Method for comprehensively adjusting weak-base three-component combination flooding after polymer flooding of first-class oil layer

Abstract

The invention relates to a weak-base three-component combination flooding comprehensive adjustment method after polymer flooding of a first-class oil layer. The problem that a proper comprehensive adjustment method is seriously lacked due to low-efficiency and ineffective circulation of dominant seepage channel development after polymer flooding of a first-class oil layer is solved. The method comprises the steps that S1, in the non-effective period of a producing well, an injection well adopts a double-height injection system, and a dominant seepage channel, injection-production balance and pressure balance are regulated and controlled; s2, in the water content decline period, large-scale separate injection is carried out, injection well measure adjustment is optimized, profile production is improved, and oil production well effectiveness is promoted; s3, in the water content low value period, the injection and production well fracturing mode is optimized; the injection-production capacity is kept; large-scale separate injection is increased, and the interval strength is optimized; and S4, in the water content rising period, high-concentration low-speed injection of the injection well is kept, and water content rising is controlled. According to the method, optimization measures of different injection stages of weak-base three-component combination flooding after polymer flooding of the first-class oil layer are adjusted, dominant seepage channels are blocked, remaining oil of medium and low permeable layers is excavated, and the block development effect is improved.

Description

Technical Field:

[0001] The present invention relates to the technical field of oil production engineering, and particularly relates to a comprehensive adjustment method for weak alkali ternary composite flooding after polymer flooding in Class I oil reservoirs. Background Art:

[0002] In the past few decades, the ternary composite flooding technology has gradually moved from laboratory research to field tests. In terms of scale, from pilot tests to large-scale promotion, the scale of the ternary composite flooding field has been continuously expanding; in terms of application scope, it has gradually expanded from Class II oil reservoirs to Class III oil reservoirs and the oil reservoirs after polymer flooding in Class I oil reservoirs; in terms of production, the reserves in use have been continuously increasing, and the production ratio has been gradually rising. The weak alkali ternary composite flooding technology in Class II oil reservoirs has gradually matured. However, due to the development of preferential flow channels in the oil reservoirs after polymer flooding in Class I oil reservoirs and serious inefficient and ineffective circulation, the weak alkali ternary composite flooding technology in Class II oil reservoirs is not applicable to it. Currently, there is no comprehensive adjustment technology for weak alkali ternary composite flooding after polymer flooding in Class I oil reservoirs. Summary of the Invention:

[0003] The present invention aims to solve the problem in the background art that there is a lack of a suitable comprehensive adjustment method for the development of preferential flow channels and serious inefficient and ineffective circulation in the oil reservoirs after polymer flooding in Class I oil reservoirs, and provides a comprehensive adjustment method for weak alkali ternary composite flooding after polymer flooding in Class I oil reservoirs. According to the characteristics of the development of preferential flow channels in Class I oil reservoirs after polymer flooding, this comprehensive adjustment method for weak alkali ternary composite flooding after polymer flooding in Class I oil reservoirs optimizes the adjustment measures in different injection stages of weak alkali ternary composite flooding after polymer flooding in Class I oil reservoirs, thereby blocking the preferential flow channels, tapping the remaining oil in medium and low permeability layers, and improving the development effect of the block.

[0004] The present invention can achieve the above object through the following technical solutions: This comprehensive adjustment method for weak alkali ternary composite flooding after polymer flooding in Class I oil reservoirs implements corresponding adjustment countermeasures according to different injection stages of the block, specifically including the following steps:

[0005] S1: During the period when the production well has not yet responded, the injection well adopts a "double high" injection system design with ultra-high molecular weight and high viscosity to regulate the preferential flow channels, adjust the injection-production balance and pressure balance;

[0006] S2: During the period when the water cut of the production well is decreasing, individual adjustment is carried out on the injection well, and large-scale separate injection is carried out to optimize the adjustment of the injection well measures, improve the profile utilization, and promote the response of the production well;

[0007] S3: During the period when the water cut of the production well is at a low value, quantify the measure principle, optimize the fracturing method of the injection-production wells, increase the intensity of the fracturing measures, and ensure the injection-production capacity; increase the large-scale separate injection and optimize the layer section strength;

[0008] S4: During the period when the water cut of the production well is rising, maintain high-concentration and low-speed injection in the injection well to control the rise of the water cut and improve the effect efficiency.

[0009] Furthermore, the "double high" injection system with ultra-high molecular weight and high viscosity in step S1 is a 25 million ultra-high molecular weight polymer and a high-viscosity injection mode above 100 mPa·s;

[0010] Furthermore, the method for regulating the preferential flow channels after polymer flooding in step S1 includes:

[0011] S1.1: Changing the injection-production streamline of the polymer flooding well pattern;

[0012] S1.2: Combining with weak alkali ASP flooding to expand the swept volume and improve the oil displacement efficiency simultaneously;

[0013] S1.3: Adopting a "double high" injection mode with ultra-high molecular weight and high viscosity during the injection process to effectively control the preferential flow channels.

[0014] Furthermore, the method of changing the injection-production streamline of the polymer flooding well pattern in step S1.1 is as follows: The wells on the original main injection-production streamline of the polymer flooding well pattern become the wells on the branch streamline during production after polymer flooding, and the wells on the original branch injection-production streamline of the polymer flooding well pattern become the wells on the main streamline during production after polymer flooding, that is, controlling the inefficient and ineffective circulation and tapping the remaining oil in the branch streamline by changing the streamline.

[0015] Furthermore, the period when the production well has not responded corresponds to the pre-polymer flooding;

[0016] The period of water cut decline in the production well corresponds to the initial stage of the main ASP slug;

[0017] The period of low water cut in the production well corresponds to the middle and late stages of the main ASP slug to the middle stage of the secondary ASP slug;

[0018] The period of water cut rise in the production well corresponds to the late stage of the secondary ASP slug to the subsequent polymer flooding.

[0019] Furthermore, in the period of low water cut in the production well in step S3, the method for optimizing the fracturing method of injection-production wells is as follows:

[0020] After polymer flooding in the first-class oil reservoir, the preferential permeation channels are well developed. When selecting layers for fracturing of the production well, the preferential flow channels should be avoided, and the thin and poor layers should be fractured to prevent breakthrough. Therefore, when fracturing the oil reservoir with preferential flow channels, selective fracturing is preferably used, and only the thin and poor layers are fractured.

[0021] Furthermore, in the period of low water cut in the production well in step S3, the principle of quantitative measures includes: the principle of well and layer selection for stimulation measures.

[0022] Furthermore, for the principle of well and layer selection for stimulation measures, fracturing of the production well is carried out for the well layers with a large decline in liquid production capacity, low water cut, and high stimulation potential.

[0023] Furthermore, in the period of water cut decline in the production well in step S2, the method for individual adjustment of injection wells includes:

[0024] Quantify and establish the classification criteria for well groups through the static parameters of injection wells, and classify them according to parameters such as effective thickness, permeability, proportion of channel sand thickness, and polymer flooding control degree; formulate targeted adjustment countermeasures according to the development characteristics.

[0025] Furthermore, the formulating of targeted adjustment countermeasures according to the development characteristics includes:

[0026] For injection wells with mainly channel development, good connectivity, good permeability, and high control degree, mainly inject with high concentration and high intensity to ensure "inject enough agent and inject good agent", and evenly adjust the profile;

[0027] For injection wells with general development, strengthen the injection in the direction of high oil saturation and optimize the injection in the direction of low oil saturation to promote the balanced response of connected oil wells;

[0028] For injection wells with poor development, adopt the method of "low concentration and low intensity" to ensure continuous injection.

[0029] Compared with the above background technology, the present invention may have the following beneficial effects:

[0030] The comprehensive adjustment method of weak alkali ternary composite flooding after polymer flooding in a class of oil layers of the present invention is of great significance for improving the test effect of weak alkali ternary composite flooding after polymer flooding in a class of oil layers. Using the comprehensive adjustment mode of "block channels, adjust balance, improve utilization, protect capacity, and control water cut", the suction thickness ratio of medium and low permeability oil layers less than 500 mD can be increased by more than 30 percentage points, and the recovery rate can be increased by more than 10 percentage points. It effectively increases the suction volume of medium and low permeability layers and effectively improves the utilization degree of medium and low permeability layers. Brief Description of the Drawings:

[0031] Figure 1 is the flow chart of the comprehensive adjustment method of the present invention;

[0032] Figure 2 is the Hall curve of the test area in the embodiment of the present invention;

[0033] Figure 3 is the relationship chart of injection-production ratio and water cut classification in the well group in the embodiment of the present invention;

[0034] Figure 4 is the cross-sectional comparison diagram of oil layers with different permeabilities in the embodiment of the present invention. Detailed Embodiment:

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below in conjunction with the drawings.

[0036] As Figure 1As shown in the figure, a comprehensive adjustment method for weak-alkali ASP flooding after polymer flooding in a certain type of oil reservoir includes the following steps:

[0037] S1: During the ineffective production period of production wells, a "dual-high" injection system design with ultra-high molecular weight and high viscosity is adopted for injection wells to regulate the dominant flow channels and adjust the injection-production balance and pressure balance; that is, the adjustment countermeasure of "blocking channels and adjusting balance".

[0038] The "dual-high" injection system with ultra-high molecular weight and high viscosity is a polymer with an ultra-high molecular weight of 25 million and a high-viscosity injection mode above 100 mPa·s.

[0039] The method for regulating the dominant flow channels after polymer flooding includes:

[0040] S1.1: Changing the injection-production streamlines of the polymer flooding well pattern; that is, the wells on the original main injection-production streamline of the polymer flooding well pattern become the wells on the diversion streamline during production after polymer flooding, and the wells on the original diversion streamline of the polymer flooding well pattern become the wells on the main streamline during production after polymer flooding, that is, controlling the inefficient and ineffective circulation and tapping the remaining oil in the diversion streamline by changing the streamlines.

[0041] S1.2: Combining with weak-alkali ASP flooding to expand the swept volume and improve the oil displacement efficiency at the same time.

[0042] S1.3: Adopting a dual-high injection mode with ultra-high molecular weight and high viscosity during the injection process to effectively control the dominant flow channels.

[0043] S2: During the water cut decline period of production wells, individual adjustments are made to injection wells, and large-scale separate injection is carried out to optimize the measure adjustment of injection wells, improve the profile utilization, and promote the effectiveness of production wells; that is, the adjustment countermeasure of "improving utilization".

[0044] The method for making individual adjustments to injection wells during the water cut decline period of production wells includes:

[0045] By using the static parameters of injection wells, a classification standard for well groups is quantitatively established and classified according to parameters such as effective thickness, permeability, proportion of channel sand thickness, and polymer flooding control degree; targeted adjustment countermeasures are formulated according to the development characteristics.

[0046] The targeted adjustment countermeasures formulated according to the development characteristics include:

[0047] For injection wells mainly developed by channels, with good connectivity, good permeability, and high control degree, high-concentration and high-intensity injection is mainly carried out to ensure "inject enough agent and inject good agent" and evenly adjust the profile; for injection wells with general development, strengthen the injection in the direction of high oil saturation and optimize the injection in the direction of low oil saturation to promote the balanced effectiveness of connected oil wells; for injection wells with poor development, adopt the "low-concentration and low-intensity" method to ensure continuous injection.

[0048] S3: During the low water cut period of the oil production well, quantify the measure principle, optimize the fracturing method of injection-production wells, increase the intensity of fracturing measures, and ensure the injection-production capacity; increase the large-scale separate injection and optimize the interval strength; this is the adjustment countermeasure of "ensuring capacity".

[0049] During the low water cut period of the oil production well, the optimization of the fracturing method of injection-production wells is as follows:

[0050] After polymer flooding in the first-class oil reservoir, the development of preferential seepage channels is significant. When selecting layers for fracturing in the oil production well, avoid the preferential seepage channels and fracture the thin and poor layers to prevent breakthrough. Therefore, when fracturing the oil reservoir with preferential seepage channels, selective fracturing is preferably used, only fracturing the thin and poor layers.

[0051] During the low water cut period of the oil production well in step S3, the quantification of measure principles includes: the well and layer selection principle for stimulation measures.

[0052] The well and layer selection principle for stimulation measures is to implement fracturing on the oil production well for the well layers with a large decline in liquid production capacity, low water cut, and high measure potential.

[0053] S4: During the water cut rising period of the oil production well, maintain high-concentration and low-rate injection in the injection well, control the rising of water cut, and improve the effect and efficiency. This is the adjustment countermeasure of "controlling water cut".

[0054] Example 1

[0055] To make the objectives, technical solutions, and advantages of the present invention clearer, in this example, one weak alkaline ASP flooding test area after polymer flooding in the first-class oil reservoir in the western part of the second northern area of the Sabei Development Zone of the Daqing Oilfield is selected as an example, and the present invention will be further described in detail with reference to the accompanying drawings.

[0056] In this example, one weak alkaline ASP flooding test area after polymer flooding in the first-class oil reservoir is selected. After implementation, the oil recovery rate can be increased by more than 10 percentage points.

[0057] The injection stage of this test area is divided into blank water flooding, pre-polymer flooding, main ASP slug, secondary ASP slug, and subsequent polymer flooding; among them, the pre-polymer flooding generally corresponds to the ineffective period, the initial stage of the main ASP slug corresponds to the water cut decline period, the middle and late stages of the main ASP slug to the middle stage of the secondary ASP slug correspond to the low value period, and the late stage of the secondary ASP slug to the subsequent polymer flooding is the water cut rising period. According to different injection stages in the block, corresponding adjustment countermeasures are implemented.

[0058] Step 1: Adopt a "double high" design for the injection well. Since the remaining oil is scattered after polymer flooding and there are preferential seepage channels, to effectively control the preferential seepage channels and mobilize the medium and low permeability layers, high-concentration and high-viscosity injection is carried out throughout the injection well, with the injection viscosity limit above 100 mPa·s, and the injection pressure of chemical flooding rises steadily.

[0059] Step 2: Optimize the injection-production parameters and balance the pressure system. Establish a relationship chart of injection-production ratio and water cut classification, such asFigure 3 As shown in Figure 3 , the test area is divided into four intervals by using the cumulative injection-production ratio and the water cut grading interval, namely the injection-increasing area, the liquid-control area, the maintaining area and the injection-control area. For the well areas with low injection-production ratio and high water cut, liquid control is mainly carried out; for the well areas with low injection-production ratio and low water cut, injection increasing is mainly carried out; for the well areas with high injection-production ratio and high water cut, injection control is mainly carried out. The relationship chart of injection-production ratio and water cut classification ( Figure 3 ), optimize parameters by region to maintain injection-production balance. After adjustment, the total pressure difference is near the original formation pressure, and the production pressure difference is within the reasonable range of 4 - 7 MPa. The pressure difference between wells is reduced to less than 0.3 MPa, and the pressure between wells is more balanced.

[0060] Step 3: Conduct personalized adjustment and large-scale separate injection to improve the degree of reservoir utilization. Design injection parameters for classified wells with a matching rate of over 90.0% to achieve a balanced increase in pressure. Implement large-scale separate injection with a separate injection rate of 85.7% to effectively alleviate the interlayer contradiction.

[0061] The specific process of the above-mentioned personalized adjustment and large-scale separate injection includes:

[0062] Quantify and establish the classification standard of well groups through the static parameters of injection wells. Divide 35 injection wells into four categories, namely A, B, C, and D, according to parameters such as effective thickness, permeability, proportion of channel sand thickness, and polymer flooding control degree. The classification standard of injection wells is shown in Table 1.

[0063] Table 1

[0064]

[0065] For type A injection wells mainly developed with channels, having good connectivity, good permeability, high control degree, and good connectivity, high-concentration and high-intensity injection is mainly carried out to ensure "inject enough agent and inject good agent" and balance the adjustment profile; for type B and C injection wells with general development, strengthen injection in the direction of high oil saturation and optimize injection in the direction of low oil saturation to promote balanced effectiveness of connected oil wells; for type D injection wells with poor development, adopt the method of "low concentration and low intensity" to ensure continuous injection. The injection parameters of classified injection wells are shown in Table 2.

[0066] Table 2

[0067]

[0068] After optimization and adjustment, the matching degree of injection parameters is 94.3%. The effects of classified wells are obvious. The pressures of classified wells rise synchronously, the pressure between wells tends to be balanced, the pressure difference between wells is reduced to less than 0.3 MPa, and a strong injection capacity is maintained.

[0069] Step 4: Optimize stimulation and injection-increasing measures to maintain a strong injection-production capacity. Quantify the measure principle, determine the technical limit, implement targeted adjustment, and keep the injection-production rate above 0.16 PV / a.

[0070] The quantitative measures principle for the optimized production increase and injection increase measures to maintain a strong injection-production capacity is as follows:

[0071] 4.1. Well and layer selection principle for production increase measures: For the well layers with a large decline in liquid production capacity, low water cut, and potential for measures, fracturing is implemented on production wells; the conditions for implementing fracturing on production wells are: 1. The thickness of the measure oil layer is greater than 5m

[0072] 2. The proportion of the first-class connected thickness is greater than 30%

[0073] 3. The proportion of the highly water-flooded thickness is less than 40%

[0074] 4. The water cut reduction is greater than 5%, and the liquid production reduction is greater than 20%

[0075] 5. The total pressure difference is greater than 0 MPa, and the flowing pressure is lower than 4.0 MPa

[0076] 4.2. Well and layer selection principle for injection increase measures:

[0077] For wells with thin thickness, poor permeability, and high injection pressure, fracturing is implemented on injection wells; the conditions for implementing fracturing on injection wells are:

[0078] 1. The permeability of the measure oil layer is less than 0.4 μm²

[0079] 2. The thickness of the oil layer is less than 7m

[0080] 3. The injection pressure is less than 0.5 MPa from the fracture pressure

[0081] 4. General pressure fracturing for thick layers and multi-fracture fracturing for thin and poor layers

[0082] Step Five: High concentration and low speed are adopted to control the water cut rising speed. During the water cut rising period, high concentration and low speed are adhered to. The injection viscosity still remains at a relatively high level, the injection pressure rises slightly steadily, and the monthly water cut rising speed drops from 0.9 percentage points in the initial stage to 0.03 percentage points.

[0083] The Hall curve is plotted using the cumulative injection volume in stages and the cumulative injection pressure. As Figure 2 shown, the Hall curve of this test area indicates that with the injection of chemical agents, the slope of the Hall curve gradually increases, establishing a better seepage resistance.

[0084] The test wells are divided into four categories according to permeability: less than or equal to 300 mD, 300 mD - 500 mD, 500 mD - 800 mD, and greater than 800 mD. Then, the effective thickness absorption ratios of each type of well in each slug are statistically calculated, and a comparison diagram of oil layer profiles with different permeabilities is made to compare the utilization conditions of oil layers with different permeabilities in each slug. The comparison diagrams of five different oil layer profiles with corresponding effective thickness absorption ratios are as Figure 4As shown. The contrast diagram of cross-sections of oil layers with different permeabilities shows that by using the comprehensive adjustment mode of "blocking channels, adjusting balance, improving utilization, maintaining capacity, and controlling water cut", the proportion of the absorption thickness of medium and low permeability oil layers less than 500 mD can be increased by more than 30 percentage points, effectively increasing the absorption volume of medium and low permeability layers and effectively improving the utilization degree of medium and low permeability layers.

[0085] Those of ordinary skill in the art will realize that the embodiments described herein are for helping readers understand the implementation methods of the present invention and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not depart from the essence of the present invention based on these technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. A comprehensive adjustment method for weak alkali ternary composite flooding after polymer flooding in a certain type of oil reservoir, characterized in that: According to different injection stages of the block, corresponding adjustment countermeasures are implemented, which specifically include the following steps: S1: During the ineffective period of the production well, the injection well adopts an injection system design with ultra-high molecular weight and high viscosity to regulate the dominant seepage channels, adjust the injection-production balance and pressure balance; S2: During the water cut decline period of the production well, individualized adjustment is carried out on the injection well, and large-scale separate injection is carried out. The adjustment measures of the injection well are optimized to improve the profile utilization and promote the effectiveness of the production well; S3: During the low water cut period of the production well, the measure principle is quantified, the fracturing method of the injection-production well is optimized, the fracturing measure intensity is increased to ensure the injection-production capacity; large-scale separate injection is increased and the interval strength is optimized; S4: During the water cut rising period of the production well, high-concentration and low-speed injection of the injection well is maintained to control the water cut rise and improve the effect efficiency.

2. The comprehensive adjustment method for weak-alkali ASP flooding after polymer flooding in a certain type of oil reservoir according to claim 1, wherein: The injection system with ultra-high molecular weight and high viscosity in step S1 is a 25-million ultra-high molecular weight polymer and a high-viscosity injection mode above 100 mPa·s.

3. The comprehensive adjustment method for weak alkali ternary composite flooding after polymer flooding in a certain type of oil reservoir according to claim 1, characterized in that: The method for regulating the dominant seepage channels after polymer flooding in step S1 includes: S1.1: Changing the injection-production flow lines of the polymer flooding well pattern; S1.2: Combining with weak alkali ASP flooding to expand the swept volume and improve the oil displacement efficiency at the same time; S1.3: Adopting a double-high injection mode with ultra-high molecular weight and high viscosity during the injection process to effectively control the dominant seepage channels.

4. The comprehensive adjustment method for weak alkali ASP flooding after polymer flooding in a certain type of oil reservoir according to claim 3, characterized in that: The way of changing the injection-production flow lines of the polymer flooding well pattern in step S1.1 is as follows: The wells on the main injection-production flow line of the original polymer flooding well pattern become the wells on the split flow line during production after polymer flooding, and the wells on the split injection-production flow line of the original polymer flooding well pattern become the wells on the main flow line during production after polymer flooding, that is, the inefficient and ineffective circulation is controlled and the remaining oil in the split flow line is tapped by changing the flow lines.

5. The comprehensive adjustment method of weak alkali ASP flooding after polymer flooding for a type of oil reservoir according to claim 1, characterized in that: The ineffective period of the production well corresponds to the pre-polymer flooding; The water cut decline period of the production well corresponds to the initial stage of the main ASP slug; The low water cut period of the production well corresponds to the middle and late stages of the main ASP slug to the middle stage of the sub-ASP slug; The water cut rising period of the production well corresponds to the late stage of the sub-ASP slug to the subsequent polymer flooding.

6. The comprehensive adjustment method for weak alkali ternary composite flooding after polymer flooding in a certain type of oil reservoir according to claim 1, characterized in that: The method for individualized adjustment of the injection well during the water cut decline period of the production well in step S2 includes: By using the static parameters of the injection well, the classification standard of the well group is quantitatively established, and classification is carried out according to parameters such as effective thickness, permeability, proportion of channel sand thickness and polymer flooding control degree, and targeted adjustment countermeasures are formulated according to the development characteristics.

7. The comprehensive adjustment method for weak alkali ASP flooding after polymer flooding in a certain type of oil reservoir according to claim 6, characterized in that: The targeted adjustment countermeasures formulated according to the development characteristics include: For the injection wells mainly developed by channels, with good connectivity, good permeability and high control degree, high-concentration and high-intensity injection is mainly carried out to evenly adjust the profile; For the injection wells with general development, injection in the direction of high oil saturation is strengthened while injection in the direction of low oil saturation is optimized to promote the balanced effectiveness of the connected oil wells; For the injection wells with poor development, a low-concentration and low-intensity method is adopted to ensure continuous injection.

8. The comprehensive adjustment method for weak-alkali ASP flooding after polymer flooding in a certain type of oil reservoir according to claim 1, characterized in that: The optimized fracturing method of the injection-production well during the low water cut period of the production well in step S3 is as follows: After polymer flooding in a type of oil reservoir, the dominant permeation channels are well developed. When selecting layers for fracturing the production well, the dominant seepage channels should be avoided and the thin and poor layers should be fractured to prevent breakthrough. Therefore, when fracturing the oil layer containing dominant seepage channels, selective fracturing is preferably used to only fracture the thin and poor layers.

9. The comprehensive adjustment method for weak alkali ternary composite flooding after polymer flooding in a certain type of oil reservoir according to claim 1, characterized in that: In step S3 during the low water cut period of the oil production well, the quantification measure principle includes the well and layer selection principle for stimulation measures.

10. The comprehensive adjustment method for weak-alkali ASP flooding after polymer flooding in a certain type of oil reservoir according to claim 9, characterized in that: For the well and layer selection principle of stimulation measures, fracturing of the oil production well is implemented for the well layers with large decline in liquid production capacity, low water cut, and potential for measures.

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