Method for retarding inversion of suction profile of injection well in later stage of chemical flooding of medium-low permeability reservoir

Abstract

The invention relates to the technical field of chemical flooding oilfield development adjustment, in particular to a method for retarding injection well suction profile inversion in the later period of medium-low permeability reservoir chemical flooding. The method comprises the steps that a target well group is determined, a chemical flooding system is continuously injected into the target well group, and original data of the target well group in the initial stage of chemical flooding system injection are recorded; chemical flooding effect data of the target well group are tracked and obtained, suction profile testing is conducted on the target well group regularly, and the suction profile uniformity degree of the target well group is obtained; the alternate injection time of the target well group is determined, alternate injection of the multi-concentration chemical flooding system is conducted on the target well group, and the alternate injection mode of the target well group is determined; and according to the alternate injection opportunity and the alternate injection mode, the alternate injection turns are determined, and reverse rotation of the suction profile of the injection well is slowed down. According to the method, the reversal process of the suction profile of the injection well in the later chemical flooding period is slowed down, the water content recovery speed can be controlled, and the oil increasing effect is improved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical flooding oil field development and adjustment, in particular to a method for slowing down injection well suction profile reversal in the late stage of chemical flooding of medium and low permeability oil reservoirs. Background Art

[0002] With the continuous deepening of oilfield development, the remaining recoverable reserves of large and medium-sized sand body high, medium and low permeability oil reservoirs are gradually decreasing, and narrow sand body medium and low permeability oil reservoirs have become the main replacement for crude oil production. At present, narrow sand body medium and low permeability oil reservoirs have low production, high development costs, and great difficulty in controlling water and controlling decline. In order to improve the development effect of low-grade oil fields and achieve cost reduction and efficiency improvement, it is necessary to take measures such as injecting chemical flooding system slugs to achieve the purpose of increasing oil production and reducing water, thereby improving the efficiency of well groups and blocks.

[0003] In actual production, existing slug displacement methods using chemical flooding systems have the following major shortcomings: First, regarding the effectiveness of the displacement slug, after the chemical flooding system slug is injected, a stable and effective chemical flooding slug should be formed throughout the entire chemical flooding process. In particular, the displacement slug should be uniformly advanced throughout the high, medium, and low permeability layers in the later stages of chemical flooding. Existing methods do not consider the problem of the displacement slug breaking through the high permeability layer as the injection pressure increases in the later stages of chemical flooding. Second, regarding dynamic response, the injection pressure rises steadily. In particular, in the later stages of chemical flooding, as the starting pressure gradient in the high, medium, and low permeability layers changes dynamically, maintaining a stable injection pressure is an effective method to prevent the chemical flooding system from breaking through the high permeability layer. However, existing methods do not consider the fact that the starting pressure gradient may reverse in the later stages of chemical flooding. Third, regarding the injection method, to ensure the effective advancement of the displacement slug in the later stages of chemical flooding in narrow sandbodies and medium- and low-permeability reservoirs, an alternating injection method can be used. Existing methods only consider the injection rate and injection concentration adjustment of continuous injection methods. Therefore, to address these shortcomings, a method for slowing down the reversal of the injection well suction profile in the later stages of chemical flooding in medium- and low-permeability reservoirs is proposed. Summary of the Invention

[0004] (1) Technical issues to be resolved The present invention provides a method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding of medium and low permeability oil reservoirs, so as to overcome the defects of the prior art in that the injection profile reversal occurs frequently in the late stage of chemical flooding, the low water content period cannot be effectively extended, the injection pressure in the late stage of chemical flooding is high, and the injection condition is poor.

[0005] (2) Technical solution To solve the above problems, the present invention provides a method for slowing down the reversal of the suction profile of an injection well in the late stage of chemical flooding in medium- and low-permeability oil reservoirs, comprising: Step S1: determining a target well group and continuously injecting a chemical flooding system into the target well group, and recording the original data of the initial stage of the chemical flooding system injection into the target well group; Step S2: tracking and acquiring chemical flooding effect data of the target well group based on the original data determined in step S1, and regularly performing injection well suction profile testing on the target well group to acquire the uniformity of the suction profile of the target well group in real time; Step S3: Based on the chemical flooding effect data and the uniformity of the suction profile obtained in step S2, the original data obtained in step S1 are compared to determine the alternating injection timing of the target well group; Step S4: performing alternating injection of a multi-concentration chemical flooding system on the target well group determined in step S1 according to the alternating injection timing determined in step S3, and determining an alternating injection mode for the target well group; Step S5: According to the alternating injection timing determined in step S3 and the alternating injection mode determined in step S4, the alternating injection rounds of the target well group are further determined to slow down the reversal of the injection well suction profile.

[0006] Preferably, in step S1, the original data of the initial stage of chemical flooding system injection into the target well group includes a preset chemical flooding slug of the target well group, a fracture pressure of the target well group, an initial chemical flooding injection pressure of the target well group, and a water cut value before chemical flooding of the target well group.

[0007] Preferably, in step S2, the chemical flooding slug range of the target well group is from zero to a preset chemical flooding slug of the target well group.

[0008] Preferably, in step S2, the chemical flooding effect data of the target well group includes the injection pressure of the target well group and the water content value of the target well group.

[0009] Preferably, in step S2, the period of regularly performing the inhalation profile test is 3-6 months.

[0010] Preferably, in step S3, in the uniformity of the suction profile of the target well group, the alternating injection timing of the target well group is the injection chemical flooding slug value when the relative suction amount of the high permeability layer increases.

[0011] Preferably, in step S4, the multi-concentration chemical flooding system includes a first chemical flooding system and a second chemical flooding system, and the concentration of the first chemical flooding system is greater than the concentration of the second chemical flooding system.

[0012] Preferably, in step S5, one round of alternating chemical flooding injection of the target well group includes a first chemical flooding system and a second chemical flooding system.

[0013] Preferably, in step S5, the injection slug of a single round of chemical flooding alternating injection of the target well group is the ratio of the remaining chemical flooding slugs of the target well group to the injection rounds, and the range of the target well group chemical flooding alternating injection rounds is 2-3 times.

[0014] (3) Beneficial effects The present invention provides a method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding of medium and low permeability oil reservoirs. In the late stage of chemical flooding, an alternating injection method is adopted to combine profile adjustment with effective displacement, thereby reducing the seepage resistance of the low permeability layer. By adjusting the injection method and controlling the injection pressure, the injection pressure in the late stage of chemical flooding is kept stable, and the starting pressure gradients of the high, medium and low permeability oil layers are kept similar, thereby enabling the chemical flooding slug to be continuously and effectively advanced, slowing down the reversal process of the suction profile in the late stage of chemical flooding, and controlling the water recovery rate. This method can not only extend the effective period of chemical flooding and improve the oil displacement effect, but also provide reference and guidance for the dynamic control and oil stabilization and water reduction technology of chemical flooding in narrow channel sand bodies in oil fields in the late stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flow chart of a method for slowing down the reversal of the suction profile of an injection well in the late stage of chemical flooding of a low permeability oil reservoir according to an embodiment of the present invention; Figure 2 This is a diagram showing the changes in injection pressure and comprehensive water content of the PF7 block as the chemical flooding system is injected into the pore volume in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] Figure 1 Flowchart of a method for slowing down the reversal of the injection well suction profile in the late stage of chemical flooding of a low permeability oil reservoir according to an embodiment of the present invention. Figure 1 As shown, the present invention provides a method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding of medium and low permeability oil reservoirs, which specifically includes: Step S1: determining a target well group and continuously injecting a chemical flooding system into the target well group, and recording the original data of the initial stage of the chemical flooding system injection into the target well group; Step S2: tracking and acquiring chemical flooding effect data of the target well group based on the original data determined in step S1, and regularly performing injection well suction profile testing on the target well group to acquire the uniformity of the suction profile of the target well group in real time; Step S3: Based on the chemical flooding effect data and the uniformity of the suction profile obtained in step S2, the original data obtained in step S1 are compared to determine the alternating injection timing of the target well group; Step S4: performing alternating injection of a multi-concentration chemical flooding system on the target well group determined in step S1 according to the alternating injection timing determined in step S3, and determining an alternating injection mode for the target well group; Step S5: According to the alternating injection timing determined in step S3 and the alternating injection mode determined in step S4, the alternating injection rounds of the target well group are further determined to slow down the reversal of the injection well suction profile.

[0018] In the present method for slowing down profile reversal, in step S1, the original data of the initial stage of chemical flooding system injection into the target well group includes the preset chemical flooding slug of the target well group, the fracture pressure of the target well group, the initial chemical flooding injection pressure of the target well group, and the water content value before chemical flooding of the target well group.

[0019] In actual application, in step S2, the chemical flooding slug range of the target well group is zero to the preset chemical flooding slug of the target well group. The chemical flooding effect data of the target well group includes the injection pressure of the target well group and the water content value of the target well group. The target well group is regularly tested for suction profiles every 3-6 months.

[0020] In the method for slowing down the profile reversal, in step S3, in the uniformity of the suction profile of the target well group, the alternating injection timing of the target well group is to inject a chemical flooding slug value when the relative suction amount of the high permeability layer increases.

[0021] In practical applications, regarding the judgment of the timing of alternate injection, for injection wells where the injection pressure maintains a steady increase in the later stage of chemical flooding, and the water cut of surrounding oil-producing wells stabilizes at a low water cut period for a period of time and then rises by more than 2 percentage points, combined with the injection well suction profile test results, alternate injection can be implemented for injection wells where the uniformity of the suction profile has deteriorated compared to the early stage.

[0022] In the present method for mitigating profile inversion, in step S4, the multi-concentration chemical flooding system includes a first chemical flooding system and a second chemical flooding system, and the concentration of the first chemical flooding system is greater than the concentration of the second chemical flooding system.

[0023] In practical applications, regarding the determination of the alternating injection method, since the well group adopts a composite ion system chemical drive, the alternating injection method of the first chemical drive system and the second chemical drive system is adopted. This is not only conducive to enhancing the plugging of the high permeability layer, but also can further play the role of low-concentration chemical drive slug in oil displacement in the medium and low permeability layers, which is conducive to further enhancing the chemical drive system's effect of expanding the swept volume, thereby slowing down the profile reversal caused by the chemical drive system entering the medium and low permeability layers, and maintaining dynamic balanced advancement of the displacement slug.

[0024] In the present method for mitigating profile reversal, in step S5, one round of chemical flooding alternating injection of the target well group includes a first chemical flooding system and a second chemical flooding system. The injection slug of a single round of chemical flooding alternating injection of the target well group is a ratio of the remaining chemical flooding slug of the target well group to the number of injection rounds. The range of the target well group chemical flooding alternating injection rounds is 2-3 times.

[0025] It should be noted that in actual application, in step S5, the calculation formula for the remaining injection chemical flooding slug of the target well group is: T=T0-T1 Among them, T is the remaining chemical flooding slug of the target well group, T0 is the preset chemical flooding slug of the target well group, and T1 is the chemical flooding slug when the target well group starts to implement alternating injection.

[0026] In practical applications, the number of alternating injection cycles is determined by the fact that, as the number of injection cycles increases, the utilization of high-permeability layers gradually increases, while the injection capacity of medium- and low-permeability layers also increases, slowing or controlling the rate of water recovery. Therefore, the number of injection cycles should be determined based on the injection pressure and the size of the remaining chemical flood slug in the later stages of chemical flooding. Generally, 2-3 cycles are optimal.

[0027] In practical applications, injecting a chemical flooding plug in the later stage slows down the process of profile reversal, which is of great practical significance for the efficient development of low-grade oil fields. The present invention provides a method for slowing down the suction profile reversal of the injection well in the later stage of chemical flooding in medium- and low-permeability oil reservoirs, including injection mode adjustment and injection pressure control. The injection mode adjustment considers the alternating injection mode of a multi-concentration chemical flooding system for the first time. This method can slow down the suction profile reversal process in the later stage of chemical flooding, thereby controlling the water recovery rate and improving the oil production effect. It provides reference and guidance for the dynamic control and oil stabilization and water reduction technology of chemical flooding in narrow channel sand bodies in oil fields. The working principle of this method for slowing down the suction profile reversal of the injection well in the later stage of chemical flooding in medium- and low-permeability oil reservoirs is described in detail below: Step 1: determine the target well group and continuously inject the chemical flooding system into the target well group, and record the original data of the initial stage of the chemical flooding system injection into the target well group; Step 2: Based on the determined original data, track and obtain the chemical flooding effect data of the target well group, and regularly test the injection well suction profile of the target well group to obtain the uniformity of the suction profile of the target well group in real time; Step 3: Based on the obtained chemical flooding effect data and the uniformity of the suction profile, compare the obtained original data to determine the alternating injection timing of the target well group; Step 4: Perform alternating injection of a multi-concentration chemical flooding system into the target well group according to the determined alternating injection timing, and determine the alternating injection method of the target well group; Step 5: Based on the determined alternating injection timing and alternating injection method, continue to determine the alternating injection rounds of the target well group to achieve the goal of slowing down the reversal of the injection well suction profile.

[0028] In this embodiment, the PF7 well group is taken as the object, that is, the target well group. In the original data, the preset chemical flooding slug of the target well group is 0.30PV, the fracture pressure of the target well group is 12.5 MPa, the initial chemical flooding injection pressure of the target well group is 8.5 MPa, and the water cut value of the target well group before chemical flooding is 95.5%.

[0029] In actual application, after the chemical flooding system was injected into the block at a pressure of nearly 0.02PV, the comprehensive water cut dropped significantly by 2 percentage points to 93.1%; after the chemical flooding system was injected at a pressure of nearly 0.14PV, the comprehensive water cut reached the lowest point of 90.5%, and the low water cut period lasted for 0.12PV; after the chemical flooding system was injected at a pressure of nearly 0.23PV, the comprehensive water cut slowly rebounded to 92.9%. At this time, the injection pressure was 11.5MPa, 1MPa away from the fracture pressure.

[0030] At the same time, in this embodiment, Figure 2 This is a graph showing the changes in injection pressure and comprehensive water content in the PF7 block during chemical flooding injection, as shown in the example of the present invention. Figure 2 As shown in the figure, when the chemical flooding system was injected at 0.23 PV, the comprehensive water cut was 92.9%, which had returned to the level before chemical flooding. Combined with the suction profile of the injection wells during the same period, the relative suction volume of the high permeability layer showed an increasing trend. Therefore, 0.23 PV is the time for the well group to switch to alternate injection.

[0031] In actual applications, the PF7 well group adopts a composite ion system chemical drive, and adopts an alternating injection method of a combination of high-concentration chemical drive system and low-concentration chemical drive system. This is not only conducive to enhancing the plugging of high-permeability layers, but also can further play the role of low-concentration chemical drive plugs in the displacement of medium and low permeability layers.

[0032] It should be noted that the combination of the profile control effect of the high-concentration slug and the displacement effect of the low-concentration slug can slow down the profile reversal phenomenon caused by the chemical flooding system entering the medium and low permeability layers.

[0033] In this example, the chemical flooding system concentration during continuous injection in the PF7 block was relatively high. The high-concentration slugs were the first composite chemical flooding system, containing 600 mg / L polymer, 1200 mg / L crosslinker, and 150 mg / L stabilizer. To ensure the effectiveness of the alternating slug displacement, low-concentration slugs, also known as the second composite chemical flooding system, were specially formulated, containing 400 mg / L polymer, 800 mg / L crosslinker, and 100 mg / L stabilizer.

[0034] In practical applications, by comprehensively considering the impact of injection rounds on displacement pressure difference and water cut, 2-3 rounds of alternating injection can be selected in the later stage of chemical flooding according to the size of the remaining slug. It should be noted that through 2-3 rounds of alternating injection, the degree of utilization of high, medium and low permeability layers in the later stage of chemical flooding can be simultaneously improved, the swept volume can be effectively expanded, the reversal of the suction profile of the injection well and the water cut recovery rate of the oil production well can be slowed down, and the purpose of stabilizing oil and controlling water can be better achieved.

[0035] In this embodiment, the PF7 well group adopts two rounds of alternating injection. Calculation shows that after the PF7 well group switches to alternating injection, the remaining chemical flooding slug is 0.07PV. Alternating injection can be performed in the form of 0.02 low concentration + 0.02 high concentration + 0.02 low concentration + 0.01 high concentration. This allows the chemical flooding system to maintain dynamic synchronous advancement in different permeability layers, expands the permeability distribution span and effective area of ​​the chemical flooding slug in the heterogeneous oil layer, thereby slowing down profile reversal and improving the overall utilization of the oil layer.

[0036] The present invention provides a method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding in medium- and low-permeability oil reservoirs. In the late stage of chemical flooding, an alternating injection method is adopted to combine profile adjustment with effective displacement, thereby reducing the seepage resistance of the low-permeability layer. By adjusting the injection method and controlling the injection pressure, the injection pressure in the late stage of chemical flooding is kept stable, and the starting pressure gradients of the high, medium and low permeability layers are kept similar, thereby continuously and effectively advancing the chemical flooding slug, slowing down the reversal process of the suction profile in the late stage of chemical flooding, and controlling the water recovery rate. This method can not only extend the effective period of chemical flooding and improve the oil displacement effect, but also provide reference and guidance for the dynamic control and oil stabilization and water reduction technology of chemical flooding in narrow channel sand bodies in oil fields in the late stage.

[0037] The above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. Ordinary technicians in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention. The scope of patent protection of the present invention should be defined by the claims.

Claims

1. A method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding of medium and low permeability oil reservoirs, characterized in that: include: Step S1: determining a target well group and continuously injecting a chemical flooding system into the target well group, and recording the original data of the initial stage of the chemical flooding system injection into the target well group; Step S2: tracking and acquiring chemical flooding effect data of the target well group based on the original data determined in step S1, and regularly performing an intake profile test on the target well group to acquire the uniformity of the intake profile of the target well group; Step S3: Based on the chemical flooding effect data and the uniformity of the suction profile obtained in step S2, the original data obtained in step S1 are compared to determine the alternating injection timing of the target well group; Step S4: performing alternating injection of a multi-concentration chemical flooding system on the target well group determined in step S1 according to the alternating injection timing determined in step S3, and determining an alternating injection mode for the target well group; Step S5: According to the alternating injection timing determined in step S3 and the alternating injection mode determined in step S4, the alternating injection rounds of the target well group are further determined to slow down the reversal of the injection well suction profile.

2. The method for slowing down the inversion of the suction profile of the injection well in the late stage of chemical flooding in medium and low permeability oil reservoirs according to claim 1, characterized in that: In step S1, the original data of the initial stage of chemical flooding injection into the target well group includes the preset chemical flooding slug of the target well group, the fracture pressure of the target well group, the initial chemical flooding injection pressure of the target well group, and the water content before chemical flooding of the target well group.

3. The method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding of medium and low permeability oil reservoirs according to claim 2, characterized in that: In step S2, the chemical flooding slug range of the target well group is from zero to a preset chemical flooding slug of the target well group.

4. The method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding of medium and low permeability oil reservoirs according to claim 1, characterized in that: In step S2, the chemical flooding effect data of the target well group includes the injection pressure of the target well group and the water content value of the target well group.

5. The method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding of medium and low permeability oil reservoirs according to claim 1, characterized in that: In step S2, the period of regularly performing the inhalation profile test is 3-6 months.

6. The method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding in medium and low permeability oil reservoirs according to claim 1, characterized in that: In step S3, in the uniformity of the suction profile of the target well group, the alternating injection timing of the target well group is to inject a chemical flooding slug value when the relative suction amount of the high permeability layer increases.

7. The method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding in medium-low permeability oil reservoirs according to claim 1, characterized in that: In step S4 , the multi-concentration chemical flooding system includes a first chemical flooding system and a second chemical flooding system, and the concentration of the first chemical flooding system is greater than the concentration of the second chemical flooding system.

8. The method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding of medium-low permeability oil reservoirs according to claim 7, characterized in that: In step S5, one round of chemical flooding alternating injection of the target well group includes a first chemical flooding system and a second chemical flooding system.

9. The method for slowing down the reversal of the suction profile of the injection well in the late stage of chemical flooding in medium-low permeability oil reservoirs according to claim 1, characterized in that: In step S5, the injection slug of a single round of chemical flooding alternating injection of the target well group is the ratio of the remaining chemical flooding slugs of the target well group to the injection rounds, and the range of the target well group chemical flooding alternating injection rounds is 2-3 times.

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