Small well spacing chemical flooding comprehensive adjustment method

Abstract

The invention discloses a small-well-spacing chemical flooding comprehensive adjustment method, relates to the field of oil production engineering, and solves the problems that indoor experiments cannot completely simulate oil reservoir conditions, the field test period is long, and the popularization and application process of a new method is affected. The method comprises the following steps: S1, an oil displacement system applied to a small well spacing test is an alkali-free ternary system; s2, carrying out quality inspection on the chemical agent to ensure the quality of the chemical agent; the injection-production well monitoring and testing period is encrypted, adjustment is conducted according to dynamic changes, and the injection quality in the chemical flooding stage is ensured; s3, measures are taken for the injection well with the small pressure space in the blank water drive stage, the injection condition is improved, and the injection agent pressure space is guaranteed; and S4, aiming at the conditions of slow injection pressure rising and high sampling agent concentration in the chemical flooding process, optimization scheme design is carried out, tracking adjustment is enhanced, and the effect of the test area is promoted. According to the adjusting method, a two-lifting and one-stopping adjusting mode is adopted for adjusting plugging, the center well is promoted to further become effective, and the test development effect is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of tertiary oil recovery, and in particular to a comprehensive adjustment method for chemical flooding with small well spacing. Background Art

[0002] Based on innovations in composite flooding phase theory, interfacial steric surfactants have been developed to optimize weak-alkali and alkali-free phase-stable intelligent transformation composite systems suitable for various oil reservoirs. While significant progress has been made in laboratory research, the inability of laboratory experiments to fully simulate reservoir conditions and the long field testing cycle have hampered the promotion and application of this method and technology. To rapidly verify the field application effects of the developed phase-stable intelligent transformation alkali-free composite flooding system, clarify understanding of development patterns, improve supporting technologies, and accelerate the promotion and application of new technologies, small-well-spacing field tests have been conducted. A small-well-spacing test platform has been constructed to support the construction of key oilfield laboratories and R&D centers, expand and improve flooding system evaluation technologies, and accelerate the promotion and application of new technologies. Summary of the Invention

[0003] The present invention addresses the problems in prior art, such as the inability of indoor experiments to fully simulate reservoir conditions and the long field testing cycles that hinder the widespread application of interfacial steric surfactant flooding systems. The present invention provides a comprehensive adjustment method for chemical flooding with small well spacing. This method optimizes the comprehensive adjustment method, employing a "two-lift, one-stop" adjustment method for plugging and regulating. This method steadily increases injection pressure in the test area, achieving increased oil production and reduced water loss in the production wells, further promoting the effectiveness of the central wells and ensuring the effectiveness of the experimental development.

[0004] The present invention solves the problem by the following technical solution: the comprehensive adjustment method of chemical flooding with small well spacing includes the following steps:

[0005] S1: The flooding system used in the small well spacing test is an alkali-free ternary system;

[0006] S2: Conduct quality inspection on chemicals to ensure their quality; intensify the monitoring and testing cycle of injection and production wells and adjust according to dynamic changes to ensure the injection quality during the chemical flooding stage;

[0007] S3: Implement measures for injection wells with small pressure space during the blank water flooding phase to improve injection conditions and ensure injection pressure space;

[0008] S4: In view of the slow injection pressure rise and high concentration of extraction agent in the chemical flooding process, we will design an optimized plan, strengthen follow-up adjustments, and promote the effectiveness of the test area.

[0009] Furthermore, the alkali-free ternary system for the small well spacing test flooding in step S1 is: polymer + compound salt + interfacial steric surfactant.

[0010] Furthermore, the step S2 of performing quality inspection on the chemical agent includes: performing quality inspection on the polymer, salt and surfactant in the oil displacement system to ensure the quality of the chemical agent.

[0011] Furthermore, the step S3 includes implementing acidizing measures and fracturing measures on the injection wells with small pressure space in the blank water flooding stage.

[0012] Furthermore, the acidification measure adopts powdered nitric acid acidification; the fracturing measure adopts short-wide fracture fracturing. Since the injection-production well spacing in the test area is small, the fracture length needs to be controlled.

[0013] Furthermore, the optimization scheme design in step S4 includes:

[0014] 4.1. Increase polymer molecular weight, gradient concentration in injection wells, and block dominant seepage channels;

[0015] 4.2. Salt concentration of the ternary system;

[0016] 4.3. Shut down injection wells with strong dominant seepage direction to alleviate plane conflicts.

[0017] Furthermore, the polymer molecular weight is increased, the injection well is gradient concentrated, and the dominant seepage channel is blocked; the specific method is:

[0018] To address the slow increase in injection pressure during the early stages of the main slug injection, the molecular weight of the injected polymer was gradually increased from 16-19 million to 25 million. The injection well was also gradient-concentrated, with the injection viscosity increased from 40 mPa·s to over 80 mPa·s to control chemical penetration and expand the swept volume.

[0019] Furthermore, the specific method for increasing the salt concentration of the ternary system is as follows: increasing the salt concentration of the main slug from 1.6wt% to 2.0wt% to promote the formation of a high-viscosity Winsor II emulsion for coordinated plugging; and at the same time, to ensure the phase transformation during the displacement process, increasing the salt concentration of the secondary slug from 1.2wt% to 1.6wt%.

[0020] Furthermore, the injection wells with strong dominant seepage direction are shut down to alleviate the plane contradiction. The specific method is as follows:

[0021] For several injection wells around the central well in the test area where the agent concentration is high and the water content drop is small, the method of stopping the injection of salt and surfactant in batches is adopted, and the concentration testing of the agent in the central well is simultaneously intensified; the direction of the dominant seepage channel is verified according to the change of the agent concentration in the central well; after verification, combined with static data, it is determined that there is a dominant seepage channel at the bottom of a certain injection well. Due to the small interlayer within the layer, it cannot be sealed, so the injection is stopped to control the breakthrough of chemical agents.

[0022] Furthermore, the method for verifying the direction of the dominant seepage channel based on the change in the concentration of the central well production agent is as follows: during the verification process, it is found that when the injection of salt and surfactant into a certain injection well is stopped, the concentration of the central well production agent drops significantly; when the injection well resumes the injection of salt and surfactant, the concentration of the central well production agent recovers; combined with static data, it is determined that there is a dominant seepage channel at the bottom of this injection well.

[0023] Compared with the above background technology, the present invention has the following beneficial effects:

[0024] The small-well spacing test flooding system is a new alkali-free ternary system (polymer + compound salt + interfacial steric surfactant). Due to the small spacing between the test injection and production wells and the complex underground connectivity, emphasis is placed on tracking and adjusting the injection and production wells, achieving "daily tracking, daily combination, and optimal adjustment." By analyzing the dynamic changes of the injection and production wells and combining them with static data, the salt and meter stop methods are adopted to identify the dominant seepage channels and optimize the comprehensive adjustment method. The injection pressure in the test area has steadily increased, and the oil wells have seen the effect of increasing oil production and reducing water flow. This has formed a new alkali-free ternary comprehensive adjustment method for small-well spacing in Class II oil layers, which is of great significance for guiding the development of alkali-free ternary flooding in Class II oil layers and provides technical reserves for stable oilfield production.

[0025] By implementing the comprehensive adjustments of the method described in this invention in a test area of ​​the Daqing Oilfield, injection pressure steadily increased, low-permeability reservoirs were mobilized, and significant oil production and water reduction effects were observed in two central wells. During the primary slugging phase, the water cut in central well A decreased significantly, while the rate of water cut recovery in central well B was slowed. During the secondary slugging phase, the low water cut period in the two central wells was further extended, increasing oil recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the injection pressure curve of the test area of ​​the embodiment of the present invention;

[0027] Figure 2 This is a comparison curve of the concentration of the extraction agent in the second central well of the embodiment of the present invention;

[0028] Figure 3 This is the injection concentration and injection viscosity curve of the embodiment of the present invention;

[0029] Figure 4 The pressure curve of the embodiment of the present invention is injected;

[0030] Figure 5 This is the daily oil production and water content curve of the central well B in the embodiment of the present invention;

[0031] Figure 6 The daily oil production and water content curve of the central well A in the embodiment of the present invention;

[0032] Figure 7 This is a flow chart of the comprehensive adjustment method for chemical flooding with small well spacing according to the present invention. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0034] like Figure 7 As shown, a comprehensive adjustment method for chemical flooding with small well spacing includes the following steps:

[0035] S1: The oil displacement system for the small well spacing test was determined to be a new alkali-free ternary system: polymer + compound salt + interfacial steric surfactant.

[0036] The polymer is a conventional oil recovery polymer with molecular weights of 16-19 million, 22 million, and 25 million, and its main component is polyacrylamide. The salt is a liquid compound salt, its main components being sodium chloride and sodium hydroxide. The interfacial steric surfactant is an enhanced oil recovery surfactant, alkyl sulfonate WJX-1, whose main components are sodium heavy alkylbenzene sulfonate, alkyl ether sulfate, and n-butanol. The interfacial steric surfactant is composed of a high-molecular-weight surfactant with good water solubility and steric hindrance, and a conventional heavy alkylbenzene sulfonate. These surfactants have a synergistic effect, significantly increasing the overall adsorption of surfactant molecules at the oil-water interface, thereby enhancing the interaction between the oil and water phases.

[0037] S2: Conduct quality inspection on chemicals to ensure their quality; intensify the monitoring and testing cycles of injection and production wells, and make timely adjustments based on dynamic changes to ensure injection quality during the chemical flooding phase;

[0038] The quality inspection of the chemical agents includes: strictly inspecting the polymers, salts and surfactants in the oil displacement system to ensure the quality of the chemical agents.

[0039] S3: Implement measures for injection wells with small pressure space during the blank water flooding phase to improve injection conditions and ensure injection pressure space;

[0040] Measures implemented for injection wells with limited pressure headroom during the blank water flooding phase included acidizing with powdered nitric acid and fracturing. The acidizing method employed was powdered nitric acid, while the fracturing method employed short, wide fractures. Due to the short distance between injection and production wells in the test area, the fracture length needed to be controlled.

[0041] S4: In view of the slow injection pressure rise and high concentration of extraction agent in the chemical flooding process, we will design an optimized plan, strengthen follow-up adjustments, and promote the effectiveness of the test area.

[0042] The optimization scheme design includes:

[0043] 4.1. Increase polymer molecular weight, increase injection well gradient concentration, and block the dominant seepage channel; the specific method is:

[0044] To address the slow increase in injection pressure during the early stages of the main slug injection, the molecular weight of the injected polymer was gradually increased from 16-19 million to 25 million. The injection viscosity was also increased from 40 mPa·s to over 80 mPa·s for the injection well gradient concentration, controlling the chemical advance and expanding the swept volume.

[0045] 4.2. Increase the salt concentration of the ternary system; the specific method is:

[0046] The salt concentration in the main slug was increased from 1.6wt% to 2.0wt% to promote the formation of high-viscosity Winsor II emulsion for coordinated plugging. At the same time, to ensure the phase conversion during the displacement process, the salt concentration in the secondary slug was increased from 1.2wt% to 1.6wt%.

[0047] 4.3. Shut down injection wells with strong dominant flow direction to alleviate the plane contradiction. The specific methods are as follows:

[0048] For several injection wells surrounding the central well in the test area, where the concentration of the extractant was high and the water cut drop was small, salt and surfactant injections were suspended in batches. Simultaneously, intensified chemical concentration testing was conducted at the central well. The direction of the dominant seepage channel was verified based on the changes in the central well's extractant concentration. During the verification process, it was discovered that when salt and surfactant injections were stopped in one injection well, the extractant concentration in the central well dropped significantly. When salt and surfactant injections were resumed, the extractant concentration in the central well recovered. Combined with static data, it was determined that a dominant seepage channel existed at the bottom of this injection well. Due to the small interlayers within the layer, plugging was impossible, so timely injection was stopped to control chemical breakthrough.

[0049] Example 1

[0050] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, taking a certain test area of ​​Daqing Oilfield as an example.

[0051] The comprehensive adjustment method for chemical flooding with small well spacing includes the following steps:

[0052] 1. Fine management to ensure the quality of chemical flooding injection

[0053] Strict quality control of chemical agents ensures their quality, achieving a 100% pass rate for polymers, salts, and surfactants. Dynamic monitoring and testing frequency is intensified after chemical flooding, with timely adjustments made based on dynamic changes to ensure injection quality. A total of 17,619 samples were collected and tested, and injection and production parameters were adjusted for 174 wells, representing a monthly adjustment rate seven times that of the industrial zone. The pilot zone injection tracking and adjustment worksheet is shown in Table 1; the pilot zone's intensified testing and inspection plan after effective production is shown in Table 2.

[0054] Table 1

[0055]

[0056] Table 2

[0057]

[0058] 2. Implement injection well measures for blank water flooding to ensure injection pressure space

[0059] The test area started blank water drive in April 2022. During the blank water drive stage, the pressure space of the injection well was small. In order to improve the injection conditions and ensure the injection pressure space, injection well measures were implemented for 6 wells, including acidizing for 5 wells and fracturing for 1 well.

[0060] (1) Acidizing injection wells 5 times

[0061] In order to improve the injection conditions and ensure the injection pressure space, five wells were acidified. After acidification, the initial injection pressure dropped by 1.4 MPa and the daily injection volume increased by 15 m 3 .

[0062] (2) Injection well fracturing 1 well

[0063] When injection well A was opened, injection was found to be difficult, so short and wide fractures with pressure were carried out. After the measures, the injection pressure dropped from 11.8MPa to 6.0MPa, the pressure space was 5.8MPa, the daily actual injection increased by 20m3, and the injection was normal.

[0064] Through adjustment measures, the injection pressure in the test area was 8.3MPa and the injection pressure space was 3.5MPa, ensuring the smooth injection of chemicals.

[0065] 3. Strengthen follow-up adjustments to promote the effectiveness of the pilot area

[0066] After the injection, the "daily tracking, daily combination, and optimal adjustment" mode was adopted. In order to address the problems of slow injection pressure rise and high concentration of production agents during the chemical flooding process, the scheme design was optimized in a timely manner, and the "two-lift and one-stop" adjustment method was adopted to block the high-permeability layer. The central well showed obvious oil-increasing and water-reducing effects.

[0067] (1) The injection pressure of the main slug increases slightly in the early stage, and the chemical agent breaks through quickly

[0068] In July 2022, the main chemical flooding plug was injected into the test area. The injection pressure of the main plug increased slightly in the early stage, rising from 8.3MPa at the end of the blank water flooding to 10.1MPa. There is still 1.7MPa of room to rise from the fracture pressure. The concentration of chemical agent produced by the two central wells continued to rise, and chemical agent breakthrough occurred. In particular, the salt concentration of central well A increased from 1696mg / L to 8478mg / L. The injection pressure curve of the test area is shown in Figure 1 ; The comparison curve of the concentration of the production agent of the two central wells is shown in Figure 2 .

[0069] (2) Adopt the “two raise and one stop” adjustment method to adjust and plug the central well to achieve further results

[0070] ① Two increases: one is to increase the polymer molecular weight, gradient concentration, and adjust the blockage of the dominant seepage channel; the other is to increase the salt concentration. The salt concentration of the main plug is increased from 1.6% to 2.0%, which promotes the formation of high-viscosity Winsor II emulsion and coordinates the blockage.

[0071] The first is to increase the molecular weight of the polymer, increase the concentration gradient, and adjust and block the advantageous seepage channels.

[0072] In order to solve the problem of slow pressure rise in the early stage of main slug injection, the molecular weight of the injected polymer was increased from 16-19 million to 25 million in a step-by-step manner, and the injection viscosity was increased from 40mPa·s to above 80mPa·s to control the chemical agent advance and expand the swept volume. The injection polymer concentration and injection viscosity curve is shown in Figure 3 ; Injection pressure curve see Figure 4 .

[0073] The second is to increase the salt concentration. The salt concentration of the main plug is increased from 1.6% to 2.0%, which promotes the formation of high-viscosity Winsor II emulsion and coordinates the plugging.

[0074] Laboratory research results show that Winsor II emulsions increase the viscosity of the oil phase, which has the effect of expanding the swept volume. Therefore, the salt concentration in the composite system's main slug was increased from 1.6wt% to 2.0wt% to promote the formation of Winsor II emulsions and control chemical breakthrough. To ensure phase transition during the displacement process, the salt concentration in the secondary slug was increased from 1.2wt% to 1.6wt%.

[0075] ② One stop: stop the dominant direction and shut down the injection wells in the direction of strong dominant seepage to alleviate the plane contradiction.

[0076] In the test area, the injection wells around the central well A with high concentration of extraction agent and small water drop were stopped in batches. At the same time, the concentration of extraction agent in the central well A was tested more frequently. According to the change of extraction agent concentration, one injection well B was determined to have the dominant seepage direction. Combined with the static data, it was determined that there was a dominant seepage channel at the bottom of the injection well. Since the interlayer in the injection well layer was small and could not be plugged, the injection was stopped in time to control the breakthrough of the chemical agent.

[0077] Through the implementation of comprehensive adjustments, the injection pressure in the test area has steadily increased, the low permeability oil layer has been mobilized, and the central well has seen a significant effect of increasing oil production and reducing water consumption. During the main slugging stage, the water content of central well A dropped significantly, from 97.1% at the end of the blank water drive to a minimum of 90.4%, with a maximum drop of 6.7 percentage points in water content and a daily oil increase of 1.8 tons; the water content recovery rate of central well B was slowed down, and after the water content stabilized between 87.9-93.5% for 3 and a half months, it began to slowly recover. During the secondary slugging stage, the low water content period of the two central wells was further extended. The water content of central well B has been stable at 93.0-95.0%, which is 1.5-3.5 percentage points lower than that of the blank water drive. The water content of central well A has been stable at 93.0-94.5%, which is 2.5-4.0 percentage points lower than that of the blank water drive, ensuring the experimental development effect. The daily oil production and water content curve of central well B is shown in Figure 5 ; Daily oil production and water content curve of center well A is shown in Figure 6 .

[0078] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the implementation methods of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. A comprehensive adjustment method for chemical flooding with small well spacing, characterized by: The following steps are involved: S1: The flooding system used in the small well spacing test is an alkali-free ternary system; S2: Conduct quality inspection on chemicals to ensure their quality; intensify the monitoring and testing cycle of injection and production wells and adjust according to dynamic changes to ensure the injection quality during the chemical flooding stage; S3: Implement measures for injection wells with small pressure space during the blank water flooding phase to improve injection conditions and ensure injection pressure space; S4: In view of the slow injection pressure rise and high concentration of extraction agent in the chemical flooding process, we will design an optimized plan, strengthen follow-up adjustments, and promote the effectiveness of the test area.

2. A comprehensive adjustment method for chemical flooding with small well spacing according to claim 1, characterized in that: The alkali-free ternary system for the small well spacing test flooding in step S1 is: polymer+compound salt+interfacial steric surfactant.

3. The method for comprehensive adjustment of chemical flooding with small well spacing according to claim 1, characterized in that: The step S2 of performing quality inspection on the chemical agent includes: performing quality inspection on the polymer, salt and surfactant in the oil displacement system to ensure the quality of the chemical agent.

4. The method for comprehensive adjustment of chemical flooding with small well spacing according to claim 1, characterized in that: The step S3 includes implementing measures for the injection wells with small pressure space in the blank water flooding stage, including: implementing acidizing measures and fracturing measures.

5. A comprehensive adjustment method for chemical flooding with small well spacing according to claim 4, characterized in that: The acidification measure adopts powder nitric acid acidification; the fracturing measure adopts short wide fracture fracturing. Since the injection and production well spacing in the test area is small, the fracture length needs to be controlled.

6. The method for comprehensive adjustment of chemical flooding with small well spacing according to claim 1, characterized in that: The optimization scheme design in step S4 includes: 4.

1. Increase polymer molecular weight, gradient concentration in injection wells, and block dominant seepage channels; 4.

2. Salt concentration of the ternary system; 4.

3. Shut down injection wells with strong dominant seepage direction to alleviate plane conflicts.

7. A comprehensive adjustment method for chemical flooding with small well spacing according to claim 6, characterized in that: The method of increasing the polymer molecular weight, gradient concentration in the injection well, and blocking the dominant seepage channel is as follows: In view of the slow increase in injection pressure in the early stage of the main slug, the molecular weight of the injected polymer was increased in steps from 16-19 million to 25 million; the injection well gradient was concentrated, and the injection viscosity was increased from 40mPa·s to above 80mPa·s to control the advancement of the chemical agent and expand the swept volume.

8. The method for comprehensive adjustment of chemical flooding with small well spacing according to claim 6, characterized in that: The specific method for increasing the salt concentration of the ternary system is as follows: increasing the salt concentration of the main slug from 1.6wt% to 2.0wt% to promote the formation of a high-viscosity Winsor II emulsion for coordinated plugging; and simultaneously increasing the salt concentration of the secondary slug from 1.2wt% to 1.6wt% to ensure phase conversion during the displacement process.

9. The method for comprehensive adjustment of chemical flooding with small well spacing according to claim 6, characterized in that: The shut down of the injection wells with strong dominant seepage direction can alleviate the plane contradiction. The specific method is as follows: For several injection wells around the central well in the test area where the agent concentration is high and the water content drop is small, the method of stopping the injection of salt and surfactant in batches is adopted, and the concentration testing of the agent in the central well is simultaneously intensified; the direction of the dominant seepage channel is verified according to the change of the agent concentration in the central well; after verification, combined with static data, it is determined that there is a dominant seepage channel at the bottom of a certain injection well. Due to the small interlayer within the layer, it cannot be sealed, so the injection is stopped to control the breakthrough of chemical agents.

10. A comprehensive adjustment method for chemical flooding with small well spacing according to claim 9, characterized in that: The method for verifying the direction of the dominant seepage channel based on the change in the concentration of the central well production agent is as follows: during the verification process, it is found that when the injection of salt and surfactant into a certain injection well is stopped, the concentration of the central well production agent drops significantly; when the injection well resumes the injection of salt and surfactant, the concentration of the central well production agent recovers; combined with static data, it is determined that a dominant seepage channel exists at the bottom of this injection well.

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