Anti-gas-channeling water-based drilling fluid for drilling high-density shale gas and preparation method of anti-gas-channeling water-based drilling fluid

Abstract

The invention discloses an anti-gas-channeling water-based drilling fluid for high-density shale gas drilling and a preparation method thereof, the water-based drilling fluid comprises base slurry, barite powder, ilmenite powder and a lubricant; the preparation method of the lubricant comprises the following steps: S1-1, preparing modified ZnS; s1-2, preparing a high-molecular polymer; s1-3, preparing a lubricating agent; the preparation method of the water-based drilling fluid comprises the following steps: S1, preparing base slurry; and S2, weighting the drilling fluid to form slurry. The prepared water-based drilling fluid conforming to high-density shale gas drilling and production in the Ordos basin is good in rock-carrying capacity and filtration loss wall-building performance, the optimal weighting feasibility is achieved at low cost, particularly, the good improvement effect on the lubricating performance in the high-density shale gas drilling process is achieved, a drill bit is effectively protected, and the drilling efficiency is improved. The service life of the drill bit is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploitation, and in particular to a water-based drilling fluid used in a high-density shale gas drill for preventing gas channeling and a preparation method thereof. Background Art

[0002] Shale gas refers to natural gas of biological origin, pyrolysis origin or a mixture of the two that is rich in organic matter, mature dark shale or high-carbon shale, which is stored and preserved due to the adsorption of organic matter or the existence of cracks and matrix pores in the rock. Shale gas is an unconventional natural gas found in reservoir rock systems dominated by organic-rich shales. It is a continuously generated biochemical gas, thermogenic gas or a mixture of the two. It can exist in a free state in natural cracks and pores, in an adsorbed state on the surface of kerogen and clay particles, and a very small amount is stored in a dissolved state in kerogen and asphaltene. The proportion of free gas is generally 20% to 85%.

[0003] The strata where shale gas is located have serious cracks and bedding development, so during the construction process, the drilling fluid has extremely high requirements for wellbore stability and wellbore collapse. Conventional water-based drilling fluid cannot solve these problems well. The traditional solution is still to use oil-based drilling fluid, but oil-based drilling fluid has disadvantages such as high preparation cost and high environmental pressure.

[0004] For the shale gas fields in the Ordos Basin, the wells are deep, the formation environment is more complex, the clay mineral content is high, and it exhibits weak expansion and crushing properties. In addition, the horizontal section of horizontal well drilling is long, which puts a more severe test on the drilling fluid. At present, some scholars have conducted research on this. For example, patent CN117535037A discloses a shale gas green water-based drilling fluid and its application, including the following components: water, bentonite, viscosity enhancer, alkalinity regulator, shale inhibitor stabilizer, filtrate reducer, shale plugging agent, lubricant and weighting material, which can achieve the stability of the well wall during shale gas drilling. However, after analysis, the water-based drilling fluid still does not meet the drilling construction of the long horizontal section horizontal well with complex formation environment mentioned above, and a more suitable water-based drilling fluid is needed. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention provides a water-based drilling fluid for high-density shale gas drilling to prevent gas channeling and a preparation method thereof.

[0006] The technical solution of the present invention is:

[0007] A high-density shale gas drill for preventing gas channeling uses a water-based drilling fluid, including base slurry, barite powder, ilmenite powder and lubricant. The base slurry includes, by weight percentage, 30-35% of potassium formate, 3-4% of bentonite, 2-3% of filtration reducer, 4-5% of anti-collapse agent PA-2, 3-4% of white oil, 2-3% of polyol MSJ, 1-2% of ultrafine CaCO3 powder, 1.5-2% of emulsified asphalt, 1-1.5% of drilling plugging agent, 0.1-0.2% of xanthan gum, 0.02-0.03% of sodium hydroxide, and the balance is water, and the lubricant accounts for 0-3% of the total volume of the water-based drilling fluid;

[0008] The density of the barite powder in the water-based drilling fluid is 1.35-1.45 g / cm 3 The density of the ilmenite powder in the water-based drilling fluid is 1.15-1.35 g / cm 3 .

[0009] Furthermore, the fluid loss reducer is prepared by mixing fluid loss reducer JT888 and fluid loss reducer SJ-2 in a weight ratio of 2:1.

[0010] Description: The two selected fluid loss reducers have been proven to have good effects in the field of shale gas drilling. Here, the two are integrated to ensure that the water-based drilling fluid of the present invention has good fluid loss reduction performance.

[0011] Furthermore, the ultrafine CaCO3 powder is a mixture of CaCO3 powder passing through a 2000 mesh sieve and CaCO3 powder passing through a 3000 mesh sieve in a weight ratio of 1:1.

[0012] Description: Two different sizes of CaCO3 powder are selected to form ultrafine CaCO3 powder to improve the rock carrying efficiency of water-based drilling fluid.

[0013] Furthermore, the emulsified asphalt is cationic emulsified asphalt, and the drilling-while-drilling plugging agent is a drilling-while-drilling plugging agent SD-I type.

[0014] Furthermore, the lubricant is obtained by coating modified ZnS with a methyl acrylate-ethylenediamine polymer, and the preparation method of the lubricant comprises the following steps:

[0015] S1. Lubricant preparation:

[0016] S1-1, preparation of modified ZnS: zinc chloride powder, sulfur powder and ethylenediamine are mixed in a molar ratio of 3:4:100 and added into a reaction kettle, heated to 180-200°C for reaction for 3-4 days, cooled to room temperature and taken out, washed and dried to obtain modified ZnS powder;

[0017] S1-2, preparation of high molecular polymer: taking a first methanol solution mixed with ethylenediamine, wherein the mass concentration of ethylenediamine in the first methanol solution is 40%, nitrogen is continuously introduced under ice bath conditions, and methyl acrylate is continuously added dropwise, wherein the volume ratio of methyl acrylate to ethylenediamine in the first methanol solution is 1:1, after the addition is completed, nitrogen is stopped from being introduced and the mixture is allowed to stand for 1 day to obtain tetraamine, nitrogen is continuously introduced under ice bath conditions, and a second methanol solution mixed with ethylenediamine is continuously added dropwise, wherein the mass concentration of ethylenediamine in the second methanol solution is 60%, and the volume ratio of ethylenediamine to methyl acrylate in the second methanol solution is 1:2, after the addition is completed, nitrogen is stopped from being introduced and the mixture is allowed to stand for 1 day, and a first generation high molecular polymer is obtained by vacuum distillation, i.e., one iteration is completed;

[0018] Subsequently, the first methanol solution is replaced with the first generation polymer, and the above steps are repeated. When the second generation polymer is obtained, the next iteration is completed. The same amount of methyl acrylate and the same amount of the second methanol solution are added in each iteration. The third generation polymer is obtained by repeating the above steps for three times.

[0019] S1-3. Preparation of lubricant: Add the modified ZnS powder obtained in step S1-1 to the third-generation high molecular polymer obtained in step S1-2, stir and repeat the above iterative process, and the fourth-generation methyl acrylate-ethylenediamine high molecular polymer coated modified ZnS obtained is the lubricant.

[0020] Furthermore, in step S1-1, the zinc chloride powder and the sulfur powder are both sieved through a 1000-mesh sieve, and are washed 3 to 4 times with deionized water at a drying temperature of 45 to 50°C.

[0021] Note: The sizes of zinc chloride powder and sulfur powder are optimized to ensure that the size of modified ZnS meets the requirements of lubricants.

[0022] Furthermore, in step S1-3, the weight ratio of the modified ZnS powder to the third generation high molecular polymer is 1:25-30.

[0023] The method for preparing a water-based drilling fluid for high-density shale gas drilling for preventing gas channeling described in any one of the above items comprises the following steps:

[0024] After step S1 is completed, proceed to the subsequent steps;

[0025] S1. Base slurry preparation: After adding water into the wellbore during the drilling construction, the pump is turned on for circulation, and then the various components of the base slurry are added in sequence, and the base slurry preparation can be completed by cyclic drilling;

[0026] S2. Weighting the drilling fluid to form slurry: During the drilling or circulation process of the base slurry, barite powder, ilmenite powder and lubricant are sequentially added into the wellbore to weight the base slurry and obtain the water-based drilling fluid.

[0027] The application of a water-based drilling fluid in a high-density shale gas drill for preventing gas channeling described in any one of the above is to use the water-based drilling fluid in the construction of shale gas horizontal well drilling, and the application method is:

[0028] During the initial drilling, the lubricant in the water-based drilling fluid accounts for 0% of the total volume of the water-based drilling fluid;

[0029] During the secondary drilling, the lubricant in the water-based drilling fluid accounts for 0 to 1% of the total volume of the water-based drilling fluid;

[0030] When drilling at the third or higher level, the lubricant in the water-based drilling fluid accounts for 1 to 3% of the total volume of the water-based drilling fluid, specifically:

[0031] When drilling a vertical well, the lubricant in the water-based drilling fluid accounts for 1 to 1.8% of the total volume of the water-based drilling fluid;

[0032] When the deflection section is advanced, the lubricant in the water-based drilling fluid accounts for 2.6-3% of the total volume of the water-based drilling fluid;

[0033] When drilling in the horizontal section, the lubricant in the water-based drilling fluid accounts for 1.8-2.6% of the total volume of the water-based drilling fluid.

[0034] The beneficial effects of the present invention are:

[0035] (1) A high-density shale gas drill for preventing gas channeling of the present invention adopts a water-based drilling fluid with potassium formate as the main component to prepare a base slurry, and barite powder, ilmenite powder and a lubricant are added to the base slurry, thereby finally obtaining a water-based drilling fluid that meets the requirements of high-density shale gas drilling in the Ordos Basin, has good rock carrying capacity, good filtration and wall-building performance, and achieves optimal weighting feasibility at a relatively low cost, especially for the lubrication performance during high-density shale gas drilling. It has a good improvement effect, effectively protects the drill bit, and prolongs the service life of the drill bit.

[0036] (2) A high-density shale gas drill for preventing gas channeling of the present invention optimizes the lubricant by preparing a water-based drilling fluid. By coating the modified ZnS powder in the polymer, the polymer can act on the mud cake of the well wall to form a lubricating film between the drill tool (especially the drill bit) and the well wall, thereby maintaining a dynamic balance between the destruction of the lubricating film structure and production and improving the dynamic stability of the lubricating film. Through the distribution of hyperbranched surface active groups and high-density branch chains, it is very easy to adsorb on the surface of bentonite particles, thereby enhancing the connection between the mud cake matrix particles and improving the friction boundary conditions of the drill tool. The modified ZnS powder is selected to be implanted in the iterative third generation. The modified ZnS powder can form a boundary lubricating film on the friction pair surface, thereby effectively improving the lubrication performance of the polymer. The modified ZnS powder and the polymer complete an iteration together. The hyperbranched surface active group distribution and high-density branch chains of the polymer can penetrate into the organic amine intercalation of the modified ZnS powder, thereby improving the correlation strength between the two.

[0037] (3) The invention provides a method for applying the water-based drilling fluid of the invention to the drilling of shale gas horizontal wells in detail. The method mainly includes adding different dosages of lubricant at different stages. In the first drilling, the surface soil is mainly drilled. The soil is loose, so no lubricant is needed. In the second drilling, the shale formation is drilled, and an appropriate amount of lubricant needs to be added. In the third drilling and above, the shale formation is frequently drilled, so the amount of lubricant needs to be increased. The lubricant is mainly added in an appropriate amount during the drilling of the vertical well section. When the inclination section is drilled, the friction between the drill bit and the rock formation reaches the maximum, so the amount of lubricant is also the maximum. The pressure on the drill bit in the horizontal section is reduced, but there is also a risk of drill sticking. Therefore, the amount of lubricant is appropriately adjusted. Finally, a set of comprehensive application methods of the water-based drilling fluid of the invention is obtained, which has guiding significance for the application of the water-based drilling fluid of the invention in the high-density shale gas drilling and production in the Ordos Basin. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart of a method for preparing a water-based drilling fluid for a high-density shale gas drill that prevents gas channeling according to the present invention;

[0039] Figure 2 It is a schematic diagram of the lubricity coefficient of the water-based drilling fluid prepared in each case in Experimental Example 2 of the present invention. DETAILED DESCRIPTION

[0040] Example 1

[0041] A high-density shale gas drill for preventing gas channeling adopts a water-based drilling fluid, including base slurry, barite powder, ilmenite powder and lubricant. The base slurry includes, by weight percentage, 33% potassium formate, 3.5% bentonite, 2.4% fluid loss reducer, 4.6% anti-collapse agent PA-2, 3.3% white oil, 2.5% polyol MSJ, 1.8% ultrafine CaCO3 powder, 1.7% cationic emulsified asphalt, 1.1% drilling plugging agent SD-I type, 0.11% xanthan gum, 0.025% sodium hydroxide, and the balance is water. The lubricant accounts for 0-3% of the total volume of the water-based drilling fluid (due to the different addition amounts of the lubricant under different working conditions, the addition amount of the lubricant cannot be calculated as a fixed value here, see Examples 14-17 for details);

[0042] The density of barite powder in water-based drilling fluid is 1.35g / cm 3 The density of ilmenite powder in water-based drilling fluid is 1.15 g / cm 3 The fluid loss reducer is a mixture of fluid loss reducer JT888 and fluid loss reducer SJ-2 in a weight ratio of 2:1, and the ultrafine CaCO3 powder is a mixture of CaCO3 powder passing through a 2000 mesh sieve and CaCO3 powder passing through a 3000 mesh sieve in a weight ratio of 1:1;

[0043] The lubricant is obtained by coating modified ZnS with a methyl acrylate-ethylenediamine polymer. The preparation method of the lubricant comprises the following steps:

[0044] S1. Lubricant preparation:

[0045] S1-1, preparation of modified ZnS: zinc chloride powder, sulfur powder and ethylenediamine are taken, and the zinc chloride powder and sulfur powder are both passed through a 1000 mesh sieve, mixed in a molar ratio of 3:4:100, added into a reactor, heated to 190°C for reaction for 3 days, cooled to room temperature and taken out, washed and dried to obtain modified ZnS powder, washed with deionized water for 3 times, and the drying temperature is 48°C;

[0046] S1-2, preparation of high molecular polymer: take a first methanol solution mixed with ethylenediamine, the mass concentration of ethylenediamine in the first methanol solution is 40%, and nitrogen is continuously introduced under ice bath conditions, and methyl acrylate is continuously added dropwise, the volume ratio of methyl acrylate to ethylenediamine in the first methanol solution is 1:1, after the addition is completed, the nitrogen is stopped and the mixture is allowed to stand for 1 day to obtain tetraamine, and nitrogen is continuously introduced under ice bath conditions, and a second methanol solution mixed with ethylenediamine is continuously added dropwise, the mass concentration of ethylenediamine in the second methanol solution is 60%, and the volume ratio of ethylenediamine to methyl acrylate in the second methanol solution is 1:2, after the addition is completed, the nitrogen is stopped and the mixture is allowed to stand for 1 day, and the first generation high molecular polymer is obtained by vacuum distillation, that is, one iteration is completed;

[0047] Subsequently, the first methanol solution is replaced with the first generation polymer, and the above steps are repeated. When the second generation polymer is obtained, the next iteration is completed. The same amount of methyl acrylate and the same amount of the second methanol solution are added in each iteration. The third generation polymer is obtained by repeating the above steps for three times.

[0048] S1-3, lubricant preparation: adding the modified ZnS powder obtained in step S1-1 to the third-generation polymer obtained in step S1-2, the weight ratio of the modified ZnS powder to the third-generation polymer being 1:25, stirring and repeating the above iterative process, and the fourth-generation methyl acrylate-ethylenediamine polymer-coated modified ZnS is obtained as a lubricant;

[0049] The method for preparing the water-based drilling fluid comprises the following steps:

[0050] S1. Base slurry preparation: After adding water into the wellbore during the drilling construction, start the pump circulation, and then add various components of the base slurry in turn, and the base slurry preparation can be completed by cyclic drilling;

[0051] S2. Drilling fluid weighting to form slurry: During the drilling or base slurry circulation process, barite powder, ilmenite powder and lubricant are sequentially added into the wellbore to weight the base slurry and obtain water-based drilling fluid.

[0052] Example 2

[0053] The difference between this embodiment and embodiment 1 is that the density of barite powder in water-based drilling fluid is 1.38 g / cm 3 .

[0054] Example 3

[0055] The difference between this embodiment and embodiment 1 is that the density of barite powder in water-based drilling fluid is 1.42 g / cm 3 .

[0056] Example 4

[0057] The difference between this embodiment and embodiment 1 is that the density of barite powder in water-based drilling fluid is 1.45 g / cm 3 .

[0058] Example 5

[0059] The difference between this embodiment and embodiment 1 is that the density of ilmenite powder in water-based drilling fluid is 1.2 g / cm 3 .

[0060] Example 6

[0061] The difference between this embodiment and embodiment 1 is that the density of ilmenite powder in water-based drilling fluid is 1.25 g / cm3 .

[0062] Example 7

[0063] The difference between this embodiment and embodiment 1 is that the density of ilmenite powder in water-based drilling fluid is 1.3 g / cm 3 .

[0064] Example 8

[0065] The difference between this embodiment and embodiment 1 is that the density of ilmenite powder in water-based drilling fluid is 1.35 g / cm 3 .

[0066] Experimental Example 1

[0067] The water-based drilling fluids prepared in Examples 1 to 8 were tested below. We prepared the drilling fluids by simulating the actual drilling temperature through indoor experiments. The simulated formation temperature was 80°C and the reaction time was 16 hours. The results were compared with the comparative examples. Compared with Example 1, Comparative Example 1 did not add barite powder, and Comparative Example 2 did not add ilmenite powder. The comprehensive properties of the water-based drilling fluids finally obtained are shown in Table 1.

[0068] Table 1 Water-based drilling fluid properties of each case

[0069]

[0070] It can be seen from the data in Table 1 that by adding weight to the base slurry, the plastic viscosity and dynamic shear force of the water-based drilling fluid increase, which is conducive to the formation of mud cakes, but the filtration loss of the water-based drilling fluid increases slightly. According to experience, the filtration loss needs to be controlled within 10 mL during shale gas drilling. Therefore, the weighting scheme of the present invention is generally feasible.

[0071] Example 9

[0072] The difference between this embodiment and embodiment 1 is that the weight ratio of the modified ZnS powder to the third-generation high molecular polymer is 1:26.

[0073] Example 10

[0074] The difference between this embodiment and embodiment 1 is that the weight ratio of the modified ZnS powder to the third-generation high molecular polymer is 1:27.

[0075] Embodiment 11

[0076] The difference between this embodiment and embodiment 1 is that the weight ratio of the modified ZnS powder to the third-generation high molecular polymer is 1:28.

[0077] Example 12

[0078] The difference between this embodiment and embodiment 1 is that the weight ratio of the modified ZnS powder to the third-generation high molecular polymer is 1:29.

[0079] Embodiment 13

[0080] The difference between this embodiment and embodiment 1 is that the weight ratio of the modified ZnS powder to the third-generation high molecular polymer is 1:30.

[0081] Experimental Example 2

[0082] The water-based drilling fluids prepared in Examples 1 and 9 to 13 were tested below. We prepared the drilling fluids by simulating the actual temperature of drilling in an indoor test. The simulated formation temperature was 80°C and the reaction time was 16 hours. The results were compared with the comparative examples. Compared with Example 1, no modified ZnS powder was added in Comparative Example 3. Compared with Example 1, no methyl acrylate-ethylenediamine polymer was added in Comparative Example 4. Only modified ZnS powder was added in Comparative Example 4. Compared with Example 1, the lubricant added in Comparative Example 5 was gear lubricant. The comprehensive performance of the water-based drilling fluids finally obtained is as follows: Figure 2 shown.

[0083] It can be seen that when the content of modified ZnS powder in the lubricant is appropriately increased, the lubricity coefficient of the lubricant decreases and the lubricity is improved, but too high a solid content in the lubricant may lead to an increase in the filtration loss. At the same time, when no modified ZnS powder is added in Comparative Example 3, the lubricity coefficient increases and the lubricity decreases, but in Comparative Example 4, the lubricity decreases more significantly without adding methyl acrylate-ethylenediamine high molecular polymer. Therefore, methyl acrylate-ethylenediamine high molecular polymer is more decisive as the base of the lubricant, and the modified ZnS powder plays a role in auxiliary lubrication. The hyperbranched polymer associates and bridges through the active N and O atoms with high density distribution in the outer layer, thereby enhancing the stability of the polymer and bentonite. At the same time, the organic amine is orderly inserted into the ZnS interlayer to form a periodic skeleton structure, and the lubrication effect is further improved by intercalation.

[0084] When gear lubricating oil is added to Comparative Example 5, the lubrication effect is poor, and it is very incompatible with the water-based drilling fluid and drilling conditions of the present invention, but it also meets the working condition requirements of mainly drilling the surface soil during the initial drilling.

[0085] Embodiment 14

[0086] This embodiment is an application of a high-density shale gas drill for preventing gas channeling using a water-based drilling fluid in embodiment 1. The water-based drilling fluid is used in the shale gas horizontal well drilling construction, and the application method is:

[0087] At the beginning of drilling, the lubricant in the water-based drilling fluid accounts for 0% of the total volume of the water-based drilling fluid;

[0088] During the secondary drilling, the lubricant in the water-based drilling fluid accounts for 0.1% of the total volume of the water-based drilling fluid;

[0089] When drilling at the third or higher level, the lubricant in the water-based drilling fluid accounts for 1 to 2.6% of the total volume of the water-based drilling fluid, specifically:

[0090] When drilling a vertical well, the lubricant in the water-based drilling fluid accounts for 1% of the total volume of the water-based drilling fluid;

[0091] When the deflection section is advanced, the lubricant in the water-based drilling fluid accounts for 2.6% of the total volume of the water-based drilling fluid;

[0092] When drilling in the horizontal section, the lubricant in the water-based drilling fluid accounts for 1.8% of the total volume of the water-based drilling fluid.

[0093] Embodiment 15

[0094] The difference between this embodiment and embodiment 14 is that:

[0095] During the secondary drilling, the lubricant in the water-based drilling fluid accounts for 0.4% of the total volume of the water-based drilling fluid;

[0096] When drilling at the third or higher level, the lubricant in the water-based drilling fluid accounts for 1.4-2.7% of the total volume of the water-based drilling fluid, specifically:

[0097] When drilling a vertical well, the lubricant in the water-based drilling fluid accounts for 1.4% of the total volume of the water-based drilling fluid;

[0098] The lubricant in the water-based drilling fluid accounts for 2.7% of the total volume of the water-based drilling fluid during the build-up section;

[0099] When drilling in the horizontal section, the lubricant in the water-based drilling fluid accounts for 2% of the total volume of the water-based drilling fluid.

[0100] Example 16

[0101] The difference between this embodiment and embodiment 14 is that:

[0102] During the secondary drilling, the lubricant in the water-based drilling fluid accounts for 0.8% of the total volume of the water-based drilling fluid;

[0103] When drilling at the third or higher level, the lubricant in the water-based drilling fluid accounts for 1.6-2.8% of the total volume of the water-based drilling fluid, specifically:

[0104] When drilling a vertical well, the lubricant in the water-based drilling fluid accounts for 1.6% of the total volume of the water-based drilling fluid;

[0105] When the deflection section is advanced, the lubricant in the water-based drilling fluid accounts for 2.8% of the total volume of the water-based drilling fluid;

[0106] When drilling in the horizontal section, the lubricant in the water-based drilling fluid accounts for 2.4% of the total volume of the water-based drilling fluid.

[0107] Embodiment 17

[0108] The difference between this embodiment and embodiment 14 is that:

[0109] During the secondary drilling, the lubricant in the water-based drilling fluid accounts for 1% of the total volume of the water-based drilling fluid;

[0110] When drilling at the third or higher level, the lubricant in the water-based drilling fluid accounts for 1.8-3% of the total volume of the water-based drilling fluid, specifically:

[0111] When drilling a vertical well, the lubricant in the water-based drilling fluid accounts for 1.8% of the total volume of the water-based drilling fluid;

[0112] When the deflection section is advanced, the lubricant in the water-based drilling fluid accounts for 3% of the total volume of the water-based drilling fluid;

[0113] When drilling in the horizontal section, the lubricant in the water-based drilling fluid accounts for 2.6% of the total volume of the water-based drilling fluid.

[0114] It should be noted that the construction methods of Examples 14 to 17 gradually increase the amount of lubricant in the water-based drilling fluid according to different formation conditions, but the cost will also increase accordingly. During actual drilling construction, even in the same well field in the Ordos Basin, the formation conditions will be different. The construction methods of Examples 14 to 17 should be reasonably selected according to the actual formation conditions. At the same time, if the drilling location is a cluster well, when the first wellbore of the cluster well is drilled, due to the complex formation conditions, multiple drill jams occur, and the wellbore uses the construction method in Example 14 or 15. When the next wellbore is drilled, the construction method in Example 16 or 17 should be planned to be selected to avoid multiple drill jams at the wellbore location. In addition to the above embodiments, we will give several groups of commonly used water-based drilling fluid formulas and preparation methods below.

[0115] Embodiment 18

[0116] The difference from Example 1 is that a high-density shale gas drill for preventing gas channeling uses a water-based drilling fluid, including base slurry, barite powder, ilmenite powder and lubricant, and the base slurry includes, by weight percentage, 30% potassium formate, 3% bentonite, 2% fluid loss reducer, 4% anti-collapse agent PA-2, 3% white oil, 2% polyol MSJ, 1% ultrafine CaCO3 powder, 1.5% cationic emulsified asphalt, 1% SD-I type while drilling plugging agent, 0.1% xanthan gum, 0.02% sodium hydroxide, and the balance is water;

[0117] The preparation method of the lubricant is different from that of Example 1 in that: S1. Preparation of lubricant: S1-1. Preparation of modified ZnS: Take zinc chloride powder, sulfur powder and ethylenediamine, and the zinc chloride powder and sulfur powder are both sieved through a 1000 mesh sieve, mixed in a molar ratio of 3:4:100, and added to a reactor, heated to 200°C for reaction for 3 days, cooled to room temperature, taken out, washed and dried to obtain modified ZnS powder, and washed 3 times with deionized water at a drying temperature of 45°C.

[0118] Embodiment 19

[0119] The difference from Example 1 is that a high-density shale gas drill for preventing gas channeling uses a water-based drilling fluid, including base slurry, barite powder, ilmenite powder and lubricant, and the base slurry includes, by weight percentage, 35% potassium formate, 4% bentonite, 3% fluid loss reducer, 5% anti-collapse agent PA-2, 4% white oil, 3% polyol MSJ, 2% ultrafine CaCO3 powder, 2% cationic emulsified asphalt, 1.5% SD-I type drilling plugging agent, 0.2% xanthan gum, 0.03% sodium hydroxide, and the balance is water;

[0120] The preparation method of the lubricant is different from that of Example 1 in that: S1. Preparation of lubricant: S1-1. Preparation of modified ZnS: Take zinc chloride powder, sulfur powder and ethylenediamine, and the zinc chloride powder and sulfur powder are both sieved through a 1000 mesh sieve, mixed in a molar ratio of 3:4:100, and added to a reactor, heated to 180°C for reaction for 4 days, cooled to room temperature, taken out, washed and dried to obtain modified ZnS powder, and washed 4 times with deionized water at a drying temperature of 50°C.

Claims

1. A high-density shale gas drill for preventing gas channeling uses a water-based drilling fluid, characterized in that: The invention comprises base slurry, barite powder, ilmenite powder and lubricant, wherein the base slurry comprises, by weight percentage, 30-35% potassium formate, 3-4% bentonite, 2-3% fluid loss reducer, 4-5% anti-collapse agent PA-2, 3-4% white oil, 2-3% polyol MSJ, 1-2% ultrafine CaCO3 powder, 1.5-2% emulsified asphalt, 1-1.5% drilling plugging agent, 0.1-0.2% xanthan gum, 0.02-0.03% sodium hydroxide, and the balance is water, and the lubricant accounts for 0-3% of the total volume of the water-based drilling fluid; The density of the barite powder in the water-based drilling fluid is 13.5-14.5 g / cm 3 The density of the ilmenite powder in the water-based drilling fluid is 1.15-1.35 g / cm 3 .

2. The high-density shale gas drill for preventing gas channeling according to claim 1 uses water-based drilling fluid, characterized in that: The fluid loss reducer is prepared by mixing fluid loss reducer JT888 and fluid loss reducer SJ-2 in a weight ratio of 2:

1.

3. The high-density shale gas drill for preventing gas channeling according to claim 1 uses water-based drilling fluid, characterized in that: The ultrafine CaCO3 powder is a mixture of CaCO3 powder passing through a 2000 mesh sieve and CaCO3 powder passing through a 3000 mesh sieve in a weight ratio of 1:

1.

4. The high-density shale gas drill for preventing gas channeling according to claim 1 uses water-based drilling fluid, characterized in that: The emulsified asphalt is cationic emulsified asphalt, and the drilling-while-plugging agent is drilling-while-plugging agent SD-I type.

5. The high-density shale gas drill for preventing gas channeling according to claim 1 uses water-based drilling fluid, characterized in that: The lubricant is obtained by coating modified ZnS with a methyl acrylate-ethylenediamine polymer. The preparation method of the lubricant comprises the following steps: S1. Lubricant preparation: S1-1, preparation of modified ZnS: zinc chloride powder, sulfur powder and ethylenediamine are mixed in a molar ratio of 3:4:100 and added into a reaction kettle, heated to 180-200°C for reaction for 3-4 days, cooled to room temperature and taken out, washed and dried to obtain modified ZnS powder; S1-2, preparation of high molecular polymer: taking a first methanol solution mixed with ethylenediamine, wherein the mass concentration of ethylenediamine in the first methanol solution is 40%, nitrogen is continuously introduced under ice bath conditions, and methyl acrylate is continuously added dropwise, wherein the volume ratio of methyl acrylate to ethylenediamine in the first methanol solution is 1:1, after the addition is completed, nitrogen is stopped from being introduced and the mixture is allowed to stand for 1 day to obtain tetraamine, nitrogen is continuously introduced under ice bath conditions, and a second methanol solution mixed with ethylenediamine is continuously added dropwise, wherein the mass concentration of ethylenediamine in the second methanol solution is 60%, and the volume ratio of ethylenediamine to methyl acrylate in the second methanol solution is 1:2, after the addition is completed, nitrogen is stopped from being introduced and the mixture is allowed to stand for 1 day, and a first generation high molecular polymer is obtained by vacuum distillation, i.e., one iteration is completed; Subsequently, the first methanol solution is replaced with the first generation polymer, and the above steps are repeated. When the second generation polymer is obtained, the next iteration is completed. The same amount of methyl acrylate and the same amount of the second methanol solution are added in each iteration. The third generation polymer is obtained by repeating the above steps for three times. S1-3. Preparation of lubricant: Add the modified ZnS powder obtained in step S1-1 to the third-generation high molecular polymer obtained in step S1-2, stir and repeat the above iterative process, and the fourth-generation methyl acrylate-ethylenediamine high molecular polymer coated modified ZnS obtained is the lubricant.

6. The high-density shale gas drill for preventing gas channeling according to claim 5 uses water-based drilling fluid, characterized in that: In the step S1-1, the zinc chloride powder and the sulfur powder are both sieved through a 1000-mesh sieve, and are washed 3 to 4 times with deionized water at a drying temperature of 45 to 50°C.

7. The high-density shale gas drill for preventing gas channeling according to claim 5 uses water-based drilling fluid, characterized in that: In the step S1-3, the weight ratio of the modified ZnS powder to the third generation high molecular polymer is 1:25-30.

8. The method for preparing a water-based drilling fluid for high-density shale gas drilling to prevent gas channeling according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Base slurry preparation: After adding water into the wellbore during the drilling construction process, the pump is turned on for circulation, and then the various components of the base slurry are added in sequence, and the base slurry preparation can be completed by cyclic drilling; S2. Weighting the drilling fluid to form slurry: During the drilling or circulation process of the base slurry, barite powder, ilmenite powder and lubricant are sequentially added into the wellbore to weight the base slurry and obtain the water-based drilling fluid.

9. The use of a water-based drilling fluid in a high-density shale gas drill for preventing gas channeling according to any one of claims 1 to 7, characterized in that: The water-based drilling fluid is used in the shale gas horizontal well drilling construction, and the application method is as follows: During the initial drilling, the lubricant in the water-based drilling fluid accounts for 0% of the total volume of the water-based drilling fluid; During the secondary drilling, the lubricant in the water-based drilling fluid accounts for 0 to 1% of the total volume of the water-based drilling fluid; When drilling at the third or higher level, the lubricant in the water-based drilling fluid accounts for 1 to 3% of the total volume of the water-based drilling fluid, specifically: When drilling a vertical well, the lubricant in the water-based drilling fluid accounts for 1 to 1.8% of the total volume of the water-based drilling fluid; When the deflection section is advanced, the lubricant in the water-based drilling fluid accounts for 2.6-3% of the total volume of the water-based drilling fluid; When drilling in the horizontal section, the lubricant in the water-based drilling fluid accounts for 1.8-2.6% of the total volume of the water-based drilling fluid.

Images