Method for judging injection property of pre-plugging agent for profile control in low-permeability reservoir and making pre-treatment scheme

Abstract

The application discloses a method for judging injection property of a profile control pre-plugging agent and formulating a pretreatment scheme for a low-permeability reservoir, which is based on analysis of four aspects, i.e., a size relationship between oil pressure and pump pressure, a pressure drop well testing double logarithmic curve characteristic chart, a normal water injection pressure variation law and a small slug test injection before profile control, to obtain a plugging agent injection property level. The application comprehensively analyzes the four aspects, i.e., the size relationship between the oil pressure and the pump pressure, the pressure drop well testing double logarithmic curve characteristic chart, the normal water injection pressure variation law and the small slug test injection before profile control, and forms a comprehensive evaluation method for the plugging agent injection property on the basis of four plugging agent injection property judgment methods. The plugging agent injection property of a profile control well is divided into three levels, i.e., I, II and III, and reasonable pretreatment schemes are formulated according to different injection property levels, so that the problem of injection failure of the plugging agent in profile control construction of a low-permeability well is solved, and the profile control construction success rate and profile control effect are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a method for judging the injection of plugging agents and formulating pretreatment schemes for low-permeability reservoirs before profile control. Background Technology

[0002] To address the issue of severely ineffective water circulation in low-permeability oilfields during the high-permeability development phase, leading to a gradual decline in the effectiveness of water injection, profile control injection of plugging agents is commonly employed to effectively seal crossflow channels and address the three major contradictions (high permeability, high efficiency, and high hysteresis) and ineffective water circulation. Therefore, improving profile control efficiency is crucial for enhancing the recovery rate of low-permeability reservoirs. However, in field profile control operations in low-permeability reservoirs, factors such as poor injectability in low-permeability reservoirs and the accumulation of impure water during long-term water injection further deteriorate injectability. This often results in difficulties in plugging agent injection, plugging agent accumulation at the wellbore, and rapid increases in operating pressure exceeding the design pressure limit. Currently, methods such as reducing the strength and dosage of plugging agents are commonly used to increase injectability and control operating pressure. However, this often leads to insufficient plugging agents to meet sealing requirements, resulting in poor profile control effects or even operation failure.

[0003] In summary, improving the injectability of plugging agents to effectively seal advantageous channels determines the success or failure of profile control in low-permeability reservoirs. Literature review shows that current domestic and international research mainly focuses on the development and application of plugging agents with low initial strength and easy injection, while research on assessing plugging agent injectability and pre-treatment of drilling wells is still in its early stages. Currently, domestic research primarily uses the pump-oil pressure difference during normal water injection to determine the potential for pressure rise during construction, which cannot predict the rate of pressure increase during construction, and the problem of poor plugging agent injectability remains unresolved. How to more accurately assess plugging agent injectability and pre-treat drilling wells based on the assessment results to effectively improve plugging agent injectability is a major challenge currently facing profile control technology in low-permeability reservoirs.

[0004] Therefore, existing technologies still need improvement. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for determining the injection characteristics of plugging agents and formulating pretreatment schemes before profile control of low-permeability reservoirs.

[0006] To address the aforementioned technical problems, some embodiments of the present invention disclose a method for judging the injectability of plugging agents before profile control in low-permeability reservoirs. The method analyzes four aspects: the relationship between oil pressure and pump pressure, the characteristic chart of the double logarithmic curve of pressure drop test well, the variation law of normal water injection pressure, and the small slug test injection before profile control, to obtain the level of plugging agent injectability.

[0007] In some embodiments, the analysis is based on four aspects: the relationship between oil pressure and pump pressure, the characteristic chart of the double logarithmic curve of pressure drop well test, the variation law of normal water injection pressure, and the small slug injection test before profile adjustment. The potential for increasing construction pressure is determined based on the relationship between oil pressure and pump pressure. Reservoir characteristics are obtained based on the characteristic chart of double logarithmic curves from pressure drop well testing; The development and changes of the crossflow channel were obtained based on the normal water injection pressure variation pattern. The pressure difference before and after the small-segment plug test was obtained based on the small-segment plug test.

[0008] In some embodiments, the pressure rise range for construction based on the relationship between oil pressure and pump pressure includes: compared to pump pressure, the lower the oil pressure, the greater the pressure rise range for construction during the injection of the plugging agent, and the better the injection performance; the higher the oil pressure, the easier it is for the construction pressure to reach the upper limit of the construction pressure, and the worse the injection performance.

[0009] In some embodiments, the range of construction pressure increase is determined based on the relationship between oil pressure and pump pressure, including: At that time, the injection performance was good; At that time, the injection rate was moderate; At that time, the injection performance was poor; Among them, P 油压 This indicates oil pressure, expressed in MPa. P 泵压 This indicates pump pressure, expressed in MPa. For dimensionless values, when hour, ,when hour, ; It is a dimensional value, with the unit MPa, and the value is equal to... .

[0010] In some embodiments, reservoir characteristics are obtained based on the characteristic chart of the double logarithmic curve of the pressure drop test. These reservoir characteristics include: There is a certain amount of reservoir space or low heterogeneity between wells; Good inter-well connectivity or the presence of fractures, large channels, or advantageous passageways; There are faults or sealed reservoirs composed of ultra-low permeability matrix.

[0011] In some embodiments, reservoir characteristics are obtained based on the double logarithmic curve feature chart of pressure drop well test. The double logarithmic curve feature chart of pressure drop well test includes: constant pressure boundary chart, finite conductivity fracture chart, infinite conductivity fracture chart, dual porosity medium chart, homogeneous reservoir chart, and fault / closed reservoir.

[0012] In some embodiments, when the pressure drop test double logarithmic curve characteristic chart is a constant pressure boundary chart, it is judged that the well-to-well connectivity is good and the degree of crossflow is high; When the characteristic chart of the double logarithmic curve of the pressure drop test is a chart of finite conductivity fracture, it is determined that a fracture exists and the plugging agent can easily enter. When the characteristic chart of the double logarithmic curve of the pressure drop test is an infinite conductivity fracture chart, it is determined that a fracture exists and the plugging agent can easily enter. When the characteristic chart of the double logarithmic curve of the pressure drop test is a double porosity medium chart, it is judged to be highly heterogeneous and to have reservoir space. When the characteristic chart of the double logarithmic curve of the pressure drop test is a homogeneous reservoir chart, it is judged to be weakly heterogeneous and the water channeling well has high permeability. When the characteristic chart of the double logarithmic curve of the pressure drop test indicates a fault / closed reservoir, it is judged to be due to poor inter-well connectivity.

[0013] In some embodiments, the development and changes of the crossflow channel are obtained based on the normal water injection pressure change pattern, including: according to the production dynamics before profile adjustment, plotting the curve of "oil pressure-daily water injection volume" with development time with "development time" as the abscissa and "oil pressure" and "daily water injection volume" as the ordinate, and under stable water injection conditions, analyzing the change pattern of oil pressure with water injection development to determine the development and changes of the crossflow channel.

[0014] In some embodiments, the development and changes of the crossflow channel are obtained based on the normal water injection pressure variation pattern, including: If the injection pressure decreases with water injection development, it is believed that long-term water injection development or fracturing has led to further development of the flow channels, which is judged as enhanced injection and a small degree of formation blockage. If the injection pressure changes little with water injection development, it is considered that the degree of development of the flow channel changes little, and the degree of formation blockage is judged to be moderate. If the injection pressure increases with water injection development, it is believed that the water quality is impure and the formation is severely blocked, and the formation pressure is determined to lead to poor injection performance.

[0015] In some embodiments, the pressure difference before and after the small slug test injection is obtained based on the small slug test injection before profile adjustment, including: injecting the test slug at the maximum construction flow rate before profile adjustment, the test slug being composed of three stages: water, polymer, and plugging agent, and judging the injectability of the plugging agent by the pressure difference before and after the test slug injection.

[0016] In some embodiments, the pressure difference before and after the slug test, obtained based on the slug test before profile adjustment, further includes: During the test injection of water or polymer slugs, the injection volume meets the following requirements: ; like They believe it has good injectability; like They believe the injection rate is moderate. like They believe the injection performance is poor. in, The value is dimensionless, where , , ; This represents the pressure difference before and after the test injection of water or polymer slug, expressed in MPa. This indicates the normal water injection pump pressure before profile control, in MPa; This indicates the normal water and oil injection pressure before profile control, in MPa; - Trial water or polymer injection time. , h; -Maximum construction discharge rate for profile adjustment, m 3 / h; -Total fluid volume for profile control construction, m 3 .

[0017] In some embodiments, the pressure difference before and after the slug test, obtained based on the slug test before profile adjustment, further includes: During the trial injection of plugging agent into the sluice gate, the injection volume met the following requirements: ; like They believe it has good injectability; like They believe the injection rate is moderate. like They believe the injection performance is poor. in, The value is dimensionless, where , , ; -Injection time of the plugging agent during trial injection , h; - Pressure difference before and after the test injection of plugging agent into the sluice, in MPa.

[0018] In some embodiments, the analysis is based on four aspects: the relationship between oil pressure and pump pressure, the characteristic chart of the double logarithmic curve of pressure drop well test, the variation law of normal water injection pressure, and the small slug injection test before profile adjustment. The injectionability assessment results obtained from the pressure rise space during construction, reservoir characteristics, changes in the flow channel development, and the pressure difference before and after the small slug test injection are used as four factors and assigned evaluation scores a, b, c, and d respectively, where a+b+c+d=100; and based on the evaluation scores, the reservoir is divided into multiple injectionability levels.

[0019] Each factor is further divided into multiple corresponding injection levels; the total score for a certain injection level is equal to the sum of the evaluation scores of each factor that determines the corresponding injection level; the injection level of the well is determined based on the total score of each injection level.

[0020] In some embodiments, multiple injection levels include three levels: I, II, and III. Level I has the best injection performance and a total score of α; Level II has moderate injection performance and a total score of β; and Level III has poor injection performance and a total score of γ. Based on the current well condition or block, the four factors are weighted and scored, and their injection performance is judged as good, medium, or poor. The scores of all factors with good injection performance are summed to obtain the α value; the scores of all factors with moderate injection performance are summed to obtain the β value; and the scores of all factors with poor injection performance are summed to obtain the γ value. Comparing the α, β, and γ values, if the α value is the largest, the overall judgment is good injection performance, with an injection performance level of I; if the β value is the largest, the overall judgment is moderate injection performance, with an injection performance level of II; and if the γ value is the largest, the overall judgment is poor injection performance, with an injection performance level of III.

[0021] On the other hand, some embodiments of the present invention also disclose a method for formulating a pretreatment scheme for plugging agent injection before profile control in low-permeability reservoirs. The method uses the aforementioned method for judging the injectability of plugging agents before profile control in low-permeability reservoirs to obtain the injectability level of the plugging agent. If the injectability level is Level I, the plugging agent is injected directly; if the injectability level is Level II, well washing is required before injecting the plugging agent; if the injectability level is Level III, acidizing and well washing are required before injecting the plugging agent.

[0022] By adopting the above technical solution, the present invention has at least the following beneficial effects: This invention provides a method for judging the injectability of plugging agents and formulating pretreatment schemes before profile control in low-permeability reservoirs. It comprehensively analyzes four aspects: the relationship between oil pressure and pump pressure, the characteristic curve of the double logarithmic curve of pressure drop test, the variation law of normal water injection pressure, and the small-slug test injection before profile control. Based on four methods for judging the injectability of plugging agents, a comprehensive evaluation method for plugging agent injectability is formed. The injectability of plugging agents in profile control wells is divided into three levels: I, II, and III. Reasonable pretreatment schemes are formulated according to different injectability levels, solving the problem of plugging agents failing to be injected during profile control in low-permeability wells, and significantly improving the success rate and effectiveness of profile control operations. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of six double logarithmic curve features of a method for judging the injection of plugging agent before profile control of a low-permeability reservoir as disclosed in some embodiments of the present invention; Figure 2 The graph shows the change of "oil pressure-daily water injection volume" over development time in a method for judging the injection of plugging agent before profile control of a low-permeability reservoir, as disclosed in some embodiments of the present invention. Figure 3 The graph shows the change of "oil pressure-daily water injection volume" over development time in a method for judging the injection of plugging agent before profile control of a low-permeability reservoir, as disclosed in some embodiments of the present invention. Figure 4 The graph shows the change of "oil pressure-daily water injection volume" over development time in a method for judging the injection of plugging agent before profile control of a low-permeability reservoir, as disclosed in some embodiments of the present invention. Figure 5 This is a water well injection pressure curve diagram of a method for judging the injectionability of plugging agent before profile control of low-permeability reservoirs, as disclosed in some embodiments of the present invention. Figure 6 This is a diagram showing the pre-profile injection curve of a small plugging section as disclosed in some embodiments of the present invention, which is a method for judging the injection performance of plugging agent before profile control in low-permeability reservoirs. Figure 7 This is a profile control construction curve diagram of a method for formulating a pretreatment scheme for plugging agent injection in a low-permeability reservoir as disclosed in some embodiments of the present invention. Figure 8 The diagram shows the profile control effect of a well group as part of a method for developing a pretreatment scheme for low-permeability reservoir profile control using plugging agent injection, as disclosed in some embodiments of the present invention. Detailed Implementation

[0025] The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of this disclosure by way of example, but should not be used to limit the scope of this disclosure. This disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0026] These embodiments are provided to make the disclosure thorough and complete, and to fully express the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​set forth in these embodiments should be interpreted as exemplary only and not as limiting.

[0027] Furthermore, the terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Terms such as "including" or "contains" mean that the element preceding the word covers the element listed after the word, and do not exclude the possibility of covering other elements as well.

[0028] It should also be noted that, in the description of this disclosure, unless otherwise expressly specified and limited, the specific meaning of each term in this disclosure can be understood by those skilled in the art as appropriate. All terms used in this disclosure have the same meaning as understood by those skilled in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted with an idealized or highly formalized meaning, unless expressly defined herein.

[0029] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0030] This invention discloses a method for judging the injectability of plugging agents before profile control in low-permeability reservoirs, and a method for formulating a pretreatment scheme for plugging agent injection based on this method. For low-permeability reservoirs, this method can more accurately predict the injectability of plugging agents in profile control wells, providing a basis for formulating reasonable pretreatment schemes, thereby improving the injectability of plugging agents in profile control wells, solving problems such as difficulty in injection during profile control well construction, plugging agent accumulation at the bottom of the well, and excessively rapid increase in construction pressure. Ultimately, this method aims to achieve deep migration of plugging agents, effective sealing of crossflow channels, and improved success rate and effectiveness of profile control construction in low-permeability reservoirs.

[0031] This invention discloses a method for judging the injectability of plugging agents before profile control in low-permeability reservoirs. This method comprehensively analyzes four aspects: the relationship between oil pressure and pump pressure, the characteristic curve of the double logarithmic curve of pressure drop test, the variation law of normal water injection pressure, and the pressure difference before and after the small slug test injection. Each method is assigned a weight, and multiple methods are combined to form a comprehensive judgment method for plugging agent injectability. The injectability is divided into three levels: I, II, and III, and corresponding pretreatment plans for profile control wells are formulated according to different levels.

[0032] To assess the injectability of the plugging agent based on oil pressure and pump pressure, the relationship between oil pressure and pump pressure during normal water injection before profile control can be used. Compared to pump pressure, lower oil pressure allows for a greater potential for pressure increase during plugging agent injection, resulting in better injectability. Higher oil pressure makes it easier to reach the upper limit of the operating pressure, leading to poorer injectability.

[0033] Specifically, At this time, the oil pressure value is relatively small compared to the pump pressure, resulting in good injection performance; At that time, the oil pressure value is moderate relative to the pump pressure, and the injection performance is moderate; At that time, the oil pressure value is relatively large compared to the pump pressure, resulting in poor injection performance; Among them, P 油压 This indicates oil pressure, expressed in MPa. P 泵压 This indicates pump pressure, expressed in MPa. For dimensionless values, when hour, ,when hour, ; It is a dimensional value, with the unit MPa, and the value is equal to... .

[0034] To assess plugging agent injection capability based on the characteristics of the double logarithmic curves from pressure drop tests, the reservoir and dominant channel characteristics can be analyzed using the double logarithmic curves from profile-adjusted wells to determine plugging agent injection capability. When inter-well connectivity is good or fractures, large pores, or dominant channels exist, the reservoir plugging agent injection capability is relatively good. When faults exist or the reservoir is sealed with an ultra-low permeability matrix, the plugging agent injection capability is relatively poor. For example... Figure 1 As shown in Table 1, this embodiment summarizes six common double logarithmic curve characteristic charts for low-permeability reservoirs and classifies the different characteristic charts into three levels: good, medium, and poor injection performance based on their reservoir and dominant channel characteristics interpretation results.

[0035] Table 1. Using double logarithmic curves to determine reservoir and dominant pathway conditions.

[0036] To determine the injection characteristics of plugging agent based on the normal water injection pressure variation pattern, the production dynamics before profile adjustment can be used to plot the "oil pressure-daily water injection" curve as development time, with "development time" as the x-axis and "oil pressure" and "daily water injection volume" as the y-axis. Under stable water injection conditions, the development and changes of the crossflow channel can be further analyzed by analyzing the oil pressure variation pattern with water injection development.

[0037] Specifically, such as Figure 2As shown, the injection pressure decreases with water injection development. Long-term water injection development or fracturing leads to further development of flow channels, enhanced injection capacity, and less formation blockage; thus, the injection capacity is good. Figure 3 As shown, the injection pressure changes little with water injection development, the degree of development of crossflow channels changes little, and the degree of formation blockage is not high; the injection capacity is moderate. Figure 4 As shown, the injection pressure increases with water injection development, water quality becomes mixed and the formation becomes severely blocked, and the formation pressure deteriorates, resulting in poor injection performance.

[0038] For assessing injectability of the small slug before profile control, the slug is injected at the maximum operational flow rate before profile control. The slug consists of three stages: water, polymer, and plugging agent. The injectability of the plugging agent is judged by the pressure difference before and after the slug injection. The larger the pressure difference, the worse the injectability; the smaller the pressure difference, the better the injectability.

[0039] Specifically, during the test injection of water or polymer slugs, the injection volume meets the following requirements: ; like They believe it has good injectability; like They believe the injection rate is moderate. like They believe the injection performance is poor. in, The value is dimensionless, where , , ; This represents the pressure difference before and after the test injection of water or polymer slug, expressed in MPa. This indicates the normal water injection pump pressure before profile control, in MPa; This indicates the normal water and oil injection pressure before profile control, in MPa; - Trial water or polymer injection time. , h; -Maximum construction discharge rate for profile adjustment, m 3 / h; -Total fluid volume for profile control construction, m 3 .

[0040] During the trial injection of plugging agent into the sluice gate, the injection volume met the following requirements: ; like They believe it has good injectability; like They believe the injection rate is moderate. like They believe the injection performance is poor. in, The value is dimensionless, where , , ; -Injection time of the plugging agent during trial injection , h; - Pressure difference before and after the test injection of plugging agent into the sluice, in MPa.

[0041] After the above four factors are judged, the following four factors are assigned evaluation scores a, b, c, and d respectively: the method for judging the relationship between normal water injection oil pressure and pump pressure, the method for judging the double logarithmic curve of pressure drop test well, the method for judging the law of change of normal water injection pressure, and the method for judging the pressure difference of the slug injection test before profile adjustment, where a+b+c+d=100. In other words, the injectionability judgment results obtained from the space for pressure increase during construction, reservoir characteristics, changes in the development of flow channels, and the pressure difference before and after the small slug injection test are used as the four factors and assigned evaluation scores a, b, c, and d respectively, where a+b+c+d=100.

[0042] The overall injection capacity is divided into three levels: I, II, and III. Level I has the best injection capacity, with a total score of α; Level II has moderate injection capacity, with a total score of β; and Level III has poor injection capacity, with a total score of γ. Based on the current well, mine, or block situation, the four factors are weighted and assigned scores. The scores for each of the three levels are summed to obtain α, β, and γ values. These values ​​are then compared. If the α value is the largest, the overall injection capacity is considered good, and the injection capacity level is I. If the β value is the largest, the overall injection capacity is considered moderate, and the injection capacity level is II. If the γ value is the largest, the overall injection capacity is considered poor, and the injection capacity level is III.

[0043] For example, when only the first factor among the four factors is judged to have good injectability, the injectionability score for Level I is α=a; when only the first two factors are judged to have good injectability, α=a+b; and so on, β and γ are calculated. If the well is judged to have Level I injectability after comparison, the overall judgment is that the well has good plugging agent injectability; if it is judged to have Level II injectability after comparison, the overall judgment is that the well has moderate plugging agent injectability; if it is judged to have Level III injectability after comparison, the overall judgment is that the well has poor plugging agent injectability.

[0044] This invention also discloses a method for formulating a pretreatment scheme for plugging agent injection before profile control in low-permeability reservoirs. The method for judging the injectability of plugging agents before profile control in low-permeability reservoirs disclosed in the above embodiments can be used to obtain the injectability level of the plugging agent. If the injectability level is Level I, the plugging agent is injected directly; if the injectability level is Level II, well washing is required before injecting the plugging agent; if the injectability level is Level III, acidizing and well washing are required before injecting the plugging agent, as shown in Table 2.

[0045] Table 2 Pretreatment Scheme

[0046] The method for judging the injectability of plugging agents before profile control in low-permeability reservoirs and the method for formulating pretreatment schemes disclosed in the above embodiments of this invention, based on four innovative methods for judging the injectability of plugging agents, form a comprehensive evaluation method for plugging agent injectability. This method classifies the injectability of plugging agents in profile control wells into three levels: I, II, and III, and formulates reasonable pretreatment schemes according to different injectability levels. This solves the problem of plugging agents not being able to be injected during profile control construction in low-permeability wells, significantly improving the success rate and effectiveness of profile control construction. In six blocks in Jilin Oilfield and Liaohe Oilfield, 30 wells in 36 sections were implemented, including 6 Class I wells in 8 sections, 18 Class II wells in 20 sections, and 6 Class III wells in 8 sections. After pretreatment, the plugging agent injection pressure rose steadily, and the highest pressure during profile control construction was always less than the upper limit of the design pressure (water injection trunk pressure). All 36 sections were injected as designed, achieving a 100% success rate. After profile control adjustments, the average daily oil production per well group increased by 1.4 tons, water cut decreased by 5%, and well efficiency reached 70%. To date, the cumulative oil production has increased by 5,576 tons, with a production-to-input ratio of ≥3.2 at $45 per barrel. The water-drive recovery rate in the Jilin Oilfield test area has increased by 0.1%.

[0047] Taking the M3-3 water well in the XM block of Jilin Oilfield as an example: ① Oil pressure 8.5 MPa, pump pressure 14.9 MPa The injection rate is moderate; ② The double logarithmic curve shows an infinitely conductive crack, indicating good injection performance; ③ The water injection pressure changes little with water injection development, such as Figure 5 As shown, the injection rate is moderate; ④ Pre-sectioning test injection of small-segment plugs: maximum construction displacement 4m 3 / h, water injection volume 20m 3 -Pour polymer 20m 3 - 40ml of plugging agent 3 ; The water injection pressure increased by 0.4 MPa, and the polymer injection pressure increased by 0.5 MPa. (N1=22, M1=12), moderate injection rate; The pressure of the plugging agent increased by 1.1 MPa. (N2=8, M2=4), moderate injection properties, test segment before profile adjustment. Figure 6 As shown.

[0048] ⑤ Comprehensive assessment of injection potential: Level II total score M3-3 is a Class II injectable substance with moderate injectability, as shown in Table 3.

[0049] Table 3M3-3 Injectability Comprehensive Evaluation Table

[0050] ⑥ Formulation of pretreatment plan before profile adjustment: Well washing before profile adjustment.

[0051] ⑦ Application effects are as follows Figure 8 As shown: the construction pressure increased from 10.5 MPa to 14.7 MPa, which is less than the upper limit of the design pressure of 14.9 MPa. The sealant was injected smoothly without any sudden pressure rise. Figure 7 After pretreatment, the injection performance of plugging agent in water well M3-3 was improved. Following the adjustment, the oil pressure increased by 1.8 MPa, the well group saw a daily oil increase of 1.8 tons, a cumulative oil increase of 781 tons, and a water cut decrease of 12.4%. The embodiments of this disclosure have now been described in detail. To avoid obscuring the concept of this disclosure, some details known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0052] While specific embodiments of this disclosure have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this disclosure. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner.

Claims

1. A method for judging the injection of plugging agent before profile control in low-permeability reservoirs, characterized in that, The plugging agent injection performance level is obtained by analyzing four aspects: the relationship between oil pressure and pump pressure, the characteristic chart of double logarithmic curve of pressure drop test, the change law of normal water injection pressure, and the small slug test injection before profile adjustment.

2. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 1, characterized in that, The analysis is based on four aspects: the relationship between oil pressure and pump pressure, the characteristic chart of the double logarithmic curve of pressure drop during well testing, the variation law of normal water injection pressure, and the small slug injection test before profile adjustment. The potential for increasing construction pressure is determined based on the relationship between oil pressure and pump pressure. Reservoir characteristics are obtained based on the characteristic chart of double logarithmic curves from pressure drop well testing; The development and changes of the crossflow channel were obtained based on the normal water injection pressure variation pattern. The pressure difference before and after the small-segment plug test was obtained based on the small-segment plug test.

3. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 2, characterized in that, Based on the relationship between oil pressure and pump pressure, the construction pressure rise range is as follows: compared to pump pressure, the lower the oil pressure, the greater the construction pressure rise range during the injection of the plugging agent, and the better the injection performance; the higher the oil pressure, the easier it is to reach the upper limit of the construction pressure, and the worse the injection performance.

4. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 2, characterized in that, Based on the relationship between oil pressure and pump pressure, the potential for increased construction pressure includes: At that time, the injection performance was good; At that time, the injection rate was moderate; At that time, the injection performance was poor; Wherein, P represents oil pressure, and the unit is MPa; P represents pump pressure, with units of MPa; For dimensionless values, when hour, ,when hour, ; It is a dimensional value, with the unit MPa, and the value is equal to... .

5. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 2, characterized in that, The reservoir characteristics obtained from the double logarithmic curve characteristic chart of pressure drop well testing include: There is a certain amount of reservoir space or low heterogeneity between wells; Good inter-well connectivity or the presence of fractures, large channels, or advantageous passageways; There are faults or sealed reservoirs composed of ultra-low permeability matrix.

6. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 2, characterized in that, The reservoir characteristics obtained based on the double logarithmic curve feature chart of pressure drop well test include: constant pressure boundary chart, finite conductivity fracture chart, infinite conductivity fracture chart, dual porosity medium chart, homogeneous reservoir chart, and fault / closed reservoir.

7. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 6, characterized in that, When the characteristic chart of the double logarithmic curve of the pressure drop test is a constant pressure boundary chart, it is judged that the inter-well connectivity is good, the degree of crossflow is high, and the plugging agent is easy to inject. When the characteristic chart of the double logarithmic curve of the pressure drop test is a chart of finite conductivity fracture, it is determined that a fracture exists and the plugging agent can easily enter. When the characteristic chart of the double logarithmic curve of the pressure drop test is an infinite conductivity fracture chart, it is determined that a fracture exists and the plugging agent can easily enter. When the characteristic chart of the double logarithmic curve of the pressure drop test is a double porosity medium chart, it is judged to be highly heterogeneous and have reservoir space. When the characteristic chart of the double logarithmic curve of the pressure drop test is a homogeneous reservoir chart, it is judged to be weakly heterogeneous and the water channeling well has high permeability. When the characteristic chart of the double logarithmic curve of the pressure drop test indicates a fault / closed reservoir, it is judged to be due to poor inter-well connectivity.

8. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 2, characterized in that, The development and changes of crossflow channels based on the normal water injection pressure variation pattern include: according to the production dynamics before profile control, plotting the curve of "oil pressure-daily water injection volume" with development time with "development time" as the abscissa and "oil pressure" and "daily water injection volume" as the ordinate, and analyzing the oil pressure variation pattern with water injection development under stable water injection conditions to determine the development and changes of crossflow channels.

9. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 8, characterized in that, The development and changes of the crossflow channels, based on the normal water injection pressure variation pattern, include: If the injection pressure decreases with water injection development, it is believed that long-term water injection development or fracturing has led to further development of the flow channels, which is judged as enhanced injection and a small degree of formation blockage. If the injection pressure changes little with water injection development, it is considered that the degree of development of the flow channel changes little, and the degree of formation blockage is judged to be moderate. If the injection pressure increases with water injection development, it is believed that the water quality is impure and the formation is severely blocked, and the formation pressure is determined to lead to poor injection performance.

10. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 2, characterized in that, The pressure difference before and after the small slug test injection obtained based on the pre-profile adjustment includes: injecting the test slug at the maximum construction flow rate before profile adjustment. The test slug consists of three stages: water, polymer, and plugging agent. The injectability of the plugging agent is judged by the pressure difference before and after the test slug injection.

11. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 10, characterized in that, The pressure difference before and after the slug test, obtained based on the pre-profile slug test, also includes: During the test injection of water or polymer slugs, the injection volume meets the following requirements: ; like They believe it has good injectability; like They believe the injection rate is moderate. like They believe the injection performance is poor. in, The value is dimensionless, where , , ; This represents the pressure difference before and after the test injection of water or polymer slug, expressed in MPa. This indicates the normal water injection pump pressure before profile control, in MPa; This indicates the normal water and oil injection pressure before profile control, in MPa; - Trial water or polymer injection time. , h; -Maximum construction discharge rate for profile adjustment, m 3 / h; -Total fluid volume for profile control construction, m 3 .

12. The method for judging the injection of plugging agent before profile control of low-permeability reservoirs according to claim 10 or 11, characterized in that, The pressure difference before and after the slug test, obtained based on the pre-profile slug test, also includes: During the trial injection of plugging agent into the sluice gate, the injection volume met the following requirements: ; like They believe it has good injectability; like They believe the injection rate is moderate. like They believe the injection performance is poor. in, The value is dimensionless, where , , ; -Injection time of the plugging agent during trial injection , h; - Pressure difference before and after the test injection of plugging agent into the sluice, in MPa.

13. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 2, characterized in that, The analysis is based on four aspects: the relationship between oil pressure and pump pressure, the characteristic chart of the double logarithmic curve of pressure drop during well testing, the variation law of normal water injection pressure, and the small slug injection test before profile adjustment. The injectionability assessment results obtained from the pressure rise space during construction, reservoir characteristics, changes in the flow channel development, and the pressure difference before and after the small slug test injection are used as four factors and assigned evaluation scores a, b, c, and d respectively, where a+b+c+d=100; and based on the evaluation scores, the reservoir is divided into multiple injectionability levels.

14. The method for judging the injection of plugging agent before profile control in low-permeability reservoirs according to claim 13, characterized in that, The multiple injection levels include three levels: I, II, and III. Among them, level I has the best injection performance and a total score of α; level II has moderate injection performance and a total score of β; and level III has poor injection performance and a total score of γ. Based on the current well condition or block, the four factors are weighted and scored, and their injection performance is judged as good, medium, or poor. The scores of all factors with good injection performance are summed to obtain the α value; the scores of all factors with moderate injection performance are summed to obtain the β value; and the scores of all factors with poor injection performance are summed to obtain the γ value. Comparing the α, β, and γ values, if the α value is the largest, the overall judgment is good injection performance, with an injection performance level of I; if the β value is the largest, the overall judgment is moderate injection performance, with an injection performance level of II; and if the γ value is the largest, the overall judgment is poor injection performance, with an injection performance level of III.

15. A method for formulating a pretreatment scheme for plugging agent injection before profile control in low-permeability reservoirs, characterized in that, The injectionability level of the plugging agent is determined by the pre-profile injection method for low-permeability reservoirs as described in any one of claims 1-14. If the injectionability level is Level I, the plugging agent is injected directly; if the injectionability level is Level II, well washing is required before the plugging agent is injected; if the injectionability level is Level III, acidizing and well washing are required before the plugging agent is injected.

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