Reservoir drilling fluid and preparation method thereof

Abstract

The invention discloses a reservoir drilling fluid and a preparation method thereof, and belongs to the technical field of oilfield chemical agent preparation, the reservoir drilling fluid comprises the following substances by weight: 50-80 parts of water, 3-5 parts of a flocculant, 2-8 parts of a polyamine inhibitor, 2-4 parts of an anti-scale agent, 1-3 parts of graphite, 4-6 parts of a mixed additive, and 1-3 parts of xanthan gum; the preparation method of the mixed additive comprises the following steps: S1, preparing alkyl glycoside and a pH adjusting solution with the concentration of 0.8-1.2% according to the mass ratio of 1: 2, mixing the alkyl glycoside and the pH adjusting solution, stirring for 20-35 minutes at the temperature of 45-55 DEG C, then adding calcium formate, and stirring to obtain a primary mixture; by preparing the mixed additive prepared by mixing substances such as alkyl glycoside and sodium nitrohumate, the drilling fluid finished product can effectively reduce the damage of a coalbed methane reservoir caused by solid phase invasion, prevent mineral hydration, promote desorption of coalbed methane on the surface of coal rock, and maintain the stability of the coalbed at the same time.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical preparation technology, specifically to a reservoir drilling fluid and its preparation method. Background Technology

[0002] Coalbed methane (CBM) is an unconventional natural gas found in coal seams. It is mainly composed of methane, primarily adsorbed on the surface of coal matrix particles, with some free in coal pores or dissolved in coal seam water. It is a semi-life mineral resource of coal. With my country's new requirements for diversified energy development, it has received increasing attention, and the exploitation of CBM has gradually expanded in scale.

[0003] my country's coal seams rich in coalbed methane are quite special, characterized by low porosity and low permeability. The main mining method is horizontal wells. In order to ensure the safety, quality, efficiency and speed of drilling operations, drilling fluid, a chemical agent, is required. It can clean the bottom of the well, keep the bottom clean, avoid repeated cutting by the drill bit, reduce wear and improve operation efficiency.

[0004] my country's coal seams rich in coalbed methane are quite special, characterized by low porosity and low permeability. The main mining method is horizontal wells. In order to ensure the safety, quality, efficiency and speed of drilling operations, drilling fluid, a chemical agent, is required. It can clean the bottom of the well, keep the bottom clean, avoid repeated cutting by the drill bit, reduce wear and improve operation efficiency.

[0005] However, in actual drilling, when the working fluid invades the reservoir, it causes some solid particles in the drilling fluid and formation particles to move, clogging the pore throat and significantly reducing the reservoir's permeability, thus affecting the oil and gas recovery rate. Currently, most drilling fluids are water-based, which have advantages such as low cost and no solid phase, and can meet the operational requirements of horizontal well drilling projects. However, this type of drilling fluid is prone to causing the expansion of clay minerals in the coal seam, affecting the seepage channels of coalbed methane. At the same time, this type of drilling fluid is prone to forming scale by combining with coal seam water, and due to its high hydration rate, its flocculation ability is also weak.

[0006] Therefore, in order to ensure the smooth extraction of coalbed methane, protect the stability of coalbed methane reservoirs, and increase the production of coalbed methane, this invention provides a novel reservoir drilling fluid and its preparation method to meet the requirements of safe coalbed methane extraction and production. Summary of the Invention

[0007] The present invention aims to solve the problems in the prior art by providing a reservoir drilling fluid and its preparation method. This invention solves the problems that current drilling fluid products are prone to causing expansion of clay minerals in coal seams during actual use, affecting the seepage channels of coalbed methane, and are also prone to scaling when combined with coal seam water, as well as having weak flocculation ability.

[0008] The objective of this invention is achieved through the following technical solution: A reservoir drilling fluid comprises the following substances in parts by weight: 50-80 parts water, 3-5 parts flocculant, 2-8 parts polyamine inhibitor, 2-4 parts scale inhibitor, 1-3 parts graphite, 4-6 parts mixed additives, and 1-3 parts xanthan gum. The preparation method of the mixed additive includes the following steps: Step S1: Prepare alkyl glycoside and pH adjustment solution with a mass ratio of 1:2. Mix the two and stir at 45-55°C for 20-35 minutes at a speed of 220-300 r / min. Then add calcium formate and stir to obtain the initial mixture. Step S2: Add 2-3% sodium nitrohumate to the initial mixture, heat to 75-90℃ and stir for 15-20 minutes at a stirring speed of 180-240 r / min, then add triethanolamine and stir at 55-60℃ for 30-50 minutes at a stirring speed of 260-320 r / min to obtain the mixed matrix; Step S3: Take magnesium chloride, sodium petroleum sulfonate and mixed matrix in a mass ratio of 1:2:7, put them into a mixer and heat and mix them. After mixing, the mixed preparation product is obtained.

[0009] Preferably, in step S1, the added mass of calcium formate is 1.5 to 2% of the total mass of the alkyl glycoside and pH adjustment solution.

[0010] Preferably, in step S2, the added mass of triethanolamine is 1.5 to 2.2% of the total mass of the initial mixture and nitrohumic acid.

[0011] Preferably, in step S3, the stirring time of magnesium chloride, sodium petroleum sulfonate and the mixed matrix is ​​controlled at 12-15 min, the stirring speed is 160-320 r / min, and the heating temperature is controlled at 80-95℃.

[0012] Preferably, the flocculant is one or more of polyferric sulfate, polyaluminum chloride (PAC), magnesium aluminum silicate, polyacrylamide, sodium polyacrylate, chitosan, and cationic melamine polymer.

[0013] Preferably, the polyamine inhibitor is one or more of polyethyleneimine, polyetheramine, alkyldiamine, and quaternary ammonium salt polyamine.

[0014] Preferably, the pH adjusting solution is one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

[0015] Preferably, the scale inhibitor is a compound of aminotrimethylphosphonic acid, hydrolyzed polymaleic anhydride, and hydroxyethylidene diphosphonic acid in a ratio of 1:1.8:1.5.

[0016] Preferably, the water is deionized water from which impurities in ionic form have been removed.

[0017] A method for preparing reservoir drilling fluid, comprising the following steps: Step 1: After preparing the raw materials according to the weight proportions, add water to the mixing tank, then add polyamine inhibitor, calcium formate, scale inhibitor and graphite and stir evenly. During the process, add potassium chloride to obtain the mixture. Step 2: Inject the mixing aid into the stirred tank, and add flocculant and xanthan gum at the same time. Heat the stirred tank and stir thoroughly to obtain the reservoir drilling fluid product. Step 3: Place the finished drilling fluid into sealed containers for packaging and storage.

[0018] Preferably, in step one, the mass of potassium chloride added is 0.8 to 1.2% of the mass of water.

[0019] Preferably, in step two, the heating temperature of the stirring vessel is controlled at 55-70℃, the stirring time is 20-35 minutes, and the stirring speed is 210-250 r / min.

[0020] The beneficial effects of this technical solution are as follows: I. The reservoir drilling fluid provided by this invention is a mixed additive made of alkyl glycosides, sodium nitrohumate, and other substances. As a raw material component, it is used to produce a storage drilling fluid, which can effectively reduce the damage to coalbed methane reservoirs caused by solid phase invasion, prevent mineral hydration, and has strong gel strength, good settling stability and rock-carrying capacity in high-angle wells. It can meet the needs of horizontal well drilling and can promote the desorption of coalbed methane on the coal and rock surface, maintain the stability of the coal seam. Its application cost is low and its use effect is good.

[0021] II. The reservoir drilling fluid provided by this invention has good filtration loss control performance, reduces the permeation of drilling fluid into the formation, and protects the reservoir.

[0022] Third, the reservoir drilling fluid provided by the present invention has strong gel strength and stability. The reservoir drilling fluid has strong gel strength, and the static shear force gradually increases over time. It has good settling stability and rock-carrying capacity in high-angle wells, which can meet the needs of horizontal well drilling.

[0023] IV. The reservoir drilling fluid provided by this invention has a density of 1.01 to 1.05 g / cm³, which is within a suitable range and will not cause excessive pressure on the reservoir. At the same time, the pH value is 7 to 10, which is weakly alkaline and has a relatively small impact on the reservoir. In addition, this invention can effectively inhibit the expansion of clay minerals in the reservoir, protect the pore structure of the reservoir, and allow the permeability of the reservoir to be well restored after drilling is completed. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0025] Example 1 This embodiment provides a reservoir drilling fluid comprising the following components by weight: 80 parts water, 3 parts flocculant, 2 parts polyamine inhibitor, 2 parts scale inhibitor, 1 part graphite, 6 parts mixing additives, and 1 part xanthan gum.

[0026] In the above raw materials, the water is deionized water from which impurities in ionic form have been removed, the flocculant is sodium polyacrylate, the polyamine inhibitor is polyethyleneimine, and the scale inhibitor is a compound of aminotrimethylphosphonic acid, hydrolyzed polymaleic anhydride, and hydroxyethylidene diphosphonic acid in a ratio of 1:1.8:1.5.

[0027] Specifically, the preparation method of the mixed additives includes the following steps: S1. Prepare an alkyl glycoside and a 0.8% pH adjustment solution (sodium hydroxide) at a mass ratio of 1:2. Mix the two and stir at 45°C for 20 minutes at a stirring speed of 300 r / min. Then add calcium formate and stir to obtain a preliminary mixture. In this step, the mass of calcium formate added is 1.5% of the total mass of the alkyl glycoside and the pH adjustment solution. S2. Add 2% sodium nitrohumate to the initial mixture, heat to 75°C and stir for 15 minutes at a stirring speed of 240 r / min; then add triethanolamine, the mass of which is 2.2% of the total mass of the initial mixture and nitrohumate; then stir at 55°C for 30 minutes at a stirring speed of 320 r / min to obtain the mixed matrix; S3. Take magnesium chloride, sodium petroleum sulfonate and mixed matrix in a mass ratio of 1:2:7, put them into a mixer and heat and mix them. The mixing time is controlled at 15 min and the stirring speed is 160 r / min. The heating temperature is controlled at 80℃. After the mixing is completed, the mixed preparation product is obtained.

[0028] Furthermore, this embodiment also provides a method for preparing reservoir drilling fluid, including the following steps: Step 1: After preparing the raw materials according to their weight proportions, add water to the mixing tank, then add polyamine inhibitor, calcium formate, scale inhibitor and graphite, and stir evenly. During this process, add potassium chloride to obtain a mixture. In this step, the mass of potassium chloride added is 0.8% of the water mass. Step 2: Inject the mixing additives into the stirred tank, along with flocculant and xanthan gum. Heat the stirred tank and stir thoroughly. The heating temperature of the stirred tank is controlled at 55℃, the stirring time is 20 minutes, and the stirring speed is 250 r / min. After that, the reservoir drilling fluid product is obtained.

[0029] Example 2 This embodiment provides a reservoir drilling fluid comprising the following components by weight: 50 parts water, 4 parts flocculant, 5 parts polyamine inhibitor, 3 parts scale inhibitor, 2 parts graphite, 5 parts mixing additives, and 2 parts xanthan gum.

[0030] In the above raw materials, the water is deionized water from which impurities in ionic form have been removed, the flocculant is polyferric sulfate and polyaluminum chloride (PAC), the polyamine inhibitor is polyetheramine, and the scale inhibitor is a compound of aminotrimethylphosphonic acid, hydrolyzed polymaleic anhydride, and hydroxyethylidene diphosphonic acid in a ratio of 1:1.8:1.5.

[0031] Specifically, the preparation method of the mixed additives includes the following steps: S1. Prepare an alkyl glycoside and a 1% pH adjustment solution (ammonia water) at a mass ratio of 1:2. Mix the two and stir at 50°C for 27.5 min at a stirring speed of 260 r / min. Then add calcium formate and stir to obtain a preliminary mixture. In this step, the mass of calcium formate added is 1.75% of the total mass of the alkyl glycoside and the pH adjustment solution. S2. Add 2.5% sodium nitrohumate to the initial mixture, heat to 82.5℃ and stir for 17.5 min at a stirring speed of 210 r / min; then add triethanolamine, the mass of which is 1.8% of the total mass of the initial mixture and nitrohumate; then stir at 57.5℃ for 40 min at a stirring speed of 290 r / min to obtain the mixed matrix; S3. Take magnesium chloride, sodium petroleum sulfonate and mixed matrix in a mass ratio of 1:2:7, put them into a mixer and heat and mix them. The mixing time is controlled at 13.5 min and the stirring speed is 240 r / min. The heating temperature is controlled at 87.5℃. After the mixing is completed, the mixed preparation product is obtained.

[0032] Furthermore, this embodiment also provides a method for preparing reservoir drilling fluid, including the following steps: Step 1: After preparing the raw materials according to their weight proportions, add water to the mixing tank, then add polyamine inhibitor, calcium formate, scale inhibitor, and graphite, and stir evenly. During this process, potassium chloride is added to obtain a mixture. In this step, the mass of potassium chloride added is 1% of the water mass. Step 2: Inject the mixing additives into the stirred tank, along with the flocculant and xanthan gum. Heat the stirred tank and stir thoroughly. The heating temperature of the stirred tank is controlled at 62.5℃, the stirring time is 27.5 minutes, and the stirring speed is 230 r / min. After that, the reservoir drilling fluid product is obtained.

[0033] Example 3 This embodiment provides a reservoir drilling fluid comprising the following components by weight: 67.5 parts water, 5 parts flocculant, 8 parts polyamine inhibitor, 4 parts scale inhibitor, 3 parts graphite, 4 parts mixing additives, and 3 parts xanthan gum.

[0034] In the above raw materials, the water is deionized water from which impurities in ionic form have been removed, the flocculant is magnesium aluminum silicate, polyacrylamide, chitosan and cationic melamine polymer, the polyamine inhibitor is alkyl diamine and quaternary ammonium salt polyamine, and the scale inhibitor is a compound of aminotrimethylphosphonic acid, hydrolyzed polymaleic anhydride and hydroxyethylidene diphosphonic acid in a ratio of 1:1.8:1.5.

[0035] Specifically, the preparation method of the mixed additives includes the following steps: S1. Prepare an alkyl glycoside and a 1.2% pH adjustment solution (containing potassium hydroxide and sodium hydroxide) at a mass ratio of 1:2. Mix the two solutions and stir at 55°C for 35 minutes at a stirring speed of 220 r / min. Then add calcium formate and stir to obtain a preliminary mixture. In this step, the mass of calcium formate added is 2% of the total mass of the alkyl glycoside and the pH adjustment solution. S2. Add 3% sodium nitrohumate to the initial mixture, heat to 90°C and stir for 20 minutes at a stirring speed of 180 r / min; then add triethanolamine, the mass of which is 1.5% of the total mass of the initial mixture and nitrohumate; then stir at 60°C for 50 minutes at a stirring speed of 260 r / min to obtain the mixed matrix. S3. Take magnesium chloride, sodium petroleum sulfonate and mixed matrix in a mass ratio of 1:2:7, put them into a mixer and heat and mix them. The mixing time is controlled at 12 min and the stirring speed is 320 r / min. The heating temperature is controlled at 95℃. After the mixing is completed, the mixed preparation product is obtained.

[0036] Furthermore, this embodiment also provides a method for preparing reservoir drilling fluid, including the following steps: Step 1: After preparing the raw materials according to their weight proportions, add water to the mixing tank, then add polyamine inhibitor, calcium formate, scale inhibitor and graphite, and stir evenly. During this process, add potassium chloride to obtain a mixture. In this step, the mass of potassium chloride added is 1.2% of the water mass. Step 2: Inject the mixing additives into the stirred tank, along with the flocculant and xanthan gum. Heat the stirred tank and stir thoroughly. The heating temperature of the stirred tank is controlled at 70℃, the stirring time is 35 minutes, and the stirring speed is 210 r / min. After that, the reservoir drilling fluid product is obtained.

[0037] Example 4 This invention provides a reservoir drilling fluid comprising the following components by weight: 70 parts water, 3 parts flocculant, 2 parts polyamine inhibitor, 3 parts scale inhibitor, 2 parts graphite, 4 parts mixing additives, and 1 part xanthan gum. In the above raw materials, the water is deionized water from which impurities in ionic form have been removed, the flocculant is sodium polyacrylate, the polyamine inhibitor is polyethyleneimine, and the scale inhibitor is a compound of aminotrimethylphosphonic acid, hydrolyzed polymaleic anhydride, and hydroxyethylidene diphosphonic acid in a ratio of 1:1.8:1.5.

[0038] Specifically, the preparation method of the mixed additives includes the following steps: Step S1: Prepare an alkyl glycoside and a 0.8% pH adjustment solution (sodium hydroxide) at a mass ratio of 1:2. Mix the two and stir at 45°C for 20 minutes at a stirring speed of 300 r / min. Then add calcium formate and stir to obtain a preliminary mixture. In this step, the mass of calcium formate added is 1.5% of the total mass of the alkyl glycoside and the pH adjustment solution. Step S2: Add 2-3% sodium nitrohumate to the initial mixture, heat to 80°C and stir for 15 minutes at a stirring speed of 200 r / min. Then add triethanolamine, the mass of which is 2.2% of the total mass of the initial mixture and nitrohumate. After that, stir at 55°C for 30 minutes at a stirring speed of 220 r / min to obtain the mixed matrix. Step S3: Take magnesium chloride, sodium petroleum sulfonate and mixed matrix in a mass ratio of 1:2:7, put them into a mixer and heat and mix them. The mixing time is controlled at 15 min, the stirring speed is 180 r / min, and the heating temperature is controlled at 80℃. After the mixing is completed, the mixed preparation product is obtained.

[0039] Furthermore, this embodiment also provides a method for preparing reservoir drilling fluid, including the following steps: Step 1: After preparing the raw materials according to their weight proportions, add water to the mixing tank, then add polyamine inhibitor, calcium formate, scale inhibitor and graphite and stir evenly. During this process, add potassium chloride to obtain a mixture. In this step, the mass of potassium chloride added is 0.8% of the mass of water. In this step, polyetheramine is selected as the polyamine inhibitor. Step 2: Inject the mixing additives into the stirred tank, along with the flocculant and xanthan gum. Heat the stirred tank and stir thoroughly. The heating temperature of the stirred tank is controlled at 55℃, the stirring time is 20 minutes, and the stirring speed is 200 r / min. The resulting reservoir drilling fluid is then obtained.

[0040] Example 5 This invention provides a reservoir drilling fluid comprising the following components by weight: 75 parts water, 3 parts flocculant, 2 parts polyamine inhibitor, 2 parts scale inhibitor, 1 part graphite, 6 parts mixing additives, and 2 parts xanthan gum. In the above raw materials, the water is deionized water from which impurities in ionic form have been removed, the flocculant is sodium polyacrylate, the polyamine inhibitor is polyethyleneimine, and the scale inhibitor is a compound of aminotrimethylphosphonic acid, hydrolyzed polymaleic anhydride, and hydroxyethylidene diphosphonic acid in a ratio of 1:1.8:1.5.

[0041] Specifically, the preparation method of the mixed additives includes the following steps: Step S1: Prepare alkyl glycoside and a 0.8% pH adjustment solution (sodium hydroxide) at a mass ratio of 1:2. Mix the two and stir at 45°C for 20 minutes at a speed of 230 r / min. Then add calcium formate and stir to obtain a preliminary mixture. In this step, the mass of calcium formate added is 1.5% of the total mass of alkyl glycoside and pH adjustment solution. Step S2: Add 3% sodium nitrohumate to the initial mixture, heat to 90°C and stir for 15 minutes at a speed of 240 r / min. Then add triethanolamine, the mass of which is 2.2% of the total mass of the initial mixture and nitrohumate. After that, stir at 55°C for 30 minutes at a speed of 240 r / min to obtain the mixed matrix. Step S3: Take magnesium chloride, sodium petroleum sulfonate and mixed matrix in a mass ratio of 1:2:7, put them into a mixer and heat and mix them. The mixing time is controlled at 15 minutes and the heating temperature is controlled at 80℃. After the mixing is completed, the mixed preparation product is obtained.

[0042] Furthermore, this embodiment also provides a method for preparing reservoir drilling fluid, including the following steps: Step 1: After preparing the raw materials according to their weight proportions, add water to the mixing tank, then add polyamine inhibitor, calcium formate, scale inhibitor and graphite and stir evenly. During this process, add potassium chloride to obtain a mixture. In this step, the mass of potassium chloride added is 0.8% of the mass of water. In this step, polyetheramine is selected as the polyamine inhibitor. Step 2: Inject the mixing aid into the stirred tank, along with the flocculant and xanthan gum. Heat the stirred tank and stir thoroughly. The heating temperature of the stirred tank is controlled at 55℃, the stirring time is 20 minutes, and the stirring speed is 220 rpm. The resulting reservoir drilling fluid is then obtained.

[0043] Comparative Example 1 This comparative example provides a reservoir drilling fluid comprising the following components by weight: 80 parts water, 3 parts flocculant, 2 parts polyamine inhibitor, 2 parts scale inhibitor, and 1 part xanthan gum. In the above raw materials, the water is deionized water from which impurities in ionic form have been removed, the flocculant is sodium polyacrylate, the polyamine inhibitor is polyethyleneimine, and the scale inhibitor is a compound of aminotrimethylphosphonic acid, hydrolyzed polymaleic anhydride, and hydroxyethylidene diphosphonic acid in a ratio of 1:1.8:1.5.

[0044] Specifically, the preparation method of this reservoir drilling fluid includes the following steps: Step 1: After preparing the raw materials according to the weight proportions, add water to the mixing tank, then add polyamine inhibitor and scale inhibitor, and mix and stir. Step 2: Inject xanthan gum and flocculant into the stirred tank, heat the stirred tank and stir thoroughly. The heating temperature of the stirred tank is controlled at 55℃, the stirring time is 20 minutes, and the stirring speed is 250 r / min. Then the reservoir drilling fluid product is obtained.

[0045] The first item, filtration loss test: The reservoir drilling fluids of Examples 1-5 and Comparative Example 1 were heated and rolled for 13 hours at a temperature of 155℃. Then, their rheological properties, API filtration loss at room temperature and HTHP filtration loss at 150℃ and 3.5MPa were measured. The results are shown in Table 1.

[0046] Table 1. Filtration loss data measurement table for Examples 1-5 and comparative examples The second item, static shear force evaluation: After aging treatment, the reservoir drilling fluid of Example 1 was placed in a rotational viscometer, and its static shear force was measured at 10s, 30s, 1min, 2min, 5min, 10min, 20min, 30min, 60min and 120min respectively. The test results are shown in Table 2.

[0047] Table 2 Static shear force test results for aged finished products in Example 1 Referring to the data in Table 2, it can be seen that the reservoir drilling fluid of Example 1 provided by the present invention has strong gel strength, good settling stability, and good rock-carrying capacity in high-angle wells, which can meet the needs of horizontal well drilling. Furthermore, the density of the reservoir drilling fluid provided by the present invention is measured to be 1.01–1.05 g / cm³. 3 pH value 7-10, expansion rate reduction rate ≥60%, contact angle reduction rate >55%, core permeability recovery rate ≥80% under wet conditions and ≥95% under dry conditions, and pulverized coal Landau volume reduction rate ≥16%.

[0048] Third item, independent comparative verification: Comparative experimental steps: Step A: Prepare reservoir drilling fluid raw materials The reservoir drilling fluid raw materials prepared in Example 1 are: water, flocculant, polyamine inhibitor, scale inhibitor, graphite, mixing additives, and xanthan gum.

[0049] Prepare the reservoir drilling fluid raw materials for the comparison ratio: water, flocculant, polyamine inhibitor, scale inhibitor, and xanthan gum.

[0050] Step B: Preparation of reservoir drilling fluid According to the formulas provided in Example 1 and Comparative Example 1, each raw material was prepared in parts by weight and the finished product was made.

[0051] Step C: Experimental Verification The drilling fluids prepared in Example 1 and the comparative example were tested for performance in accordance with the People's Republic of China National Standard GB / T16783.1-2006 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids".

[0052] Step D: Comparative Analysis The properties of the drilling fluids prepared in Example 1 and the comparative example were analyzed, and the differences between the two were compared to verify the effect of the mixed additives on the solid content.

[0053] Table 3: Component Parameters of Example 1 and Comparative Example Table 4: Comparison of data parameters obtained from actual tests of reservoir drilling fluids provided in Example 1 and the comparative example. As can be seen from the national standard test, the drilling fluid provided in Example 1 of this invention has better comprehensive performance parameters than the drilling fluid provided in the comparative example. The low surface tension helps to maintain the suspension of solid particles, while the low apparent viscosity and low funnel viscosity help to clean the wellbore and well wall, reducing solid phase deposition during actual operation. In practical applications, it can promptly generate flocculation for fine coal dust generated during drilling operations, and can be quickly removed by ground solids control equipment, thereby effectively reducing the blockage damage to the coal seam caused by the solid phase of the drilling fluid.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A reservoir drilling fluid, characterized in that, The following substances are included in parts by weight: 50-80 parts water, 3-5 parts flocculant, 2-8 parts polyamine inhibitor, 2-4 parts scale inhibitor, 1-3 parts graphite, 4-6 parts mixing additives, and 1-3 parts xanthan gum; The preparation method of the mixed additive includes the following steps: Step S1: Prepare alkyl glycoside and pH adjustment solution with a mass ratio of 1:

2. Mix the two and stir at 45-55°C for 20-35 minutes at a speed of 220-300 r / min. Then add calcium formate and stir to obtain the initial mixture. Step S2: Add 2-3% sodium nitrohumate to the initial mixture, heat to 75-90℃ and stir for 15-20 minutes at a stirring speed of 180-240 r / min, then add triethanolamine and stir at 55-60℃ for 30-50 minutes at a stirring speed of 260-320 r / min to obtain the mixed matrix; Step S3: Take magnesium chloride, sodium petroleum sulfonate and mixed matrix in a mass ratio of 1:2:7, put them into a mixer and heat and mix them. After mixing, the mixed preparation product is obtained.

2. The reservoir drilling fluid according to claim 1, characterized in that: In step S1, the added mass of calcium formate is 1.5 to 2% of the total mass of the alkyl glycoside and pH adjustment solution.

3. The reservoir drilling fluid according to claim 1, characterized in that: In step S2, the added mass of triethanolamine is 1.5 to 2.2% of the total mass of the initial mixture and nitrohumic acid.

4. The reservoir drilling fluid according to claim 1, characterized in that: In step S3, the stirring time of magnesium chloride, sodium petroleum sulfonate and the mixed matrix is ​​controlled at 12-15 min, the stirring speed is 160-320 r / min, and the heating temperature is controlled at 80-95℃.

5. The reservoir drilling fluid according to claim 1, characterized in that: The flocculant is one or more of the following: polyferric sulfate, polyaluminum chloride (PAC), magnesium aluminum silicate, polyacrylamide, sodium polyacrylate, chitosan, and cationic melamine polymer.

6. The reservoir drilling fluid according to claim 1, characterized in that: The polyamine inhibitor is one or more of polyethyleneimine, polyetheramine, alkyldiamine, and quaternary ammonium salt polyamine.

7. The reservoir drilling fluid according to claim 1, characterized in that: The pH adjusting solution is one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

8. The reservoir drilling fluid according to claim 1, characterized in that: The scale inhibitor is a compound of aminotrimethylphosphonic acid, hydrolyzed polymaleic anhydride, and hydroxyethylidene diphosphonic acid in a ratio of 1:1.8:1.

5.

9. A reservoir drilling fluid according to claim 1, characterized in that: The water is deionized water from which impurities in ionic form have been removed.

10. A method for preparing reservoir drilling fluid according to any one of claims 1-9, comprising the following steps: Step 1: After preparing the raw materials according to the weight proportions, add water to the mixing tank, then add polyamine inhibitor, calcium formate, scale inhibitor and graphite and stir evenly. During the process, add potassium chloride to obtain the mixture. Step 2: Inject the mixing aid into the stirred tank, and add flocculant and xanthan gum at the same time. Heat the stirred tank and stir thoroughly to obtain the reservoir drilling fluid product. Step 3: Place the finished drilling fluid into sealed containers for packaging and storage.

11. The method for preparing reservoir drilling fluid according to claim 10, characterized in that: In step one, the mass of potassium chloride added is 0.8 to 1.2% of the mass of water.

12. The method for preparing reservoir drilling fluid according to claim 11, characterized in that: In step two, the heating temperature of the stirring vessel is controlled at 55-70℃, the stirring time is 20-35 minutes, and the stirring speed is 210-250 r / min.

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