Ultralow-density leakage-proof workover fluid and preparation method thereof

Abstract

The invention belongs to the technical field of drilling and workover fluids, and particularly discloses an ultralow-density leakage-proof workover fluid which is formed by mixing a base fluid and a microbubble fluid, wherein the base solution comprises a structure stabilizer, a tackifying filtrate reducer, a pH regulator, a bactericide, a corrosion inhibitor, a surfactant and water; the microbubble liquid comprises a foaming agent, a foam stabilizer and water. The preparation method of the workover fluid comprises the following steps: firstly preparing the base fluid, then preparing the microbubble liquid, finally adding the microbubble liquid into the base fluid, and uniformly mixing to obtain a finished product. The workover fluid disclosed by the invention has the remarkable effects that the workover fluid is good in viscosity and cutting improving effect, short in natural degradation period and small in damage to a reservoir, can be suitable for various oil and gas wells, well killing and workover operations with the formation pressure coefficient being lower than 1.0, can greatly reduce the use amount of conventional working fluid so as to shorten the flowback period, and is relatively low in requirement on production equipment and convenient to implement.

Description

Technical Field

[0001] This invention relates to the field of drilling and workover fluid technology, and more specifically to a special working fluid for the field of oil and gas engineering. Background Technology

[0002] In the mid-to-late stages of oil and gas well development, due to reservoir stimulation and insufficient injection-production ratios, formation pressure gradually decreases. Consequently, during conventional well workover operations, various degrees of leakage often occur, leading to problems such as the inability to perform workover or high workover risks. When the loss of workover fluid is excessive, it not only increases workover costs but also causes reservoir contamination due to incompatibility between the workover fluid and formation fluids.

[0003] Well workover fluids are primarily formulated with clean water as a base. Different components, such as viscosifiers, corrosion inhibitors, weighting agents (inorganic salts, organic salts, barite powder), and pH adjusters, are added to the water to adjust the fluid's performance parameters and achieve different operational objectives. In existing technologies, the density of well workover fluids is generally greater than or equal to 1.0 g / cm³. 3 When applied to oil and gas wells with a formation pressure coefficient of less than 1.0, there will inevitably be working fluid leakage due to positive pressure differential.

[0004] To reduce the density of workover fluid, it can be foamed. However, existing foaming techniques for workover fluids all involve adding a foaming agent to a base fluid with a certain viscosity and shear, followed by foaming to reduce the overall density of the system. Current technologies primarily employ aeration methods (mixing gas, aeration) and mechanical foaming methods (high-pressure jetting, high shearing). The main drawback of aeration methods is that the viscosity and shearing of the base fluid during aeration causes significant resistance to bubble rise, leading to agglomeration and ultimately slippage and breakage. Mechanical foaming methods commonly use high-pressure jetting and high-shearing methods. High-pressure jetting has the disadvantage of requiring a high-performance pump. Conventional centrifugal pumps are prone to air blockage due to the system's gas content, resulting in difficulties in water delivery. While plunger pumps can effectively overcome air blockage, as the system's gas content increases further, the system becomes easily compressed, reducing pump efficiency and limiting the lower density limit of the system. The disadvantage of high-shear cycling is that it requires high-speed stirring equipment. Most of the known similar published patents adopt this method, requiring a speed of 5000-8000 r / min. This type of method is easy to implement in the laboratory, but it is difficult to implement in the pilot-scale process and has strong limitations.

[0005] For example, Chinese patent CN115197683A discloses a leak-proof low-density microbubble workover fluid and its preparation method. The foaming process involves adding sodium-based bentonite to water, then adding a bactericide, viscosifier, drag reducer, foaming agent, and foam stabilizer, mixing thoroughly, and then aerating the fluid to achieve foaming. However, this foaming method has the following drawbacks: adding foaming agents and foam stabilizers to the workover fluid base increases the viscosity and shear of the entire system; the bubbles introduced into the workover fluid tend to aggregate, grow larger, and slip, leading to increased density and decreased low-density stability. Summary of the Invention

[0006] To address the above technical problems, the present invention aims to provide an ultra-low density well workover fluid and its preparation method, wherein "ultra-low density" means a density below 1.0 g / cm³. 3 .

[0007] The main technical solutions adopted to achieve one of the objectives of this invention are as follows: An ultra-low density leak-proof well repair fluid is characterized by being composed of a base fluid and a microbubble fluid in a weight ratio of 10:1-5; The base liquid comprises, by weight, 0.4-0.6 parts of structural stabilizer, 1-2 parts of thickener and filtration loss reducer, 0.05-0.1 parts of pH adjuster, 0.05-0.1 parts of bactericide, 0.05-0.1 parts of corrosion inhibitor, 0.1-0.3 parts of surfactant, and 100 parts of water. The microbubble solution comprises 0.1-6.0 parts of foaming agent, 0.1-0.3 parts of foam stabilizer, and 100 parts of water.

[0008] The microbubble liquid undergoes a foaming treatment.

[0009] The bactericide is at least one of formaldehyde and acetaldehyde; The surfactant is at least one of fluorocarbon surfactants, alkyl glucosides, and fatty acid glycerides.

[0010] The main technical solutions adopted to achieve the second objective of this invention are as follows: A method for preparing an ultra-low density leak-proof well workover fluid includes the following steps: Step 1: Add the required amounts of structural stabilizer, thickener and filtration reducer, pH adjuster, bactericide, corrosion inhibitor and surfactant to the required amount of water in sequence, and stir evenly to obtain the base solution; Step 2: Add the required amount of foaming agent and foam stabilizer to the required amount of water in sequence, mix evenly, and then foam to obtain microbubble liquid; Step 3: Add the microbubble liquid to the base fluid according to the weight ratio, and stir evenly to obtain ultra-low density leak-proof well repair fluid.

[0011] By employing the above technical solutions, the density of the workover fluid can be reduced by mixing the foamed microbubble fluid with the base fluid, achieving an ultra-low density (density below 1.0 g / cm³). 3 This is the basis for the state; at the same time, avoiding the introduction of high-viscosity base fluid into the foaming process can optimize the foaming effect and improve the performance parameters of the workover fluid. Attached Figure Description

[0012] Figure 1 This is a flowchart of the present invention; Figure 2 Comparison of the appearance of pre-foamed and post-foamed well-workover fluids after preparation; Figure 3 This is a comparison of the appearance of pre-foamed and post-foamed well-keeping fluids after standing for 8 hours. Detailed Implementation

[0013] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0014] Examples 1-8: An ultra-low density leak-proof well workover fluid is composed of a base fluid and a microbubble fluid. The base fluid includes a structure stabilizer, a viscosity increaser and filtration reducer, a pH adjuster, a bactericide, a corrosion inhibitor, a surfactant, and water. The microbubble fluid includes a foaming agent, a foam stabilizer, and water. The microbubble fluid is foamed to form a foam.

[0015] The composition of the workover fluids in Examples 1-8, by weight, is shown in Table 1:

[0016] Examples 9-17: A base fluid for an ultra-low density leak-proof well workover fluid includes a structure stabilizer, a viscosity increaser and filtration loss reducer, a pH adjuster, a bactericide, a corrosion inhibitor, a surfactant, and water. The structural stabilizer is a biopolymer; the biopolymer is at least one of xanthan gum, hydroxypropyl guanidine gum, and sodium carboxymethyl cellulose; the thickening and filtration loss reducing agent is carboxymethyl starch; the pH adjuster is at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate; the bactericide is at least one of formaldehyde and acetaldehyde; the corrosion inhibitor is at least one of imidazoline corrosion inhibitors, nitrate corrosion inhibitors, and nitrite corrosion inhibitors; and the surfactant is at least one of fluorocarbon surfactants, alkyl glucosides, and fatty acid glycerides.

[0017] When the selected structural stabilizer is a polysaccharide biopolymer and the viscosity enhancer and filtration reducer is carboxymethyl starch, both are self-degradable materials with self-degradation capabilities. After well completion, the ultra-low density leak-proof workover fluid that enters the formation can naturally degrade under the action of formation temperature, causing low damage to the reservoir and not affecting the reservoir or gathering and transportation pipelines. Specifically, the fluorocarbon surfactant is any one of fluorocarbon surfactant FC-4430, fluorocarbon surfactant FSO-100, fluorocarbon surfactant FS-3100 and fluorocarbon surfactant FC209; The alkyl glucoside is alkyl glucoside APG-0814 or alkyl glucoside APG0810; The fatty acid glycerides are any one of fatty acid glycerides type 34, fatty acid glycerides type 36, fatty acid glycerides type 38, and fatty acid glycerides type 40.

[0018] Specifically, the component proportions in the base liquids of Examples 9-17, by weight, are shown in Table 2:

[0019] Examples 18-53: A microbubble fluid for leak prevention and well repair, comprising a foaming agent, a foam stabilizer, and water.

[0020] The foaming agent is at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, synthetic fire-fighting foam liquid, fluoroprotein foam liquid, and aqueous film-forming foam liquid; the foam stabilizer is dodecyl alcohol.

[0021] The fluoroprotein foam liquid is either fluoroprotein foam liquid FP or fluoroprotein foam liquid FFFP; the aqueous film-forming foam liquid is aqueous film-forming foam liquid AFFF.

[0022] Specifically, the component proportions of the microbubble solutions in Examples 18-53, by weight, are shown in Table 3:

[0023] Examples 54-58: An ultra-low density leak-proof well-keeping fluid, by weight, is a mixture of base fluid and microbubble fluid; the component ratios of the ultra-low density leak-proof well-keeping fluids in Examples 54-58 are shown in Table 4:

[0024] The base liquid in Table 4 is selected from the base liquid components of any of the embodiments 9-17, and the microbubble liquid is selected from the microbubble liquid components of any of the embodiments 18-53.

[0025] Example 59: A method for preparing an ultra-low density leak-proof well workover fluid, comprising the following steps: Step 1: Prepare the base solution; Under normal temperature and pressure conditions, add the required amounts of structural stabilizer, thickener and filtration reducer, pH adjuster, bactericide, corrosion inhibitor and surfactant to the required amount of water in sequence, and stir evenly to obtain the base solution; Step 2: Prepare the microbubble solution; Under normal temperature and pressure conditions, the required amount of foaming agent and foam stabilizer are added to the required amount of water in sequence, mixed evenly, and then foamed to obtain microbubble liquid; the density of the microbubble liquid is controlled to be 15g / L-50g / L, the particle size is 30μm-200μm, and the half-life is 30min-50min.

[0026] Step 3: Prepare the well workover fluid; Under normal temperature and pressure conditions, the microbubble liquid is added to the base liquid and stirred evenly to obtain an ultra-low density leak-proof well repair fluid.

[0027] The workover fluids in Examples 1-8 and 54-58 were all prepared according to the method described in this example.

[0028] Example 60: An ultra-low density leak-proof well repair fluid is composed of a base fluid and a microbubble fluid in a weight ratio of 10:1. By weight, the base liquid comprises 0.4 parts xanthan gum, 1 part carboxymethyl starch, 0.05 parts sodium hydroxide, 0.05 parts formaldehyde, 0.05 parts imidazoline corrosion inhibitor BP8212, 0.1 parts fluorocarbon surfactant FC-4430 and 100 parts water; The microbubble solution comprises, by weight, 0.1 parts sodium dodecyl sulfate, 0.1 parts sodium dodecylbenzene sulfonate, 0.1 parts dodecanol and 100 parts water.

[0029] The preparation method of well workover fluid is as follows: Step 1: Prepare the base solution Add all of the xanthan gum, carboxymethyl starch, sodium hydroxide, formaldehyde, imidazoline corrosion inhibitor BP8212, and fluorocarbon surfactant FC-4430 to 100 parts of water in sequence; stir well to obtain the base solution. Step 2, prepare the microbubble solution Add all of the sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and dodecyl alcohol to 100 parts of water in sequence; then foam the mixture to obtain a microbubble solution. The density of the microbubble solution was controlled at 45 g / L-50 g / L, the particle size at 150 μm-200 μm, and the half-life at ≥30 min.

[0030] Step 3: Prepare the workover fluid Microbubble solution was added to the base solution at a weight ratio of 10:1; after thorough mixing, a density of 0.9 g / cm³ was obtained. 3 Ultra-low density leak-proof well repair fluid.

[0031] Example 61: An ultra-low density leak-proof well repair fluid is composed of a base fluid and a microbubble fluid in a weight ratio of 10:1. By weight, the base solution comprises 0.4 parts xanthan gum, 1 part carboxymethyl starch, 0.05 parts potassium hydroxide, 0.05 parts acetaldehyde, 0.05 parts Lan-5 nitric acid corrosion inhibitor, 0.1 parts alkyl glucoside APG-0814, and 100 parts water; The microbubble solution comprises, by weight, 0.1 parts sodium dodecyl sulfate, 0.1 parts sodium dodecylbenzene sulfonate, 0.5 parts sodium fatty alcohol polyoxyethylene ether sulfate, 0.15 parts dodecyl alcohol, and 100 parts water.

[0032] The preparation method of well workover fluid is as follows: Step 1: Prepare the base solution Add all of the xanthan gum, carboxymethyl starch, carboxymethyl starch, potassium hydroxide, acetaldehyde, Lan-5 nitric acid corrosion inhibitor, and alkyl glucoside APG-0814 to 100 parts of water in sequence; stir well to obtain the base solution. Step 2, prepare the microbubble solution Add all of the sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, and dodecyl alcohol to 100 parts of water in sequence; then foam the mixture to obtain a microbubble solution. The density of the microbubble solution was controlled at 30 g / L-40 g / L, the particle size at 100 μm-150 μm, and the half-life at ≥30 min.

[0033] Step 3: Prepare the workover fluid Microbubble solution was added to the base solution at a weight ratio of 10:1; after thorough mixing, a density of 0.85 g / cm³ was obtained. 3 Ultra-low density leak-proof well repair fluid.

[0034] Example 62: An ultra-low density leak-proof well repair fluid is composed of a base fluid and a microbubble fluid in a weight ratio of 10:2. By weight, the base liquid comprises 0.5 parts xanthan gum, 1.2 parts carboxymethyl starch, 0.05 parts sodium carbonate, 0.05 parts formaldehyde, 0.05 parts nitrite corrosion inhibitor AQ-700, 0.1 parts fatty acid glyceride type 34, and 100 parts water; The microbubble solution comprises, by weight, 0.1 parts sodium dodecyl sulfate, 0.1 parts sodium dodecylbenzene sulfonate, 0.5 parts sodium fatty alcohol polyoxyethylene ether sulfate, 0.5 parts synthetic fire-fighting foam solution (mass concentration of 6%), 0.2 parts dodecyl alcohol, and 100 parts water.

[0035] The preparation method of well workover fluid is as follows: Step 1: Prepare the base solution Add all of the xanthan gum, carboxymethyl starch, sodium carbonate, formaldehyde, nitrite corrosion inhibitor AQ-700, and fatty acid glyceride type 34 to 100 parts of water in sequence; stir well to obtain the base solution. Step 2, prepare the microbubble solution Add all of the sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, synthetic fire-fighting foam liquid (mass concentration of 6%), and dodecyl alcohol to 100 parts of water in sequence; then foam the mixture to obtain microbubble liquid. The density of the microbubble solution was controlled at 25 g / L-30 g / L, the particle size at 50 μm-100 μm, and the half-life at ≥40 min.

[0036] Step 3: Prepare the workover fluid Microbubble solution was added to the base solution at a weight ratio of 10:2; after thorough mixing, a density of 0.75 g / cm³ was obtained. 3 Ultra-low density leak-proof well repair fluid.

[0037] Example 63: An ultra-low density leak-proof well repair fluid is composed of a base fluid and a microbubble fluid in a weight ratio of 10:4. By weight, the base liquid comprises 0.5 parts xanthan gum, 1.4 parts carboxymethyl starch, 0.05 parts sodium hydroxide, 0.05 parts formaldehyde, 0.05 parts imidazoline corrosion inhibitor, 0.1 parts fluorocarbon surfactant FC-4430, and 100 parts water; By weight, the microbubble solution comprises 0.2 parts sodium dodecyl sulfate, 0.2 parts sodium dodecylbenzene sulfonate, 0.8 parts sodium fatty alcohol polyoxyethylene ether sulfate, 0.5 parts synthetic fire-fighting foam liquid (mass concentration of 6%), 0.5 parts fluoroprotein foam liquid FFFP (mass concentration of 3%), 0.15 parts dodecyl alcohol, and 100 parts water.

[0038] The preparation method of well workover fluid is as follows: Step 1: Prepare the base solution Add all of the xanthan gum, carboxymethyl starch, sodium hydroxide, formaldehyde, imidazoline corrosion inhibitor, and fluorocarbon surfactant FC-4430 to 100 parts of water in sequence; stir well to obtain the base solution. Step 2, prepare the microbubble solution Add all of the sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, synthetic fire-fighting foam liquid (6% by mass), fluoroprotein foam liquid FFFP (3% by mass), and dodecyl alcohol to 100 parts of water in sequence; then foam the mixture to obtain microbubble liquid. The density of the microbubble solution was controlled at 20 g / L-25 g / L, the particle size at 30 μm-80 μm, and the half-life at ≥40 min.

[0039] Step 3: Prepare the workover fluid Microbubble solution was added to the base solution at a weight ratio of 10:4; after thorough mixing, a density of 0.72 g / cm³ was obtained. 3 Ultra-low density leak-proof well repair fluid.

[0040] Example 64: An ultra-low density leak-proof well repair fluid is composed of a base fluid and a microbubble fluid in a weight ratio of 10:5. By weight, the base solution comprises 0.6 parts xanthan gum, 1.8 parts carboxymethyl starch, 0.05 parts potassium hydroxide, 0.05 parts acetaldehyde, 0.05 parts nitric acid corrosion inhibitor, 0.1 parts alkyl glucoside APG-0814, and 100 parts water; By weight, the microbubble solution comprises 1 part sodium fatty alcohol polyoxyethylene ether sulfate, 0.5 parts synthetic fire-fighting foam solution (6% by mass), 0.5 parts fluoroprotein foam solution FFFP (3% by mass), 0.5 parts aqueous film-forming foam solution AFFF (3% by mass), 0.2 parts dodecanol, and 100 parts water.

[0041] The preparation method of well workover fluid is as follows: Step 1: Prepare the base solution Add all of the xanthan gum, carboxymethyl starch, potassium hydroxide, acetaldehyde, nitrate corrosion inhibitor, and alkyl glucoside APG-0814 to 100 parts of water in sequence; stir well to obtain the base solution. Step 2, prepare the microbubble solution Add all of the sodium fatty alcohol polyoxyethylene ether sulfate, synthetic fire-fighting foam liquid (6% by mass), fluoroprotein foam liquid FFFP (3% by mass), aqueous film-forming foam liquid AFFF (3% by mass), and dodecanol to 100 parts of water in sequence; then foam the mixture to obtain microbubble liquid. The density of the microbubble solution was controlled at 15 g / L-20 g / L, the particle size at 30 μm-80 μm, and the half-life at ≥50 min.

[0042] Step 3: Prepare the workover fluid Microbubble solution was added to the base solution at a weight ratio of 10:5; after thorough mixing, a density of 0.60 g / cm³ was obtained. 3Ultra-low density leak-proof well repair fluid.

[0043] Compare with Example 1: The only difference between this comparative example and Example 60 is that the base liquid does not contain the structural stabilizer xanthan gum.

[0044] Compare with Example 2: The only difference between this comparative example and Example 60 is that the base liquid does not contain the thickening and filtration loss reducing agent - carboxymethyl starch.

[0045] Compare with Example 3: The only difference between this comparative example and Example 60 is that the base liquid does not contain a surfactant—fluorocarbon surfactant FC-4430.

[0046] Experimental Example 1: Performance Investigation of Base Liquid Experimental Methods: The base liquid prepared in Example 60 was allowed to stand for 7 days. The density, funnel viscosity, initial shear, final shear, apparent viscosity, plastic viscosity, dynamic shear force, and surface tension of the base liquid were tested before and after standing for 7 days. The experimental results are shown in Table 5.

[0047] As shown in Table 5, after the base liquid prepared in Example 60 was left to stand for 7 days, the structural stabilizer in the base liquid system gradually degraded, and the viscosity-shear (apparent viscosity, plastic viscosity and dynamic shear force) decreased until it became consistent with water. However, the surfactant component in the base liquid did not become ineffective as the structural stabilizer degraded.

[0048] Experimental Example 2: Comprehensive Performance Evaluation of Well Workover Fluid Experimental methods: The density, funnel viscosity, initial shear, final shear, apparent viscosity, plastic viscosity, dynamic shear force, and surface tension of the ultra-low density leak-proof well-keeping fluids prepared in Examples 60-64 and Control Examples 1-3 were tested. The experimental results are shown in Table 6.

[0049] Table 6 shows the test results of Examples 60-64, indicating that the well workover fluid of the present invention has good comprehensive performance indicators.

[0050] A comparison of the test results from Example 60, Comparative Example 1, and Comparative Example 2 shows that, compared to using both the structural stabilizer (xanthan gum) and the viscosity enhancer / filtration reducer (carboxymethyl starch) simultaneously, using only the structural stabilizer (xanthan gum) or the viscosity enhancer / filtration reducer (carboxymethyl starch) significantly reduces the shear force, apparent viscosity, plastic viscosity, and dynamic shear force of the workover fluid. Therefore, in workover fluids, the structural stabilizer (xanthan gum) and the viscosity enhancer / filtration reducer (carboxymethyl starch) have good compatibility and a significant synergistic shear enhancement effect; their combined use can greatly improve various indicators.

[0051] The test results of Example 60 and Comparative Example 3 show that adding an appropriate amount of surfactant (fluorocarbon surfactant FC-4430) to the workover fluid can effectively reduce the surface tension of the workover fluid and prevent reservoir "water lock".

[0052] Experiment Example 3: Stability Study of Well Workover Fluid Experimental method: The ultra-low density leak-proof well repair fluids prepared in Examples 60-64 and Control Example 3 were left to stand for 48 hours. The suspension stability of the ultra-low density leak-proof well repair fluids before and after standing for 48 hours was investigated. The experimental results are shown in Table 7. The ultra-low density leak-proof well-keeping fluids prepared in Examples 1 and 2 were left to stand for 12 hours. The suspension stability of the ultra-low density leak-proof well-keeping fluids before and after standing for 12 hours was investigated. The experimental results are shown in Table 7.

[0053] In Table 7, the parameters of the workover fluids in Examples 60-64 and Control Examples 1, 2, and 3 before settling are consistent with those in Table 6;

[0054] Among rheological parameters, static shear force (initial shear and final shear) is an important indicator for evaluating the suspension stability of ultra-low density leak-proof well-keeping fluid.

[0055] As shown in Table 7, the ultra-low density leak-proof well repair fluids obtained in Examples 60-64 exhibit strong microbubble suspension stability, low bubble slippage and rise rate, and low density loss rate after standing for 48 hours, meeting the requirements for on-site construction.

[0056] Based on the test results of Example 60, Comparative Example 1, and Comparative Example 2, it can be seen that the structural stabilizer (xanthan gum) and the viscosity enhancer and filtration reducer (carboxymethyl starch) have good compatibility and can work together synergistically to produce a superior shearing effect in the workover fluid. However, the workover fluid obtained by using the structural stabilizer (xanthan gum) or the viscosity enhancer and filtration reducer (carboxymethyl starch) alone does not meet the requirements for suspended microbubbles, has poor density stability, and exhibits rapid bubble slippage. Within 12 hours, all bubbles have slipped out, which cannot meet the requirements of conventional workover operation cycles.

[0057] Based on the test results of Example 60 and Comparative Example 3, it can be seen that when no surfactant (fluorocarbon surfactant FC-4430) is added to the well workover fluid, the surface tension of the well workover fluid is high, which can easily cause reservoir "water lock".

[0058] Experimental Example 4: Application of the ultra-low density leak-proof well-keeping fluid of the present invention in oil and gas wells with a formation pressure coefficient of less than 1.0.

[0059] Specific application methods of workover fluid on site: Determine the density of the workover fluid based on the pressure coefficient provided by the geological design and the corresponding density supplementary value added according to the well control requirements of the oil and gas well. Before well control, perform a backwashing process, confirming the single-well dosage at 1.5 times the casing volume above the pump hanger depth. During on-site construction, circulate at a rate of 400-500 L / min until the inlet and outlet densities are consistent. Then stop the circulation and workover operation. After observing that there are no abnormalities at the wellhead, proceed to the next step.

[0060] Field test results: Based on 3 field tests, the effectiveness rate was 100%. Compared with adjacent wells, the average fluid consumption was reduced by more than 30 cubic meters, and the average recovery period was reduced by more than 3 days.

[0061] Previous well workover operations at a certain oil well have shown severe leakage, with conventional working fluid (density 1.0-1.03 g / cm³) being ineffective. 3 The initial return volume after the reverse circulation well control operation was over 60 cubic meters. The formation pressure coefficient of this well is 0.7, the wellbore volume above the pump hanger is 18 cubic meters, and the planned density is 0.8 g / cm³. 3 30 cubic meters of ultra-low density leak-proof workover fluid were used for reverse circulation well control operations. During the reverse circulation process, the circulation pump pressure continuously increased. After 20 cubic meters of circulation, fluid began to return from the outlet. After 25 cubic meters of circulation, the inlet and outlet densities were consistent, both at 0.8 g / cm³. 3 After stopping the pump and allowing it to stand for one hour, no abnormalities were found at the wellhead, and the next step of the operation was carried out. During this period, the fluid return was normal. This reduced the working fluid loss of a single well by more than 30 cubic meters, thereby shortening the drainage cycle.

[0062] Experimental Example 5: Under normal temperature and pressure conditions, two portions of the base liquid, each 600 ml, were prepared according to the formula of Example 62; at the same time, two portions of foaming stock solution were prepared according to the formula of Example 62. The foaming stock solution was in the state before the microbubble liquid was foamed, and the microbubble liquid was obtained after the foaming of the foaming stock solution.

[0063] Pre-foaming group: Mix one part of the base liquid and one part of the foaming stock liquid at a weight ratio of 10:1, and then introduce air to foam it to obtain pre-foamed well workover fluid; Post-foaming group: Air is introduced into another part of the foaming stock solution to foam micro foam; then the micro foam is added to another part of the base solution at a weight ratio of 10:1 and mixed evenly to obtain post-foaming well workover fluid.

[0064] The foaming conditions and foaming time were the same for both the pre-foaming group and the post-foaming group – 15 minutes. During foaming, gas can be introduced into the foaming target using an air pump and micro-pore air stones, or a foaming machine can be used to foam the target.

[0065] Comparing the appearance of pre-foamed and post-foamed well-workover fluids, the results are as follows: Figure 2As shown, the beaker on the left contains pre-foamed well-fixing fluid, and the beaker on the right contains post-foamed well-fixing fluid. Figure 2 It can be seen that the bubble size of the well-draining fluid foamed first is larger, while the bubble size of the well-draining fluid foamed later is smaller.

[0066] The performance parameters of the pre-foamed and post-foamed well workover fluids were tested, and the results are shown in Table 8:

[0067] As can be seen from Table 8, the performance parameters of the pre-foamed well-work fluid are relatively poor, while the performance parameters of the post-foamed well-work fluid are relatively good.

[0068] After the pre-foamed and post-foamed well-workover fluids were allowed to stand for 8 hours respectively, their appearance was observed, and the results are as follows: Figure 3 As shown; the left beaker contains pre-foamed well-fixing fluid, and the right beaker contains post-foamed well-fixing fluid. From Figure 3 It can be seen that after standing for 8 hours, the bubble size of the first foaming well-draining fluid is larger, while the bubble size of the second foaming well-draining fluid is smaller.

[0069] After the pre-foamed and post-foamed well-workover fluids were allowed to stand for 8 hours, their performance parameters were tested. The results are shown in Table 9.

[0070] As can be seen from Table 9, the performance parameters of the pre-foamed well-working fluid are relatively poor after standing for 8 hours, while the performance parameters of the post-foamed well-working fluid are relatively good after standing for 8 hours.

[0071] Combination Figure 2 , 3 Mechanism analysis was conducted using Tables 8 and 9: With the same base fluid formulation and microfoam foaming agent formulation, the pre-foamed well-workover fluid, due to its higher viscosity-shear ratio, resulted in larger bubble sizes after foaming, making it prone to slippage and breakage, and exhibiting relatively lower performance parameters. Conversely, the post-foamed well-workover fluid, with its relatively lower viscosity-shear ratio, produced smaller bubble sizes after foaming, making them less prone to slippage and breakage. This allows the post-foamed well-workover fluid to effectively reduce the size of closed-cell microbubbles, increase viscosity-shear ratio, increase specific surface area, enhance shear lifting and viscosity-increasing effects, and prolong the density stabilization period of the foam system. Even after standing for 8 hours, it maintains good performance parameters, thus improving the suspension stability of the well-workover fluid.

[0072] Mechanical foaming equipment often achieves better foaming results, but those skilled in the art also know that high-viscosity-shear foaming systems are prone to clogging the foaming net of mechanical foaming equipment. Therefore, mechanical foaming equipment is more suitable for low-viscosity-shear foaming systems. Thus, it can be predicted that even if mechanical foaming equipment is used to foam the pre-foamed and post-foamed workover fluids separately, the performance parameters of the pre-foamed workover fluid will not be as good as those of the post-foamed workover fluid.

[0073] Compared with the prior art, the beneficial effects of the present invention are as follows: First, the surfactant added to the base fluid of this invention can effectively reduce the surface tension of the ultra-low density leak-proof well repair fluid, promote backflow, prevent "water lock", and thus reduce the damage of the working fluid to the reservoir. Secondly, the ultra-low density anti-leakage well workover fluid of the present invention reduces its own density, thereby reducing the static fluid column pressure and making it similar to the formation pressure, thus reducing the phenomenon of working fluid entering the reservoir under positive pressure differential. Due to its high viscosity and shear characteristics, it can increase the seepage resistance and the "gas resistance" effect of microbubbles in the reservoir seepage channel, further reducing the leakage of working fluid and minimizing the problem of long drainage cycles caused by leakage.

[0074] Third, the preparation process has lower equipment requirements, making it more suitable for mass production and easier to implement.

[0075] The ultra-low density well workover fluid of this invention uses structural stabilizers and viscosity enhancers and filtration reducers, both of which are polysaccharide biopolymers. It has good viscosity and shearing effects, a short natural degradation cycle, and minimal damage to the reservoir. It can be used in various oil and gas wells with a formation pressure coefficient of less than 1.0 for well control and workover operations. It can significantly reduce the amount of conventional working fluid used, thereby shortening the flowback cycle.

[0076] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. An ultra-low density leak-proof well-maintaining fluid, characterized in that... It is composed of a base liquid and a microbubble liquid with a weight ratio of 10:1-5; The base liquid comprises, by weight, 0.4-0.6 parts of structural stabilizer, 1-2 parts of thickener and filtration loss reducer, 0.05-0.1 parts of pH adjuster, 0.05-0.1 parts of bactericide, 0.05-0.1 parts of corrosion inhibitor, 0.1-0.3 parts of surfactant, and 100 parts of water. The microbubble solution comprises 0.1-6.0 parts of foaming agent, 0.1-0.3 parts of foam stabilizer, and 100 parts of water; The microbubble liquid undergoes a foaming treatment; The bactericide is at least one of formaldehyde and acetaldehyde; The surfactant is at least one of fluorocarbon surfactants, alkyl glucosides, and fatty acid glycerides.

2. The ultra-low density leak-proof well-keeping fluid according to claim 1, characterized in that: The structural stabilizer is a biopolymer.

3. The ultra-low density leak-proof well-keeping fluid according to claim 2, characterized in that: The biopolymer is at least one of xanthan gum, hydroxypropyl guanidine gum, and sodium carboxymethyl cellulose.

4. The ultra-low density leak-proof well-keeping fluid according to claim 1, characterized in that: The thickening and filtration loss reducing agent is carboxymethyl starch.

5. The ultra-low density leak-proof well-keeping fluid according to claim 1, characterized in that: The pH adjuster is at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate.

6. The ultra-low density leak-proof well-keeping fluid according to claim 1, characterized in that: The corrosion inhibitor is at least one of imidazoline corrosion inhibitors, nitrate corrosion inhibitors, and nitrite corrosion inhibitors.

7. The ultra-low density leak-proof well-keeping fluid according to claim 1, characterized in that: The foaming agent is at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, synthetic fire-fighting foam liquid, fluoroprotein foam liquid, and aqueous film-forming foam liquid.

8. The ultra-low density leak-proof well-keeping fluid according to claim 1, characterized in that: The foam stabilizer is dodecayl alcohol.

9. A method for preparing the ultra-low density leak-proof well-keeping fluid according to any one of claims 1-8, characterized in that... Follow these steps: Step 1: Add the required amounts of structural stabilizer, thickener and filtration reducer, pH adjuster, bactericide, corrosion inhibitor and surfactant to the required amount of water in sequence, and stir evenly to obtain the base solution; Step 2: Add the required amount of foaming agent and foam stabilizer to the required amount of water in sequence, mix evenly, and then foam to obtain microbubble liquid; Step 3: Add the microbubble liquid to the base fluid according to the weight ratio, and stir evenly to obtain ultra-low density leak-proof well repair fluid.

10. The method for preparing the ultra-low density leak-proof well-keeping fluid according to claim 9, characterized in that: In step two, the density of the microbubble solution is 15 g / L-50 g / L, the particle size is 30 μm-200 μm, and the half-life is 30 min-50 min.

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