Collaborative optimization process for class-II oil layer weak-base three-component combination flooding injection system

Abstract

The invention discloses a collaborative optimization process for a class-II oil layer weak-base three-component combination flooding injection system, and solves the problem that the coincidence rate of an overall scheme of a three-component system is low due to the fact that it is difficult to ensure that alkali concentration is injected according to design in a single-well injection scheme design along with increase of the number of class-II oil layers. The method comprises the following steps: S1, establishing a ternary flooding agent concentration cooperative adjustment technology chart, and determining the alkali concentration of a single well; s2, determining a single well of which the alkali concentration exceeds a reasonable range due to the fact that the polymer concentration is not in a reasonable range based on the determined alkali concentration of the single well by applying the chart; and S3, measures are taken for the single well with the polymer concentration not within the reasonable range and the alkali concentration exceeding the reasonable range, so that the polymer concentration and the alkali concentration of the injection wells in the whole area are kept within the reasonable range. According to the process, targeted measures are taken for different types of injection wells, the oil layer condition can be effectively improved, the scheme coincidence rate and the injection quality qualification rate are increased, and a solid foundation is laid for more effectively displacing remaining oil.

Description

Technical Field

[0001] This invention relates to the field of tertiary oil recovery technology, and in particular to a synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs. Background Technology

[0002] Over the past few decades, ternary composite flooding technology has gradually moved from laboratory research to field trials, and from pilot tests to large-scale promotion. The scale of field applications of ternary composite flooding has continuously expanded, the amount of reserves utilized has increased, and the production ratio has gradually risen. While certain development results have been achieved in the fields, supporting technologies have also been gradually improved. However, many technical problems still hinder the large-scale promotion and application of ternary composite flooding technology. Weakly alkaline ternary composite flooding fully utilizes the different functions of alkali, surfactant, and polymer, as well as the synergistic effects between the agents, to achieve good oil displacement effects, possessing the dual benefits of expanding the swept volume and improving oil displacement efficiency. However, with the increase in the number of Class II oil layers and the increase in planar and vertical heterogeneity, it is difficult to ensure that the alkali concentration is injected according to the designed scheme in the design of single-well injection plans.

[0003] According to existing ternary fluid mixing technology, a low-pressure binary fluid is prepared by polymer and surfactant, and a high-pressure binary fluid is prepared by alkali and surfactant. After uniform mixing according to the design scheme, the two are injected into individual wells. The alkali concentration and polymer concentration in the mixed displacement fluid are inversely proportional. However, as the number of Class II oil layers increases, the horizontal and vertical heterogeneity increases, resulting in significant differences between individual wells. This leads to some poorly developed wells receiving lower polymer concentrations, resulting in excessively high alkali concentrations; conversely, some wells with better development receive higher polymer concentrations, resulting in excessively low alkali concentrations. This phenomenon leads to a low overall compliance rate of the ternary system scheme, failing to meet the design requirements and impacting the block development effect. Summary of the Invention

[0004] This invention addresses the problem in the prior art where, with the increase in the number of Class II oil-bearing layers, it is difficult to guarantee the alkali concentration in the single-well injection scheme design, leading to a low overall scheme compliance rate of the ternary system. It provides a synergistic optimization process for a weakly alkaline ternary composite flooding injection system in Class II oil-bearing layers. This synergistic optimization process, by taking targeted measures for different types of injection wells, can effectively improve reservoir conditions, increase scheme compliance rate and injection quality qualification rate, laying a solid foundation for more effective displacement of residual oil.

[0005] The present invention solves its problems through the following technical solution: the synergistic optimization process of the weakly alkaline ternary composite flooding injection system for Class II oil reservoirs includes the following steps:

[0006] S1: Based on a weakly alkaline ternary composite flooding injection system, the injected polymer concentration was determined according to the development status of individual wells throughout the area. The high-pressure end alkali concentration was clarified by combining the correspondence between alkali concentration and polymer concentration to ensure a reasonable alkali concentration throughout the area. A technical chart for the coordinated adjustment of ternary flooding agent concentration was established.

[0007] Determine the alkali concentration in a single well;

[0008] S2: Using the established ternary flooding agent concentration synergistic adjustment technology chart, based on the determined alkali concentration of a single well, identify single wells where the polymer concentration is not within a reasonable range, resulting in the alkali concentration exceeding the reasonable range;

[0009] S3: Implement measures for single wells where the polymer concentration is outside the reasonable range, resulting in the alkali concentration exceeding the reasonable range, so that the polymer concentration and alkali concentration of all injection wells in the area are kept within the reasonable range.

[0010] Furthermore, in the weak base ternary composite flooding injection system of step S1, the main agents in the high-pressure binary system are alkali and surfactant; the main agents in the low-pressure binary system are polymer and surfactant, and the polymer and alkali concentrations are inversely proportional.

[0011] Furthermore, the appropriate value for the alkali concentration in step S1 is 1.08-1.32%.

[0012] Furthermore, the appropriate alkali concentration in step S1 is 1.2%.

[0013] Furthermore, the method for establishing the technical pattern for synergistic adjustment of ternary flooding agent concentration in step S1 is as follows:

[0014] The appropriate injection polymer concentration should be determined based on the development status of a single well, while the low-pressure binary end polymer concentration should be clearly defined.

[0015] The alkali concentration at the high-pressure binary end and the single-well ratio are determined based on the reasonable value of the alkali concentration in the whole area and the corresponding relationship between the polymer concentration and alkali concentration in a single well.

[0016] Curves were fitted using the correlation between polymer and alkali concentrations, and a technical chart for synergistic adjustment of ternary flooding agent concentration was established.

[0017] Furthermore, the single wells in step S2 where the polymer concentration is outside the range, resulting in the alkali concentration exceeding the reasonable range, are respectively poorly developed injection wells and well-developed injection wells.

[0018] Furthermore, step S3, for single wells where the polymer concentration is outside the acceptable range, resulting in the alkali concentration exceeding the reasonable range, implements the following measures:

[0019] For poorly developed injection wells, polymer concentration can be increased by combining fracturing measures;

[0020] For well-developed injection wells, the polymer concentration was reduced by sealing large channels in conjunction with profile control measures, thereby keeping the polymer and alkali concentrations of injection wells throughout the region within a reasonable range.

[0021] Furthermore, the poorly developed injection wells are those whose effective thickness is more than 50% lower than the overall area or whose permeability is more than 30% lower than the overall area.

[0022] Furthermore, the well-developed injection wells are defined as those with an effective thickness that is more than 30% higher than the overall thickness or a permeability that is more than 20% higher than the overall permeability.

[0023] Furthermore, the fracturing measures specifically include:

[0024] Fracturing was carried out, with whole-well fracturing in the fracturing sections. Selective fracturing was used for multiple thin and poor-quality layers, while conventional fracturing was used for thick oil layers.

[0025] Compared with the above-mentioned background technology, the present invention has the following beneficial effects:

[0026] This invention relates to a synergistic optimization technology for a weakly alkaline ternary composite flooding injection system in Class II oil reservoirs. By taking targeted measures for different types of injection wells, it effectively improves reservoir conditions, increases the compliance rate of the plan and the qualification rate of injection quality, lays a solid foundation for more effective displacement of residual oil, and can ensure the development effect of the block.

[0027] In field applications, for poorly developed injection wells, fracturing measures were used to increase polymer concentration; for well-developed injection wells, profile control measures were used to plug large channels and reduce polymer concentration, while alkali concentration remained within a reasonable range. In the study area, the alkali concentration compliance rate of injection wells reached over 96%, the injection quality compliance rate reached over 98%, and the enhanced oil recovery rate reached over 20%. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the synergistic optimization process of the weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to the present invention.

[0029] Figure 2 This is a diagram illustrating the synergistic adjustment technology of the ternary flooding agent concentration according to an embodiment of the present invention;

[0030] Figure 3 This is a tracking curve of the quality qualification rate of injection into a Class II oil layer in a certain block according to an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0032] like Figure 1As shown, a synergistic optimization process for a weakly alkaline ternary composite flooding injection system in Class II reservoirs includes the following steps:

[0033] S1: Based on the weakly alkaline ternary composite flooding injection system, the injection polymer concentration is determined according to the development status of individual wells in the whole area. The high-pressure end alkali concentration is determined by combining the correspondence between alkali concentration and polymer concentration to ensure that the alkali concentration in the whole area is reasonable. A technical chart for the coordinated adjustment of ternary flooding injection agent concentration is established to determine the alkali concentration of individual wells. The reasonable value of the alkali concentration in step 1 is 1.08-1.32%.

[0034] In the weak base ternary composite flooding injection system, the main agents in the high-pressure binary system are alkali and surfactant; the main agents in the low-pressure binary system are polymer and surfactant, and the polymer and alkali concentrations are inversely proportional.

[0035] The method for establishing a technical chart for the synergistic adjustment of ternary flooding agent concentration is as follows:

[0036] The appropriate injection polymer concentration should be determined based on the development status of a single well, while the low-pressure binary end polymer concentration should be clearly defined.

[0037] At the same time, based on the reasonable value of alkali concentration in the whole area and the corresponding relationship between polymer concentration and alkali concentration in a single well, the alkali concentration at the high-pressure binary end and the single-well ratio are determined.

[0038] Curves were fitted using the correlation between polymer and alkali concentrations, and a technical chart for synergistic adjustment of ternary flooding agent concentration was established.

[0039] S2: Using the established ternary flooding agent concentration synergistic adjustment technology chart, based on the determined alkali concentration of a single well, identify single wells where the polymer concentration is not within a reasonable range, resulting in the alkali concentration exceeding the reasonable range;

[0040] The wells whose polymer concentration was outside the range, resulting in alkali concentrations exceeding the reasonable range, were classified as poorly developed injection wells and well-developed injection wells.

[0041] The poorly developed injection wells are those whose effective thickness is more than 50% lower than the overall area or whose permeability is more than 30% lower than the overall area.

[0042] The wells with good development are those whose effective thickness is more than 30% higher than that of the whole area or whose permeability is more than 20% higher than that of the whole area.

[0043] S3: For single wells where the polymer concentration is outside the reasonable range, resulting in the alkali concentration exceeding the reasonable range, implement measures to ensure that the polymer and alkali concentrations of all injection wells in the entire area remain within the reasonable range. Specific measures are as follows:

[0044] For poorly developed injection wells, polymer concentration can be increased by combining fracturing measures;

[0045] For well-developed injection wells, the polymer concentration was reduced by sealing large channels in conjunction with profile control measures, thereby keeping the polymer and alkali concentrations of injection wells throughout the region within a reasonable range.

[0046] Example 1

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the following description, taking a Class II oil reservoir test area in a certain block of Daqing Oilfield as an example, will be further detailed with reference to the accompanying drawings.

[0048] 1. A technical chart for synergistic adjustment of ternary flooding agent concentration was established.

[0049] In the weakly alkaline ternary composite flooding injection system, the main agents in the high-pressure binary system are alkali and surfactant, while the main agents in the low-pressure binary system are polymer and surfactant. The polymer and alkali concentrations are inversely proportional. With the increase in the number of Class II oil layers, the horizontal and vertical heterogeneity increases, resulting in significant differences between individual wells. This leads to some poorly developed wells (effective thickness more than 50% lower than the overall area or permeability more than 30% lower than the overall area) injecting lower polymer concentrations, resulting in excessively high alkali concentrations; conversely, some wells with better development (effective thickness more than 30% higher than the overall area or permeability more than 20% higher than the overall area) inject higher polymer concentrations, resulting in excessively low alkali concentrations. The reasonable alkali concentration for injecting ternary main slugs in the study area should be around 1.2% (with a fluctuation of 10%), and the reasonable range should be 1.08-1.32%. Figure 1 This approach can achieve better development results and economic benefits. Therefore, based on the development status of individual wells, we determine a reasonable polymer injection concentration. On this basis, we clarify the polymer concentration at the low-pressure binary end. Simultaneously, based on the reasonable value of the overall alkali concentration (approximately 1.2%) and the correlation between polymer and alkali concentrations, we determine the alkali concentration at the high-pressure binary end and the single-well ratio. After clarifying the above information, we use the correlation between polymer and alkali concentrations to fit curves and establish a technical chart for the coordinated adjustment of ternary flooding agent concentrations, such as... Figure 2 As shown, the reasonable range of polymer concentration and alkali concentration for single-well injection is clearly defined.

[0050] Taking this test area as an example, targeted measures were taken for different types of injection wells using charts to improve reservoir conditions and increase the compliance rate of the treatment plan and the quality qualification rate of injection. The demonstration area contained 114 injection wells. Among them, 10 wells with poor development had an effective thickness of only 8.6m, 5.1m lower than the overall area, and a permeability of 305mD, 115mD lower than the overall area. For these 10 injection wells, polymer concentrations were increased in conjunction with fracturing measures. Conversely, 12 injection wells with better development had an effective thickness of 16.8m, 3.1m higher than the overall area, and a permeability of 501mD, 81mD higher than the overall area. For these 12 injection wells, polymer concentrations were reduced by combining profile control and plugging of large channels. This ensured that the polymer and alkali concentrations of the injection wells throughout the area remained within reasonable ranges, effectively improving the compliance rate of the treatment plan and the quality qualification rate of injection. The concentration classification of the ternary system prepared for single wells after treatment is shown in Table 1.

[0051] Table 1

[0052]

[0053]

[0054] The tracking curve for the quality qualification rate of injection into the Class II oil reservoir in this block is as follows: Figure 3 As shown. Based on the above research findings, the injection quality qualification rate in the study area reached over 98%. Figure 3 This laid the foundation for maximizing the recovery rate of the block.

[0055] 2. Select one well in the demonstration area with an alkali concentration higher than and one well with a concentration lower than a reasonable range, and implement measures accordingly.

[0056] In this embodiment, one fracturing well and one profile adjustment well were selected in the demonstration area. After the measures were implemented, the concentration of the injected chemical agent in each well met the requirements of the plan.

[0057] 1) Effect of fracturing in injection wells

[0058] Well A has a sandstone thickness of 14.3m, an effective thickness of 9.2m, and a permeability of 253mD. Based on the single-well development status and dynamic parameters, the injected concentration was 1790mg / L, and the alkali concentration was 1.35%, which did not meet the design requirements. Therefore, fracturing was implemented on the well. The fracturing interval was full-well fracturing, with selective fracturing for multiple thin and poor-quality layers and conventional fracturing for thick oil layers. After the measures were taken, the polymer concentration was adjusted to 1920mg / L, and the alkali concentration reached 1.29%, both meeting the design requirements.

[0059] 2) Effect of injection well profile control implementation

[0060] Well B has a sandstone thickness of 18.9m, an effective thickness of 13.3m, and a permeability of 444mD. Based on the single-well development status and dynamic parameters, the injection concentration in this well was 2750mg / L, and the alkali concentration was 0.88%, which did not meet the design requirements. Therefore, profile control was implemented for this well, targeting the section where the single-layer injection volume reached more than 60%. After the measures were taken, the polymer concentration was adjusted to 2280mg / L, and the alkali concentration reached 1.09%, both meeting the design requirements.

[0061] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the implementation methods of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the present invention.

Claims

1. A synergistic optimization process for a weakly alkaline ternary composite flooding injection system in Class II oil reservoirs, characterized in that: Includes the following steps: S1: Based on the weak-alkali ternary composite flooding injection system, the injection polymer concentration was determined according to the development status of individual wells in the whole area. The high-pressure end alkali concentration was determined by combining the correspondence between alkali concentration and polymer concentration to ensure that the alkali concentration in the whole area is reasonable. A technical chart for the coordinated adjustment of ternary flooding agent concentration was established to determine the alkali concentration of individual wells. S2: Using the established ternary flooding agent concentration synergistic adjustment technology chart, based on the determined alkali concentration of a single well, identify single wells where the polymer concentration is not within a reasonable range, resulting in the alkali concentration exceeding the reasonable range; S3: Implement measures for single wells where the polymer concentration is outside the reasonable range, resulting in the alkali concentration exceeding the reasonable range, so that the polymer concentration and alkali concentration of all injection wells in the area are kept within the reasonable range.

2. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to claim 1, characterized in that: In the weak base ternary composite flooding injection system of step 1, the main agents in the high-pressure binary system are alkali and surfactant; the main agents in the low-pressure binary system are polymer and surfactant, and the polymer and alkali concentrations are inversely proportional.

3. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to claim 1, characterized in that: The appropriate alkali concentration for step 1 is 1.08-1.32%.

4. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to claim 3, characterized in that: The appropriate alkali concentration for step 1 is 1.2%.

5. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to claim 1, characterized in that: The method for establishing the technical chart for the synergistic adjustment of the concentration of the ternary flooding agent in step 1 is as follows: The appropriate injection polymer concentration should be determined based on the development status of a single well, while the low-pressure binary end polymer concentration should be clearly defined. The alkali concentration at the high-pressure binary end and the single-well ratio are determined based on the reasonable value of the alkali concentration in the whole area and the corresponding relationship between the polymer concentration and alkali concentration in a single well. Curves were fitted using the correlation between polymer and alkali concentrations, and a technical chart for synergistic adjustment of ternary flooding agent concentration was established.

6. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to claim 1, characterized in that: In step 2, the single wells whose polymer concentration was outside the range, resulting in an alkali concentration exceeding the reasonable range, were respectively poorly developed injection wells and well-developed injection wells.

7. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to claim 1, characterized in that: The measures to be implemented in step S3 for single wells where the polymer concentration is outside the range, resulting in the alkali concentration exceeding the reasonable range, are as follows: For poorly developed injection wells, polymer concentration can be increased by combining fracturing measures; For well-developed injection wells, the polymer concentration was reduced by sealing large channels in conjunction with profile control measures, thereby keeping the polymer and alkali concentrations of injection wells throughout the region within a reasonable range.

8. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to claim 6 or 7, characterized in that: The poorly developed injection wells are those whose effective thickness is more than 50% lower than the overall area or whose permeability is more than 30% lower than the overall area.

9. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system for Class II oil reservoirs according to claim 6 or 7, characterized in that: The wells with good development are defined as those with an effective thickness that is more than 30% higher than the overall thickness or a permeability that is more than 20% higher than the overall permeability.

10. The synergistic optimization process for a weakly alkaline ternary composite flooding injection system in a Class II oil reservoir according to claim 7, characterized in that: The fracturing measures are specifically as follows: Fracturing was carried out, with whole-well fracturing in the fracturing sections. Selective fracturing was used for multiple thin and poor-quality layers, while conventional fracturing was used for thick oil layers.

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