阅读说明：本技术 一种钻井用多功能液体、页岩气用钻井流体及其制备方法和应用 (Multifunctional liquid for well drilling, drilling fluid for shale gas and preparation method and application thereof ) 是由 许明标 周姗姗 由福昌 于 2021-08-09 设计创作，主要内容包括：本发明提供了一种钻井用多功能液体、页岩气用钻井流体及其制备方法和应用,涉及油田化学技术领域。本发明提供的钻井用多功能液体,以质量份数计,包括以下制备原料：丝氨酸：10～30份；赖氨酸-甘氨酸共聚物：60～90份；苏氨酸：5～20份；天冬氨酸：10～20份；水：10～40份。本发明提供的钻井用多功能液体同时具有润滑、降滤失和抑制三种功能；除可有效改善钻井液润滑性能外,对钻井液体系的降滤失及抑制性能均有一定改善作用,以该多功能液体为原料制备的钻井流体能够有效解决页岩气水平井井壁失稳问题。(The invention provides a multifunctional liquid for well drilling, a drilling fluid for shale gas and a preparation method and application thereof, and relates to the technical field of oilfield chemistry. The invention provides a multifunctional liquid for well drilling, which comprises the following preparation raw materials in parts by mass: serine: 10-30 parts; lysine-glycine copolymer: 60-90 parts; threonine: 5-20 parts of a solvent; aspartic acid: 10-20 parts; water: 10-40 parts. The multifunctional liquid for drilling provided by the invention has three functions of lubricating, reducing filtration loss and inhibiting; the drilling fluid prepared by taking the multifunctional liquid as a raw material can effectively solve the problem of instability of the wall of a shale gas horizontal well.)

1. The multifunctional liquid for well drilling is characterized by comprising the following preparation raw materials in parts by mass:

serine: 10-30 parts;

lysine-glycine copolymer: 60-90 parts;

threonine: 5-20 parts of a solvent;

aspartic acid: 10-20 parts;

water: 10-40 parts.

2. The drilling fluid for shale gas is characterized by comprising the following preparation raw materials in parts by mass:

water: 65-90 parts;

multifunctional liquid: 10-35 parts;

alkalinity regulator: 0.1-2.0 parts;

coating agent: 0.1-1.0 part;

fluid loss additive: 1.0-4.0 parts;

rheology modifier: 0.1-0.7 parts;

anti-collapse plugging agent: 1.0-3.0 parts;

barite: 0-100 parts;

the multifunctional liquid is the multifunctional liquid for well drilling according to claim 1.

3. The shale gas drilling fluid of claim 2, wherein the alkalinity modifier comprises one or more of sodium hydroxide, sodium carbonate, and potassium hydroxide.

4. The shale gas drilling fluid of claim 2, wherein the coating agent is polyacrylamide.

5. The shale gas drilling fluid of claim 2, wherein the fluid loss additive is a natural starch or a modified starch.

6. The shale gas drilling fluid of claim 2, wherein the rheology modifier comprises one or more of xanthan gum, tamarind gum, konjac gum, fenugreek gum, guar gum, and locust bean gum.

7. The shale gas drilling fluid of claim 2, wherein the anti-sloughing plugging agent comprises one or more of potassium nitrohumate, natural resins, and oxidized bitumen.

8. The shale gas drilling fluid of claim 2, wherein the barite has a particle size of 200 to 1000 mesh.

9. A method of making the shale gas drilling fluid of any of claims 2 to 8, comprising the steps of:

and mixing the preparation raw materials to obtain the drilling fluid for the shale gas.

10. Use of the shale gas drilling fluid as defined in any one of claims 2 to 8 or the shale gas drilling fluid prepared by the preparation method as defined in claim 9 in shale gas horizontal wells.

Technical Field

The invention relates to the technical field of oilfield chemistry, in particular to a multifunctional liquid for well drilling, a drilling fluid for shale gas and a preparation method and application thereof.

Background

Shale gas as an important unconventional natural gas resource occupies a great position in oil and gas resource exploration in China in recent years. The shale gas exploration work in China mainly focuses on the Sichuan basin and the periphery thereof, the Ordos basin and the main basins in the northwest region. The shale has a compact structure, and in order to more effectively exploit oil and gas resources, the horizontal well is the best choice for shale gas exploitation, and is a drilling and well completion mode for increasing the oil drainage area, and a section of well bore with a length and a bore diameter is drilled along the direction of a reservoir, so that the oil drainage area of the reservoir is increased, the yield is improved, a single oil field is developed to the maximum extent, the proportion of newly drilled wells is reduced, and the investment is reduced. With the continuous progress of the technology, the horizontal displacement is longer and longer, and the requirement on the lubricity of a drilling fluid system for a horizontal well is higher and higher. Because the shale brittle mineral content in China is high and reaches more than 40%, natural cracks and induced cracks are easy to form under the action of external force such as artificial fracturing, the shale in China has good brittleness characteristics, a crack system with more developed rock cores has certain chemical activity, complex accidents such as borehole wall instability and the like often occur in the drilling process of a horizontal well, and the drilling time and cost are increased.

The oil-based drilling fluid has excellent lubricating property in the application process of the horizontal well, can effectively reduce friction torque in the drilling process, and can effectively ensure the stability of a well wall and have better rheological control capability. However, facing increasingly severe environmental protection issues, the use of oil-based drilling fluids is increasingly limited. Although the common water-based drilling fluid can solve the problem of environmental pollution of the oil-based drilling fluid, the problems of large friction torque and poor well wall stabilizing effect of the water-based drilling fluid are particularly prominent when the common water-based drilling fluid is applied to a horizontal well, and the application of the common water-based drilling fluid in a shale gas horizontal well is restricted.

Chinese patent CN202010528243.8 discloses a water-based drilling fluid for extended reach wells, which can solve the problem of lubrication of extended reach wells, but does not evaluate the influence of the water-based drilling fluid on the stability of well walls, especially the stability of the well walls of horizontal wells. The problems of horizontal well lubrication and well wall stability are key problems to be solved by the shale gas horizontal well.

Disclosure of Invention

The invention aims to provide a multifunctional liquid for drilling, a drilling fluid for shale gas and a preparation method and application thereof.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a multifunctional liquid for well drilling, which comprises the following preparation raw materials in parts by mass:

serine: 10-30 parts;

lysine-glycine copolymer: 60-90 parts;

threonine: 5-20 parts of a solvent;

aspartic acid: 10-20 parts;

water: 10-40 parts.

The invention provides a drilling fluid for shale gas, which comprises the following preparation raw materials in parts by mass:

water: 65-90 parts;

multifunctional liquid: 10-35 parts;

alkalinity regulator: 0.1-2.0 parts;

coating agent: 0.1-1.0 part;

fluid loss additive: 1.0-4.0 parts;

rheology modifier: 0.1-0.7 parts;

anti-collapse plugging agent: 1.0-3.0 parts;

barite: 0-100 parts;

the multifunctional liquid is the multifunctional liquid for well drilling in the technical scheme.

Preferably, the alkalinity regulator comprises one or more of sodium hydroxide, sodium carbonate and potassium hydroxide.

Preferably, the coating agent is polyacrylamide.

Preferably, the fluid loss additive is a natural starch or a modified starch.

Preferably, the rheology modifier comprises one or more of xanthan gum, tamarind gum, konjac gum, fenugreek gum, guar gum and locust bean gum.

Preferably, the anti-collapse plugging agent comprises one or more of potassium nitrohumate, natural resin and oxidized asphalt.

Preferably, the particle size of the barite is 200-1000 meshes.

The invention provides a preparation method of the drilling fluid for shale gas, which comprises the following steps:

and mixing the preparation raw materials to obtain the drilling fluid for the shale gas.

The invention provides application of the drilling fluid for shale gas in the technical scheme or the drilling fluid for shale gas prepared by the preparation method in the technical scheme in a shale gas horizontal well.

The invention provides a multifunctional liquid for well drilling, which comprises the following preparation raw materials in parts by mass: serine: 10-30 parts; lysine-glycine copolymer: 60-90 parts; threonine: 5-20 parts of a solvent; aspartic acid: 10-20 parts; water: 10-40 parts. In the invention, a polyglycine chain segment in a lysine-glycine copolymer has stronger hydrophobicity, and a large amount of amino groups on a side chain of the polylysine chain segment exist to ensure that the polylysine chain segment has hydrophilicity, so that the multifunctional liquid has amphiphilic nano property, in the drilling fluid, the multifunctional liquid is adsorbed on the surfaces of clay particles in an aqueous solution through hydrogen bonds, so that negative charges on the surfaces of the clay particles are in positive valence, a hydration layer is thickened, the coalescence stability of the clay particles is improved, the clay particles keep smaller particle size and have reasonable particle size distribution, and thus a thin, tough, compact-structure high-quality filter cake is generated, and the filtration loss is reduced. The amino acid with positive electricity in the multifunctional liquid rapidly controls the most active hydration point and is firmly fixed on the surface of the clay particles, hydration and osmotic hydration of the surface of the clay particles are prevented, the hydrophobic section assists to inhibit hydration, hydration stress generated when filtrate enters a stratum is reduced, and the rising degree of the pore pressure of the stratum is reduced.

The multifunctional liquid for drilling provided by the invention has three functions of lubricating, reducing filtration loss and inhibiting; the drilling fluid prepared by taking the multifunctional liquid as a raw material can effectively solve the problem of instability of the wall of a shale gas horizontal well.

The invention provides a drilling fluid for shale gas, which comprises the following preparation raw materials in parts by mass: water: 65-90 parts; multifunctional liquid: 10-35 parts; alkalinity regulator: 0.1-2.0 parts; coating agent: 0.1-1.0 part; fluid loss additive: 1.0-4.0 parts; rheology modifier: 0.1-0.7 parts; anti-collapse plugging agent: 1.0-3.0 parts; barite: 0-100 parts; the multifunctional liquid is the multifunctional liquid for well drilling in the technical scheme. The drilling fluid for shale gas provided by the invention belongs to drilling fluid, meets the requirement of environmental protection, and solves the problems of insufficient lubricity and poor well wall stabilizing effect in the application process of the conventional water-based drilling fluid system in a shale gas horizontal well. In the invention, the alkalinity regulator can regulate the pH value of the system and assist in improving the functions of raw materials such as the anti-collapse plugging agent and the like; the coating agent can inhibit the hydration expansion and dispersion of the shale; the filtrate reducer can reduce the filtrate loss of the drilling fluid and reduce the problems of hydration expansion of shale, instability of well walls and the like caused by the invasion of filtrate into the stratum; the anti-collapse plugging agent can maintain the stable performance of the drilling fluid and ensure the stability of the well wall; the barite can improve the density of the drilling fluid and balance the formation pressure; the multifunctional liquid for drilling can effectively improve the lubricating property of the water-based drilling fluid, has certain improvement effect on the filtration loss reduction and inhibition performance of a drilling fluid system, and can effectively solve the problem of instability of the wall of a shale gas horizontal well by compounding other raw materials.

The results of the examples show that the shale gas drilling fluid provided by the invention has the lubricity which is comparable to that of an oil-based drilling fluid, and when the addition amount of the multifunctional liquid is 35 parts by weight, the lubricating coefficient of the multifunctional liquid is as low as 0.060, which is close to 0.056 of the oil-based drilling fluid, and meanwhile, the multifunctional liquid has the anti-wear performance which is superior to that of the oil-based drilling fluid; compared with a polymer potassium chloride drilling fluid system, the drilling fluid for shale gas provided by the invention has smaller influence on the cohesive force and compressive strength of rocks after being soaked, is equivalent to an oil-based drilling fluid, and is beneficial to solving the problem of instability of the wall of a shale gas horizontal well; the drilling fluid for shale gas provided by the invention still has good rheological and lubricating properties after being polluted by external pollutants.

The applicable temperature range of the drilling fluid for shale gas provided by the invention is 20-120 ℃, and the operation requirements of most shale gas wells can be met.

Drawings

FIG. 1 is a graph showing the change in compressive strength of shale when soaked in different drilling fluid systems;

FIG. 2 is a graph comparing the characteristics of the cohesion and internal friction angle of shale soaked in different drilling fluid systems.

Detailed Description

The invention provides a multifunctional liquid for well drilling, which comprises the following preparation raw materials in parts by mass:

serine: 10-30 parts;

lysine-glycine copolymer: 60-90 parts;

threonine: 5-20 parts of a solvent;

aspartic acid: 10-20 parts;

water: 10-40 parts.

In the present invention, unless otherwise specified, the starting materials for the preparation are all commercially available products well known to those skilled in the art.

The multifunctional liquid for drilling comprises, by mass, 10-30 parts of serine, preferably 15-20 parts of serine.

The multifunctional liquid for well drilling comprises 60-90 parts by weight of lysine-glycine copolymer, preferably 65-75 parts by weight of serine. The method for preparing the lysine-glycine copolymer is not particularly required, and a method known to those skilled in the art can be used. In the inventionIn a specific example, the preparation method of the lysine-glycine copolymer includes: dissolving 75 parts by weight of benzyloxyhydroxyl-L-lysine cyclic internal anhydride in 50 parts by weight of N, N-dimethylformamide in a nitrogen environment, transferring the mixture to a reaction bottle, adding 0.002 part by weight of hexamethyldisilazane into the reaction bottle to initiate polymerization, and stirring the mixture at room temperature for 3 days; dissolving 25 parts by mass of glycine-N-carboxyanhydride in N, N-dimethylformamide, adding the obtained solution into the reaction bottle, and carrying out polymerization reaction for 3d at room temperature; after the polymerization reaction is finished, adding the solution into 220mL of anhydrous ether, stirring, fully settling, filtering and drying; the resultant was dissolved in 50 parts by mass of trifluoroacetic acid, and 0.6 part by mass of HBr/CH was added₃And (3) stirring and reacting the COOH mixed solution for 12 hours, washing, filtering and drying to obtain the lysine-glycine copolymer.

The multifunctional liquid for well drilling provided by the invention comprises 5-20 parts of threonine, preferably 10-15 parts of serine by mass.

The multifunctional liquid for drilling comprises, by mass, 10-20 parts of aspartic acid, preferably 10-15 parts of serine.

Based on the mass parts of the serine, the multifunctional liquid for well drilling provided by the invention comprises 10-40 parts of water, and preferably 20-35 parts of water.

The preparation method of the multifunctional liquid for well drilling has no special requirements, and the multifunctional liquid for well drilling can be prepared by uniformly mixing the preparation raw materials.

The invention provides a drilling fluid for shale gas, which comprises the following preparation raw materials in parts by mass:

water: 65-90 parts;

multifunctional liquid: 10-35 parts;

alkalinity regulator: 0.1-2.0 parts;

coating agent: 0.1-1.0 part;

fluid loss additive: 1.0-4.0 parts;

rheology modifier: 0.1-0.7 parts;

anti-collapse plugging agent: 1.0-3.0 parts;

barite: 0-100 parts;

the multifunctional liquid is the multifunctional liquid for well drilling in the technical scheme.

In the present invention, unless otherwise specified, the starting materials for the preparation are all commercially available products well known to those skilled in the art.

The preparation raw material of the drilling fluid for shale gas comprises, by mass, 65-90 parts of water, and preferably 70-80 parts of water. In the present invention, the water is preferably fresh water.

The preparation raw material of the drilling fluid for shale gas comprises 10-35 parts by weight of multifunctional liquid, preferably 20-30 parts by weight of water. In the invention, the multifunctional liquid is the multifunctional liquid for well drilling in the technical scheme. In the present invention, the sum of the parts by mass of the water and the multifunctional liquid is preferably 100 parts.

The preparation raw material of the drilling fluid for shale gas comprises, by weight, 0.1-2.0 parts of alkalinity regulator, preferably 0.2-0.5 parts of alkalinity regulator, and more preferably 0.3-0.4 parts of alkalinity regulator. In the present invention, the alkalinity regulator preferably includes one or more of sodium hydroxide, sodium carbonate and potassium hydroxide.

The preparation raw material of the drilling fluid for shale gas comprises 0.1-1.0 part by weight of coating agent, preferably 0.2-0.3 part by weight of water. In the present invention, the coating agent is preferably polyacrylamide; the molecular weight of the polyacrylamide is preferably 600-700 ten thousand.

The preparation raw material of the drilling fluid for shale gas comprises, by weight, 1.0-4.0 parts of a fluid loss additive, and preferably 2.0-3.0 parts of water. In the present invention, the fluid loss additive is preferably a natural starch or a modified starch, more preferably a modified starch. The modified starch is used as the fluid loss agent, and compared with natural starch, the modified starch has the advantages of good fluid loss effect, high action speed, small influence on plastic viscosity, large influence on dynamic shear force and benefit for carrying drill cuttings.

In the present invention, the preparation method of the modified starch preferably includes: mixing potato starch, cassava starch, canna edulis ker starch, water caltrop starch, sodium hydroxide, chloroacetic acid and water, injecting the obtained mixture into a spiral extruder, controlling the temperature to be 100-110 ℃, extruding the starch from a spiral extrusion port, then instantly puffing and drying, and then sequentially coarsely crushing and finely grinding the puffed starch to obtain the modified starch. In the invention, the mass ratio of the potato starch, the cassava starch, the canna starch, the water caltrop starch, the sodium hydroxide, the chloroacetic acid and the water is preferably 10-30: 10-30: 10-45: 0 to 20: 1-3: 5-15: 100-180, more preferably 18-20: 15-25: 30-40: 5-10: 1.5-3: 8-12: 130 to 150. In the present invention, the water is preferably deionized water.

In the present invention, the particle size of the modified starch is preferably 120 mesh.

The preparation raw material of the drilling fluid for shale gas comprises, by weight, 0.1-0.7 part of a rheological modifier, preferably 0.2-0.3 part of water. In the present invention, the rheology modifier preferably includes one or more of xanthan gum, tamarind gum, konjac gum, fenugreek gum, guar gum, and locust bean gum, and more preferably a mixture of xanthan gum, tamarind gum, konjac gum, and guar gum. In the invention, when the rheology modifier is a mixture of xanthan gum, tamarind gum, konjac glucomannan and guar gum, the mass ratio of the xanthan gum, tamarind gum, konjac glucomannan and guar gum is preferably 20-65: 0-2: 10-30: 10-25, more preferably 30-60: 10-20: 10-30: 15-25, and still more preferably 40-55: 15-20: 20-25.

The preparation raw material of the drilling fluid for shale gas comprises, by weight, 1.0-3.0 parts of an anti-collapse plugging agent, and preferably 2.0-2.5 parts of water. In the present invention, the anti-collapse plugging agent preferably comprises one or more of potassium nitrohumate, natural resin and oxidized asphalt, and more preferably a mixture of potassium nitrohumate, natural resin and oxidized asphalt. In the invention, when the anti-collapse plugging agent is a mixture of potassium nitrohumate, natural resin and oxidized asphalt, the mass ratio of the potassium nitrohumate to the natural resin to the oxidized asphalt is preferably 30-55: 20-50: 20 to 50, more preferably 30 to 50:25 to 45:30 to 40.

The preparation raw material of the drilling fluid for shale gas comprises 0-100 parts by weight of barite, preferably 80 parts by weight of water. In the invention, the particle size of the barite is preferably 200-1000 meshes, and more preferably 350 meshes.

The invention also provides a preparation method of the drilling fluid for shale gas, which comprises the following steps: and mixing the preparation raw materials to obtain the drilling fluid for the shale gas. The present invention has no special requirement on the specific mixing process, and the mixing process known to those skilled in the art can be adopted.

The invention also provides application of the drilling fluid for shale gas in the technical scheme or the drilling fluid for shale gas prepared by the preparation method in the technical scheme in a shale gas horizontal well.

The drilling fluid for shale gas provided by the invention can effectively solve the problems of horizontal well lubrication and well wall stability.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Dissolving 75 parts by weight of benzyloxyhydroxyl-L-lysine cyclic internal anhydride in 50 parts by weight of N, N-dimethylformamide in a nitrogen environment, transferring the mixture to a reaction bottle, adding 0.002 part by weight of hexamethyldisilazane into the reaction bottle to initiate polymerization, and stirring the mixture at room temperature for 3 days; dissolving 25 parts by mass of glycine-N-carboxyanhydride in N, N-dimethylformamide, adding the obtained solution into the reaction bottle, and carrying out polymerization reaction for 3d at room temperature; after the polymerization reaction, the solution was added to 220mL of anhydrous ether and stirredStirring, fully settling, filtering and drying; the resultant was dissolved in 50 parts by mass of trifluoroacetic acid, and 0.6 part by mass of HBr/CH was slowly added₃And (3) stirring and reacting the COOH mixed solution for 12 hours, washing, filtering and drying to obtain the lysine-glycine copolymer.

Mixing serine, the lysine-glycine copolymer, threonine, aspartic acid and water according to the mass ratio of 10:70:15:10:30 to obtain multifunctional liquid;

fully stirring 90 parts by mass of fresh water and 10 parts by mass of multifunctional liquid to obtain a mixed solution.

Example 2

A lysine-glycine copolymer was prepared by the preparation method of example 1.

Mixing serine, the lysine-glycine copolymer, threonine, aspartic acid and water according to a mass ratio of 15:75:20:10:30 to obtain multifunctional liquid;

and fully stirring 80 parts by mass of fresh water and 20 parts by mass of multifunctional liquid to obtain a mixed solution.

Example 3

A lysine-glycine copolymer was prepared by the preparation method of example 1.

Mixing serine, the lysine-glycine copolymer, threonine, aspartic acid and water according to a mass ratio of 10:90:10:10:40 to obtain multifunctional liquid;

fully stirring 65 parts by mass of fresh water and 35 parts by mass of multifunctional liquid to obtain a mixed solution.

Example 4

Mixing 90 parts by mass of fresh water, 10 parts by mass of multifunctional liquid, 0.2 part by mass of sodium hydroxide, 0.3 part by mass of coating agent, 3.0 parts by mass of filtrate reducer, 0.2 part by mass of rheological modifier, 3.0 parts by mass of anti-collapse plugging agent and 80 parts by mass of barite, and fully stirring to obtain the drilling fluid for shale gas.

The mass ratio of serine, lysine-glycine copolymer, threonine, aspartic acid and water in the multifunctional liquid is 20:70:15:10: 40.

The fluid loss additive is modified starch, and the preparation method of the modified starch comprises the following steps: uniformly mixing 30 parts by weight of potato starch, 15 parts by weight of cassava starch, 30 parts by weight of canna edulis ker starch, 5 parts by weight of water caltrop starch, 1 part by weight of sodium hydroxide, 10 parts by weight of chloroacetic acid and 130 parts by weight of deionized water, injecting the mixture into a screw extruder, controlling the temperature to be 105 ℃, extruding the starch from a screw extrusion port, instantly puffing and drying, coarsely crushing and finely grinding the puffed starch, and sieving the starch with a 120-mesh sieve to obtain the modified starch.

The rheology modifier is a mixture of xanthan gum, tamarind gum, konjac glucomannan and guar gum, wherein the mass ratio of the xanthan gum to the tamarind gum to the konjac gum to the guar gum is 30:20:30: 15.

The anti-collapse plugging agent is a mixture of potassium nitrate humate, natural resin and oxidized asphalt, wherein the mass ratio of the potassium nitrate humate to the natural resin to the oxidized asphalt is 30:25: 35.

Example 5

Mixing 80 parts by mass of fresh water, 20 parts by mass of multifunctional liquid, 0.3 part by mass of sodium hydroxide, 0.2 part by mass of coating agent, 2.5 parts by mass of filtrate reducer, 0.2 part by mass of rheological modifier, 2.5 parts by mass of anti-collapse plugging agent and 80 parts by mass of barite, and fully stirring to obtain the drilling fluid for shale gas.

The mass ratio of serine, lysine-glycine copolymer, threonine, aspartic acid and water in the multifunctional liquid is 10:60:20:20: 35.

The fluid loss additive is modified starch, and the preparation method of the modified starch comprises the following steps: uniformly mixing 20 parts by weight of potato starch, 20 parts by weight of cassava starch, 35 parts by weight of canna edulis ker starch, 10 parts by weight of water caltrop starch, 1.5 parts by weight of sodium hydroxide, 15 parts by weight of chloroacetic acid and 140 parts by weight of deionized water, injecting the mixture into a screw extruder, controlling the temperature to be 105 ℃, extruding the starch from a screw extrusion port, instantly puffing and drying, coarsely crushing and finely grinding the puffed starch, and sieving the starch with a 120-mesh sieve to obtain the modified starch.

The rheology modifier is a mixture of xanthan gum, tamarind gum, konjac glucomannan and guar gum, wherein the mass ratio of the xanthan gum to the tamarind gum to the konjac gum to the guar gum is 40:15:15: 25.

The anti-collapse plugging agent is a mixture of potassium nitrate humate, natural resin and oxidized asphalt, wherein the mass ratio of the potassium nitrate humate to the natural resin to the oxidized asphalt is 30:45: 40.

Example 6

Mixing 70 parts by mass of fresh water, 30 parts by mass of multifunctional liquid, 0.5 part by mass of sodium hydroxide, 0.3 part by mass of coating agent, 2.5 parts by mass of filtrate reducer, 0.2 part by mass of rheological modifier, 3.0 parts by mass of anti-collapse plugging agent and 80 parts by mass of barite, and fully stirring to obtain the drilling fluid for shale gas.

The mass ratio of serine, lysine-glycine copolymer, threonine, aspartic acid and water in the multifunctional liquid is 10:70:5:15: 40.

The fluid loss additive is modified starch, and the preparation method of the modified starch comprises the following steps: uniformly mixing 10 parts by weight of potato starch, 20 parts by weight of cassava starch, 40 parts by weight of canna starch, 5 parts by weight of water caltrop starch, 1 part by weight of sodium hydroxide, 5 parts by weight of chloroacetic acid and 150 parts by weight of deionized water, injecting the mixture into a screw extruder, controlling the temperature to be 105 ℃, extruding the starch from a screw extrusion port, instantly puffing and drying, coarsely crushing and finely grinding the puffed starch, and sieving the starch with a 120-mesh sieve to obtain the modified starch.

The rheology modifier is a mixture of xanthan gum, tamarind gum, konjac glucomannan and guar gum, wherein the mass ratio of the xanthan gum to the tamarind gum to the konjac gum to the guar gum is 60:10:10: 15.

The anti-collapse plugging agent is a mixture of potassium nitrate humate, natural resin and oxidized asphalt, wherein the mass ratio of the potassium nitrate humate to the natural resin to the oxidized asphalt is 50:20: 30.

Example 7

Mixing 65 parts by mass of fresh water, 35 parts by mass of multifunctional liquid, 0.4 part by mass of sodium hydroxide, 0.3 part by mass of coating agent, 2.0 parts by mass of filtrate reducer, 0.3 part by mass of rheological modifier, 2.0 parts by mass of anti-collapse plugging agent and 80 parts by mass of barite, and fully stirring to obtain the drilling fluid for shale gas.

The mass ratio of serine, lysine-glycine copolymer, threonine, aspartic acid and water in the multifunctional liquid is 10:65:20:20: 40.

The fluid loss additive is modified starch, and the preparation method of the modified starch comprises the following steps: uniformly mixing 18 parts by weight of potato starch, 25 parts by weight of cassava starch, 30 parts by weight of canna edulis ker starch, 8 parts by weight of water caltrop starch, 3 parts by weight of sodium hydroxide, 8 parts by weight of chloroacetic acid and 180 parts by weight of deionized water, injecting the mixture into a screw extruder, controlling the temperature to be 105 ℃, extruding the starch from a screw extrusion port, instantly puffing and drying, coarsely crushing and finely grinding the puffed starch, and sieving the starch with a 120-mesh sieve to obtain the modified starch.

The rheology modifier is a mixture of xanthan gum, tamarind gum, konjac glucomannan and guar gum, wherein the mass ratio of the xanthan gum to the tamarind gum to the konjac gum to the guar gum is 55:20:30: 25.

The anti-collapse plugging agent is a mixture of potassium nitrate humate, natural resin and oxidized asphalt, wherein the mass ratio of the potassium nitrate humate to the natural resin to the oxidized asphalt is 55:45: 30.

Comparative example 1

100 parts by mass of fresh water.

Comparative example 2

100 parts by mass of white oil.

Comparative example 3

100 parts by mass of fresh water and 3 parts by mass of polyamine are fully and uniformly stirred to obtain the polyurethane.

Comparative example 4

Oil-based drilling fluids: fully mixing 80 parts by mass of white oil, 20 parts by mass of saturated calcium chloride water, 2.0 parts by mass of a main emulsifier, 1.0 part by mass of an auxiliary emulsifier, 0.8 part by mass of a shear improver, 1.5 parts by mass of an alkalinity regulator, 2.0 parts by mass of organic soil, 3.0 parts by mass of a filtrate reducer, 3.0 parts by mass of a plugging agent and 100 parts by mass of barite to obtain the oil-based drilling fluid.

Comparative example 5

Polymer potassium chloride drilling fluid: fully mixing 100 parts by mass of seawater, 3.0 parts by mass of bentonite, 0.2 part by mass of sodium carbonate, 0.4 part by mass of polyanionic cellulose, 0.5 part by mass of polyacrylamide, 5 parts by mass of potassium chloride, 1.5 parts by mass of hydroxypropyl starch, 1.0 part by mass of sulfonated asphalt, 1.5 parts by mass of sulfonated phenolic resin and 30 parts by mass of barite to obtain the polymer potassium chloride drilling fluid.

Comparative example 6

Example 4 in chinese patent CN202010528243.8 was used as comparative example 6:

70 parts by mass of seawater, 30 parts by mass of multifunctional base fluid, 0.1 part by mass of sodium hydroxide, 0.4 part by mass of coating agent, 2.0 parts by mass of filtrate reducer, 0.1 part by mass of rheological regulator, 2.0 parts by mass of anti-collapse plugging agent and 80 parts by mass of barite are mixed and fully stirred to obtain the water-based drilling fluid.

The mass ratio of the castor oil sodium phosphate, the maleic acid-acrylic acid copolymer, the polyethylene glycol monooleate and the water in the multifunctional base liquid is 30:75:10: 30. The mass ratio of the potato starch, the cassava starch, the canna edulis ker starch and the water caltrop starch in the filtrate reducer is 15:25:10: 15. The rheological control agent comprises xanthan gum, tamarind gum, guar gum and locust bean gum at a mass ratio of 60:15:5: 15. The mass ratio of potassium humate to natural resin in the anti-collapse plugging agent is 30: 25.

Test example 1

The drilling fluid performances of examples 1-7 and comparative examples 1-6 were tested, and the basic performances of the drilling fluids were tested, with the results shown in table 1.

TABLE 1 lubricating and antiwear Properties of the drilling fluids of examples 1-7 and comparative examples 1-6

Drilling fluid	Coefficient of lubricity	Anti-wear block
			Example 1	0.092	8
Example 2	0.050	10
			Example 3	0.045	10
Example 4	0.088	9
			Example 5	0.080	10
Example 6	0.071	10
			Example 7	0.060	10
Comparative example 1	0.34	3
			Comparative example 2	0.038	4
Comparative example 3	0.33	3
			Comparative example 4	0.056	8
Comparative example 5	0.17	5
			Comparative example 6	0.064	10

The test results in the table 1 show that the multifunctional liquid and water are mixed and then used as the dispersed phase in the drilling fluid to be compared with the common fresh water and white oil in the evaluation of the examples 1 to 3, and as the addition of the multifunctional liquid is increased, the lubricating coefficient of the dispersed phase is reduced from 0.092 to 0.045, which is close to the white oil and is obviously superior to the fresh water; as can be seen from the anti-wear data, the difference between the anti-wear performance of the fresh water and the anti-wear performance of the white oil is not great, while the multifunctional liquid has better anti-wear performance, and when the adding amount of the multifunctional liquid is 20 parts by mass, the anti-wear performance can reach 10 blocks.

The drilling fluid for shale gas prepared by using the multifunctional liquid has the advantages that the friction coefficient of the system is gradually reduced and the anti-wear capacity is gradually enhanced along with the increase of the addition of the multifunctional liquid, and when the addition of the multifunctional liquid is 35 parts by mass, the friction coefficient of the system is 0.060 which is close to 0.056 of an oil-based drilling fluid; and the abrasion resistance of the drilling fluid prepared by the multifunctional liquid can reach 10 blocks, and the abrasion resistance of the drilling fluid prepared by the multifunctional liquid is only 8 blocks, which shows that the drilling fluid prepared by the multifunctional liquid can reduce the friction resistance and the casing abrasion. The lubricating and anti-wear effects of the drilling fluid for the shale gas constructed by the multifunctional liquid are equivalent to those of the drilling fluid in the comparative example 6.

Test example 2

The inhibition performance of the multifunctional liquid and the inhibition performance of the drilling fluid for shale gas prepared from the multifunctional liquid are respectively evaluated, and the results are respectively compared and evaluated with the performances of common liquid water, oil and oil-based drilling fluid for preparing drilling fluid and polymer potassium chloride drilling fluid, and are shown in table 2.

TABLE 2 evaluation of the inhibition Properties of examples 1 to 7 and comparative examples 1 to 6

As can be seen from table 2, the data of comparative examples 1 to 3 and examples 1 to 3 indicate that the viscosity and shear force are low without adding the earth-moving powder, the fresh water thickening is obvious after adding 20% of the earth-moving powder, the values of 6 turns and 3 turns can only be measured, and the values are large, and the viscosity and shear force are low after mixing the multifunctional liquid and the water according to a certain proportion and adding 20% of the earth-moving powder, indicating that the multifunctional liquid can effectively inhibit the hydration and pulping of the earth-moving powder. The data of examples 4 to 7 show that the drilling fluid for shale gas prepared by the multifunctional liquid has small increase of the system viscosity and the shear force value after 20% of the earth moving powder is added, and the drilling fluid for shale gas provided by the invention can effectively inhibit clay hydration and slurrying. The anti-swelling rate and the rolling recovery rate of the drilling fluid for shale gas provided by the invention are both over 90%, which shows that the system can effectively inhibit clay hydration dispersion and swelling, and the inhibition effect of the drilling fluid is equivalent to that of the drilling fluid provided by the comparative example 6.

Test example 3

In order to evaluate the filtrate loss reduction performance of the multifunctional liquid, 3% of bentonite-based slurry and 0.4 part of xanthan gum are added in corresponding proportion and in the embodiment for fully stirring because of low viscosity; the low-pressure and low-pressure water loss refers to the water loss volume of 0.7MPa, 25 ℃ and 30 min; the PPT plugging filtration loss refers to the water loss volume of a sand disc used for replacing filter paper at 3.5MPa, 120 ℃ and 30min, and the results are shown in Table 3.

TABLE 3 fluid loss performance of example 1 and comparative examples 1-6

The data in table 3 show that the water loss at low temperature and low pressure is gradually reduced with the increase of the dosage of the multifunctional liquid, which indicates that the multifunctional liquid has better plugging and fluid loss reducing effects. The method is characterized in that a polyglycine chain segment in a lysine-glycine copolymer has stronger hydrophobicity, and a large amount of amino groups on a side chain of the polylysine chain segment exist to enable the polyglycine chain segment to have hydrophilicity, so that the multifunctional liquid has amphiphilic nanometer property, in the drilling fluid, the multifunctional liquid is adsorbed on the surfaces of clay particles in an aqueous solution through hydrogen bonds, negative charges on the surfaces of the clay particles are in positive valence, a hydration layer is thickened, the coalescence stability of the clay particles is improved, the clay particles keep smaller particle size and have reasonable particle size distribution, a thin and tough high-quality filter cake with a compact structure is generated, and the filtration loss is reduced.

Test example 4

Drilling fluid properties for examples 4-7 and comparative examples 4-6 are shown in Table 4.

TABLE 4 drilling fluid Performance for examples 4-7 and comparative examples 4-6

In table 4, Φ 3 refers to the six-speed rotational viscometer 3-revolution reading, dimensionless; the high-temperature high-pressure water loss refers to the water loss volume of 3.5MPa, corresponding to the aging temperature and 30 min.

As can be seen from Table 4, the drilling fluid for shale gas provided by the invention has the performance capable of meeting the drilling requirement of a shale gas horizontal well.

Test example 5

In order to evaluate the influence of the drilling fluid for shale gas on the stability of the shale borehole wall, the shale core is soaked in the drilling fluid respectively in comparative examples 4 to 6 and examples 4 to 7, and the compressive strength, the cohesion and the internal friction angle of the core are respectively tested under the conditions of the confining pressure of 20MPa and the confining pressure of 40MPa, and the results are shown in the figures 1-2. FIG. 1 illustrates the change in compressive strength of shale when soaked in different drilling fluid systems; FIG. 2 shows the characteristics of shale cohesion and internal friction angle under soaking of different drilling fluid systems. Wherein the original parameters in fig. 1-2 refer to the uninflated shale core.

After the shale core is soaked in different fluids, the strength characteristics of the rock sample change. The data in figures 1-2 show that after the polymer potassium chloride drilling fluid is soaked, when the confining pressure is 20MPa, the compressive strength of the shale core is reduced by 48.8% compared with the original compressive strength, the oil-based drilling fluid is reduced by 22.7%, while the drilling fluid for shale gas is reduced by about 22.8%, and the drilling fluid for shale gas is reduced by 43.8% compared with the drilling fluid for shale gas; after soaking, the internal friction angle and the cohesion of the rock core and the rock compression resistance are respectively reduced by 62.1 percent and 34.4 percent through a polymer potassium chloride drilling fluid system, 36.6 percent and 7.0 percent through an oil-based drilling fluid, 37.2 percent and 7.2 percent through a drilling fluid for shale gas, and 60.0 percent and 29.0 percent through a comparative example 6.

From the above data, it can be seen that the effect on rock strength after soaking shale gas with a drilling fluid approaches an oil base, indicating that the drilling fluid for shale gas has a comparable ability to stabilize the borehole wall as the oil base. The drilling fluid for shale gas has a significantly better ability to stabilize the borehole wall than the polymeric potassium chloride drilling fluid and the water-based drilling fluid provided in comparative example 6. The main reason why the well wall stabilizing capability of the drilling fluid for shale gas is close to that of an oil-based drilling fluid is that amino acid with positive charges in the multifunctional liquid rapidly controls the most active hydration point and is firmly fixed on the surface of clay particles to prevent the surface of the clay particles from hydrating and permeating hydration, meanwhile, the hydrophobic section assists in inhibiting hydration, the hydration stress generated when filtrate enters a stratum is reduced, the increase degree of the pore pressure of the stratum is reduced, meanwhile, nanoparticles in the multifunctional liquid can effectively plug stratum microcracks, the filtrate is further prevented from invading the stratum, the increase degree of the water content of the stratum caused by the invasion of the filtrate is reduced, the decrease degree of rock strength is inhibited, and the effect of effectively stabilizing the well wall is achieved.

According to the test results of the embodiment and the comparative example, the drilling fluid for shale gas provided by the invention can meet the requirements of a shale gas horizontal well on lubrication and well wall stability, and has good inhibition and plugging properties.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.