Water control type workover fluid and preparation method thereof

Abstract

The invention discloses a water control type workover fluid and a preparation method thereof. The water control type workover fluid is prepared from the following components in parts by weight: 2 parts of a clay stabilizer, 0.2-1 part of a high-temperature chelating agent, 0.5-1 part of a corrosion inhibition bactericide, 1-2 parts of a waterproof locking agent, 5 parts of a phase change agent and 100 parts of filtered seawater. The method comprises the following steps: filtering the filtered seawater until suspended particles are less than 30 microns in standard value, sequentially adding a clay stabilizer, a high-temperature chelating agent, a corrosion inhibition bactericide, a water blocking prevention agent and a phase change agent, and uniformly stirring to obtain the water control type workover fluid. After the workover fluid enters a reservoir, the oil phase starting pressure can be reduced, the oil-water interfacial tension can be reduced, the effect of inhibiting water content rising after well workover is achieved, the workover fluid can be matched with different field operation types, and the recovery period of an oil well can be shortened.

Description

A water-controlled well workover fluid and its preparation method Technical Field

[0001] This invention relates to the field of oilfield chemistry, and in particular to a water-controlled well workover fluid and its preparation method. Background Technology

[0002] Currently, offshore oilfield well workover operations commonly utilize acidic chelating workover fluids that chelate divalent metal ions such as calcium and magnesium. Because of their acidity, these fluids possess a certain dissolving ability against reservoir minerals. Simultaneously, with oilfield development, the porosity and permeability in the near-wellbore zone gradually increase. These factors lead to significant fluid loss during workover operations, causing a gradual increase in oil phase start-up pressure and a sudden rise in water cut after well resumption of production.

[0003] Currently, reservoir protection efforts mainly focus on drilling and completion fluids for low-permeability reservoirs, with limited experience available for research on workover fluids for low-pressure, low-permeability reservoirs. Therefore, it is necessary to develop a water-controlled workover fluid. Summary of the Invention

[0004] This invention addresses the technical problem of increased water cut after well workover using existing workover fluid systems by providing a water-controlled workover fluid and its preparation method. This workover fluid effectively inhibits the increase in water cut after workover, reduces oil-water interfacial tension, suppresses the expansion of clay minerals, and also features good reservoir compatibility and low cost.

[0005] Firstly, the present invention provides a water-controlled well workover fluid, which is achieved by the following technical solution.

[0006] A water-controlling well workover fluid comprises the following components in parts by weight: 2 parts clay stabilizer, 0.2-1 parts high-temperature chelating agent, 0.5-1 parts corrosion inhibitor and bactericide, 1-2 parts waterproofing agent, 5 parts phase change agent, and 100 parts filtered seawater.

[0007] Furthermore, the clay stabilizer is a quaternary ammonium salt cationic polymer, specifically polydiallyldimethylammonium chloride, which primarily inhibits the hydration and swelling of expansive clay.

[0008] Furthermore, the high-temperature chelating agent is an organic acid, specifically aminotrimethylenephosphonic acid or hydroxyethylidene diphosphonic acid. The high-temperature chelating agent possesses both acidic dissolving properties and chelating effects on high-valence metal ions, thereby relieving reservoir damage caused by incompatibility between various working fluids and formation water, and clearing shielding ring damage that cannot be removed by negative pressure unblocking after horizontal well completion.

[0009] Furthermore, the corrosion inhibitor and bactericide is a cationic surfactant, specifically, an alkyl imidazoline quaternary ammonium salt. This corrosion inhibitor and bactericide has excellent film-forming properties on steel, effectively preventing corrosion caused by oxygen, carbon dioxide, and hydrogen sulfide, while also possessing bactericidal effects.

[0010] Furthermore, the waterproofing agent is a fluorocarbon surfactant, specifically a perfluorodecyl ether fluorocarbon surfactant or a perfluorodecyl polyoxyethylene ether fluorocarbon surfactant, to prevent water lock damage to low-permeability reservoirs.

[0011] Furthermore, the phase change agent is a low-carbon alcohol, specifically ethylene glycol or glycerol, which eliminates or reduces the crude oil starting pressure gradient.

[0012] Furthermore, the suspended particles in the filtered seawater are smaller than 30 μm.

[0013] Secondly, the present invention provides a method for preparing a water-controlled well workover fluid, which is achieved by the following technical solution.

[0014] A method for preparing the above-mentioned water-controlled well workover fluid includes the following steps: adding a specified amount of clay stabilizer, high-temperature chelating agent, corrosion inhibitor and bactericide, waterproofing agent and phase change agent to a portion of filtered seawater, mixing and stirring evenly, then adding another portion of filtered seawater, and stirring and mixing evenly again to obtain the water-controlled well workover fluid.

[0015] Furthermore, after adding each additive to the filtered seawater, it is necessary to stir for at least 10 minutes until the additive is completely dissolved.

[0016] This application has the following beneficial effects.

[0017] (1) After the workover fluid of the present invention enters the reservoir, it can reduce the oil phase start-up pressure and reduce the oil-water interface tension, thus inhibiting the rise in water cut after workover; (2) The workover fluid of the present invention can not only match different types of operations on site, but also shorten the recovery cycle of oil wells. Detailed Implementation

[0018] The present patent application will be further described below with reference to the embodiments. Unless otherwise specified, the materials used in the preparation process in the following embodiments have not undergone further processing and have been commercially available.

[0019] The polydiallyl dimethyl ammonium chloride used in the following embodiments of this application was purchased from Henan Junfa Chemical Co., Ltd.

[0020] The aminotrimethylenephosphonic acid used in the following embodiments of this application was purchased from Hubei Guangao Biotechnology Co., Ltd.

[0021] The alkyl imidazoline quaternary ammonium salt used in the following embodiments of this application was purchased from Guangrao County Kerui Biotechnology Co., Ltd.

[0022] The perfluorodecyl ether fluorocarbon surfactants used in the following embodiments of this application were purchased from Shanghai Futian Chemical Technology Co., Ltd.

[0023] The ethylene glycol used in the following embodiments of this application was purchased from Jingzhou Longhua Petrochemical Co., Ltd.

[0024] Example 1: A method for preparing a water-controlled well workover fluid (to prepare 100m...) 3 (For example), the steps include: cleaning the mud tank with seawater, filtering the seawater until the suspended particle value is less than 30μm, and then adding 50m of filtered seawater. 3 2000 kg of polydiallyl dimethyl ammonium chloride, 200 kg of aminotrimethylene phosphonic acid, 1000 kg of alkyl imidazoline quaternary ammonium salt, 1000 kg of perfluorodecyl ether fluorocarbon surfactant, and 5000 kg of ethylene glycol are mixed thoroughly, and then 50 m³ of filtered seawater is added. 3 Then stir and mix thoroughly to obtain 100m 3 The water-controlled well workover fluid contains polydiallyl dimethyl ammonium chloride, aminotrimethylene phosphonic acid, alkyl imidazoline quaternary ammonium salt, perfluorodecyl ether fluorocarbon surfactant, and ethylene glycol at mass fractions of 2%, 0.2%, 1%, 1%, and 5%, respectively.

[0025] Example 2: A method for preparing a water-controlled well workover fluid (to prepare 50m...) 3 (For example), the steps include: cleaning the mud tank with seawater, filtering the seawater until the suspended particle value is less than 30μm, and then adding 25m of filtered seawater. 3 Mix 500 kg of polydiallyldimethylammonium chloride, 250 kg of aminotrimethylenephosphonic acid, 500 kg of alkyl imidazoline quaternary ammonium salt, 250 kg of perfluorodecyl ether fluorocarbon surfactant, and 750 kg of ethylene glycol until homogeneous. Then add 25 m³ of filtered seawater. 3 Then stir and mix thoroughly to obtain 50m 3 The water-controlled well workover fluid contains polydiallyl dimethyl ammonium chloride, aminotrimethylene phosphonic acid, alkyl imidazoline quaternary ammonium salt, perfluorodecyl ether fluorocarbon surfactant, and ethylene glycol at mass fractions of 2%, 1%, 2%, 1%, and 3%, respectively.

[0026] Performance Testing 1. Evaluation of Phase Change Agent's Reduction of Reservoir Wettability Four samples were prepared: filtered seawater + 0wt% ethylene glycol, filtered seawater + 5wt% ethylene glycol, filtered seawater + 10wt% ethylene glycol, and filtered seawater + 20wt% ethylene glycol. The contact angle of simulated injected water on the core surface before and after core immersion was measured using an OCA20 video optical contact angle meter. The results are shown in Table 1.

[0027] Table 1 Evaluation results of the reduction in reservoir wettability by different concentrations of phase change agents Experimental results show that as the concentration of phase change agent increases, the contact angle gradually decreases. When the concentration of phase change agent is 20%, the contact angle is 0, and the reservoir is completely hydrophilic, indicating that the phase change agent has the ability to change the wettability of the reservoir.

[0028] 2. Evaluation of the effect of phase change agent on crude oil viscosity reduction: Four samples were prepared: filtered seawater + 0 wt% ethylene glycol, filtered seawater + 5 wt% ethylene glycol, filtered seawater + 10 wt% ethylene glycol, and filtered seawater + 20 wt% ethylene glycol. The viscosity of different systems was measured at 60℃ using a DV-II type Brookfield viscometer. The results are shown in Table 2.

[0029] Table 2 Evaluation results of crude oil viscosity reduction by different concentrations of phase change agents Experimental results show that as the concentration of phase change agent increases, the viscosity of crude oil continues to decrease. When the concentration of phase change agent is 20% and the volume ratio of crude oil to experimental fluid is 6:4, the viscosity of crude oil can be reduced to 6.76 mPa·s, indicating that phase change agent can effectively reduce the viscosity of crude oil.

[0030] 3. Evaluation of clay stabilizer in well workover fluid system: Seven samples were prepared using filtered seawater + 0 wt% polydiallyl dimethyl ammonium chloride, filtered seawater + 0.5 wt% polydiallyl dimethyl ammonium chloride, filtered seawater + 1.0 wt% polydiallyl dimethyl ammonium chloride, filtered seawater + 1.5 wt% polydiallyl dimethyl ammonium chloride, filtered seawater + 2.0 wt% polydiallyl dimethyl ammonium chloride, filtered seawater + 2.5 wt% polydiallyl dimethyl ammonium chloride, and filtered seawater + 3.0 wt% polydiallyl dimethyl ammonium chloride. The anti-swelling rate of different systems at room temperature was determined by centrifugation method according to SY / T5971-94 "Performance Evaluation Method of Clay Stabilizer for Water Injection". The results are shown in Table 3.

[0031] Table 3. Anti-swelling properties of bentonite at different dosages of polydiallyl dimethyl ammonium chloride Evaluation results show that as the amount of polydiallyldimethylammonium chloride increases, the anti-swelling rate increases. When the amount of polydiallyldimethylammonium chloride is 1.5%, its anti-swelling rate for bentonite reaches over 90%.

[0032] 4. Evaluation of High-Temperature Chelating Agents in Well Workover Fluid Systems: Four samples were prepared: filtered seawater + 0.4 wt% aminotrimethylenephosphonic acid, filtered seawater + 0.8 wt% aminotrimethylenephosphonic acid, filtered seawater + 1 wt% aminotrimethylenephosphonic acid, and filtered seawater + 2 wt% aminotrimethylenephosphonic acid. Different concentrations of calcium ions were added at 100℃ to evaluate the ability of aminotrimethylenephosphonic acid to chelate calcium ions. The results are shown in Table 4.

[0033] Table 4. Chelating ability of aminotrimethylenephosphonic acid to calcium ions Experimental results show that aminotrimethylenephosphonic acid does not precipitate when mixed with calcium ions of different concentrations at high temperatures, indicating a strong ability to chelate calcium ions.

[0034] 5. Evaluation of Waterproof Locking Agent in Well Workover Fluid System: Seven samples were prepared, consisting of filtered seawater + 0 wt% perfluorodecyl ether fluorocarbon surfactant, filtered seawater + 0.5 wt% perfluorodecyl ether fluorocarbon surfactant, filtered seawater + 1.0 wt% perfluorodecyl ether fluorocarbon surfactant, filtered seawater + 1.5 wt% perfluorodecyl ether fluorocarbon surfactant, filtered seawater + 2.0 wt% perfluorodecyl ether fluorocarbon surfactant, filtered seawater + 3.0 wt% perfluorodecyl ether fluorocarbon surfactant, and filtered seawater + 4.0 wt% perfluorodecyl ether fluorocarbon surfactant. The interfacial tension of the different systems was measured at room temperature, and the results are shown in Table 5.

[0035] Table 5. Experimental data on interfacial tension of perfluorodecyl ether fluorocarbon surfactants with different dosages. The evaluation results show that the performance of perfluorodecyl ether fluorocarbon surfactants tends to stabilize after an increase of 2%.

[0036] 6. Evaluation of Water Control Performance of the Workover Fluid System The water control performance of the workover fluid system prepared in Example 1 was evaluated. Referring to the petroleum and natural gas industry standard SY / T6540-2002 "Indoor Evaluation Method for Damage to Oil Reservoirs by Drilling Fluid and Completion Fluid", the change in water cut after displacement of the core sample with kill fluid was investigated. The experimental results are shown in Table 6.

[0037] Table 6 Evaluation Results of Water Control in Well Workover Fluid System Experimental results show that when formation water displaces 20 PV, the core water cut is 50.5%. When displaced to 40 PV, the water cut is 53.0%. Further increasing the displacement volume does not significantly increase the core water cut, because formation water cannot effectively remove residual oil (kerosene) from the core. Displacing 20 PV with workover fluid increases the core water cut to 72.5%, indicating that the workover fluid system of this invention can effectively control reservoir water production and also has a certain ability to displace residual oil from the core.

[0038] 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 water-controlled well workover fluid, characterized in that: It includes the following components by weight: 2 parts clay stabilizer, 0.2-1 parts high-temperature chelating agent, 0.5-1 parts corrosion inhibitor and bactericide, 1-2 parts waterproofing agent, 5 parts phase change agent, and 100 parts filtered seawater.

2. The water-controlling well workover fluid according to claim 1, characterized in that: The clay stabilizer is a quaternary ammonium salt cationic polymer, and the quaternary ammonium salt cationic polymer is polydiallyldimethylammonium chloride.

3. The water-controlling well workover fluid according to claim 1, characterized in that: The high-temperature chelating agent is an organic acid, and the organic acid is selected from aminotrimethylene phosphonic acid or hydroxyethylidene diphosphonic acid.

4. The water-controlling well workover fluid according to claim 1, characterized in that: The corrosion inhibitor and bactericide is a cationic surfactant, and the cationic surfactant is selected from alkyl imidazoline quaternary ammonium salts.

5. The water-controlling well workover fluid according to claim 1, characterized in that: The waterproofing agent is a fluorocarbon surfactant, which is selected from perfluorodecyl ether fluorocarbon surfactants or perfluorodecyl polyoxyethylene ether fluorocarbon surfactants.

6. The water-controlling well workover fluid according to claim 1, characterized in that: The phase change agent is a low-carbon alcohol, and the low-carbon alcohol is selected from ethylene glycol or glycerol.

7. The water-controlling well workover fluid according to claim 1, characterized in that: The suspended particles in the filtered seawater are less than 30 μm.

8. A method for preparing the water-controlling well workover fluid according to any one of claims 1-7, characterized in that: The process includes the following steps: adding a specified amount of clay stabilizer, high-temperature chelating agent, corrosion inhibitor, bactericide, waterproofing agent, and phase change agent to a portion of filtered seawater, mixing and stirring until homogeneous, then adding another portion of filtered seawater, and stirring and mixing until homogeneous again to obtain a water-controlled well workover fluid.

9. The preparation method according to claim 8, characterized in that: After adding each additive to the filtered seawater, it must be stirred for at least 10 minutes until the additive is completely dissolved.

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