A perforating layer selection method for a post-polymer flooding remaining oil tapping well
By effectively classifying the oil layer thickness and analyzing the injection and production situation, selective perforation was implemented, which solved the problem of water flow following the original path in the remaining oil wells after polymer flooding, thus improving the tapping effect and recovery rate.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DAQING OILFIELD CO LTD
- Filing Date
- 2025-01-14
- Publication Date
- 2026-07-14
AI Technical Summary
After polymer flooding, during the perforation process of newly added submerged wells, water flow tends to follow the original path, resulting in significant differences within the formation and making subsequent adjustments difficult, thus affecting the tapping effect of the remaining oil.
By effectively classifying the oil layer thickness and selectively determining the perforation interval and perforation thickness based on the injection and production situation and oil saturation distribution, the water flow rate of oil layers with high water flooding ratio can be reduced, while the water flow rate of inferior channels or new channels can be increased.
It improved the potential tapping effect of remaining oil, reduced internal contradictions in the oil reservoir, and increased the recovery rate by 0.23 percentage points.
Smart Images
Figure CN122390190A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of oilfield production engineering technology, specifically a perforation layer selection method for drilling submerged wells for residual oil after polymer flooding. Background Technology
[0002] With the rapid advancement of polymer flooding technology, many polymer-flooded blocks have entered the subsequent waterflooding stage, with production gradually decreasing. Based on the geological characteristics of various oilfield types, domestic and international researchers have developed a variety of effective technologies to improve reservoir properties and tap into remaining oil potential, all of which have achieved good economic benefits. Commonly used techniques for tapping remaining oil potential include horizontal well technology, well-to-injection conversion, logging in old wells, polymer flooding, water shut-off and profile control, layer subdivision, unstable water injection, and well density optimization. Well density optimization involves perforating new wells, typically perforating the entire target layer. However, for thick, highly permeable layers, most of the water flow will still follow its original path after perforation, resulting in significant intra-layer variations and making subsequent adjustments difficult. Summary of the Invention
[0003] To overcome the shortcomings of existing methods for perforating newly added submerged wells, such as water flow following the original path and large differences within the formation, this invention provides a perforation layer selection method for submerged wells with remaining oil after polymer flooding. This method can reduce the water flow in the dominant channel and increase the water flow through the inferior channel or the new channel, thereby reducing internal contradictions in the oil layer, improving the tapping effect of remaining oil, and achieving the goal of increasing production and efficiency.
[0004] The technical solution of this invention is: a perforation layer selection method for tapping submerged wells with residual oil after polymer flooding, comprising:
[0005] S1. Select several wells of the same type that have been perforated in the target layer and have profile test results within a block, classify the perforated oil layer according to the effective thickness, and determine the injection and production status of the oil layer under different effective thickness levels.
[0006] The well being tapped is either an injection well or a production well; the injection / production status refers to the fluid intake status of the injection well or the fluid production status of the production well.
[0007] S2. For wells of the same type as those in step S1 that need to be perforated to tap the remaining oil in the block, classify the oil layers according to the effective thickness in step S1, and classify the oil layers according to the effective thickness level range of the injection and production situation determined in step S1.
[0008] S3. Determine the perforation section and perforation thickness of the submerged well based on the oil reservoir type.
[0009] Furthermore, in step S1, the effective thickness of the oil layer is classified according to the development of the block. When the well being tapped is an injection well, the injection and production of the oil layer under different effective thickness levels in the block are compared, and the effective thickness level range is divided into three situations: good, medium and poor injection and production.
[0010] Furthermore, step S3 includes S31-1, for layers with good injection and production conditions, the oil layer is subdivided into several segments, and the vertical oil saturation distribution is determined. The subdivided segments with low oil saturation are selected as non-perforated segments, while the remaining segments are perforated normally.
[0011] Furthermore, in step S31-1, after subdividing the well-injected and produced layers into several segments, digital modeling is used to simulate the reservoir development and historical development process of the block to obtain the current vertical oil saturation distribution.
[0012] Furthermore, in step S31-1, the injection thickness is the layer thickness minus the thickness of the subdivided layer with low oil saturation.
[0013] Furthermore, step S3 includes S31-2, where, for formations with good injection and production conditions, based on the connectivity between the tapped well and the surrounding oil and water wells that have already been perforated in the target formation, and referring to the injection and production profile monitoring results of the surrounding wells, the formations with good injection and production conditions in the surrounding wells are selected as non-perforated formations, and the remaining formations are perforated.
[0014] Furthermore, in step S31-2, the perforated thickness is the layer thickness minus the non-perforated thickness, where the non-perforated thickness is the thickness of the submerged well connected to the layer as shown by the logging curve.
[0015] Furthermore, step S3 includes S32, where for a formation with moderate injection and production conditions, if the monitoring results of the injection and production profiles of surrounding wells show that the injection and production conditions of that formation in that area are poor, then all wells in that formation are perforated; if the monitoring results of the injection and production profiles of surrounding wells show that the injection and production conditions of that formation in that area are good, then step S31-1 or step S31-2 is performed.
[0016] Furthermore, step S3 includes S33, where all layers classified as having poor injection and extraction conditions are injected.
[0017] This invention offers the following advantages: By employing the above-mentioned scheme, the method classifies oil layers according to their effective thickness and considers both the fluid intake of injection wells and the fluid production of production wells. This guides the perforation selection and perforation thickness design for remaining oil wells after polymer flooding, reducing water flow in high-water-flooded oil layers, increasing water flow through inferior or new channels, mitigating internal oil layer conflicts, and improving the potential tapping effect of remaining oil. Numerical simulation results show that compared to conventional methods that uniformly perforate all layers, this method can increase the recovery rate by 0.23 percentage points. Attached Figure Description
[0018] Figure 1 This is a flowchart of the present invention;
[0019] Figure 2 This is a schematic diagram of determining the perforation thickness of injection well X by referring to the injection profile of surrounding wells in Example 1. Detailed Implementation
[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0021] Depend on Figure 1 As shown, a perforation layer selection method for tapping remaining oil wells after polymer flooding is presented. This method provides a layer selection and perforation thickness design method for oil layers of different thicknesses in newly added tapping wells. Tapping wells that need to perforate the target layer to tap the remaining oil include injection wells and production wells. The perforation layer selection and perforation thickness design methods for injection wells and production wells are described separately here.
[0022] For injection wells that perforate the target layer to tap into remaining oil, the following steps are adopted:
[0023] S1. Select several injection wells in the block that have perforated the target layer and have profile test results, classify the perforated oil layer according to the effective thickness, and determine the fluid absorption of the oil layer under different effective thickness levels.
[0024] When classifying the effective thickness of oil reservoirs, the development of the block needs to be considered. When the oil reservoir thickness is large, the effective thickness of each level can be large, and when the oil reservoir thickness is small, the effective thickness of each level can be small. Based on this, the liquid absorption of oil reservoirs under different effective thickness classifications is statistically analyzed, and the liquid absorption of oil reservoirs under different effective thickness levels within the block is compared to determine the effective thickness level range for three conditions: good, medium, and poor liquid absorption.
[0025] S2. For injection wells within the block that need to be perforated to tap the remaining oil, classify each oil layer according to the effective thickness in step S1, and categorize the oil layers according to the effective thickness range of good fluid absorption, medium fluid absorption, and poor fluid absorption determined in step S1.
[0026] S3. Determine the perforation section and perforation thickness of the submerged well based on the oil layer type. In this step, the perforation section and perforation thickness of the submerged well are determined for layers with good fluid absorption, medium fluid absorption, and poor fluid absorption, respectively.
[0027] For layers with good liquid absorption, one of the following two methods can be used:
[0028] S31-1, the stratigraphic level is subdivided into several segments. Through digital modeling, the reservoir development and historical development process of the block are simulated to determine the current vertical oil saturation distribution. After determining the vertical oil saturation distribution, the oil saturation of each sub-layer is compared. The sub-segments with relatively low oil saturation are selected as non-perforated segments, while the remaining segments are perforated normally. The perforated thickness is the stratigraphic level thickness minus the thickness of the sub-segments with low oil saturation.
[0029] S31-2, for formations with good fluid absorption, analyze the connectivity between the submerged well and surrounding perforated oil and water wells in the target formation. Referring to the injection-production profile monitoring results of surrounding wells, select the formation with good fluid absorption as the non-perforated formation, and perforate the remaining formations. The perforated thickness is the formation thickness minus the non-perforated thickness, where the non-perforated thickness is the thickness of the submerged well connected to the formation as shown by the well logging curve.
[0030] For layers with moderate liquid absorption, the following method is used:
[0031] S32, For formations with moderate fluid absorption, based on the injection-production profile monitoring results of surrounding wells that have already perforated the target formation, determine whether to fully perforate the submerged well or control the perforation thickness. If the surrounding well injection-production profile monitoring results show poor fluid absorption in this area and formation, then the submerged well should fully perforate this formation; if the surrounding well injection-production profile monitoring results show good fluid absorption in this area and formation, then proceed to step S31-1 or step S31-2.
[0032] Step S3 further includes S33, where all layers classified as having poor liquid absorption are ejected.
[0033] For production wells that tap into the target formation to extract remaining oil, the following steps are adopted:
[0034] Step S4: Select several production wells in the block that have perforated the target layer and have profile test results, classify the perforated oil layer according to the effective thickness, and determine the fluid production of the oil layer under different effective thickness levels.
[0035] Similarly, when classifying the effective thickness of oil reservoirs, the development of the block needs to be considered. When the oil reservoir thickness is large, the effective thickness of each level can be large, and when the oil reservoir thickness is small, the effective thickness of each level can be small. Based on this, the fluid production of oil reservoirs under different effective thickness classifications is statistically analyzed, and the fluid production of oil reservoirs under different effective thickness levels within the block is compared to determine the effective thickness level range for three conditions: good, medium, and poor fluid production.
[0036] Step S5: For the production wells in the block that need to be perforated to tap the remaining oil, classify the oil layers according to their effective thickness and categorize them according to the effective thickness range of the production situation.
[0037] Step S6: Determine the perforation interval and perforation thickness of the deep well based on the oil layer type. For layers with good production, medium production, and poor production, determine the perforation interval and perforation thickness of the production well respectively.
[0038] For layers with good fluid production, one of the following two methods can be used:
[0039] S61-1, the stratigraphic level is subdivided into several segments. Through digital modeling, the reservoir development and historical development process of the block are simulated to determine the current vertical oil saturation distribution. After determining the vertical oil saturation distribution, the oil saturation of each sub-layer is compared. The sub-segments with relatively low oil saturation are selected as non-perforated segments, while the remaining segments are perforated normally. The perforated thickness is the stratigraphic level thickness minus the thickness of the sub-segments with low oil saturation.
[0040] S61-2, for formations with good production, analyze the connectivity between the submerged well and surrounding perforated oil and water wells in the target formation. Referring to the injection-production profile monitoring results of surrounding wells, select the formation with good production in the surrounding wells as the non-perforated formation, and perforate the remaining formations. The perforated thickness is the formation thickness minus the non-perforated thickness, where the non-perforated thickness is the thickness of the submerged well connectivity shown on the well logging curve for that formation.
[0041] For layers with moderate fluid production, the following method is used:
[0042] S62, For formations with moderate production, based on the injection-production profile monitoring results of surrounding wells that have already perforated the target formation, determine whether to fully perforate the submerged well or control the perforation thickness. If the surrounding well injection-production profile monitoring results show poor production in this area and formation, then the submerged well should fully perforate this formation; if the surrounding well injection-production profile monitoring results show good production in this area and formation, then proceed to step S61-1 or step S61-2.
[0043] Step S6 further includes S63, which involves completely blasting open all layers classified as having poor liquid production.
[0044] When implementing this perforation layer selection method for residual oil wells after polymer flooding, the injection wells and production wells are perforated separately, without any order of precedence.
[0045] Example 1:
[0046] Block A plans to tap the remaining oil in a certain layer after polymer flooding. The tapping wells will be perforated according to the following steps for layer selection and perforation thickness design. In this embodiment, the steps are to construct the injection well first and then the production well.
[0047] S1. Select injection wells within Block A that have perforated the target layer and have profile test results. Divide the perforated oil layer into 6 levels according to its effective thickness: <1m, 1m-2m, 2m-3m, 3m-4m, 4m-5m, and >5m. Based on this, statistically analyze the fluid absorption of the oil layer under different effective thickness levels. Comparing the fluid absorption of the oil layer under different effective thickness levels, determine that the effective thickness level with good fluid absorption is >4m, the effective thickness level with medium fluid absorption is 2m-4m, and the effective thickness level with poor fluid absorption is <2m, as detailed in Table 1.
[0048] Table 1. Statistics on injection well thickness classifications and profiles in Block A.
[0049]
[0050] S2. Injection well X is a deep well that needs to penetrate the target layer. It has 10 sub-layers, which are classified according to their effective thickness and categorized according to the classification in step 1. Among them, there is one layer with an effective thickness of >5m, which is a layer with good fluid absorption; two layers with an effective thickness of 1m to 2m and seven layers with an effective thickness of <1m are all layers with poor fluid absorption; there are no layers with moderate fluid absorption in injection well X.
[0051] S3: For the PI31 layer, which is classified as having good liquid absorption, the thickness of the perforated section should be controlled during perforation. One of the following methods can be used to determine the controllable perforated section and thickness:
[0052] S31-1. PI31 is subdivided into 6 segments, from top to bottom: PI31-1, PI31-2, PI31-3, PI31-4, PI31-5, and PI31-6. Numerical simulation results show that the oil saturation from top to bottom is 0.2535%, 0.2503%, 0.2435%, 0.2391%, 0.2290%, and 0.2272%, respectively. Comparing the oil saturation of each sub-layer, it can be seen that PI31-5 and PI31-6 have relatively low oil saturation, representing the dominant channels of the PI31 layer. Therefore, these are selected as non-perforated segments, while the remaining segments are perforated normally. The perforated thickness is the layer thickness minus the thickness of the sub-segments with low oil saturation. The total thickness of PI31 is 7.2 μm. Subtracting the thickness of PI31-5 and PI31-6 (2.4 μm), the perforated thickness is 4.8 μm.
[0053] S31-2. Analyze the connectivity between injection well X and surrounding oil and water wells that have already perforated the target layer. See [link / reference]. Figure 2 Based on the monitoring results of the injection and production profiles of surrounding wells, it is known that the bottom of the PI31 layer has good fluid absorption, therefore it is considered a non-perforated section. From the logging curves, the thickness of the connection between injection well X and the bottom of the PI31 layer with good fluid absorption in the surrounding wells is approximately 2.6m. Therefore, the perforated thickness is the total thickness of PI31: 7.2 - 2.6 = 4.6m.
[0054] S32. No formations in this well are classified as having moderate fluid absorption; this process is omitted.
[0055] S33. For the 9 layers classified as having poor liquid absorption, all of them were punctured, with a puncture thickness of 7.0m.
[0056] S4. Select production wells within Block A that have perforated the target layer and have profile test results. Divide the perforated oil layer into six levels based on its effective thickness: <1m, 1m–2m, 2m–3m, 3m–4m, 4m–5m, and >5m. Based on this, statistically analyze the fluid production of the oil layer under different effective thickness levels. Comparing the fluid production of the oil layer under different effective thickness levels, determine that the effective thickness level with good fluid production is >3m, the effective thickness level with medium fluid production is 2m–3m, and the effective thickness level with poor fluid production is <2m (see Table 2).
[0057] Table 2. Statistics on different thickness grades and profiles of produced wells in Block A.
[0058]
[0059] Step 5: Well Y, the production well, is a deep-well that needs to be perforated through the target layer. It is also classified according to its effective thickness, and further categorized based on the effective thickness range determined in Step 4: good production, medium production, and poor production. Then, perforation selection and perforation thickness design are performed for different layers. Ultimately, of the seven sub-layers developed in production well Y, one is classified as a layer with good production, with a perforation thickness of 7.1m after deducting a 2.8m section of the good production layer; the other six are classified as poor production, all of which are perforated, with a perforation thickness of 3.3m.
[0060] In the end, 17 injections and 19 extractions were carried out in the submerged wells in Block A. The perforation thickness was controlled in 10 injections and 8 extractions using the above method. All the sub-layers of the remaining submerged wells were perforated.
[0061] This method classifies oil layers according to their effective thickness and considers the fluid absorption of injection wells and the fluid production of production wells. It guides the perforation selection and perforation thickness design for remaining oil wells after polymer flooding, reducing water flow in high-water-flooded layers and increasing water flow through disadvantageous or new channels. This reduces internal conflicts within the oil layer and improves the potential for remaining oil extraction. Numerical simulation results show that this method can increase the recovery rate by 0.23 percentage points compared to conventional methods that uniformly perforate all layers.
[0062] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.
Claims
1. A method for perforation layer selection in deep-well drilling of residual oil after polymer flooding, characterized in that... include: S1. Select several wells of the same type that have been perforated in the target layer and have profile test results within a block, classify the perforated oil layer according to the effective thickness, and determine the injection and production status of the oil layer under different effective thickness levels. The well being tapped is either an injection well or a production well; the injection / production status refers to the fluid intake status of the injection well or the fluid production status of the production well. S2. For wells of the same type as those in step S1 that need to be perforated to tap the remaining oil in the block, classify the oil layers according to the effective thickness in step S1, and classify the oil layers according to the effective thickness level range of the injection and production situation determined in step S1. S3. Determine the perforation section and perforation thickness of the submerged well based on the oil reservoir type.
2. The perforation layer selection method for tapping submerged wells for residual oil after polymer flooding according to claim 1, characterized in that: In step S1, the effective thickness of the oil layer is classified according to the development of the block. When the well is a submersible well, the injection and production of the oil layer under different effective thickness levels in the block are compared, and the effective thickness level range is divided into three situations: good, medium and poor injection and production.
3. The perforation layer selection method for tapping submerged wells with residual oil after polymer flooding according to claim 2, characterized in that: Step S3 includes S31-1, where for layers with good injection and production conditions, the oil layer is subdivided into several segments, and the vertical oil saturation distribution is determined. Subdivided segments with low oil saturation are selected as non-perforated segments, while the remaining segments are perforated normally.
4. The perforation layer selection method for tapping submerged wells for residual oil after polymer flooding according to claim 3, characterized in that: In step S31-1, after subdividing the well-injected and produced layers into several segments, digital modeling is used to simulate the reservoir development and historical development process of the block to obtain the current vertical oil saturation distribution.
5. The perforation layer selection method for tapping residual oil wells after polymer flooding according to claim 3, characterized in that: In step S31-1, the injection thickness is the layer thickness minus the thickness of the subdivided layer with low oil saturation.
6. The perforation layer selection method for tapping submerged wells with residual oil after polymer flooding according to claim 3, characterized in that: Step S3 includes S31-2, where, for formations with good injection and production conditions, based on the connectivity between the tapped well and the surrounding oil and water wells that have already been perforated in the target formation, and referring to the injection and production profile monitoring results of the surrounding wells, the formations with good injection and production conditions in the surrounding wells are selected as non-perforated formations, and the remaining formations are perforated.
7. The perforation layer selection method for tapping residual oil wells after polymer flooding according to claim 6, characterized in that: In step S31-2, the perforated thickness is the layer thickness minus the non-perforated thickness, where the non-perforated thickness is the thickness of the submerged well connected to the layer as shown by the logging curve.
8. The perforation layer selection method for tapping submerged wells with residual oil after polymer flooding according to claim 3, characterized in that: Step S3 includes S32, where for a formation with moderate injection and production conditions, if the injection and production profile monitoring results of surrounding wells show that the injection and production conditions of this formation in this area are poor, then all wells in this formation will be perforated; if the injection and production profile monitoring results of surrounding wells show that the injection and production conditions of this formation in this area are good, then step S31-1 or step S31-2 will be performed.
9. The perforation layer selection method for tapping submerged wells with residual oil after polymer flooding according to claim 3, characterized in that: Step S3 includes S33, where all layers classified as having poor injection and production conditions are perforated.