CN114058359B - Preparation method and application of degraded gel system for drilling and plugging of deepwater and ultra-deepwater fractured reservoir - Google Patents

Abstract

The invention relates to the technical field of ultra-deep water oil and gas development, and discloses a high-efficiency degradation gel system suitable for drilling plugging in deep water and ultra-deep water fractured reservoirs, as well as its preparation method, composition and application. The invention discloses a high-efficiency degradable gel system for drilling plugging in fractured reservoirs, which is specifically composed of: 100% water, 2.0-3.8% water-soluble polymer, and 0.8-2.2% dynamic covalent borate bond crosslinking agent , stabilizer 0.01-0.05%, hydrophilic fiber 0.07-0.8%; the high-efficiency degradation gel system of the present invention has adjustable gelation time, high gel strength, strong plugging ability, and can effectively prevent fractures during drilling. The gel system also has the advantages of short gel breaking time, low viscosity of residual liquid after gel breaking, and little damage to fractured reservoirs. A high-efficiency degradation gel system suitable for drilling and plugging in fractured reservoirs.

Description

Preparation method and method of degradable gel system for drilling plugging in deepwater and ultra-deepwater fractured reservoirs application

technical field

The invention relates to the technical field of ultra-deep water oil and gas development, in particular to a high-efficiency degradable gel system suitable for drilling and plugging in deep-water and ultra-deep water fractured reservoirs, and an efficient degradable gel for drilling and plugging in deep-water and ultra-deep water fractured reservoirs The preparation method, composition and related application of the system.

Background technique

In recent years, with the increasing demand for oil and gas resources in my country, the contradiction between oil and gas supply and demand has become increasingly prominent. my country's offshore oil and gas resources are very rich, especially in the deep water area of the South my country Sea. The industry refers to waters with a depth of more than 500 meters as deep water, and waters with a depth of more than 1,500 meters as ultra-deep water. In order to ensure the safety of domestic oil and gas supply and the contradiction between supply and demand, in recent years, the exploration and development of oil and gas resources in my country has been steadily moving towards deep water and ultra-deep water oil and gas. However, the investment cost of deepwater and ultra-deepwater oil and gas development is very high, which puts forward higher requirements for efficient, rapid and economical oil and gas development. my country's deepwater and ultra-deepwater oil and gas resources in the South China Sea are very rich, but reservoir fractures are well developed, and leakage and malignant leakage are prone to occur during the drilling process, seriously affecting drilling safety.

A large amount of drilling fluid leakage into the reservoir will cause very serious pollution and damage to the reservoir. During the drilling process, it is necessary to prevent leakage to ensure operational safety and reduce pollution and damage to the reservoir. However, the current existing technology is difficult to Reaching this goal has seriously affected the safety of deepwater and ultra-deepwater operations and the efficiency of oil and gas extraction.

my country's South China Sea is rich in deep-water oil and gas resources, but in some blocks, reservoir fractures are developed, the drilling fluid safe density window is narrow, and the problem of lost circulation is prominent, which may easily cause drilling fluid to enter the formation from the wellbore through the lost channel, which will not only prolong the drilling cycle , Increase drilling costs, affect geological logging, pollute reservoirs, affect production capacity, and seriously cause a series of serious accidents such as blowout, stuck pipe, well collapse, and wellbore scrapping. For fractured leakage, the commonly used plugging method is to use polymer gel system. Polymer gel plugging technology uses polymer gels to cross-link each other to form a viscoelastic body with a three-dimensional cage structure. It has strong deformability and can enter cracks and holes through extrusion deformation without being restricted by leakage channels. Space, staying in the leaky layer position, forming a plugging layer through solidification reaction or volume expansion at the leaky layer position, which has the advantages of low plugging slurry density, adjustable gelation time, and strong plugging slurry filtration capacity. Currently commonly used polymer gel main agents usually contain hydrophilic groups such as amino groups, hydroxyl groups, and carboxyl groups in their structures, such as polyacrylamide and its derivatives, polyvinyl alcohol, and hydroxypropyl guar gum. The types of gel cross-linking agents can be divided into complex cross-linking type and covalent cross-linking type. The complex type cross-linked gel system is mainly based on the complexation of metal ions and gel main agents, such as chromium compounds, boric acid compounds, aluminum salt compounds, titanium salt compounds, etc., covalent cross-linked gel The system is that the functional groups in the polymer react with the cross-linking agent to connect with covalent bonds to form a spatial network structure, such as phenolic resin, urotropine, ethyleneimine, etc. Although the currently commonly used polymer gel plugging system has strong viscoelasticity and deformability, it is difficult to control the cross-linking gelation time, and the plugging material cannot accurately enter the leakage zone, and cannot adapt to the changing downhole environment. , the plugging efficiency is low, and it is easy to cause accidents such as pipe sticking and drilling blockage, especially the current gel system formed by ionic cross-linking and covalent bond cross-linking. The polymer cross-linking structure is stable and difficult to degrade. The pollution and damage of the oil and gas reservoir section are very large, so it is not suitable for the plugging operation of the reservoir section, but mainly used for the plugging of fractured drilling in the non-reservoir section.

Chinese patent CN111961160A discloses a kind of active polymer for polymer gel plugging agent and its preparation method and application. It is prepared by reverse microemulsion polymerization of hydrophobic monomer and acrylamide monomer, and the prepared gel plugging agent has high temperature resistance and strong gelling strength; Chinese patent CN112480887A discloses A temperature-sensitive gel plugging agent based on cellulose, which can change its phase characteristics with the change of the formation temperature field. It is an easy-flowing liquid before being injected into the formation. A solid plugging agent with adhesive and elastic characteristics; Chinese patent CN112250787A discloses a gel particle plugging agent with self-healing properties. The self-healing plugging material has the characteristics of recovery after damage. Inject into formation fractures, and form an integral gel after healing to achieve the purpose of effectively sealing crack pores; Chinese patent CN111732941A discloses a supramolecular gel plugging slurry and its preparation method, the gel plugging components include polymer Diethyl diallyl ammonium chloride, sodium chloride, polypentadienamide, water, the supramolecular gel plugging slurry is mainly used for plugging lost circulation layers during drilling, and has good plugging effect and good rheological properties and other characteristics; Chinese patent CN111117582A discloses a controllable cross-linking gel plugging agent and its preparation method. The controllable cross-linking gel plugging agent has controllable cross-linking time, good fluidity and easy pumping and other advantages, it can be squeezed into the leakage layer under formation temperature and pressure to form a whole immobile gel, thereby improving the bearing strength and plugging effect, and not easy to repeat leakage; Chinese patent CN111410941A discloses a temperature-sensitive gel particle plugging agent, the temperature-sensitive gel particle plugging agent of the present invention can adapt to different crack widths, has the advantages of high temperature resistance, high expansion rate, controllable expansion triggering conditions, and stable polymer after expansion; Chinese patent CN111534292A discloses A semi-interpenetrating network gel plugging material for oil and gas fields and its preparation method, wherein the plugging material interpenetrates or entangles polyvinylpyrrolidone and polyacrylamide polymer cross-linked networks to form a chemical blend network system , has high gel strength and high shear toughness under high temperature conditions, has higher pressure bearing capacity and excellent plugging effect; Chinese patent CN109054785B discloses the preparation method and method of gel plugging slurry for drilling and plugging slurry Slug plugging method, the gel plugging slurry includes water, special gel, bridging material, connecting material and filling material, has short static waiting time, quick effect, and can quickly form a structure at the crack of the lost formation. However, the degradation properties of these different types of gel systems are weak, the degradation efficiency in the reservoir is low, the time is long, and it is easy to cause serious damage to the oil and gas reservoir, so it is not suitable for plugging of fractured oil and gas reservoirs.

Chinese patent CN106928948A discloses a non-crosslinked gel plugging system, including non-crosslinked polymer and water solvent, the non-crosslinked polymer in the non-crosslinked gel plugging system forms a gel through physical crosslinking, which The gel-like gel is not easy to mix with oil, gas and water, has good pumping performance, is easy to enter the fracture and can automatically stop, fully expels formation fluid, and effectively occupies and fills the space of underground leakage fractures and holes; Chinese patent CN102358771A discloses a temperature-resistant, non-crosslinked, degradable gel plugging agent and its preparation method. After dissolving, it forms a structural gel with good shear thinning property, which is a liquid that can be pumped and flowed without Cross-linking, real fluid plugging, easy construction. However, these non-crosslinked gel plugging systems have low strength and weak pressure bearing capacity, making it difficult to plug fractured oil and gas reservoirs.

Protecting oil and gas reservoirs from damage is an important technical measure in the process of petroleum exploration and development. The quality of this work is directly related to whether new oil and gas layers, oil and gas fields and correct evaluation of reserves can be discovered in time, and it is conducive to improving the quality of oil and gas wells. Production and economics of oil and gas field development. Especially in fractured oil and gas reservoirs, how to take into account the leak prevention and plugging of drilling and reservoir protection is a very difficult problem, and there is still no good technical means at present. Therefore, in view of the contradiction between leakage prevention and plugging and reservoir protection in the drilling process of fractured oil and gas reservoirs, it is very urgent to research and develop new high-efficiency degradable gel plugging materials and systems, which is the key to realizing fractured oil and gas storage. Key technologies for layer protection and efficient development.

The purpose of the present invention is to prepare a gel plugging system that can be degraded efficiently. The gel plugging system is mainly composed of water-soluble polymer molecules and a crosslinking agent containing a special structure. The physical and chemical cross-linking occurs through the cross-linking method of dynamic covalent bonds within the range, forming a gel with high strength to achieve the goal of pressure-bearing plugging for fractured reservoirs, preventing leakage and ensuring normal drilling operations. When drilling After the operation, the gel system is very easy to break the bond under the action of the peroxide breaker under the change of the pH value of the external environment, and quickly degrade into small molecular substances and then flow back out to realize the unblocking of reservoir fractures , reduce damage to fractured oil and gas reservoirs, and achieve the goal of both leak prevention and plugging in the drilling process of fractured oil and gas reservoirs and reservoir protection. The technology of this invention fundamentally improves the traditional fractured reservoir leak prevention and plugging technology and method, realizes the goal of both leak prevention and plugging in fractured oil and gas reservoir drilling and reservoir protection, and ensures the high-efficiency exploitation of deep water and ultra-deep water oil and gas .

Contents of the invention

The purpose of the present invention is to overcome the difficulty in satisfying the leak prevention and plugging of fractured oil and gas reservoir drilling and the protection of reservoirs in the prior art, and the technical requirements of deep water and ultra-deep water fractured oil and gas reservoir drilling and exploitation. . A preparation method and application of a high-efficiency degradable gel plugging system suitable for deepwater and ultra-deepwater drilling fluids are provided.

The invention uses a dynamic covalent borate bond cross-linking agent to effectively cross-link water-soluble polymers to form high-strength gels, which can effectively seal fractured reservoirs during drilling operations and prevent leakage , to ensure normal drilling operations; during the use of the prepared high-efficiency degradable gel system, the temperature, pressure and fracture width of deep-water and ultra-deep-water fractured reservoirs can be reasonably optimized. It can effectively plug the fractured reservoir with a fracture width of 0.5mm-3.2mm, and the maximum pressure bearing capacity can reach 7.2MPa; the gel system prepared by the present invention It has a certain pH sensitive characteristic. In the subsequent degradation process, it can degrade faster with the decrease of external pH. After the drilling operation is over, add a strong oxidant gel breaker solution, and the gel system can quickly degrade under weak acidic conditions. Degradation, to achieve unplugging of reservoir fractures, reduce damage to fractured oil and gas reservoirs, and can effectively save operating time, which is very suitable for deep-water and ultra-deep-water drilling with expensive offshore operations; the high-efficiency The preparation method of the degradable gel system is easy to operate on site, can meet the technical requirements of deep water and ultra-deep water drilling, and is suitable for reservoir temperature conditions of 60-110°C. In general, the gel plugging system prepared by the present invention can achieve both leak prevention and plugging and reservoir protection in the drilling process of fractured oil and gas reservoirs, and is a highly degradable and suitable for fractured reservoirs. The new gel plugging system is beneficial to save deep water and ultra-deep water operation time, reduce the damage of deep water and ultra-deep water fractured oil and gas reservoirs, and help to improve the efficient production of deep water and ultra-deep water oil and gas. It is a simple, efficient, reservoir damage A new technology for leak prevention and plugging of small fractured oil and gas reservoirs.

In order to achieve the above object, the present invention has prepared a high-efficiency degradable gel system suitable for drilling plugging in deep-water and ultra-deep-water fractured reservoirs, wherein the high-efficiency degradation gel system is specifically composed of: Water 100%, water-soluble polymer 2.0-3.8%, dynamic covalent borate bond cross-linking agent 0.8-2.2%, stabilizer 0.01-0.05%, hydrophilic fiber 0.07-0.8%.

The dynamic covalent borate bond crosslinking agent described therein has the molecular structure shown in formula (a), wherein R The group can be a kind of in -OH group, methyl group, ethyl group, isopropyl group; Wherein The R2 group may be one of phenyl, ethanolamine, and C8-C14 alkyl.

The specific process of the preparation method of the dynamic covalent borate bond cross-linking agent described therein is: (1) Weigh a certain amount of component I having the molecular structure shown in formula (II) and dissolve it in a certain amount of In hot water, wherein R1 group can be a kind of in H atom, methyl group, ethyl group, isopropyl group; (2) under stirring condition, stirring speed is 200-300 rev/min, gradually in reaction solution Add a certain amount of component II, wherein component II can be a kind of in sodium hydroxide, potassium hydroxide, keep component I: the mass and number ratio of component II and water is 1: (0.58-1.26): (2.80-3.55); (3) Control the reaction temperature, keep the temperature at 85-90°C, and react for 120-150 minutes under stirring to obtain a light-colored transparent solution; (4) The temperature of the reaction solution is naturally cooled to 40-50°C , under stirring conditions of 300-500 rev/min, gradually add a certain amount of component III with molecular structure shown in formula (c), keep component I: the mass and number ratio of component III is 1: (1.53- 3.10); (5) Heating to control the temperature of the reaction solution at 95-98 ° C, and gradually reducing the stirring speed to 50-100 rpm, and the reaction ends after 180-300 minutes, that is, the dynamic covalent borate bonded joint agent.

Wherein the water-soluble polymer is a water-soluble polymer containing branched chains such as hydroxyl groups, which can be one or a combination of polyvinyl alcohol, hydroxypropyl guar gum, xanthan gum, and hydroxyethyl cellulose , wherein the degree of polymerization of polyvinyl alcohol is 1700-1800, the number average molecular weight is 80,000-120,000, the relative molecular weight of xanthan gum is 1.2-2.5 million, the molar substitution degree of hydroxyethyl cellulose is 1.8-1.9, the viscosity ( 1% solution, 20°C) is 15000-18000mPa.S.

Wherein the stabilizer is one or a combination of thiourea, sodium sulfite, sodium bisulfite, acetaldehyde oxime and sodium erythorbate.

Wherein the hydrophilic fiber is one or a combination of sepiolite fiber, lignin fiber and polyvinyl alcohol fiber, and the fiber length is 2-4mm; wherein the water can be fresh water, on-site water or seawater.

The specific process of the preparation method of the high-efficiency degradable gel system for drilling plugging in deep-water and ultra-deep-water fractured reservoirs is as follows: Weigh a certain amount of fresh water, on-site water or seawater, and add stabilizer, Hydrophilic fibers and water-soluble polymers; after the polymers are fully dissolved, add a proportional dynamic covalent borate bond crosslinking agent under stirring; then heat up to the set temperature, the polymer molecules and dynamic covalent boron The ester bond cross-linking agent continuously undergoes cross-linking reaction to prepare a high-efficiency degradation gel system.

The high-efficiency degradable gel system for drilling plugging in deep water and ultra-deep water fractured reservoirs of the present invention has the advantages of adjustable gel forming time, strong pressure bearing capacity of the gel, high plugging strength, and strong anti-pollution ability such as on-site drilling fluid. It can be applied to oil and gas reservoir temperatures of 60-110°C, and has efficient pressure-bearing plugging capabilities, high-efficiency degradation and better reservoir protection effects.

During the use of the high-efficiency degradable gel system for drilling plugging in deep water and ultra-deep water fractured reservoirs of the present invention, the component content of the gel system can be rationally optimized according to the temperature, pressure and fracture width of the fractured reservoir to realize Pressure-bearing plugging function of fractured oil and gas reservoirs.

Another object of the present invention is to provide the preparation method and application of the above-mentioned high-efficiency degradation gel system for drilling plugging in deep-water and ultra-deep-water fractured reservoirs. The preparation method is simple to operate and can meet the technical requirements of deep-water and ultra-deep-water drilling.

Through above-mentioned technical scheme, the advantage of the present invention is:

(1) Through a dynamic covalent borate bond cross-linking agent, the water-soluble polymer can be effectively cross-linked to form a high-strength gel, and a high-efficiency degradation gel suitable for 60-110 ° C is prepared The strength of the gel system is high, which can effectively seal the fractured reservoir during drilling operations, prevent leakage, and ensure normal drilling operations. After the drilling operation is over, the gel system has strong degradation ability and can quickly Degraded into small molecular substances and discharged back to achieve unplugging in reservoir fractures, reduce damage to fractured oil and gas reservoirs, and achieve the goal of leak prevention and plugging and reservoir protection during the drilling process of fractured oil and gas reservoirs , is a new gel plugging system suitable for fractured reservoirs that can be degraded efficiently.

(2) The high-efficiency degradation gel system prepared by the present invention has certain pH-sensitive characteristics. During the subsequent degradation process, it can degrade faster as the external pH decreases, which will help reduce the damage to the reservoir. Very helpful in maintaining reservoir connectivity.

(3) During the use of the high-efficiency degradation gel system prepared by the present invention, the temperature, pressure, and fracture width of deep-water and ultra-deep-water fractured reservoirs can be reasonably optimized to optimize the component content of the gel system to realize the reduction of fractured oil and gas. Pressure-bearing plugging of reservoirs to prevent vicious drilling loss.

(4) The high-efficiency degradable gel system prepared by the present invention can effectively plug fractured reservoirs with a fracture width of 0.5mm-3.2mm, and the maximum pressure bearing capacity can reach 7.2MPa.

(5) The high-efficiency degradable gel system involved in the present invention has fast degradation speed and high degradation efficiency, can effectively save working time, and is very suitable for deep-water and ultra-deep-water drilling where offshore operation costs are expensive.

(6) The preparation method of the high-efficiency degradable gel system involved in the present invention is easy to operate on site and can meet the technical requirements of deep water and ultra-deep water drilling.

detailed description

The present invention will be described in detail below by way of examples.

In the following examples and comparative examples:

The gel plugging system prepared according to the standard GB/T 16783.1-2014 "Drilling Fluid Field Test Part 1 Water-based Drilling Fluid", and the gel plugging system was tested with reference to the standard GB/T 29170-2012 "Oil and Natural Gas Industry Drilling Fluid Laboratory Test". The performance of glue plugging system.

"Parts" described in Examples and Test Examples are all "parts by mass".

The raw materials used in the examples and comparative examples are conventional commercially available products, and are products well known to those skilled in the art.

Example 1

This example is to illustrate the dynamic covalent borate bond crosslinking agent prepared by the method of the present invention.

Weigh 100 parts by weight of component I having a molecular structure shown in formula (II) and dissolve it in 292 parts by weight of hot water at 65°C, wherein the R1 group is a methyl group; (2) under stirring conditions , the stirring speed is 200 rpm, gradually add 87 parts by weight of component II potassium hydroxide to the reaction solution; (3) control the reaction temperature, keep the temperature at 90°C, and react for 120 minutes under stirring to obtain a light-colored transparent solution; (4) when the temperature of the reaction solution is naturally cooled to 40°C, under 300 rev/min stirring conditions, gradually add 210 parts by weight of component III with the molecular structure shown in formula (c), wherein the R2 group is Ethanolamine group; (5) Heating to control the temperature of the reaction solution at 95-98° C., and gradually reducing the stirring speed to 60-rpm, and the reaction ends after 240 minutes. As a result, a dynamic covalent borate bond crosslinker was prepared, labeled as S1.

Example 2

This example is to illustrate the high-efficiency degradation gel system for drilling and plugging in deep-water and ultra-deep-water fractured reservoirs prepared by the method of the present invention.

Take 100 parts by weight of indoor fresh water according to the weight ratio, and add 0.03 parts by weight of stabilizer sodium sulfite, 0.3 parts by weight of sepiolite fiber (fiber length 3mm), and 3.2 parts by weight of polyvinyl alcohol under stirring conditions at room temperature. (the number average molecular weight is 100,000); after the polymer is fully dissolved, 1.75 parts by weight of dynamic covalent borate bond cross-linking agent S1 is added under stirring, and then the temperature is raised to a certain temperature to prepare a high-efficiency degradation gel system.

Results The high-efficiency degradation gel system prepared was marked as S2.

Example 3

This example is to illustrate the high-efficiency degradation gel system for drilling and plugging in deep-water and ultra-deep-water fractured reservoirs prepared by the method of the present invention.

Take by weighing 100 parts by weight of indoor fresh water according to the weight ratio, add 0.03 parts by weight of stabilizer sodium sulfite, 0.6 parts by weight of lignin fiber (fiber length 4mm), 3.5 parts by weight of polyvinyl alcohol ( The number average molecular weight is 120,000); after the polymer is fully dissolved, 2.0 parts by weight of dynamic covalent borate bond cross-linking agent S1 is added under stirring; then the temperature is raised to a certain temperature to prepare a high-efficiency degradation gel system.

Results The high-efficiency degradation gel system prepared was marked as S3.

Example 4

This example is to illustrate the high-efficiency degradation gel system for drilling and plugging in deep-water and ultra-deep-water fractured reservoirs prepared by the method of the present invention.

Take 100 parts by weight of indoor fresh water according to the weight ratio, and add 0.04 parts by weight of thiourea stabilizer, 0.3 parts by weight of lignin fiber (fiber length 4mm) and sea foam of 0.2 parts by weight under stirring at room temperature The mixed water-soluble polymer of stone fiber (fiber length 3mm) mixed fiber, 2.3 weight parts polyvinyl alcohol (number average molecular weight is 120,000) and 0.6 weight part xanthan gum (number average molecular weight is 2,000,000); After dissolving, 1.83 parts by weight of dynamic covalent borate bond cross-linking agent S1 was added under stirring; then the temperature was raised to a certain temperature to prepare a high-efficiency degradation gel system.

Results The high-efficiency degradation gel system prepared was marked as S4.

Example 5

This example is to illustrate the high-efficiency degradation gel system for drilling and plugging in deep-water and ultra-deep-water fractured reservoirs prepared by the method of the present invention.

Take 100 parts by weight of indoor fresh water according to the weight ratio, and add 0.04 parts by weight of thiourea stabilizer, 0.3 parts by weight of lignin fiber (fiber length 4mm) and sea foam of 0.2 parts by weight under stirring at room temperature Mixed water-soluble polymer of stone fiber (fiber length 3mm) mixed fiber, 2.0 parts by weight of hydroxyethyl cellulose (viscosity is 16000mPa.S) and 0.5 part by weight of xanthan gum (number average molecular weight is 2,000,000); After fully dissolving, add 1.92 parts by weight of dynamic covalent borate bond cross-linking agent S1 under stirring; then raise the temperature to a certain temperature to prepare a high-efficiency degradation gel system.

Results The high-efficiency degradation gel system prepared was marked as S5.

Example 6

This example is to illustrate the high-efficiency degradation gel system for drilling and plugging in deep-water and ultra-deep-water fractured reservoirs prepared by the method of the present invention.

Take 100 parts by weight of indoor fresh water according to the weight ratio, and add 0.04 parts by weight of thiourea stabilizer, 0.3 parts by weight of lignin fiber (fiber length 4mm) and sea foam of 0.2 parts by weight under stirring at room temperature Mixed water-soluble polymer of stone fiber (fiber length 3mm) mixed fiber, 2.3 parts by weight of hydroxyethyl cellulose (viscosity is 18000mPa.S) and 0.5 part by weight of xanthan gum (number average molecular weight is 2.2 million); After fully dissolving, add 0.92 parts by weight of dynamic covalent borate bond cross-linking agent S1 under stirring; then raise the temperature to a certain temperature to prepare a high-efficiency degradation gel system.

Results The high-efficiency degradation gel system prepared was marked as S6.

Comparative example 1

The gel system was prepared according to the same method as in Example 2, except that the dynamic covalent borate bond cross-linking agent S1 prepared by the method of the present invention was replaced by an organic chromium cross-linking agent commonly used in the field.

Take 100 parts by weight of indoor fresh water according to the weight ratio, and add 0.03 parts by weight of stabilizer sodium sulfite, 0.3 parts by weight of sepiolite fiber (fiber length 3mm), and 3.2 parts by weight of polyvinyl alcohol under stirring conditions at room temperature. (the number average molecular weight is 100,000); after the polymer is fully dissolved, 1.75 parts by weight of an organic chromium crosslinking agent is added under stirring; then the temperature is raised to a certain temperature to prepare a gel plugging system.

Results The gel plugging system prepared was marked as DS1.

Comparative example 2

The gel system was prepared according to the same method as in Example 2, except that the dynamic covalent borate bond cross-linking agent S1 prepared by the method of the present invention was replaced by an organoboron cross-linking agent commonly used in the field.

Take 100 parts by weight of indoor fresh water according to the weight ratio, and add 0.03 parts by weight of stabilizer sodium sulfite, 0.3 parts by weight of sepiolite fiber (fiber length 3mm), and 3.2 parts by weight of polyvinyl alcohol under stirring conditions at room temperature. (the number average molecular weight is 100,000); after the polymer is fully dissolved, 1.75 parts by weight of an organic crosslinking agent is added under stirring; then the temperature is raised to a certain temperature to prepare a gel plugging system.

Results The gel plugging system prepared was marked as DS2.

Comparative example 3

The gel system was prepared according to the same method as in Example 2, except that the dynamic covalent borate bond cross-linking agent S1 prepared by the method of the present invention was replaced by an organic chromium cross-linking agent commonly used in the field.

Take 100 parts by weight of indoor fresh water according to the weight ratio, and add 0.03 parts by weight of stabilizer sodium sulfite, 0.3 parts by weight of sepiolite fiber (fiber length 3mm), and 3.2 parts by weight of polyvinyl alcohol under stirring conditions at room temperature. (the number-average molecular weight is 100,000); after the polymer is fully dissolved, add a mixed cross-linking agent of 1.0 parts by weight of an organic chromium cross-linking agent and 0.75 parts by weight of an organic boron cross-linking agent; then heat up to a certain temperature to prepare A gel plugging system is obtained.

Results The gel plugging system prepared was marked as DS3.

test case 1

The GSC (Gel Strength Codes) visual code method of Sydansk was used to measure the gelation time of the gel, that is, the gelation time of the polymer gel was determined by observing the gel to grade D. The gelation times of the gel systems prepared in different examples and comparative examples tested are shown in Table 1.

Table 1

According to the experimental results in Table 1, it can be seen that the gelation time of the gel system prepared in the examples of the present invention is between 65-108 minutes at different temperatures, and the gelation time of the gel system prepared in the comparative example at 80° C. Gel time was between 63-72 minutes. Comparing the gelation time of the gel systems prepared respectively in the comparative examples and comparative examples at 80°C, it shows that the dynamic covalent borate ester bonding agent can properly Delaying the cross-linking reaction rate is beneficial to smoothly pump the gel to the target layer for plugging during the drilling and plugging operation. When the target layer is reached, further cross-linking reaction is performed to generate high-strength gel to achieve the purpose of plugging.

test case 2

The plugging evaluation device was used to test the plugging ability of the gel systems prepared in different examples and comparative examples, and the results are shown in Table 2.

Table 2 Group No temperature/℃ Crack width/mm Pressurization time/min Maximum bearing pressure/MPa gel plugging effect S2 80 1.5 13 6.2 (Breakthrough) Pressure 6.2MPa S3 85 1.5 19 7.5 successful blocking S4 60 1.5 15 7.2 (Breakthrough) Pressure 7.2MPa S5 95 1.5 20 7.5 successful blocking S6 95 1.5 15 7.2 successful blocking DS1 80 1.5 17 5.3 (Breakthrough) Pressure 5.3MPa DS2 80 1.5 twenty one 5.0 (breakthrough) Pressure 5.0MPa DS3 90 1.5 25 5.5 (breakthrough) Pressure 5.5MPa

According to the experimental results in Table 2, it can be seen that the plugging and pressure bearing capacity of the gel system prepared in the examples of the present invention is between 6.2-7.2 MPa at different temperatures, and the gel system prepared in the comparative example is at 80°C. The lower plugging pressure bearing capacity is between 5.0-5.5MPa. It shows that compared with traditional organic chromium and organic boron cross-linking agents, dynamic covalent borate-bonding agents are more favorable for gel cross-linking to form a network structure to generate a higher-strength gel system.

Test case 3

The plugging evaluation device was used to test the plugging ability and effect of the gel system prepared in the example on different widths of cracks under different temperature conditions, and the results are shown in Table 3.

table 3

According to the experimental results in Table 3, it can be seen that the gel system prepared in the examples of the present invention can effectively seal cracks with a width of 3.5mm at 65°C-110°C, and the pressure bearing capacity can reach 5.8MPa or above, showing better crack sealing ability.

Test case 4

After the gel systems prepared in Examples and Comparative Examples were aged and maintained at different temperatures for 72 hours, they were fully cross-linked to form a high-strength gel, and then a certain concentration of 8.0% strong oxidant potassium persulfate was added to the gel system. solution, and a small amount of dilute hydrochloric acid was added dropwise to adjust the pH value of the solution. The gel breaking time and residual liquid viscosity after gel breaking were tested for different gel systems at different temperatures and pH values. The results are shown in Table 4.

Table 4 Group No temperature/℃ Solution pH Gel breaking time/h Residue viscosity/mPa.S S2 80 4.0 6.5 27 S2 80 5.0 8.0 30 S2 85 6.0 9.0 38 S2 60 4.0 7.0 29 S5 60 4.0 7.3 33 S5 90 4.0 6.2 35 S5 110 5.0 6.7 26 DS1 80 4.0 12.0 186 DS1 80 5.0 12.0 195 DS1 80 6.0 12.3 212

According to the experimental results in Table 4, it can be seen that the gel breaking time of the gel system prepared in the embodiment of the present invention is shorter than that of the comparative example under different temperature conditions, and the viscosity of the raffinate after the gel breaking is significantly higher than that of the comparative example. The raffinate viscosity after is low, and this illustrates that the gel system of the present invention has higher gel breaking speed and efficiency; And the efficiency will be further accelerated, showing better pH sensitivity, which shows that the gel system formed by the dynamic covalent borate bond cross-linking agent can achieve efficient degradation under weak acidic conditions and reduce the impact on cracks. The damage of oil and gas reservoirs realizes the reservoir protection in the process of plugging of fractured oil and gas reservoirs.

Test case 5

In order to test the protection effect of the gel system, see Table 6-9 for the experimental results.

The gel system prepared in Examples and Comparative Examples was firstly tested for plugging fractured cores, and then the plugged cores were soaked in a strong oxidant potassium persulfate solution with a concentration of 8.0%, and a small amount of dilute hydrochloric acid was added dropwise to adjust the solution The pH value was 4, and it was taken out after soaking for a certain period of time. The recovery of the core permeability was measured by nitrogen reverse displacement on the core flow device. The results are shown in Table 5.

table 5

According to the experimental results in Table 5, it can be seen that the gel system prepared by the examples of the present invention has a higher permeability recovery rate than the gel system prepared by the comparative example, indicating that the gel system prepared by the examples of the present invention has a higher Good reservoir protection effect.

The preferred embodiments of the present invention have been described in detail above, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the disclosed content of the present invention. All belong to the protection scope of the present invention.

Claims (3)

1. A degradable gel system suitable for drilling plugging in deep water and ultra-deep water fractured reservoirs, characterized in that, the degradable gel system, in parts by weight, is specifically composed of: 100 parts of water, water-soluble polymer 2.0-3.8 parts of compound, 0.8-2.2 parts of dynamic covalent borate bond cross-linking agent, 0.01-0.05 parts of stabilizer, 0.07-0.8 parts of hydrophilic fiber; The dynamic covalent borate bond crosslinking agent described therein has the molecular structure shown in formula (a), wherein R The group can be a kind of in -OH group, methyl group, ethyl group, isopropyl group; Wherein The R2 group can be one of phenyl, ethanolamine, and carbon atom C8-C14 alkyl;

The specific process of the preparation method of the dynamic covalent borate bond cross-linking agent described therein is: (1) weigh a certain amount of component I having the molecular structure shown in formula (b) and dissolve it in a certain amount of In hot water, wherein the R1 group can be a kind of in -OH group, methyl group, ethyl group, isopropyl group; (2) under stirring condition, stirring speed is 200-300 rev/min, gradually to reaction Add a certain amount of component II to the liquid, wherein component II can be one of sodium hydroxide and potassium hydroxide, and keep the ratio of component I:component II and water to be 1:(0.58～1.26 ): (2.80～3.55); (3) control reaction temperature, keep temperature at 85～90 ℃, react under stirring for 120～150 minutes, obtain light-colored transparent solution; At 50 DEG C, under 300-500 rev/min stirring conditions, gradually add a certain amount of component III with molecular structure shown in formula (c), keep component I: the mass and number ratio of component III is 1:( 1.53～3.10); (5) Heating to control the temperature of the reaction solution at 95～98°C, and gradually reducing the stirring speed to 50-100 rpm, and the reaction ends after 180～300 minutes, and the dynamic covalent borate is prepared bond cross-linking agent; Wherein the stabilizer is one or a combination of thiourea, sodium sulfite, sodium bisulfite, acetaldehyde oxime, and sodium erythorbate; Wherein said hydrophilic fiber is one or a combination of sepiolite fiber, lignin fiber and polyvinyl alcohol fiber, and the fiber length is 2-4mm. 2. According to the requirement of claim 1, the described a kind of degradable gel system suitable for deep water and ultra-deep water fractured reservoir drilling plugging is characterized in that the water-soluble polymer is a water-soluble polymer containing branched chains such as hydroxyl High molecular polymer, which can be one or a combination of polyvinyl alcohol, hydroxypropyl guar gum, xanthan gum, and hydroxyethyl cellulose, wherein the degree of polymerization of polyvinyl alcohol is 1700-1800, and the number average molecular weight is 80,000-120,000, the relative molecular weight of xanthan gum is 1.2-2.5 million, the molar substitution degree of hydroxyethyl cellulose is 1.8-1.9, and the viscosity of 1% solution at 20°C is 15,000-18,000 mPa.s. 3. According to claim 1, the degradable gel system suitable for drilling plugging in deep water and ultra-deep water fractured reservoirs is characterized in that the water can be fresh water, on-site water or sea water.