CN114058359A - Preparation method and application of efficient degradation gel system for drilling and plugging deep-water and ultra-deep-water fractured reservoir - Google Patents
Preparation method and application of efficient degradation gel system for drilling and plugging deep-water and ultra-deep-water fractured reservoir Download PDFInfo
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- C09K8/62—Compositions for forming crevices or fractures
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Abstract
The invention relates to the technical field of ultra-deep water oil and gas development, and discloses an efficient degradation gel system suitable for drilling and plugging of deep water and ultra-deep water fractured reservoirs, a preparation method, a composition and an application thereof. The invention discloses an efficient degradation gel system for plugging a fractured reservoir well, which comprises the following specific components: 100 percent of water, 2.0 to 3.8 percent of water-soluble polymer, 0.8 to 2.2 percent of dynamic covalent boric acid ester bond crosslinking agent, 0.01 to 0.05 percent of stabilizer and 0.07 to 0.8 percent of hydrophilic fiber; the efficient degradation gel system has the advantages of adjustable gel forming time, high gel strength, strong plugging capability and capability of effectively preventing fractured leakage in the drilling process, has the advantages of short gel breaking time, low viscosity of residual liquid after gel breaking and small damage to fractured reservoirs, realizes the reservoir protection target in the drilling leakage prevention and plugging process of the fractured reservoirs, and is the efficient degradation gel system suitable for the drilling and plugging of the fractured reservoirs.
Description
Technical Field
The invention relates to the technical field of ultra-deep water oil and gas development, in particular to a preparation method, composition and related application of an efficient degradation gel system suitable for deep water and ultra-deep water fractured reservoir drilling plugging.
Background
In recent years, with the increase of the demand of oil and gas resources in China, the contradiction between oil and gas supply and demand is increasingly prominent. China is rich in ocean oil and gas resources, particularly rich oil and gas resources are stored in the deep water field of south China sea, and deep sea areas with water more than 500 meters are called deep water in the industry, and deep water with water more than 1500 meters is called ultra-deep water. In order to guarantee the contradiction between the supply safety and supply demand of domestic oil and gas, the exploration and development of oil and gas resources in China are steadily moving towards the direction of oil and gas in deep water and ultra-deep water in recent years. However, the investment cost of deep water and ultra-deep water oil and gas development is very high, and higher requirements are put forward on efficient, rapid and economic exploitation of oil and gas. The oil gas resources in deep water and ultra-deep water in south China sea are very rich, but reservoir cracks develop, leakage, malignant leakage and the like are easy to occur in the drilling process, and the safe drilling is seriously influenced.
A large amount of drilling fluid leaks into a reservoir stratum, so that very serious pollution and damage are caused to the reservoir stratum, leakage is prevented in the drilling process, operation safety is guaranteed, pollution and damage to the reservoir stratum are reduced, the existing prior art cannot achieve the aim, and the deepwater and ultra-deepwater operation safety and oil and gas exploitation efficiency are seriously influenced.
The deep water oil gas resources in south China sea are rich, but in some blocks, reservoir fractures develop, the safe density window of drilling fluid is narrow, the problem of well leakage is prominent, the drilling fluid is easy to enter the stratum from a borehole through a leakage channel, the drilling period is prolonged, the drilling cost is increased, geological logging is influenced, the reservoir is polluted, the productivity is influenced, and a series of severe accidents such as blowout, stuck drilling, well collapse, borehole abandonment and the like are seriously caused. For fracture leakage, a common method of plugging is to use a polymer gel system. The polymer gel plugging technology is a viscous elastomer with a three-dimensional cage-shaped structure formed by cross-linking polymer gels, has strong deformability, can be not limited by a leakage channel, enters cracks and hole spaces through extrusion deformation, is retained at a leakage layer position, and forms a plugging layer through a curing reaction or a bulk expansion action at the leakage layer position. The main agent of the polymer gel commonly used at present generally contains hydrophilic groups such as amino, hydroxyl, carboxyl and the like in the structure, such as polyacrylamide and derivatives thereof, polyvinyl alcohol, hydroxypropyl guar gum and the like. The types of the gel crosslinking agent can be classified into a complex crosslinking type and a covalent crosslinking type. The complex crosslinked 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 and the like, and the covalent crosslinked gel system is formed by the reaction of functional groups in polymers and crosslinking agents and the covalent bond connection, so that a spatial network structure is formed, such as phenolic resin, urotropine, ethylene imine and the like. Although the conventional polymer gel plugging system has high viscoelasticity and deformability, the cross-linking gelling time is difficult to control, a plugging material cannot accurately enter a leaking layer position and cannot adapt to a continuously changing underground environment, the plugging efficiency is low, accidents such as drill sticking, drilling hole plugging and the like are easily caused, particularly, the conventional gel system formed by ionic cross-linking and covalent cross-linking has a stable polymer cross-linking structure and is difficult to degrade, has great pollution and damage to an oil and gas storage layer section, is not suitable for plugging operation of the storage layer section, and is mainly used for non-storage layer section fractured drilling plugging.
Chinese patent CN111961160A discloses an active polymer for a macromolecular gel plugging agent, a preparation method and application thereof, wherein the active polymer is prepared by polymerizing a hydrophobic monomer and an acrylamide monomer through reverse microemulsion in the presence of a functional cross-linking agent, a chain extender, an initiator and ethylenediamine tetraacetic acid, and the prepared gel plugging agent has higher temperature resistance and stronger gel forming strength; chinese patent CN112480887A discloses a temperature-sensitive gel plugging agent based on cellulose, which can change the phase characteristics of the gel along with the change of the temperature field of the stratum, is a liquid which is easy to flow before being injected into the stratum, and is converted into a solid plugging agent with strong adhesiveness and elastic characteristics after being injected into the stratum through crosslinking; chinese patent CN112250787A discloses a gel particle plugging agent with self-healing property, the self-healing plugging material has the characteristic of being recoverable after being damaged, and is injected into a stratum fracture in a particle form, and the whole gel can be formed after healing, so that the aim of effectively plugging the pore of the fracture is fulfilled; chinese patent CN111732941A discloses a supramolecular gel leakage-stopping slurry and a preparation method thereof, wherein the gel leakage-stopping component comprises poly diethyl diallyl ammonium chloride, sodium chloride, polypentadienamide and water, and the supramolecular gel leakage-stopping slurry is mainly used for stopping a leakage layer during drilling and has the characteristics of good leakage-stopping effect, good rheological property and the like; chinese patent CN111117582A discloses a controllable cross-linking type gel plugging agent and a preparation method thereof, the controllable cross-linking type gel plugging agent has the advantages of controllable cross-linking time, good fluidity, easy pumping and the like, and can be extruded into a leaking layer to form an integral immobile gel under the temperature and pressure of a stratum, thereby improving the bearing strength and the plugging effect and being not easy to lose repeatedly; chinese patent CN111410941A discloses a temperature-sensitive gel particle plugging agent suitable for fractured leakage formation, which can adapt to different fracture widths and has the advantages of high temperature resistance, high expansion rate, controllable expansion initiation conditions and stable expanded polymer; chinese patent CN111534292A discloses a semi-interpenetrating network gel plugging material for oil and gas fields and a preparation method thereof, wherein the plugging material forms a chemical blending network system after mutually penetrating or intertwining through a polyvinylpyrrolidone and a polyacrylamide polymer cross-linked network, has high gelling strength and high shear toughness under the condition of high temperature, and has higher pressure-bearing capacity and excellent plugging effect; chinese patent CN109054785B discloses gel plugging slurry for well drilling, a preparation method of the plugging slurry and a slug plugging method, the gel plugging slurry comprises water, special gel, bridging material, connecting material and filling material, has short static coagulation waiting time and quick response, and can quickly form a structure at a crack of a leakage stratum. However, these different types of gel systems have weak degradation performance, low degradation efficiency in reservoirs, long time, and are prone to severe damage to oil and gas reservoirs, and are not suitable for plugging fractured oil and gas reservoirs.
Chinese patent CN106928948A discloses a non-crosslinked gel plugging system, which comprises a non-crosslinked polymer and a water solvent, wherein the non-crosslinked polymer in the non-crosslinked gel plugging system forms gel through physical crosslinking, and the gel is not easy to mix with oil, gas and water, has better pumping performance, is easy to enter cracks and can automatically stop, fully drains and drives formation fluid, and effectively occupies and fills the space of underground leaking seams and holes; chinese patent CN102358771A discloses a temperature-resistant, non-crosslinking and degradable gel plugging agent and a preparation method thereof, a structural gel with good shearing and diluting properties is formed after dissolution, the gel is a liquid which can be pumped and flows, crosslinking is not needed, the real fluid plugging is realized, and the construction is convenient. However, the non-crosslinked gel plugging systems have low strength and weak pressure bearing capacity, and are difficult to plug fractured oil and gas reservoirs.
The protection of oil and gas reservoirs from being damaged is an important technical measure in the process of oil exploration and development, the quality of the work is directly related to whether new oil and gas reservoirs and oil and gas fields can be found in time and the right evaluation of reserves is carried out, and the improvement of the yield of the oil and gas wells and the economic benefit of the oil and gas field development is facilitated. Particularly, how to consider leakage prevention and plugging of a drilling well and reservoir protection of a fractured oil and gas reservoir is a very difficult problem, and a better technical means is not provided at present. Therefore, aiming at the contradiction that the leakage prevention and the reservoir protection are difficult to be blended and consistent in the current drilling process of the fractured oil and gas reservoir, the research and development of novel efficient degradation gel plugging materials and systems are very urgent, and the method is a key technology for realizing the protection and the efficient development of the fractured oil and gas reservoir.
The invention aims to prepare a gel plugging system capable of being efficiently degraded, which mainly adopts the physical and chemical crosslinking action of water-soluble polymer molecules and a crosslinking agent containing a special structure in a crosslinking mode of a dynamic covalent bond within a certain time range under a certain temperature condition to form gel with higher strength to achieve the aim of bearing and plugging a fractured reservoir stratum, prevent leakage and ensure normal drilling operation, after the drilling operation is finished, the gel system is very easy to generate bond fracture under the action of a peroxide gel breaker when the pH value and the like of the external environment change, is quickly degraded into small molecular substances and then is discharged back, realizes the blockage removal of reservoir cracks, reduces the damage to the fractured oil and gas reservoir and realizes the aim of leakage prevention and leakage stoppage in the drilling process of the fractured oil and gas reservoir and the aim of reservoir protection. The technology fundamentally improves the traditional leakage-proof and plugging technology and method for the fractured reservoir, realizes the aim of both leakage-proof and plugging of the drilling of the fractured oil and gas reservoir and reservoir protection, and ensures the efficient exploitation of deepwater and ultra-deepwater oil and gas.
Disclosure of Invention
The invention aims to overcome the technical problems that the leakage prevention and plugging of the drilling of the fractured oil and gas reservoir and the reservoir protection are difficult to meet simultaneously and the technical requirements of the drilling and exploitation of the fractured oil and gas reservoir in deep water and ultra-deep water in the prior art cannot be met. Provides a preparation method and application of a high-efficiency degradation gel plugging system suitable for deep water and ultra-deep water drilling fluid.
According to the invention, the water-soluble high molecular polymer is effectively crosslinked to form high-strength gel through the dynamic covalent boric acid ester bond crosslinking agent, so that a fractured reservoir can be effectively blocked during drilling operation, the leakage is prevented, and the normal drilling operation is ensured; the prepared high-efficiency degradation gel system can reasonably optimize the component content of the gel system, realize the pressure-bearing leak stoppage of the fractured oil and gas reservoir, prevent the malignant leakage of a drilling well, effectively block the fractured reservoir with the fracture width of 0.5mm-3.2mm and achieve the maximum pressure-bearing capacity of 7.2 MPa; the gel system prepared by the invention has certain pH sensitivity, can be rapidly degraded along with the reduction of the external pH in the subsequent degradation process, and can be rapidly degraded under the weak acid condition by adding the strong oxidant gel breaker solution after the drilling operation is finished, so that the blockage removal of a reservoir fracture is realized, the damage to a fractured oil and gas reservoir is reduced, the operation time can be effectively saved, and the gel system is very suitable for deep water and ultra-deep water drilling with expensive offshore operation cost; the preparation method of the efficient degradation gel system is simple in field operation, can meet the technical requirements of deep water and ultra-deep water drilling, and is suitable for reservoir temperature conditions of 60-110 ℃. In general, the gel plugging system prepared by the invention realizes the aim of leakage prevention and plugging in the drilling process of a fractured oil and gas reservoir and the aim of reservoir protection, is a novel gel plugging system which is capable of being degraded efficiently and is suitable for the fractured reservoir, is beneficial to saving the operation time of deepwater and ultra-deepwater, reducing the damage of the fractured oil and gas reservoir of deepwater and ultra-deepwater and improving the efficient production of deepwater and ultra-deepwater oil and gas, and is a novel leakage prevention and plugging technology for the fractured oil and gas reservoir with simplicity, high efficiency and small reservoir damage.
In order to achieve the purpose, the invention prepares an efficient degradation gel system suitable for drilling and plugging of deep-water and ultra-deep-water fractured reservoirs, wherein the efficient degradation gel system comprises the following specific components in percentage by weight: 100 percent of water, 2.0 to 3.8 percent of water-soluble polymer, 0.8 to 2.2 percent of dynamic covalent boric acid ester bond crosslinking agent, 0.01 to 0.05 percent of stabilizing agent and 0.07 to 0.8 percent of hydrophilic fiber.
Wherein the dynamic covalent borate ester bond cross-linking agent has a molecular structure shown in a formula (a), wherein an R1 group can be one of-OH group, methyl, ethyl and isopropyl; wherein the R2 group can be one of phenyl, ethanolamine group, C8-C14 alkyl.
The preparation method of the dynamic covalent boric acid ester bond cross-linking agent comprises the following specific processes: (1) weighing a certain amount of component I with a molecular structure shown in formula (II) and dissolving in a certain amount of hot water at 60-75 ℃, wherein the R1 group can be one of H atom, methyl, ethyl and isopropyl; (2) under the condition of stirring, the stirring speed is 200-300 revolutions per minute, a certain amount of component II is gradually added into the reaction liquid, wherein the component II can be one of sodium hydroxide and potassium hydroxide, and the mass part ratio of the component I to the component II to water is kept to be 1 to (0.58-1.26) to (2.80-3.55); (3) controlling the reaction temperature, keeping the temperature at 85-90 ℃, and reacting for 120-150 minutes under stirring to obtain a light-colored transparent solution; (4) when the temperature of the reaction liquid is naturally cooled to 40-50 ℃, gradually adding a certain amount of component III with the molecular structure shown in the formula (c) under the stirring condition of 500 revolutions per minute at 300-; (5) heating to control the temperature of the reaction solution at 95-98 ℃, gradually reducing the stirring speed to 50-100 r/min, and finishing the reaction after 180-300 min to obtain the dynamic covalent borate bond crosslinking agent.
The water-soluble polymer is a water-soluble high polymer containing hydroxyl and other branched chains, and can be one or a combination of polyvinyl alcohol, hydroxypropyl guar gum, xanthan gum and hydroxyethyl cellulose, wherein the polymerization degree of the polyvinyl alcohol is 1700-1800, the number average molecular weight is 8-12 ten thousand, the relative molecular weight of the xanthan gum is 120-250 ten thousand, the molar substitution degree of the hydroxyethyl cellulose is 1.8-1.9, and the viscosity (1% solution, 20 ℃) is 15000-18000 mPa.S.
Wherein the stabilizer is one or a combination of thiourea, sodium sulfite, sodium bisulfite, acetaldoxime 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 2-4 mm; wherein the water may be fresh water, field water or sea water.
The preparation method of the efficient degradation gel system for drilling and plugging of the deepwater and ultra-deepwater fractured reservoir comprises the following specific processes: weighing a certain amount of fresh water, field water or seawater, and adding the stabilizer, the hydrophilic fiber and the water-soluble polymer in sequence according to a proportion under the condition of stirring at room temperature; after the polymer is fully dissolved, adding a dynamic covalent borate bond crosslinking agent in proportion under stirring; then the temperature is raised to a set temperature, the polymer molecules and the dynamic covalent boric acid ester bond cross-linking agent are subjected to cross-linking reaction continuously, and the high-efficiency degradation gel system is prepared.
The efficient degradation gel system for drilling and leaking stoppage of the deepwater and ultra-deepwater fractured reservoir has the advantages of adjustable gelling time, strong gel bearing capacity, high plugging strength, strong on-site drilling fluid resistance and other pollution capacities, can be suitable for the temperature of the oil and gas reservoir at 60-110 ℃, and has efficient bearing plugging capacity, efficient degradability and better reservoir protection effect.
The high-efficiency degradation gel system for drilling and plugging of the deep-water and ultra-deep-water fractured reservoir disclosed by the invention can reasonably optimize the component content of the gel system according to the temperature, pressure, fracture width and the like of the fractured reservoir and realize the pressure-bearing and plugging functions of the fractured oil and gas reservoir.
The invention also aims to provide a preparation method and application of the efficient degradation gel system for drilling and plugging of the deepwater and ultra-deepwater fractured reservoirs.
Through the technical scheme, the invention has the advantages that:
(1) the dynamic covalent boric acid ester bond cross-linking agent can realize effective cross-linking of water-soluble high-molecular polymers to form high-strength gel, and a gel system which is suitable for efficient degradation at 60-110 ℃ is prepared, has high strength, can effectively block fractured reservoirs during drilling operation, prevents leakage, ensures normal drilling operation, has strong degradation capability after the drilling operation is finished, can be quickly degraded into small molecular substances to be discharged back, realizes blockage removal of reservoir fractures, reduces damage to the fractured oil and gas reservoirs, realizes the aims of leakage prevention and reservoir protection in the drilling process of the fractured oil and gas reservoirs, and is a brand-new gel leakage blocking system which is suitable for the fractured reservoirs and can be efficiently degraded.
(2) The high-efficiency degradation gel system prepared by the invention has certain pH sensitivity, can be rapidly degraded along with the reduction of the external pH in the subsequent degradation process, is favorable for reducing the damage to a reservoir and is very favorable for maintaining the connectivity of the reservoir.
(3) The high-efficiency degradation gel system prepared by the invention can be used for reasonably optimizing the component content of the gel system, realizing the pressure-bearing leak stoppage of a fractured oil and gas reservoir and preventing the vicious leakage of a drilling well in the temperature, the pressure, the fracture width and the like of the deep-water and ultra-deep-water fractured reservoir.
(4) The high-efficiency degradation gel system prepared by the invention can effectively block a fractured reservoir with the fracture width of 0.5-3.2 mm, and the maximum pressure bearing capacity can reach 7.2 MPa.
(5) The high-efficiency degradation gel system has high degradation speed and high degradation efficiency, can effectively save the operation time, and is very suitable for deep water and ultra-deep water drilling with expensive offshore operation cost.
(6) The preparation method of the efficient degradation gel system is simple in field operation 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:
and testing the gel plugging system prepared from the 1 st part of water-based drilling fluid according to the drilling fluid field test of the standard GB/T16783.1-2014, and testing the performance of the gel plugging system by referring to the test of the drilling fluid laboratory test of the oil and gas industry of the standard GB/T29170-2012.
The "parts" described in the examples and test examples are "parts by mass".
The raw materials used in the examples and comparative examples are all conventional commercial products and are well known to those skilled in the art.
Example 1
This example illustrates a dynamic covalent boronic ester bond crosslinker prepared by the method of the present invention.
Weighing 100 parts by weight of a component I with a molecular structure shown in a formula (II) according to a weight ratio, and dissolving the component I in 292 parts by weight of 65 ℃ hot water, wherein an R1 group is methyl; (2) under the condition of stirring, the stirring speed is 200 revolutions per minute, and 87 parts by weight of potassium hydroxide of the component II are gradually added into the reaction solution; (3) controlling the reaction temperature, keeping the temperature at 90 ℃, and reacting 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 ℃, under the stirring condition of 300R/min, 210 parts by weight of a component III having a molecular structure represented by formula (c) is gradually added, wherein the R2 group is an ethanolamine group; (5) heating to control the temperature of the reaction solution at 95-98 ℃, gradually reducing the stirring speed to 60-rpm, and finishing the reaction after 240 minutes. As a result, a dynamic covalent boronic ester bond crosslinker was prepared, labeled S1.
Example 2
This example illustrates an efficient degradation gel system for drilling and plugging deep and ultra-deep water fractured reservoirs prepared by the method of the present invention.
Weighing 100 parts by weight of fresh indoor water according to the weight ratio, and sequentially adding 0.03 part by weight of sodium sulfite serving as a stabilizer, 0.3 part by weight of sepiolite fibers (the fiber length is 3mm) and 3.2 parts by weight of polyvinyl alcohol (the number average molecular weight is 10 ten thousand) under the condition of stirring at room temperature; and after the polymer is fully dissolved, adding 1.75 parts by weight of dynamic covalent borate ester bond crosslinking agent S1 while stirring, and then heating to a certain temperature to prepare the high-efficiency degradation gel system.
The result is a highly efficient degradation gel system, designated S2.
Example 3
This example illustrates an efficient degradation gel system for drilling and plugging deep and ultra-deep water fractured reservoirs prepared by the method of the present invention.
Weighing 100 parts by weight of fresh indoor water according to the weight ratio, and sequentially adding 0.03 part by weight of sodium sulfite serving as a stabilizer, 0.6 part by weight of lignin fiber (the fiber length is 4mm) and 3.5 parts by weight of polyvinyl alcohol (the number average molecular weight is 12 ten thousand) under the condition of stirring at room temperature; after the polymer is fully dissolved, 2.0 parts by weight of dynamic covalent borate ester bond crosslinking agent S1 is added under stirring; then heating to a certain temperature to prepare the high-efficiency degradation gel system.
The result is a highly efficient degradation gel system, designated S3.
Example 4
This example illustrates an efficient degradation gel system for drilling and plugging deep and ultra-deep water fractured reservoirs prepared by the method of the present invention.
Weighing 100 parts by weight of indoor fresh water according to the weight ratio, and sequentially adding 0.04 part by weight of thiourea stabilizer, 0.3 part by weight of lignin fiber (the fiber length is 4mm), 0.2 part by weight of sepiolite fiber (the fiber length is 3mm) mixed fiber, 2.3 parts by weight of polyvinyl alcohol (the number average molecular weight is 12 ten thousand) and 0.6 part by weight of mixed water-soluble polymer of xanthan gum (the number average molecular weight is 200 ten thousand) under the condition of stirring at room temperature; after the polymer was fully dissolved, 1.83 parts by weight of a dynamic covalent boronic acid ester bond crosslinking agent S1 was added with stirring; then heating to a certain temperature to prepare the high-efficiency degradation gel system.
The result is a highly efficient degradation gel system, designated S4.
Example 5
This example illustrates an efficient degradation gel system for drilling and plugging deep and ultra-deep water fractured reservoirs prepared by the method of the present invention.
Weighing 100 parts by weight of fresh indoor water according to the weight ratio, and sequentially adding 0.04 part by weight of thiourea stabilizer, 0.3 part by weight of lignin fiber (the fiber length is 4mm), 0.2 part by weight of sepiolite fiber (the fiber length is 3mm) mixed fiber, 2.0 part by weight of hydroxyethyl cellulose (the viscosity is 16000mPa.S) and 0.5 part by weight of mixed water-soluble polymer of xanthan gum (the number average molecular weight is 200 ten thousand) under the condition of stirring at room temperature; after the polymer was fully dissolved, 1.92 parts by weight of a dynamic covalent boronic acid ester bond crosslinking agent S1 was added with stirring; then heating to a certain temperature to prepare the high-efficiency degradation gel system.
The result is a highly efficient degradation gel system, designated S5.
Example 6
This example illustrates an efficient degradation gel system for drilling and plugging deep and ultra-deep water fractured reservoirs prepared by the method of the present invention.
Weighing 100 parts by weight of fresh indoor water according to the weight ratio, and sequentially adding 0.04 part by weight of thiourea stabilizer, 0.3 part by weight of lignin fiber (the fiber length is 4mm), 0.2 part by weight of sepiolite fiber (the fiber length is 3mm) mixed fiber, 2.3 parts by weight of hydroxyethyl cellulose (the viscosity is 18000mPa.S) and 0.5 part by weight of mixed water-soluble polymer of xanthan gum (the number average molecular weight is 220 ten thousand) under the condition of stirring at room temperature; after the polymer is fully dissolved, 0.92 weight part of dynamic covalent boric acid ester bond crosslinking agent S1 is added under stirring; then heating to a certain temperature to prepare the high-efficiency degradation gel system.
The result is a highly efficient degradation gel system, designated S6.
Comparative example 1
A gel system was prepared in the same manner as in example 2, except that: the organic chromium crosslinking agent commonly used in the field at present is used for replacing the dynamic covalent borate ester bond crosslinking agent S1 prepared by the method.
Weighing 100 parts by weight of fresh indoor water according to the weight ratio, and sequentially adding 0.03 part by weight of sodium sulfite serving as a stabilizer, 0.3 part by weight of sepiolite fibers (the fiber length is 3mm) and 3.2 parts by weight of polyvinyl alcohol (the number average molecular weight is 10 ten thousand) under the condition of stirring at room temperature; after the polymer is fully dissolved, adding 1.75 parts by weight of organic chromium crosslinking agent under stirring; and then heating to a certain temperature to prepare the gel plugging system.
The result was a gel plugging system, labeled as DS 1.
Comparative example 2
A gel system was prepared in the same manner as in example 2, except that: the organic boron crosslinking agent commonly used in the field at present is used for replacing the dynamic covalent borate ester bond crosslinking agent S1 prepared by the method.
Weighing 100 parts by weight of fresh indoor water according to the weight ratio, and sequentially adding 0.03 part by weight of sodium sulfite serving as a stabilizer, 0.3 part by weight of sepiolite fibers (the fiber length is 3mm) and 3.2 parts by weight of polyvinyl alcohol (the number average molecular weight is 10 ten thousand) under the condition of stirring at room temperature; after the polymer was sufficiently dissolved, 1.75 parts by weight of an organic crosslinking agent was added under stirring; and then heating to a certain temperature to prepare the gel plugging system.
The result was a gel plugging system, labeled as DS 2.
Comparative example 3
A gel system was prepared in the same manner as in example 2, except that: the organic chromium crosslinking agent commonly used in the field at present is used for replacing the dynamic covalent borate ester bond crosslinking agent S1 prepared by the method.
Weighing 100 parts by weight of fresh indoor water according to the weight ratio, and sequentially adding 0.03 part by weight of sodium sulfite serving as a stabilizer, 0.3 part by weight of sepiolite fibers (the fiber length is 3mm) and 3.2 parts by weight of polyvinyl alcohol (the number average molecular weight is 10 ten thousand) under the condition of stirring at room temperature; after the polymer is fully dissolved, adding a mixed crosslinking agent of 1.0 weight part of organic chromium crosslinking agent and 0.75 weight part of organic boron crosslinking agent under stirring; and then heating to a certain temperature to prepare the gel plugging system.
The result was a gel plugging system, labeled as DS 3.
Test example 1
The gel formation time of the polymer gel was determined by observing the gel to grade D using the GSC (gel Strength codes) visual code method from Sydansk. The gel-forming time of the gel systems prepared in the different examples and comparative examples tested is shown in table 1.
TABLE 1
From the experimental results of table 1, it can be seen that: gel systems prepared in the examples of the present invention have gel forming times of 65-108 minutes at different temperatures, and gel systems prepared in the comparative examples have gel forming times of 63-72 minutes at 80 ℃. Gel systems respectively prepared in the comparative examples and the comparative examples have gelling time at 80 ℃, which shows that compared with the traditional organic chromium and organic boron crosslinking agents, the dynamic covalent boric acid ester bonding crosslinking agent can properly delay the crosslinking reaction rate, is favorable for smoothly pumping the gel to reach a plugging target layer in the drilling plugging operation process, and generates high-strength gel to realize the plugging purpose after further crosslinking reaction after reaching the target layer.
Test example 2
The plugging evaluation device is adopted to test the plugging capability of the gel systems prepared in different examples and comparative examples on cracks, and the results are shown in table 2.
TABLE 2
| Group number | Temperature/. degree.C | Crack width/mm | Pressurization time/min | Maximum bearing pressure/MPa | Gel plugging effect |
| S2 | 80 | 1.5 | 13 | 6.2 (burst) | Bearing pressure of 6.2MPa |
| S3 | 85 | 1.5 | 19 | 7.5 | Successful plugging |
| S4 | 60 | 1.5 | 15 | 7.2 (burst) | Bearing pressure of 7.2MPa |
| S5 | 95 | 1.5 | 20 | 7.5 | Successful plugging |
| S6 | 95 | 1.5 | 15 | 7.2 | Successful plugging |
| DS1 | 80 | 1.5 | 17 | 5.3 (burst) | Bearing pressure of 5.3MPa |
| DS2 | 80 | 1.5 | 21 | 5.0 (break) | Bearing pressure of 5.0MPa |
| DS3 | 90 | 1.5 | 25 | 5.5 (burst) | Bearing pressure of 5.5MPa |
From the experimental results of table 2, it can be seen that: the gel system prepared by the embodiment of the invention has the plugging and pressure-bearing capacity of 6.2-7.2MPa at different temperatures, and the gel system prepared by the comparative example has the plugging and pressure-bearing capacity of 5.0-5.5MPa at the temperature of 80 ℃. Compared with the traditional organic chromium and organic boron crosslinking agents, the dynamic covalent boric acid ester crosslinking agent is more beneficial to the generation of a high-strength gel system in a network structure through gel crosslinking.
Test example 3
The gel system prepared in the example was tested for plugging ability and effect on cracks of different widths at different temperatures using a plugging evaluation device, and the results are shown in table 3.
TABLE 3
From the experimental results of table 3, it can be seen that: the gel system prepared by the embodiment of the invention can effectively block the crack with the width of 3.5mm at the temperature of 65-110 ℃, the pressure bearing capacity reaches 5.8MPa or above, and the gel system shows better crack blocking capacity.
Test example 4
After aging and curing the gel systems prepared in the examples and the comparative examples at different temperatures for 72 hours, the gel systems are fully crosslinked to form high-strength gel, then a certain amount of strong oxidant potassium persulfate solution with the concentration of 8.0% is added into the gel system, a small amount of dilute hydrochloric acid is added dropwise to adjust the pH value of the solution, and the gel breaking time and the residual liquid viscosity after gel breaking of the different gel systems at different temperatures and under different pH values are tested, and the results are shown in Table 4.
TABLE 4
| Group number | Temperature/. degree.C | pH of the solution | Gel breaking time/h | Viscosity of raffinate/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 |
From the experimental results of table 4, it can be seen that: gel breaking time of the gel system prepared by the embodiment of the invention under different temperature conditions is shorter than that of a comparative gel breaking time, and the viscosity of residual liquid after gel breaking is obviously lower than that of the residual liquid after the comparative gel breaking, which shows that the gel system of the invention has higher gel breaking speed and efficiency; the gel breaking time of the gel system prepared by the embodiment of the invention is reduced along with the pH value of the solution, the gel breaking speed and efficiency are further accelerated, and the gel system shows better pH value sensitivity, which shows that the gel system formed by the dynamic covalent boric acid ester bond cross-linking agent can be efficiently degraded under the weak acid condition, the damage to the fractured oil and gas reservoir is reduced, and the reservoir protection in the plugging process of the fractured oil and gas reservoir is realized.
Test example 5
In order to test the reservoir protection effect of the gel system, the results are shown in tables 6-9.
The gel systems prepared in the examples and the comparative examples are used for carrying out plugging experiments on fractured cores, then the cores after plugging are soaked in a strong oxidizing agent potassium persulfate solution with the concentration of 8.0%, a small amount of dilute hydrochloric acid is dropwise added to adjust the pH value of the solution to be 4, the cores are taken out after being soaked for a certain time, the recovery conditions of the permeability of the cores are measured by using a nitrogen reverse displacement on a core flow device, and the results are shown in table 5.
TABLE 5
From the experimental results of table 5, it can be seen that: the gel system prepared by the embodiment of the invention has higher permeability recovery rate than the gel system prepared by the comparative example, which shows that the gel system prepared by the embodiment of the invention has better reservoir protection effect.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (5)
1. The efficient degradation gel system is suitable for drilling and plugging of deepwater and ultra-deepwater fractured reservoirs and is characterized by comprising the following components in percentage by weight: 100 percent of water, 2.0 to 3.8 percent of water-soluble polymer, 0.8 to 2.2 percent of dynamic covalent boric acid ester bond crosslinking agent, 0.01 to 0.05 percent of stabilizer and 0.07 to 0.8 percent of hydrophilic fiber;
wherein the dynamic covalent borate ester bond cross-linking agent has a molecular structure shown in a formula (a), wherein an R1 group can be one of-OH group, methyl, ethyl and isopropyl; wherein the R2 group can be one of phenyl, ethanolamine group, C8-C14 alkyl;
the preparation method of the dynamic covalent boric acid ester bond cross-linking agent comprises the following specific processes: (1) weighing a certain amount of component I with a molecular structure shown in formula (b) and dissolving in a certain amount of hot water at 60-75 ℃, wherein the R1 group can be one of-OH group, methyl, ethyl and isopropyl; (2) under the condition of stirring, the stirring speed is 200-300 revolutions per minute, a certain amount of component II is gradually added into the reaction liquid, wherein the component II can be one of sodium hydroxide and potassium hydroxide, and the mass part ratio of the component I to the component II to water is kept to be 1 to (0.58-1.26) to (2.80-3.55); (3) controlling the reaction temperature, keeping the temperature at 85-90 ℃, and reacting for 120-150 minutes under stirring to obtain a light-colored transparent solution; (4) when the temperature of the reaction liquid is naturally cooled to 40-50 ℃, gradually adding a certain amount of component III with the molecular structure shown in the formula (c) under the stirring condition of 500 revolutions per minute at 300-; (5) heating to control the temperature of the reaction solution at 95-98 ℃, gradually reducing the stirring speed to 50-100 r/min, and finishing the reaction after 180-300 min to obtain the dynamic covalent borate bond crosslinking agent.
2. According to the claim 1, by the above technical solution, the high efficiency degradation gel system suitable for drilling and plugging of deep water and ultra-deep water fractured reservoir is characterized in that the water soluble polymer is a water soluble high molecular polymer containing branched chains such as hydroxyl groups, and can be one or a combination of polyvinyl alcohol, hydroxypropyl guar gum, xanthan gum and hydroxyethyl cellulose, wherein the polymerization degree of the polyvinyl alcohol is 1700-1800, the number average molecular weight is 8-12 ten thousand, the relative molecular weight of the xanthan gum is 120-250 ten thousand, the molar substitution degree of the hydroxyethyl cellulose is 1.8-1.9, and the viscosity (1% solution, 20 ℃) is 15000-18000 mpa.s.
3. According to the claim 1, through the technical scheme, the efficient degradation gel system suitable for the drilling and plugging of the deep water and ultra-deep water fractured reservoirs is characterized in that the stabilizer is one or a combination of thiourea, sodium sulfite, sodium bisulfite, acetaldoxime and sodium erythorbate.
4. According to the claim 1, through the technical scheme, the efficient degradation gel system suitable for deep water and ultra-deep water fractured reservoir drilling plugging is characterized in that the hydrophilic fiber is one or a combination of sepiolite fiber, lignin fiber and polyvinyl alcohol fiber, and the fiber length is 2-4 mm.
5. According to the claim 1, through the technical scheme, the efficient degradation gel system suitable for the drilling plugging of the deep-water and ultra-deep-water fractured reservoirs is characterized in that the water can be fresh water, field water or seawater.
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