A method for plugging removal and efficiency prolonging of polymer injection well

Abstract

The application discloses a method for increasing the plugging removal effect of a polymer injection well, which comprises the following steps: injecting a permeation dispersant into the polymer injection well as a preflush slug, then injecting a depolymerization liquid as a first treatment liquid slug, shutting down the well for a period of time, then injecting a treatment acid as a second treatment liquid slug, injecting an anti-agglomerant as a postflush slug, finally injecting field water as a displacement liquid, shutting down the well for a period of time, and then performing polymer flooding. The method can increase the plugging removal effect of the polymer injection well by adding the permeation dispersant, the depolymerization liquid and the treatment acid, and can prolong the effective period of the plugging removal by adding the anti-agglomerant.

Description

Technical Field

[0001] This invention relates to the field of oilfield unblocking technology, and in particular to a method for extending the effectiveness of unblocking polymer injection wells. Background Technology

[0002] Polymer flooding is a crucial method for enhancing oil recovery in oilfields, effectively improving mobility ratios, increasing sweep efficiency, and stabilizing oil production while controlling water flow. However, during polymer flooding, due to the interaction between the polymer and reservoir minerals, polymers are easily adsorbed and retained on the sandstone surface, leading to formation blockage. Furthermore, the high viscosity of the polymer solution strongly entrains particles, potentially exacerbating particle migration within formation pores. This manifests as increased injection pressure, inadequate injection, or even complete failure to inject polymer. Simultaneously, after unblocking measures are implemented in polymer-blocked wells, the unblocking is often incomplete, and the characteristic of polymer adsorption and retention on the sandstone surface persists, resulting in poor unblocking effects and short-lived effectiveness of the measures.

[0003] Chinese invention patent CN112342004A discloses a hydrophobic modifier and a polymer flooding method for improving the unblocking effect of polymer injection wells. The method includes: injecting the hydrophobic modifier into the formation of the polymer injection well to improve the unblocking effect; shutting in the well for at least 24 hours; and then injecting polymer from the well for polymer flooding. This method only provides a way to reduce polymer adsorption and retention during polymer flooding; it does not provide a process for unblocking polymer injection wells. Conventional unblocking processes for polymer injection wells only consider the removal of complex scale such as polymers, inorganic scale, and clay during the unblocking process, without considering the continued presence of polymers adsorbed and retained on the sandstone surface, resulting in a short unblocking effectiveness period. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for extending the effectiveness of polymer injection well unclogging. This method enhances the unclogging effect by adding a penetrating dispersant, a depolymerizing fluid, and a treatment acid, and extends the effective period of unclogging by adding an anti-agglomeration agent.

[0005] The present invention is achieved by the following technical solution.

[0006] A method for extending the effectiveness of polymer injection well unclogging includes the following steps: A permeation dispersant is injected into the polymer injection well as a pre-flush slug, followed by a depolymerization fluid as the first treatment fluid slug. After a period of shut-in reaction, a treatment acid is injected as the second treatment fluid slug, an anti-agglomeration agent is injected as a post-flush slug, and finally, field-mixed injection water is injected as a displacement fluid. After a period of shut-in reaction, polymer flooding is then carried out.

[0007] Furthermore, the penetrating dispersant comprises the following components in weight percentage: 1-3% sodium dodecyl sulfate, 2-4% citric acid, 2-4% acetic acid, and the balance being water.

[0008] Furthermore, the volume of the pre-flush slug is equal to the reservoir pore volume within a cylindrical area centered on the injection well, with a radius of 0.8 to 1.2 meters and a height equal to the effective thickness of the reservoir.

[0009] Furthermore, the depolymerization solution comprises the following components in weight percentage: 1-2% citric acid, 0.5-1.2% ferrous chloride, 1.0-1.5% sodium persulfate, and the balance being water.

[0010] Furthermore, the volume of the first processing fluid slug is equal to the reservoir pore volume within a cylindrical area centered on the injection well, with a radius of 0.8 to 1.2 meters and a height equal to the effective thickness of the reservoir.

[0011] Furthermore, the treated acid comprises the following components in weight percentage: 5-12% hydrochloric acid, 2-4% acetic acid, 2-6% fluoroboric acid, 1-5% hexadecyltrimethylammonium bromide, and the balance being water.

[0012] Furthermore, the volume of the second processing fluid slug is equal to the reservoir pore volume within a cylindrical area centered on the injection well, with a radius of 1.0 to 1.2 meters and a height equal to the effective thickness of the reservoir.

[0013] Furthermore, the anti-agglomeration agent includes γ-aminopropyltriethoxysilane and / or phenyltrimethoxysilane.

[0014] Furthermore, the anti-agglomeration agent comprises the following components in weight percentage: 0.5-1.0% γ-aminopropyltriethoxysilane, 0.01-0.03% acetic acid, 2-9% ethanol, and the balance being water.

[0015] Furthermore, the anti-agglomeration agent comprises the following components in weight percentages: 0.5-1% phenyltrimethoxysilane, 0.01-0.03% acetic acid, 2-9% isopropanol, and the balance being water.

[0016] Furthermore, the anti-agglomeration agent comprises the following components in weight percentage: 0.5-1.0% γ-aminopropyltriethoxysilane, 0.5-1% phenyltrimethoxysilane, 0.03-0.06% acetic acid, 2-9% ethanol, 2-9% isopropanol, and the balance being water.

[0017] Furthermore, the volume of the post-positioned liquid slug is equal to the reservoir pore volume within a cylindrical area centered on the injection well, with a radius of 1.5 to 2 meters and a height equal to the effective thickness of the reservoir.

[0018] Furthermore, the volume of the displacement fluid is equal to the tubing volume of the polymer injection well's injection slug, in order to completely squeeze the anti-agglomeration agent into the reservoir.

[0019] Furthermore, the well shut-in time is 12-36 hours.

[0020] This application has the following beneficial effects.

[0021] This invention's process involves adding a penetrating dispersant to clean the surface oil and contaminants of composite scale, increasing the contact area between the depolymerization solution and the polymer scale. Simultaneously, it disperses the polymer scale, improving the degradation rate of the polymer scale by the depolymerization agent. The addition of the depolymerization solution effectively degrades the polymer scale adsorbed and retained in the near-wellbore reservoir, exposing the mud particles and inorganic scale encapsulated within the polymer scale. The addition of a treatment acid further removes inorganic scale, expands near-wellbore porosity, and restores and improves permeability. Finally, the addition of an anti-agglomeration agent alters the near-wellbore wettability through adsorption, forming a hydrophobic layer, reducing injection resistance, and extending the effective period of unblocking. The process provided by this invention is also applicable to unblocking operations in controlled-drive wells. Detailed Implementation

[0022] The present patent application will be further described below with reference to the embodiments.

[0023] Unless otherwise specified, the experimental methods used in the following preparation examples and embodiments are conventional methods; unless otherwise specified, the materials and reagents used in the following preparation examples and embodiments are commercially available.

[0024] Example 1

[0025] In March 2019, the A1 polymer injection well in the Bohai S oilfield underwent unclogging. First, 20 cubic meters of permeate-dispersant, 14 cubic meters of depolymerizing fluid, and 12 cubic meters of displacement fluid were extruded forward. The well was shut in for 24 hours. Then, 30 cubic meters of treatment acid, 90 cubic meters of anti-agglomeration agent, and 12 cubic meters of displacement fluid were extruded forward. In the above unclogging process, the permeate-dispersant composition (all components are percentages by mass) was: 3% sodium dodecyl sulfate, 4% citric acid, and 3% acetic acid; the depolymerizing fluid composition was: 2% citric acid, 1% ferrous chloride, and 1% sodium persulfate; the main components of the treatment acid were: 10% hydrochloric acid, 2% acetic acid, 6% fluoroboric acid, and 5% hexadecyltrimethylammonium bromide; and the main components of the anti-agglomeration agent were: 1.0% γ-aminopropyltriethoxysilane, 0.03% acetic acid, and 8% ethanol. Referring to the evaluation standard "QHS 2019-2020 Implementation Specifications and Effect Evaluation Methods for Chemical Unblocking Technology of Injection Wells", the injection pressure of this well before unblocking was 12.5 MPa, and the daily injection volume was 357.41 m³. 3 / d, injection pressure after unblocking is 7.0MPa, daily injection volume is 451.80m³. 3 / d, formation apparent water absorption index increased by 125.73%, effective for 397 days.

[0026] Example 2

[0027] In May 2020, the F16H well in the Bohai B oilfield underwent unblocking. The process involved first extruding 20 cubic meters of permeabilizing dispersant, 20 cubic meters of depolymerizing fluid, and 14 cubic meters of displacement fluid, followed by a 24-hour shut-in period. Then, 36 cubic meters of treatment acid, 86 cubic meters of anti-agglomeration agent, and 14 cubic meters of displacement fluid were extruded. The permeabilizing dispersant composition (all percentages by mass) was 3% sodium dodecyl sulfate, 4% citric acid, and 3% acetic acid; the depolymerizing fluid composition was 2% citric acid, 1% ferrous chloride, and 1% sodium persulfate; the treatment acid composition was 10% hydrochloric acid, 2% acetic acid, 6% fluoroboric acid, and 5% hexadecyltrimethylammonium bromide; and the anti-agglomeration agent composition was 1% phenyltrimethoxysilane, 0.03% acetic acid, and 8% ethanol. Referring to the evaluation standard "QHS 2019-2020 Implementation Specifications and Effect Evaluation Methods for Chemical Unblocking Technology of Injection Wells", the injection pressure of this well before unblocking was 12.0 MPa, and the daily injection rate was 211.68 m³. 3 / d, injection pressure after unblocking is 4.0MPa, daily injection volume is 446.4m³. 3 / d, formation apparent water absorption index increased by 532.65%, effective for 316 days.

[0028] Example 3

[0029] In June 2020, the A2 polymer injection well in the Bohai S oilfield underwent unclogging. First, 28 cubic meters of permeate-dispersant, 18 cubic meters of depolymerizing fluid, and 15 cubic meters of displacement fluid were extruded forward. The well was shut in for 24 hours. Then, 40 cubic meters of treatment acid, 110 cubic meters of anti-agglomeration agent, and 15 cubic meters of displacement fluid were extruded forward. In the above unclogging process, the permeate-dispersant composition (all components are percentages by mass) was: 3% sodium dodecyl sulfate, 4% citric acid, and 3% acetic acid; the depolymerizing fluid composition was: 2% citric acid, 1% ferrous chloride, and 1% sodium persulfate; the main components of the treatment acid were: 10% hydrochloric acid, 2% acetic acid, 6% fluoroboric acid, and 5% hexadecyltrimethylammonium bromide; the main components of the anti-agglomeration agent were: 1.0% γ-aminopropyltriethoxysilane, 1% phenyltrimethoxysilane, 0.06% acetic acid, 8% ethanol, and 8% isopropanol. Referring to the evaluation standard "QHS2019-2020 Implementation Specifications and Effect Evaluation Methods for Chemical Unblocking Technology of Injection Wells", the injection pressure of this well before unblocking was 11.8 MPa, and the daily injection volume was 146.32 m³. 3 / d, injection pressure after unblocking is 5.7MPa, daily injection volume is 223.56m³. 3 / d, formation apparent water absorption index increased by 216.3%, effective period 508 days.

[0030] Example 4

[0031] In September 2021, the B1 well in the Bohai N oilfield underwent unblocking. The process involved first extruding 24 cubic meters of permeabilizing dispersant, 16 cubic meters of depolymerizing fluid, and 14 cubic meters of displacement fluid, followed by a 24-hour shut-in period. Then, 35 cubic meters of treatment acid, 96 cubic meters of anti-agglomeration agent, and 14 cubic meters of displacement fluid were extruded. The permeabilizing dispersant composition (all percentages by mass) was 3% sodium dodecyl sulfate, 4% citric acid, and 3% acetic acid. The depolymerizing fluid composition was 2% citric acid, 1% ferrous chloride, and 1% sodium persulfate. The main components of the treatment acid were 10% hydrochloric acid, 2% acetic acid, 6% fluoroboric acid, and 5% hexadecyltrimethylammonium bromide. The main components of the anti-agglomeration agent were 1.0% γ-aminopropyltriethoxysilane, 1% phenyltrimethoxysilane, 0.06% acetic acid, 8% ethanol, and 8% isopropanol. Referring to the evaluation standard "QHS2019-2020 Implementation Specifications and Effect Evaluation Methods for Chemical Unblocking Technology of Injection Wells", the injection pressure of this well before unblocking was 10.9 MPa, and the daily injection volume was 274.86 m³. 3 / d, injection pressure after unblocking is 6.3MPa, daily injection volume is 456.73m³. 3 / d, the apparent water absorption index is increased by 187.5%, and the shelf life is 459 days.

[0032] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for extending the effectiveness of polymer injection well unclogging, characterized in that: Includes the following steps: Inject a permeation dispersant into the polymer injection well as a pre-flush slug, then inject a depolymerization fluid as the first treatment fluid slug. After shutting in the well for a period of time, inject a treatment acid as the second treatment fluid slug, inject an anti-agglomeration agent as a post-flush slug, and finally inject field-mixed water as a displacement fluid. After shutting in the well for a period of time, polymer flooding is then carried out. The penetrating dispersant comprises the following components by mass percentage: sodium dodecyl sulfate 1-3%, citric acid 2-4%, acetic acid 2-4%, and the balance being water; The depolymerization solution comprises the following components in weight percentage: 1-2% citric acid, 0.5-1.2% ferrous chloride, 1.0-1.5% sodium persulfate, and the balance being water; The treated acid comprises the following components by mass percentage: 5-12% hydrochloric acid, 2-4% acetic acid, 2-6% fluoroboric acid, 1-5% hexadecyltrimethylammonium bromide, with the balance being water; The anti-agglomeration agent includes γ-aminopropyltriethoxysilane and / or phenyltrimethoxysilane.

2. The method for unclogging and extending the effectiveness of polymer injection wells according to claim 1, characterized in that: The volume of the pre-flush slug is equal to the reservoir pore volume within a cylindrical area centered on the injection well, with a radius of 0.8 to 1.2 meters and a height equal to the effective thickness of the reservoir.

3. The method for unclogging and extending the effectiveness of polymer injection wells according to claim 1, characterized in that: The volume of the first processing fluid slug is equal to the reservoir pore volume within a cylindrical area centered on the injection well, with a radius of 0.8 to 1.2 meters and a height equal to the effective thickness of the reservoir.

4. The method for unclogging and extending the effectiveness of polymer injection wells according to claim 1, characterized in that: The volume of the second processing fluid slug is equal to the reservoir pore volume within a cylindrical area centered on the injection well, with a radius of 1.0 to 1.2 meters and a height equal to the effective thickness of the reservoir.

5. The method for unclogging and extending the effectiveness of polymer injection wells according to claim 1, characterized in that: The volume of the post-positioned liquid slug is equal to the reservoir pore volume within a cylindrical area centered on the injection well, with a radius of 1.5 to 2 meters and a height equal to the effective thickness of the reservoir.

6. The method for unclogging and extending the effect of polymer injection wells according to claim 1, characterized in that: The volume of the displacement fluid used is equal to the tubing volume of the polymer injection well's slug.