Clay-free drilling fluid cake remover, preparation method and application thereof, and method for removing clay-free drilling fluid cake

Abstract

The present application relates to the technical field of petroleum engineering, in particular to a composition of clay-free drilling fluid cake remover, a clay-free drilling fluid cake remover and its preparation method and application, and a method for removing clay-free drilling fluid cake. The composition comprises hydrochloric acid, hydrofluoric acid, corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent and cleanup agent; wherein the weight ratio of the hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent and cleanup agent is 10-20:0.5-5:0.1-5:0-0.5:0.1-2:0.1-2:0.5-3:0.01-2. The remover containing the composition can promote the loosening of the clay-free drilling fluid cake from the well wall and the flushing and carrying out of the wellbore, break the barrier formed between the oil and gas seepage and the wellbore, and maximize the reduction of oil and gas flowback pressure, thereby facilitating the release of natural productivity of the production layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of petroleum engineering, in particular to a composition of a clay-free drilling fluid mud cake remover, a clay-free drilling fluid mud cake remover and a preparation method and application thereof, and a method for removing clay-free drilling fluid mud cake. BACKGROUND

[0002] The physical property of tight sandstone gas reservoir is poor, and the matrix permeability is very low. In the drilling and completion operation, although the mud cake formed by the drilling fluid on the well wall blocks the further invasion of the solid phase and the liquid phase into the production layer, a part of the solid phase and the liquid phase will still enter the reservoir. In order to reduce the damage of the solid phase particles to the reservoir, a clay-free low solid phase drilling fluid is often used, which does not contain barite and clay particles. In the drilling process, no other solid phase particles are added except for some acid-soluble particles according to the need, although the plugging damage of the solid phase particles to the reservoir can be reduced, a mud cake will still be formed on the reservoir section, forming a barrier between the oil and gas seepage and the wellbore, increasing the oil and gas flowback pressure, and being not conducive to the release of the natural productivity of the production layer. Therefore, when open hole or liner completion is used, in order to improve the natural productivity, the mud cake formed on the well wall needs to be removed.

[0003] At present, the methods for removing the drilling fluid mud cake can be divided into chemical method and physical method. The chemical method mainly uses chemical treatment agents to treat the solid phase particles and the drilling fluid treatment agents in the mud cake, so as to finally remove the mud cake. The physical method mainly uses large displacement well flushing to repeatedly flush and clean the mud cake on the well wall, so that the mud cake falls off from the well wall. In addition to the acid-soluble solid phase particles, the clay-free drilling fluid mud cake mainly contains artificial synthetic high molecular weight polymers, filtration reducers and other treatment agents. Acidification can effectively remove the acid-soluble skeleton particles in the mud cake, but cannot remove the polymers. The effective methods for removing the polymers include enzyme hydrolysis method and oxidation degradation method. However, the biological enzyme breaker can degrade the cellulose high polymer and effectively remove the mud cake. The biological enzyme is a high molecular protein substance, which will invade the reservoir again after removing the mud cake, causing secondary pollution to the reservoir. Moreover, the enzyme has selectivity and the use conditions are not easy to control. Compared with the enzyme hydrolysis method, the oxidation degradation method has better effect, but the selection and addition amount optimization of the oxidizing agent are the key. For example, the method for oxidizing and degrading the polymers by using strong oxidizing agents such as chlorine dioxide and hydrogen peroxide is prone to safety accidents in the actual application process, and the oxidizing agents can corrode the equipment and pipelines. Ammonium persulfate produces sulfate in the formation, which may form inorganic scale such as calcium sulfate.

[0004] Therefore, there is an urgent need for a remover suitable for the clay-free drilling fluid mud cake. SUMMARY

[0005] The present application aims to overcome the problems of the prior art, such as the inability to efficiently remove mud cake, the formation of mud cake in the reservoir well section, the formation of a barrier between the oil and gas seepage and the wellbore, the increase of oil and gas flowback pressure, and the adverse effect on the natural productivity release of gas production, and provides a new clay-free drilling fluid mud cake remover, a preparation method and application thereof, and a clay-free drilling fluid mud cake removal method.

[0006] To achieve the above-mentioned purpose, the present application provides a clay-free drilling fluid mud cake remover composition, which comprises: hydrochloric acid, hydrofluoric acid, corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, and cleanup agent.

[0007] The weight ratio of the hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, and cleanup agent is 10-20:0.5-5:0.1-5:0-0.5:0.1-2:0.1-2:0.5-3:0.01-2.

[0008] The present application provides a clay-free drilling fluid mud cake remover, which comprises: hydrochloric acid, hydrofluoric acid, corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, cleanup agent, and water.

[0009] The content of the hydrochloric acid is 10-20wt%, the content of the hydrofluoric acid is 0.5-5wt%, the content of the corrosion inhibitor is 0.1-5wt%, the content of the chlorine dioxide is 0-0.5wt%, the content of the iron ion stabilizer is 0.1-2wt%, the content of the clay stabilizer is 0.1-2wt%, the content of the penetrant is 0.5-3wt%, the content of the cleanup agent is 0.01-2wt%, and the content of the water is 60.5-90wt%.

[0010] The present application provides a preparation method of a clay-free drilling fluid mud cake remover, which comprises: mixing hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, cleanup agent, and water to obtain the remover.

[0011] The weight ratio of the hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, cleanup agent, and water is 10-20:0.5-5:0.1-5:0-0.5:0.1-2:0.1-2:0.5-3:0.01-2:60.5-90.

[0012] The present application provides the application of the remover provided in the second aspect or the remover prepared by the method provided in the third aspect in tight sandstone gas reservoirs.

[0013] The fifth aspect of the present application provides a method for removing clay-free drilling fluid cake, the method comprising: contacting a removing agent with the clay-free drilling fluid cake and allowing the removing agent to react with the clay-free drilling fluid cake to obtain a cake removing fluid; wherein the removing agent is selected from the removing agent provided in the second aspect or the removing agent prepared by the method provided in the third aspect.

[0014] Compared with the prior art, the present application has the following advantages:

[0015] (1) The composition of the clay-free drilling fluid cake removing agent provided by the present application can promote the clay-free drilling fluid cake to be loose and separated from the well wall and flushed out of the wellbore, break the barrier formed between the oil and gas seepage and the wellbore, minimize the oil and gas flowback pressure, facilitate the release of natural productivity of the production layer, avoid or reduce damage to tight gas reservoirs, increase production, and improve economic development benefits, by limiting the components and the content of each component in the composition and combining the mutual synergistic effect between the components.

[0016] (2) The preparation method of the clay-free drilling fluid cake removing agent provided by the present application is simple, and especially by limiting the order of adding each component, the performance of the removing agent can be further improved.

[0017] (3) The removing agent provided by the present application can be used for tight sandstone gas reservoirs to efficiently promote the clay-free drilling fluid cake to be loose and dry, completely separated from the well wall, and easily flushed out of the wellbore, which is beneficial to the release of natural productivity of the production layer.

[0018] (4) The removing agent provided by the present application can be used for removing clay-free drilling fluid cake, and the dissolution rate of the clay-free drilling fluid cake can reach 99.58%. DETAILED DESCRIPTION

[0019] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are provided as approximations. Any numerical value, however, can inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. The endpoints of the ranges of values (as well as possible individual values within the ranges) in this disclosure are presented solely for the purposes of providing examples range and / or a general understanding of the subject matter. Said ranges are presented

[0020] In the present application, unless otherwise specified, "first" and "second" do not represent the order of precedence, nor do they limit the respective materials or steps, but are only used to distinguish that they are not the same material or step. For example, "first mixing" and "second mixing" only represent that they are not the same mixing.

[0021] The first aspect of the present application provides a composition of clay-free drilling fluid cake remover, which comprises: hydrochloric acid, hydrofluoric acid, corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent and cleanup agent;

[0022] The weight ratio of the hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent and cleanup agent is 10-20:0.5-5:0.1-5:0-0.5:0.1-2:0.1-2:0.5-3:0.01-2.

[0023] The inventors of the present application have found that by limiting the composition to include specific components (i.e. hydrochloric acid, hydrofluoric acid, corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent, cleanup agent and water) and specific contents of each specific component, and the synergistic effect between each component, the purpose of efficient dissolution of the cake is achieved.

[0024] Specifically, the hydrochloric acid in the composition is used to dissolve the ultra-fine calcium carbonate in the cake; the hydrofluoric acid is used to dissolve the sand particles and argillaceous components mixed in the cake, and maintain a low pH value to prevent the generation of new precipitates; the corrosion inhibitor is used to regulate the dissolution rate of the acid; the strong oxidizing property of the chlorine dioxide can promote the degradation of the C-C chain of the polymer thickener, filtration reducer and other treatment agents in the cake; at the same time, under the auxiliary action of the cleanup agent and the penetrating agent, the interfacial tension is effectively reduced, the structure of the cake is destroyed, the adhesion of the cake is reduced, the dense cake is loosened, and the cake is quickly and completely separated and dispersed from the well wall, which facilitates the flushing and carrying out of the wellbore, removes the barrier formed between the oil and gas seepage and the wellbore, maximally reduces the oil and gas flowback pressure, and removes the near-wellbore blockage; the cleanup agent also helps to reduce the Jamin effect, eliminate water lock damage, prevent organic blockage, restore and increase the permeability of the near-wellbore zone, facilitate the release of natural productivity of the production zone, increase the yield, and improve the development economic benefit; the iron ion stabilizer is used to prevent free iron ions from entering the reservoir pores to generate Fe(OH)3 precipitation to block the pore throat and cause secondary reservoir damage; the clay stabilizer is used to inhibit the hydration and swelling of the clay minerals in the reservoir to block the pore throat, thereby reducing the permeability of the near-wellbore zone.

[0025] In some embodiments of the present application, preferably, the weight ratio of the hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent and cleanup agent is 12-15:1-3:0.5-3:0.2-0.3:0.5-1:0.3-1:1-1.5:0.1-1. The use of the preferred weight ratio is more conducive to improving the cake dissolution and destruction effect of the remover.

[0026] In some embodiments of the present application, preferably, the weight ratio of the hydrochloric acid and the hydrofluoric acid is 3-10:1, for example, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 10:1, and any value in the range consisting of any two of the numerical values, preferably 4-7:1. With the preferred conditions, it is more conducive to the dissolution of the ultra-fine calcium carbonate, sand grains and argillaceous components in the mud cake.

[0027] In some embodiments of the present application, preferably, the corrosion inhibitor is an acid corrosion inhibitor, preferably selected from the organic amine corrosion inhibitor. In the present application, the organic amine corrosion inhibitor can be obtained by commercial purchase, for example, the pickling corrosion inhibitor with the trade name CRS3-1 from Jingmen Zhuding New Material Co., Ltd.; or can be prepared.

[0028] In some embodiments of the present application, preferably, the iron ion stabilizer contains an iron complexing agent and an iron reducing agent; further preferably, the iron complexing agent is selected from at least one of citric acid and / or its complex, EDTA and / or its complex, dihydroxymaleic acid and / or its complex, and gluconolactone and / or its complex, preferably at least one of citric acid, EDTA, dihydroxymaleic acid and gluconolactone; and the iron reducing agent is preferably selected from sulfurous acid and / or erythorbic acid.

[0029] In some embodiments of the present application, preferably, the citric acid complex includes but is not limited to ferric citrate; the EDTA complex includes but is not limited to Cu-EDTA, Zn-EDTA, etc.; and the dihydroxymaleic acid complex includes but is not limited to Sm-dihydroxymaleic acid, Cd-dihydroxymaleic acid.

[0030] In some embodiments of the present application, further preferably, the weight ratio of the iron complexing agent and the iron reducing agent in the iron ion stabilizer is 1:0.2-0.8, for example, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.8, and any value in the range consisting of any two of the numerical values, preferably 1:0.3-0.5. Such a setting is used to prevent free iron ions from entering the reservoir pores to form Fe(OH)3 precipitation to plug the pore throats and cause secondary reservoir damage.

[0031] In some embodiments of the present application, preferably, the clay stabilizer is selected from an organic stabilizer, preferably selected from a polyquaternary ammonium salt; further preferably, the weight average molecular weight of the polyquaternary ammonium salt is >1000 g / mol. In the present application, the polyquaternary ammonium salt can be obtained by commercial purchase, for example, the clay stabilizer quaternary amine salt for fracturing (acidification) with the trade name JOP-2 from Dongying Baowze Energy Technology Co., Ltd., or the clay stabilizer polyquaternary ammonium salt for fracturing acidification with the trade name BD1-13 from Sichuan Bede Petroleum Technology Development Co., Ltd.

[0032] In some embodiments of the present application, preferably, the penetrating agent is selected from anionic surfactants, including but not limited to sodium dodecyl benzene sulfonate.

[0033] In some embodiments of the present application, preferably, the cleanup agent is selected from polyhydric alcohol type nonionic surfactants, including but not limited to mild non-irritating fatty alcohol polyoxyethylene ether.

[0034] The second aspect of the present application provides a clay-free drilling fluid cake remover, which comprises: hydrochloric acid, hydrofluoric acid, corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent, cleanup agent and water.

[0035] The content of the hydrochloric acid is 10-20wt%, the content of the hydrofluoric acid is 0.5-5wt%, the content of the corrosion inhibitor is 0.1-5wt%, the content of the chlorine dioxide is 0-0.5wt%, the content of the iron ion stabilizer is 0.1-2wt%, the content of the clay stabilizer is 0.1-2wt%, the content of the penetrating agent is 0.5-3wt%, the content of the cleanup agent is 0.01-2wt%, and the content of the water is 60.5-90wt%, based on the total weight of the remover.

[0036] In the present application, the types and limits of the corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent and cleanup agent are in accordance with the above limits, and the present application does not repeat them.

[0037] In the present application, the remover refers to a clay-free drilling fluid cake remover, unless otherwise specified.

[0038] In some embodiments of the present application, preferably, the content of the hydrochloric acid is 12-15wt%, the content of the hydrofluoric acid is 1-3wt%, the content of the corrosion inhibitor is 0.5-3wt%, the content of the chlorine dioxide is 0.2-0.3wt%, the content of the iron ion stabilizer is 0.5-1wt%, the content of the clay stabilizer is 0.3-1wt%, the content of the penetrating agent is 1-1.5wt%, the content of the cleanup agent is 0.1-1wt%, and the content of the water is 75-85wt%, based on the total weight of the remover. The preferred conditions are more conducive to improving the cake dissolution rate of the remover.

[0039] The clay-free drilling fluid cake remover provided by the present application has a very good dissolution and damage effect on the clay-free drilling fluid cake. The cake can be quickly dissolved and dispersed, which is conducive to being completely removed from the well wall and flushed out of the well bottom, and dredging the oil and gas seepage channel from the reservoir to the wellbore.

[0040] According to the present application, preferably, the mud cake of the scavenger has a dissolution rate of ≥ 95%, preferably ≥ 99%.

[0041] According to the present application, without special circumstances, the dissolution rate parameter is measured by the following method: take a mud cake, dry and weigh for use, wherein the mud cake is dried in a constant temperature drying oven at 105℃±3℃ for 3h, taken out and cooled in a closed dryer for 30min, weighed, and weighed to 0.01g according to the conventional standard, i.e., the "drying and weighing method"; the sample is placed on a four-axis magnetic stirrer, heated, the dried mud cake is put into the scavenger, and after 30min of reaction, filtered, dried and weighed, and the dissolution rate is calculated; wherein the calculation formula of the dissolution rate parameter is as follows:

[0042]

[0043] The third aspect of the present application provides a preparation method of a clay-free drilling fluid mud cake scavenger, characterized in that the method comprises: mixing hydrochloric acid, hydrofluoric acid, an inhibitor, chlorine dioxide, an iron ion stabilizer, a clay stabilizer, a penetrating agent, a cleanup agent and water to obtain the scavenger.

[0044] Preferably, the weight ratio of the hydrochloric acid, the hydrofluoric acid, the inhibitor, the chlorine dioxide, the iron ion stabilizer, the clay stabilizer, the penetrating agent, the cleanup agent and the water is 10-20:0.5-5:0.1-5:0-0.5:0.1-2:0.1-2:0.5-3:0.01-2:60.5-90.

[0045] In the present application, without special circumstances, the types and limitations of the inhibitor, the optional chlorine dioxide, the iron ion stabilizer, the clay stabilizer, the penetrating agent and the cleanup agent are in accordance with the above limitations, and the present application does not repeat them.

[0046] In the present application, the types of the mixing have a wide selection range, as long as the hydrochloric acid, the hydrofluoric acid, the inhibitor, the chlorine dioxide, the iron ion stabilizer, the clay stabilizer, the penetrating agent, the cleanup agent and the water are uniformly mixed.

[0047] In the present application, in order to prevent bubbles during preparation, the penetrating agent and the cleanup agent are preferably added last. Preferably, the mixing process comprises:

[0048] (1) first mixing the hydrochloric acid, the hydrofluoric acid, the inhibitor, the chlorine dioxide, the iron ion stabilizer, the clay stabilizer and the water to obtain a mixed product;

[0049] (2) second mixing the mixed product, the penetrating agent and the cleanup agent to obtain the scavenger.

[0050] In some embodiments of the present application, preferably, the conditions of the first mixing include: temperature of 10-35℃, preferably 20-30℃; time of 20-60min, preferably 30-45min; rotation speed of 50-80rpm, preferably 60-70rpm.

[0051] In some embodiments of the present application, preferably, the conditions of the second mixing include: temperature of 10-35℃, preferably 20-30℃; time of 20-60min, preferably 30-45min; rotation speed of 50-80rpm, preferably 60-70rpm.

[0052] The fourth aspect of the present application provides an application of the scavenger provided in the second aspect, or the scavenger prepared by the method provided in the third aspect, in a tight sand gas reservoir.

[0053] The fifth aspect of the present application provides a method for removing clay-free drilling fluid cake, which comprises: contacting and reacting a scavenger with a clay-free drilling fluid cake to obtain a cake removing fluid; wherein the scavenger is selected from the scavenger provided in the second aspect, or the scavenger prepared by the method provided in the third aspect.

[0054] In some embodiments of the present application, preferably, the ratio of the scavenger in L to the clay-free drilling fluid cake in g is 1:1-10, for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:8, 1:10, and any value in the range between any two values, preferably 1:1-5. By using the preferred conditions, the clay-free drilling fluid cake has a good effect of being dissolved and eroded, the near wellbore is unblocked, the reservoir pollution is reduced, and the natural productivity is improved.

[0055] In some embodiments of the present application, preferably, the conditions of the reaction include: temperature of 60-120℃, preferably 80-100℃; time of 10-60min, preferably 30-45min.

[0056] According to a particularly preferred embodiment of the present application, a clay-free drilling fluid cake scavenger comprises: hydrochloric acid, hydrofluoric acid, corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrating agent, cleanup agent, and water.

[0057] The content of the hydrochloric acid is 12-15wt%, the content of the hydrofluoric acid is 1-3wt%, the content of the corrosion inhibitor is 0.5-3wt%, the content of the chlorine dioxide is 0-0.5wt%, preferably 0.2-0.3wt%, the content of the iron ion stabilizer is 0.5-1wt%, the content of the clay stabilizer is 0.3-1wt%, the content of the penetrating agent is 1-1.5wt%, the content of the cleanup aid is 0.1-1wt%, and the content of the water is 75-85wt%, based on the total weight of the scavenger.

[0058] The weight ratio of the hydrochloric acid to the hydrofluoric acid is 4-7:1.

[0059] The iron ion stabilizer contains an iron complexing agent and an iron reducing agent, and the weight ratio of the iron complexing agent to the iron reducing agent in the iron ion stabilizer is 1:0.3-0.5.

[0060] The present application will be described in detail below through examples.

[0061] The corrosion inhibitor is an acid pickling corrosion inhibitor with a brand of CRS3-1 purchased from Jingmen Zhuding New Material Co., Ltd.

[0062] The clay stabilizer is a clay stabilizer quaternary ammonium salt for fracturing (acidification) with a brand of JOP-2 purchased from Dongying Baize Energy Technology Co., Ltd., or a clay stabilizer poly cationic quaternary ammonium salt for fracturing acidification with a brand of BD1-13 purchased from Sichuan Bede Petroleum Technology Development Co., Ltd.

[0063] Example 1

[0064] (1) The hydrochloric acid, the hydrofluoric acid, the corrosion inhibitor (CRS3-1), the chlorine dioxide, the iron ion stabilizer, the clay stabilizer (JOP-2) and the water are first mixed (the temperature is 25℃, the time is 30min, and the rotating speed is 60rpm) to obtain a mixed product;

[0065] The iron ion stabilizer is an iron complexing agent (citric acid) and an iron reducing agent (sulfurous acid), and the weight ratio of the iron complexing agent to the iron reducing agent is 1:0.3.

[0066] (2) The above mixed product, the penetrating agent (sodium dodecyl benzene sulfonate) and the cleanup aid (fatty alcohol polyoxyethylene ether) are second mixed (the temperature is 25℃, the time is 30min, and the rotating speed is 60rpm) to obtain 0.5L of the scavenger S1.

[0067] The weight ratio of the hydrochloric acid, the hydrofluoric acid, the corrosion inhibitor, the chlorine dioxide, the iron ion stabilizer, the clay stabilizer, the penetrating agent, the cleanup aid and the water is 15:3:2.5:0.3:1:1:1.2:0.8:75.2.

[0068] Example 2

[0069] (1) Hydrochloric acid, hydrofluoric acid, corrosion inhibitor (CRS3-1), iron ion stabilizer, clay stabilizer (JOP-2) and water were first mixed (temperature 25℃, time 30min, rotation speed 60rpm) to obtain a mixed product;

[0070] The iron ion stabilizer is an iron complexing agent (citric acid) and an iron reducing agent (sulfurous acid), and the weight ratio of the iron complexing agent to the iron reducing agent is 1:0.3.

[0071] (2) The above mixed product, penetrant (sodium dodecyl benzene sulfonate) and flushing aid (fatty alcohol polyoxyethylene ether) were second mixed (temperature 25℃, time 30min, rotation speed 60rpm) to obtain 0.5L of scavenger S2.

[0072] The weight ratio of hydrochloric acid, hydrofluoric acid, corrosion inhibitor, iron ion stabilizer, clay stabilizer, penetrant, flushing aid and water is 15:3:2.5:1:1:1.5:0.8:75.2.

[0073] Example 3

[0074] (1) Hydrochloric acid, hydrofluoric acid, corrosion inhibitor (CRS3-1), iron ion stabilizer, clay stabilizer (BD1-13) and water were first mixed (temperature 20℃, time 30min, rotation speed 60rpm) to obtain a mixed product;

[0075] The iron ion stabilizer is an iron complexing agent (EDTA) and an iron reducing agent (erythorbic acid), and the weight ratio of the iron complexing agent to the iron reducing agent is 1:0.4.

[0076] (2) The above mixed product, penetrant (sodium dodecyl benzene sulfonate) and flushing aid (fatty alcohol polyoxyethylene ether) were second mixed (temperature 20℃, time 30min, rotation speed 60rpm) to obtain 0.5L of scavenger S3.

[0077] The weight ratio of hydrochloric acid, hydrofluoric acid, corrosion inhibitor, iron ion stabilizer, clay stabilizer, penetrant, flushing aid and water is 13:2.5:2:0.8:1:1.2:0.5:80.

[0078] Example 4

[0079] (1) Hydrochloric acid, hydrofluoric acid, corrosion inhibitor (CRS3-1), iron ion stabilizer, clay stabilizer (JOP-2) and water were first mixed (temperature 30℃, time 30min, rotation speed 60rpm) to obtain a mixed product;

[0080] The iron ion stabilizer is an iron complexing agent (gluconolactone) and an iron reducing agent (sulfurous acid), and the weight ratio of the iron complexing agent and the iron reducing agent is 1:0.5;

[0081] (2) The above mixture, penetrant (sodium dodecyl benzene sulfonate) and drainage aid (fatty alcohol polyoxyethylene ether) were mixed for the second time (temperature 30℃, time 30min, rotation speed 60rpm) to obtain 0.5L of scavenger S4.

[0082] The weight ratio of hydrochloric acid, hydrofluoric acid, corrosion inhibitor, iron ion stabilizer, clay stabilizer, penetrant, drainage aid and water is 12:2:1.5:0.8:0.8:1:0.5:81.4.

[0083] Example 5

[0084] According to example 2, except that the weight ratio of hydrochloric acid, hydrofluoric acid, corrosion inhibitor, iron ion stabilizer, clay stabilizer, penetrant, drainage aid and water was replaced by 20:5:0.1:1.5:0.1:0.5:1.5:71.3, and the other conditions were the same, 0.5L of scavenger S5 was obtained.

[0085] Example 6

[0086] According to example 2, except that the weight ratio of hydrochloric acid and hydrofluoric acid was replaced by 16:2, and the other conditions were the same, 0.5L of scavenger S6 was obtained.

[0087] Example 7

[0088] According to example 2, except that the weight ratio of iron complexing agent and iron reducing agent in the iron ion stabilizer was replaced by 1:0.8, and the other conditions were the same, 0.5L of scavenger S7 was obtained.

[0089] Example 8

[0090] According to example 2, except that the iron ion stabilizer was replaced by iron complexing agent, and the other conditions were the same, 0.5L of scavenger S8 was obtained.

[0091] Example 9

[0092] According to example 2, except that hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, drainage aid and water were directly mixed, 0.5L of scavenger S9 was obtained.

[0093] Comparative example 1

[0094] According to the method of example 2, except that the weight ratio of hydrochloric acid and hydrofluoric acid was replaced by 9:9, and the other conditions were the same, 0.5L of scavenger DS1 was obtained.

[0095] Comparative Example 2

[0096] According to the method of Example 2, except that the weight ratio of hydrochloric acid, hydrofluoric acid, corrosion inhibitor, iron ion stabilizer, clay stabilizer, penetrating agent, cleanup aid and water is replaced by 25:6:5.5:2.5:2.5:0.1:2.5:55.9, and the rest of the conditions are the same, 0.5L of cleanup agent DS2 is obtained.

[0097] Comparative Example 3

[0098] According to the method of Example 2, except that no hydrofluoric acid is added, and the rest of the conditions are the same, 0.5L of cleanup agent DS3 is obtained.

[0099] Test Example

[0100] Preparation of mud cake: 500ml of clay-free drilling fluid is prepared according to the weight ratio of water, Na2CO3, XC, QS-2 (adipic acid plasticizer), sodium formate, SL-PAC and HV-CMC (high viscosity carboxymethyl cellulose sodium) is 100:0.2:0.3:5:10:2.5:3, and the mud cake is prepared by API filtration method.

[0101] The cleanup agents (S1-S9 and DS1-DS3) prepared in Examples 1-9 and Comparative Examples 1-3 are respectively contacted with the above mud cake and reacted to obtain mud cake cleanup fluid, wherein the reaction conditions include a temperature of 90°C and a time of 30min.

[0102] Among them, the physical parameters of mud cake dissolution rate are listed in Table 1, and the dispersion evaluation parameters of mud cake are listed in Table 2.

[0103] The dissolution rate parameter is measured by the following method: take a portion of mud cake, dry and weigh for use, wherein the mud cake is subjected to the conventional standard, i.e. "dry in a constant temperature drying oven at 105°C±3°C for 3h, take out and cool in a closed desiccator for 30min, weigh, and weigh to 0.01g"; place the sample on a four-axis magnetic stirrer, heat, and put the dried mud cake into the cleanup agent, after 30min of reaction, filter, dry and weigh, and calculate the dissolution rate; wherein the calculation formula of the dissolution rate parameter is as follows:

[0104]

[0105] Mud cake dispersion evaluation: take a portion of mud cake, directly put into the cleanup agent, after 30min of reaction, observe and analyze the integrity of the mud cake.

[0106] Table 1

[0107]

[0108] Table 2

[0109]

[0110]

[0111] From the results of Table 1-2, it can be seen that the cleaning agent prepared in Examples 1-9 has a good dissolution and damage effect on the clay-free drilling fluid mud cake, and the dissolution rate is more than 97%, and the highest can reach 99.58%. The mud cake can be quickly dissolved and dispersed, which is beneficial to be completely removed from the well wall and flushed out of the bottom of the well, and to dredge the oil and gas seepage channel of the reservoir to the wellbore.

[0112] Compared with Example 2-3, the cleaning agent prepared in Example 1 has a higher dissolution rate.

[0113] Compared with Example 5, the cleaning agent prepared in Example 2 has a higher dissolution rate.

[0114] Compared with Example 6, the cleaning agent prepared in Example 2 has a higher dissolution rate.

[0115] Compared with Example 7, the cleaning agent prepared in Example 2 has a higher dissolution rate.

[0116] Compared with Example 8, the cleaning agent prepared in Example 2 has a higher dissolution rate.

[0117] Compared with Example 9, the cleaning agent prepared in Example 2 has a higher dissolution rate.

[0118] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A clay-free drilling fluid mud cake remover for tight sandstone gas reservoirs, characterized in that, The cleaning agent includes: hydrochloric acid, hydrofluoric acid, corrosion inhibitor, optional chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, drainage aid and water; Based on the total weight of the cleaning agent, the content of hydrochloric acid is 10-20 wt%; the content of hydrofluoric acid is 0.5-5 wt%; the content of corrosion inhibitor is 0.1-5 wt%; the content of chlorine dioxide is 0-0.5 wt%; the content of iron ion stabilizer is 0.1-2 wt%; the content of clay stabilizer is 0.1-2 wt%; the content of penetrant is 0.5-3 wt%; the content of drainage aid is 0.01-2 wt%; and the content of water is 60.5-90 wt%. The weight ratio of hydrochloric acid to hydrofluoric acid is 4-7:1; the iron ion stabilizer contains an iron complexing agent and an iron reducing agent, and the weight ratio of the iron complexing agent to the iron reducing agent in the iron ion stabilizer is 1:0.3-0.5; the iron complexing agent is selected from at least one of citric acid, ferric citrate, EDTA, Cu-EDTA, Zn-EDTA, dihydroxymaleic acid, Sm-dihydroxymaleic acid, Cd-dihydroxymaleic acid, and gluconolactone; the iron reducing agent is selected from sulfurous acid and / or isoascorbic acid; The mud cake dissolution rate of the cleaning agent is ≥95%.

2. The cleaning agent according to claim 1, wherein, Based on the total weight of the cleaning agent, the content of hydrochloric acid is 12-15 wt%; the content of hydrofluoric acid is 1-3 wt%; the content of corrosion inhibitor is 0.5-3 wt%; the content of chlorine dioxide is 0.2-0.3 wt%; the content of iron ion stabilizer is 0.5-1 wt%; the content of clay stabilizer is 0.3-1 wt%; the content of penetrant is 1-1.5 wt%; the content of drainage aid is 0.1-1 wt%; and the content of water is 75-85 wt%.

3. The cleaning agent according to claim 1, wherein, The cleaning agent has a mud cake dissolution rate of ≥99%.

4. The cleaning agent according to any one of claims 1-3, wherein, The corrosion inhibitor is an acid pickling corrosion inhibitor; The clay stabilizer is selected from organic stabilizers; The penetrant is selected from anionic surfactants; The drainage aid is selected from polyol-type nonionic surfactants.

5. The cleaning agent according to claim 4, wherein, The corrosion inhibitor is selected from organic amine corrosion inhibitors; The iron chelating agent is selected from at least one of citric acid, EDTA, dihydroxymaleic acid, and gluconolactone; The clay stabilizer is selected from polyquaternary ammonium salts; The penetrant is selected from sodium dodecylbenzenesulfonate; The drainage aid is selected from fatty alcohol polyoxyethylene ether.

6. A method for preparing a clay-free drilling fluid mud cake remover for tight sandstone gas reservoirs, characterized in that, The method includes: mixing hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, drainage aid and water to obtain a cleaning agent; The weight ratio of hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, drainage aid and water is 10-20:0.5-5:0.1-5:0-0.5:0.1-2:0.1-2:0.5-3:0.01-2:60.5-90. The weight ratio of hydrochloric acid to hydrofluoric acid is 4-7:1; the iron ion stabilizer contains an iron complexing agent and an iron reducing agent, and the weight ratio of the iron complexing agent to the iron reducing agent in the iron ion stabilizer is 1:0.3-0.

5.

7. The method according to claim 6, wherein, The weight ratio of hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer, penetrant, drainage aid and water is 12-15:1-3:0.5-3:0.2-0.3:0.5-1:0.3-1:1-1.5:0.1-1:75-85; The mixing process includes: (1) The hydrochloric acid, hydrofluoric acid, corrosion inhibitor, chlorine dioxide, iron ion stabilizer, clay stabilizer and water are mixed for the first time to obtain a mixed product; (2) The mixture, penetrant and drainage aid are mixed for a second time to obtain the scavenging agent.

8. A method for removing clay-free drilling fluid cake, characterized in that, The removal method includes: contacting and reacting a cleaning agent with clay-free drilling fluid cake to obtain a cake removal solution; The cleaning agent is selected from the cleaning agent according to any one of claims 1-5, or the cleaning agent prepared by the method according to claim 6 or 7.

9. The cleaning method according to claim 8, wherein, The ratio of the cleaning agent (in L) to the clay-free drilling fluid cake (in g) is 1:1-10.

10. The cleaning method according to claim 9, wherein, The ratio of the cleaning agent (in L) to the clay-free drilling fluid cake (in g) is 1:1-5.

11. The cleaning method according to claim 9, wherein, The reaction conditions include: a temperature of 60-120℃ and a time of 10-60 min.

12. The cleaning method according to claim 11, wherein, The reaction conditions include: a temperature of 80-100℃ and a time of 30-45 min.

Images