection development effect of low - grade reservoirs in the embodiments of the present application;

[0056] Figure 2 is a schematic diagram of the ultimate oil - displacement efficiency obtained from the water - flooding experiment;

[0057] Figure 3a is a well network deployment plan of development unit 1; Figure 3b is a well network deployment plan of development unit 2;

[0058] Figure 4 is a schematic diagram of permeability changes under different reservoir energy reduction levels. Detailed Implementation

[0059] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0060] In the following description, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The following description provides multiple embodiments of the invention, which can be substituted or combined with each other. Therefore, this application can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then this application should also be considered to include embodiments containing one or more other possible combinations of features A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0061] Example 1

[0062] As shown in Figure 1, the evaluation method for the water injection development effect of low-grade oil reservoirs in this application includes: S1, collecting core-scale ultimate displacement efficiency data; S2, collecting well pattern control reserve degree data; S3, calculating the sweep efficiency of low-grade water-driven oil reservoirs; S4, correcting the sweep efficiency based on changes in reservoir physical parameters caused by near-wellbore contamination and reservoir energy decline; and S5, calculating the reference recovery rate and evaluating the development effect.

[0063] This application can accurately evaluate the development effect of low-grade reservoirs, which is conducive to the efficient development of low-grade reservoirs.

[0064] Example 2

[0065] Existing methods for evaluating development effectiveness mostly rely on collecting field production dynamic data from target or reference wells. These methods require high completeness and reliability of the production dynamic data and involve a large volume of data collection and processing. Furthermore, due to the unique geological development characteristics of low-grade reservoirs, existing methods struggle to consider fluid flow patterns within them, limiting the applicability of effective evaluation methods for low-grade reservoirs. On the other hand, core flow experiments conducted on target reservoirs during the exploration and development of low-grade reservoirs typically reveal the essential flow patterns of reservoir fluids, but this data is not fully utilized in existing development evaluation methods. Therefore, this invention proposes a novel method for evaluating the effectiveness of water injection development in low-grade reservoirs, based on core flow experiments and considering the reservoir's development characteristics. This method effectively avoids collecting and processing large amounts of cumbersome production dynamic data, fully utilizes the flow characteristics and dynamic physical property evolution of low-grade reservoirs, and accurately evaluates the development effectiveness of low-grade reservoirs, thus facilitating their efficient development.

[0066] The evaluation method for water injection development of low-grade reservoirs in this application includes: (1) collecting core-scale data on the ultimate displacement efficiency: using representative cores from the target block of the low-grade reservoir, collecting and organizing water-drive experimental data of such cores to obtain the ultimate displacement efficiency at the core scale. (2) collecting data on the degree of well network control of reserves: dividing the target block into development units, collecting the well network control reserves and geological reserves of each development unit, and calculating the degree of well network control of reserves. (3) calculating the sweep efficiency of low-grade water-drive reservoirs: based on collecting the production pressure, injection pressure, starting pressure gradient, and well spacing of low-grade reservoirs, calculating the water-drive sweep efficiency by trial calculation of the maximum sweep angle of water drive. (4) correcting the influence of dynamic physical property evolution on the sweep efficiency: considering the changes in reservoir physical property parameters caused by near-well contamination and reservoir energy decline, correcting the sweep efficiency. (5) calculating the reference recovery rate and evaluating the development effect. The details are introduced below.

[0067] (1) Collect core-scale data on the ultimate oil displacement efficiency. Water flooding experiment refers to core displacement experiment conducted using cores from low-grade oil reservoir blocks. The specific implementation steps are as follows:

[0068] (1.1) The core was placed in the core holder, and after vacuuming, the core was fully saturated with simulated oil. The mass m of the oil phase that entered the core was recorded. ini ;

[0069] (1.2) Inject formation water into one side of the core holder at a uniform speed, injecting water at a rate of 50 times the core pore volume;

[0070] (1.3) Record the volume V of water injected into the core at different times t. wThe mass m of the simulated oil displaced from the core out Combined with pore volume V φ Calculate the cumulative displacement pore volume ratio N corresponding to time t. PV With oil displacement efficiency ED.

[0071] N PV =V w / V φ (1)

[0072] ED = m out / m ini (2)

[0073] (1.4) Using the collected cumulative displacement pore volume multiple N PV Plot the relationship curve between the oil displacement efficiency (ED) data and the oil displacement efficiency data.

[0074] (1.5) Based on N PV The relationship between ED and the limiting oil displacement efficiency was determined by analyzing their respective curves. The relationship shows that as the cumulative displacement pore volume ratio increases, the oil displacement efficiency initially increases significantly, then the growth gradually levels off until it reaches a limiting stable value, where the oil displacement efficiency ED no longer increases with the cumulative displacement pore volume ratio N. PV As the number of cores increases, the oil displacement efficiency at this point becomes the limiting oil displacement efficiency R at the core scale. 理想 .

[0075] (2) The method for collecting well network control reserve level data, dividing development units, and calculating the well network reserve control level of each unit is as follows:

[0076] (2.1) For the same low-grade oil reservoir, reservoirs with similar reservoir properties, located in the same hydrodynamic system, in the same set of development layers, and in contiguous regional locations and with similar production times are divided into a development unit.

[0077] (2.2) Collect the geological reserves Ω of each development unit i Ω of well network controlled reserves within each unit 井网，i Calculate the well network control reserve level B for each unit. 井网，i The calculation method is as follows

[0078] B 井网，i =Ω 井网，i / Ω i (3)

[0079] (3) Calculate the sweep efficiency of low-grade water-drive reservoirs. The specific steps for calculating the sweep efficiency of low-grade water-drive reservoirs are as follows:

[0080] (3.1) Combine the location information of oil and water wells in the target block with the well layout method, and calculate the average distance d between oil and water wells;

[0081] (3.2) Collect the starting pressure gradient test data of the low-grade oil reservoir cores in the target block to obtain the starting pressure gradient λ of the reservoir fluid flow;

[0082] (3.3) Based on the production dynamic data of oil and water wells, obtain the bottom hole pressure p of the water injection well. i Production well bottom pressure p w .

[0083] (3.4) Combining core porosity and permeability test data with formation fluid property data, the reservoir permeability k and formation fluid mixing viscosity μ are obtained. The mixing viscosity μ is calculated as follows:

[0084]

[0085] Where: μ o Oil phase viscosity, mPa·s; μ w The viscosity of the aqueous phase is mPa·s; S iw S represents the instantaneous water saturation. iwc To constrain water saturation, S ior This represents the residual oil saturation.

[0086] (3.5) Using a trial-and-error method, calculate the maximum value α of the water drive sweep angle that satisfies the following formula. max .

[0087]

[0088] The parameters and their units in the formula are as follows: k is the formation permeability, 10 -3 μm 2 μ is the viscosity of the formation mixed fluid, mPa·s; λ is the starting pressure gradient, MPa / m; p i The bottom pressure of the injection well is 0.1 MPa; p w The pressure of the oil well is 0.1 MPa.

[0089] (3.6) Calculate the sweep coefficient B 波及 The calculation formula is:

[0090] B 波及 =2α max / π (6)

[0091] (4) Correcting the impact of dynamic property evolution on the sweep efficiency. Dynamic property evolution refers to the changes in reservoir permeability caused by the decrease in reservoir energy as the oilfield development process progresses. At the same time, pollution is prone to occur in the near-wellbore area, which further reduces the permeability and thus affects the sweep range of injected water. It is necessary to further correct the sweep efficiency. The specific steps are as follows:

[0092] (4.1) Collect stress sensitivity test data of target blocks of low-grade oil reservoirs, analyze the permeability change law when reservoir energy decreases, and correct the current permeability of the reservoir with reference to the current reservoir energy level in the block.

[0093] (4.2) Considering near-wellbore contamination, collect the additional pressure drop Δp caused by near-wellbore contamination. s .

[0094] (4.3) Considering the impact of stress sensitivity and near-wellbore contamination on the sweep efficiency, the calculation method is the same as in step 3.5. max When the discriminant formula is changed to:

[0095]

[0096] Using the corrected α max The calculated sweep efficiency is denoted as EV. eff .

[0097] (4.4) Calculate the correction coefficient B considering the dynamic evolution of physical properties. 演变

[0098] B 演变 =EV eff / B 波及 (8)

[0099] (5) Calculate the reference recovery rate and evaluate the development effect. The specific steps for calculating the reference recovery rate and evaluating the development effect are as follows:

[0100] (5.1) Calculate the reference recovery rate R 参考 The calculation method is as follows:

[0101] R 参考 =R 理想 ×B 井网 ×B 波及 ×B 演变 (9)

[0102] (5.2) The current recovery level of the target block is compared with the reference recovery rate calculated by this method to make an evaluation result. When the recovery level of the target low-grade oil reservoir is lower than 60% of the reference recovery rate, the development effect of the target oil reservoir is poor; when the recovery level of the target low-grade oil reservoir is between 60% and 80% of the reference recovery rate, the development effect of the target oil reservoir is moderate; and when the recovery level of the target low-grade oil reservoir is higher than 80% of the reference recovery rate, the development effect of the target oil reservoir is good.

[0103] The difference between this invention and the prior art is that this invention combines the microscopic seepage characteristics of the core with macroscopic development parameters, making fuller use of the existing core test data in the oilfield, and taking into account the characteristics of the reservoir development stage and the evolution law of dynamic physical property parameters, thereby achieving an accurate quantitative evaluation of the reservoir development effect.

[0104] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0105] 1. It avoids the need for staff to collect and organize large amounts of production dynamic data such as fluid production and oil production, overcomes the strong dependence on on-site production dynamic data in most current reservoir development effect evaluations, greatly improves the work efficiency of staff, and saves data processing time and valuable computing and storage resources.

[0106] 2. This invention fully utilizes various test data from core samples of low-grade oil reservoirs during the current field exploration and development phase. The collection and processing of this type of data requires relatively little work and can fully reflect the geological and fluid seepage characteristics of low-grade oil reservoirs. Starting from the reservoir microstructure, it fully considers various factors affecting the effectiveness of waterflooding during development, especially the dynamic evolution mechanism of reservoir properties during development. This allows for efficient and accurate evaluation of the water injection development effect in low-grade oil reservoirs, overcoming the shortcomings of most current evaluation methods that rely primarily on static assessments. This invention provides a basis for formulating reasonable development plans and remediation measures for low-grade oil reservoirs, facilitating their efficient development.

[0107] Example 3

[0108] This section takes a low-grade oil reservoir block in Jiangsu Oilfield as an example and illustrates the application effect of this technology with specific examples.

[0109] Referring to step one, collect test data from waterflooding experiments of representative cores from the target block, as shown in Table 1. Utilize the recorded cumulative displacement pore volume multiple N... PV The cumulative displacement efficiency (ED) and the cumulative displacement efficiency (Rd) were plotted, as shown in Figure 2. It can be observed that as the cumulative displacement pore volume ratio increases, the displacement efficiency gradually stabilizes, and the limiting displacement efficiency (Rd) reaches a certain level. 理想 It is 51%.

[0110] Table 1. Water-driven oil recovery efficiency test data

[0111]

[0112] Referring to step two, data on the degree of well network control of reserves were collected. Based on the development unit division criteria, the target block was divided into two development units. Figure 3 shows the well network deployment and reserve control map for the two development units. As shown in Figure 3, the geological reserves and well network-controlled reserves of each development unit are summarized in Table 2. The water drive control degree B for the two development units was calculated respectively. 井网 The figures are 81.00% and 77.45%, respectively.

[0113] Table 2 Geological reserves and well-controlled reserves of the two development units

[0114]

[0115] Referring to step three, first refer to sections (3.1), (3.2), and (3.3) to collect basic data on production pressure, injection pressure, starting pressure gradient, well spacing, and relative permeability characteristic parameters of the low-grade reservoir in the target block, as shown in Tables 3 and 4 respectively.

[0116] Table 3. Penetration rate and production system related parameters of the two development units.

[0117]

[0118] Table 4 Characteristic parameters of the relative permeability curves of the two development units

[0119]

[0120] Then, following step (3.4), based on the data in Table 4 and formula (4), the mixed viscosity μ can be calculated to be 0.41344 mPa·s. Furthermore, according to step (3.5), substituting the data from Table 3 into formula (5), the calculated maximum sweep angle α of the water-drive system is obtained. max The angle is 46.8°; then, according to step (3.6), the water drive sweep efficiency B is calculated using formula (6). 波及 It is 0.52.

[0121] Referring to step four, first, following step (4.1), collect the stress sensitivity test data of the target block of the low-grade reservoir, as shown in Table 5. Figure 4 is a schematic diagram of permeability changes under different reservoir energy reduction levels. As shown in Figure 4, the reservoir permeability changes accordingly with the decrease in reservoir energy level. It was found that under the current reservoir energy level, that is, when the current reservoir energy level decreases by 6.33 MPa compared to the original energy level, the reservoir permeability is 74.6% of the initial permeability, that is, the current reservoir permeability keff is 46.998 mD.

[0122] Table 5. Stress sensitivity test data of the development unit

[0123]

[0124]

[0125] Simultaneously, following step (4.2), collect the additional pressure drop Δp caused by near-wellbore contamination. s It is 0.804 MPa.

[0126] Following step (4.3) and referring to formula (7), calculate the maximum sweep angle of the water drive considering the evolution of dynamic physical property parameters. The required parameter values ​​are shown in Table 6. Calculate the corrected α. max The angle is 37.9°. The corrected EV is calculated according to formula (6). eff It is 0.421.

[0127] Table 6. Penetration rate and production system related parameters of the two development units.

[0128]

[0129] Following step (4.4), referring to formula (8), EV eff 0.421 and B 波及 Dividing by 0.52, we get B. 演变 It is 0.81.

[0130] Referring to step five, and following step (5.1), calculate the reference recovery rate R for the two development units. 参考 The required data are shown in Table 7. The calculated reference recovery rates for the two development units are 17.4% and 16.6%, respectively.

[0131] Table 7. Statistical table of data required for reference recovery rate calculation of the two development units.

[0132]

[0133] According to step (5.2), and considering the current recovery rates of the two blocks, which are 13.8% and 12.4% respectively, accounting for 79.3% and 74.5% of the corresponding reference recovery rates, both are between 60% and 80% of the reference recovery rate. Based on the evaluation criteria, the water injection development effect of the two development units in this low-grade reservoir block can be determined to be moderate.

[0134] Based on the parameter calculations for evaluating the development effectiveness above, it can be found that R... 理想 波及 井网 演变 ​​​The main factors limiting the development of this study block are the low permeability and poor displacement effect caused by the dense pore-throat structure of the reservoir itself, and the low sweep efficiency of the reservoir under the existing well network deployment and working system. The development potential can be tapped by reservoir fracturing, improving the flow capacity of reservoir fluids, and optimizing the production system that matches the well network deployment. This provides a direction for further guiding the effective development of the reservoir.

[0135] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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 evaluating the effectiveness of water injection development in low-grade oil reservoirs, characterized in that, include: S1, collect core-scale data on ultimate displacement efficiency; S2, collects data on the degree of well network control of reserves; S3, Calculate the sweep efficiency of low-grade water-drive reservoirs; including: S3.1, combining the well layout of oil and water wells to statistically analyze the location information of oil and water wells in the target block, and statistically average the well spacing d; S3.2, collect the starting pressure gradient test data of the core samples of low-grade reservoirs in the target block to obtain the starting pressure gradient λ of reservoir fluid flow; S3.3, combine the production dynamic data of oil and water wells to obtain the bottom hole pressure p of the injection wells. i Production well bottom pressure p w S3.4, Combining core porosity and permeability testing with formation fluid property data, the reservoir permeability k and formation fluid mixing viscosity μ are obtained, where the mixing viscosity μ is calculated as follows: Where: μ o Oil phase viscosity, mPa·s; μ w The viscosity of the aqueous phase is mPa·s; S iw S represents the instantaneous water saturation. iwc To constrain water saturation, S ior Given residual oil saturation; S3.5, using a trial-and-error method, calculate the maximum value α of the water drive sweep angle α that conforms to the following formula. max : The parameters and their units in the formula are as follows: k is the formation permeability, 10 -3 μm 2 μ is the viscosity of the formation mixed fluid, mPa·s; λ is the starting pressure gradient, MPa / m; p i The bottom hole pressure of the injection well is 0.1 MPa; p w Given the bottom hole pressure of the production well is 0.1 MPa; S3.6, calculate the sweep efficiency B. 波及 The calculation formula is B. 波及 =2α max / π (6)S4, Based on the changes in reservoir physical parameters caused by near-wellbore contamination and reservoir energy decline, the sweep efficiency is corrected; including: S4.1, collecting stress sensitivity test data of the target block of low-grade oil reservoir, analyzing the permeability change law when reservoir energy declines, and correcting the current permeability of the reservoir with reference to the current reservoir energy level in the block; S4.2, considering near-wellbore contamination, collecting the additional pressure drop Δp caused by near-wellbore contamination. s S4.3, Considering stress sensitivity and near-wellbore contamination, the sweep efficiency is corrected. The calculation method is the same as in step S3 initially, and α is calculated in step 3.

5. max When the discriminant formula is changed to: Using the corrected α max The calculated sweep efficiency is denoted as EV. eff S4.4, Calculate the correction coefficient B considering the dynamic evolution of physical properties. 演变 B 演变 =EV eff / B 波及 (8)S5, calculate the reference recovery rate and evaluate the development effect.

2. The method for evaluating the effectiveness of water injection development in low-grade oil reservoirs according to claim 1, characterized in that, Step S1 includes: using representative cores from the target block of the low-grade oil reservoir, collecting and organizing the waterflooding experimental data of the representative cores, and obtaining the ultimate oil displacement efficiency at the core scale.

3. The method for evaluating the effectiveness of water injection development in low-grade oil reservoirs according to claim 1 or 2, characterized in that, Step S1 includes: S1.1, placing the core into the core holder, evacuating the vacuum, and then fully saturating the core with simulated oil, recording the mass m of the saturated oil phase. ini S1.2, Inject formation water into one side of the core holder at a uniform rate, injecting water at a volume 50 times the pore volume of the core; S1.3, Record the volume V of the injected water at different times t. w The mass m of the simulated oil displaced from the core out Combined with pore volume V φ Calculate the cumulative displacement pore volume ratio N corresponding to time t. PV With oil displacement efficiency ED, N PV =V w / V φ (1) ED = m out / m ini (2)S1.4, using the collected cumulative displacement pore volume multiple N PV Plot the relationship curve between the oil displacement efficiency (ED) data and the S1.5, based on N. PV The relationship curve between ED and the limiting oil displacement efficiency is determined by analyzing the changing trend of the curves.

4. The method for evaluating the effectiveness of water injection development in low-grade oil reservoirs according to claim 3, characterized in that, Step S1.5 includes: [The text abruptly ends here, likely due to an incomplete sentence or a missing section.] PV The relationship between the displacement efficiency ED and the cumulative displacement pore volume ratio shows that the displacement efficiency increases with the increase of the cumulative displacement pore volume ratio N, until it reaches a limiting stable value, that is, the displacement efficiency ED no longer increases with the cumulative displacement pore volume ratio N. PV As the number of cores increases, the oil displacement efficiency at this point becomes the limiting oil displacement efficiency R at the core scale. 理想 .

5. The method for evaluating the effectiveness of water injection development in low-grade oil reservoirs according to claim 1 or 2, characterized in that, Step S2 includes: dividing the target block into development units, collecting the well network controlled reserves and geological reserves of each development unit, and calculating the degree of well network controlled reserves.

6. The method for evaluating the effectiveness of water injection development in low-grade oil reservoirs according to claim 1 or 2, characterized in that, Step S2 includes: S2.1, dividing reservoirs of the same low grade that meet the first preset condition in terms of reservoir properties, are located in the same hydrodynamic system, belong to the same set of development strata and are geographically contiguous, and whose production time meets the second preset condition into a development unit; S2.2, collecting the geological reserves Ω of each development unit. i Ω of well network controlled reserves within each unit 井网，i Calculate the well network control reserve level B for each unit. 井网，i The calculation method is B. 井网，i =Ω 井网，i / Ω i (3).

7. The method for evaluating the effectiveness of water injection development in low-grade oil reservoirs according to claim 1 or 2, characterized in that, Step S3 includes: based on the collection of production pressure, injection pressure, start-up pressure gradient, and well spacing of low-grade reservoirs, calculating the water drive sweep efficiency by trial calculation of the maximum sweep angle of water drive.

8. The method for evaluating the effectiveness of water injection development in low-grade oil reservoirs according to claim 4, characterized in that, Step S5 includes: S5.1, calculating the reference recovery rate R 参考 , and the calculation method is: R 参考 =R 理想 ×B 井网 ×B 波及 ×B 演变 (9) S5.2, comparing the current production degree of the target block with the reference recovery rate calculated in step S5.1 to make an evaluation result. When the production degree of the target low-grade oil reservoir is lower than 60% of the reference recovery rate, the development effect of the target low-grade oil reservoir is L1. When the production degree of the target low-grade oil reservoir is between 60% and 80% of the reference recovery rate, the development effect of the target low-grade oil reservoir is L2. When the production degree of the target low-grade oil reservoir is higher than 80% of the reference recovery rate, the development effect of the target low-grade oil reservoir is L3, where L1 < L2 < L3. The larger the value of the development effect, the better the development effect.

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