An acid-washable high-density completion fluid and a method of making the same

Abstract

The application provides an acid-washing high-density completion fluid and a preparation method thereof. The raw materials of the completion fluid include: 100 parts of water, 0.5-1.5 parts of a high-temperature viscosity-increasing and filtration-reducing agent, 0.2-0.6 parts of potassium hydroxide, 3-5 parts of a lignite resin filtration-reducing agent, 2-4 parts of a sulfonated asphalt plugging agent, 0.5-3 parts of a dispersion viscosity-reducing agent, 5-10 parts of potassium formate, 2-3 parts of a silicone filtration-reducing agent, 160-400 parts of an acid-soluble weighting agent and 5-6 parts of an inhibitor. The completion fluid system has good high-temperature stability, pressure-bearing temporary plugging reservoir protection and acid-washing and plugging removal capacity, can better prevent the high-density weighting agent from settling in the completion process, can promote the harmful solid-liquid phase to be discharged as much as possible after completion, can improve the reservoir permeability and the reservoir production, can timely flow back the drilling and completion fluid leaked to the formation from a single well bore, and can ensure that the drilling and completion fluid in the formation is discharged as completely as possible.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling technology, specifically to an acid-washable high-density completion fluid and its preparation method. Background Technology

[0002] Oil and gas well development includes drilling, completion, and production processes. Completion fluid refers to the process of connecting the wellbore with the formation in a specific structure after an open-hole well has been drilled to the designed depth. Completion technology requires the ability to effectively connect the oil and gas layers to the wellbore, minimizing resistance to oil and gas flow; effectively isolating oil, gas, and water layers to prevent crosstalk; meeting the requirements for stratified development and management for multi-layered oil and gas formations; overcoming or reducing the impact of wellbore collapse and sand production; and ensuring the integrity of the completion string and wellbore to guarantee long-term stable production of the oil and gas well.

[0003] The purpose of oil and gas well completion is to maximize the connection between formations, thereby ensuring the highest production and recovery rates. Broadly speaking, any fluid used in contact with the producing formation due to operational needs is called completion fluid. In specific production processes, the external fluid used before oil testing that comes into contact with the oil and gas formation is called completion fluid, such as drilling (oil and gas formation) fluid, perforation fluid, fracturing / acidizing fluid, etc. The main functions of completion fluid are: balancing formation pressure, protecting the reservoir and reducing damage to it, maintaining downhole cleanliness, providing good corrosion protection, and maintaining the stability of various properties within the well, thereby ensuring the safe and smooth completion operation. Based on the characteristics of the continuous phase, completion fluids can be divided into three main categories: gas-based, oil-based, and water-based completion fluids, with water-based completion fluids being the most widely used.

[0004] Water-based completion fluids can be divided into two categories: solids-free completion fluids and solids-containing completion fluids. Reports on water-based solids-free completion fluids with densities exceeding 2.0 g / cm³ are rare; these mainly consist of bromide salts, formates, and organic salts. Cesium formate, a formate salt, can achieve high densities and has good performance; however, due to its limited mineral resources (the two main mining areas are located overseas, and its high price limits its use), its production costs are prohibitively high. Water-based solids-containing completion fluids have adjustable densities, but the solid phases they contain are either insoluble or poorly soluble in acids. Once they clog reservoir pores and throats, they are difficult to flush out or remove, causing significant damage to the reservoir and severely impacting subsequent oil and gas production. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide an acid-washable high-density completion fluid and its preparation method.

[0006] To achieve the above objectives, the present invention provides an acid-washable high-density completion fluid, comprising, by weight, the following raw materials: 100 parts water, 0.5-1.5 parts high-temperature viscosity enhancer and filtration loss reducer, 0.2-0.6 parts potassium hydroxide, 3-5 parts lignite resin filtration loss reducer, 2-4 parts sulfonated asphalt plugging agent, 0.5-3 parts dispersing viscosity reducer, 5-10 parts potassium formate, 2-3 parts organosilicon filtration loss reducer, 160-400 parts acid-soluble weighting agent, and 5-6 parts inhibitor;

[0007] The raw materials of the acid-soluble weighting agent include: 50-120 parts of barite powder, 40-100 parts of limestone powder, 20-60 parts of iron ore powder, 30-40 parts of weighting agent, 10-40 parts of backflow agent and 10-40 parts of galena powder.

[0008] The raw materials of the backflow agent include: 4-20 parts of surfactant, 3-10 parts of polyaspartic acid, 2-6 parts of sodium tungstate, and 1-4 parts of corrosion inhibitor.

[0009] Liquid phases entering the reservoir in completion fluid can cause water lock, while solid phases can clog reservoir pores and prevent backflow. Additionally, the expansion of reservoir clay particles upon contact with water can also lead to a decrease in reservoir productivity. The acid-washable high-density completion fluid of this invention, through optimized formulation, forms a dense temporary plugging layer near the wellbore to prevent liquids and solids from entering the reservoir. After completion, an acidizing process is used to dissolve the temporary plugging layer near the wellbore, opening reservoir channels, improving reservoir recovery rate, reducing reservoir damage, and increasing single-well productivity.

[0010] The completion fluid system of this invention exhibits excellent high-temperature stability, pressure-bearing temporary plugging reservoir protection, and acid washing and unblocking capabilities. It effectively prevents the sedimentation of high-density weighting agents during completion, promotes the removal of harmful solid and liquid phases after completion, increases reservoir permeability, and improves reservoir production. It also promptly returns drilling and completion fluid lost from the wellbore into the formation, ensuring that the drilling and completion fluid within the formation is removed as completely as possible. The acid-soluble weighting agent of this invention can increase density, seal the formation of a temporary plugging layer, and provide acid washing and returnability.

[0011] The high-density completion fluid of this invention can maintain good settling stability and fluidity under high temperature and high pressure downhole conditions, solving the problems of high-temperature instability and poor fluidity of high-density completion fluid during high temperature and high pressure well completion operations. It creates a favorable working environment for high temperature and high pressure well completion operations in deep oil and gas fields, and can quickly acidize and flow back after completion operations, thereby increasing single-well productivity and creating economic value.

[0012] In the above-mentioned acid-washable high-density completion fluid, preferably, the surfactant is a siloxane surfactant and / or a polyether-modified polysiloxane; the corrosion inhibitor is a biological corrosion inhibitor, which is phytic acid and / or chitosan.

[0013] In the aforementioned acid-washable high-density completion fluid, preferably, the weighting agent is potassium formate and / or sodium sulfite. The weighting agent of this invention does not contain inert weighting materials.

[0014] In the above-mentioned acid-washable high-density completion fluid, preferably, the high-temperature viscosity-enhancing and filtration-reducing agent is 2-acrylamido-2-methylpropanesulfonic acid and / or polyacrylamide.

[0015] In the above-mentioned acid-washable high-density completion fluid, preferably, the sulfonated asphalt plugging agent is sulfonated asphalt plugging agent FT-1.

[0016] In the above-mentioned acid-washable high-density completion fluid, preferably, the dispersing viscosity reducer is a polycarboxylate dispersing viscosity reducer and / or a polycarboxylate amine dispersing agent.

[0017] In the above-mentioned acid-washable high-density completion fluid, preferably, the organosilicon filtration loss reducer is organosilicon asphalt.

[0018] In the above-mentioned acid-washable high-density completion fluid, preferably, the inhibitor is one or a combination of two or more of polyamine, polyol, and hexadecylpyridine chloride.

[0019] The present invention also provides a method for preparing the above-mentioned acid-washable high-density completion fluid, which includes the following steps:

[0020] S1: Dissolve surfactant, polyaspartic acid, sodium tungstate, and bio-corrosion inhibitor in water, adjust the pH and viscosity of the solution to obtain the backflow solution;

[0021] S2: Barite powder, limestone powder, iron ore powder, weighting agent, and galena powder are ground and dispersed in the return liquid to obtain an acid-soluble weighting agent;

[0022] S3: Dissolve the high-temperature viscosity enhancer and filtration loss reducer in water, add potassium hydroxide, lignite resin filtration loss reducer, sulfonated asphalt plugging agent, dispersing viscosity reducer, potassium formate, organosilicon filtration loss reducer and inhibitor, mix evenly, and then add the acid-soluble weighting agent to obtain the acid-washable high-density completion fluid.

[0023] In the above-mentioned method for preparing acid-washable high-density completion fluid, preferably, in step S1, the pH value of the solution is adjusted to 8-10 and the viscosity is 50-100 mPa·s.

[0024] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned acid-washable high-density completion fluid includes the following steps:

[0025] (1) First, prepare an acid-soluble weighting agent. The preparation of the acid-soluble weighting agent includes: weighing a certain amount of surfactant, polyaspartic acid, sodium tungstate and corrosion inhibitor, dissolving the surfactant, polyaspartic acid and the like in an appropriate amount of water to form a uniform solution, then gradually adding sodium tungstate and other additives into the solution and stirring thoroughly to ensure that the components are mixed uniformly, adjusting the pH value, viscosity and other performance parameters of the solution as needed to meet specific formation conditions and operational requirements, filtering the prepared backflow agent through a filter to remove impurities and particles, and forming a backflow agent;

[0026] (2) Weigh a certain amount of barite powder, limestone powder, iron ore powder, weighting agent and galena powder auxiliary material, grind the weighed raw materials to obtain finer particle size and better dispersibility, mix the ground mixture with the flowback agent prepared above, adjust the density, particle size distribution and other performance parameters of the weighting agent as needed, and add appropriate amount of surfactant, dispersant and other auxiliary agents to improve the dispersibility and stability of the weighting agent in the completion fluid, filter the prepared weighting agent through a filter to remove impurities and particles, dry the filtered weighting agent to obtain qualified acid-soluble weighting agent, package the qualified acid-soluble weighting agent into packaging units of appropriate size for storage and transportation, conduct quality testing on the prepared weighting agent to ensure that it meets the relevant standards and requirements, record the key parameters and performance indicators in the preparation process for subsequent quality traceability and improvement;

[0027] (3) Then, take 100 parts of clean water and pour it into a beaker. Under a stirring speed of 6000-8000 r / min, slowly add 0.5-1.5 parts of AMPS additive to the water and stir until completely dissolved. Then, add 0.2-0.6 parts of KOH, 3-5 parts of lignite resin filtration reducer, 2-4 parts of sulfonated asphalt plugging agent FT-1, 0.5-3 parts of polycarboxylate dispersing viscosity reducer, 5-15 parts of potassium formate, 2-3 parts of organosilicon asphalt and stir, and 5-6 parts of inhibitor. Stir while adding each time to ensure that each raw material is evenly dispersed in the liquid until it is evenly mixed and dissolved. Finally, add the prepared acid-soluble weighting agent to the required density to obtain an acid-washable high-density completion fluid system.

[0028] The technical solution provided by this invention has the following beneficial effects:

[0029] (1) The acid-washable high-density completion fluid system of the present invention has good high-temperature stability, effectively preventing the sedimentation of high-density weighting agents during the completion process, and effectively solving the complex downhole problems caused by the sedimentation of weighting agents when high-density completion fluid remains stagnant downhole for a long time during completion operations. The high-temperature stability achieved by the present invention is not only due to the effect of a high-temperature viscosity enhancer and filtration reducer, but also because the asphalt-based and lignite resin-based viscosity reducers added in the present invention are high-temperature resistant components. Only when these materials work together in a certain ratio and compatibility can the expected effect be achieved, and the temperature resistance performance of a single material can be exceeded.

[0030] (2) The acid-washable high-density completion fluid system of the present invention has good acid washing and unblocking capabilities, stabilizes the contact of the completion fluid with formation clay particles, prevents their dispersion and expansion, thereby maintaining the stability and rheological properties of the completion fluid, promotes the flowback of drilling and completion fluid after completion, and promptly returns the drilling and completion fluid lost from the wellbore into the formation, ensuring that the drilling and completion fluid in the formation is discharged as completely as possible, thereby minimizing its obstruction to formation oil production, and eliminating the damage caused by long-term soaking of the formation by the drilling and completion fluid. It effectively solves the problem that the solid phase contained in the currently used high-density completion fluid with solid phase is not acid-soluble or difficult to acid-soluble, and once it forms a blockage, it is difficult to flow back or remove, which causes great damage to the reservoir and seriously affects the later oil and gas production. The acid-soluble weighting agent used in the present invention not only needs to achieve the effect of acid solubility, but also needs to maintain sufficient stability in high-temperature and high-pressure wells, and at the same time, it needs to be removed and flowed back through acid washing and downhole pressure, so as to completely restore production capacity.

[0031] (3) The acid-washable high-density completion fluid system of the present invention has good plugging performance and low filtration loss, effectively solving the problem of reservoir damage and reduced oil and gas production caused by water lock. The organosilicon asphalt, asphalt, lignite resin and weighting agent added in the present invention play a role in plugging, reducing filtration loss and regulating rheology through a limited ratio; currently commonly used completion fluids with a density exceeding 2.4 g / cm³ 3 In such cases, loss of fluidity or poor fluidity, as well as uncontrollable settling instability and water loss, may occur. However, this invention, through optimized formulation, allows the completion fluid to achieve a density of 2.7 g / cm³. 3 It also has good fluidity and high-temperature settling stability.

[0032] (4) The acid-washable high-density completion fluid system of this invention uses a high-temperature resistant polymer to replace bentonite, reducing the irreversible damage to the reservoir caused by the introduction of harmful solids. Currently, high-density completion fluids with solid phases all use bentonite as a thickening and suspending agent. However, bentonite is an active material that can cause irreversible damage to the reservoir. Currently known polymers that can replace bentonite rarely have the ability to withstand temperatures up to 220°C or achieve a completion fluid density of 2.4 g / cm³ without using bentonite. 3 The above.

[0033] (5) The acid-washable high-density completion fluid system of this invention can withstand temperatures up to 220°C, and creatively achieves a maximum completion fluid density of 2.7 g / cm³. 3 It can still maintain good fluidity and thermal settling stability, overcoming the limitations of traditional solid-phase completion fluids using barite weighting agents, where the highest density can only be prepared to 2.4 g / cm³. 3 This addresses the limitations and solves the technical challenges currently faced in drilling and completion operations for high-temperature and high-pressure wells. Currently, very few completion fluids can achieve a density of 2.8 g / cm³. 3 The main issue is that the density of the currently used weighting agent is 4.2 g / cm³. 3 Formulated with a high density exceeding 2.4 g / cm³ 3 This can lead to the completion fluid becoming too thick, or even thickening at high temperatures, losing its fluidity and failing to meet the fluidity requirements for well completion operations. According to a specific embodiment of the present invention, the completion fluid of the present invention is prepared with a density of 2.7 g / cm³. 3 Even at that time, it still has good rheological properties, very low filtration loss, and the ability to withstand high temperatures up to 220℃.

[0034] (6) This invention, through the research and screening of indoor treatment agents, selects high-temperature resistant polymers to replace bentonite, ensuring the stability of the system, reducing HTHP filtration loss, and enhancing the structural strength; by optimizing particle size distribution and combining with sulfonated materials to improve mud cake quality, it effectively prevents water molecules from entering the reservoir and causing reservoir damage; organic salts are used to reduce the activity of the completion fluid and enhance the system's inhibition ability; at the same time, acid-soluble high-density weighting materials and plugging agents are selected to reduce the solid content of the system, constructing a system with a temperature resistance of up to 220℃ and a density of 1.1-2.7 g / cm³. 3 The system is an acid-washable completion fluid system. This system has good high-temperature stability, pressure-bearing temporary plugging reservoir protection and acid washing and unblocking capabilities. It effectively prevents the settling of high-density weighting agents during the completion process and meets the requirements of completion operations. Detailed Implementation

[0035] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0036] Example 1

[0037] This invention provides an acid-washable high-density completion fluid, the preparation method of which is as follows:

[0038] By weight, the raw materials for acid-washable high-density completion fluid include: 100 parts water, 1 part AMPS additive (high-temperature viscosity enhancer and filtration reducer), 0.4 parts KOH, 3 parts lignite resin filtration reducer, 3 parts sulfonated asphalt plugging agent FT-1, 0.5 parts polycarboxylate dispersing viscosity reducer, 5 parts potassium formate, 2 parts organosilicon asphalt, 168 parts acid-soluble weighting agent, and 5 parts inhibitor.

[0039] The raw materials of the acid-soluble weighting agent, by weight, include: 50 parts barite powder, 40 parts limestone powder, 20 parts iron ore powder, 30 parts weighting agent, 10 parts backflow agent, and 10 parts galena powder auxiliary material.

[0040] By weight, the raw materials for the backflow agent include: 4 parts surfactant, 3 parts polyaspartic acid, 2 parts sodium tungstate, and 1 part corrosion inhibitor.

[0041] The preparation method of acid-washable high-density completion fluid is as follows:

[0042] First, an acid-soluble weighting agent is prepared. The preparation of the acid-soluble weighting agent includes: weighing a certain amount of surfactant, polyaspartic acid, sodium tungstate and corrosion inhibitor; dissolving the surfactant, polyaspartic acid, etc. in an appropriate amount of water to form a uniform solution; then, gradually adding sodium tungstate and other additives to the solution and stirring thoroughly to ensure that the components are uniformly mixed; adjusting the pH value, viscosity and other performance parameters of the solution as needed to meet specific formation conditions and operational requirements; filtering the prepared flowback agent through a filter to remove impurities and particles to form the flowback agent.

[0043] Weigh out a certain amount of barite powder, limestone powder, iron ore powder, weighting agent, and galena powder as auxiliary materials. Grind the weighed raw materials to obtain finer particle size and better dispersibility. Mix the ground mixture with the flowback agent prepared above. Adjust the performance parameters of the weighting agent, such as density and particle size distribution, as needed. Appropriate amounts of surfactants, dispersants, and other auxiliary agents can be added to improve the dispersibility and stability of the weighting agent in the completion fluid. Filter the prepared weighting agent through a filter to remove impurities and particles. Dry the filtered weighting agent to obtain qualified acid-soluble weighting agent. Pack the qualified acid-soluble weighting agent into appropriately sized packaging units for storage and transportation. Perform quality testing on the prepared weighting agent to ensure that it meets relevant standards and requirements. Record the key parameters and performance indicators in the preparation process for subsequent quality traceability and improvement.

[0044] Then, take 100 parts of clean water and pour it into a beaker. Slowly add 1 part of AMPS additive to the water while stirring at a speed of 6000-8000 r / min. Stir until completely dissolved. Then, add 0.4 parts of KOH, 3 parts of lignite resin filtration reducer, 3 parts of sulfonated asphalt plugging agent FT-1, 0.5 parts of polycarboxylate dispersing viscosity reducer, 5 parts of potassium formate, 2 parts of organosilicon asphalt, and 5 parts of inhibitor to the beaker in sequence and stir. Stir while adding each ingredient to ensure that each ingredient is evenly dispersed in the liquid until it is evenly mixed. Finally, add 168 parts of the acid-soluble weighting agent prepared above to the required density to obtain an acid-washable high-density completion fluid system.

[0045] Example 2

[0046] This invention provides an acid-washable high-density completion fluid, the preparation method of which is as follows:

[0047] By weight, the raw materials for acid-washable high-density completion fluid include: 100 parts water, 1 part AMPS additive (high-temperature viscosity enhancer and filtration reducer), 0.6 parts KOH, 3 parts lignite resin filtration reducer, 12 parts sulfonated asphalt plugging agent FT-12, 1 part polycarboxylate dispersing viscosity reducer, 10 parts potassium formate, 3 parts organosilicon asphalt, 250 parts acid-soluble weighting agent, and 5 parts inhibitor.

[0048] The raw materials of the acid-soluble weighting agent, by weight, include: 80 parts barite powder, 60 parts limestone powder, 30 parts iron ore powder, 30 parts weighting agent, 20 parts backflow agent, and 30 parts galena powder auxiliary material.

[0049] By weight, the raw materials for the backflow agent include: 6 parts surfactant, 6 parts polymer, 4 parts sodium tungstate, and 2 parts corrosion inhibitor.

[0050] This invention provides a method for preparing the acid-washable high-density completion fluid according to the above-mentioned technical solution, comprising: firstly preparing an acid-soluble weighting agent, wherein the preparation of the acid-soluble weighting agent includes: weighing a certain amount of surfactant, polymer, sodium tungstate and corrosion inhibitor, dissolving the surfactant, polymer, etc. in an appropriate amount of water to form a uniform solution, then gradually adding sodium tungstate and other additives to the solution and stirring thoroughly to ensure that the components are uniformly mixed, adjusting the pH value, viscosity and other performance parameters of the solution as needed to meet specific formation conditions and operational requirements, and filtering the prepared flowback agent through a filter to remove impurities and particles to form a flowback agent;

[0051] Weigh out a certain amount of barite powder, limestone powder, iron ore powder, weighting agent, and galena powder as auxiliary materials. Grind the weighed raw materials to obtain finer particle size and better dispersibility. Mix the ground mixture with the flowback agent prepared above. Adjust the performance parameters of the weighting agent, such as density and particle size distribution, as needed. Appropriate amounts of surfactants, dispersants, and other auxiliary agents can be added to improve the dispersibility and stability of the weighting agent in the completion fluid. Filter the prepared weighting agent through a filter to remove impurities and particles. Dry the filtered weighting agent to obtain qualified acid-soluble weighting agent. Pack the qualified acid-soluble weighting agent into appropriately sized packaging units for storage and transportation. Perform quality testing on the prepared weighting agent to ensure that it meets relevant standards and requirements. Record the key parameters and performance indicators in the preparation process for subsequent quality traceability and improvement.

[0052] Then, 100 parts of clean water were poured into a beaker. Under a stirring speed of 6000-8000 r / min, 1 part of AMPS additive was slowly added to the water and stirred until completely dissolved. Then, 0.6 parts of KOH, 3 parts of lignite resin filtration reducer, 2 parts of sulfonated asphalt plugging agent FT-1, 1 part of polycarboxylate dispersing viscosity reducer, 10 parts of potassium formate, 3 parts of organosilicon asphalt and 5 parts of inhibitor were added to the beaker and stirred. During each addition, stirring was carried out to ensure that each raw material was evenly dispersed in the liquid until it was evenly mixed and dissolved. Finally, 250 parts of the acid-soluble weighting agent prepared above were added to the required density to obtain an acid-washable high-density completion fluid system.

[0053] Example 3

[0054] This invention provides an acid-washable high-density completion fluid, the preparation method of which is as follows:

[0055] By weight, the raw materials for acid-washable high-density completion fluid include: 100 parts water, 0.8 parts AMPS additive (high-temperature viscosity enhancer and filtration reducer), 0.6 parts KOH, 3 parts lignite resin filtration reducer, 12 parts sulfonated asphalt plugging agent FT-12, 1.5 parts polycarboxylate dispersing viscosity reducer, 10 parts potassium formate, 3 parts organosilicon asphalt, 317 parts acid-soluble weighting agent, and 6 parts inhibitor.

[0056] The raw materials of the acid-soluble weighting agent, by weight, include: 100 parts barite powder, 97 parts limestone powder, 30 parts iron ore powder, 30 parts weighting agent, 20 parts backflow agent, and 30 parts galena powder auxiliary material.

[0057] By weight, the raw materials for the backflow agent include: 4 parts surfactant, 8 parts polymer, 5 parts sodium tungstate, and 3 parts corrosion inhibitor.

[0058] The present invention provides a method for preparing an acid-washable high-density completion fluid according to the above-mentioned technical solution: first, an acid-soluble weighting agent is prepared, the preparation of which includes: weighing a certain amount of surfactant, polymer, sodium tungstate and corrosion inhibitor, dissolving the surfactant, polymer, etc. in an appropriate amount of water to form a uniform solution, then gradually adding sodium tungstate and other additives to the solution and stirring thoroughly to ensure uniform mixing of the components, adjusting the pH value, viscosity and other performance parameters of the solution as needed to meet specific formation conditions and operational requirements, and filtering the prepared flowback agent through a filter to remove impurities and particles to form the flowback agent;

[0059] Weigh out a certain amount of barite powder, limestone powder, iron ore powder, weighting agent, and galena powder as auxiliary materials. Grind the weighed raw materials to obtain finer particle size and better dispersibility. Mix the ground mixture with the flowback agent prepared above. Adjust the performance parameters of the weighting agent, such as density and particle size distribution, as needed. Appropriate amounts of surfactants, dispersants, and other auxiliary agents can be added to improve the dispersibility and stability of the weighting agent in the completion fluid. Filter the prepared weighting agent through a filter to remove impurities and particles. Dry the filtered weighting agent to obtain qualified acid-soluble weighting agent. Pack the qualified acid-soluble weighting agent into appropriately sized packaging units for storage and transportation. Perform quality testing on the prepared weighting agent to ensure that it meets relevant standards and requirements. Record the key parameters and performance indicators in the preparation process for subsequent quality traceability and improvement.

[0060] Then, 100 parts of clean water were poured into a beaker. Under a stirring speed of 6000-8000 r / min, 0.8 parts of AMPS additive were slowly added to the water and stirred until completely dissolved. Then, 0.6 parts of KOH, 3 parts of lignite resin filtration reducer, 2 parts of sulfonated asphalt plugging agent FT-1, 1.5 parts of polycarboxylate dispersing viscosity reducer, 10 parts of potassium formate, 3 parts of organosilicon asphalt and 6 parts of inhibitor were added to the beaker in sequence. During each addition, the mixture was stirred to ensure that each raw material was evenly dispersed in the liquid until it was evenly mixed and dissolved. Finally, 317 parts of the acid-soluble weighting agent prepared above were added to the required density to obtain an acid-washable high-density completion fluid system.

[0061] Example 4

[0062] This invention provides an acid-washable high-density completion fluid, the preparation method of which is as follows:

[0063] By weight, the raw materials for acid-washable high-density completion fluid include: 100 parts water, 0.5 parts AMPS additive (high-temperature viscosity enhancer and filtration reducer), 0.6 parts KOH, 3 parts lignite resin filtration reducer, 12 parts sulfonated asphalt plugging agent FT-12 parts, 2 parts polycarboxylate dispersing viscosity reducer, 15 parts potassium formate, 3 parts organosilicon asphalt, 400 parts acid-soluble weighting agent, and 6 parts inhibitor.

[0064] The raw materials of the acid-soluble weighting agent, by weight, include: 120 parts barite powder, 100 parts limestone powder, 60 parts iron ore powder, 40 parts weighting agent, 40 parts backflow agent, and 40 parts galena powder auxiliary material.

[0065] By weight, the raw materials for the backflow agent include: 20 parts surfactant, 10 parts polymer, 6 parts sodium tungstate, and 4 parts corrosion inhibitor.

[0066] The preparation method of acid-washable high-density completion fluid is as follows: First, an acid-soluble weighting agent is prepared. The preparation of the acid-soluble weighting agent includes: weighing a certain amount of surfactant, polymer, sodium tungstate and corrosion inhibitor, dissolving the surfactant, polymer, etc. in an appropriate amount of water to form a uniform solution, then gradually adding sodium tungstate and other additives to the solution and stirring thoroughly to ensure that the components are uniformly mixed, adjusting the pH value, viscosity and other performance parameters of the solution as needed to meet specific formation conditions and operational requirements, and filtering the prepared flowback agent through a filter to remove impurities and particles to form the flowback agent;

[0067] Weigh out a certain amount of barite powder, limestone powder, iron ore powder, weighting agent, and galena powder as auxiliary materials. Grind the weighed raw materials to obtain finer particle size and better dispersibility. Mix the ground mixture with the flowback agent prepared above. Adjust the performance parameters of the weighting agent, such as density and particle size distribution, as needed. Appropriate amounts of surfactants, dispersants, and other auxiliary agents can be added to improve the dispersibility and stability of the weighting agent in the completion fluid. Filter the prepared weighting agent through a filter to remove impurities and particles. Dry the filtered weighting agent to obtain qualified acid-soluble weighting agent. Pack the qualified acid-soluble weighting agent into appropriately sized packaging units for storage and transportation. Perform quality testing on the prepared weighting agent to ensure that it meets relevant standards and requirements. Record the key parameters and performance indicators in the preparation process for subsequent quality traceability and improvement.

[0068] Then, 100 parts of clean water were poured into a beaker. Under a stirring speed of 6000-8000 r / min, 0.5 parts of AMPS additive were slowly added to the water and stirred until completely dissolved. Then, 0.6 parts of KOH, 3 parts of lignite resin filtration reducer, 2 parts of sulfonated asphalt plugging agent FT-1, 2 parts of polycarboxylate dispersing viscosity reducer, 15 parts of potassium formate, 3 parts of organosilicon asphalt and 6 parts of inhibitor were added to the beaker and stirred. During each addition, stirring was carried out to ensure that each raw material was evenly dispersed in the liquid until it was evenly mixed and dissolved. Finally, 400 parts of the acid-soluble weighting agent prepared above were added to the required density to obtain an acid-washable high-density completion fluid system.

[0069] Comparative Example 1

[0070] Select a saturated brine polysulfonate system, which includes the following components in parts by weight: 100 parts water, 2 parts bentonite, 0.1 parts high-temperature resistant sulfonate polymer, 1.0 part potassium hydroxide, 12 parts sulfonating agent, 4 parts sulfonated asphalt, 0.7 parts pH adjuster (potassium carbonate), 7 parts potassium chloride, 22 parts sodium chloride, and barite powder to be added to the required density as needed.

[0071] The preparation method of the above-mentioned saturated brine polysulfonate system is as follows: Pour 100 parts of water into a beaker, slowly add 2 parts of bentonite to the water while stirring at 600 r / min, stir evenly, pre-hydrate and cure for 24 h, then add 1.0 part of KOH, 0.1 parts of high temperature sulfonate polymer, 12 parts of sulfonation treatment agent, 4 parts of sulfonated asphalt, 0.7 parts of pH adjuster (potassium carbonate), 7 parts of potassium chloride, and 22 parts of sodium chloride to the beaker while stirring at 6000-8000 r / min, until mixed evenly, and finally add barite to the required density to obtain the saturated brine polysulfonate system.

[0072] Comparative Example 2

[0073] Select a high-density, high-temperature resistant drilling fluid. The high-density, high-temperature resistant drilling fluid system comprises the following components in parts by weight:

[0074] 100 parts water, 2 parts bentonite, 0.3 parts composite metal ion polymer, 12 parts high temperature stabilizer RZ-1, 1.0 part potassium hydroxide, 4 parts sulfonated phenolic resin, 0.3 parts polymer viscosity reducer XY-27, and modified barite powder to be added to the required density as needed.

[0075] The preparation method of the above-mentioned ultra-high density high-temperature resistant drilling fluid is as follows: Pour 100 parts of clean water into a beaker, slowly add 2 parts of bentonite to the water while stirring at 600 r / min, stir evenly, pre-hydrate and cure for 24 hours, then add 1.0 part of KOH, 0.3 parts of composite metal ion polymer, 2 parts of high-temperature stabilizer, 1.0 part of sulfonated phenolic resin, and 0.3 parts of polymer viscosity reducer XY-27 to the beaker while stirring at 6000-8000 r / min, until mixed evenly, and finally add modified barite to the required density to obtain the ultra-high density high-temperature resistant drilling fluid system.

[0076] Comparative Example 3

[0077] The difference from Example 1 is that the acid-soluble weighting agent is modified hydroxyapatite, while the rest of the composition and preparation method are the same as in Example 1.

[0078] Application Example 1

[0079] The densities of Examples 1-4, Comparative Example 1, and Comparative Example 2 were tested respectively, and the rheological properties and API filtration loss after high-temperature hot rolling are detailed in Table 1 below. The hot rolling temperature was 220℃, and the hot rolling time was 16h.

[0080] Table 1. Results of Conventional Performance Tests of Completion Fluid System

[0081]

[0082] As shown in Table 1 above, the density of the completion fluid provided in Example 1 is 2.0 g / cm³, based on the evaluation test. 3 After hot rolling, the apparent viscosity was 47 mPa·s, the plastic viscosity was 40 mPa·s, the dynamic shear stress was 7 Pa, and the HTHP filtration loss was 9.4 mL. The density of the completion fluid provided in Example 2 was 2.3 g / cm³. 3 After hot rolling, the apparent viscosity was 43.5 mPa·s, the plastic viscosity was 36.5 mPa·s, the dynamic shear stress was 7 Pa, and the HTHP filtration loss was 10 mL. The density of the completion fluid provided in Example 3 was 2.5 g / cm³. 3 After hot rolling, the apparent viscosity was 55 mPa·s, the plastic viscosity was 45 mPa·s, the dynamic shear stress was 10 Pa, and the HTHP filtration loss was 8.7 mL. The density of the completion fluid provided in Example 4 was 2.7 g / cm³. 3 After hot rolling, the apparent viscosity was 71 mPa·s, the plastic viscosity was 60 mPa·s, the dynamic shear stress was 11 Pa, and the HTHP filtration loss was 9.0 mL. The density of the saturated brine polysulfonate completion fluid provided in Comparative Example 1 was 2.3 g / cm³. 3After hot rolling, the apparent viscosity was 79 mPa·s, the plastic viscosity was 64 mPa·s, the dynamic shear force was 15 Pa, and the HTHP filtration loss was 23.2 mL. Comparative Example 2 provided an ultra-high density, high-temperature resistant completion fluid with a density of 2.4 g / cm³. 3 Before hot rolling, the rheological properties of the fluid were measured at room temperature. After hot rolling, the apparent viscosity was 72.5 mPa·s, the plastic viscosity was 56 mPa·s, the dynamic shear stress was 16.5 Pa, and the HTHP filtration loss was 30.4 mL. Comparative Example 3 provided an ultra-high density completion fluid with a density of 2.5 g / cm³. 3 The rheological properties of the acid-washable high-density completion fluids provided in Examples 1-4 were undetectable by a six-speed rotational viscometer before and after hot rolling. By comparison, the parameters of the acid-washable high-density completion fluids provided in Examples 1-4 were superior to those of the completion fluid systems provided in Comparative Examples 1 and 2. Comparative Examples 1, 2, and 3 all exhibited high-temperature instability after hot rolling, with HTHP filtration loss or loss of fluidity failing to meet construction requirements. The density of the acid-washable high-density completion fluid provided in the embodiments of this invention is 2.0-2.7 g / cm³. 3 After hot rolling, the apparent viscosity is 43.5-71 mPa·s, the plastic viscosity is 36.5-60 mPa·s, the dynamic shear force is 7-11 Pa, the AP filtration loss is 2.6-3.8 mL, and the HTHP filtration loss is 8.7-10 mL. The performance difference before and after hot rolling is not significant, indicating that this system can meet the requirements of resisting high temperature of 220℃ and can meet the construction requirements of high temperature and high pressure well completion operations.

[0083] The temperature resistance of the system in Comparative Example 1 cannot reach 220℃, which does not meet the construction requirements of high-temperature and high-pressure wells; Comparative Example 2 uses bentonite and modified barite for weighting, which has high solids content and poor rheological properties, and becomes unstable at 220℃; Comparative Example 3 uses an acid-washable weighting agent, which cannot increase the density to 2.5 g / cm³. 3 Because its density reaches 2.5 g / cm³ 3 At that time, the system had lost its fluidity and could no longer meet the requirements for well completion.

[0084] Application Example 2

[0085] The high-temperature settling stability of the completion fluids prepared in Examples 2 and 4, and Comparative Examples 1 and 2 were tested. The test method was as follows: after each completion fluid sample was left to stand at 220℃ for 3, 7, 10, and 15 days, the bottom was probed with a glass rod, and the experimental phenomena were recorded. The static settling stability of the drilling and completion fluid was evaluated by measuring the density difference between the upper and lower layers: first, the completion fluid was added to a stainless steel container and left to stand statically for a period of time at a specific temperature; then, the density ρ of the upper part of the drilling and completion fluid column (lower free liquid layer) was measured. top and the density ρ at the bottom bottomThe difference in density between the upper and lower layers can be obtained, i.e., the static density difference. The magnitude of static settlement stability is represented by the static settlement factor SF, SF = ρ bottom / (ρ bottom +ρ top The closer the static settlement factor value is to 0.5, the better the settlement stability; conversely, the lower the value, the worse the settlement stability of the completion fluid. Specific parameters for the settlement stability test results are detailed in Table 2 below.

[0086] Table 2. Settlement stability tests of different completion fluids

[0087]

[0088]

[0089] The experimental results show that the completion fluids provided in Examples 1-4, after being left to stand at 220℃ for 15 days, all reached the bottom freely using the drop rod method, with no hard sediment at the bottom. The static sedimentation factor (SF) was less than 0.525, indicating that the completion fluids prepared in Examples 1-4 of this invention can remain non-settling after prolonged high-temperature standing, meeting the requirements for long-term downhole operations. In contrast, the completion fluid in Comparative Example 1, after being left to stand at high temperature for 7 days, did not allow the glass rod to reach the bottom freely, and a large amount of soft sediment appeared at the bottom; the completion fluid in Comparative Example 2, after being left to stand at high temperature for 3 days, also did not allow the glass rod to reach the bottom freely, and a large amount of soft sediment appeared at the bottom; the completion fluid in Comparative Example 3, after being left to stand at high temperature for 3 days, also did not allow the glass rod to reach the bottom freely, and a large amount of soft sediment appeared at the bottom. This indicates that the completion fluids in Comparative Examples 1, 2, and 3 do not meet the requirement of not settling during long-term downhole operations at 220℃.

[0090] Under high temperature and pressure, the molecular activity of chemical materials in high-density completion fluid intensifies, leading to the breakage and degradation of some material molecular chains. Inert solid particles dehydrate and aggregate, causing system instability, sedimentation of high-density materials, and impacting completion operations. This can even bury tools, resulting in economic losses. The high-density completion fluid of this invention has a density as high as 2.7 g / cm³. 3 At that time, no sediment was found at the bottom after standing at high temperature for 15 days, which is superior to the commonly used comparative systems 1, 2 and 3.

[0091] Application Example 3

[0092] The acid solubility of the drilling fluid in Examples 1-4 and Comparative Examples 1-2 was tested separately. Test method: After testing the medium-pressure filtration loss of the drilling fluid, the drilling fluid cake was scraped off and dried to constant weight in a constant temperature oven at 60°C. 10.04g of the dried drilling fluid cake was soaked in 200mL of 15% hydrochloric acid solution and reacted in a constant temperature oven at 60°C for 2 hours. The mixture was then filtered, and the residue was washed with deionized water until the pH of the filtered solution was approximately 7. The filtered residue was dried to constant weight in a constant temperature oven at 60°C, and the mass of the residue and filter paper was recorded as m1. A blank test was performed, measuring the mass of filter paper dried to constant weight in a constant temperature oven at 60°C after filtration with water, and this mass was recorded as m2. The formula for calculating the acid solubility Ra is:

[0093]

[0094] The detailed test results are shown in Table 3 below.

[0095] Table 3 Acid solubility of mud cake for different completion fluids

[0096]

[0097] As shown in Table 3 above, the completion fluid systems provided in Examples 1-4 all have a mud cake acid dissolution rate greater than 94%. During the completion operation, the mud cake and temporary plugging layer formed near the well wall can be quickly dissolved and dispersed by acid, which is conducive to being completely removed from the well wall and flushed out of the bottom of the well, clearing the channel from the reservoir to the wellbore, improving the permeability recovery value of the reservoir, reducing the skin coefficient, and increasing the single well productivity.

[0098] Application Example 4

[0099] Using a dynamic damage assessment device and referring to the petroleum industry standard SY / T 6540-2002, "Indoor Evaluation Method for Damage to Oil Reservoirs by Drilling Fluid and Completion Fluid," the reservoir permeability recovery value was determined for core samples obtained on-site. The maximum breakthrough pressure of the core samples after contamination with different completion fluid systems was also determined as the initial flow pressure. The specific test results are detailed in Table 4 below.

[0100] Table 4. Dynamic Core Damage Evaluation for Different Completion Fluids

[0101]

[0102] As shown in Table 4 above, the permeability recovery values ​​of the acid-washable high-density completion fluids of the present invention in Examples 1-4 are all greater than 90%, and their flowback pressures are all less than 0.15 MPa, which is lower than that of Comparative Examples 1, 2, and 3. The permeability recovery values ​​after 2 hours of unblocking with organic acid all reached over 100%, and the production capacity could be fully restored after acid unblocking with almost no damage to the reservoir, which is better than that of Comparative Examples 1, 2, and 3. This indicates that the acid-washable high-density completion fluid system of the present invention has excellent acid unblocking and self-flowback capabilities, causes little damage to the reservoir, and can be quickly restored and put into production after acid unblocking.

[0103] The permeability recovery value of the high-density acid washing completion fluid of the present invention before acidizing is significantly better than that of the comparative example, and the initial flow pressure is much lower than that of the comparative example, indicating that the completion fluid system of the present invention can self-flow back and improve the permeability recovery value; the permeability after acidizing and unblocking for 2 hours reached 100%, indicating that the temporary plugging layer formed by the high-density completion fluid of the present invention near the well wall can be dissolved by organic acid, opening the reservoir pore throat channel and quickly restoring production capacity.

Claims

1. A washable high-density completion fluid, comprising, by mass parts: 100 parts water, 0.5-1.5 parts high-temperature viscosity improver and filtration loss reducer, 0.2-0.6 parts potassium hydroxide, 3-5 parts lignite resin filtration loss reducer, 2-4 parts sulfonated asphalt plugging agent, 0.5-3 parts dispersing viscosity reducer, 5-10 parts potassium formate, 2-3 parts organosilicon filtration loss reducer, 160-400 parts acid-soluble weighting agent, and 5-6 parts inhibitor; The raw materials of the acid-soluble weighting agent include: 50-120 parts of barite powder, 40-100 parts of limestone powder, 20-60 parts of iron ore powder, 30-40 parts of weighting agent, 10-40 parts of backflow agent and 10-40 parts of galena powder. The raw materials of the backflow agent include: 4-20 parts of surfactant, 3-10 parts of polyaspartic acid, 2-6 parts of sodium tungstate, and 1-4 parts of corrosion inhibitor.

2. The acid-washable high-density completion fluid according to claim 1, wherein, The surfactant is a siloxane surfactant and / or a polyether-modified polysiloxane; the corrosion inhibitor is a biological corrosion inhibitor, which is phytic acid and / or chitosan.

3. The acid-washable high-density completion fluid according to claim 1, wherein, The weighting agent is potassium formate and / or sodium sulfite.

4. The acid-washable high-density completion fluid according to claim 1, wherein, The high-temperature thickening and filtration reduction agent is 2-acrylamido-2-methylpropanesulfonic acid and / or polyacrylamide.

5. The acid-washable high-density completion fluid according to claim 1, wherein, The sulfonated asphalt plugging agent is sulfonated asphalt plugging agent FT-1.

6. The acid-washable high-density completion fluid according to claim 1, wherein, The dispersing and viscosity reducing agent is a polycarboxylate dispersing and viscosity reducing agent and / or a polycarboxylate amine dispersing agent.

7. The acid-washable high-density completion fluid according to claim 1, wherein, The organosilicon filtration loss reducer is organosilicon pitch.

8. The acid-washable high-density completion fluid according to claim 1, wherein, The inhibitor is one or a combination of two or more of polyamines, polyols, and hexadecylpyridine chloride.

9. A method for preparing the acid-washable high-density completion fluid according to any one of claims 1-8, comprising the following steps: S1: Dissolve surfactant, polyaspartic acid, sodium tungstate, and bio-corrosion inhibitor in water, adjust the pH and viscosity of the solution to obtain the backflow solution; S2: Barite powder, limestone powder, iron ore powder, weighting agent, and galena powder are ground and dispersed in the return liquid to obtain an acid-soluble weighting agent; S3: Dissolve the high-temperature viscosity enhancer and filtration loss reducer in water, add potassium hydroxide, lignite resin filtration loss reducer, sulfonated asphalt plugging agent, dispersing viscosity reducer, potassium formate, organosilicon filtration loss reducer and inhibitor, mix evenly, and then add the acid-soluble weighting agent to obtain the acid-washable high-density completion fluid.

10. The method for preparing acid-washable high-density completion fluid according to claim 9, wherein, In S1, the pH of the solution is adjusted to 8-10, and the viscosity is 50-100 mPa·s.

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