A surface-modified acid-soluble weighting agent, its preparation method and application

Abstract

This invention relates to the field of oil and gas drilling technology, specifically disclosing a surface-modified acid-soluble weighting agent, its preparation method, and its application. The surface-modified acid-soluble weighting agent comprises 80-99 wt% hydroxyapatite and 0.5-3 wt% surface modifier, and has a density of 2.9-3.2 g / cm³. 3 The surface-modified acid-soluble weighting agent of this invention can increase the weight of drilling fluid to 1.7 g / cm³, provided that the acid solubility is ≥80%. 3 It can still maintain good rheological properties, filtration loss, and settling stability, thus achieving the goal of simultaneously ensuring good drilling fluid rheological properties, filtration loss, settling stability, and acid dissolution and plugging effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas drilling technology, and particularly relates to a surface-modified acid-soluble weighting agent, a preparation method and application thereof. BACKGROUND

[0002] In the oil and gas drilling operation, when the formation pressure is high, a weighting agent needs to be added to the drilling fluid to increase the drilling fluid density to balance the formation pressure and maintain the wellbore stability, so as to avoid well collapse, well kick and even blowout accidents, and ensure the safety of drilling.

[0003] In the oil and gas drilling, especially in the drilling process of high-pressure well, the content of solid-phase weighting agent and clay and other fine particles in the drilling fluid is high, and the rheological property is difficult to control. At present, the drilling fluid viscosity and shear force are mainly reduced by adding water dilution or adding viscosity reducer, but this will cause the structure strength of the drilling fluid to be reduced, the suspension capacity of the weighting agent and the cuttings to be reduced, and the barite to be settled, often leading to a vicious cycle of "weighting - viscosity and shear force increasing - dilution and adding dispersant - density decreasing due to settlement - weighting again", and inducing downhole accidents. In the drilling process of the oil and gas reservoir section, not only the weighting agent needs to be used to increase the density of the drilling fluid to balance the formation pressure, but also the problem of post-deposition plugging needs to be considered, that is, the plugging can be removed by acid soaking or other physical and chemical measures during the completion or stimulation operation. Therefore, the drilling fluid weighting agent used in the reservoir drilling needs to consider the weighting effect, the rheological property and the settlement stability of the drilling fluid, and the effective post-deposition plugging.

[0004] Barite is the most commonly used weighting agent for drilling fluid in oilfields at present, and its main component is barium sulfate, and the density can reach 4.3 g / cm 3CN110205104A discloses a strong plugging drilling fluid composition, which contains water, bentonite, Na2CO3, shale inhibitor, filtrate reducer, viscosity reducer, anti-collapse agent, nano plugging agent, lubricant and weighting agent. The shale inhibitor is modified asphalt GLA, the anti-collapse agent is ultra-fine calcium carbonate C80, and the nano plugging agent is polyethylene glycol surface modified nano graphene. The particle size distribution of the shale inhibitor is 10-25 μm, the particle size distribution of the anti-collapse agent is 2-5 μm, and the particle size distribution of the nano plugging agent is 30-80 nm. The content of bentonite is 2-6 parts by weight, the content of Na2CO3 is 0.1-1 part by weight, the content of the shale inhibitor is 1-10 parts by weight, the content of the filtrate reducer is 1-10 parts by weight, the content of the viscosity reducer is 0.1-6 parts by weight, the content of the anti-collapse agent is 1-15 parts by weight, the content of the nano plugging agent is 0.1-5 parts by weight, the content of the lubricant is 0.5-5 parts by weight, and the content of the weighting agent is 90-130 parts by weight. The filtrate reducer is sulfomethyl phenolic aldehyde resin SMP-3, the viscosity reducer is amphoteric ion polymer XY-27, the lubricant is graphite, and the weighting agent is barite.

[0005] However, barite is insoluble in water and acid and cannot be dissolved by acid in reservoir reconstruction, which can cause permanent reservoir damage and seriously affect the development benefit of oil reservoirs.

[0006] High-density weighting agents such as iron ore powder have good weighting effect, but are prone to sedimentation, have poor stability, and are difficult to be dissolved and plugged by acid after entering the reservoir. CN103589412A discloses an oil-based drilling fluid mud cake cleaning fluid for shale gas development, which comprises a cleaning agent, a weighting agent, and water. The weight percentage of each component is as follows: cleaning agent: 10%-30%; weighting agent: 0%-60%; and water: the balance. The cleaning agent is composed of non-ionic surfactants and mutual solvents. The non-ionic surfactants are fatty acid polyoxyethylene ether, polyoxyethylene fatty acid ester, polyoxypropylene fatty acid ester, alkyl phenol polyoxyethylene ether, allyl alcohol polyoxyalkyl ether, fatty acid polyoxyethylene ester, and polyoxyethylene stearate, which can be used alone or in combination. The mutual solvents are methanol, ethanol, isopropyl alcohol, diethylene glycol monobutyl ether, monohydric fatty alcohol, polyhydric fatty alcohol, and polyhydric fatty ether, which can be used alone or in combination. The weighting agent is ultra-fine iron ore powder.

[0007] Calcium carbonate can be dissolved by acid, and is friendly to reservoir. After well completion, the weighting agent around the well wall can be dissolved by acid to achieve plugging removal and reduce reservoir pollution. However, the density of calcium carbonate is low, the solid content required for weighting drilling fluid is high, the interaction between solid particles is strong, the risk of agglomeration is high, the thickening effect is large, and the weighting limit is low. For example, the patent "calcium carbonate spacer fluid for cementing in large porosity and easy leakage oil and gas layer" with publication number CN 09233765A records: a calcium carbonate spacer fluid for cementing in large porosity and easy leakage oil and gas layer, including 100 parts by weight of clean water, 2.4-2.8 parts of flushing agent, 0.13-0.21 parts of diluent, 1.1-5.6 parts of suspension stabilizer, 0.24-3.36 parts of drag reduction agent, 18-205 parts of calcium carbonate weighting agent and 0.05-0.12 parts of defoaming agent; wherein the calcium carbonate weighting agent is composed of 6-10% by mass fraction of light calcium carbonate with particle size of 80-120 mesh, 10-15% of light calcium carbonate with particle size of 120-160 mesh and 75-84% of light calcium carbonate with particle size of 160-200 mesh.

[0008] The tridymic manganese tetroxide has good acid solubility, but its preparation process is special, the particle size is small and easy to agglomerate, and the price is expensive. For example, the patent with the publication number CN114539989A "spherical high-density micro-nano acid-soluble weighting material, its preparation method and application", the weighting material is composed of the following components by mass fraction: 30-70 parts of nano tridymic manganese tetroxide, 30-65 parts of micro tridymic manganese tetroxide, and 0-5 parts of dispersing agent. Further, the dispersing agent is one or more selected from the group consisting of C12-C18 fatty acid, OP-4 and Span80. Further, the nano tridymic manganese tetroxide is prepared by the following steps: taking 50-70 parts by mass of black manganese ore powder and 10-20 mol / L sodium hydroxide solution 20-30 parts by mass, putting into an autoclave, stirring uniformly, then nitrogen gas is passed at 0.5-0.7 MPa, 5-10 parts by mass of octanol and 1-5 parts by mass of butanol are added, heated to 200-220℃ and reacted for 3-4 hours, then filtered, washed, pyrolyzed at 750-900℃ for 1-2.5 hours to obtain nano tridymic manganese tetroxide. Further, the black manganese ore powder is crushed to 100 mesh by black manganese ore powder with a purity of more than 75%. Further, the micro tridymic manganese tetroxide is prepared by the following steps: under the condition of oil bath 98℃-120℃, 40-60 parts by volume of 0.5-1.5 mol / L MnSO4 solution and 20-30 parts by volume of ammonia water are mixed and stirred, pH=10-11.5, after stirring for 0.5-2h, 5-10 parts by volume of 95% ethanol is added, and 1-10 parts by volume of 10% H2O2 is added dropwise; after cooling, filtering, washing and drying, micro tridymic manganese tetroxide is obtained. Further, the volume ratio of ammonia gas to water in the ammonia water is 1:1-1:1.5. Further, the drying is kept at 110-130℃ in the non-blast state of the blast drying oven for 5-7.5h. Further, the weighting material is black-brown liquid, the particle size range is 0.2-15μm, and the median particle size is 6-8μm; preferably, the hydrochloric acid solubility of the weighting agent is greater than 99.50%; preferably, the density of the weighting agent is greater than 4.70g / cm 3 ; preferably, the weighting agent has a high sphericity microstructure, the specific surface area is >1.5m 2 / g; preferably, the magnetic remanence of the weighting agent is <0.0014meu, and the magnetic permeability is <8.5x10 -6 . According to another aspect of the present application, a preparation method of the above-mentioned spherical high-density micro-nano acid-soluble weighting material is provided. The preparation method comprises the following steps: mixing 30-70 parts of nano tridymic manganese tetroxide, 30-65 parts of micro tridymic manganese tetroxide, and 0-5 parts of dispersing agent by mass fraction to obtain a spherical high-density micro-nano acid-soluble weighting material.

[0009] At present, domestic and foreign scholars improve the dispersion effect of weighting agent in drilling fluid by surface modification process, improve the sedimentation stability, that is, by changing the surface properties of the weighting agent, the weighting agent particles have stronger hydrophilicity or lipophilicity, the effect of the solvent layer between the particles is enhanced, the dispersion of the weighting agent particles in the drilling fluid is improved, and the drilling fluid has better suspension stability and other performances. But breakthrough has not been made in the research on reservoir protection type drilling fluid weighting agent used in drilling oil and gas layers.

[0010] Therefore, it is necessary to develop a reservoir-friendly weighting agent considering the weighting effect, drilling fluid performance regulation and post-acid dissolution plugging, so as to realize the dual goals of safe drilling and protection of oil and gas layers. SUMMARY

[0011] In order to overcome the problems of poor sedimentation stability and difficult to plug of the existing barite weighting agent, and the problems of low weighting limit and large thickening effect of the existing acid-soluble calcium carbonate weighting agent, the present application provides a surface-modified acid-soluble weighting agent and a preparation method and application thereof. The density and weighting limit of the surface-modified acid-soluble weighting agent are obviously higher than those of the existing acid-soluble weighting agent calcium carbonate, and the prepared drilling fluid has good rheological property, filtration property and sedimentation stability.

[0012] The technical scheme of the present application is as follows:

[0013] One of the present application provides a surface-modified acid-soluble weighting agent, the weighting agent comprises 80-99wt% hydroxyapatite, 0.5-3wt% surface modifier; the surface modifier comprises ethylenetriamine pentamethylene phosphonic acid sodium salt, which accounts for 50-100wt% of the surface modifier.

[0014] Further, the ethylenetriamine pentamethylene phosphonic acid sodium salt is one or several of ethylenetriamine pentamethylene phosphonic acid disodium, ethylenetriamine pentamethylene phosphonic acid pentasodium, and ethylenetriamine pentamethylene phosphonic acid heptasodium.

[0015] Further, the surface modifier further comprises one or several of aminotrimethylene phosphonic acid tetrasodium, aminotrimethylene phosphonic acid pentasodium, hydroxyethylidene diphosphonic acid disodium, and bis 1, 6-hexylene triamine pentamethylene phosphonic acid sodium, which accounts for 0-50wt% of the surface modifier.

[0016] Further, the weighting agent further comprises other components, and the sum of the weight percentages of hydroxyapatite and the surface modifier is 100%; the other components are one or several of calcium carbonate, dolomite, barite, and quartz.

[0017] Further, the density of the weighting agent is 2.9-3.2g / cm 3 .

[0018] Further, the acid-soluble rate of the weighting agent in a 10% HCl solution is ≥80%.

[0019] The second aspect of the present application provides a preparation method of the surface-modified acid-soluble weighting agent, comprising the following steps:

[0020] (1) mixing hydroxyapatite and other components (when available) in water to obtain an acid-soluble weighting agent suspension;

[0021] (2) adding a surface modifier to the acid-soluble weighting agent suspension obtained in step (1), adjusting the pH value to 7-9, and controlling the modification reaction at 15-95°C;

[0022] (3) filtering, washing, and drying the suspension after the modification reaction in step (2) to obtain the surface-modified acid-soluble weighting agent.

[0023] Further, the stirring speed is controlled to be 100-20000 r / min during the mixing in step (1).

[0024] Further, the pH value is adjusted by adding NaOH in step (2).

[0025] Further, the modification reaction in step (2) is controlled as follows: the stirring speed is 300-12000 r / min, and the reaction time is 0.2-3 h.

[0026] The third aspect of the present application provides the application of the surface-modified acid-soluble weighting agent, i.e., using the weighting agent as a drilling fluid in oil and gas drilling.

[0027] Further, the surface-modified acid-soluble weighting agent is added to the drilling fluid for drilling operations in the oil and gas reservoir section, and the density adjustment range of the weighting agent is controlled to be 1.2 g / cm 3 -1.7 g / cm 3 .

[0028] Further, after the drilling operation in the oil and gas reservoir section is completed, the acidizing fluid or the acid liquid used for acidizing is used for plugging removal.

[0029] Compared with the prior art, the present application mainly has the following beneficial technical effects:

[0030] The surface-modified acid-soluble weighting agent of the present application can be added to the drilling fluid, and under the premise of ensuring good rheological property, filtration property, and sedimentation stability, the density of the drilling fluid is increased to 1.7 g / cm 3, and the acid-soluble rate of the surface-modified acid-soluble weighting agent is greater than or equal to 88%. The surface-modified acid-soluble weighting agent not only can achieve the goal of increasing the drilling fluid density to balance the formation pressure, but also can ensure that the acid liquid used in subsequent completion and stimulation operations can be effectively dissolved after drilling, so as to remove the plugging to the reservoir and effectively protect the reservoir. The surface-modified acid-soluble weighting agent solves the problems that the existing high-density weighting agents such as barite cannot be dissolved by acid and the existing acid-soluble weighting agents such as calcium carbonate can be dissolved by acid but have a low weight limit and a large thickening effect. DETAILED DESCRIPTION

[0031] The application will be described in detail below with reference to the examples.

[0032] The drilling fluid formula used for evaluating the performance of the surface-modified acid-soluble weighting agent in the examples is as follows.

[0033] Formula 1:

[0034] The polymer lubricating anti-sloughing water-based drilling fluid includes the following components by mass:

[0035] 100 parts of water, 4 parts of bentonite, 0.2 parts of sodium hydroxide, 0.12 parts of polyacrylamide, 0.6 parts of sodium carboxymethyl cellulose, 2 parts of asphalt anti-sloughing agent, 1 part of emulsified paraffin, and 1 part of white oil.

[0036] Formula 2:

[0037] The seawater-based anti-sloughing water-based drilling fluid includes the following components by mass:

[0038] 100 parts of seawater, 5 parts of bentonite, 0.25 parts of sodium hydroxide, 0.4 parts of partially hydrolyzed polyacrylamide, 1.5 parts of sodium carboxymethyl cellulose, 2.5 parts of asphalt anti-sloughing agent, 2 parts of extreme pressure lubricant, and 0.7 parts of polyalcohol.

[0039] Example 1

[0040] 1. The surface-modified acid-soluble weighting agent has the following composition:

[0041] 80 wt% of hydroxyapatite, 9.5 wt% of dolomite, 10% of quartz, and 0.5 wt% of ethylenetriamine pentamethylene phosphonic acid disodium.

[0042] 2. The preparation method of the surface-modified acid-soluble weighting agent includes the following steps:

[0043] (1) The hydroxyapatite, dolomite, and quartz are placed in water and stirred at 500 r / min to obtain an acid-soluble weighting agent suspension;

[0044] (2) The acid-soluble weighting agent suspension obtained in step (1) is placed in a 50°C water bath, stirred at 300 r / min, and then ethylenetriamine pentamethylene phosphonic acid disodium is added, followed by the addition of NaOH to adjust the pH value to 7, and the reaction is allowed to proceed for 0.3 h under stirring;

[0045] (3) The suspension obtained after step (2) is filtered, washed, and dried to obtain the surface-modified acid-soluble weighting agent.

[0046] The density of the above surface-modified acid-soluble weighting agent is 3.0 g / cm 3 The formula 1 drilling fluid is weighted to a density of 1.2 g / cm 3 .

[0047] Example 2

[0048] 1. The surface-modified acid-soluble weighting agent comprises:

[0049] 99 wt% hydroxyapatite, 0.8 wt% ethylenetriamine pentamethylene phosphonic acid penta-sodium, and 0.2 wt% amino trimethylene phosphonic acid penta-sodium.

[0050] 2. A method for preparing a surface-modified acid-soluble weighting agent, comprising the following steps:

[0051] (1) Hydroxyapatite is placed in water and stirred at 100 r / min to obtain an acid-soluble weighting agent suspension;

[0052] (2) The acid-soluble weighting agent suspension obtained in step (1) is placed in a 40°C water bath, stirred at 500 r / min, and then ethylenetriamine pentamethylene phosphonic acid penta-sodium and amino trimethylene phosphonic acid penta-sodium are added, followed by the addition of NaOH to adjust the pH value to 7.5, and the reaction is allowed to proceed for 3 h under stirring;

[0053] (3) The suspension obtained after step (2) is filtered, washed, and dried to obtain the surface-modified acid-soluble weighting agent.

[0054] The density of the above surface-modified acid-soluble weighting agent is 3.0 g / cm 3 The formula 2 drilling fluid is weighted to a density of 1.4 g / cm 3 .

[0055] Example 3

[0056] 1. The surface-modified acid-soluble weighting agent comprises:

[0057] 87 wt% hydroxyapatite, 5.5 wt% calcium carbonate, 6% barite, 1 wt% ethylenetriamine pentamethylene phosphonic acid hepta-sodium, 0.3 wt% amino trimethylene phosphonic acid tetra-sodium, and 0.2 wt% hydroxyethylidene diphosphonic acid disodium.

[0058] 2. A method for preparing a surface-modified acid-soluble weighting agent, comprising the following steps:

[0059] (1) Hydroxyapatite, calcium carbonate and barite are placed in water and stirred at 20,000 r / min to obtain an acid-soluble weighting agent suspension;

[0060] (2) The acid-soluble weighting agent suspension obtained in step (1) is placed in a 95°C water bath, stirred and added with seven sodium ethylenetriamine pentamethylene phosphonate, four sodium aminotri(methylene) phosphonate and two sodium hydroxyethylidene diphosphonate, then NaOH is added to adjust the pH value to 9, and the mixture is stirred at 12,000 r / min for 1 h and then stirred at 1,000 r / min for 2 h;

[0061] (3) The suspension after step (2) is filtered, washed and dried to obtain a surface-modified acid-soluble weighting agent.

[0062] The density of the above surface-modified acid-soluble weighting agent is 3.0 g / cm 3 , and the formula 1 drilling fluid is weighted to a density of 1.6 g / cm 3 .

[0063] Example 4

[0064] 1. The surface-modified acid-soluble weighting agent comprises:

[0065] 90 wt% hydroxyapatite, 7% barite, 2 wt% ethylenetriamine pentamethylene phosphonate disodium, 0.5 wt% aminotri(methylene) phosphonate tetrasodium and 0.5 wt% bis 1,6-hexylene triamine pentamethylene phosphonate sodium.

[0066] 2. A method for preparing the same, comprising the following steps:

[0067] (1) Hydroxyapatite and barite are placed in water and stirred at 8,000 r / min to obtain an acid-soluble weighting agent suspension;

[0068] (2) The acid-soluble weighting agent suspension obtained in step (1) is placed in a 15°C water bath, stirred and added with ethylenetriamine pentamethylene phosphonate disodium, aminotri(methylene) phosphonate tetrasodium and bis 1,6-hexylene triamine pentamethylene phosphonate sodium, then NaOH is added to adjust the pH value to 8, and the mixture is stirred at 4,000 r / min for 2 h;

[0069] (3) The suspension is filtered, washed and dried to obtain a surface-modified acid-soluble weighting agent.

[0070] The density of the above surface-modified acid-soluble weighting agent is 3.0 g / cm 3 , and the formula 2 drilling fluid is weighted to a density of 1.7 g / cm 3 .

[0071] Test Example 1

[0072] The acid-solubility of the surface-modified acid-soluble weighting agents prepared in different examples was tested, and the specific results are shown in Table 1.

[0073] Table 1 Acid-solubility of surface-modified acid-soluble weighting agents prepared in different examples

[0074]

[0075] The results in Table 1 show that the acid-solubility of the surface-modified acid-soluble weighting agents prepared in Examples 1-4 reaches 87.9%-97.6% after being soaked in 10% HCl solution for 4h, indicating that they have excellent acid-solubility effect. After the drilling operation in the oil and gas reservoir section is completed, the acid-soluble weighting agents can be used for plugging removal by using acidizing acid or acidic completion fluid, thereby avoiding reservoir pollution caused by solid plugging of reservoir pore throats.

[0076] Test Example 2

[0077] The properties of the drilling fluids of different examples before and after 120℃ / 16h hot rolling were evaluated, and the specific results are shown in Table 2.

[0078] Table 2 Experimental results of performance evaluation of drilling fluids of different examples before and after 120℃ / 16h hot rolling

[0079]

[0080] The results in Table 2 show that the surface-modified acid-soluble weighting agents prepared in Examples 1-4 have good rheological properties of the drilling fluids with densities of 1.2g / cm 3 , 1.4g / cm 3 , 1.6g / cm 3 , and 1.7g / cm 3 , under the premise of acid-solubility reaching 87.9%-97.6%, low plastic viscosity after 120℃ / 16h hot rolling, moderate dynamic shear force, dynamic plastic ratio after hot rolling maintained at 0.38-0.47, which is within the range of 0.36-0.48 recognized by the industry as being able to ensure good wellbore cleaning effect, and sedimentation coefficient less than 0.52, indicating that the drilling fluids have excellent sedimentation stability, and API filtration loss of the drilling fluids after hot rolling is all ≤4.5mL, indicating excellent filtration loss and wall building property. Therefore, the surface-modified acid-soluble weighting agents of the present application achieve the simultaneous guarantee of rheological property, filtration property, sedimentation stability, and acid-solubility effect of the drilling fluids.

Claims

1. A surface-modified acid-soluble weighting agent, characterized by, The weighting agent comprises 80-99wt% hydroxyapatite, 0.5-3wt% surface modifier; the surface modifier comprises sodium salt of ethylenetriamine pentamethylene phosphonic acid, which accounts for 50-100wt% of the surface modifier; the sodium salt of ethylenetriamine pentamethylene phosphonic acid is one or several of disodium ethylenetriamine pentamethylene phosphonic acid, penta-sodium ethylenetriamine pentamethylene phosphonic acid, hepta-sodium ethylenetriamine pentamethylene phosphonic acid.

2. The surface-modified acid-soluble weighting agent of claim 1, wherein, The surface modifier further comprises one or several of tetra-sodium aminotri(methylene) phosphonate, penta-sodium aminotri(methylene) phosphonate, di-sodium hydroxyethylidene diphosphonate, sodium bis 1,6-hexylene triamine pentamethylene phosphonate, which accounts for 0-50wt% of the surface modifier.

3. The surface-modified acid-soluble weighting agent of claim 1, wherein, The weighting agent further comprises other components, which account for 100% of the sum of the weight percentage of hydroxyapatite and surface modifier; the other components are one or several of calcium carbonate, dolomite, barite, quartz.

4. The surface-modified acid-soluble weighting agent of claim 1, wherein, The density of the weighting agent is 2.9-3.2 g / cm 3 .

5. The surface-modified acid-soluble weighting agent of claim 1, wherein, The acid-soluble rate of the weighting agent in a solution with a concentration ≥10% HCl is ≥80%.

6. A method of preparing the surface-modified acid-soluble weighting agent of any one of claims 1-5, characterized in that, The method comprises the following steps: (1) mixing hydroxyapatite and optional other components in water to obtain a suspension of acid-soluble weighting agent; (2) adding a surface modifier to the suspension of acid-soluble weighting agent obtained in step (1), adjusting the pH value to 7-9, and controlling the modification reaction at 15-95℃; (3) filtering, washing and drying the suspension after the modification reaction in step (2) to obtain a surface-modified acid-soluble weighting agent.

7. The method of claim 6, wherein the surface-modified acid-soluble weighting agent is prepared by the steps of: The stirring speed is controlled to be 100-20000r / min during the mixing in step (1).

8. The method of claim 6, wherein the surface-modified acid-soluble weighting agent is prepared by the steps of: The pH value is adjusted by adding NaOH in step (2).

9. The method of claim 6, wherein the surface-modified acid-soluble weighting agent is prepared by the steps of: The modification reaction in step (2) is controlled as follows: the stirring speed is 300-12000r / min, and the reaction time is 0.2-3h.

10. Use of the surface-modified acid-soluble weighting agent of any one of claims 1-5, or the surface-modified acid-soluble weighting agent obtained by the method of any one of claims 6-9, characterized in that: The weighting agent is used as a weighting agent for drilling fluid in oil and gas drilling.

11. Use of a surface-modified acid-soluble weighting agent according to claim 10, characterized in that: The surface-modified acid-soluble weighting agent is added to drilling fluid for drilling operation in oil and gas reservoir section, and the density adjustment range of the weighting agent is controlled in 1.2g / cm 3 -1.7g / cm 3 .

12. Use of a surface-modified acid-soluble weighting agent according to claim 10 or 11, characterized in that, The acid-soluble weighting agent is used for plugging removal by acid completion fluid or acidizing after the drilling operation in the oil and gas reservoir section is completed.

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