# Patent

## Title
Reservoir protecting agent composition and broad-spectrum drilling liquid and use thereof

## Abstract

The present subject matter relates to a reservoir protecting agent composition, consisting of non-fluorescent sulfonated asphalt, micron-sized cellulose, and a reservoir protecting agent, wherein, the reservoir protecting agent is composed of structural units denoted by the following formula (1), formula (2), and formula (3). The present subject matter further provides a broad-spectrum drilling fluid that contains the reservoir protecting agent composition. The present subject matter further provides a use of the broad-spectrum drilling fluid in oil and gas well drilling. When the broad-spectrum drilling fluid provided in the present subject matter is used in oil and gas well drilling in reservoirs with different structures, it exhibits good rheology property, temperature tolerance, and anti-collapse and protection performance.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to Chinese Patent Application No. 201510072867.2 filed on Feb. 11, 2015 and entitled “Reservoir Protecting Agent Composition, Broad-Spectrum Drilling Fluid and Use Thereof,” the entire content of which is fully incorporated here by reference.
FIELD OF THE INVENTION
The present subject matter relates to a reservoir protecting agent composition, a broad-spectrum drilling fluid, and use of the broad-spectrum drilling fluid.
BACKGROUND OF THE INVENTION
Drilling fluids are reputed as the blood for bore wells. Good drilling fluid techniques are one of the important guarantees for safe, high-quality, efficient, and quick well drilling production. Drilling fluids are required in the development of oil fields.
Effective reservoir protection is an effective guarantee for improving the rate of oil and gas recovery, so that the skin factor can be an optimal negative value. If the drilling fluid is designed or used inappropriately in the well drilling process, the liquid and solid in the drilling fluid may intrude into the oil reservoir and have physical and chemical reactions with clay and other minerals in the oil and gas layer. Consequently, the permeability in the oil layer in the immediate vicinity of the well may be decreased severely, and the resistance against air and gas flow towards the bottom of the well may be increased, resulting in reduced oil yield.
Usually, reservoirs that are different in permeability from each other have different structural characteristics, and different drilling fluid systems have to be applied for them. For example, the permeability of high/ultra-high permeability reservoirs is 500 mD or above. For high-permeability reservoirs, the permeability can be 500-2,000 mD; for ultra-high permeability reservoirs, the permeability can be 2,000 mD or above. The permeability of medium-permeability reservoirs is 100-200 mD. The permeability of low-permeability reservoirs is 10 ̃100 mD; the permeability of ultra-low permeability reservoirs is lower than 10 mD. Damages to the reservoir may occur owing to many factors, for example, blockage resulted from the solid particles carried by the drilling fluid and particles produced in the drilling process, reservoir damages resulted from hydrated expansion, dispersion and migration of clay minerals; the intrusion of the working filtrate (e.g., drilling fluid) into the reservoir may result in damages such as clay swelling, dispersion and migration, and water blocking, and have impacts on the accuracy of well logging; especially, it will be more difficult to drain off the drilling fluid if the foreign fluid in the drilling fluid has physical and chemical reactions with the reservoir fluid or reservoir rock; consequently, the oil and gas resources in the reservoir may be contaminated. For different reservoirs, damages may occur at different levels. Therefore, a protecting agent that is applicable to a specific reservoir structure often is inapplicable to other reservoir structures.
Up to now, though long-time researches on reservoir protective drilling fluid techniques have been made in China and foreign countries, and techniques such as shielded temporary plugging technique, fractal geometry-based temporary plugging technique, D90 ideal temporary plugging technique, broad-spectrum temporary plugging technique, alkali soluble micron-sized cellulose temporary plugging technique, D50 temporary plugging technique, filming technique, oil film technique, etc., have been developed, the protective effect of these techniques is not ideal for protection of reservoirs different in permeability. These techniques have to be improved further. The root cause is that these techniques don't take consideration of the reservoir damages such as water blocking and water sensitivity incurred by spurt loss, and the plugging effect of these techniques should be further improved under some conditions.
The existing drilling fluids have properties that can essentially meet the requirement for cuttings carrying and well wall stability, but don't provide an ideal reservoir protection effect, and the core permeability recovery value of the reservoir is low. Though temporary plugging agents are added in these drilling fluids, the plugging performance is not high because the matching relation between the pore throat size and the particle size of temporary plugging agent is not taken into consideration fully. Consequently, the filtrate may intrude into the reservoir and thereby results in damages such as water sensitivity and water blocking, etc.
SUMMARY OF THE INVENTION
The present subject matter relates to a reservoir protecting agent composition, a broad-spectrum drilling fluid, and use of the broad-spectrum drilling fluid.


DETAILED DESCRIPTION
Hereunder some embodiments of the present subject matter will be detailed. It should be appreciated that the embodiments described here are only provided to describe and explain the present subject matter, but shall not be deemed as constituting any limitation to the present subject matter.
To overcome the drawbacks in existing drilling fluids used in oil and well drilling in the prior art, the present subject matter provides a reservoir protecting agent composition and a broad-spectrum drilling fluid that are applicable to reservoirs with different structures and have high reservoir protection performance, and use of the drilling fluid.
To attain the objects described above, the present subject matter provides a reservoir protecting agent composition, consisting of non-fluorescent sulfonated asphalt, micron-sized cellulose, and a reservoir protecting agent, wherein, the reservoir protecting agent is composed of structural units denoted by formula (1), (2), and (3):




wherein, R1, R2, R3, R4, and R5 independently are H, C1-C4 alkyl or C1-C4 alkoxyl; R6 is C1-C6 alkyl; R6′ is H or C1-C4 alkyl; R7 is C1-C10 alkyl; M is H or an alkali metal; a molar ratio of the structural units denoted by formula (1):the structural units denoted by formula (2):the structural units denoted by formula (3) is 1:0.3-1.5:0.3-1; a weight-average molecular weight of the protecting agent is 60,000-70,000 g/mol.

The present subject matter further provides a broad-spectrum drilling fluid containing the above-mentioned reservoir protecting agent.
The present subject matter further provides use of the broad-spectrum drilling fluid in oil and gas well drilling.
When the broad-spectrum drilling fluid containing the reservoir protecting agent composition according to the present subject matter is used in oil and gas well drilling in reservoirs with different structures, it exhibits good rheology property, temperature tolerance, anti-collapse and protection performance.
Other aspects and advantages of the present subject matter will be further detailed in the embodiments hereunder.
The present subject matter provides a reservoir protecting agent composition, comprising non-fluorescent sulfonated asphalt, a micron-sized cellulose, and a reservoir protecting agent, wherein, the reservoir protecting agent is composed of structural units denoted by formula (1), (2), and (3):




wherein, R1, R2, R3, R4, and R5 independently are H, C1-C4 alkyl or C1-C4 alkoxyl; R6 is C1-C6 alkyl; R6′ is H or C1-C4 alkyl; R7 is C1-C10 alkyl; M is H or an alkali metal; a molar ratio of the structural units denoted by formula (1):the structural units denoted by formula (2):the structural units denoted by formula (3) is 1:0.3-1.5:0.3-1; a weight-average molecular weight of the protecting agent is 60,000-70,000 g/mol.

Usually, when a drilling fluid is prepared, the structural characteristics of different reservoirs should be taken into consideration appropriately. Different drilling fluid formulations should be selected for reservoirs in different structures. Especially, to protect the reservoir more effectively, great efforts must be made to develop a protecting agent for protecting the reservoir according to the structural characteristics of the reservoir, such as pore size, pore throat size, well temperature, etc. To that end, through long-term practice and in-depth analysis and research, the inventor has found: when a composition composed of the non-fluorescent sulfonated asphalt, a micron-sized cellulose, and a reservoir protecting agent according to the present subject matter is used as a protecting agent in a drilling fluid, the drilling fluid can be applied for protection of reservoirs in a wide range of permeability, without special consideration of the matching between the protecting agent and a specific reservoir structure. It is conjectured that the reason may be: the micron-sized cellulose in the composition has some directional effect in the drilling fluid flow process and always tends to get close to the area in vicinity of the well wall where the shearing rate is the lowest; in addition, the non-fluorescent sulfonated asphalt can attach to the surface of reservoir rock quickly and fill up pore throats and fractures, and can cover the rock surface and improve the quality of mud cakes. Thus, the micron-sized cellulose and the non-fluorescent sulfonated asphalt can work with each other to accomplish temporary plugging in low-permeability, medium-permeability, or high-permeability reservoirs, leaving enough time for the reservoir protecting agent to concentrate and form colloidal particles so as to achieve further rock plugging and protection.
There is no particular restriction on the non-fluorescent sulfonated asphalt in the present subject matter. In other words, the non-fluorescent sulfonated asphalt can be any conventional non-fluorescent sulfonated asphalt in the art, such as FT-1 from Zhengzhou Yuhua Auxiliaries Co., Ltd., China, FT-1 from Shandong Yanggu Jiangbei Chemicals Co., Ltd., China, and FT-1 from Shandong Dongying Guangyun Industry and Trade Co., Ltd., China.
According to the present subject matter, the micron-sized cellulose can accomplish plugging of smaller pore throats and fractures, and can fill up larger pore throats and fractures by curling. In addition, some fibrous particles can enter into pore throats or fractures near the well wall and improve the strength and integrality of mud cakes, so that the mud cakes have high erosion resistance capability. The micron-sized cellulose can be any conventional micron-sized cellulose in the art, such as the micron-sized cellulose from Henan Luyuan Co., Ltd., China, the micron-sized cellulose from Shenzhen Shenruipu Technology Co., Ltd., China, and the micron-sized cellulose from Baoji Fiber Co., Ltd., China.
To attain a better plugging effect, in another embodiment, the micron-sized cellulose is in a granular form in 10-30 μm diameter, 2-200 μm length (more preferably 50-150 μm), and 20-60 μm median grain diameter.
To improve the synergy among the three components in the composition, in another embodiment, the weight ratio of the reservoir protecting agent, the micron-sized cellulose, and the non-fluorescent sulfonated asphalt is 100:100-200:100-200, and more preferably is 100:100-150:100-150.
According to the present subject matter, the reservoir protecting agent can work with the non-fluorescent sulfonated asphalt and the micron-sized cellulose to form a polymer film on the reservoir rock. The reservoir protecting agent is an amphiphilic polymer, which contains hydrophilic sulfonate groups and a large quantity of benzene rings and hydrophobic acrylate groups. When the amphiphilic polymer serving as the reservoir protecting agent is used with the non-fluorescent sulfonated asphalt and the micron-sized cellulose together in the drilling fluid for well drilling, the strongly hydrophilic sulfonate groups will attach to the surface of the clay, so that the hydrated film on the surface of the clay is thickened, and thereby the diffused electric doublet layer on the surface of the clay is enhanced, and flocculation or agglomeration of the clay incurred by high temperature and high-salinity electrolytes can be effectively prevented. Hence, the protecting agent can endow the drilling fluid with outstanding temperature tolerance, salinity tolerance, and filter loss reduction properties. In addition, the hydrophilic sulfonate groups can attach to the surface of reservoir rock and overlying clay shale, while the hydrophobic groups extend outward from the rock surface; thus, a hydrophobic film can be formed on the rock surface. The hydrophobicity can inhibit the permeation of free water in the drilling fluid into the reservoir rock and clay shale. Thus, on one hand, the reservoir is protected against the damages from the drilling fluid; on the other hand, the hydrated expansion and dispersion of the clay shale can be inhibited.
According to the present subject matter, to obtain a polymer serving as a reservoir protecting agent for drilling fluid with higher performance, in another embodiment, in the structural units denoted by formula (1), (2), and (3), which constitute the protecting agent, R1, R2, R3, R4, and R5 independently are H, C1-C3 alkyl or C1-C3 alkoxyl. In another embodiment, R1, R2, R3, R4, and R5 independently are H, methyl, ethyl, methoxyl or ethyoxyl; further in another embodiment, R1, R2, R3, R4, and R5 are H, methyl or ethyl.
According to the present subject matter, R6 preferably is C1-C4 alkyl, and more preferably is methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or tert-butyl.
According to the present subject matter, R6′ preferably is H, methyl or ethyl, and more preferably is H or methyl.
According to the present subject matter, R7 preferably is C2-C10 alkyl, more preferably is C2-C8 alkyl, further more preferably is C2-C7 alkyl, still further more preferably is —CH2—C(CH3)2—CH2—, —C(CH3)2—CH2—, —CH2—C(CH3)2—, —CH2—C(CH3)2—CH2—CH2—, —CH2—CH2—, —CHCH3—CH2— or —CH2—CHCH3—CH2—, and particularly preferably is —C(CH3)2—CH2—.
According to the present subject matter, M preferably is H, Na, K or Li, and more preferably is H or Na.
In another embodiment of the present subject matter, in the structural units denoted by formula (1), (2), and (3), which constitute the amphiphilic polymer, R1, R2, R3, R4, and R5 are H, R6 is n-butyl, R6′ is H, and R7 is —C(CH3)2—CH2—.
In another embodiment of the present subject matter, in the structural units denoted by formula (1), (2), and (3), which constitute the amphiphilic polymer, R1, R2, R4, and R5 are H, R3 is methyl, R6 is ethyl, R6′ is H, and R7 is —C(CH3)2—CH2—.
In another embodiment of the present subject matter, in the structural units denoted by formula (1), (2), and (3), which constitute the amphiphilic polymer, R1, R2, R3, R4, and R5 are H, R6 is ethyl, R6′ is H, and R7 is —C(CH3)2—CH2—.
In another embodiment, the weight-average molecular weight of the reservoir protecting agent is 64,000-70,000 g/mol. In another embodiment, the molecular weight distribution coefficient Mw/Mn of the reservoir protecting agent is 1.1-1.3.
According to the present subject matter, to balance the effect of the hydrophobic end and the effect of the hydrophilic end in the reservoir protecting agent and enhance the cooperation between the protecting agent and the non-fluorescent sulfonated asphalt to attain the objective of reservoir plugging, in another embodiment, in the protecting agent, the molar ratio of the structural units denoted by formula (1):the structural units denoted by formula (2):the structural units denoted by formula (3) is 1:0.4-1:0.3-0.7.
According to the present subject matter, the reservoir protecting agent can be prepared through any conventional polymerization reaction, as long as the obtained reservoir protecting agent has the structure and composition characteristics required in the present subject matter. In another embodiment, the method for preparation of the reservoir protecting agent in the present subject matter comprises: in presence of an initiator, subjecting a chemical compound represented by formula (4), a chemical compound represented by the formula (5), and a chemical compound represented by formula (6) to contact with an emulsifier in water to obtain an emulsified mixture and have a polymerization reaction, at a molar ratio of the chemical compound represented by formula (4):the chemical compound represented by the formula (5):the chemical compound represented by formula (6) equal to 1:0.3-1.5:0.3-1; the weight-average molecular weight of the polymer obtained through the polymerization reaction is 60,000-70,000 g/mol;




wherein, R1, R2, R3, R4, and R5 independently are H, C1-C4 alkyl or C1-C4 alkoxyl; R6 is C1-C6 alkyl; R6′ is H or C1-C4 alkyl; R7 is C1-C10 alkyl; M is H or an alkali metal.

Wherein, the structural units of the reservoir protecting agent depend on the chemical compound represented by formula (4), the chemical compound represented by formula (5), and the chemical compound represented by formula (6); the chemical compound represented by formula (4), the chemical compound represented by formula (5), and the chemical compound represented by formula (6) can be selected according to the desired structure of the reservoir protecting agent. Moreover, R1, R2, R3, R4, R5, R6, R6′, R7, and M are preferably selected within the scopes described above.
In another embodiment, the chemical compound represented by formula (4) is one or more of styrene, p-methyl styrene, and p-ethyl styrene.
In another embodiment, the chemical compound represented by formula (5) is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, and propyl methacrylate.
In another embodiment, the chemical compound represented by formula (6) is one or more of 2-acrylamide-2-methyl propanesulfonic acid and 2-acrylamide propanesulfonic acid.
In another embodiment, the molar ratio of the chemical compound represented by formula (4):the chemical compound represented by formula (5):the chemical compound represented by formula (6) is 1:0.4-1:0.3-0.7.
The polymerization reaction among the chemical compound represented by formula (4), the chemical compound represented by formula (5), and the chemical compound represented by formula (6) is an emulsion polymerization reaction actually. Hence, an emulsifier must be added in the polymerization reaction. To enable the above monomers to have a reaction among them more uniformly and more completely, in the present subject matter, in another embodiment, the chemical compound represented by formula (4), the chemical compound represented by formula (5), and the chemical compound represented by formula (6) are mixed with water to form a mixture, and then an emulsifier is added into the mixture to obtain an emulsified mixture.
Wherein, based on the total weight of the emulsified mixture, the total content amount of the chemical compound represented by formula (4), the chemical compound represented by formula (5), and the chemical compound represented by formula (6) preferably is 55-65 wt. %. In another embodiment, the content amount of the chemical compound represented by formula (4) is 20-28 wt. %. In another embodiment, the content amount of the chemical compound represented by formula (5) is 10-16 wt. %. In another embodiment, the content amount of the chemical compound represented by formula (6) is 15-28 wt. %.
There is no particular restriction on the emulsifier in the present subject matter, as long as the chemical compound represented by formula (4), the chemical compound represented by formula (5), and the chemical compound represented by formula (6) are controlled to have an emulsion polymerization reaction with the method disclosed in the present subject matter and the protecting agent according to the present subject matter is obtained. In another embodiment, based on the total weight of the emulsified mixture, the concentration of the emulsifier is 4-5 wt. %. In another embodiment, the emulsifier is one or more of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, sodium diisopropyl naphthalene sulfonate, alkylphenol polyoxyethylene ether, and tributylphenol polyoxyethylene ether.
The concentration of the initiator can vary in a wide range, as long as the reservoir protecting agent disclosed in the present subject matter can be obtained. In another embodiment, based on the total weight of the emulsified mixture, the concentration of the initiator is 0.4-0.55 wt. %. In another embodiment, the initiator is one or more of azodiisobutyronitrile, dilauroyl peroxide, potassium persulfate, ammonium persulfate, benzoyl peroxide, and hydrogen peroxide.
In view of the high activity of the initiator, in the present subject matter, an inactive gas can be fed into the reaction system to expel oxygen in the reaction system and thereby keep the polymerization reaction in inert atmosphere before the polymerization reaction, wherein, the inactive gas is a gas that will not participate in the polymerization reaction and can expel oxygen, such as nitrogen, helium, or neon, etc. The inactive gas can be fed for 25-50 min, for example.
Likewise, to control the reaction rate of the polymerization reaction, preferably the emulsified mixture is heated up to 60-70° C. before the inactive gas is fed; then, the initiator can be added, and the polymerization reaction can be started.
According to the present subject matter, preferably, the conditions of the polymerization reaction include: temperature is 70-85° C., time is 4-5.8 h. Through a polymerization reaction under such conditions, a reservoir protecting agent that is especially suitable for the composition in the present subject matter can be obtained.
The reservoir protecting agent according to the present subject matter can be obtained after the polymerization reaction. To extract the reservoir protecting agent, the resultant mixed solution can be cooled after the polymerization reaction is completed, and the pH of the resultant mixed solution can be adjusted to 8.5-10 with 20-30 wt. % of water solution of an alkali metal hydroxide (e.g., water solution of sodium hydroxide, or water solution of potassium hydroxide, etc.) to obtain a precipitate; then, the precipitate can be separated from the mixed solution and dried at 95-105° C., so as to obtain a solid protecting agent, which can be used as the reservoir protecting agent for drilling fluid in the present subject matter.
The present subject matter further provides a broad-spectrum drilling fluid, which contains the reservoir protecting agent composition described above.
With the reservoir protecting agent composition as a major protecting agent component, especially, with the reservoir protecting agent composition as the sole protecting agent component, the broad-spectrum drilling fluid provided in the present subject matter can be applied for protection of reservoirs in various ranges of permeability. Therefore, those skilled in the art can appreciate that the drilling fluid is reputed as a “broad-spectrum drilling fluid”.
To give a better play to the reservoir plugging and protection effect of the reservoir protecting agent composition in the oil and gas well drilling process, preferably, the content amount of the reservoir protecting agent composition is 2-3 wt. % of in the drilling fluid.
There is no particular restriction on the drilling fluid system that contains the reservoir protecting agent composition in the present subject matter. In other words, the drilling fluid system can be any conventional drilling fluid system in the art, as long as the reservoir protecting agent composition according to the present subject matter is added into the conventional drilling fluid system. As such a conventional drilling fluid system, for example, the drilling fluid can be one or more of potassium chloride-poly alcohol drilling fluid, organosilicon drilling fluid, and cationic drilling fluid. The potassium chloride-poly alcohol drilling fluid can be any potassium chloride-poly alcohol drilling fluid well known to those skilled in the art; for example, it can be one or more of potassium chloride-polyethylene glycol drilling fluid, potassium chloride-polypropylene glycol drilling fluid, potassium chloride-ethylene glycol/propylene glycol copolymer drilling fluid, potassium chloride-polyglycerol drilling fluid and potassium chloride-polyvinyl glycol drilling fluid. The organosilicon drilling fluid can be any organosilicon drilling fluid well known to those skilled in the art, and the organosilicon in the organosilicon drilling fluid can be selected from one or more of sodium methylsiliconate, potassium methylsiliconate, and silicone-potanssium humate. The cationic drilling fluid can be any cationic drilling fluid well known to those skilled in the art; for example, the cations in the cationic drilling fluid can be selected from one or more of 2,3-epoxypropyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, and cationic polyacrylamide.
In another embodiment, the drilling fluid according to the present subject matter further contains one or more of bentonite, sodium carbonate, alkali metal hydroxide, inhibitor, temperature-tolerant filtrate reducer, filtrate reducer, temperature-tolerant inhibitor, and flocculant.
Wherein, the bentonite refers to clay which contains montmorillonite as the main mineral component and can endow the drilling fluid with viscous shearing force and filtration and wall building properties. For example, the bentonite can be sodium bentonite and/or calcium bentonite, preferably sodium bentonite. In another embodiment, the content amount of the bentonite is 2-4 wt. %, more preferably 2-3 wt. %.
Wherein, the inhibitor has an effect of inhibiting hydrated expansion of clay minerals in rock. For example, the inhibitor can be one or more of polyamine (CFY-01), potassium polyacrylate, and potassium-ammonium hydrolyzed polyacrylonitrile. In another embodiment, the content amount of the inhibitor is 3-4 wt. %.
Wherein, the temperature-tolerant filtrate reducer has an effect of reducing filter loss in drilling fluid and is temperature tolerant. For example, the temperature-tolerant filtrate reducer can be one or more of humic acid resin and polyanionic cellulose. In another embodiment, the content amount of the temperature-tolerant filtrate reducer is 2-3 wt. %.
Wherein, the filtrate reducer has an effect of reducing filter loss in drilling fluid. For example, the filtrate reducer can be one or more of polyethylene glycol, low-viscosity polyanionic cellulose, hydroxypropyl starch, and compound cellulose. In another embodiment, the content amount of the filtrate reducer is 5-8 wt. %.
Wherein, the temperature-tolerant inhibitor has an effect of inhibiting hydrated expansion of clay minerals in rock. For example, the temperature-tolerant inhibitor can be one or more of sulfonated phenolic resin and sulfomethylated phenolic resin. In another embodiment, the content amount of the temperature-tolerant inhibitor is 3-7 wt. %.
Wherein, the flocculant is mainly used to neutralize some electronegative or electropositive particles or grains that are difficult to separate in water with electropositive or electronegative groups to decrease the electric potential of the particle or grains and keep them in a stable state, and utilize its aggregation property to concentrate the particles or grains, so that the particles or grains can be separated physically or chemically. For example, the flocculant can be one or more of polyacrylamide and sodium polyacrylate. In another embodiment, the content amount of the flocculant is 0.2-3 wt. %.
The above additives can be commercially available products, or can be prepared with conventional methods in the art. They will not be further detailed hereunder.
In the drilling fluid according to the present subject matter, in another embodiment, the content amount of NaCl is 3-4 wt. %. In another embodiment, the content amount of sodium carbonate is 0.1-0.3 wt. %. In another embodiment, the content amount of the alkali metal hydroxide is 0.3-0.5 wt. % (as a component of the drilling fluid, the alkali metal hydroxide can improve the mud-making performance of the bentonite, and can be one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide, and preferably is sodium hydroxide).
In another embodiment of the present subject matter, a drilling fluid is provided, which contains 2-3 wt. % of reservoir protecting agent composition, 2-3 wt. % of bentonite, 3-4 wt. % of polyamine inhibitor, 2-3 wt. % of sulfomethylated phenolic resin, 5-8 wt. % of polyethylene glycol, 3-4 wt. % of NaCl, 0.1-0.3 wt. % of sodium carbonate, 0.3-0.5 wt. % of NaOH, 3-4 wt. % of sulfonated phenolic resin, 0.5-1 wt. % of low-viscosity polyanionic cellulose, and 0.2-0.5 wt. % of polyacrylamide.
The present subject matter further provides a use of the broad-spectrum drilling fluid in oil and gas well drilling.
When the broad-spectrum drilling fluid is used in oil and gas well drilling, the synergetic effect of the three components in the reservoir protecting agent composition can be effectively leveraged so as to protect the reservoir effectively. The broad-spectrum drilling fluid is applicable to protection of reservoirs different in permeability, and is especially suitable for protection of reservoirs with 5-2,000 mD permeability.
Hereunder the present subject matter will be further detailed in some embodiments.
In the following examples, the weight-average molecular weight is measured with a gel permeation chromatograph (GPC) (GPC Model E2695 from Waters Company (a USA company)); the molecular weight distribution coefficient is the ratio of the weight-average molecular weight to the number-average molecular weight measured with the GPC.
Preparation Example 1
Add styrene (62 g, 0.59 mol), butyl acrylate (35.6 g, 0.28 mol) and 2-acrylamide-2-methyl propanesulfonic acid (42.1 g, 0.2 mol) into 100 mL water to form a primary mixture, add 5.9 g of sodium dodecyl benzene sulfonate (from Chengdu Micxy Chemicals Co., Ltd.) to obtain an emulsified mixture, feed nitrogen for 30 min into the emulsified mixture, heat up the emulsified mixture to 70° C. and add 0.6 g of ammonium persulfate into it, and then further heat up the emulsified mixture to 75° C. and keep it at the temperature for 5 h; after the reaction is completed, cool down the reaction solution to 30° C., add 20 wt. % of water solution of sodium hydroxide to adjust the pH to 8.5, and then add 10 mL methanol and stir to obtain a precipitate; dry the obtained precipitate at 100° C. and grind it into powder; thus, 131 g solid protecting agent A1 (yellowish powder) in 0.7-0.8 μm particle size is obtained, which is the protecting agent described in the present subject matter. The weight-average molecular weight of the protecting agent is 67,521 g/mol, and the molecular weight distribution coefficient is 1.3; analyzed by H-NMR spectroscopy and C-NMR spectroscopy, the polymer contains structural units denoted by formula (1), structural units denoted by formula (2), and structural units denoted by formula (3) at 1:0.47:0.34 mole ratio.
Preparation Example 2
Add p-methyl styrene (52 g, 0.44 mol), ethyl acrylate (25.6 g, 0.26 mol) and 2-acrylamide-2-methyl propanesulfonic acid (62.1 g, 0.3 mol) into 100 mL water to form a primary mixture, add 6.7 g of sodium dodecyl sulfate (from Zibo Jujin Chemicals Co., Ltd., China) to obtain an emulsified mixture, feed nitrogen for 30 min into the emulsified mixture, heat up the emulsified mixture to 75° C. and add 0.7 g of azodiisobutyronitrile into it, and then further heat up the emulsified mixture to 85° C. and keep it at the temperature for 4.5 h; after the reaction is completed, cool down the reaction solution to 30° C., add 30 wt. % of water solution of sodium hydroxide to adjust the pH to 9.5, and then add 10 mL methanol and stir to obtain a precipitate; dry the obtained precipitate at 100° C. and grind it into powder; thus, 145 g solid protecting agent A2 (yellowish powder) in 0.7-0.8 μm particle size is obtained, which is the protecting agent described in the present subject matter. The weight-average molecular weight of the protecting agent is 64,582 g/mol, and the molecular weight distribution coefficient is 1.3; analyzed by H-NMR spectroscopy and C-NMR spectroscopy, the polymer contains structural units denoted by formula (1), structural units denoted by formula (2), and structural units denoted by formula (3) at 1:0.59:0.68 molar ratio.
Preparation Example 3
Add styrene (52 g, 0.5 mol), methyl acrylate (38.4 g, 0.45 mol) and 2-acrylamide-2-methyl propanesulfonic acid (62.1 g, 0.3 mol) into 100 mL water to form a primary mixture, add 6.5 g of sodium diisopropyl naphthalene sulfonate (from Sichuan Cloud Bird Technology Development Co., Ltd., China, the same below) to obtain an emulsified mixture, feed nitrogen for 40 min into the emulsified mixture, heat up the emulsified mixture to 70° C. and add 0.8 g of dilauroyl peroxide into it, and then further heat up the emulsified mixture to 75° C. and keep it at the temperature for 5.5 h; after the reaction is completed, cool down the reaction solution to 35° C., add 25 wt. % of water solution of sodium hydroxide to adjust the pH to 9, and then add 10 mL methanol and stir to obtain a precipitate; dry the obtained precipitate at 100° C. and grind it into powder; thus, 142 g solid protecting agent A3 (yellowish powder) in 0.6-0.75 μm particle size is obtained, which is the protecting agent described in the present subject matter. The weight-average molecular weight of the protecting agent is 68,427 g/mol, and the molecular weight distribution coefficient is 1.2; analyzed by H-NMR spectroscopy and C-NMR spectroscopy, the polymer contains structural units denoted by formula (1), structural units denoted by formula (2), and structural units denoted by formula (3) at 1:0.9:0.6 molar ratio.
Comparative Preparation Example 1
Add styrene (31.2 g, 0.3 mol), butyl acrylate (25.6 g, 0.2 mol) and 2-acrylamide-2-methyl propanesulfonic acid (31 g, 0.15 mol) into 100 mL water to form a primary mixture, add 3 g of sodium dodecyl benzene sulfonate to obtain an emulsified mixture, feed nitrogen for 30 min into the emulsified mixture, heat up the emulsified mixture to 65° C. and add 0.3 g of ammonium persulfate into it, and then further heat up the emulsified mixture to 70° C. and keep it at the temperature for 4 h; after the reaction is completed, cool down the reaction solution to 40° C., add 20 wt. % of water solution of sodium hydroxide to adjust the pH to 9, and then add 5 mL methanol and stir to obtain a precipitate; dry the obtained precipitate at 100° C. and grind it into powder; thus, 77 g solid protecting agent B1 (yellowish powder) is obtained, which is the protecting agent described in the present subject matter. The weight-average molecular weight of the protecting agent is 55,346 g/mol, and the molecular weight distribution coefficient is 1.3; analyzed by H-NMR spectroscopy and C-NMR spectroscopy, the polymer contains structural units denoted by formula (7), structural units denoted by formula (8), and structural units denoted by formula (9) at 1:0.67:0.5 molar ratio.
Comparative Preparation Example 2
Add styrene (52 g, 0.5 mol), methyl acrylate (51.2 g, 0.6 mol) and 2-acrylamide-2-methyl propanesulfonic acid (41.4 g, 0.2 mol) into 100 mL water to form a primary mixture, add 7.5 g of sodium diisopropyl naphthalene sulfonate to obtain an emulsified mixture, feed nitrogen for 40 min into the emulsified mixture, heat up the emulsified mixture to 65° C. and add 1.5 g of dilauroyl peroxide into it, and then further heat up the emulsified mixture to 70° C. and keep it at the temperature for reaction for 6.5 h; after the reaction is completed, cool down the reaction solution to 40° C., add 25 wt. % of water solution of sodium hydroxide to adjust the pH to 9, and then add 3.5 mL methanol and stir to obtain a precipitate; dry the obtained precipitate at 100° C. and grind it into powder; thus, 121 g solid protecting agent B2 (yellowish powder) in 0.6-0.7 μm particle size is obtained, which is the protecting agent described in the present subject matter. The weight-average molecular weight of the protecting agent is 75,347 g/mol, and the molecular weight distribution coefficient is 1.3; analyzed by H-NMR spectroscopy and C-NMR spectroscopy, the polymer contains structural units denoted by formula (1), structural units denoted by formula (2), and structural units denoted by formula (3) at 1:1.2:0.4 molar ratio.
Examples 1-3
These examples are provided here to describe the reservoir protecting agent composition and drilling fluid according to the present subject matter. Prepare drilling fluids Y1-Y3 with the following formulation: 3 wt. % of protecting agent composition (see Table 1 for the composition), 2 wt. % of sodium bentonite (from Zhengzhou Huajing Chemicals Co., Ltd., China), 3.5 wt. % of polyamine inhibitor (from Zhengzhou Huajing Chemicals Co., Ltd., China), 2.5 wt. % of sulfomethylated phenolic resin (from Zhengzhou Huajing Chemicals Co., Ltd., China), 5.5 wt. % of polyethylene glycol (PEG from Zhengzhou Huajing Chemicals Co., Ltd., China, the same below), 4 wt. % of sulfonated phenolic resin (from Zhengzhou Huajing Chemicals Co., Ltd., China), 1 wt. % of low-viscosity cellulose polyanionic cellulose (from Zhengzhou Huajing Chemicals Co., Ltd., China), 0.2 wt. % of polyacrylamide (from Zhengzhou Huajing Chemicals Co., Ltd., China), 0.8 wt. % of NaCl, 0.3 wt. % of Na2CO3, 0.2 wt. % of NaOH, and water (remaining content amount).
Example 4
This example is provided here to describe the reservoir protecting agent composition and drilling fluid according to the present subject matter. Prepare drilling fluid Y4 with the following formulation: 2 wt. % of protecting agent composition (see Table 1 for the composition), 3 wt. % of bentonite, 0.2 wt. % of Na2CO3, 0.2 wt. % of NaOH, 0.5 wt. % of sulfomethylated phenolic resin, 6 wt. % of KCl, 2.5 wt. % of hydroxypropyl starch (from Yanggu Longquan Chemicals Co., Ltd., China), 3 wt. % of sodium polyacrylate (from Yanggu Longquan Chemicals Co., Ltd., China), 0.6 wt. % of polyanionic cellulose, and 2 wt. % of polyethylene glycol.
Comparative Example 1
Prepare with the method described in example 1, but without adding reservoir protecting agent composition, to obtain a drilling fluid DY1.
Comparative Example 2
Prepare with the method described in embodiment 1, but the protecting agent composite does not contain non-fluorescent sulfonated asphalt (see Table 1 for the composition), to obtain a drilling fluid DY2.
Comparative Example 3
Prepare with the method described in example 1, but the protecting agent composition does not contain a reservoir protecting agent (see Table 1 for the composition), to obtain a drilling fluid DY3.
Comparative Example 4
Prepare with the method described in example 1, but the protecting agent composition does not contain a micron-sized cellulose (see Table 1 for the composition), to obtain a drilling fluid DY4.
Comparative Example 5
Prepare with the method described in example 1, but the composition of the reservoir protecting agent composition is that shown in Table 1, to obtain a drilling fluid DY5.
Comparative Example 6
Prepare with the method described in example 1, but the composition of the reservoir protecting agent composition is that shown in Table 1, to obtain a drilling fluid DY6.











TABLE 1









Weight Ratio of






Protecting agent:



Reservoir 
Cellulose Manufacturer
Non-Fluorescent
Cellulose: 



Protecting 
Diameter μm/Length μm/
Sulfonated Asphalt
Non-Fluorescent


Example
agent
Median Grain Diameter μm
Manufacturer
Sulfonated Asphalt







Example 1
A1
Henan Luyuan Co., 
Zhengzhou Yuhua 
100:100:100




Ltd./10-20 μm/
Auxiliaries Co., Ltd.





50-90 μm/20-30 μm




Example 2
A2
Shenzhen Shenpurui 
Shangdong Yanggu 
100:150:100




Technology Co., Ltd./
Jiangbei Chemicals Co.,





20-30 μm/100-150 μm/
Ltd.





30-40 μm




Example 3
A3
Baoji Fiber Co., Ltd./
Shandong Dongying 
100:100:100




15-25 μm/100-150 μm/
Guangyun Industry and 





50-60 μm
Trade Co., Ltd.



Example 4
A1
Henan Luyuan Co., Ltd./
Zhengzhou Yuhua 
100:150:100




10-20 μm/50-90 μm/
Auxiliaries Co., Ltd.





20-30 μm




Comparative
/
/
/
/


example 1






Comparative
A1
The same as example 1
/
100:100:100


example 2






Comparative
/
The same as example 1
The same as example 1
100:100:100


example 3






Comparative
A1
/
The same as example 1
100:100:100


example 4






Comparative
B1
The same as example 1
The same as example 1
The same as example 1


example 5






Comparative
B2
The same as example 1
The same as example 1
The same as example 1


example 6









Test Example 1
Rheology property test: take 400 mL above drilling fluids Y1-Y4 and DY1-DY6 respectively, stir for 5 min at a low speed, and then measure the apparent viscosity (AV, mPa.$), plastic viscosity (PV, mPa.$), dynamic shearing force (YP, Pa), 10 s and 10 min static shearing force, and API water loss under moderate pressure (API, FL, mL) of the drilling fluids respectively as per GB/T16783.1-2006. The results are shown in Table 2.












TABLE 2





Drilling
AV
PV
YP
10 s/10 min
API.FL


Fluid
(mPa.s)
(mPa.s)
(Pa)
(Pa/Pa)
(mL)







Y1
91
53
45
4.5/7  
0.5


Y2
85
55
43
5/6
0.2


Y3
86
57
42
5.5/6.5
0.4


Y4
79
53
46
  5/6.5
0.4


DY1
82
51
41
5/7
6.3


DY2
86
52
42
5.5/7.5
2.1


DY3
84
59
47
  5/6.5
2.2


DY4
81
54
42
5.5/7.5
2.4


DY5
88
51
41
5.5/7  
0.9


DY6
86
55
42
5.5/7  
0.7









It can been seen in Table 2: when the reservoir protecting agent composition according to the present subject matter is used in the drilling fluid, the API filter loss can be reduced to 0.2-0.5 mL. When the reservoir protecting agent composition is not used, the filter loss is maximum, as high as 6.3 mL; when any two of the non-fluorescent sulfonated asphalt, micron-sized cellulose, and reservoir protecting agent are used in combination, the filter loss is 2.1-2.4 mL, which is relatively high; when the protecting agent B1 or B2 is used with the non-fluorescent sulfonated asphalt and micron-sized cellulose in combination, the filter loss is 0.7-0.9 mL, which is also relatively high.
Test Example 2
Temperature tolerance test: take 400 mL above drilling fluids Y1-Y4 and DY1-DY6 respectively, stir for 20 min at a high speed, load the drilling fluids into aging cans and then load the aging cans into a roller furnace and roll for 16 h at 150° C. temperature; then, take out the aging cans and cool down them to room temperature (about 20° C.), stir for 5 min at a high speed, and then measure the apparent viscosity (AV, mPa.$), plastic viscosity (PV, mPa.$), dynamic shearing force (YP, Pa), 10 s and 10 min static shearing force, API water loss under moderate pressure (API.FL, mL), and water loss under high temperature and high pressure (HTHP.FL, mL) of the drilling fluids respectively as per GB/T16783.1-2006. The results are shown in Table 3.













TABLE 3





Drilling
AV
PV
YP
10 s/10 min
API.FL
HTHP.FL


Fluid
(mPa.s)
(mPa.s)
(Pa)
(Pa/Pa)
(mL)
(mL)







Y1
92
51
44
5/7
0.5
1.3


Y2
83
53
46
5.5/6  
0.2
0.5


Y3
84
54
43
  6/6.5
0.4
0.8


Y4
81
54
43
5.5/7  
0.4
1.2


DY1
83
53
47
5.5/7  
6.4
13.7 


DY2
82
55
45
5.5/6.5
0.7
1.6


DY3
80
52
43
5.5/7  
0.6
1.3


DY4
78
55
47
  6/6.5
0.8
1.8


DY5
83
53
43
6.5/7  
0.8
1.9


DY6
87
56
44
5.5/6.5
1.0
2.3









It can been seen in Table 3: when the reservoir protecting agent composition according to the present subject matter is used in the drilling fluid, the API filter loss can be reduced to 0.2-0.5 mL, and the HTHP filter loss can be reduced to 0.5-1.3 mL. When the reservoir protecting agent composition is not used, the API filter loss is maximum, as high as 6.4 mL, and the HTHP filter loss is 13.7 mL; when any two of the non-fluorescent sulfonated asphalt, micron-sized cellulose, and reservoir protecting agent are used in combination, the API filter loss is 0.6-0.8 mL, which is relatively high, and the HTHP filter loss is 1.3-1.8 mL; when the protecting agent B1 or B2 is used with the non-fluorescent sulfonated asphalt and micron-sized cellulose in combination, the API filter loss is 0.8-1 mL, and the HTHP filter loss is 1.9-2.3 mL.
Test Example 3
Assessment of recovery rate of clay shale: add 350 mL above drilling fluids Y1-Y4 and DY1-DY6 and 50 g dry drill cuttings (6-10 mesh drill cuttings dried at 150° C.) into aging cans respectively, and carry out aging at 120° C. for 16 h; filter the mixtures after aging through a 40 mesh sieve and flush with tap water respectively; dry the drill cuttings after flushing at 105° C., weigh, and calculate the recovery rate of clay shale=weight of dried drill cuttings/initial weight of drill cuttings×100%.
Assessment of linear expansion of clay shale: take rock powder obtained through drying and grinding, and prepare the rock powder into core blocks (press for 5 min at 4 MPa pressure) for assessment; start a M4600 linear expansion tester for clay shale, mount the core blocks in the tester, make zero adjustment, and then pour the drilling fluids Y1-Y4 and DY1-DY6 respectively; start the test, and record the linear expansion (mm) once every 0.5 h; compare with a reference solution (distilled water), and calculate the linear expansion reduction rate=(measured height −initial height)/initial height×100%. The results are shown in Table 4.











TABLE 4










Rolling
Linear Expansion




Recovery
Reduction Rate of



Drilling
Rate of Clay
Clay Shale (%)














Fluid
Shale (%)
2 h
4 h
6 h
8 h


















Y1
88
86.1
84.2
82.3
81.2



Y2
87.3
85.4
84.6
82.1
80.2



Y3
86.4
85.3
84.2
82.5
80.7



Y4
87.2
85.7
84.2
82.5
80.4



DY1
89.1
87.9
85.4
84.3
82.5



DY2
85.4
84.2
82.5
81.4
80.6



DY3
87.6
85.4
83.7
81.7
80.3



DY4
86.3
85.4
83.9
82.7
81.1



DY5
87.9
85.4
83.9
81.4
80.4



DY6
86.3
85.7
84.8
82.5
81.7



DY7
87.4
85.1
83.7
82.1
81.3










It can be seen in Table 4: the drilling fluid system has high inhibition capability, wherein, among Y1-Y4, the rolling recovery rate of clay shale is 86% or above, and the 8 h linear expansion reduction rate of clay shale is 80% or above. Thus, the drilling fluid system can meet the requirements in actual drilling.
Test Example 4
Test the reservoir protection performance of the drilling fluids Y1-Y4 and DY1-DY6 in a JHMD-1 HTHP dynamic filter loss tester as per SYT6540-2002 “Method for Lab Assessment of Drilling and Completion Fluids Damaging Oil Formation”. The results are shown in Table 5;
Wherein, the original permeability of the rock core used in the test is the initial value shown in Table 5.












TABLE 5












Recovery Rate of













Permeability/%












Rock
Permeability to Oil/10−3 μm2

After End













Drilling 
Core 
Initial
After
Plugging
After
Face 


Fluid
No.
Value
Plugging
Rate/%
Damage
Cutting
















Y1
1
125.3
5.76
95.4
95.7
97.2


Y2
2
12.5
0.21
98.3
97.1
99.1


Y3
3
542.3
22.78
95.8
94.3
96.5


Y4
4
342.6
22.3
93.5
92.9
94.1


DY1
5
128.7
31.66
75.4
77.5
80.2


DY2
6
52.7
10.38
80.3
81.2
83.2


DY3
7
41.9
7.5
82.1
80.1
82.4


DY4
8
5.9
1.08
81.7
81.2
82.7


DY5
9
78.4
9.88
87.4
88.5
90.4


DY6
10
92.4
10.44
88.7
87.1
91.2


DY7
11
23.4
3.21
86.3
87.2
89.7









It is seen in Table 5: when the reservoir protecting agent composition according to the present subject matter is used in a drilling fluid, a good reservoir plugging effect and high permeability recovery capability can be obtained. For example, the plugging rate can be 93% or above, and the permeability recovery rate can be 94% or above.
In summary, it is obvious that the protecting agent composition has a synergetic effect. When the weight ratio of the protecting agent:cellulose:non-fluorescent sulfonated asphalt is 100:150:100, an optimal reservoir protection effect can be attained. Thus, when the protecting agent composition is used in a drilling fluid, a broad-spectrum reservoir protection effect can be obtained.
While some preferred embodiments of the present invention are described above, the present invention is not limited to the details in those embodiments. Those skilled in the art can make modifications and variations to the technical scheme of the present invention, without departing from the spirit of the present invention. However, all these modifications and variations shall be deemed as falling into the protected domain of the present invention.
In addition, it should be noted that the specific technical features described in above embodiments can be combined in any appropriate form, provided that there is no conflict. To avoid unnecessary repetition, the possible combinations are not described specifically in the present invention.
Moreover, different embodiments of the present invention can be combined freely as required, as long as the combinations don't deviate from the ideal and spirit of the present invention. However, such combinations shall also be deemed as falling into the scope disclosed in the present invention.

## Claims

1. A reservoir protecting agent composition, consisting of non-fluorescent sulfonated asphalt, a micron-sized cellulose, and a reservoir protecting agent, wherein,
the reservoir protecting agent is composed of structural units denoted by formula (1), formula (2), and formula (3):




wherein, R1, R2, R3, R4, and R5 independently are H, C1-C4 alkyl or C1-C4 alkoxyl; R6 is C1-C6 alkyl; R6′ is H or C1-C4 alkyl; R7 is C1-C10 alkyl; M is H or an alkali metal; wherein a molar ratio of the structural units denoted by formula (1):the structural units denoted by formula (2):and the structural units denoted by formula (3) is 1:0.3-1.5:0.3-1; and wherein a weight-average molecular weight of the protecting agent is 60,000-70,000 g/mol.

2. The composition according to claim 1 wherein a weight ratio of the reservoir protecting agent:the micron-sized cellulose:the non-fluorescent sulfonated asphalt is 100:100-200:100-200.

3. The composition according to claim 1 wherein the micron-sized cellulose is in a granular form, in 10-30 μm diameter, 2-200 μm length, and 20-60 μm median grain diameter.

4. The composition according to claim 1 wherein R1, R2, R3, R4, and R5 independently are H, methyl, ethyl, methoxyl or ethyoxyl.

5. The composition according to claim 4 wherein R6 is methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, or tert-butyl.

6. The composition according to claim 4 wherein R6′ is H, methyl, or ethyl.

7. The composition according to claim 5 wherein R6′ is H, methyl, or ethyl.

8. The composition according to claim 4 wherein R7 is —CH2—C(CH3)2—CH2—, —C(CH3)2—CH2—, —CH2—C(CH3)2—, —CH2—C(CH3)2—CH2—CH2—, —CH2—CH2—, —CHCH3—CH2—, or —CH2—CHCH3—CH2—.

9. The composition according to claim 5 wherein R7 is —CH2—C(CH3)2—CH2—, —C(CH3)2—CH2—, —CH2—C(CH3)2—, —CH2—C(CH3)2—CH2—CH2—, —CH2—CH2—, —CHCH3—CH2—, or —CH2—CHCH3—CH2—.

10. The composition according to claim 6 wherein R7 is —CH2—C(CH3)2—CH2—, —C(CH3)2—CH2—, —CH2—C(CH3)2—, —CH2—C(CH3)2—CH2—CH2—, —CH2—CH2—, —CHCH3—CH2—, or —CH2—CHCH3—CH2—.

11. The composition according to claim 7 wherein R7 is —CH2—C(CH3)2—CH2—, —C(CH3)2—CH2—, —CH2—C(CH3)2—, —CH2—C(CH3)2—CH2—CH2—, —CH2—CH2—, —CHCH3—CH2—, or —CH2—CHCH3—CH2—.

12. The composition according to claim 4 wherein M is H, Na, K, or Li.

13. The composition according to claim 11 wherein M is H, Na, K, or Li.

14. The composite according to claim 1 wherein the weight-average molecular weight of the reservoir protecting agent is 64,000-70,000 g/mol.

15. The composite according to claim 14 wherein molecular weight distribution coefficient of the reservoir protecting agent is 1.1-1.3.

16. The composition according to claim 1 wherein the molar ratio of the structural units denoted by formula (1):the structural units denoted by formula (2):the structural units denoted by formula (3) is 1:0.4-1:0.3-0.7.

17. A broad-spectrum drilling fluid containing the reservoir protecting agent composition according to claim 1.

18. The broad-spectrum drilling fluid according to claim 17 wherein the content amount of the reservoir protecting agent composition is 2-3 wt. %.

19. A broad-spectrum drilling fluid for use in oil and gas well drilling according to claim 1.

20. The broad-spectrum drilling fluid for use in oil and gas well drilling to claim 19 wherein the reservoir permeability in the oil and gas well is 5-2,000 mD.